Effective local anesthesia is the bedrock of pain control in endodontics. Regardless of the clinician’s skills, endodontic treatment cannot be delivered without effective pain control. This chapter reviews the pharmacology of local anesthetics and the relative advantages and limitations of various anesthetics and routes of administration. Other chapters in this book provide complementary information on the use of local anesthetics in diagnosis (see Chapter 1), the treatment of emergency patients (see Chapter 2), and the development of a comprehensive pain-control plan (see Chapter 19). The authors assume that the reader is familiar with various anesthetic injection techniques; several excellent texts are available for review regarding this point.¹¹⁶^,¹⁵⁸

Mechanisms of Action for Anesthetics

Most dental pharmacology courses teach that local anesthetics block sodium channels by partitioning into two types, the uncharged basic form of the molecule (RN), which crosses cell membranes, and the charged acid form of the molecule (RNH⁺), which binds to the inner pore of the sodium channel. As a first approximation, this model is reasonably accurate. However, molecular research has demonstrated the existence of at least nine subtypes of voltage-gated sodium channels (VGSCs) that differ in their expression pattern, biophysical properties, and roles in mediating peripheral pain (Table 20-1). These channels have a clear clinical relevance.^18,^101,¹⁴³

TABLE 20-1 Voltage-Gated Sodium Channels and Pain

The broad class of VGSCs can be divided into channels that are blocked by a toxin (tetrodotoxin [TTX]) and those that are resistant to the toxin (TTX-R). Most TTX-R channels are found primarily on nociceptors (e.g., Na_v 1.8 and Na_v 1.9).²⁷³ These channels also are relatively resistant to local anesthetics²¹⁶ and are sensitized by prostaglandins.⁸³ As is explained later in the chapter, the presence of TTX-R sodium channels may explain why local anesthetics are less effective when injected into patients with odontalgia. Moreover, the sensitization of these channels by prostaglandins suggests that rapid-acting nonsteroidal antiinflammatory drugs (NSAIDs) may be useful as a pretreatment to enhance the efficacy of local anesthetics in patients with odontogenic pain¹¹²^,¹⁷⁹ (see Chapter 19). Many of the adverse effects of local anesthetics are attributed to their ability to block other VGSCs expressed in the central nervous system (CNS) or heart (see Table 20-1).

VGSCs consist of an alpha (α) and a beta (β) subunit. The α subunit serves as a voltage sensor, leading to channel activation and sodium ion passage when the channel detects an electrical field. The biologic basis for an electrical pulp tester, therefore, is the generation of a small electrical field across the dental pulp that can activate VGSCs.¹⁰¹ Interestingly, sensitization of TTX-R channels by prostaglandins lowers the activation threshold and increases the amount of sodium ions that flow through the channel.⁸³ Put another way, an inflammation-induced elevation in prostaglandin levels sensitizes TTX-R channels, leading to depolarization at lower levels of stimulus strengths. This may explain the increased responsiveness to electrical pulp testing seen in patients with irreversible pulpitis.

Local anesthetics have other mechanisms that may contribute to their pharmacology for treating odontogenic pain. For example, local anesthetics modulate certain G protein–coupled receptors (GPCRs). The GPCRs are a major class of cell membrane receptors, and many classes of dental drugs (e.g., opioids, catecholamines) and endogenous mediators produce their effects by activating specific GPCRs and their related second messenger pathways. Studies suggest that local anesthetics inhibit the G-alpha-q (G_αq) class of GPCRs, which includes receptors activated by inflammatory mediators such as bradykinin.¹⁰⁸ Local anesthetics may therefore block the actions of a major hyperalgesic agent.

Other studies have indicated that local anesthetics potentiate the actions of the G-alpha-i (G_αi) class of GPCRs.¹¹ This could have a major effect in potentiating the actions of vasoconstrictors, including the newly recognized analgesic role that vasoconstrictors play in inhibiting pulpal nociceptors.²⁰^,¹⁰⁰ Prolonged alteration of GPCR function might explain why analgesia obtained with long-acting local anesthetics persists well beyond the period of anesthesia.^40,^55,¹⁸⁵ More research is needed on this exciting aspect of local anesthetic pharmacology.

Clinically Available Local Anesthetics

The most common forms of injectable local anesthetics are in the amide class. In 2003, the American Dental Association specified a uniform color code for dental cartridges to prevent confusion among brands (see www.ada.org/prof/resources/topics/color.asp) (Table 20-2). Local anesthetics can be divided roughly into three types: short duration (30 minutes of pulpal anesthesia), intermediate duration (60 minutes of pulpal anesthesia), and long duration (over 90 minutes of pulpal anesthesia). However, clinical anesthesia does not always follow these guidelines, depending on whether the local anesthetic is used as a block or for infiltration. For example, bupivacaine is classified as a long-acting agent, and when it is used in an inferior alveolar nerve (IAN) block, this is true.⁵⁸ But when it is used for infiltration for anterior teeth, it has a shorter duration of anesthetic action than 2% lidocaine with 1:100,000 epinephrine⁴³^,⁹⁰ (discussed in more detail later in the chapter).

TABLE 20-2 Local Anesthetics Available in the United States

Selection of a Local Anesthetic: Possible Adverse Effects, Medical History, Preoperative Anxiety

Possible Adverse Effects

Possible adverse reactions to local anesthetics can be divided into six major categories: cardiovascular reactions, systemic effects, methemoglobinemia, peripheral nerve paresthesia, allergic reactions to the anesthetic and/or latex, and reactions to anesthetics containing a sulfite antioxidant. These reactions range from fairly common (e.g., tachycardia after intraosseous injection of 2% lidocaine with 1:100,000 epinephrine) to extremely rare (e.g., allergic reactions to lidocaine).

Cardiovascular Reactions

Although classic research studies have reported that large dosages or intravenous (IV) injections of local anesthetics were required to produce cardiovascular effects,¹¹⁴^,²⁶² it now is well recognized that even comparatively small amounts of epinephrine can induce measurable tachycardia after nerve block or intraosseous injection.^59,^85,²²⁰ Several authors have reported increases in heart rate with infiltration injections and nerve blocks using 2% lidocaine with 1:100,000 epinephrine^1,^102,^140,^234,²⁶¹; others have reported that no significant changes in heart rate occurred or that the changes were clinically insignificant.^173,^260,²⁶⁴ When specific information was given on dosing and heart rate increases, several studies found mean heart rate increases.^1,^102,^139,²⁶¹ Two studies found increases on average of about 4 beats/min with approximately 20 µg of epinephrine¹⁰²^,¹³⁹; three studies recorded increases of 10 to 15 beats/min with 45 to 80 µg of epinephrine^1,^139,²³⁴; and one study found increases of approximately 21 beats/min using 144 µg of epinephrine.²⁶¹ Increasing the amount of epinephrine in an infiltration or block injection therefore increases the likelihood of an elevated heart rate.

Tachycardia after injection is primarily a pharmacologic effect. The cardiovascular effects are the result of α-adrenoceptor stimulation by systemic distribution of the vasoconstrictor throughout the vascular compartment. The patient may also report heart palpitations associated with anxiety or fear and may experience transient tachycardia and changes in blood pressure. Large doses or inadvertent IV injection may lead to lidocaine toxicity and CNS depression.⁶¹^,¹⁸⁹ To reduce this risk, the clinician should always aspirate before making the injection, inject slowly, and use dosages within accepted guidelines. The maximal dosages for local anesthetics are listed in Table 20-2.

Systemic Effects

The acute toxicity of an overdose of a local anesthetic often is the result of inadvertent IV administration or of a cumulative large dose (e.g., repeated injections). As shown in Table 20-1, VGSCs are found in the CNS and the myocardium, the two major areas of anesthetic-induced toxicity. Although systemic effects from a local anesthetic are rare, they can include an initial excitatory phase (e.g., muscle twitching, tremors, grand mal convulsions) and a subsequent depressive phase (e.g., sedation, hypotension, and respiratory arrest).⁴⁸^,⁶¹ It should be noted that symptomatic management (possibly including cardiopulmonary resuscitation [CPR], airway support, and supplemental oxygen) is the primary response to this adverse event.¹³⁵^,¹³⁷ An acute hypotensive crisis with respiratory failure also has been interpreted as the result of hypersensitivity to local anesthetics³⁰; these patients should be evaluated with allergy testing. To reduce the risk of systemic effects from anesthetics, the clinician must always aspirate before giving the injection and must use dosages within accepted guidelines (see Table 20-2). Finder and Moore⁶¹ proposed a “rule of 25” as a simple means of remembering maximal local anesthetic dosages: with currently formulated local anesthetic cartridges, it generally is safe to use one cartridge of local anesthetic for every 25 pounds of patient weight (e.g., six cartridges for a patient weighing 150 pounds [67.5 kg]).

Methemoglobinemia

Metabolism of certain local anesthetics (e.g., prilocaine, benzocaine, articaine, and to a lesser extent lidocaine) can produce a metabolite that causes methemoglobinemia; this effect often occurs several hours after injection of the local anesthetic.¹⁶²^,²⁷⁶ Typical signs and symptoms include cyanosis, dyspnea, emesis, and headache. In a study on benzocaine-induced methemoglobinemia, 67% of reported adverse effects of benzocaine were associated with methemoglobinemia; of these events, 93% occurred with spray formulations of benzocaine, and only one case involved the gel formulation.¹⁸⁶ To reduce the risk of methemoglobinemia, clinicians should take care to refrain from giving excessive dosages of local anesthetics.

Peripheral Nerve Paresthesia

Postinjection paresthesia is a rare adverse effect of local anesthetics.^96,^162,²⁸² A retrospective study reported that articaine is associated with a fivefold higher incidence of paresthesia compared with lidocaine.⁹⁶ A recent study evaluated patients referred with a diagnosis of damage to the inferior alveolar and/or lingual nerve which could only have resulted from an IAN block.²¹² Thirty-five percent were caused by a lidocaine formulation, and 30% were caused by an articaine formulation. The conclusion was that there was not a disproportionate nerve involvement from articaine. However, with any paresthesia, documentation of the patient’s reported area of altered sensation, the type of altered sensation (e.g., anesthesia, paresthesia, dysesthesia), and regular follow-up are important.

Allergic Reactions to Local Anesthetics and Latex

The amide local anesthetics appear to have little immunogenicity and therefore have an extremely low rate of allergic reactions.²³⁹ One study included more than 140 patients specifically referred for allergy testing because of adverse effects after injection of a local anesthetic; none of these patients had hypersensitivity reactions to intradermal local anesthetics,²²⁸ but case reports of hypersensitivity reactions after administration of local anesthetics have been published.^19,^30,^187,²³⁹ Some concern has been raised that the rubber latex stopper in dental anesthetic cartridges might be a source of allergen to patients allergic to latex. In a review of this literature (1966 to 2001), Shojaei and Haas²⁴¹ concluded that some evidence for exposure to the latex allergen exists, although no causal study has been published.

Reactions to Anesthetic Formulations Containing a Sulfite Antioxidant

Local anesthetic formulations that contain vasoconstrictors also contain sulfite to prevent oxidation of this agent. Sulfite-induced reactions came to prominence with the report of six deaths after exposure to salad bars or homemade wine.⁶ Common reported signs and symptoms include allergic-like reactions such as urticaria, bronchospasm, and anaphylaxis. Risk factors include an active history of asthma (perhaps 5% of asthmatics are at risk) and atopic allergy. The use of local anesthetics without vasoconstrictors is a possible alternative with these patients. No sulfite reaction in dental practice has ever been documented, possibly because the amount of sulfite in local anesthetic cartridges is relatively small.

Effects of Systemic Diseases or Conditions on Local Anesthetics

Several systemic diseases or disorders may require modification of the dosage of local anesthetic. Cardiac patients (e.g., those with unstable angina pectoris, history of myocardial infarction or stroke within the past 6 months, severe hypertension, uncontrolled congestive heart failure, or heart transplant) should not receive a local anesthetic containing a vasoconstrictor and should consult their physicians before undergoing endodontic treatment.¹⁸⁹ A review suggests that patients with Hodgkin’s disease or breast cancer who have received radiation treatment to the chest are at risk for radiation-induced coronary artery disease, and this condition also may require medical consultation regarding a reduced dosage of local anesthetic containing a vasoconstrictor.⁶⁵

Alcoholics have been found to be more sensitive to painful stimulation.²⁵⁴ Alcoholics with a history of depression/unhappiness may also have shallower pulpal anesthesia.⁶² In contrast, alcoholics in recovery may not be at increased risk for inadequate pain control with local anesthesia.⁶²

Any of the commonly available local anesthetics are safe for use in pregnant or lactating women.⁹⁷ The most important aspect of care with pregnant patients is to eliminate the source of pain by performing the indicated endodontic treatment; this reduces the need for systemic medications.⁹⁷

Local anesthetics may interact with a patient’s medications, so a thorough review of the medical history is an absolute requirement. Potential drug-drug interactions occur primarily with the vasoconstrictors in local anesthetic formulations (Table 20-3). Judicious use of local anesthetic solutions without vasoconstrictors (e.g., 3% mepivacaine) is a reasonable alternative for adult patients.

