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Rabbit Dentistry | Anesthesia | Dental Anatomy

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  abbits haveadiphyodont dentition (i.e.,characterized by successive developmentof deciduous and permanent sets of teeth),although the deciduous first incisors aregenerallyshed around birth and go unno-ticed. 1–4  The deciduous second incisors and pre-molars are present at birth and exfoliate withinamonth after birth. 2,4,5  The dental formula for the permanent denti-tion in rabbits is as follows (Figure 1):I 2 ⁄ 1 :C 0 ⁄ 0 :P 3 ⁄ 2 :M 3 ⁄ 3 =28 Allpermanent teeth in rabbitsare elodont (i.e.,continuously growing,“open-rooted”) 6 (Fig-ure 2).Some authors use theterm aradicular hypsodont  ,indicating that the teeth have Article #  2 ABSTRACT: CE Incisor malocclusion is common in rabbits.If this condition occurs as an isolated entityat an early age,it probably has a genetic srcin.Incisor malocclusion in older animals isusually secondary to,or occurs concomitantly with,premolar–molar malocclusion.Therefore,patients with incisor malocclusion should always receive a comprehensiveoral examination.Incisor–premolar–molar malocclusion with periodontal and endodon-tic disease is a disease complex that mayinclude incisor malocclusion,distortion of thepremolar–molar occlusal plane,sharp points or spikes,periodontal disease,periapicalchanges,apical elongation,oral soft tissue lesions,and maxillofacial abscess formation.Itis unclear whether this syndrome has a genetic,dietary,or metabolic srcin.Therapeuticoptions for incisor–premolar–molar malocclusion with periodontal and endodontic dis-ease may include occlusal adjustment of involved teeth,extraction of teeth severelyaffected by endodontic and/or periodontal disease,and abscess debridement.Becauserabbits with dental disease often haveconcurrent disease processes,a thorough systemicevaluation is usually indicated before initiating dental treatment.Balanced anesthetictechnique with careful monitoring,attention to supportive care,and client education areimportant in successfullytreating rabbits with dental disease. along anatomic crown,erupt continuously,andremain open-rooted. 1,7  The presence of maxillary second incisors,also known as  peg teeth ,behindthe first incisors is typical in lagomorphs. 1,8  The first incisors are very long and curved inrabbits.The maxillaryfirst incisors andmandibular incisors grow at rates of 2 and 2.4mm/wk,respectively. 9  The enamel of the inci-sors is not distributed uniformly around thetooth;the enamel is thicker on the facial aspectand thinner on the lingual aspect. 8  There are nocanine teeth.Rabbits have a typical herbivoreocclusion:The premolars and molars aregrouped as a functional unit with a relatively horizontal occlusal surface with transverseenamel folds (i.e.,lophodont teeth) for shred-ding and grinding tough fibrous food. 10  Theenamel folds correspond to deep invaginationof  September 2005  671 COMPENDIUM Dentistry in Pet Rabbits Frank J.M.Verstraete,DrMedVet Anna Osofsky,DVM University of California,Davis Send comments/questions via email editor@CompendiumVet.com orfax 800-556-3288 .Visit CompendiumVet.com for full-text articles,CE testing,and CE test answers. R  the enamel on the palatal side of the maxillary cheek teeth and the buccal side of the mandibular cheek teeth. 5,8,10 Enamel folds are filled with cementum-likematerial and are visible on the outside as developmentalgrooves. 5,8  The peripheral enamel is thickest on the lin-gual surfaces of the maxillary cheek teeth and the buccalsurfaces of the mandibular cheek teeth. 8  The masseter muscle is much larger than the temporalmuscle,and the coronoid process is smallcompared with that of carnivores (as anadaptation of eating tough,fibrous foods). 11  The occlusion is anisognathous—the maxil-lary arch is wider than the mandibular arch. The occlusal plane is angled approximately 10°toward horizontal 1 (Figure 1).The shapeof the temporomandibular joint mainly allows considerable lateral movement but very little rostrocaudal movement. 1,12  Themandibular incisors occlude between themaxillary first and second incisors. 13 DENTAL DISEASE SYNDROMESClinical Signs of Dental Problems Many signs of dental disease in rabbitsare nonspecific. 14–17  Animals with painfulteeth,jaws,or oral mucosa may be reluctantto eat or may not be able to prehend,chew,or swallow food well.Although food bowlsmust be refilled,clients may notice thattheir animal is steadily losing weightbecause food is often scattered rather thaneaten.Fecal pellets often become smallerbecause a rabbit is eating less,or,if a rabbitis completely anorectic,fecal output may cease completely.Body fur may appearunkempt if a painful animal no longer usesits mouth for grooming;animals may grindtheir teeth frequently because of discomfort.Maxillofacial abnormalities may be palpableor evident on inspection.Excessive saliva-tion (i.e.,“slobbers”) is common.Palpablefacial or mandibular swellings may be dueto periapical pathosis or soft tissue infectionand abscessation.Ocular and/or nasal dis-charge is suggestive of dental disease.Dis-comfort while the clinician manipulates the jaw and inability to completely close themouth may be present.Incisor overgrowthand/or malocclusion are often evident dur-ing preliminary visual inspection.Despite the fact thatdental disease in rabbits is usually chronic,these patientscan present as emergencies due to acute decompensation. Incisor Malocclusion Incisor malocclusion is common in pet rabbits (Figure3).If this condition occurs as an isolated entity at an early age,it is probably due to maxillary brachygnathia,which COMPENDIUMSeptember 2005Dentistry in Pet Rabbits 672 CE Figure 1. Dentition of the rabbit (Oryctolagus cuniculus) :A: Occlusal view of the maxillae. B: Occlusal view of the mandibles. C: Lateral view. D: Frontal view illustrating the angle of the occlusal plane between the premolarsand molars.