[Micro-CT analysis of tooth development of C57BL/6 mice strain]

Objective: To investigate the normal process of tooth development of C57BL/6 mouse strain by using micro-CT for better understanding about the tooth development of the human being and other species. Methods: A total of 54 C57BL/6 mice were used at postnatal day 1 (P1), P3, P7, P10, P14, P21, P28, P42 and P56 (n=6 for each age group). After euthanasia, the skulls and alveolar bones (with molars) were isolated and scanned by micro-CT scanner. After three dimensional reconstruction, the developmental status of the crown and root(s) for each tooth type was examined in different views. Results: The tooth development of mice from birth to mature (P56) could be divided into three stages. The first stage was from P1 to P14, in which the crowns of all the first, second and third molars had formed, while the roots had not fully developed yet. The second stage was from ablactation (P21) to P28, in which all the roots of the molars had reached their normal length, and the apical foramens had closed. Due to the mastication and occlusal abrasion, the incisors exhibited sharp cutting edges at the buccal enamel layer, and the corresponding molars formed a pit-to-fossa articulated relationship. The third stage was from P42 to P56, in which the root canal differentiation occurred, and 1-2 canal configuration was formed in several flat roots. The development of molar roots had completed and the apexes were enlarged due to the deposition of cementum around. Conclusions: In the process of mouse tooth development, the mineralization of the cusps, followed by crown formation and roots elongation, was precisely regulated in a spatial-temporal pattern. The incisors and the molars exhibited different modes of development.