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Residual dentin thickness and biomechanical performance of post-and-core-restored mandibular premolars: A finite
Yi Sun1, Ze-Feng Wang2, Yue-Dan Xu1
1Dental Resident, Department of Prosthodontic, Stomatology Hospital, School of Stomatology, Zhejiang University School of Medicine, Clinical Research Center for Oral Diseases of Zhejiang Province, Key Laboratory of Oral Biomedical Research of Zhejiang Province, Cancer Center of Zhejiang University, Engineering Research Center of Oral Biomaterials and Devices of Zhejiang Province, Hangzhou, PR China.
Statement Of Problem:
Endodontically treated teeth often require post-and-core restorations for structural support because of extensive hard tissue loss. Assessment of the effect of the residual dentin thickness on the biomechanical performance of these restorations is lacking.
Purpose:
The purpose of this study was to evaluate the residual dentin thickness in mandibular premolars after post-and-core restorations using cone beam computed tomography (CBCT) and to analyze the stress distribution with finite element analysis (FEA).
Material And Methods:
The CBCT data from 236 mandibular premolars having undergone post-and-core restorations were examined. An imaging software program (NNT; NewTom) was used to measure the buccolingual and mesiodistal root diameters in cross-sections 5 to 11 mm from the radiologic apex. The CBCT derived measurements were subsequently integrated into an FEA model. A 3-dimensional (3D) mandibular premolar model reflecting the residual dentin thickness was created with a computer-aided design software program (Hypermesh 9.0; Altair Engineering). A static force of 100 N was applied directly to the buccal cusp tip at 45, 60, 75, and 90 degrees to the long axis of the tooth, and the stress distribution of dentin was analyzed by using an FEA software program (ANSYS APDL 18.0; Ansys Inc).
Results:
CBCT analysis showed that the buccolingual root diameter was wider than the mesiodistal diameter and that the residual dentin thickness of the buccal aspect was approximately 0.3 mm thinner compared with the lingual aspect along the root. The proportions of residual dentin thickness values in the buccolingual direction of the mandibular premolar teeth no less than 1 mm exceeded 96.2% at 5 to 11 mm from the apex. The proportions of residual dentin thickness values in the mesiodistal direction of the mandibular premolar teeth >1 mm were 92.1% and 88.2% at 11 mm from the apex after post space preparation and decreased further to 70.8% and 58.9% at 5 mm from the apex. The von Mises stresses of the mandibular premolar model with residual dentin thickness were mainly localized to the cervical area (region C, cervix) and the post apex (region A, apex) in the buccolingual direction. Tensile and compressive stress were concentrated on regions C and A on the buccal and lingual sides, respectively. The actual residual dentin thickness model demonstrated higher maximum tensile stress compared with the 1-mm residual dentin thickness model under various loading conditions.
Conclusions:
During the process of post space preparation in mandibular premolars, sufficient dentin thickness should be retained in the apical region. The tensile stresses of mandibular premolars after clinical post-and-core restoration were mainly concentrated in the cervical area and the post apex, and the maximum tensile stress value was higher than the ideal 1-mm residual dentin thickness model.
