Periodontal disease in the horse – are we making any progress?

Periodontal disease has been recognised in domesticated horses since the early literature ¹ and afflicts horses of all breeds in domestic management with a prevalence in the uk reported as 13.8% ² and with increasing prevalence with age³. It is also prevalent in aged donkeys.

The disease is undoubtedly chronically painful and can lead to reduced weight gain, masticatory pain, depressed demeanour and reduced athletic output. The clinical signs that are well known and include dysmastication, hypersalivation, halitosis and particularly of preserved long-fibre forage, hypersalivation, oral pain and intolerance of harness. Less common signs include trigeminal neuropathic pain that manifests as pain, dental loss and osteomyelitis.

The aetiolpathogenesis and risk factors are described ³. These include the presence of diastemata between the cheek teeth, and dental misalignment, the presence of impacted food in these diastemata which in turn putrefies with the release of inflammatory mediators ^4,5,6,7 . These stimulate the progressive destruction of the collagen fibres of the periodontal ligament ⁴ in an apical direction, and in severe cases, lysis of interproximal bone. More recently the microbiology of periodontitis has revealed it to be a complex interaction between pathogens and host immune responses ⁵ This becomes non-reversible in chronic cases which can progress to loosening and loss of dentition. Primary periodontitis appears to be unusual in horses. Lesions are more prevalent in the mandibular arcade than the maxilla¹ .

Management of the disease is multi-modal and persistence is necessary. The predisposing anatomical risk factors may be persistent. Regular oral examinations to identify the pathology are advisable for most domestic horses. Odontoplasty to improve mastication and occlusion will help to minimise drift and misalignments if there is a tendency to these trends. However empirical excessive odontoplasty that flattens the occlusal surfaces is both pointless and contra-indicated. However, reduction of excessive transverse ridges precisely can be helpful to prevent these acting as plunger cusps that impact food into diastemata.

The key to short term improvement is the removal of impacted food material from diastemata. This deep, firmly impacted, putrefying material can be troublesome and challenging to remove. Commonly used techniques involve using metal interdental picks, high pressure irrigation and specially made forceps to manually retrieve food fibres. This can be challenging technically, time consuming and difficult. The horses will generally be painful and require moderately heavy sedation to achieve this and this may require supplementation using regional analgesia. In some cases food clearance is impossible without interproximal odontoplasty ^8,9 . This has been shown to be effective in the treatment of periodontitis, particularly for valve-confirmation diastema. This involves very precise removal of the interproximal mesial and distal margins of teeth inter-proximally to enable food clearance (to a width of 3-4mm) taking care not to exposes superficial dental pulp that can lie just a few mm beneath the interproximal peripheral cementum and enamel

Irrigation of the periodontal pockets after food clearance helps to remove residual food, inflammatory mediators and non-vital tissue. This often exposes painful gingiva with mucosal ulceration that can extend deep to the alveolar crest. Topical medication of the periodontal pocket with perioceuticals such as oxytetracy clene, or haemostatic sponges is practiced but not yet validated. The challenge is to prevent-re-impaction once periodontal debridement has been achieved. Clearly frequent repetition is often impractical although this would probably be effective. Insertion of material to obturate the diastemata has become fashionable but efficacy remains unproven. Temporary stenting using polyvinylsiloxane is widely practiced that can enable salivary flow and prevents food impaction. This appears to be effective in the short term but such products should be removed after a few weeks to mitigate any cytoxicity 10. More recently it has become fashionable to use temporary luting cement containing calcium hydroxide to obturate such diastemata although the rationale for using such long-lasting materials is obscure. Possibly the calcium hydroxide contributes to disinfection of the diastemata, although careful freeing of any debris from the periodontal pocket is necessary. In order to bridge the diastema then careful preparation etc. bonding and adherence of a composite to either interproximal space is necessary. This can only be performed with after controlling haemorrhage and reducing acute inflammation. Inevitably there is relative movement between the teeth so bonding to both interproximal surfaces is contra-indicated. Such diastema bridges are semi-permanent and can remain in situ to manage toe disease during the course of a season. However they require careful pre-preparation and are time consuming to place and may not be available t all patients.

Prevention of the disease is also possible using dietary modification. Afflicted horses can be fed a modified diet avoiding preserved long- fibre forage (such as chaff, haylage and hay) substituting it with grazing and fibre or grass pellets. These do not become so firmly entrapped in the diastemata. There is possibly an effect of the oral pH resulting from certain food types but much research needs to be done to determine the effect of different feeds on salivary buffering and its significance as a risk factor for this syndrome.

Analgesia using non-steroidal drugs is an important component in managing severe cases. In addition to the effect on inflammation such drugs enable more normal mastication by providing analgesia. Antimicrobials not usually indicated unless there is systemic or sever disease affecting the mandible.