Sedation and restraint

The presence of concurrent diseases, such as cardiac disease, arthritis, and muscle wasting, needs to be taken into consideration when sedating and restraining geriatric equids for dental treatment. In general, lower doses of anesthetic and sedative agents are required in older horses, as they have increased sensitivity and decreased clearance of commonly used agents.¹⁹ The type and likely duration of dental treatment need to be determined prior to commencement of any treatments to assist in choosing the appropriate restraint methods. If a painful procedure is to be performed, the use of local nerve blocks will decrease the amount of systemic sedation and analgesia that is required.

Low dosages of alpha-2-adrenoceptor agonists, such as xylazine, romifidine hydrochloride or detomidine hydrochloride, in combination with low dosage of butorphanol tartrate for pain control, can be sufficient for most dental procedures in geriatric equids. Although butorphanol has five times the analgesic activity of morphine, the analgesia persists for only 15–20 minutes. Geriatric equids may be very fractious to extraction of worn, loose teeth, but butorphanol administered just prior to extraction usually provides sufficient analgesia. A continuous IV drip of detomidine or detomidine/butorphanol²⁰ may be used instead of repeated dosing of these drugs. Use of a head support is recommended during dental procedures, but it should be used with stocks or after backing the horse into a corner to minimize slumping of the forelimbs and over-extension of the head, with possible atlanto-occipital subluxation.

Another option if significant dental treatment is required, especially in a fractious patient, is the use of short general anesthesia.²¹ The drawback to general anesthesia is the development of long bone fractures during recovery if insufficient assistance is available to help the horse rise. Protracted malnutrition may produce osteoporosis and so increase the risk of this sequel in older patients.

Heavily sedated geriatric horses, when left alone and unstimulated following dental procedures, are more susceptible to falling off their feet than younger horses. Judicious use of tolazoline HCl (100–200 mg in a slow IV injection) is indicated to partially reverse the effects of alpha-2-adrenoceptor agonists. If the sedation is insufficiently reversed after 15 to 20 minutes, the tolazoline HCl administration may be repeated using half to one-third of the initial dosage.

Incisor disorders

The incisor arcades in older equids often have disorders, such as excessive wear, corresponding overgrowths in the opposite teeth, malocclusions, missing teeth, and displaced teeth. Excessive wear of an entire incisor arcarde, most commonly the maxillary incisors, is usually as a result of a behavioral problem, such as crib-biting or wind-sucking. With loss of teeth or excessive incisor wear, repeated regular floating of the opposing teeth is required to maintain a level occlusal surface. Excessive reduction of severely overgrown incisors may expose pulp horns, and it is advisable to reduce overgrown incisors, in stages some months apart, to stimulate normal secondary dentin deposition to protect the occlusal aspect of the pulps. The tapering of incisors towards their apical aspect results in the development of incisor diastemata with the accumulation of food, in some older horses.

Geriatric equid incisors often have abnormal occlusal surfaces, such as a ventral convex curvature (’smile’), a dorsal convex curvature (‘frown’) or a diagonal (to left or right side) surface (’slant mouth or slope mouth’). These changes are often secondary to disorders of the cheek teeth and a resultant abnormal masticatory action. Once cheek teeth disorders have been corrected, these incisor table abnormalities can be corrected, in stages if severe. ‘Smile’ mouth appears to be very common in donkeys and was present in 96 % of aged donkeys with dental disease and 99 % of donkeys without dental disease⁴ (Fig. 18.3). Therefore, smile mouth may be regarded as a normal appearance in aged donkeys and should not be corrected unless inhibiting normal masticatory action.

Fig. 18.3 The typical ‘smile’ mouth appearance of the incisor occlusal surface observed in most aged donkeys.

Functional incisor/molar occlusion in the presence of abnormal incisor occlusal surfaces may be determined by measuring the excursion to molar contact (EMC) distances. EMC is measured by putting the incisors arcades into centric occlusion and then pushing the mandible laterally until the upper and lower cheek teeth arcades touch and (due to their angulated occlusal surfaces) the incisors just begin to separate. The distance is measured from the center of the maxillary incisor arcade (interproximal space of 101 and 201) to the center of the mandibular incisors (interproximal space of 301 and 401). The EMC measurements are made on each side. When in centric occlusion, if the center points of the incisor arcades do not align with each other, then the offset distance is either added or subtracted from the center-to-center point measurement (Fig. 18.4).

