Common Disorders of the Teeth

Recent studies, both clinical and post-mortem, have highlighted the importance of the dental health of the donkey by reporting on the prevalence of dental disorders.

One study reported a prevalence of 74% for disorders in the incisors, ranging from 56.8% in the youngest group to 90.3% in the oldest. Others documented a very high prevalence in disorders in the cheek teeth (CT) ranging from 62% to 93% and in both working and retired donkeys. There was an increasing prevalence with age, proving the importance of routine dental examination and care in order to prevent the emergence of acquired disorders.

Developmental disorders may eventually lead to the onset of acquired problems. This demonstrates the importance of dental care from a young age, correcting or managing developmental disorders in order to limit further problems. Identification of the primary cause of the dental disorder is necessary as it may need to be treated before further work is carried out.

DEVELOPMENTAL DISORDERS

Breeding from affected animals is not recommended where developmental disorders are diagnosed.

The common developmental disorders seen in donkeys follow, but this is not an exhaustive list.

Craniofacial abnormalities

These need early detection and treatment to prevent development into more severe conditions.

Donkeys may present skeletal alterations in the craniofacial bones that may potentially lead to incorrect dental occlusion and function.

Over and underjet are less severe abnormalities and may have a smaller impact on the donkey's capacity for prehension and chewing.

Over and underbite, and wry nose are less common, but more severe and may block the correct chewing movement. In extreme cases this may cause the inversion of the normal angle in the incisors occlusal surface, or alterations of the bone base. This will affect the normal growing rate of the facial and mandible bones and increase the possibility of soft tissue damage.

More commonly, permanent alterations in the occlusal surface of both incisors and CT may occur. Teeth most often affected are the 06s and 11s.

Clinical alterations as a result include:

• Brachygnathism which describes overjet and overjet with overbite. This affects the occlusal aspect of the maxillary incisors rostral to the occlusal aspect of the mandibular incisors, leaving them with or without contact.

• Prognathism which describes underjet and underjet with underbite. This affects the occlusal aspect of the mandibular incisors rostral to the occlusal aspect of the maxillary incisors, leaving them with or without contact.

• ‘Wry nose’ or Campylorhinus Lateralis which is caused by variable degrees of lateral premaxillary (incisive) and maxillary bone deviation.

Note: some extreme cases of Craniofacial abnormalities in newborn donkeys will result in an inability to create vacuum in the oral cavity, leaving them unable to suckle.

These have been found to be particularly prevalent in endangered species of donkeys (one study noted a 49.3% prevalence) and this highlights the importance of using responsible breeding programmes.

Dental dysplasia

This is relatively uncommon. It is an alteration to the normal tooth and includes dilacerations (abnormal bending of the teeth), alterations in the size and shape, double teeth and concrescence, with roots of adjacent teeth joined by cementum.

As this is a developmental disorder with possible genetic links, animals presenting with this disorder should not be used for breeding purposes.

Polyodontia

This is relatively uncommon but very important. It is the presence of excessive teeth.

Fully erupted supernumerary teeth are reported with an increasing prevalence in elderly donkeys, suggesting a late-onset eruption process.

Supernumerary teeth are usually located in the caudal aspects of the maxillary CT when they are found in the donkey and are therefore easily missed. Counting the CT will help to identify the disorder (6 per row), or counting the interproximal spaces (5 per row). They are classified as:

• Supplemental teeth - presenting normal crown and root morphology

• Dysmorphic teeth - presenting abnormal size and shape

  • haplodont (conical crown with a single root)
  • tuberculate(several tubercles with deep indentations on the occlusal surface)

• Connate teeth - a result of a partial splitting of an embryonic tooth, being composed of at least two tooth elements.

The presence of supernumerary teeth can lead to acquired disorders such as axial displacements, dental overgrowths, dental-related soft tissue damage, diastemata formation, periodontal disease and development of secondary sinusitis.

Retained deciduous teeth

This is the presence of deciduous teeth beyond their normal time of shedding. Retention of the deciduous teeth affect the normal eruption process of the underlying and occasionally the adjacent permanent dentition.

A knowledge of eruption times of the teeth for donkeys is important to avoid premature removal of deciduous teeth, which may affect the underlying developing permanent tooth.