TABLE 20-3 Possible Drug Interactions With Vasoconstrictors

Drugs	Possible Adverse Effects	Recommendations
TRICYCLIC ANTIDEPRESSANTS
Amitriptyline, doxepin	Increased cardiovascular responses	Reduce or eliminate vasoconstrictors
NONSELECTIVE β-BLOCKERS
Nadolol, propranolol	Hypertension, bradycardia	Reduce or eliminate vasoconstrictors
RECREATIONAL DRUGS
Cocaine	Hypertension, myocardial infarction, dysrhythmias	Instruct patient to abstain from drug use for 48 hours before procedure; do not use vasoconstrictors
COMT INHIBITORS
Entacapone, tolcapone	Increased cardiovascular responses	Reduce or eliminate vasoconstrictors
ANTIADRENERGIC DRUGS
Guanadrel, guanethidine	Increased cardiovascular responses	Reduce or eliminate vasoconstrictors
NONSELECTIVE α-ADRENERGIC BLOCKERS
Chlorpromazine, clozapine, haloperidol	Increased cardiovascular responses	Reduce or eliminate vasoconstrictors
DIGITALIS
Digoxin	Dysrhythmias (especially with large dosage of vasoconstrictor)	Reduce or eliminate vasoconstrictor
THYROID HORMONES
Levothyroxine	Dysrhythmias (especially with large dosage of vasoconstrictor)	Euthyroid: No precaution Hyperthyroid: Reduce or eliminate vasoconstrictors
MONOAMINE OXIDASE³⁵ INHIBITORS
Furazolidone, linezolid, selegiline, tranylcypromine	No interaction	None

Modified from Naftalin L, Yagiela JA: Vasoconstrictors: indications and precautions. Dent Clin North Am 46:733, 2002.

Authors have found that women try to avoid pain more than men, accept it less, and fear it more.^51,^60,^147,¹⁸⁸ A study found women find postsurgical pain more intense than males, but men are more disturbed than women by low levels of pain that lasts several days.¹⁸⁸ Another study found gender differences in analgesia for postoperative endodontic pain.²³³ Anxiety may also modulate differences in pain responses between males and females. We should be aware that women might react differently to pain than men.⁶⁰

Clinical Anesthesia and Routes of Administration

Recognition is growing that evidence-based therapeutics offers an excellent source of information that should become an aspect of treatment in conjunction with the practitioner’s clinical skills and the patient’s particular needs. In many areas of dentistry, this is a limited concept because few randomized, placebo-controlled, double-blind clinical trials have been conducted. However, this is not the case with dental pharmacology. The astute clinician can make informed decisions on various local anesthetics and routes of injection based on a large collection of well-designed clinical trials. The following discussion focuses on the clinical aspects of local anesthesia, with special emphasis on endodontics.

Important Clinical Factors in Local Anesthesia

Traditional Methods of Confirming Anesthesia

Traditional methods of confirming anesthesia usually involve questioning the patient (“Is your lip numb?”), soft-tissue testing (e.g., lack of mucosal responsiveness to a sharp explorer), or simply beginning treatment. However, these approaches may not be effective for determining pulpal anesthesia.^28,^106,^169,²⁶⁶ Moreover, from a research perspective, they provide only bimodal responses (e.g., yes or no) and therefore are of little use for detecting parametric differences between anesthetics or routes of injection.

Determining Pulpal Anesthesia in Painless Vital Teeth

Anesthesia in painless vital teeth can be measured more objectively by applying a cold refrigerant (Fig. 20-1) or by using an electric pulp tester (EPT; Fig. 20-2). Application of cold or the electric pulp tester can be used to test the tooth under treatment for pulpal anesthesia before a clinical procedure is started.^26,^52,^120,¹⁵⁴

FIG. 20-1 A cold refrigerant may be used to test for pulpal anesthesia before the start of a clinical procedure.

(Courtesy Coltene Whaledent, Mahwah, NJ.)

FIG. 20-2 An electric pulp tester also may be used to test for pulpal anesthesia before a clinical procedure is started.

(Courtesy SybronEndo, Orange, CA.)

Determining Pulpal Anesthesia in Painful Vital Teeth

In painful vital teeth and after administration of local anesthesia, the cold test or electric pulp tester can be used to test for pulpal anesthesia before an endodontic procedure is started.^36,^52,^200,²¹⁷ If the patient responds to the stimulus, pulpal anesthesia has not been obtained, and supplemental anesthesia should be administered. However, in painful vital teeth (e.g., irreversible pulpitis), the lack of a response to pulp testing may not guarantee pulpal anesthesia.^52,^200,²¹⁷ Therefore, if a patient experiences pain when the endodontic procedure is started, supplemental anesthesia is indicated regardless of the responsiveness to pulpal testing. If the chamber is necrotic and the canals are vital, no objective test can predict the level of clinical anesthesia.

Patient Who Has Had Previous Difficulty With Anesthesia

Anesthesia is more likely to be unsuccessful in patients who report a history of previous difficulty with anesthesia.¹²⁹ These patients generally make comments such as “Novocaine doesn’t work on me” or “It takes a lot of shots to get my teeth numb.” A good clinical practice is to ask the patient if dentists previously have had difficulty obtaining anesthesia in the individual’s mouth. If the answer is yes, supplemental injections should be considered.

Failure to Achieve Anesthesia in Patients With Pain

Obtaining anesthesia often is difficult in patients with endodontic pain who have pulpal pathosis. A number of explanations have been proposed for this.¹⁰¹ One is that conventional anesthetic techniques do not always provide profound pulpal anesthesia, and patients with preexisting hyperalgesia may be unable to tolerate any noxious input. Another explanation relates to the theory that inflamed tissue has a lower pH, which reduces the amount of the base form of anesthetic that penetrates the nerve membrane. Consequently, less of the ionized form is available in the nerve to achieve anesthesia. This explanation does not account for the mandibular molar with pulpitis that is not readily blocked by an inferior alveolar injection administered at some distance from the area of inflammation. Correlating localized inflammatory changes with failure of the IAN block is difficult.

Another explanation for failure is that nerves arising from inflamed tissue have altered resting potentials and decreased excitability thresholds.²⁴^,²⁶⁸ Two studies demonstrated that local anesthetics were unable to prevent impulse transmission because of these lowered excitability thresholds.¹⁸⁰^,²⁶⁸ Another factor might be the TTX-R sodium channels, which are resistant to the action of local anesthetics²³² and are increased in inflamed dental pulp.²⁷¹^,²⁷³ A related factor is the increased expression of sodium channels in pulps diagnosed with irreversible pulpitis.^250,^271,²⁷³

Finally, patients in pain often are apprehensive, which lowers the pain threshold. Therefore practitioners should consider supplemental techniques (e.g., intraosseous injections^197,^200,^206,²¹⁷ or periodontal ligament injections³⁶) if an IAN block fails to provide pulpal anesthesia for patients with irreversible pulpitis.

Use of Topical Anesthetics

Fear of needle insertion is a major cause of apprehension in dental patients.^138,^177,¹⁷⁸ Although some studies have demonstrated the effectiveness of topical anesthetics,^102,^108,^192,²¹⁵ others have shown no significant pain reduction.^82,^131,¹⁶³ Interestingly, one study showed that patients who thought they were receiving a topical anesthetic anticipated less pain regardless of whether they actually received the anesthetic.¹⁶³ The most important aspect of a topical anesthetic may not be its clinical effectiveness but rather its psychologic effect on the patient who believes the practitioner is doing everything possible to prevent pain.

Reversing the Action of Local Anesthesia

Phentolamine mesylate (0.4 mg in a 1.7 ml cartridge, OraVerse, Novalar Pharmaceuticals, San Diego, CA) is a recently developed agent that shortens the duration of soft-tissue anesthesia. The duration of soft-tissue anesthesia is longer than pulpal anesthesia and is often associated with difficulty eating, drinking, and speaking.¹⁰⁴^,¹⁴⁴ The greatest value of using OraVerse is in the majority of dental procedures where postoperative pain is not of concern. However, some endodontic patients may benefit from the use of a reversal agent when they have speaking engagements, important meetings, or perform in musical or theatrical events. OraVerse may be used to shorten the duration of soft-tissue anesthesia if the patient presents with an asymptomatic tooth and little postoperative pain is anticipated.

Mandibular Anesthesia with 2% Lidocaine and 1:100,000 Epinephrine

Because failure occurs most often with the IAN block,¹²⁹ factors that modify mandibular anesthesia must be carefully reviewed. The technique for administering an IAN block can be reviewed in available textbooks.¹¹⁶^,¹⁵⁸ This discussion reviews the expected outcomes after administration of a conventional IAN block to asymptomatic patients using 1.8 ml of 2% lidocaine with 1:100,000 epinephrine (Xylocaine, Lignospan, Octocaine). Although anesthesia requirements vary among dental procedures, the following discussion concentrates on pulpal anesthesia.

Anesthetic Success

One way to define anesthetic success is the percentage of subjects who achieve two consecutive 80 readings on electric pulp testing within 15 minutes and continuously sustain this lack of responsiveness for 60 minutes. In other words, the objective is to achieve anesthesia within 15 minutes and to have it last 1 hour. This endpoint is as important for restorative dentistry as it is for endodontic treatment, so it is used as a benchmark for clinically significant information from research on local anesthetics. Using this criterion, the percentage of cases in which anesthesia was obtained after IAN block injections ranged from 35% (lateral incisor) to 60% (first premolar and first molar).* It is important to note that all patients from these studies reported a positive lip sign (e.g., profound lip numbness); therefore profound lip numbness does not predict pulpal anesthesia. However, lack of soft-tissue anesthesia is a useful indicator that the block injection was not administered accurately for that patient. Missed blocks occur in about 5% of cases, and the clinician should readminister the nerve block before continuing with treatment.

Anesthetic Failure

Anesthetic failure can be defined as the percentage of subjects who never achieved two consecutive 80 EPT readings at any time during a 60-minute period. Using this criterion, anesthetic failure ranged from 11% (first premolar) to 32% (lateral incisor).†

Noncontinuous Anesthesia

Another measure of mandibular anesthesia is noncontinuous anesthesia, which may be related to the action of the anesthetic solution on the nerve membrane (blocking and unblocking the sodium channels). This occurs in about 12% to 20% of cases in mandibular teeth.*

Slow Onset

After a conventional IAN block injection, the onset of pulpal anesthesia occurs within 10 to 15 minutes in most cases (Fig. 20-3).† Slow onset can be defined as the percentage of subjects who achieved an 80 EPT reading after 15 minutes. In mandibular teeth, slow onset occurs in 19% to 27% of patients.

FIG. 20-3 Incidence of first mandibular molar anesthesia as determined by lack of response to electrical pulp testing at the maximum setting (percentage of 80 readings) across time for 60 minutes.

Duration

The duration of action for pulpal anesthesia in the mandible is very good.‡ If patients are anesthetized initially, anesthesia usually persists for approximately hours.⁵⁸ Fig. 20-3 depicts the time course for complete pulpal anesthesia for an asymptomatic first molar, as defined by the percentage of patients who did not respond to an 80 stimulus (EPT) across time for 60 minutes. Most patients achieved pulpal anesthesia within 15 minutes and had a duration of anesthesia of at least 1 hour, but the success rate was not 100% for the population.

Alternative Anesthetic Solutions for the Inferior Alveolar Nerve Block

Plain Solutions: 3% Mepivacaine (Carbocaine, Polocaine, Scandonest) and 4% Prilocaine (Citanest Plain)

In a study of volunteers without dental pathosis, anesthesia from IAN injection of 3% mepivacaine plain and 4% prilocaine plain were as effective as 2% lidocaine with 1:100,000 (Fig. 20-4).¹⁶⁹ A clinical study of patients with irreversible pulpitis also found that 3% mepivacaine and 2% lidocaine with 1:100,000 epinephrine were equivalent for IAN blocks.³⁶ These findings support the selection of 3% mepivacaine as a local anesthetic when medical conditions or drug therapies suggest caution in the administration of solutions containing epinephrine.

