Abstract: Objective: To study the effect of dentin shoulders on fracture strength of post-core crown restorated mandibular incisors by using the method of in vitro mechanical test and finite element analysis. Methods: Five groups of dentin shoulder collars with different shapes were designed for mandibular incisors. After post-core crown restoration, the bending test was performed on an electronic universal testing machine to study the effect of dentin shoulder collar position on the bending strength of the tooth. The mandibular incisors were scanned by CBCT to obtain the three-dimensional CT scanning data. The post-core crown restoration models of mandibular incisors with different dentinal shoulder collar shapes were established by Mimics, Geomagic, Ansys, and other software. The occlusion loading was simulated to analyze the von Mises stress distribution. Results: The fracture strength of buccal dentin shoulder collar and 2.0 mm intact dentin shoulder collar was the highest, followed by that of tongue dentin shoulder collar and near-middle dentin shoulder collar, and the fracture strength of tooth without dentin shoulder collar was the smallest. When 2.0 mm intact dentin collar was retained, the stress distribution of remaining tooth tissue was close to those of buccal dentin collar and lingual dentin collar. The stress distribution was uniform and the stress was relatively small. However, when retaining the near-middle dentin shoulder collar and the non-dentin shoulder collar, there was different degrees of stress concentration at the tongue side of tooth neck, and the stress was relatively large. Conclusion: Preserving 2.0 mm intact dentin shoulder collar can effectively improve the fracture strength of affected teeth. Retaining buccal tooth tissue as much as possible is helpful to enhance the fracture strength of the restored mandibular incisors.

Key words: dentin shoulder collar, fracture strength, mandibular incisor, finite element analysis, biomechanics