Caps which are digitally loose, displaced, fractured and/or have a clear visible and palpable demarcation between deciduous and permanent teeth should be extracted, although commonly they will exfoliate upon routine equilibration. Unequivocally retained caps and their fragments should also be extracted.

Recent studies show that teeth fragments are more commonly found on the medial aspect of the CT rows in donkeys, so extra care is needed during the extraction of these fragments to avoid laceration of the great palatine artery.

The most common deciduous teeth to be retained are central and corner incisors (01s and 03s) and deciduous 08s.

Retained deciduous teeth may lead to food stasis, gingivitis and in more severe cases to periodontitis and apical infection of underlying permanent teeth.

Eruption cysts

These are observed routinely in juvenile donkeys. They are enlarged, focal swellings beneath young permanent premolars, located in the developing apex region and palpable in the mandible and maxillae regions.

Studies have shown that there is no association with eruption cysts and retained CT, but cysts may be exacerbated by the retention of deciduous crowns, overcrowding and impaction. However, it is advisable to examine all cases of mandibular/maxillary swellings for the presence of retained deciduous CT.

Eruption cysts are usually much easier to diagnose in the mandible, probably due to the presence of overlying facial muscles that makes their detection more difficult in the maxilla region.

In miniature breeds, eruption cysts in the maxilla may affect the nasolacrimal duct causing epiphora, which resolves with increasing age.

Abnormal dental eruption, displacements and developmental diastemata

Donkeys with the normal number of teeth may present gross displacements and/or rotations of incisors and CT, due to intrinsic developmental reasons, retained deciduous teeth or as a result of previous trauma.

The mechanisms described in equids for the formation of developmental diastemata in the CT rows are directly related with abnormal dental eruption and teeth displacements: an inadequate eruption of the caudally angulated rostral cheek tooth (06) and rostrally angulated caudal CT (10s and 11s) or due to dental buds developing too far apart.

A similar mechanism may explain the high prevalence of 03s distally displaced, recently described in donkeys - lack of rostro-mesial compression from the 03s, which usually keeps the occlusal aspect of the incisor arcade acting as a single unit.

ACQUIRED DISORDERS

The common acquired disorders seen in donkeys follows, although this is not an exhaustive list.

Hypodontia

This is a loss of teeth and is seen in both incisors and CT and is common in donkeys and particularly in the geriatric. Periodontal disease is the main cause of premature loss of teeth in adult donkeys, but trauma and dental disorders may also lead to hypodontia.

The complete dental formula for donkeys is 44 teeth, although there are acknowledged variations in the presence or absence of canines and wolf teeth. Therefore, the absence of these teeth should not be considered to be hypodontia.

Abnormalities in the occlusal surface

Abnormalities in wear increase with age and affect the occlusal surface of both incisors and CT. It is the effect of abnormal wear between ipsilateral opposing teeth, leading to a potential restriction to mandibular movement and soft tissue damage. It is the most common disorder of CT and is mainly seen as enamel overgrowths affecting all CT.

It can be presented as:

• Ventral curvature of the incisor arcade may be normal or may be an abnormality secondary to CT disorders interfering with the correct chewing movement. Phased correction is advised where clinical justification exists; balancing and correcting the disorders of CT, while restoring the occlusal normal incisor conformation.

• Focal overgrowths affecting the 06s and the 11s; may be associated with class II or III incisor malocclusion.

• Overgrowth of the complete tooth due to poor or absent occlusal contact is not uncommon and frequently bilateral. They may be caused by displaced, dysplastic, worn, absent, additional or fractured occlusal counterparts. The overgrown teeth may interfere with normal chewing movement and may predispose to the development of wave mouth or shear mouth:

  • Wave mouth: undulating appearance of the occlusal surface of the CT in a rostro-caudal plane.

  • Shear Mouth: the presence of a steeper angle in the occlusal surface of the CT row in the palate-buccal plane.

  • Smooth mouth, or advanced senile excavation, maybe seen in geriatrics and is a reduction or complete loss of occlusal enamel ridges.

Studies in working equids suggest a high prevalence of CT enamel overgrowth and the majority of associated soft tissue lesions are located on the cheeks beside the maxillary 06s and 07s. This corresponds with areas where halters or nosebands may exert pressure and may indicate a different aetiology for this disorder.

