Peripheral caries (or peripheral cement defects) is defined by "the deterioration or loss of cementum" which forms the outer layer of our horses' teeth. This cement surrounds the enamel and has a 2-fold function. At the level of the reserve crown (the part of the molar that is still in the gum) and the root of the tooth, cementum is necessary to obtain a good attachment of the tooth to its surrounding tissue (the periodontal ligament). At the level of the clinical crown (the part of the tooth visible in the mouth), the cement has a protective function for the extremely hard but fragile enamel. It is pre-eminently the cement (with its large and smooth surface) that comes into contact with food during chewing. Horses that develop peripheral caries have a significantly higher risk of developing periodontitis (whether or not associated with diastemata), plaque (indicating a disturbed oral flora), soft tissue injuries such as cheek and tongue mucosa and pathological fractures.
Fig; schematic representation of the top view of a lower molar (more specifically triadan 406)
Causes of peripheral cemental defects / caries
As in humans, caries in our horses is a multifactorial disease. Three main factors include: the tooth surface & (the composition of) the saliva + the nutrition + the microbial flora in the oral cavity. What proportion each of these components has and how they relate to each other in the development of this disease is not yet entirely clear, more scientific research is essential in this regard.
In any case, the horse's diet and drinking water play an important role. A diet that is too acidic (maize, acid silage, ...) affects the peripheral cement. In some horses we see an almost complete loss of peripheral cement.
No cement but cement coming from the reserve crown
Caries due to maize feeding
Also all kinds of dental problems that hamper the horse in its food intake or that lead to stagnation of food around the teeth contribute to this condition. Even parasites (gasterophilus spp.) can cause gum recession and papillary necrosis, which may be the start of food stagnation, pH reduction and thus caries formation. A recent study also stated that "the reduced production and flow of saliva through the oral cavity when feeding times are shortened are likely to be relevant factors in increasing the risk of dental caries. "*
Thus, housing and stable management are also likely to be relevant. Little is known about the influence of e.g. chronic stress on the composition of the saliva and thus on its buffering capacity. This buffering capacity varies greatly between horses and between different samples taken from the same horse.
There are clear indications that once the process of cementation has started, a vicious circle often begins. The removal of the initial cause does not solve the problem in itself.
Regular monitoring and prevention whenever possible remain the key in managing this condition. Treatment of underlying dental pathology, appropriate nutrition and management are important.
Know that this condition is not (always) irreversible: cement is produced throughout the horse's life and restoration of cement (at the level of the reserve crown) is therefore possible. Since horses exhibit lifelong eruption of their molars, new cement is constantly exposed in the oral cavity.
Loss of cement in the interdental space
Loss of cement in the interdental space, tooth plaque and focal carious areas
Loss of cement in the interdental space, food impaction and focal carious areas
*Source: Equine peripheral cemental defects and dental caries: Four case reports. T. Lundström, D. Birkhed