FIG. 20-4 Incidence of first mandibular molar anesthesia: comparison of 3% mepivacaine to 2% lidocaine with 1:100,000 epinephrine. Results were determined by lack of response to electrical pulp testing at the maximum setting (percentage of 80 readings) across time for 50 minutes. No significant difference between the two solutions was noted.

4% Prilocaine With 1:200,000 Epinephrine (Citanest Forte) and 2% Mepivacaine With 1:20,000 Levonordefrin (Carbocaine With Neo-Cobefrin)

In a study of volunteers without dental pathosis, IAN injection of 4% prilocaine with 1:200,000 epinephrine or 2% mepivacaine with 1:20,000 levonordefrin worked as well as 2% lidocaine with 1:100,000 in achieving pulpal anesthesia.¹⁰⁶

Levonordefrin has 75% α activity and only 25% β activity, making it seemly more attractive than epinephrine (50% α activity and 50% β activity).¹⁵⁸ However, levonordefrin is marketed as a 1:20,000 concentration in dental cartridges.¹⁵⁸ Clinically, the higher concentration of levonordefrin makes it equipotent to epinephrine in clinical and systemic effects,⁹²^,¹⁰⁶ so 1:20,000 levonordefrin offers no clinical advantage over 1:100,000 epinephrine.

Articaine With 1:100,000 Epinephrine (Septocaine)

Articaine has been reported to provide very effective local anesthesia.²³⁶ It was approved for use in the United States in April 2000 and is marketed as Septocaine (Septodont, New Castle, DE) and as a 4% solution with either 1:100,000 or 1:50,000 epinephrine.¹⁶²^,¹⁸⁴ Articaine is classified as an amide. It has a thiophene ring (instead of a benzene ring, as do the other amide local anesthetics) and an extra ester linkage, which results in hydrolysis of articaine by plasma esterases.¹⁶² A number of studies have evaluated articaine and concluded that it is safe when used in appropriate doses.* Lidocaine and articaine have the same maximal dose of 500 mg for adult patients (recommended dose: 6.6 to 7 mg/kg), but the maximum number of cartridges is different because of the differences in drug concentration (see Table 20-2).¹⁵⁸

Clinical Effectiveness of Articaine for Inferior Alveolar Nerve Blocks

The available literature indicates that articaine is equally effective when statistically compared to other local anesthetics.^† When comparing the anesthetic efficacy of 4% articaine with 1:100,000 epinephrine to 2% lidocaine with 1:100,000 epinephrine for IAN blocks, one study found that the two solutions were not significantly different (Fig. 20-5).¹⁷⁶ Two studies found no difference in efficacy between 4% articaine with 1:100,000 and 1:200,000 epinephrine.¹⁸⁴^,²⁵⁹ Another study compared the anesthetic efficacy of 4% articaine with 1:100,000 epinephrine to 2% lidocaine with 1:100,000 epinephrine for IAN blocks in patients experiencing irreversible pulpitis, in mandibular posterior teeth.³² The success rate (none or mild pain upon endodontic access or initial instrumentation) for the IAN block using the articaine solution was 24% and for the lidocaine solution success was 23%. There was no significant difference between the articaine and lidocaine solutions. Neither solution resulted in an acceptable rate of anesthetic success in mandibular posterior teeth. In summary, repeated clinical trials have failed to demonstrate any statistical superiority of articaine over lidocaine for nerve blocks.

FIG. 20-5 Incidence of first mandibular molar anesthesia: comparison of 4% articaine with 1:100,000 epinephrine to 2% lidocaine with 1:100,000 epinephrine. Results were determined by lack of response to electrical pulp testing at the maximum setting (percentage of 80 readings) across time for 60 minutes. No significant difference between the two solutions was noted.

^†References 32, 50, 94, 95, 160, 161, 176, 263, and 281.

Articaine and Uncorroborated Insurance Carrier Warning

A letter was sent to thousands of U.S. dentists in 2006 by insurer Emery and Webb/Ace USA stating, “…we have noticed an increase in reversible and, in some cases, nonreversible paresthesias (with Septocaine) … We are writing you to alert you to these events in hopes that you will not fall victim to one of these incidents.”¹⁵⁶ Knowledgeable dentists and educators communicated their concerns, and a Notice of Retraction was issued:

Unfortunately, we at Emery & Webb discovered upon further review, and subsequent to the mailings, that both documents contained inaccuracies and an alarmist tone, which was not warranted … Emery and Webb has not noted an increase in malpractice claims or lawsuits in connection with articaine … It should be made clear that Emery and Webb has not conducted any scientific investigation, sampling, testing, or other investigation of the articaine anesthetic, and has no independent knowledge or data which would restrict the use of the product.¹⁵⁶

Astute clinicians should be very careful of Web chat sites and colleagues’ clinical endorsements, because they may not accurately reflect the correct information regarding articaine.

Long-Acting Anesthetics

Clinical trials with bupivacaine (Marcaine) and etidocaine (Duranest) have been done in patients undergoing oral surgery,⁴⁶^,²³⁰ endodontic treatment,⁵⁵^,¹⁸⁵ and periodontic treatment.⁴⁰^,¹⁵¹ Etidocaine was recently withdrawn from the market by DENTSPLY Pharmaceuticals (York, PA). Bupivacaine provides prolonged analgesia and is indicated when postoperative pain is anticipated, but not all patients want lip numbness for an extended period.²³⁰ Patients should be questioned about their preference. Bupivacaine has a somewhat slower onset than lidocaine, but its duration of pulpal anesthesia in the mandible is almost twice as long (approximately 4 hours; Fig. 20-6).⁵⁸

FIG. 20-6 Incidence of first mandibular molar anesthesia: comparison of 0.5% bupivacaine with 1:200,000 epinephrine to 2% lidocaine with 1:100,000 epinephrine. Results were determined by lack of response to electrical pulp testing at the maximum setting (percentage of 80 readings) across time for 6 hours. The bupivacaine solution showed a longer duration of anesthesia than the lidocaine solution.

Ropivacaine (Naropin), a relatively new long-acting local anesthetic, is a structural homolog of bupivacaine.¹³² A number of studies have shown that ropivacaine has a lower potential for toxic CNS and cardiovascular effects than bupivacaine but produces equivalent pharmacologic effects.¹³² Ropivacaine and levobupivacaine are being developed as potentially new local anesthetics based on their stereochemistry. Both are S-isomers and are thought to cause less toxicity than the racemic mixture of bupivacaine currently marketed.²⁴⁵ A clinical trial has indicated that levobupivacaine showed significantly better postoperative pain control at 4 and 24 hours after infiltration injection than ropivacaine.²⁰⁵ Because of their decreased potential for cardiac and CNS toxicity, ropivacaine and levobupivacaine may replace bupivacaine with epinephrine in clinical dental practice.

Alternative Injection Sites

Gow-Gates and Vazirani-Akinosi Techniques

Some clinicians have reported that the Gow-Gates technique⁸⁸ has a higher success rate than the conventional IAN block injection,¹⁵⁷^,¹⁵⁸ but controlled experimental studies have failed to show superiority of the Gow-Gates technique.^2,^84,^182,²⁵⁸ Neither has the Vazirani-Akinosi technique^3,^84,¹⁵⁸ been found superior to the standard inferior alveolar injection.^84,^164,^246,^258,²⁸⁸ In a small study of 21 patients, no difference was found between lidocaine (11 patients) and articaine (10 patients) formulations for the Gow-Gates injection in patients with irreversible pulpitis.²⁴⁰ These techniques do not replace the conventional IAN block. The Vazirani-Akinosi technique is indicated for cases involving a limited mandibular opening.

Incisive Nerve Block at the Mental Foramen

The incisive nerve block alone is successful for anesthetizing the premolar teeth,^121,^193,²⁷⁵ but it does not anesthetize the central and lateral incisors.¹⁹³ A slow injection (60 seconds) did not increase success over a fast injection (15 seconds).²⁷⁵ The combination of an incisive nerve block and an IAN block increases success of anesthetization of mandibular first molars, but an intraosseous or PDL injection is a better choice for supplemental anesthesia of the first molar if the IAN block fails.¹⁹³

Infiltration Injections of a Lidocaine Solution

Labial or lingual infiltration injections alone are not very effective for obtaining pulpal anesthesia in mandibular teeth.^94,^95,²⁸⁶ A combination of labial and lingual infiltration significantly increases success in anterior teeth over either labial or lingual infiltration alone.¹⁷² Adding a labial infiltration (1.8 ml of 2% lidocaine with 1:100,000 epinephrine) to a conventional IAN injection increases the success of pulpal anesthesia in mandibular anterior teeth but not in the mandibular first molar.³³^,⁶⁴

Mandibular First Molar Infiltration Injections of an Articaine Solution

Four studies showed articaine was significantly better than lidocaine for a primary buccal infiltration of the mandibular first molar.^38,^122,^124,²²⁵ Success rates (two consecutive 80 readings with the electric pulp tester) of 64%, 54%, 64% to 70%, and 87% were recorded for an articaine formulation in these studies. However, the duration of pulpal anesthesia declined over 60 minutes.

Mandibular First Molar Infiltration Injections of an Articaine Solution Following an Inferior Alveolar Nerve Block

A recent study found 4% articaine with 1:100,000 epinephrine resulted in a higher success rate (88%) than 2% lidocaine with 1:100,000 epinephrine (71% success rate) for mandibular first molar buccal infiltrations following an IAN block.⁹⁸ Success was defined as achieving two consecutive 80 readings within 10 minutes following the IAN block plus infiltration injections, and the 80 reading was continuously sustained through the 60th minute. The finding is important to dentists and patients because we now have a way to help anesthetize the mandibular first molar when the IAN block fails in asymptomatic patients.

Attempts to Increase Success of the Inferior Alveolar Nerve Block

Increasing the Volume of Anesthetic

A possible method for increasing anesthetic success is to double the injection volume of local anesthetic solution. However, increasing the volume of 2% lidocaine with epinephrine to 3.6 ml (two cartridges) does not increase the incidence of pulpal anesthesia with the IAN block (Fig. 20-7).*

FIG. 20-7 Incidence of first mandibular molar anesthesia: comparison of 3.6 ml and 1.8 ml of 2% lidocaine with 1:100,000 epinephrine. Results were determined by lack of response to electrical pulp testing at the maximum setting (percentage of 80 readings) across time for 60 minutes. No significant difference between the two volumes was noted.

Increasing the Epinephrine Concentration

A second approach for increasing the success of the IAN block is to increase the concentration of epinephrine. However, when this technique was evaluated in clinically normal teeth, no advantage was seen in using a higher concentration (1:50,000) of epinephrine.⁴²^,²⁶⁷

Addition of Hyaluronidase

Hyaluronidase reduces the viscosity of the injected tissue, permitting a wider spread of injected fluids.⁷ Early studies in dentistry found that an IAN block was more easily attained and was more complete when hyaluronidase was added to an anesthetic solution.¹³⁶^,¹⁵⁵ However, a controlled clinical trial found that adding hyaluronidase to a lidocaine solution with epinephrine did not statistically increase the incidence of pulpal anesthesia in IAN blocks.²²² In addition, hyaluronidase increased the occurrence of adverse effects (i.e., increased pain and trismus).²²²

Carbonated Anesthetic Solutions

Experimentally, carbonated anesthetic solutions are more effective because the anesthetic is trapped in the nerve.²⁸ In addition, carbon dioxide (CO₂) has a synergistic relationship with local anesthetics and a direct depressant action on nerves.²⁸ However, a controlled clinical study was unable to demonstrate a superior effect of lidocaine hydrocarbonate in IAN blocks.²⁸

Diphenhydramine as a Local Anesthetic Agent

Diphenhydramine (Benadryl) has been advocated for patients who are allergic to commonly used local anesthetics. Two studies found diphenhydramine was less effective than lidocaine for extractions.¹⁷⁴^,²⁷² Another study found the combination of lidocaine/diphenhydramine with epinephrine and diphenhydramine with epinephrine were significantly less effective for pulpal anesthesia than lidocaine with epinephrine for IAN blocks.²⁷⁷ They also found that the diphenhydramine solutions were more painful upon injection and had a high incidence of moderate postoperative pain.