Fig. 18.4 In this 20-year-old Saddle bred horse, the mandibular center point is offset to the horse’s right by 10 mm (distance between the black arrows). EMC to the right is 8 mm (18 mm minus the 10 mm offset; blue to adjacent black arrow) and to the left is 24 mm (14 mm plus the 10 mm offset; red to adjacent black arrow). Measurement is made from the center of the maxillary incisors to the center of the mandibular incisors.

The average EMC distance for a 450 Kg horse is 12.3 mm.²² This distance, coupled with the average maximum excursion distance of 45 mm ±5 mm,²³ demonstrates that a normal equid’s masticatory cycle is about 22–25 % incisor occlusion and about 75–78 % cheek teeth occlusion. Horses with heads shorter than average (Quarter horse length), have an average EMC distance less than 12.3 mm, while the EMC in longer headed horses is greater than 12.3. The mean EMC in miniature horses is about 4 mm, while the mean value in a draught horse is about 16 mm. This difference in EMC in different sized heads is because the pivot point or vertex for lateral excursion is the temporomandibular joint (TMJ). Lines drawn from the TMJ to each of the center points diverge more the further they are from the TMJ and diverge less the nearer they are to the TMJ.

Reducing EMC distances within a range of 12–16 mm should be done carefully, with reduction of tall teeth performed in 1-mm thick stages on tall incisors, before re-assessing EMC. A 1-mm reduction in incisor height can decrease the EMC by 4 mm or more. Experience indicates that total reduction should be limited to 3 mm in one session or no more than a 10 mm change in the EMC. Horses with incisor malocclusions having reasonably normal or shorter than normal EMC distances do not need incisor correction; they have functional incisor malocclusions (Fig. 18.5).

Fig. 18.5 Horse in Fig. 18.4 after correction. 103 (not visible) was reduced by 3 mm; this tooth was displaced caudally and was not interfering with cheek teeth occlusion but was making contact with 404. Teeth 402 and 403 were reduced 2.5 mm. EMC to left is now 14 mm and EMC to right has not changed. The incisors are not level but are now functional, and the horse can chew with more left cheek teeth occlusion.

Correction of a ‘smile’ should begin on the mandibular incisor arcade, removing 1-mm thick layers until the arcade is level, or the reduction (3 mm) or EMC (10 mm) limits are reached (Fig. 18.6). The lateral maxillary incisors are also reduced, if needed. ‘Frown’ correction reduction is begun on the maxillary arcade then the mandibular arcade, if needed. Correction should always commence on the 03s (corner incisors). If excursion or reduction limits are reached before reduction of the 01s (central incisors) is needed, incisor contact will be maintained on the 01s and possibly part or all of the 02s (intermediates), depending on the severity of the malocclusion.

Fig. 18.6 ’Smile’ malocclusion. Correction is initiated on 303 and 403 by removing 1 mm at the tallest point and tapering toward 301 and 401. (Black wedges). If reduction ceases before 101 and 201 are reduced, incisor contact will be maintained on the 01s and possibly the 02s.

Periodontal disease

The formation of senile diastemata in the incisors may lead to food impaction and periodontal disease. However, as these teeth are not exposed to any grinding masticatory forces, these diastemata are very rarely associated with deep periodontal pockets. These diastemata and associated (usually) mild periodontal disease can be managed by regular cleaning of the impacted food by the owner. In more severe cases of food impaction, which may be difficult to remove on the caudal aspect of the incisors, these diastemata can be widened using a diastema burr or rotary saw. The accumulation of calculus on the canines and 03s may also cause mild, localized periodontitis, which does not appear to cause any clinical signs (Fig. 18.7). Accumulation of large amounts of calculus can result in more severe gingivitis, with hyperemia and recession of the gingival margin. Removal of the calculus at every dental examination/treatment temporarily relieves the associated periodontal disease. Frequent brushing of the canines by the owners using a normal tooth brush may slow down re-accumulation of calculus.

Fig. 18.7 Calculus accumulation on both mandibular canines and the 203s in a 28-year-old donkey. There is mild gingival hyperemia associated with the calculus on 304.

