Anatomic variations of the root canal of the rat according to age.

The mesial canal of the first lower molar of the rat has been used as an experimental model in Endodontics. The present study involves a detailed analysis of its structural variations as a function of age and thus contributes to its characterization and adequate use as an experimental model. We evaluated 60 molars of Wistar rats of different body weight: (group 1: 300-399 g, n=22; group 2: 400-499 g, n=16; group 3: 600-700 g, n=22). The samples were radiographed employing a standardized system. Total canal length and volume were measured on enlarged projections of the radiographs. Canal diameter was measured at coronary, middle and apical levels and employed to estimate the area of canal cross-section as an indicator of potential flow or metabolic interchange. From the second age group onwards, we detected radicular hypercementosis that increased canal length and resulted in the formation of a complex apical delta. The canal diameter decreased very significantly in the apical third. The estimated flow expressed in terms of the area of cross-section on the projection decreased from 1.2 mm2 in Group 1 to 0.05 mm2 in Group 2. Group 3 did not differ significantly from Group 2. The present results reveal that the spontaneous, age-related variations in canal anatomy described herein must be considered when performing experimental endodontics in rats.