Caries in the infundibulum of the second upper premolar tooth in the horse

The anterior infundibulum of maxillary P2, or the occlusal surface at the site of the infundibulum, in 117 horses and ponies, 77 with and 40 without caries in this tooth, was sampled for bacteriological analyses between 1990 and 2004. Samples were transported in VMGA III medium and then inoculated onto MSB agar. The approximate number of bacteria was counted in each sample and the isolates were characterised biochemically, using a commercial kit.All 50 samples taken from carious lesions after 2002 were positive for an S. mutans-like strain, i.e. S. devriesei. The bacteria were also found in four of the control animals, but were much less numerous than in samples from caries-affected horses. None of the swabs taken prior to 2002 were positive for this bacteria.Our results demonstrate that S. devriesei can colonise the infundibulum of P2 of the horse upper jaw, which can be fatal for the dental tissue. We conclude that S. devriesei is strongly associated with P2 caries in horses.The development of dental caries in humans has been discussed in terms of an interaction between three main factors: bacteria, substrate, and teeth [1]. Owing to their ability to produce extracellular polysaccharides (polyglucans) from sucrose, certain bacterial species, e.g. streptococci, can adhere more easily to the tooth surface [2]. Members of the group of mutans streptococci (e.g. S. mutans and S. sobrinus) are unique in this sense, since their polyglucans are more water insoluble and become sticky when produced in dental plaque [1]. Tooth defects in the form of small fissures or enamel cracks, on the occlusal surface facilitate bacterial colonisation. In a favourable environment, such as the presence of abundant sugars within a tooth fissure, these bacteria produce lactic acids [3,4] in a manner that decreases the pH below the critical levels for demineralisation of cement, (pH < 6.7) [1] and enamel (pH ~ 5.5) [5,6]. A decrease in pH appears to cause very similar damage in human and equ