Morphological study on dental caries induced in WBN/KobSlc rats (Rattus norvegicus) fed a standard laboratory diet

In our previous studies, WBN/KobSlc was characterized as a rat strain in which only males began to develop pancreatitis, and then presented with diabetic symptoms. In the course of studying their pancreatic inflammation, we detected molar caries in prediabetic males feeding on a standard diet (CRF-1) widely used for experimental animals. The purpose of this study is to confirm whether the WBN/KobSlc strain is caries-susceptible to the diet reported to be non-cariogenic, and to examine the effect of a prediabetic condition on their dental caries. For a morphological study, 25 male WBN/KobSlc rats aged 3.2–7.8 months and 24 females of the same strain aged 3.3–6.6 months were used, along with 10 males and 10 females of 8.2-month-old F344 rats. Marked dental caries were detected in the mandibular molars of male and female WBN/KobSlc rats regardless of pancreatitis, although no similar changes were observed in any teeth of the F344 strain fed the same diet. Soft X-ray examination revealed that the caries began in the crown and progressed horizontally and vertically, and that a severe radiolucent lesion extensively expanded to the entire crown, corresponding to a macroscopically deleted molar. The caries had gradually developed mainly in the second mandibular molar from more than 3.5 months of age, while none were seen in any rats before that time. The WBN/KobSlc rats were caries-susceptible even to the standard laboratory diet, and pancreatitis was not directly associated with the onset of dental caries in this strain.