Early detection and treatment of abnormalities of wear can avoid its development into more severe conditions. Maintenance of the correct occlusal angle can reduce the risk of development to a severe condition. This varies between 12.5° and 30° throughout the length of the arcades and between the maxillary and mandibular CT. The variations occur in a rostro-caudal sense and are indirectly proportional; for example a maxillary CT with a higher degree will be seen with a lower degree in the ipsilateral opposite mandibular CT.

Dental displacements

This is a variation in the normal position of the tooth and is commonly found affecting the mandibular molars (triadan 3/409 and/or 10), both in a vestibular and lingual/palatal sense. It can lead to diastemata formation, periodontal disease and soft tissue trauma.

Displacements may result from lack of space during eruption, or due to incorrect orthodontic forces in the oral cavity.

Most commonly, dental displacements occur when the donkey is juvenile; the displacements may be extremely slight and easily missed. Continuous eruption and/or disproportionate occlusal forces during mastication leading to food stasis, the potential development of a focal overgrowth and consequently to the rostro-lingual/palatal displacement and acquired diastemata in the in the interproximal spaces (IPS).

If diagnosed early, displaced teeth are infinitely easier to treat; profiling of the clinical crown at the direction of displacement allows for the alignment of the arcade to be improved and may be enough to correct the orthodontic forces and even resolve associated diastemata. An increased frequency of routine dental treatments may be necessary to treat and maintain displaced teeth.

Radiographs of displacements identified very early on may provide clues as to the causes and/or likely directions of the impending displacement.

If not treated, dental displacements may be quite severe and if periodontal disease has not advanced sufficiently, these teeth may have very solid attachments.

Veterinary extraction of severely displaced CT is one course of action, yielding very good results in terms of resolution of tissue trauma and localised periodontal disease. Extreme caution must be used when extracting CT that are very steeply angled (some are virtually horizontal) as incorrect use of molar forceps will readily cause fracture to one or more apices.

Periodontal disease

Periodontal disease (PD) is a leading cause of dysmastication, weight loss and tooth loss and is regarded as one of the most painful oral conditions. With a prevalence of 34% in equids of all ages rising to 85% in aged donkeys; there is a key correlation between advancing age and increased incidence.

Studies in donkeys indicate an age-related increase in the number of CT affected per donkey, together with an increase in the severity of disease. In the case of the incisors an increase in the number of teeth affected was seen in older animals, but there was not an increase in the severity of the disease.

Periodontal disease is infection and inflammation of the structures surrounding the tooth, including gingiva, periodontal ligaments, cementum and alveolar bone. Common signs of dental disease are rarely demonstrated in donkeys unless they are severe. Some of the most common signs of periodontal disease can include:

• oral malodour

• food pocketing

• excess salivation/inability to retain saliva within the mouth

• dysmastication.

PD may arise from multiple circumstances but generally it occurs secondary to food stasis. In the CT almost 90% of teeth diagnosed with PD were caused by diastemata. Other causes of PD include peripheral caries and retained deciduous CT.

The rostral and caudal cheek teeth have diametrically opposed angulation of the reserve crowns which serves to force the teeth into tight apposition upon eruption, functioning as a single unit. Similarly, arcade compression is present in the incisors in healthy subjects. Disturbances to the apposition of teeth, usually at the interproximal spaces, will allow food to become static.

The risk factors for PD include:

• dental displacements

• dental rotations

• dysplasia

• polyodontia

• diastema(ta)

• abnormal mesio-distal contact at the interproximal spaces (non-parallel for example)

• abnormal spacing of crowns

• abnormal/disturbance to mesial compression

• missing teeth

• fractures

• retention of deciduous caps

• calculus deposition

• normal age related tapering of the teeth

• focal/total crown overgrowths

• loss of or inadequate peripheral or interproximal cement (including peripheral caries).

Once ingesta becomes static, it decomposes leading to proliferation of periodontopathogenic bacteria; subsequently generating an inflammatory response and a self- perpetuating cycle of gingival recession and further food stasis. This cycle continues, allowing the disease to spread further around the crown, and extending apically until the ligament is sufficiently diseased that the tooth exfoliates.