Addition of Meperidine to Lidocaine

Two studies found the addition of meperidine (Demerol) to a lidocaine formulation did not increase the success of the IAN block.¹⁶^,⁸⁷

Factors in Failure of the Inferior Alveolar Nerve Block

Accessory Innervation

The mylohyoid nerve is the accessory nerve most often cited as a cause of failure of mandibular anesthesia.⁷⁰^,²⁷⁸ A controlled clinical trial compared the IAN block alone to a combination of the IAN block and mylohyoid nerve block using 2% lidocaine with 1:100,000 epinephrine (Fig. 20-8), which was aided by the use of a peripheral nerve stimulator.³⁴ The investigators found that the mylohyoid injection did not significantly enhance pulpal anesthesia of the IAN block (Fig. 20-9), so the study does not support the hypothesis that the mylohyoid nerve is a major factor in failure of the IAN block.

FIG. 20-8 Injection site for the mylohyoid nerve block.

FIG. 20-9 Incidence of first mandibular molar anesthesia: comparison of the combination mylohyoid infiltration plus the inferior alveolar nerve block to the inferior alveolar nerve block alone. Results were determined by lack of response to electrical pulp testing at the maximum setting (percentage of 80 readings) across time for 60 minutes. No significant difference between the two techniques was noted.

Accuracy of Injection

It has been theorized that an inaccurate injection contributes to inadequate mandibular anesthesia, but a number of studies determined that use of a medical ultrasound unit or radiographs to guide needle placement for IAN blocks did not result in more successful pulpal anesthesia.^14,^74,⁹⁹ The authors of these studies speculated that the anesthetic solution migrated along the path of least resistance, which was determined by fascial planes and structures encountered in the pterygomandibular space. These studies highlight an important clinical point: Lack of pulpal anesthesia is not necessarily the result of an inaccurate injection.

Needle Deflection

Needle deflection has been proposed as a cause of failure with the IAN block.³⁷^,⁴⁵^,^107a Several in vitro studies have shown that beveled needles tend to deflect toward the nonbeveled side (i.e., away from the bevel).* To compensate for this, a bidirectional needle rotation technique using the computer-assisted Wand (CompuDent, Milestone Scientific, Deerfield, IL) has been proposed in which the Wand handpiece assembly and needle are rotated in a fashion similar to the rotation of an endodontic hand file.^107a The technique was found to reduce deflection during insertion of the needle. A controlled clinical trial compared the anesthetic success of the conventional IAN block using two needle insertion methods.¹³³ No significant difference in anesthetic success was seen when the needle bevel was oriented away from the mandibular ramus (so that the needle would deflect toward the mandibular foramen [50% success]) and when the bidirectional Wand needle rotation technique was used (56% success).¹³³ Neither technique resulted in an acceptable rate of anesthetic success in patients with irreversible pulpitis.

Needle Bevel and Success

In asymptomatic subjects, the orientation of the needle bevel away or toward the mandibular ramus for an IAN block did not affect anesthetic success or failure.²⁵² Therefore, the use of commercial needles with markers to indicate needle bevel is not necessary.

Speed of Injection and Success

A slow IAN block injection (60 seconds) resulted in higher success rates (electric pulp testing) than a rapid injection (15 seconds).¹²³

Cross-Innervation

Cross-innervation from the contralateral inferior alveolar nerve has been implicated in failure to achieve anesthesia in anterior teeth after an IAN injection. Experimentally, cross-innervation occurs in incisors²²⁷^,²⁸⁶ but plays a very small role in failure with IAN block.

A Theory on Why Failure Occurs With the Inferior Alveolar Nerve Block in Asymptomatic Patients

The central core theory may be the best explanation of why failure occurs with the IAN block.⁴⁷^,²⁵⁵ According to this theory, nerves on the outside of the nerve bundle supply molar teeth, and nerves on the inside of the nerve bundle supply anterior teeth (Fig. 20-10). Even if deposited at the correct site, the anesthetic solution may not diffuse into the nerve trunk and reach all nerves to produce an adequate block. Although this theory may explain the higher experimental failure rates with the IAN block in anterior teeth compared with posterior teeth *, it does not explain the increased failure rate observed in painful teeth.

FIG. 20-10 Central core theory. The axons in the mantle bundle supply the molar teeth, and those in the core bundle supply the anterior teeth. The extraneural local anesthetic solution diffuses from the mantle to the core.

(Modified from De Jong RH: Local anesthetics, St Louis, 1994, Mosby.)

Enhancement of Mandibular Anesthesia in Asymptomatic Patients

Supplemental Intraligamentary Injection

Experimental studies in volunteers without dental pathosis have shown that the addition of an intraligamentary injection of 2% lidocaine with 1:100,000 epinephrine (delivered with a high-pressure syringe) to an IAN block significantly increased the success of pulpal anesthesia for 23 minutes.²⁹ The short incidence of anesthesia was related to the small amount of anesthetic solution administered.

Supplemental Intraosseous Injection

Several studies have shown that supplemental Stabident intraosseous injection, when added to an IAN block and using local anesthetics with vasoconstrictors, significantly increased the success of pulpal anesthesia for 60 minutes in the first molar (Fig. 20-11).^54,^92,²⁵¹ The intraosseous injection was more successful than the periodontal ligament injection because more anesthetic solution was delivered with the intraosseous injection. The addition of a supplemental intraosseous injection reduced the incidence of slow onset of pulpal anesthesia to zero compared with the IAN block alone (18% incidence).⁵⁴

FIG. 20-11 Incidence of first mandibular molar anesthesia: comparison of the combination intraosseous injection of 2% lidocaine with 1:100,000 epinephrine plus the inferior alveolar nerve block to the inferior alveolar nerve block alone. Results were determined by lack of response to electrical pulp testing at the maximum setting (percentage of 80 readings) across time for 60 minutes. The combination technique was significantly better at all postinjection times.

Another clinical study has shown that the use of 3% mepivacaine as a supplemental intraosseous injection after an IAN block significantly increased the success of pulpal anesthesia for 30 minutes (Fig. 20-12).⁷⁷ The shorter duration of the 3% mepivacaine, compared with 2% lidocaine with 1:100,000 epinephrine, was related to the lack of a vasoconstrictor.

FIG. 20-12 Incidence of first mandibular molar anesthesia: comparison of the combination intraosseous injection with 3% mepivacaine plus the inferior alveolar nerve block to the inferior alveolar nerve block alone. Results were determined by lack of response to electrical pulp testing at the maximum setting (percentage of 80 readings) across time for 60 minutes. The combination technique proved significantly better for approximately 30 minutes.

Use of Mannitol

An Ohio State University research group studied the use of mannitol to increase the efficacy of nerve blocks. Mannitol, a hyperosmotic sugar solution, is thought to temporarily disrupt the protective covering (perineurium) of sensory nerves, allowing the local anesthetic to gain entry to the innermost part of the nerve.⁸ These researchers found that the use of mannitol in combination with lidocaine increased anesthetic success in IAN blocks about 15% to 20%. The drug combination may be introduced sometime in the future.

Maxillary Anesthesia with 2% Lidocaine and 1:100,000 Epinephrine

Descriptions of conventional techniques for maxillary anesthesia are available for review in numerous articles and textbooks.¹¹⁶^,¹⁵⁸

Clinically, maxillary anesthesia is more easily obtained than mandibular anesthesia.¹²⁹ As a frame of reference, the most commonly used injection for anesthetization of maxillary teeth is infiltration with 1.8 ml of 2% lidocaine (1:100,000 epinephrine).

Success Rate

In anterior and posterior teeth, infiltration anesthesia results in a high incidence (90% to 95%) of successful pulpal anesthesia (obtaining an 80 reading on an EPT that ranges from 0 to 80 in intensity).* Failure (never achieving an 80 reading) occurs about 5% to 10% of the time.† Maxillary infiltration anesthesia, therefore, is more successful than an IAN block. The technique does not achieve 100% pulpal anesthesia because of individual variations in response to the drug used and variations in anatomy and tooth position.

Onset of Anesthesia

The onset of pulpal anesthesia usually occurs within 5 to 7 minutes,^90,^126,^166,¹⁷⁵ but slow onset of anesthesia (defined in these cases as achieving an 80 EPT reading after 7 minutes) occurs about 20% of the time in first molars.^90,^126,^166,¹⁷⁵

Duration of Anesthesia

The potential problem with infiltration anesthesia in the maxilla is duration. The incidence of short duration of anesthesia (achieving an 80 reading and then losing this reading) ranges from about 60% in lateral incisors to 38% in first molars.^90,^126,^166,¹⁷⁵ Pulpal anesthesia in anterior teeth starts to decline after about 20 to 30 minutes; in molar teeth, anesthesia declines after about 30 to 45 minutes. These time courses have clinical implications. In an emergency endodontic procedure on a first molar, the pulp usually can be removed within 20 to 30 minutes, so the duration of anesthesia is of little consequence. However, if the practitioner is preparing to obturate the tooth and this procedure takes an hour, the patient might experience pain. Therefore additional local anesthetic should be administered.

Time Course of Pulpal Anesthesia for the Maxillary First Molar

Fig. 20-13 shows the time course for complete pulpal anesthesia for an asymptomatic first molar, as defined by the percentage of patients who do not respond to an 80 EPT stimulus across time. Some patients (20%) had a slow onset of anesthesia until around 11 minutes. The overall success rate (no response at the 80 reading) is 95% to 100%, with peak effects observed at around 30 minutes after injection.

FIG. 20-13 Incidence of first maxillary molar anesthesia, as determined by lack of response to electrical pulp testing at the maximum setting (percentage of 80 readings) across time for 60 minutes.

Significance of Lip Numbness

Soft-tissue anesthesia (lip or cheek numbness) is not necessarily related to the duration of pulpal anesthesia. Pulpal anesthesia does not last as long as soft-tissue anesthesia^90,^166,¹⁷⁵

Alternative Anesthetic Solutions for Infiltration Injections

Plain Solutions: 3% Mepivacaine (Carbocaine, Polocaine, Scandonest) and 4% Prilocaine (Citanest Plain)

Solutions of 3% mepivacaine plain and 4% prilocaine plain provide a short duration of pulpal anesthesia, averaging about 15 to 20 minutes (Fig. 20-14),¹²⁶^,¹⁶⁶ and are indicated for procedures of short duration. These agents are generally not as safe as solutions with vasoconstrictors if large volumes are administered, because they are rapidly absorbed systemically, resulting in excessive plasma concentrations and possible toxic reactions.¹⁵⁸

FIG. 20-14 Incidence of first maxillary molar anesthesia: comparison of 3% mepivacaine to 2% lidocaine with 1:100,000 epinephrine. Results were determined by lack of response to electrical pulp testing at the maximum setting (percentage of 80 readings) across time for 60 minutes. The 3% mepivacaine showed a shorter duration of anesthesia than the lidocaine solution.

4% Prilocaine With 1:200,000 Epinephrine (Citanest Forte)

The effect of 4% prilocaine (1:200,000 epinephrine) is similar to that of an infiltration injection with 2% lidocaine (1:100,000 epinephrine).¹²⁶

Articaine With 1:100,000 Epinephrine (Septocaine)

Several studies have shown that articaine with epinephrine was similar in action to prilocaine with epinephrine and lidocaine with epinephrine for maxillary infiltration injections.^50,^94,^95,²⁶³ A recent study found maxillary infiltration of 4% articaine with 1:100,000 epinephrine statistically improved anesthetic success, when compared to 2% lidocaine with 1:100,000 epinephrine, in the lateral incisor but not in the first molar. ⁵⁷

0.5% Bupivacaine With 1:200,000 Epinephrine (Marcaine)

Success rates (no response to EPT) with bupivacaine range from 80% to 95% in the maxillary lateral incisor, compared with 50% in the maxillary second premolars.^43,^90,^132,²⁵⁷ Although bupivacaine provides long-term anesthesia in the mandible, it does not provide prolonged pulpal anesthesia with maxillary infiltration injection.^43,^90,¹³² In the lateral incisor, bupivacaine has a shorter duration of pulpal anesthesia than lidocaine.⁴³^,⁹⁰ In the first molar, bupivacaine’s duration of pulpal anesthesia is equivalent to that of lidocaine.⁹⁰

Extending the Duration of Maxillary Infiltrations

Increasing the Solution Volume

For maxillary infiltrations, increasing the volume of 2% lidocaine with 1:100,000 epinephrine from 1.8 ml to 3.6 ml provided a statistically longer duration of pulpal anesthesia.¹⁷⁵ A repeated infiltration of 1.8 ml of 2% lidocaine with 1:100,000 epinephrine given 30 minutes following an initial infiltration of 1.8 ml of 2% lidocaine with 1:100,000 epinephrine significantly improved the duration of pulpal anesthesia (from 37 minutes through 90 minutes) in the maxillary lateral incisor²³⁸ (Fig. 20-15).

