Abstract:

Objective To analyze the root canal diameter of the mandibular first premolar by using finite element analysis to simulate the stress distribution of dentin under three different preparation methods，and to provide the basis for clinical root canal preparation strategies of the mandibular first premolars. Methods Twenty-one patients with complete cone beam computed tomography （CBCT） images were selected. The original DICOM format data from CBCT were imported into Mimics 21.0 software to measure the root canal diameter at 3， 6， 9， and 12 mm from the apex and the root canal taper was segmentally calculated. Based on this， three-dimensional finite element models of the dental and periodontal tissues were constructed. Control group， maximum diameter preparation group， uniform preparation group， and 0.06 taper instrument preparation group were designed. In ANSYS Workbench 17.0 finite element analysis software， a 200 N load was applied to the buccal， lingual， and occlusal surfaces in various groups， and the stresses on dentin in various groups were analyzed. Results The analysis of root canal taper at 3-6 mm， 6-9 mm， and 9-12 mm from the apex of mandibular first premolar teeth showed that the taper was similar in the mesial-distal direction at 3-6 mm from the apex. The average taper in the buccal-lingual direction at 6-9 mm from the apex was 0.29， which was greater than the taper in the apical 1/3 and coronal 1/3. Under the same load， the peak stress values in dentin of mandibular first premolar teech in various groups were increased sequentially： 4.693 6， 16.304 0， 14.278 0， and 18.682 0 MPa. The stress in maximum diameter preparation group concentrated on the canal wall with the highest stress value. The stress in uniform preparation group concentrated on the root surface，and the stress values on each section were lower than those in maximum diameter preparation group. The stress in 0.06 taper instrument preparation group concentrated on the apical 1/3 of the root surface. Conclusion The root canal of the mandibular first premolar has a unique elliptical taper shape， and there are significant differences in diameter and taper between the mesial-distal and buccal-lingual directions. Different preparation methods result in different stress distributions on the canal wall， and the uniform preparation is the best method for enlarging the canal.

Key words: Vertical root fracture, Root canal diameter, Root canal preparation, Finite element analysis, Stress analysis