On radiography, the lamina dura and periodontal space offer key information as to the extent and severity of disease; professionals need to be able to identify indicators such as uniformity of the periodontal space, lysis of the lamina dura or ankyloses of the crown to the underlying bone. While ancillary diagnostics such as radiography aid the realisation of the clinical picture, it must be understood that radiographs, regardless of quality, may not clearly demonstrate incipient disease. In other species, changes only present once greater than 50% demineralisation occurs.

Facial grimacing, loss of body condition (usually gradual), evasion, chewing the bit, frothy saliva, increased feeding times and teeth grinding may give indications that the animal is experiencing pain (albeit not necessarily dental related). More directly associated clinical signs include face rubbing (and consequent skin lesions), dysmastication, inability to retain saliva in the mouth, head tilting during eating (especially with forage), unilateral mastication, dysprehension and increased average faecal fibre length (optimal is circa 2mm with anything over 3.5mm being indicative of dental disease).

As previously highlighted, the PDL is a sensitive structure and PD is painful, therefore adequate sedation and anaesthesia must be administered before measuring the depths of periodontal lesions.

Even though periodontal disease is commonly bilateral, it is always worth performing lateral excursion to cheek tooth contact of the mandible pre and post sedation (typically, lesions may be noted to the restricted or evaded- painful-side).

Be aware that even subtle periodontal lesions can be an indicator of apical disease (i.e. pinprick openings in the gingiva above/below the affected tooth).

The table includes recommended regimes for treatment at each stage of disease.

Progression of severe periodontal disease can in turn lead to a descending infection causing apical abscessation and or sinusitis. Severe infection may lead to loss of bone, loose teeth and/or sinusitis. It could result in clinical signs such as; excessive salivation, oral malodour, inappetence/anorexia, colic (especially impaction), hyperlipaemia, and weight/condition loss.

Attachment loss

It is possible to estimate approximate levels of attachment loss in affected regions/teeth by combining probing depth data with age related anatomical knowledge and evidence gained from the oral examination. Probing depths of around 15mm in a younger equid with a reserve crown length of 70mm+ interprets into attachment loss of less than 25%. The same probing depths in an older animal with just 20mm of reserve crown length and the attachment loss is over 50%. Diagnostic radiography will aid accurate assessment of attachment loss if required.

Diastemata

Diastemata are gaps, typically pathological, between the teeth and have a prevalence of 49.9% in all equids of all ages.

Donkeys should have 6 cheek teeth tightly opposed to each other to act as a single grinding unit. This is facilitated by a caudal angulation of the 06 and a rostral angulation of the 11. Any detectable space between the cheek teeth can be defined as a diastema. Diastemata in donkeys are more commonly found on the mandibular arcades compared to the maxillary, with the most common site for diastema formation in the mandibular arcades being between triadan positions 09/10 and 10/11, followed by 06/07. In maxillary arcades the most common positions are 06/07 and 07/08.

The proportion of cases of open diastemata increases significantly in aged donkeys and horses over 15 years old. This should encourage professionals to undertake very thorough examinations in patients under this age and be proactive in the identification and treatment of early stages of periodontal disease.

Diastemata formation can be classified as primary or secondary according to the cause:

Primary diastemata. Developmental due to:

• inadequate rostrocaudal angulation.

• dental buds developing too far apart.

• developmentally displaced/rotated teeth.

Secondary diastemata. Acquired due to:

• displaced teeth.

• senile diastemata – as teeth age they taper towards their roots.

• tooth drift due to hypodontia.

• supernumerary teeth.

Diastema can be classified as:

• open – interproximal space between the mesial and distal crowns is approximately the same width throughout the depth of the diastema, or

• valve – interproximal space between the mesial and distal crowns is narrower at the occlusal aspect; may be closed or open at the occlusal surface.

Valve diastema especially, cause food to become packed within the space, leading to periodontal disease and clinical problems.

Acquired diastemata are a common disorder of the donkey; they are an age related disorder, increasing in severity and prevalence with age. Diastema with food entrapment and associated periodontal disease is a very painful disorder that may be difficult to diagnose, especially in the more caudal mandibular area.