FIG. 20-15 Incidence of maxillary lateral incisor pulpal anesthesia using an initial infiltration and a repeated infiltration 30 minutes later (both infiltrations used 1.8 ml of 2% lidocaine with 1:100,000 epinephrine). Results were determined by lack of response to electrical pulp testing at the maximum setting (percentage of 80 readings). The repeated infiltration injection significantly prolonged the duration of pulpal anesthesia.

Alternative Maxillary Injection Techniques

Posterior Superior Alveolar (PSA) Nerve Block

The PSA nerve block provides pulpal anesthesia for the second and third molars and in some first molars.¹⁵⁴ Generally, with the first molar, an additional buccal infiltration injection may be needed after the PSA block to ensure patient comfort. The PSA injection often is indicated when all the molar teeth require anesthesia. If the procedure involves the first molar, an infiltration injection is a better choice because it is more predictable for pulpal anesthesia than the PSA injection.

Infraorbital Nerve Block

The infraorbital nerve block produces profound lip numbness.¹²^,¹²⁵ It successfully anesthetizes the first and second premolars, but the duration of pulpal anesthesia is less than 60 minutes.¹²^,¹²⁵ The infraorbital block does not successfully anesthetize the pulps of the central or lateral incisors.¹²^,¹²⁵ Essentially, this injection technique is the same as an infiltration injection over the premolar teeth for pulpal anesthesia.

Second Division Nerve Block

The second division nerve block successfully anesthetizes the pulps of molar teeth and about 50% of the second premolars.²²^,¹⁶⁵ It does not routinely anesthetize the pulps of anterior teeth.²²^,¹⁶⁵ The high tuberosity approach is preferred over the greater palatine technique because the success rate is similar and the procedure is less painful.²²

Palatal–Anterior Superior Alveolar (P-ASA) Nerve Block

Traditionally, maxillary anterior teeth have been anesthetized with an infiltration injection near the apex of the target tooth. In the late 90s the P-ASA injection, a site-specific injection for maxillary anterior teeth, was introduced.⁶⁸^,⁶⁹ The P-ASA injection involves a palatal injection into the incisive canal and derives its name from the injection’s supposed ability to anesthetize both the right and left anterior superior alveolar nerves (Fig. 20-16). A P-ASA injection of 0.9 to 1.4 ml of anesthetic solution has been reported to produce anesthesia of the maxillary incisors and usually the canines, with an expected duration of approximately 60 minutes.⁶⁸ One study compared the anesthetic efficacy of 2% lidocaine with 1:100,000 epinephrine and 3% mepivacaine using the computer-assisted Wand Plus injection system and the P-ASA injection route.²³ Neither anesthetic produced greater than 58% successful pulpal anesthesia and therefore would not clinically ensure predictable pulpal anesthesia for the four maxillary incisors and canines.

FIG. 20-16 Distribution of the maxillary division of the trigeminal nerve, showing the anterior superior alveolar (ASA) nerve, the middle superior alveolar (MSA) nerve, and the posterior superior alveolar (PSA) nerve.

Moreover, 30% to 43% of patients report moderate to severe pain from the needle insertion for the P-ASA injection.¹⁹⁵ For needle placement into the incisive canal, 54% to 58% of subjects reported moderate to severe pain. For deposition of the anesthetic solution, 8% to 12% of subjects reported moderate pain. Postoperatively, approximately 12% to 18% of the subjects experienced temporary numbness or paresthesia of the incisive papilla, and 20% to 28% had swelling or soreness of the incisive papilla. The P-ASA injection, therefore, can be a painful injection, and it has a low to modest success rate.

Anterior Middle Superior Alveolar (AMSA) Nerve Block

The AMSA injection is another new technique for anesthetizing maxillary teeth.^66,^67,⁶⁹ The AMSA injection site is located palatally at a point that bisects the premolars and is approximately halfway between the midpalatine raphe and the crest of the free gingival margin (Fig. 20-17). The AMSA injection supposedly can anesthetize both the anterior and middle superior alveolar nerves^66,^67,⁶⁹ (see Fig. 20-16). Injection of 0.6 to 1.4 ml of anesthetic solution has been reported to produce pulpal anesthesia of the maxillary central and lateral incisors, canines, and first and second premolars, with an expected duration of 45 to 60 minutes.^66,^67,⁶⁹ A bilateral AMSA injection supposedly anesthetizes 10 maxillary teeth, extending from the second premolar on one side to the second premolar on the opposite side.⁶⁷

FIG. 20-17 Palatal injection site for the anterior middle superior alveolar (AMSA) injection.

Two studies of the AMSA technique found rather modest to low success rates, slow onset, and declining duration of pulpal anesthesia over 60 minutes.⁷³^,¹⁴⁶ The AMSA injection would not ensure predictable pulpal anesthesia from the second premolar to the central incisor.⁷³^,¹⁴⁶ Moreover, the AMSA injection, whether made with a computer-assisted injection system or a conventional syringe, produced moderate pain on needle insertion in 32% to 38% of study subjects and moderate pain upon solution deposition in 25% to 40% of subjects.¹⁹⁸

When the Wand Plus was used for the AMSA injection, statistically lower pain ratings were recorded for deposition of the anesthetic solution. However, regardless of whether the Wand Plus or a conventional syringe is used, the AMSA injection can be a painful injection, and it has a low to modest success rate.

Supplemental Anesthesia

Supplemental injections are essential when, as frequently occurs, anesthesia from conventional injections is inadequate and the pain is too severe for the practitioner to proceed. Three such supplemental techniques can be used: the intraligamentary injection, the intraosseous injection, or the intrapulpal injection.

If the patient has profound lip numbness and experiences pain upon endodontic access, repeating the IAN block does not help the problem. Clinicians may think another injection is helpful because the patient sometimes achieves pulpal anesthesia after the second injection, but the patient may simply be experiencing slow onset of pulpal anesthesia from the first injection.

Infiltrations of Articaine Following Maxillary or Mandibular Anesthesia in Patients With Irreversible Pulpitis

Using a visual analog scale to evaluate success, no significant differences were found between an articaine solution and a lidocaine solution when used as a supplemental infiltration after IAN blocks or maxillary infiltrations in patients with irreversible pulpitis.²²⁹ In a small study of 19 patients, no difference was found between lidocaine (9 patients) and articaine (10 patients) formulations in maxillary infiltrations for patients with irreversible pulpitis.²⁴⁰

Supplemental Buccal Infiltration of Articaine After a Failed Inferior Alveolar Nerve Block in Patients With Irreversible Pulpitis

A recent study found that when IAN block failed, there was only a 58% success rate for a supplemental buccal infiltration of 1.8 ml of 4% articaine with 1:100,000 epinephrine in mandibular posterior teeth in patients with irreversible pulpitis.¹⁶⁷ This success rate was much lower than a supplemental intraosseous injection.

Intraligamentary Anesthesia

The technique for intraligamentary injection of anesthesia is reviewed in a number of published papers and textbooks.

Success of Intraligamentary Injection

The success of supplemental intraligamentary injections in achieving pulpal anesthesia for endodontic procedures has been reported to be 50% to 96%.^36,^159,^249,²⁶⁹ Intraligamentary injection produced a 50% to 79% success rate in endodontic treatment when used as a primary anesthetic technique.¹²⁷^,¹⁵⁹ If the first intraligamentary injection failed, reinjection was successful in 71% of patients, for an overall success rate of 92%.²⁶⁹ Similar results have been reported by other investigators.³⁶^,²⁴⁹ Intraligamentary injection is not successful in mandibular anterior teeth.¹⁷²^,²⁷⁴

Mechanism of Action

An intraligamentary injection forces anesthetic solutions through the cribriform plate into the marrow spaces around the tooth.^53,^72,^215,^248,²⁷⁰ The primary route is not via the periodontal ligament, and unlike the intrapulpal injection,¹⁷^,²⁶⁵ the mechanism of action is not a pressure anesthesia.⁵⁶^,¹⁸³ The intraligamentary injection should be considered an intraosseous injection.

Back-Pressure

Studies have shown that the most important factor for anesthetic success with an intraligamentary injection is injection under strong back-pressure.²⁴⁸^,²⁶⁹ Pressure is necessary to force the solution into the marrow spaces.

Anesthetic Solutions

A vasoconstrictor significantly increases the efficacy of an intraligamentary injection.^89,^128,^134,^170,²³⁷ Injection of a vasoconstrictor alone (1:100,000 epinephrine) does not produce pulpal anesthesia.²³⁷ Anesthetic solutions with reduced vasoconstrictor concentrations (bupivacaine or etidocaine with 1:200,000 epinephrine) are not very effective with this technique.^89,^119,¹²⁸

Amount of Solution Delivered

Usually about 0.2 ml of solution is deposited with each mesial and distal injection, using a traditional or pressure syringe. The exact amount is not always known because some of the anesthetic solution may escape from the sulcus during the injection.

Injection Discomfort

When an intraligamentary injection is given as a primary injection, needle insertion and injection of the anesthetic solution are only mildly discomforting in posterior teeth⁴¹^,¹⁵⁹^,²³⁷^,²⁷⁴; however, in maxillary lateral incisors, an intraligamentary injection can be painful.²⁷⁴

When the intraligamentary injection is given as a supplemental injection to anesthetize symptomatic vital teeth (i.e., in irreversible pulpitis), the patient may have moderate pain.⁵² Patients should be informed of this possibility.

Onset of Anesthesia

The onset of anesthesia is immediate with an intraligamentary injection,* which means no waiting period is required for the anesthesia to take effect.

Duration

Experimental studies with the EPT have shown that when the intraligamentary injection is given as a primary injection, the duration of profound pulpal anesthesia is approximately 10 to 20 minutes.^183,^237,²⁷⁴ When the injection is used as a supplemental technique in asymptomatic teeth after an IAN block, the duration of pulpal anesthesia is approximately 23 minutes.²⁹ Therefore, when the intraligamentary injection is used as a supplemental technique in endodontic therapy, the clinician must work fairly quickly and be prepared to reinject if profound anesthesia dissipates.

Postoperative Discomfort

Most patients have postoperative discomfort (mostly mild pain) when an intraligamentary injection is used as a primary technique.^41,^237,²⁷⁴ Most of this discomfort occurs the first day after injection, and the duration of discomfort averages 14 hours to 3 days.^41,^237,²⁷⁴ Postinjection discomfort is related to damage from insertion of the needle and not from the pressure of solution deposition.⁴¹ About 40% of patients report that the tooth feels high in occlusion.²³⁷^,²⁷⁴

When an intraligamentary injection is used as a supplemental technique for endodontic therapy, pain from the intraligamentary injection probably occurs in addition to any postoperative pain from the endodontic treatment.

Avulsion

In a letter to the editor of the Journal of the American Dental Association, Nelson¹⁹¹ reported on the avulsion of a tooth following intraligamentary injections. However, no clinical or experimental study has reported avulsion or loosening of teeth with this technique.^183,^237,²⁷⁴ Avulsion should not be a concern with intraligamentary injections.

Selective Anesthesia

Although some have reported that the intraligamentary injection can be used in the differential diagnosis of pulpally involved teeth,¹⁵³^,²⁴² experimental studies have shown that adjacent teeth may also become anesthetized with intraligamentary injection for a single tooth.^183,^237,²⁷⁴ Therefore the intraligamentary injection should not be used for differential diagnosis.

Systemic Effects

When a high-pressure syringe was used in dogs, intraligamentary injection of solutions containing epinephrine caused cardiovascular responses similar to those seen with IV injections.²⁴⁷ Clinical studies using a high-pressure syringe in human beings found that intraligamentary injections of such solutions did not significantly change the heart rate, rhythm, amplitude, or the blood pressure.²⁵^,¹⁹⁴ These studies support the conclusion that intraligamentary injections do not cause significant changes in heart rate in human beings.

