Acta Veterinaria Scandinavica 2007, 49:10 http://www.actavetscand.com/content/49/1/10 PF2igcuarreies2 P2 caries. A and B: Intra-oral photographs of caries in the rostral infundibulum of a maxillary P2. A) Black arrow indicates a carious lesion. B) An investigation probe inserted into a carious lesion. 000, 100 000 – 1 million, > 1 million CFU/ml. The iso- lates were characterised biochemically, using a commer- cially available kit (API Rapid ID32 Strep, API System, Biomerieux, Marcy 1Étoile, France) according to the man- ufacturer's instructions. The bacteria isolated from the car- ious lesions of the first six horses sampled during 2002 were also characterised taxonomically. The result of this characterisation has been presented elsewhere [16]. Fisher's exact test was used for statistical evaluation. This project was approved by the Uppsala Animal Ethics Committee, diary no. C 231/4. Results There was no growth of S. mutans-like bacteria in samples taken from carious lesions during the years 1990 – 1999. On the contrary, the results of incubation on MSB agar and biochemical characterisation showed that all samples taken from carious lesions after 2002 were positive for the S. mutans-like strain, S. devriesei. Of these 50 animals with caries, 24 had carious lesions bilaterally in P2s of the upper jaw. In 20 of the 30 animals with caries sampled as an internal control, S. devriesei was also found in samples from the occlusal surface of the mandibular P3 on the opposite side (Table 1). The presence of S. devriesei colo- nies was significantly smaller in the control animals than in the samples taken from horses and ponies with carious lesions (p < 0.0001, 3 df). Among the control animals, four were positive for S. devriesei at the P2 position and of these horses three also had positive samples taken at the internal control site. The samples from the remaining 36 control animals were all negative for S. mutans-like bacte- ria. On the MSB agar plate, the S. devriesei isolates showed a copious production of polysaccharides (Fig. 7). Discussion Carious lesions are reported to mainly occur in cheek teeth of the upper jaw [20]. The gross anatomy differs between the upper and lower jaws with respect to the infundibula, which are absent in the mandibular cheek teeth. The infundibula in upper cheek teeth are usually incompletely filled by infundibular cementum and both Baker [8] and Kilic et al. [21] reported a high incidence of severe caries in this area. The incomplete filling with cementum could of course be looked upon as a typical predilection site, that is a damaged or incomplete tooth surface, where bacteria can easily adhere and colonise compared to the intact surface. Baker [8] suggested that Honma et al. [9] misnamed cemental hypoplasia as a car- ious lesion. However, it may be difficult to clinically define the difference between hypoplasia and caries of the cementum. In our experience, the caries definition used in the present study, – a progressive decalcification and destruction of the cementum, enamel and dentin in the infundibulum -, is more practical for clinical use. Page 4 of 9 (page number not for citation purposes)