Topical Anesthetic Agents

Some topical anesthetic agents are available over-the-counter to the public and can be purchased at local food and drug stores (Figure 6-1). People of all ages use them to ease pain from teething, braces, apthous ulcers (canker sores), dentures, or toothaches.

Whether being applied professionally or in the comfort of your home (Tables 6-1 and 6-2), intraoral topical anesthetics should ideally be nonallergenic and produce no damage to the tissue to which it is applied. It should consist of a pain-free application, have an acceptable taste, and be able to remain at the site of application. Also, it must produce reliable, effective anesthesia with a sufficient duration and not induce systemic toxicity (Box 6-1).

To provide pain management before the administration of conventional local anesthetic injections, topical gels or ointments are applied with a cotton tip applicator. The site of penetration should first be dried using a 2 × 2 gauze square to increase visibility and accurate placement of the topical anesthetic (Figure 6-3). Only a small amount of gel or ointment on the applicator tip is necessary to achieve the desired result (Figure 6-4). Student dental hygienists and even experienced clinicians can often apply excessive amounts of topical anesthesia, leading to an unnecessary effect on surrounding tissue. This excess mixes with the saliva and may anesthetize areas such as the tongue, soft palate, or pharynx. The topical agent should remain at the site of penetration for 1 to 2 minutes (depending on the concentration of the topical anesthetic) to ensure effectiveness (Figure 6-5). If these steps are followed, anesthesia should be achieved to a depth of approximately 2 to 3 mm into the tissue (Procedure 6-1). This helps provide comfort during the initial penetration of the local anesthetic needle.

Topical anesthetics in liquid form are also used in dentistry. Liquids provide anesthesia to a wide area. They are especially useful when trying to decrease a patient’s gag reflex, thereby making placement of impression materials or radiograph film more comfortable and tolerable. The use of a liquid for a more site-specific procedure requires an applicator. Cetacaine (Cetylite, Pennsauken, N.J.), which is available only by prescription, is administered by either a cotton pellet or via blunted cannula to deliver the anesthetic subgingivally (Figure 6-6). Another liquid, HurriPak (Beutlich Pharmaceuticals) is designed primarily for the use of subgingival placement by using irrigation syringes with plastic tips (Figure 6-7). These are indicated when attempting to increase comfort during prophylaxis or nonsurgical periodontal therapy procedures.

Gels, ointments, and liquids often come in multidose containers, but some products are packaged in single unit-dose applications. Lollicaine (Centrix), HandiCaine Stix (Topex Sultan Healthcare), and CaineTips (J Morita) are some of the products available through dental suppliers. These single unit–dose applications can also be found in over-the-counter products such as Orajel medicated tooth swabs (Figure 6-8). Individual packaging is less messy, helps prevent possible cross-contamination, and allows monitoring of the dose.

Sprays are also used to deliver topical anesthesia. Unmetered sprays are not recommended because they do not allow control of the amount of anesthetic dispensed, nor are they easily contained at a specific site. However, the use of a metered spray with a disposable nozzle enables control over the amount of agent being dispensed, thus decreasing the risk for systemic toxicity (Figure 6-9). Both the Institute of Safe Medication Practices (ISMP) and the U.S. Food and Drug Administration (FDA) have released advisory statements informing the public of the association between benzocaine and methemoglobinemia, wherein methemoglobin builds up in the blood, hindering the effective transport of oxygen to body tissues (see Chapter 7).

Patch delivery of a topical anesthetic is advantageous because the patch can be placed directly on the delivery site and then adheres to the tissue. Transdermal patches are used regularly in medicine on intact skin to administer certain medications or to provide local dermal analgesia. For example, Synera (ZARS Pharma, Salt Lake City, Utah) is an FDA-approved peel-and-stick topical anesthetic patch that numbs intact skin before minor needle procedures and superficial dermatologic procedures.³ Lidoderm (Endo Pharmaceuticals, Chadds Ford, Pa.) is also an FDA-approved adhesive patch that provides pain relief from postherpetic neuralgia, commonly called after-shingles pain.⁴ These patches are not used intraorally, however.

Patches available for intraoral topical anesthesia are limited. The first FDA-approved transoral anesthetic patch, DentiPatch, was introduced in 1996 by Noven Pharmaceuticals, but the manufacturer discontinued the product. Currently the only patch available for intraoral use is Topicale GelPatch (Premier Dental Co.) (Figure 6-10).

Regardless of the form and method of delivery, there is more than one option for delivering topical anesthetics to dental patients. Furthermore, dental hygienists must be aware that patients often self-medicate using these same drugs in over-the-counter formulations and should query their patients before administering any anesthetic agents.

High plasma concentrations of topical anesthetics can produce adverse effects and results when patients are exposed to excessive amounts of the drugs. Children, elderly, and medically compromised individuals are more susceptible to the adverse reactions of topical anesthetics. Methemoglobinemia, a rare, but serious condition can occur resulting in a decrease in the amount of oxygen being carried through the blood stream. Signs and symptoms of methemoglobinemia include pale, gray or blue colored skin, lips and/or nailbeds, fatigue, shortness of breath, headache and lightheadedness. These signs and symptoms can occur within minutes to hours after topical benzocaine administration. Most of the cases reported are in children under two years of age, prompting the FDA to release a safety announcement in 2011 regarding OTC benzocaine teething preparations and more recently another in 2014 regarding prescription viscous lidocaine use for soothing gums in children (Box 6-3). Adult patients with breathing problems such as asthma, emphysema, and COPD, those with heart disease, and smokers are also at a greater risk for complications related to methemoglobinemia.

Possible localized adverse effects include irritation, stinging or burning at the site of application, sloughing, tissue discoloration, and temporary alteration in taste perception. The most prominent of the systemic effects of topical anesthetics are in the central nervous system and cardiovascular system. Excitatory effects of the central nervous system are often displayed at the initial signs and symptoms of overdose. Some of these signs and symptoms include dizziness, visual disturbances, tinnitus, disorientation, unusual nervousness or apprehension, and localized involuntary muscular activity. The excitatory manifestations may be very brief or not occur at all, in which case the first manifestation would be a depressant response, such as slurred speech, drowsiness, and respiratory impairment. Toxic overdoses result in seizures, unconsciousness, and respiratory arrest. In the cardiovascular system, patients may experience bradycardia and hypotension, leading to rare cases of cardiac arrest (see Chapter 15).

Allergic reactions associated with topical anesthetics are rare. Benzocaine and tetracaine are both esters, which increases their potential for an allergic reaction; however the risks are still low. Anaphylaxis is very rare with topical anesthetics. Any reaction would likely be delayed and not present itself until after the patient has left the dental office. Those mild allergic reactions can include swelling and raised welts on the skin, itching, or burning. Some allergic reactions occur up to 2 days after the anesthetic is given.

Although these adverse reactions are rare, the potential does exist. It is important to take all precautions necessary to minimize or avoid or prevent them (Box 6-4)