Food entrapment causes gingivitis and mechanical irritation. Accumulation of ingesta and or foreign bodies may be extreme and may cause severe buccal or lingual trauma.

Diastema are strongly correlated to impaction colic in donkeys and over 90% of diastemata demonstrate PD. In some rarer instances, diastema(ta) may exist in the absence of periodontal disease;

• late/delayed extraction of retained deciduous incisors (often resultant diastema(ta) do not resolve and the PD is transient)

• abnormal spacing of teeth (may be a breed normal for incisor teeth in Mammoth donkeys)

• transient diastema during deciduous tooth loss and the eruption of the permanent crown

• some age related tapering of the apices in older equids resulting in diastemata which may exist independent of PD.

Caries

Caries is described as the progressive dissolution of the calficied components of a tooth as a result of bacterial fermentation of carbohydrates. In equids, dental caries is typically observed within the infundibulum (infundibular caries) or at the peripheral cement (peripheral caries). Peripheral caries may also be noted on the occlusal surface.

The presence of caries has been reported in equids in global literature since the 1960s, but a recent study in horses in the UK has found that the prevalence of peripheral caries and infundibular caries was 51.7% and 45.5%, respectively.

Caries may be found on any teeth within the oral cavity, for example the labial aspects of the incisors, but the more commonly affected cheek teeth are described here:

Infundibular caries

The maxillary cheek teeth have two, blind ending ‘funnel’ like infundibulum, seen at the occlusal surface as crescent shaped enamel infolds (arching away from the lateral wall). These sagittal elongated cups extend to around 80% of the crown length and are normally completely filled with cementum, which in younger equids demonstrates an apical blood supply. There are some instances however, where there is an interruption or even a complete absence of cementum filling (hypoplasia). As the tooth erupts and wears at the occlusal surface, the hypoplastic areas devoid of cement will emerge as cavities and consequently may become packed with ingesta and thus commences the disease process.

The disease process itself may take years, with ingesta trapped within the infundibulum providing a substrate for bacterial fermentation. Soluble carbohydrates are metabolised by bacteria (thought to include Streptococcus devriesei) and the resultant change in pH dissolves calcium hydroxyapatite of the local dental tissues.

Cemental hypoplasia is reported to affect up to 65% of maxillary cheek teeth, but the disease process may not limit itself to infundibular cement; acidic decay may expand to the neighbouring enamel, dentine, pulp and even the apices of the tooth. In fact, in later stages, infundibula may coalesce and lead to sagittal fracture as the significantly weakened structure continues to be subject to forces of attrition.

Caries lesions may spread to affect the pulp and lead to endodontic infection, this may account for around 16% of maxillary apical sepsis cases. There is also the potential for infundibula to present as dysplastic; patent infundibula is less frequently diagnosed and only fairly recently described in veterinary text. Infundibular dysplasia may lead to non-endodontic apical infection.

Studies have shown that the 109 and 209 teeth (followed by the maxillary 06 and 11s) are most at risk of infundibula aplasia thought to be potentially due to premature disengagement of the apical blood supply following eruption (the 09 teeth have no deciduous precursor and are the first permanent crowns to erupt).

Two European studies identified that triadan 106 and 206 were also associated with the development of infundibular caries in both horses and donkeys. The presence of streptococcus devreisi was strongly correlated with infundibular caries in horses at this location.

The maxillary 09 teeth are commonly affected with extensive caries. They also demonstrate the least grossly normal infundibula. 109 and 209 are the most common site for dental fractures. 16% of apical infections in maxillary cheek teeth occur as a result of infundibula caries; of which the maxillary 09s are commonly affected.

Infundibular and peripheral caries are most commonly identified during routine dental examination. In clinically normal horses, just 12% present with normal cemental infundibula filling.

Potential infundibular caries risk factors:

1. presence of peripheral caries

2. concurrent dental disorders (other than infundibular caries)

3. increasing age.

Additionally, horses in South West England were significantly less likely to have infundibular caries than horses in other regions of England and Scotland.

It is important to examine the secondary dentine adjacent to infundibular and peripheral caries lesions and ensure the margins of the dental tissues are discreet and well-defined. Check for ‘bleeding’ of colour especially around secondary dentine; flaws to the secondary dentine are not always holes. Suspicious lesions may warrant radiography, especially if accompanied by clinical signs of dental/sinus disease.

