Formation of Cariogenic Impactions in Rats

Large particles of rice in a modified HWC ration produced cariogenic impactions in the second transverse fissures of the first mandibular molars and in the transverse fissures of the second mandibular molars of rats. These particles were captured in caries-susceptible rats by the longitudinal sulcus terminating in each fissure. Hoppert's ' observations on rats fed the Hoppert-Webber-Canniff (HWC) diet have shown that carious lesions are usually filled with impactions of food materials, and that often these impactions contain large pieces of rice. These facts have suggested that the coarse pieces of rice promoted impactions, which have been favorable sites for the carious process in caries-susceptible rats. This investigation, therefore, has aimed to determine whether there are anatomic characteristics in the mandibular molar teeth of caries-susceptible rats that facil-itate the capture of large particles of rice, and whether such structures are lacking or deficient in the mandibular molars of rats resistant to caries. Hunt, Rosen, and Hoppert's study2 of the gross morphology of the maxillary and mandibular molars of young rats, and of the occlusion of the molars, has led to a hypothesis that explains the role of coarse particles of grain in producing impactions, and therefore caries, in mandibular molars. The former paper should be read to under-stand the mechanics of the building of im-pactions described here. Material and Methods Caries-resistant and caries-susceptible rats were from the strains built by Hunt, Hop