Abstract: Objective: To compare the stress distribution and retention effects of lower molar residual crowns restored by post-core crown, endocrown and inlaycrown using the finite element analysis, and to explore the optimized repair plan of lower molar residual crowns. Methods: The healthy and integral left mandibular first molar of volunteer was selected as the experimental sample. Their imaging data was collected by cone beam CT (CBCT) scanning. Then the complete finite element model of the mandibular first molar was reconstructed by reverse engineering software such as Mimics, Geomagic and CATIA. On this base, three groups of models of lower molar residual crowns with the clinical crown heights of 1, 2, and 3mm were constructed. Meanwhile, the finite element models of post-core crown, endocrown, and inlaycrown were established to repair the three groups of residual crowns mentioned above; there were nine experimental groups. In the Abaqus software, the vertical and oblique static loads were applied on the models to simulate the forces produced during chewing, and the forced rotational displacement load was applied on the models to simulate the dislocation of restorations. Then the stress peak and stress distribution cloud map of von Mises in dentin of the models in various groups, as well as the force generated by restorations to resist dislocation and the damage of adhesive during dislocating were all observed. Results: The von Mises stress peak results were inlaycrown > endocrown > post-core crown in vertical load and endocrown > inlaycrown > post-core crown in oblique load. According to the stress distribution cloud map, the root apical 1/3 of post-core crown, the pulp floor of endocrown and the dental cervix and root of inlaycrown was found obviously in the stress concentration. The non-axial retention force results were post-core crown > inlaycrown > endocrown in the 1 mm residual crown group, and inlaycrown > post-core crown > endocrown in the 2 and 3 mm residual crown groups. According to stiffness degradation contours of resin adhesive layer, the cracked areas of adhesive during dislocation was inlaycrown > endocrown > post-core crown. Conclusion: From the perspectives of protecting dental tissue and maintaining the stability of restorations, the post-core crown is an ideal restoration for repairing the lower molar residual crowns.

Key words: post-core crown, endocrown, inlaycrown, finite element analysis, biomechanical analysis