A recent study showed caries affecting the full length of the infundibulum in 8.2% of infundibula studied, most commonly in the 12–20 year age group, and concluded that this would be likely to predispose the tooth to pathologic fracture.

IC has been classified and graded as follows:

• grade 0 no infundibular lesion or just small central ‘vascular’ channel

• grade 1 caries of infundibular cementum only

• grade 2 caries of infundibular cementum and enamel

• grade 3 caries of infundibular cementum, enamel and dentine

• grade 4 loss of integrity of the tooth.

Peripheral caries

Peripheral caries (PC) is the dissolution of the calcified non-occlusal surfaces of the clinical crown, commencing with the peripheral cementum.

Subgingival cementum is sustained by the periodontium; following eruption into the mouth, the vascular supply is terminated and thus peripheral cementum at the clinical crown is considered inert. Trauma and/or disease at this location is irreparable.

When dental tissues are formed, developmental cells (odontoblasts, ameloblasts and cementoblasts) secrete protein and an organic matrix resulting in partially mineralised tissues. Subsequently, tissues are loaded with mineral; primarily calcium hydroxyapatite.

Under the acidogenic theory of caries in humans, it is proposed that the bacterial fermentation of carbohydrates create acids. Should the resultant drop in pH of dental plaque fall below 5.5 (critical level) then caries is initiated by the release of mineral ions from the hydroxyapatite crystals. It is proposed that the same ensues in cementum but at a reduced acidic level (pH 6.7).

The cyclical pH response to dietary fermentable carbohydrates is similar in the presence or absence of caries. Teeth affected by dental caries however, remain under the critical level for extended periods because the initial pH of the plaques is lower.

PC has been positively correlated to food stasis, presence of plaque and painful periodontal disease with a high prevalence in the UK (~45%) and Australia (~59%). PC is recognised as a cause of premature wear and crown fractures in addition to pulpar insult in severe cases.

PC can be progressive and invasive, affecting the cemental infolds and deeper dental tissue layers. In the author’s experience, in severe cases the teeth can be markedly friable, warranting additional care when performing routine equilibration.

While the significance of local, superficial lesions remains unclear, there can be no doubt that moderate to severe PC presents a significant welfare issue for equids.

Table showing increasing prevalence of PC over time.

The UK’s most commonly and severely PC affected teeth are Triadan 09–11 in all cheek teeth rows.

Data from studies in Sweden (Gere and Dixon, 2010) further supports the caudal three teeth in each quadrant as the most commonly diagnosed, albeit the most commonly observed classification of the disease was 1.2, with less than 1% of subjects demonstrating higher levels.

It may or may not be coincidence that the majority of the saliva secreted into the oral cavity is from ducts positioned rostrally, which may reduce the buffering effect in the caudal regions of the mouth; particularly in the presence of food stasis.

Risk factors include:

• horses and donkeys fed diets rich in haylage, or refined starch and concentrates (or a combination of all three)

• feeding of oaten hay (common in Australia)

• presence of infundibular caries

• presence of diastema/periodontal disease and/or the presence of multiple concurrent dental disorders other than infundibular caries

• 2.1–3.0 kg concentrates per day

• living in South East England and South West England

• dental fractures.

Table showing the classification of peripheral caries (Borkent et al., 2016).

Calculus

Calculus deposition occurs at dentition local to salivary ducts; the pH of the saliva once ejected from the duct serves to calcify plaque coating the crown. Elderly donkeys may present with considerable malodorous deposits at the canines and incisors, but also around the maxillary premolars, that are adjacent to the ostium of the parotid duct.

The lower canines may erupt in very close proximity to the incisors, frequently allowing for mass accumulation of calculus covering canines and typically the corner incisors. It is likely that as incisor eruption decelerates and canine eruption is static in mature animals, the opportunity for calculus exfoliation is minimised hence the build up becomes significant in aged animals.

Calculus may cause localised gingivitis, but may lead to more serious degrees of periodontitis especially in the canines, so its removal is very important at a supra and subgingival level.

