Influence of desalivation in rats on incidence of caries in intact cagemates.

The evidence that dental caries is an infectious and transmitted disease in rodents is unequivocal. However, the factors controlling the transmission of micro-organisms from one animal to another have not been extensively explored. Results from previous studies in our laboratory showed that desalivated animals became infected by Streptococcus sobrinus in a shorter period of time than did intact animals. Furthermore, an additional study in our laboratory showed that animals with intact salivary function caged with desalivated animals harbored more S. sobrinus immediately following establishment of infection than did intact animals housed with other intact animals. Therefore, it seemed appropriate to determine the influence on caries development of caging a desalivated animal with an intact animal. In this study, intact Sprague-Dawley rats were caged with desalivated animals; additional groups of intact animals were housed with chlorhexidine-treated animals that were either intact or desalivated. Although chlorhexidine suppressed both caries development and the level of infection by S. sobrinus, nevertheless, intact animals caged with desalivated animals invariably developed more caries than did intact animals housed with other intact animals. Treating intact animals with chlorhexidine did not affect caries scores in untreated intact cagemates. Overall, the results suggest that a highly acidogenic flora with enhanced virulence (including S. sobrinus) is selected in the desalivated animals; this flora is apparently readily transmitted to intact cagemates, leading to enhanced levels of smooth-surface caries.