Abstract:

Objective To investigate the anatomic feature of the canal isthmus of mandibular permanent incisors by Micro-CT. Methods Thirty-three mandibular permanent incisors with two canals were selected through the radiograph in proximal view. These teeth were then scanned using Micro-CT and reconstructed. The scanning layer thickness was 20 μm. We observed the apical 6 mm of the 33 roots, and 300 sections were gained each tooth, giving a total of 9 900 sections. The numbers of canals at each level in the apical 6 mm were recorded. The num - bers of sections showing isthmuses at each level of the root canals were recorded too. Data were analyzed using the Chi-square statistic to test the null hypothesis that location of the sections in each of the apical 6 mm and presence of the isthmus were independent. The minimum root canal wall thickness was measured in each of the apical 6 mm of the roots. Results Isthmuses were found to be present at all levels with prevalence from 10.0% to 85.5%. The Chi-square test indicated a significant difference in the distribution of isthmuses with section（P=0.001）. The incidence of isthmuses was higher at the apical 3-6 mm level, and the highest incidence（85.5%） was at 5 mm level. There were many more sections containing complete isthmuses（49.7%） than those containing partial isthmuses（4.5%）. The thickness of the minimum root canal was less than 0.5 mm. Conclusion The mandibular incisors have a high incidence of isthmus and are narrow in proximal direction. Debridement of the isthmus is a major challenge during surgical and nonsurgical root canal treatment.

Key words: canal anatomy, mandibular incisor, canal isthmus, root canal wall thickness