There appears to be less sexual dimorphism (regarding the canines) than demonstrated in horses and ponies and so both male and female donkeys and mules may be affected.

When calculus accumulates on the lateral edges of the CT it may well hinder ingesta enroute to deglutition and cause food stagnation at the interproximal spaces and along the free margin of the gingiva. Calculus re-growth at the premolars may be as rapid as >1cm thickness in under six months, consequently affected patients warrant very regular attention.

Calculus may become very sharp and ulcerate adjacent soft tissues occasionally to a severe extent. Calculus deposits should not be underestimated with regard to pathogenesis and traumatic risk to soft tissue.

Fractures

The pathologic or traumatic injury of the teeth, affecting part or all of its components.

In the uncomplicated fracture, only the external components of the teeth (cementum, enamel and sometimes, the dentine) are affected, whereas in the complicated fractures, the pulp cavity is exposed directly or indirectly.

Traumatic deciduous incisor fractures are relatively common and are often avulsions of the rostral mandible/pre-maxilla. Traumatic fractures of typically the central permanent incisors is common in male donkeys (even geldings) and is frequently witnessed as being caused by kicks.

Pathological fractures are more common than traumatic fractures in the CT. Due to the anatomy of CT, all fractures (even small slab fractures) should be carefully inspected using dental probes and a mirror/oroscope to assess if the pulp has been compromised.

Some donkeys have been observed with small fractures in the rostral aspect of 06s that appeared to be the site of former small focal overgrowths that fractured under the high pressures of normal equine mastication. The secondary dentine at pulp horn 6 was inevitably involved in these donkeys, but appeared to be sealed off. Failure to seal off pulp could result in bacterial invasion and a resulting apical infection.

Apical infection

Extension of pulpar disease through the apical foramen into the peri-apical (apical) periodontal tissues, with infections usually spreading around the apex, causing clinical changes to the alveoli and supporting bones. A perio- endodontic infection may also occur.

These infections may be a consequence of many of the disorders previously described (fractures, caries, and periodontal disease), but may occur as a result of anachoresis (blood-born bacterial infection).

Pulp exposure may also occur due to iatrogenic damage. Excessive use of electromechanical instrumentation carries a risk of thermogenesis as well as excessive crown reduction. The hypsodont tooth of the donkey only erupts continuously, it does not grow continuously. A conservative approach is always recommended and phased reductions of abnormal structures in the mouth will also avoid pulpar exposure.

The clinical signs caused by apical infections are directly related with the site and age of the infected tooth, and the duration and the extent of the infection.

Infection in the mandibular CT, especially in younger donkeys, may lead to fistula formation with the drainage local to the affected tooth.

In the maxillary CT, if the caudal 3–4 maxillary cheek teeth are infected, maxillary sinusitis may be present with unilateral mucopurulent nasal discharge. When the more rostral maxillary CT are infected, rostral maxillary swellings and sinus tracts into the nasal cavity may also occur.

Donkeys can be very hairy, so even major swellings and fistulas may go unnoticed.

SOFT TISSUE LESIONS

Lesions may be seen in the soft tissues; mainly ulcers and chronic oral scarring. These are often due to direct contact with sharp and abnormal dental structures, both developmental and acquired. The main causes for these lesions are reported as pointed enamel overgrowths, focal overgrowths, dental displacements, shear mouth and presence of supernumerary teeth.

Lesions seen in the soft tissues of working donkeys may also result from incorrect handling procedures such as the use of very aggressive bits, or traditional restraint systems with tight nosebands and /or other components that may compress soft tissues against the teeth. In all cases the primary cause should be addressed in addition to treating the lesion.

Periodontal tissues may also be affected, in cases of periodontal disease, affecting initially the gum, but progressing and affecting deeper tissues, in case of periodontitis.

DENTAL AND ORAL NEOPLASIA

Dental and oral neoplasia is either uncommon or underreported in donkeys. Primary oral and dental neoplasia can be classified by the tissue of origin as:

1. Soft tissue neoplasia: Squamous cell carcinoma, sarcoid, fibroma/ fibrosarcoma, melanoma, ossifying fibroma, myxoma complex, haemangiosarcoma, salivary adenocarcinoma.

