Formation of the periodontal attachment in developing rabbit permanent incisors.

Permanent incisors from fetal New Zealand white rabbits aged 25-30 days in utero and from 1-20 days postnatally were processed for light microscopy. Examination of longitudinal and cross-sections revealed that cementum deposition and fiber attachment first occurred at 27 days in utero. A tooth-to-bone course of principal fibers confined to lateral aspects of the teeth was observed in 29-day fetal incisors, whereas lingually the periodontal ligament remained undeveloped as late as 5 days postnatally. In 20-day postnatal incisors, the development of the functional periodontal ligament was complete as evidenced by the fiber arrangement on all aspects of the root-analogue tooth surface. This study shows that 25-26-day fetal rabbit permanent incisors represent the end of the follicular phase, whereas 27-day fetal to 20-day postnatal teeth demonstrate distinct histologic characteristics of initial, incomplete and complete periodontal fiber attachment.