More recently, a more severe form of incisor periodontal disease has been recognized in geriatric equids that is associated with cemental hyoplasia, and hyperplasia and radiographic lytic changes.^24–27 The exact etiopathogenesis of this disease has not been determined, but pathological studies show it to be an odontoclastic resorption of affected incisors (also of canine teeth) with subsequent marked deposition of cement on these teeth, termed equine odontoclastic tooth resorption and hypercementosis (EOTRH; discussed in Ch. 10). Affected animals may present with clinical signs associated with pain, such as masticatory and bitting problems, and halitosis (Fig. 18.8). Initially, this condition presents as mild gingival inflammation and edema with small lytic changes in the mid reserve crown incisor on radiographic examination.²⁵ With progression of the condition, draining tracts may develop in the gingiva, and this may be accompanied by gingival recession, or marked subgingival swelling of incisors, reflecting hypercementosis of their reserve crown and apex. Radiographically, progression of the disease is characterized by lysis of the incisors in an apical direction and an increase in the thickness of the lytic areas to involve the dentin. Loss of interdental bone and widening of the periodontal ligament may also be observed on radiographs. Clinically advanced cases may have painful mobile incisors. Hypercementosis (subgingival nodular enlargements) of portions or all of the subgingival incisors may also be observed on radiographs in some advanced cases (Fig. 18.9).

Fig. 18.8 Enlargement of thickness of reserve crown of 203 and 303 (identical to 103 and 403) due to hypercementosis associated with equine odontoclastic tooth resorption and hypercementosis. The horse was asymptomatic, and the disease was identified on oral examination. All the incisors were stable and non-painful to manipulation, but firm palpation of 303 and 403 reserve crowns was painful.

Fig. 18.9 This 20-year-old Thoroughbred was reported to refuse to bite carrots for over one year. Enlargement of all incisor reserve crowns is prominent with gingival recession, and draining tracts visible (at arrows). Radiographs showed extensive lysis and hypercementosis of 103 and 203, typical of equine odontoclastic tooth resorption and hypercementosis, with radiographic changes in all the other incisors.

Due to the predominance of resorptive lesions in this condition, it has been proposed to be more similar to feline tooth resorption than to a primary periodontal disease.²⁴ Feline tooth resorption has been shown to start as focal lesions at the cemento-enamel junction, indicating that local factors appear to play a role in the etiopathogenesis.²⁸ Feline tooth resorption has an initial resorptive phase where there is odontoclastic resorption of dentin and destruction of the periodontal ligament and alveolar bone.²⁹ This is followed by cementum and bone deposition during the reparative phase. Thus far, bone deposition and dento-alveolar ankylosis, as described in feline tooth resorption, has not been described in equids. Treatments with long-term antibiotics and steroids have been unsuccessful and extraction of affected incisors has been the only treatment to alleviate the clinical signs associated with this disease.

Canine teeth disorders

The most common abnormality observed in canine teeth is, as noted, the accumulation of calculus, which may cause mild local periodontal disease. This calculus is easily removed with the use of forceps. Excessive calculus accumulation on the mandibular canines has also been associated with corresponding tongue ulcers. Rarely, canine teeth may be displaced or enlarged and interfere with the bit. Canine teeth have very long, well embedded reserve crowns, and extraction of these teeth should not be performed without prior radiography. The canine teeth are often floated, purportedly to prevent bitting problems or injuries to operators’ hands and arms during dental procedures. Extreme floating or even cutting of these canine teeth may expose the pulp cavity and result in apical infections. Enlargement of the clinical crown, exposure of the alveolar bone or reserve crown, and the presence of pain if the canine is palpated, percussed or subjected to a cold substance (piece of ice), are all indications for radiographic evaluation of the canine.

Cheek teeth disorders

Dental abnormalities of wear encountered in geriatric equids are the same abnormalities that are recognized in younger equids, but they have reached an advanced stage over a prolonged period of time. These disorders, e.g., shear mouth, wave mouth, and focally overgrown teeth, are often complicated by the lack of reserve crown and hence, instability of teeth within the alveolus, which results in displacement and eventually loss of teeth (Fig. 18.10).

Fig. 18.10 Loss of maxillary cheek teeth 208, 209, and 210 is due to loss of reserve crown in this geriatric donkey. Also note the large, open diastema between 107 and 108 and the loss of infundibular enamel in 108, indicating the presence of a high degree of wear in these teeth and the beginning of ‘smooth mouth’.