2. Osteogenic neoplasia: osteoma, osteosarcoma.

3. Odontogenic neoplasia: ameloblastoma, ameloblastic odontoma, complex odontoma, compound odontoma, cementoma, peripheral odontogenic fibroma.

A number of non-neoplastic oral masses, such as: papilloma, polyp, aneurismal bone cyst, fibrous dysplasia, foreign body granuloma, gingival hyperplasia and dental cysts are also seen.

Literature in regards to oral and dental neoplasia in donkeys is very poor and intermittent, with a lingual sarcoma reported in a review paper (Davis et al) and a case report of focal gingival hyperplasia (Rodrigues et al).

The Donkey Sanctuary have found that gingival hyperplasia and osteomas are more frequently encountered in their own donkeys and two oral sarcomas and a suspect squamous cell carcinoma have been reported. These are described in this chapter.

Gingival hyperplasia

This is the most common mass encountered in the donkeys at The Donkey Sanctuary. Gingival hyperplasia is not a neoplastic process, but more of a hyperplastic reaction secondary to a primary cause of irritation, most commonly tartar formation.

Gingival hyperplasia is sometimes referred to as epulis. Epulis is a non- specific clinical term which refers to a gingival nodule and includes a variety of neoplastic and non-neoplastic conditions such as gingival hyperplasia and peripheral odontogenic fibroma (former fibromatous epulis) among others.

Macroscopically, gingival hyperplasia appears as a single smooth, round or irregular, pink, relatively firm nodule adjacent to teeth. In aged donkeys, gingival hyperplasia may appear more proliferative, but there is no evidence this lesion is neoplastic.

Microscopic examination reveals marked epidermal hyperplasia with or without various degrees of submucosal inflammation-gingivitis and fibrosis.

This is not a neoplastic lesion and, in most cases, will remain untreated.

Osteoma

There is a debate whether osteomas are true neoplasms or hamartomas (bone dysplasia). Macroscopically, osteomas are solitary, pedunculated or sessile, focally expansile, round bony masses that arise from the periosteal surface and the base merges with the underlying cortical bone. These bony masses are usually located at the horizontal ramus of the mandible and have smooth contour.

Several cases have been identified at The Donkey Sanctuary but there was no further diagnostic investigation as the masses did not raise any clinical concern.

Differential diagnosis should include ossifying fibromas.

Oral sarcoma

Two cases of oral sarcomas have been diagnosed at The Donkey Sanctuary. The donkeys affected were both geldings, 12 and 19-year-old respectively. The masses were located at the lower lip and the lower rostral gingiva and were round, firm, and pink. The mass located in the gingiva was locally invasive and displaced 303 laterally.

Histopathological examination was performed in both cases and revealed a focally invasive, non-encapsulated, non-demarcated mesenchymal neoplasm composed of spindle shaped neoplastic cells forming short, interlacing streams and bundles on a moderate amount of fibrous or myxomatous stroma.

The mitotic index was low. There was mild to moderate anisocytosis and anisokaryosis. Both masses were described as sarcomas. Further investigation, such as immunohistochemistry, in order to further characterise the origin of the sarcomas was not performed.

The gingival sarcoma was focally invasive, expansile and destructive and the donkey was euthanised following an assessment of it's welfare. In contrast, the lip sarcoma was surgically excised and did not reoccur to date.

Squamous Cell Carcinoma

Squamous cell carcinoma, a malignant neoplasm of the stratified squamous epithelium that has predilection at the mucosal junctions and is the most common oral neoplasm in horses, appears to be uncommon, if not very rare in donkeys.

At The Donkey Sanctuary, there is only one case of a 21-year-old gelding donkey that was diagnosed with a suspect oral, well differentiated squamous cell carcinoma.

Macroscopically, firmly attached to the gingiva laterally to 309 and 310, an elongated, irregular mass was identified. An incisional biopsy revealed a well differentiated, focally infiltrative epithelial neoplasm composed of polygonal epithelial cells forming lobules, nests and branching cords supported by a moderate amount of fibrous stroma.

The diagnosis of a well differentiated squamous cell carcinoma was made based on the biopsy findings.

Treatment with intralesional injection with cisplatin resulted in slight reduction of the size of the lesion.
The lesion is growing slowly.