(Reprinted with permission from Verstraete FJM:Advances in diagnosis andtreatment of small exotic mammal dental disease. Semin Avian Exot Pet Med  12[1]:37–48,2003.) ABCD  has a genetic srcin. 13,18,19 Some authors use the term mandibular prognathism ,whichimplies that the mandible istoo long. 13,16 However,in mostcases,especially in small rabbitbreeds,the maxilla is too short, whereas the mandible is a nor-mal length;therefore,the term maxillary brachygnathia  is pre-ferred. 1,18 Because of abnormalincisor occlusion,insufficientattrition occurs,resulting inexcessive overgrowth of theincisors. 13  The maxillary inci-sors,with their inherently greater curvature,typically curlinto the oral cavity,whereasthe mandibular incisors grow in a dorsofacial direction.If left untreated,trauma to the lip,palate,and other maxillo-facial structures may occur. A total lack of dietary material for gnawing may alsoresult in incisor overgrowth.Incisor overgrowth may occur subsequent to the loss or fracture of an opposingincisor.This may be caused by the animal falling orbeing dropped. 16 Fracture of an incisor tooth may resultin pulpal necrosis,periapical disease,and cessation of growth and eruption.Incisor malocclusion may also be secondary to,oroccur concomitantly with,premolar–molar malocclu-sion.Conversely,incisor malocclusion may lead to pre-molar–molar malocclusion if incisor malocclusionprevents normal mastication.In fact,incisor malocclu-sion without premolar–molar abnormalities may be rela-tively rare,especially in older rabbits. 16  Therefore,patients with incisor malocclusion should always begiven a comprehensive oral examination. Therapeutic options for incisor malocclusion include: ã  Tooth height reduction every 3 to 6 weeks,or asneeded,and appropriate dietary adjustment ã Extraction of involved teeth Incisor–Premolar–Molar Malocclusion withPeriodontal and Endodontic Disease Patients with incisor–premolar–molar malocclusion with periodontal and endodontic disease typically pre-sent with a history of noticeable weight loss (or evenemaciation),ocular or nasal discharge,and/or maxillo-facial abscessation (Figures 4 and 5).This disease com-plex may include the following components 13,16–18,20–23 : ã Incisor overgrowth/malocclusion occurs,as already described.In addition,apical overgrowth or “rootelongation”occurs. September 2005COMPENDIUMDentistry in Pet Rabbits  673 CE Figure 3. A rabbit with severe incisor malocclusion. Note the soft tissue trauma to theupper lips caused by the mandibular incisors.Lateral view.Frontal view. Lingual  Facial  DentinDentinBoneEnamelPulpGingivaEnamel Figure 2. Basic structure of the rabbit incisor. (Illustrationby Felecia Paras)  ã Irregularity of the premolar–molar occlusal planeoccurs,resulting in a so-called “step-mouth,”“wave-mouth,”and/or sharp point or “spike”formation.Sharppoints typically occur on the lingual aspect of themandibular teeth and buccal aspect of the maxillary teeth. ã Intraoral elongation of premolars and molars occurs, with possible lingual or buccal deviation. ã Periodontal disease occurs,with increased mobility of,and pathologic diastema formation between,pre-molars and molars. ã Premolar–molar periapical changes occur,with apicalelongation and possible cortical perforation. ã Soft tissue lesions associated with sharp points onpremolars and molars develop on the oral mucosa. ã Submandibular,maxillofacial,or retrobulbar abscessesform.It is unclear whether this disease complex has a genetic,dietary,or metabolic origin (or any combination of twoor more of those factors).The pathophysiologic rela-tionship among orthodontic,periodontal,and endodon-tic lesions is equally unclear.Not all patients show allcomponents of the disease complex;however,even a rel-atively minor premolar–molar malocclusion should beconsidered an important clinical finding.It has beenhypothesized that nutritional osteodystrophy caused by calcium and vitamin D deficiency is the main cause of advanced dental disease in rabbits. 16,20 It has recently been shown that affected animals have elevated parathy-roid hormone levels and lower calcium levels. 24  Therapeutic options for incisor–premolar–molar mal-occlusion with periodontal and endodontic disease may include: ã Occlusal adjustment of involved teeth ã Extraction of teeth severely affected by endodonticand/or periodontal disease ã  Abscess debridement In very severe cases,euthanasia may be considered. Although regular occlusal adjustments do not addresssome underlying lesions (e.g.,apical elongation),normalchewing and tooth wear may be regained. 12 ANESTHESIAPreanesthetic Evaluation  A preanesthetic evaluation is indicated in all dentalcases when a procedure requiring general anesthesia isplanned.This evaluation should ideally include a physi-cal examination,complete blood cell count,and bio-chemical profile.Whole-body radiographs should beobtained if indicated. 25  A comprehensive evaluation isimportant because dental patients can have concurrentdiseases (e.g.,pneumonia,cardiac or renal disease),gen-eral debilitation,and/or severe gastrointestinal (GI) sta-sis due to dental disease.The concurrent problems may require additional supportive care to stabilize patientsand reduce the anesthetic risk. 26 In addition,affectedpatients likely require frequent anesthesia to managetheir dental disease,so a good understanding of theiroverall condition is important.Hematologic changesassociated with dental disease are generally nonspecific COMPENDIUMSeptember 2005Dentistry in Pet Rabbits 674 CE Figure 4. Incisor–premolar–molar malocclusion with periodontal and endodontic disease (clinical aspects). Incisor malocclusion and coronally elongated premolars.Extraoral abscessation.
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