A post-mortem survey of dental disease in geriatric donkeys (estimated median age 31 years) showed a very high prevalence (93 %) of dental disease; with diastemata (85 %), missing (56 %), displaced (43 %) and worn teeth (34 %) being the most common dental disorders present³⁰ (Fig. 18.11). Studies in horses have also shown an increased prevalence of dental disease in older age groups.^1,2,31–33 A comparison of clinical dental disorders in different age groups of donkeys (age range 2–53) showed a significant increase in the prevalence of dental disease in donkeys over 20 years of age (≥88 % prevalence) compared to donkeys younger than 20 years (≤64 %).⁴ More specifically, a significant increase in the prevalence of diastemata, missing teeth, overgrown teeth, worn teeth, displaced teeth, and periodontal disease with increasing age has been shown, in particular in donkeys over 20 years of age.⁴ As expected, the prevalence of enamel points decreased significantly with age, to a prevalence of less than 20 % in donkeys older than 20 years, as compared to >40 % prevalence in donkeys under 20 years of age.⁴

Fig. 18.11 Severe bilateral lateral displacement of the 310 and 410 is present in this 38-year-old donkey. There is also moderate lateral displacement of the 407.

Treatments of cheek teeth disorders in geriatric equids are often limited by the lack of reserve crown. Dental treatment should be aimed at preserving as much of the functional occlusal surface for mastication as possible, while ensuring oral comfort. Sharp enamel overgrowths should be floated to prevent soft tissue trauma to the cheeks (maxillary cheek teeth) or tongue (mandibular cheek teeth). Cheek teeth diastemata are often a result of tapering reserve crowns and loss of angulation of the rostral and caudal cheek teeth (’senile diastemata’), and, therefore, the cause of these diastemata cannot be eliminated (Fig. 18.12). As diastemata often involve the caudal cheek teeth,^30,34 it is essential that a dental mirror and good light source are used to evaluate these. Impacted food should be flushed out, and the severity of associated periodontal disease determined. Very often, the only treatment for diastemata is to reduce the opposing cheek teeth occlusal surface by 2–3 mm to decrease the impaction of food into the diastema, particularly if there are focal transverse overgrowths secondary to the diastemata.³⁴ Some clinicians advise filling the base of cleaned diastemata with dental impression material (as later described), but no objective studies are available on its efficacy in treating any type of periodontal disease in the horse. Following removal of cheek teeth overgrowths, mild-to-moderate periodontal disease may be arrested or its progression slowed by oral rinsing with diluted chlorhexidine gluconate (5 ml of 2 % chlorhexidine added to one liter of water). The owner should rinse the mouth out once a day for 10 days, then twice weekly. Some horses object to the taste of chlorhexidine and may become briefly anorectic. If this occurs, a flavored 0.12 % chlorhexidine (or human mouthwash) can be used as a rinse, 50 to 100 ml per rinse. The mouth should be rinsed with lukewarm water to remove food particles prior to the chlorhexidine rinsing.

Fig. 18.12 Multiple senile diastemata of both mandibular cheek teeth rows in a donkey of 27 years. Some of these diastemata have adjacent severe periodontitis and deep periodontal pockets (arrow).

Periodontal disease is an important disease in geriatric equids and has been shown to occur in 80 % of horses over 20 years of age² (Fig. 18.13). If the periodontal disease is severe and associated with periodontal pockets, the application of an antibiotic oral gel (Doxirobe [doxycycline] Gel, Pfizer Animal Health) with impression material may allow temporary alleviation of the inflammation and allow healing of the periodontal pocket.^35,36 In contrast to small animals where the accumulation of calculus is an important cause of periodontal disease,³⁷ cheek teeth calculus is less common in equids and is not a major cause of periodontal disease. Cheek teeth calculus accumulation has been observed in 19 % of geriatric donkeys at post mortem, predominantly on the maxillary 07, 08, and 09 cheek teeth³⁰ (Fig. 18.14). Cheek teeth calculus often accumulates secondary to food stagnation in equids that have painful dental disease and subsequent decreased normal masticatory movements. These teeth are beside the salivary duct opening that possibly provides much of the mineral component for calculus.

Fig. 18.13 Slight wave mouth with overgrowths of 410 and 411 and moderate peripheral caries. Diastemata are present in all the interdental spaces in this cheek teeth row, but the diastema between 408/409 has severe periodontal disease and food pocketing associated with it.