Needle Gauge

Different needle gauges (25, 27, or 30) have been shown to be equally effective.¹⁵⁹^,²⁶⁹

Ligamental Syringes

Special ligamental syringes have not proved any more effective than a standard syringe.^41,^249,²⁶⁹

Safety to the Periodontium

Clinical and animal studies have demonstrated the relative safety of the intraligamentary injection technique.* Minor transient damage occurs only at the site of needle penetration, and the tissue subsequently undergoes repair. In very rare cases, periodontal abscesses and deep pocket formation have occurred after intraligamentary injections.²⁹^,²⁷⁴ A very small clinical risk of periodontal abscess formation and bone loss exists with this technique, and although these effects are rare, the clinician should be aware of them. Localized areas of root resorption after intraligamentary periodontal ligament injections have also been reported.²⁰⁷^,²²³

Safety to the Pulp

Clinical and animal studies have shown that intraligamentary injections have no permanent effect on the pulp.^† However, intraligamentary injection of a solution with epinephrine produces a rapid, prolonged decrease in blood flow.¹³⁴ Some have suggested that using this injection technique during restorative procedures could result in accumulation of inflammatory mediators that would not be effectively removed because of the reduced blood flow.¹³⁴ This hypothesis was directly tested, and intraligamentary injection of an anesthetic solution containing a vasoconstrictor in conjunction with a deep cavity preparation did not produce a more severe reaction than in controls (cavity preparation only).²¹¹ Rather, the depth of the cavity preparation was the most important factor dictating pulpal responses. Intraligamentary injections are therefore unlikely to cause pulpal necrosis.

Safety in Primary Teeth

One study has shown that intraligamentary injection of primary teeth may cause enamel hypoplasia of the developing permanent teeth.²¹ The effect noted was not caused by the injection technique but by the anesthetics used—that is, the cytotoxic anesthetic agents bound to the enamel matrix in the developing tooth germ. The same effect seemingly would be produced by an infiltration injection next to the developing tooth, so the recommendation that intraligamentary injections be used with great care on primary teeth close to developing permanent teeth²¹ may not be correct.

Safety in Periodontally Involved Sites

Intraligamentary injections have been shown to be safe in cases of mild to moderate gingival inflammation or incipient periodontitis.³⁹

Precautions

No research as yet has shown how painful an intraligamentary injection would be or if it would result in anesthesia in teeth with cellulitis or abscess formation (symptomatic necrotic teeth with periradicular radiolucencies).

New Technology for Intraligamentary Injections: The Wand

A computer-assisted local anesthetic delivery system was introduced by Milestone Scientific (Livingstone, NJ) that can be used to administer an intraligamentary injection. The Wand (also called CompuDent or CCLAD) accommodates a standard local anesthetic cartridge that is linked by sterile microtubing to a disposable, penlike handpiece with a Luer-Lok needle (Fig. 20-18). The device is activated by a foot control, which automates the infusion of local anesthetic solution at a controlled rate. Two flow rates, slow or fast, may be initiated and maintained by a foot pedal control. The fast rate delivers 1.4 ml of solution in 1 minute. The slow rate delivers 1.4 ml of solution in approximately 4 minutes, 45 seconds. The slow rate is used for the intraligamentary injection.

FIG. 20-18 Wand computer-assisted local anesthetic delivery unit. The handpiece assembly and microtubing are also shown.

(Courtesy CompuDent/Milestone Scientific, Livingston, NJ.)

Anesthetic Success of the Intraligamentary Injection, Using the Wand in Asymptomatic Vital Teeth

An experimental study recently compared the anesthetic efficacy of primary intraligamentary injection of 1.4 ml of 4% articaine with 1:100,000 epinephrine and 1.4 ml of 2% lidocaine with 1:100,000 epinephrine administered with a computer-controlled local anesthetic delivery system in the mandibular first molar.¹³Successful pulpal anesthesia (two consecutive 80 EPT readings) was obtained 86% of the time with the articaine solution and 74% of the time with the lidocaine solution. No significant difference was seen between the articaine and lidocaine solutions. The duration of pulpal anesthesia ranged from 31 to 34 minutes, longer than the 10 minutes recorded in a similar study using a pressure syringe and 0.4 ml of a lidocaine solution.²⁷⁴ Therefore the computer-controlled local anesthetic delivery system offers the advantage of increasing the duration of pulpal anesthesia; however, the anesthesia slowly decreases over 60 minutes.

Anesthetic Success of the Intraligamentary Injection Using the Wand in Symptomatic Vital Teeth

Supplemental intraligamentary injection, administered with a computer-controlled anesthetic delivery system in mandibular posterior teeth diagnosed with irreversible pulpitis after failure of an IAN injection, produced a 56% anesthesia success rate.¹⁹⁶ These results were somewhat disappointing because the computer-controlled anesthetic delivery system should have been capable of delivering approximately 1.4 ml of anesthetic solution with the intraligamentary injection by consistent maintenance of a precise flow rate.

Intraosseous Anesthesia

Stabident and X-Tip Systems

The intraosseous route delivers a local anesthetic solution directly into the cancellous bone adjacent to the tooth to be anesthetized. Infiltration injections of lidocaine formulations are not effective for anesthesia of the mandibular molar teeth because of the thickness of the cortical plate; therefore dentists do not attempt infiltration anesthesia in the posterior mandible. The intraosseous injection overcomes this problem by allowing direct access to the cancellous bone. One clinical study directly compared the infiltration and intraosseous injection techniques, using 1.8 ml of 2% lidocaine with 1:100,000 epinephrine in the maxillary lateral incisor.²⁰¹ The two techniques produced similar results, except that the intraosseous technique had a quicker onset and a shorter duration of anesthesia (Fig. 20-19).

FIG. 20-19 Incidence of anesthesia for intraosseous and infiltration injections. Results were determined by lack of response to electrical pulp testing at the maximum setting (percentage of 80 readings) across time for 60 minutes. The intraosseous injection showed a quicker onset and a shorter duration of anesthesia.

Two intraosseous systems have been studied clinically: the Stabident system (Fairfax Dental Inc, Miami, FL) and the X-tip system (DENTSPLY, Tulsa, OK). Two other anesthetic systems have been introduced: the IntraFlow (Pro-Dex Inc, Irvine, CA) and the Comfort Control Syringe (DENTSPLY International, York, PA). The IntraFlow system combines a slow-speed handpiece with an anesthetic cartridge dispenser system and a rotating needle/drill. The anesthetic solution is delivered after the cortical bone is perforated. When the IntraFlow system was used as a primary technique in a small group of 15 patients with irreversible pulpitis, an 87% success rate was reported (two consecutive 80 readings with a pulp tester).²¹⁶ While encouraging, more research on the IntraFlow system is needed. The Comfort Control Syringe is an electronic delivery system and has five preprogrammed injection rates. No published controlled studies have evaluated the Comfort Control Syringe system in clinical dentistry.

The Stabident system is composed of a slow-speed, handpiece-driven perforator, a solid 27-gauge wire with a beveled end that drills a small hole through the cortical plate (Fig. 20-20). The anesthetic solution is delivered to cancellous bone through the 27-gauge, ultrashort injector needle placed into the hole made by the perforator (Fig. 20-21).

FIG. 20-20 Stabident perforator, a solid 27-gauge wire with a beveled end that is placed in a slow-speed handpiece.

FIG. 20-21 The anesthetic solution is delivered to the cancellous bone through the needle placed into the hole made by the perforator.

The X-tip anesthesia delivery system consists of an X-tip that separates into two parts, the drill and the guide sleeve (Fig. 20-22). The drill, a special hollow needle, leads the guide sleeve through the cortical plate, whereupon it is separated and withdrawn. The remaining guide sleeve is designed to accept a 27-gauge needle for injection of the anesthetic solution (Fig. 20-23). The guide sleeve is removed after the intraosseous injection is complete.

FIG. 20-22 The X-tip anesthesia delivery system consists of an X-tip (top) that separates into two parts: the drill (a special hollow needle) and the guide sleeve component (bottom).

FIG. 20-23 Anesthetic solution is injected through the X-tip guide sleeve.

The technique for intraosseous injection of anesthesia using the Stabident or X-tip system can be reviewed in the systems’ instruction manuals or in published papers.^35,^78,²¹⁸^-²²⁰

Perforation Pain and Solution Deposition with Irreversible Pulpitis

Generally the Stabident system produces a very low incidence of moderate pain from perforation and solution deposition in asymptomatic patients.^35,^78,²¹⁸^-²²⁰ A higher incidence was reported when the system was used to make intraosseous injections in mandibular posterior teeth with irreversible pulpitis. Up to 9% of patients reported moderate to severe pain after perforation, and 5% to 31% reported moderate to severe pain during deposition of the anesthetic solution.²⁰⁰^,²¹⁷

With the X-tip system, 48% of patients with irreversible pulpitis had moderate to severe pain with perforation, and 27% had moderate pain with solution deposition.¹⁹⁷ Patients with irreversible pulpitis may experience a transient but moderate to severe pain on perforation and solution deposition when either the Stabident or X-tip system is used. The higher pain ratings, compared with those for asymptomatic teeth, are probably related to preexisting hyperalgesia, which leads to increased pain responsiveness and preoperative anxiety.

Perforator Breakage

In about 1% of cases, the metal perforator separates from the plastic shank during use.^35,^54,^79,^197,²¹⁸^-²²⁰ The metal wire is easily removed with a hemostat. This separation usually occurs during a difficult perforation (e.g., dense cortical bone); the wire probably is heated excessively, causing the plastic hub to melt. No perforator breakage (metal perforator breaking into parts) has been reported in numerous studies.^35,^54,^79,^197,²¹⁸^-²²⁰

Optimal Location for Injection Site

Injection at a site distal to the tooth to be anesthetized produces the best anesthesia.* Maxillary and mandibular second molars are an exception to this rule. A mesial site should be selected for these teeth because of the increased thickness of the cortical plate in the mandible and the difficulty with perforation and needle placement at a distal site.

Onset of Anesthesia

The onset of anesthesia is immediate,* which eliminates the waiting period.

Site Selection: Attached Gingiva or Alveolar Mucosa

Both the Stabident and X-tip intraosseous systems instruct the user to locate the perforation site in attached gingiva. The gingival site allows the perforation to be made through a minimal thickness of cortical bone and generally is equidistant between adjacent root structures. However, because the guide sleeve remains in place with the X-tip system, two studies have successfully used it in alveolar mucosa at a more apical location.⁷⁹^,¹⁹⁷ The X-tip system has a definite clinical advantage over the Stabident system, because the X-tip perforation may be made at an apical location in unattached gingiva. If the Stabident system is used apically in alveolar mucosa, the hole for delivering the anesthetic solution is almost impossible to find. The clinician may want to consider using the X-tip in an apical location in specific clinical situations. For example, when periodontal pocketing does not allow perforation into cancellous bone through the more coronal attached gingiva or when interproximal space is lacking (i.e., roots are too close together), the X-tip system can be used to achieve pulpal anesthesia. If the Stabident system fails, the clinician may want to consider using the X-tip apically to achieve pulpal anesthesia.

Success of the Inferior Alveolar Nerve Block in Patients With Irreversible Pulpitis

Clinical studies of endodontics in patients with irreversible pulpitis have found that success (mild or no pain upon endodontic access or initial instrumentation) with the IAN block occurred between 19% and 56% of the time.* These studies would indicate that anesthesia is often difficult to achieve in irreversible pulpitis with only the IAN block.

Success of Intraosseous Anesthesia With Irreversible Pulpitis

Stabident System

In a clinical trial on patients with posterior teeth with irreversible pulpitis, a supplemental mandibular intraosseous Stabident injection (1.8 ml of 2% lidocaine with 1:100,000 epinephrine) was 91% successful in achieving total pulpal anesthesia.²⁰⁰ A second clinical trial evaluated the Stabident intraosseous injection in patients with irreversible pulpitis when conventional local anesthetic techniques failed. These researchers found that an initial supplemental intraosseous injection (0.45 to 0.9 ml of 2% lidocaine with 1:100,000 epinephrine) was successful in 79% of posterior mandibular teeth.²⁰⁶ A second intraosseous injection of the remaining cartridge increased the success rate to 91%. Therefore, initially giving a quarter to a half cartridge of 2% lidocaine with 1:100,000 epinephrine was less successful than initially giving a full cartridge. A third clinical trial in patients with mandibular teeth with irreversible pulpitis showed that supplemental intraosseous injection of 1.8 ml of 3% mepivacaine increased the success rate to 80% compared with the IAN block alone (25% success).²¹⁷ A repeat intraosseous injection of 1.8 ml of 3% mepivacaine increased the success rate to 98%. Therefore one cartridge of 3% mepivacaine plain is not as effective as one cartridge of 2% lidocaine with 1:100,000 epinephrine. However, injection of 3% mepivacaine does not produce the tachycardia observed with solutions that contain epinephrine.

