Equine cheek teeth diastemata (interdental gaps) and associated periodontal disease remains one of the most painful dental conditions seen in everyday clinical practice. Despite this, it is still largely undiagnosed and neglected as a dental disease. In many cases, an effective remedial dental rasp, addressing all the issues of imbalances, will result in a significant improvement in the diastema. In contrast, in cases where there are other factors involved, or there is no improvement with conservative treatment, more advanced treatment techniques should not be delayed. Correct treatment can result in resolution or at least significant improvement in the periodontal disease.
Pathophysiology of diastemata
Diastemata often result in the development of periodontal disease which encompasses the gingiva, periodontal ligament, peripheral cementum and alveolar bone. In horses, periodontitis is in almost all cases secondary to food impaction (Figure 1). Food impaction causes mechanical irritation of the gingiva and allows prolific growth of bacteria, resulting in inflammation. The increased immune response from the host causes the release of inflammatory mediators including cytokines, resulting in an increase in the destruction of periodontal tissue and collagen breakdown. As the disease progresses, periodontal disease may extend to the deeper periodontal ligament and alveolar bone, resulting in apical disease.
Diastema may be a primary developmental disease, occurring in horses with cheek teeth buds developing too far apart (more common in larger breeds) or where there is very little rostro-caudal angulation of cheek teeth resulting in interdental spaces between cheek teeth. Displaced teeth may also be developmental, sometimes observed in larger breeds but also in small and miniature breeds when there is overcrowding of teeth and lack of space.
Diastemata may also be secondary due to loss of teeth with mesial drifting of remaining teeth in a cheek teeth row, or secondary to partial mesial or distal crown fractures, allowing food impaction. In advanced cases of diastemata and periodontal disease, teeth may become more displaced due to the destruction of periodontal disease. In cases of dental neglect, with irregular sharp enamel points, overgrowths and exaggerated transverse ridges, small diastemata may develop secondary to abnormal mastication and wear.
Senile diastemata are common in geriatric horses (cheek teeth and incisors) due to the natural age-related narrowing of teeth and gradual decrease in rostro-caudal angulation.
Diastemata may also be classed as valve (open at the gingival margin, narrow or in contact at the occlusal margin) or open (parallel) depending on the shape of the interdental space. Valve diastemata are more commonly seen in the caudal interdental spaces, and open diastemata more commonly seen in geriatric horses (Figure 2). Valve diastemata may be more problematic to treat initially, but may have a better chance of complete resolution with treatment. Diastemata are most commonly seen in the mandibular cheek teeth, but can present in maxillary cheek teeth. Treatment of maxillary cheek teeth is often more difficult due to the wider tooth shape and close contact with the buccal cheeks that promote food packing.
Horses rarely present with clinical signs of diastemata and it is mostly a diagnosis noted on routine dental examination. However, in advanced cases, horses will invariably start to exhibit some clinical signs starting with subtle changes such as eating forage slower, not finishing the usual amount or quidding of hay/haylage. In extreme cases where the diastema food impaction results in localised ulceration of the cheeks or tongue, horses may also present with excessive salivation (Figure 3). Horses with diastemata and secondary periodontal disease are more likely to quid than with other advanced dental disorders as the condition is often bilateral.
Diagnosis of diastemata can easily be missed on routine dental examinations if there is no direct visualisation of the cheek teeth, especially as more caudal mandibular diastemata are most common (Figure 4). Diagnosis requires a well-sedated horse and examination with a full mouth speculum, good light source and dental mirror as a minimum. A small amount of food impaction in the caudal mandibular cheek teeth and buccal aspect of the maxillary cheek teeth can be difficult to observe and very often look mild on initial inspection, but may reveal deep periodontal pockets upon further investigation. The use of an oroscope greatly facilitates diagnosis and allows for more accurate and complete assessment of the associated periodontal disease. Removal of the food is required to enable assessment of the degree of periodontitis and periodontal pocket depth. In more advanced cases, radiographs may be indicated to assess the extent of periodontal ligament and alveolar bone involvement and the possible presence of periodontal-endodontic lesions.
The two most important principles of treating diastemata are cleaning out the periodontal pockets to ensure that all the food is removed, and that a well-balanced remedial rasp is performed ensuring all irregular overgrowths are addressed and the correct occlusal angles are maintained. Mild cases of diastemata with no other perpetuating factors will usually resolve with this treatment alone. A short re-examination interval (six to eight weeks) is recommended to ensure that the diastemata and gingivitis have resolved. Moderate and severe cases of diastemata with deeper periodontal pockets will often require more advanced treatments, such as partial or complete interproximal odontoplasty (diastema widening; Figure 5), interdental bridging and, in some cases, extraction of severely affected teeth.
Complete widening of diastema, from occlusal surface to gingival level, was the first described technique for the advanced treatment of diastema. This is a technique that has to be performed very carefully and skilfully to avoid iatrogenic damage to pulp horns and surrounding soft tissues. The principle is that the widened space will allow food to move in and out (ie won’t become trapped, and allows the gingiva to heal). With continued dental eruption and healthy gingiva, the new crown will have a tight interdental space again.
The use of partial widening (widening to only partial depth of the interproximal space) is now preferred in the majority of cases as it comes with less risk to the individual teeth, and will result in faster resolution to tight interdental spaces (ie less widened crown to wear out; Figure 6). This technique should be performed with oroscope guidance to ensure that there is correct placement of the diastema burr and the burred surface is regularly checked to ensure that there is no risk of pulp exposure.
Bridging or occluding diastemata with dental materials without partial or complete widening has to be done with great caution as the material may push further down into the periodontal pockets and not only prevent the gingiva from healing but may cause more trauma. This is particularly relevant in the case of valve and maxillary diastemata. Temporary bridging with soft materials such as polysiloxane impression putty or a human periodontal dressing (eg Coepack) may be performed. These should always be re-evaluated and removed after a few weeks as they should not remain in situ long term. The use of hard dental composite for bridges should be reserved for experienced clinicians as incorrect placement of these may be associated with severe discomfort and further complications. Any hard bridge placed between the teeth should always be accompanied by a technique for mechanical bonding with some form of retention odontoplasty to prevent apical drift.
In cases with severely displaced or rotated teeth, extraction is indicated. Any other cases with severe radiographic changes indicative of secondary apical disease should also be extracted. Mild to moderate periodontal ligament involvement with or without interdental alveolar bone changes will still have a good chance of resolution with the correct treatment (Figure 7). Care should be taken not to misinterpret reversible apical periodontitis from more severe secondary dental endodontic disease (“perio-endo” disease).
Treatment with NSAIDs to reduce inflammation and provide analgesia is recommended. Dietary modification may be required in many cases. If possible, complete grass turnout for four to six weeks post-treatment will aid gingival repair. The feeding of short chopped forage should be avoided as that may impact within the diastema, but soaked pelleted forage or fibre beet may be used as a fibre supplement.
Diastemata are highly prevalent in the equine population and it is a significant and painful disease. Regular and careful dental examinations are recommended to ensure that they are identified early on. Mild cases may be treated conservatively, but there should be no delay in advanced treatments of even moderate cases to prevent progression to severe disease and potential tooth loss.