Fig. 18.14 Calculus accumulation on the buccal aspect of 207 and 208 in a geriatric (33-year-old) donkey. There is also a diastema with food impaction and periodontal pocketing between 208 and 209, and displacements of 209 and 210 (arrow).

Excessive cheek teeth overgrowths resulting in ‘step mouth’ should be reduced as much as possible (Fig. 18.15). If overgrowths are more than a few mm high, the initial reduction should be done in stages (e.g., 3 mm at a time) at 2–3-month intervals to prevent potential pulp horn exposure. As these overgrowths are secondary to missing, displaced, or ‘cupped out’ teeth in the opposing cheek teeth row, treatment needs to be repeated at regular intervals, to prevent re-development of these overgrowths to an extent that they are interfering with masticatory movements or causing soft tissue damage. These overgrowths do not have to be fully reduced (Fig. 18.16). Severely displaced teeth should be extracted if they are protruding into the cheeks or tongue and causing chronic ulceration and pain. Mild to moderately displaced teeth with focal overgrowths on the displaced and opposing teeth due to the malocclusion can be managed by reducing the overgrowths if the teeth are not digitally loose. Overgrown, slightly loose teeth may re-attach firmly if overgrowths are removed. However, if teeth are very loose or have marked periodontal disease and diastemata, extraction is the most appropriate treatment. Oral extraction of displaced teeth, particularly if still well embedded in the alveolus, may be complicated by the limited space between the cheek and tooth and the inability to satisfactorily apply molar extractors. Therefore, careful consideration must be given to the potential duration of the procedure and the required sedation to a debilitated geriatric equid.

Fig. 18.15 Severely overgrown maxillary cheek tooth resulting in’step mouth’. This overgrown tooth needs to be reduced in stages to prevent potential pulpal exposure. Also note the associated periodontal disease and gingival recession.

Fig. 18.16 Corresponding maxillary (A) and mandibular (B) cheek teeth rows that illustrate severely overgrown maxillary cheek teeth secondary to worn and missing mandibular cheek teeth, with mandibular soft tissue trauma. There are also multiple maxillary cheek teeth diastemata with food impaction. Note the presence of the rudimentary 205 (first premolar, wolf tooth).

Wave mouth is believed to develop as a result of the oldest teeth in the mouth (09s) wearing and becoming ‘cupped out’ prior to younger adjacent teeth, thus causing uneven wear in a cheek teeth row (Fig. 18.17).³⁸ Treatment of wave mouth consists of floating excessively overgrown teeth to theoretically create a straight (or slightly concave) occlusal surface in the cheek teeth rows in a rostrocaudal direction, in mild cases. However, in the usually more severe cases of wave mouth, only the area of maximal overgrowth can be reduced without removal of very significant amounts of the reserve crown. The aim is to create maximal occlusal contact surface area and allow for the normal range of mandibular jaw movement for efficient mastication. The cheek teeth row must not be floated to the height of worn teeth, but rather the overgrowth on the opposing tooth should be floated. When reducing overgrown cheek teeth, it is important to remember the normal occlusal angle of mandibular (18–31°) and maxillary (12–9°) cheek teeth in a lingual-buccal and buccal-palatal direction, respectively.³⁹

Fig. 18.17 ‘Wave mouth’ in a right mandibular cheek teeth row with a medially displaced 408 and 406, an overgrown 410, and worn 411. A large diastema between 407 and 408 with periodontal disease and gingival recession is also present, as is moderate peripheral caries of the 406 and 407, most likely secondary to food stagnation due to abnormal masticatory action.

Other abnormalities of wear may result in further malocclusions, with geriatric equids usually presented with multiple dental disorders. Prolonged overgrowths of the 106, 206, 311 and 411 may result in restricted rostrocaudal movement and contribute to more pronounced generalized cheek teeth overgrowths.

Ultimately, most geriatric equids with dental disease need to have regular (6-monthly or annually) dental examinations and treatment as appropriate on welfare grounds to ensure oral comfort and masticatory efficiency. It is highly likely that those with significant dental wear or disease will require supplemental feeding to maintain a suitable body weight, and this is particularly so in the colder months when green forage is not available. Owners need to be educated on the long-term management of geriatric equids, with particular emphasis on the formulation of an appropriate diet.