X-Tip System

One clinical trial evaluated a supplemental X-tip intraosseous injection (1.8 ml of 2% lidocaine with 1:100,000 epinephrine) in patients with irreversible pulpitis when a conventional IAN block failed.¹⁹⁷ The X-tip injection site was 3 to 7 mm apical to the mucogingival junction of the mandibular molar or premolar tooth. The results showed an 82% success rate for anesthesia; it also showed an 18% failure rate caused by backflow of the anesthetic solution into the oral cavity. These researchers concluded that when an IAN block fails to provide profound pulpal anesthesia, the X-tip system, when used in an apical location without backflow of the anesthetic solution into the oral cavity, successfully achieves pulpal anesthesia in mandibular posterior teeth with irreversible pulpitis.

Intraosseous Success With an Articaine Solution in Patients With Irreversible Pulpitis

For posterior teeth diagnosed with irreversible pulpitis, the supplemental intraosseous injection of 1.8 ml of 4% articaine with 1:100,000 epinephrine was 86% successful when the IAN block failed.¹⁵ Therefore, the success rate of the articaine solution was similar to a solution of lidocaine.

Repeating the Intraosseous Injection

Repeating the intraosseous injection, using 1.4 ml of 2% lidocaine with 1:100,000 epinephrine 30 minutes after the initial intraosseous injection, provided an additional 15 to 20 minutes of pulpal anesthesia—similar to the duration of the initial intraosseous injection.¹¹⁷

Key to Successful Intraosseous Injection

The key to a successful intraosseous injection is flow of the anesthetic into the cancellous space. If anesthetic solution leaks out of the perforation site into the oral cavity, no anesthetic effect is achieved. Reperforation or use of another perforation site is a practical way to gain access to the cancellous bone in such cases. In fewer than 10% of cases, constricted cancellous spaces may limit the distribution of the anesthetic solution around the apices of the teeth.* In such cases, failure may result even if the anesthetic solution is delivered intraosseously.

Duration

In patients with irreversible pulpitis, supplemental intraosseous injection using either the Stabident or X-tip system provided anesthesia for the entire débridement appointment.^197,^200,²¹⁷

Timing of Intraosseous Injection

Considering the high failure rate of the IAN block in patients in pain, prudent practice would be to give all patients with irreversible pulpitis a supplemental intraosseous injection after an IAN block—that is, once the signs of lip numbness have developed, an intraosseous injection should be given. This technique significantly reduces pain and allows treatment to start sooner.

Many practitioners do not use this regimen because clinicians essentially do what they were taught in their initial clinical training, and sometimes change can be difficult. For example, a 1998 study in the Journal of the American Medical Association urged the use of anesthesia during circumcision⁵; nevertheless, up to 96% of baby boys currently don’t receive anesthesia. Because many physicians were taught during their residencies not to administer anesthesia, changing their practice philosophy probably will be a slow process. This is a common problem in many health care disciplines, and it emphasizes the need for practitioners to stay current with recent advances.

Anesthetic Success in Painful Teeth With Totally Necrotic Pulps and Radiolucent Areas

No study has investigated the use of intraosseous anesthesia in patients with painful teeth, totally necrotic pulps, and radiolucent areas. In a preliminary study performed at Ohio State, anesthetic solution deposition was very painful in these teeth, and the study had to be terminated.

Anesthetic Success in Partially Vital Teeth

The intraosseous injection should work in teeth in which the chamber is necrotic, the canals are vital or partially vital, and widening of the periodontal ligament can be seen radiographically. A recent history of hot and cold sensitivity should differentiate this condition from that of a necrotic tooth experiencing an acute exacerbation (Phoenix abscess).

Systemic Effects of Intraosseous Injection

Cardiovascular Effects

A transient increase in heart rate has been reported in 46% to 93% of cases involving Stabident and X-tip intraosseous injection of solutions containing epinephrine or levonordefrin.* Four clinical trials using techniques such as objective electrocardiographic recordings and pulse oximetry have shown that subjects experienced a transient tachycardia (mean increase of 12 to 32 beats/min) after Stabident intraosseous injection of 1.8 ml of 2% lidocaine with 1:100,000 epinephrine, 2% mepivacaine with 1:20,000 levonordefrin, or 1.8 ml of 1.5% etidocaine with 1:200,000 epinephrine.^27,^92,^221,²⁵¹ Another clinical trial reported transient tachycardia after intraosseous injection, but not with infiltration injection, of 1.8 ml of 2% lidocaine with 1:100,000 epinephrine in the maxillary anterior region.²⁷⁹ Generally, all these studies showed that the heart rate returned to baseline readings within 4 minutes in most patients. Therefore injection of anesthetic solutions containing vasoconstrictors, using either the Stabident or X-tip systems, results in a transient tachycardia. No significant change in diastolic, systolic, or mean arterial blood pressure has been observed with intraosseous injection of 2% lidocaine with 1:100,000 epinephrine.²⁷^,²²¹

An intraosseous injection of 1.4 ml of 2% lidocaine with 1:100,000 epinephrine with the Wand (CompuDent, CCLAD, Milestone Scientific, Livingston, NJ) at a fast rate resulted in a significantly higher heart rate when compared to a slow solution deposition using either the Wand or traditional syringe.²⁵⁶

Clinical Significance of Increased Heart Rate

Although the patient is likely to notice the transient tachycardia that occurs after Stabident or X-tip intraosseous injection of 2% lidocaine with 1:100,000 epinephrine, it generally is not clinically significant in healthy patients.²²¹ The clinical significance, cardiovascular effects, and contraindications to the use of vasoconstrictors in intraosseous injections have been reviewed.²²¹

Lack of Heart Rate Effect Of 3% Mepivacaine in Intraosseous Anesthesia

No significant tachycardia occurs when 3% mepivacaine is used for intraosseous anesthesia.⁷⁷^,²²¹ Clinicians should keep in mind that this anesthetic is an alternative for intraosseous injection in patients whose medical condition or drug therapy suggests caution in the use of solutions containing epinephrine or levonordefrin.⁷⁷^,²²¹

Cautious Use of Long-Acting Anesthetics for Intraosseous Anesthesia

In an attempt to increase the duration of pulpal anesthesia with intraosseous injections, some clinicians may consider using long-acting anesthetics. Bupivacaine (Marcaine) and etidocaine (Duranest) are long-acting anesthetics but only for IAN blocks. Long-acting anesthetics do not show an extended duration of anesthesia when injected by the intraosseous or maxillary infiltration routes.^43,^90,^109,²⁵¹ Bupivacaine and etidocaine have cardiotoxic effects¹⁰ and for intraosseous anesthesia basically are equivalent to 2% lidocaine with epinephrine in terms of efficacy, duration, and heart rate effects. Therefore bupivacaine and etidocaine offer no advantage clinically and should not be used for intraosseous anesthesia.

Plasma Levels of Lidocaine After Intraosseous Injection

Some authors have cautioned that administration of an overly large volume of local anesthetic with an intraosseous injection could lead to overdose reactions.¹¹³ One experimental study using volunteers found that injection of 1.8 ml of 2% lidocaine with 1:100,000 epinephrine produced venous plasma levels of lidocaine that were the same for maxillary anterior intraosseous and infiltration injections (Fig. 20-24).²⁷⁹Although systemic concentrations of vasoconstrictors have a short-lived effect on the heart rate, the plasma concentration of lidocaine delivered with intraosseous injection is no more than that delivered with infiltration, so the intraosseous technique should not be considered an intravascular injection with regard to lidocaine. Also, if it were an intravascular injection, little or no anesthetic effect would be demonstrated—that is, all the local anesthetic solution would be carried into the vascular system, with none left for pulpal anesthesia. Obviously, clinical and experimental studies have demonstrated clinical anesthesia with intraosseous techniques.* Therefore the precautions for the maximum amount of lidocaine for an infiltration injection would seem to apply to an intraosseous injection.

FIG. 20-24 Mean plasma concentrations of lidocaine for the intraosseous and infiltration injection techniques. No statistical differences were seen between the two techniques at any time period.

Postoperative Discomfort

When intraosseous injections are given with the Stabident system, either as a primary or a supplemental technique, most patients report no or only mild pain; approximately 2% to 15% report moderate pain.^35,^92,²¹⁸^-²²⁰ Less postoperative discomfort is reported for the Stabident intraosseous injection than for periodontal ligament injection.²³⁷

One study found that significantly more men experienced postoperative pain with the X-tip system than with the Stabident system.⁷⁸ The authors interpreted these results as being due to the denser, more mineralized bone in the posterior mandible in men and to the fact that the diameter of the X-tip perforating system is larger than that of the Stabident perforator, meaning that the X-tip system generates more frictional heat during perforation. In patients with irreversible pulpitis, the postoperative pain of the endodontic procedure likely adds to any postoperative pain from the intraosseous injection.

Postoperative Problems

With the Stabident system, fewer than 5% of patients develop swelling or exudate at the site of perforation.^35,^92,²¹⁸^-²²⁰ The X-tip system may show a higher incidence of postoperative swelling clinically.⁷⁸ With both systems, swelling or exudate (or both) may persist for weeks after the injection, but this resolves with time.^35,^78,^92,²¹⁸^-²²⁰ Slow healing of perforation sites may be the result of overheating of the bone caused by pressure during perforation.

With both the Stabident and X-tip systems, approximately 4% to 15% of patients report that for a few days, the tooth “feels high” during chewing.^35,^78,^92,²¹⁸^-²²⁰ This feeling most likely is an increased awareness to biting that results from soreness in the area caused by damage from perforation or inflammation of the bone. The incidence for the intraosseous injection is lower than that reported for the periodontal ligament injection (36% to 49%).⁴¹^,²³⁷

Intrapulpal Injection

In about 5% to 10% of mandibular posterior teeth with irreversible pulpitis, supplemental injections, even when repeated, do not produce profound anesthesia; pain persists when the pulp is entered. This is an indication for an intrapulpal injection.

The major drawback of the intrapulpal injection technique is that the needle is placed and the injection is made directly into a vital and very sensitive pulp; this injection is often moderately to severely painful.²⁰⁰ Because endodontics currently offers more successful methods of supplemental anesthesia, the intrapulpal injection should be given only after all other supplemental techniques have failed. Another disadvantage of the technique is the possible duration of pulpal anesthesia (15 to 20 minutes). The bulk of the pulpal tissue must be removed quickly, at the correct working length, to prevent reoccurrence of pain during instrumentation. Yet another disadvantage is that the pulp obviously must be exposed to allow direct injection. Anesthetic problems frequently occur before exposure while the clinician is still working in dentin.^196,^197,^200,²¹⁷

The advantage of the intrapulpal injection is that it produces profound anesthesia if given under back-pressure.¹⁷^,²⁶⁵ The onset of anesthesia is immediate, and no special syringes or needles are required. The methods for this technique can be found in many excellent endodontic textbooks. As mentioned previously, strong back-pressure is a major factor in achieving successful intrapulpal anesthesia.¹⁷^,²⁶⁵ Depositing the anesthetic solution passively into the chamber is insufficient because the solution will not diffuse throughout the pulp.

Management of Specific Endodontic Situations

Irreversible Pulpitis

When irreversible pulpitis is a factor, the teeth that are most difficult to anesthetize are the mandibular molars, followed by the mandibular premolars, the maxillary molars and premolars, and the mandibular anterior teeth. The fewest problems arise in the maxillary anterior teeth.

In some teeth, irreversible pulpitis is the condition in the apical portion of the canals; the tissue in the chamber is necrotic and does not respond to pulp testing. The pulp chamber can be entered easily, but when attempts are made to place a file to length, severe pain results. Intraosseous injections are helpful in these cases, and an intrapulpal injection may be used. However, irreversible pulpitis must be differentiated from a symptomatic necrotic tooth with apical pathosis. In the latter condition, it is unknown whether intraosseous injections are effective, and bacteria may be forced into the periradicular tissues by an intrapulpal injection.

Mandibular Teeth

Up until the 1980s, before supplemental intraligamentary and intraosseous injections became popular, clinicians would administer conventional anesthesia. After signs of soft-tissue anesthesia became evident, the pain abated and the patient relaxed. Local anesthesia produced the classic soft-tissue signs and relieved the painful symptoms, but pain frequently resulted when the access opening was begun or the pulp was entered. Currently, this pain has been significantly reduced with supplemental techniques.

Integration of the results of many recent clinical trials has changed the paradigm for anesthesia in these cases. Now, after administering conventional anesthesia and observing signs of soft-tissue anesthesia (which is required for a successful supplemental injection), the clinician administers an intraosseous injection. The patient should be informed that the tooth is not as numb as desired and that a little extra anesthetic will ensure his or her comfort. The clinician then explains that this extra anesthetic is placed next to the tooth and that the patient may feel some discomfort during the injection. For mandibular teeth with irreversible pulpitis, the supplemental intraosseous injection has evolved into a routine second injection, which is made before the clinician places a rubber dam and begins the access opening preparation.

The authors recommend using 1.8 ml of 3% mepivacaine plain (e.g., 3% Carbocaine) for the intraosseous injection. The basis for this recommendation is not the cardiovascular risks associated with anesthetic solutions containing a vasoconstrictor but rather the results of clinical research, which indicate that 3% mepivacaine is reasonably effective and has no clinical side effect of increased heart rate.⁷⁷^,²²¹ A few patients may overreact to the heart rate increase produced by solutions containing epinephrine, making treatment difficult or time consuming because the patient must be calmed before treatment can begin. However, many clinicians also use 2% lidocaine with 1:100,000 epinephrine for intraosseous anesthesia. Individual clinicians may want to experiment to determine which anesthetic solution (3% mepivacaine or 2% lidocaine with epinephrine) works best for them.

After anesthesia has been given, the rubber dam is placed, and the access preparation is slowly begun. The patient should be assured that the procedure will be stopped if he or she feels pain.

If the initial pain occurs in dentin, the rubber dam is removed and another cartridge of 3% mepivacaine administered, which should be successful.²¹⁷ Again, the clinician should make sure that lip numbness has developed from the IAN block and that the anesthetic solution is deposited into medullary bone.

If the initial pain occurs when the pulp is entered, the rubber dam is removed, and another cartridge of 3% mepivacaine is administered. If the patient still has pain, an intrapulpal injection is given. Prudent practitioners often modify the access preparation under these conditions by creating a straight-line shaft that directly opens the pulp tissue with little lateral access preparation (i.e., creating an entry hole the size of a #2 round bur). This provides quick access to the pulp, and the small size of the access facilitates intrapulpal injection with high back-pressure if this technique is indicated.

Maxillary Molar and Premolar Teeth

The initial anesthetic dose of 2% lidocaine with 1:100,000 epinephrine is doubled (to 3.6 ml) for the buccal infiltration.¹⁷⁵ A small amount of anesthetic solution usually is administered palatally for the rubber dam retainer. Although fewer anesthetic problems develop with the maxillary molars and premolars than with the mandibular posterior teeth, the clinician should be aware that they can occur.²⁰⁰ Administration of an intraosseous injection before proceeding with access may prove helpful in anesthetizing these teeth. As an alternative, the clinician can administer the anesthetic and then test the pulp with an EPT or cold refrigerant. If the response is negative, access preparation may proceed. If the response is positive, an intraosseous injection should be given. The clinician must keep in mind that pulp testing may not guarantee pulpal anesthesia in teeth with irreversible pulpitis.^52,^200,²¹⁷ Therefore, if a patient experiences pain despite a negative result on pulp testing, an intraosseous injection should be given.

Infiltration anesthesia does not last as long in maxillary teeth as in mandibular teeth. If the patient experiences pain during the later stages of instrumentation, an additional infiltration injection is necessary. Occasionally, pain is experienced in the palatal canal of molars. Infiltration over the palatal apex with 0.5 ml of anesthetic solution enhances pulpal anesthesia and may prove helpful.⁹¹

Maxillary Anterior Teeth

Anesthetic can be administered initially as a labial infiltration. Articaine with 1:100,000 epinephrine may be used.⁵⁷ Palatal anesthesia may be necessary for the rubber dam clamp. Although supplemental anesthesia is not often necessary, the intraosseous injection should be successful when given. The duration of anesthesia may be less than 1 hour. An additional infiltration injection may be necessary if the patient experiences pain during the later stages of instrumentation.

Symptomatic Teeth With Total Pulp Necrosis and Periradicular Radiolucencies

Symptomatic teeth with total pulp necrosis and periradicular radiolucencies are an indicator of pain in the periradicular tissue. These teeth may be painful to manipulation and movement during treatment and require extra care.

For mandibular teeth, the IAN block (and long buccal injection) are given in all situations. For maxillary teeth with no swelling, anesthesia is administered with conventional infiltration or a block. If soft-tissue swelling is present (i.e., cellulitis or abscess), infiltration should be done on either side of the swelling, or a block should be administered (second division nerve block, PSA nerve block or infraorbital nerve block). These provide some degree of bone and soft-tissue anesthesia. After signs of anesthesia are observed, the rubber dam is placed, and the access is begun slowly. The pulp chamber usually can be entered without causing the patient discomfort if the tooth is not torqued excessively. Hand and rotary file shaping can be performed without causing much pain if instruments are used with gentleness and care.

Occasionally, the conventional injections do not provide profound anesthesia, particularly in the maxillary teeth. Although results from clinical trials are lacking for treating this region, anecdotal experience suggests that careful consideration of a supplemental injection consisting of an additional palatal infiltration injection may be helpful.

Asymptomatic Teeth With Total Pulp Necrosis and Periradicular Radiolucencies

Asymptomatic teeth with pulp necrosis are the easiest to anesthetize; patient comfort usually is attained without difficulty. Although it may be tempting to proceed without anesthesia, the patient may have pain during instrumentation.

The conventional injections are administered: IAN block and long buccal injection for mandibular teeth, infiltration injections for maxillary teeth. The clinician then proceeds with access and file placement. The patient usually is comfortable in such cases. Rarely, some discomfort may be felt during canal preparation, requiring an intraosseous injection. An intrapulpal injection should not be given, because bacteria and debris may be forced from the canal into the periradicular tissue. Additional infiltration may be necessary in the maxilla if anesthesia begins to wear off.

Incision and Drainage

Clinicians should always attempt to achieve some degree of anesthesia before performing an incision and drainage procedure, because patients tolerate such procedures better. In the mandible, a conventional IAN injection and long buccal injection are given. In the maxilla, 1.8 ml of 2% lidocaine with 1:100,000 epinephrine is infiltrated on both sides of the facial swelling. As an alternative, because we are mostly concerned with soft-tissue anesthesia, a PSA or second division nerve block can be used for premolar and molar teeth and an infraorbital injection given for anterior teeth. For palatal swelling, 0.5 ml of 2% lidocaine with 1:100,000 epinephrine is infiltrated over the greater palatine foramen (molar and premolar teeth) or nasopalatine foramen (anterior teeth). These injections should not be used if swelling is present over the foramen; infiltration should be done on either side of the swelling. The Wand system reduces the pain of palatal injections. Except in a few studies,^9,^86,²³⁵ the computer-assisted injection system caused less pain than the conventional syringe technique for AMSA, palatal injections, and IAN block injections.*

Profound anesthesia usually is difficult to achieve in these cases, and this must be explained to the patient. The swelling is not injected, because traditionally it has been believed that injection directly into a swelling is contraindicated. Reasons for this included the possible spread of infection and the contention that the inflamed tissue’s lower pH would make the anesthetic solution less effective. These ideas may have some merit, but swellings are not injected basically because it is very painful and relatively ineffective. An area of cellulitis has an increased blood supply, and an anesthetic injected into this area is largely carried away into the systemic circulation, which diminishes the anesthetic’s local effectiveness. (See Chapters 2 and 15 for additional information on incision and drainage procedures.)

Periradicular Surgery

In the mandible, the inferior alveolar and long buccal injections are reasonably effective. Additional buccal infiltration injections in the vestibule may be useful to achieve vasoconstriction, particularly in the mandibular anterior region. In the maxilla, infiltration injections are generally effective; usually larger volumes are necessary to provide anesthesia over the surgical field.

If the area of operation is inflamed, anesthesia may not be totally successful. After the flap is reflected, if anesthesia is inadequate, attempts to enhance or regain anesthesia (through additional infiltrations or injecting the sensitive area) are not particularly effective. The effectiveness of surgical anesthesia is decreased by half when compared to anesthesia for nonsurgical procedures, because when reflecting a flap and opening into bone, the anesthetic solution is diluted by bleeding and removed by irrigation.²⁸⁴

As a prophylactic measure, an intraosseous injection using an anesthetic agent with 1:100,000 epinephrine may be administered at the site—after the above injections and before the surgery. This seems to enhance depth of anesthesia and may provide better hemostasis.

Use of a long-acting anesthetic has been advocated for surgery.⁴⁶^,²³⁰ In the mandible, this is reasonably effective. In the maxilla, long-acting agents have a shorter duration of anesthesia and decreased epinephrine concentrations, which result in more bleeding during surgery.⁴⁰^,²⁸⁴

After periradicular surgery, administration of a long-acting anesthetic has been suggested.¹⁵⁸ However, postsurgical pain is usually not severe and can be managed by analgesics.¹⁷¹

Interim Treatment for Irreversible Pulpitis Using Pulpotomy

Patients often have to decide between extraction and endodontic treatment for irreversible pulpitis. Because of financial circumstances, patients may choose extraction if they are only presented with two choices. One study performed pulpotomies in patients with irreversible pulpitis and restored the teeth with IRM or IRM base/glass ionomer core.¹⁶¹ They found pain was present in 10% of patients at 6 months and in 22% at 12 months. While not ideal, the third option of pulpotomy and temporary restoration may allow the patient time to find the means to finance complete endodontic treatment.^49,^130,¹⁶⁸

Pain Reduction in Irreversible Pulpitis When Endodontic Treatment Is Impossible

Endodontic débridement (pulpectomy or pulpotomy) most predictably relieves the pain of irreversible pulpitis.²⁰⁴ When débridement is not possible, clinicians may prescribe strong analgesics and penicillin in an attempt to relieve the pain. Unfortunately, the pain persists, and penicillin has no effect on the pain of untreated irreversible pulpitis.¹⁹⁰ One clinical trial evaluated pain reduction in untreated irreversible pulpitis by giving an intraosseous injection of Depo-Medrol (a long-acting methylprednisolone).⁷⁶ Clinically, the authors found that Depo-Medrol reduced the pain to manageable levels for up to 7 days before the patient received endodontic treatment, supporting this as a method for controlling a patient’s pain until definitive endodontic treatment can be performed.

Oral Conscious Sedation

Oral conscious sedation is beneficial in reducing patient’s anxiety, but it is not a way to reduce pain during dental treatment.¹⁵⁰ Profound local anesthesia is still required to control the patient’s pain.

Summary and Future Directions

The emergence of evidence-based dentistry has rapidly drawn interest across all fields of dentistry. Fortunately, the large number of high-quality, randomized, controlled studies in anesthesia and analgesia provide a wealth of information supporting evidence-based recommendations. The practitioner must focus on high-quality research when making clinical decisions. In contrast, little evidence is available when decisions are based on clinical anecdotes or advertisements. This chapter adopted the evidence-based approach in providing a comprehensive summary of local anesthetic clinical trials for the treatment of patients with endodontic pain.

The prudent practitioner knows that there is no “magic bullet” in pain control. Rather, the clinician must be knowledgeable about the advantages and disadvantages of several anesthetic-vasoconstrictor combinations and the various routes of injection. Clearly, judicious selection of the combination local anesthetics, possibly delivered through multiple sites of injection, is likely to provide predictable anesthesia with minimal exposure to side effects.

Research continues in the development of new or improved anesthetics. Investigations on extended-duration anesthetic formulations suggest that local anesthetics may prove useful for treating postprocedural pain.⁸⁰^,²⁸⁹ In the future, clinicians may be able to provide anesthesia of a specific area for a day or maybe a number of days using liposomal-encapsulated anesthetic agents. The timing of anesthesia would be tailored by how the liposome is formulated to dissolve and the amount of drug in the liposome.

The use of adjuvants to shorten the onset or increase the duration of local anesthetics also has been evaluated. The addition of hyaluronic acid significantly increases bupivacaine anesthesia in rats.²⁵³ Tramadol has both a unique central mechanism of action and peripheral anesthetic properties. For patients in pain, 30 to 200 mg of tramadol significantly enhanced postoperative analgesia when combined with 1.5% mepivacaine.²²⁴ Other studies have shown that the addition of 1 mg of morphine to a local anesthetic solution significantly increases postoperative analgesia in human beings and animals.⁶³^,¹⁴⁸ Clonidine directly inhibits pulpal pain neurons⁹⁹ and enhances anesthesia when combined with a local anesthetic.¹¹¹^,¹⁴¹ Also, it does not increase the risk of cardiotoxicity seen with local anesthetics.⁹³ In a clinical model of postsurgical pain, the combination of lidocaine with bupivacaine produced better long-term pain control than lidocaine alone.¹⁴⁵

Considerable ongoing research is directed at the development of new local anesthetic formulations that allow clinicians to better treat patients in pain.

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