Biomechanical Performance Of One-piece Glass Fiber Post-core In Three Kinds Of Different Root Canal Morphologies Of Residual Roots: Finite Element Analysis

Objective: Using Finite Elements Analysis(FEA),the study investigates the stress and displacement differences of three different root canal morphologies(normal,oversized,and dumbbell-shaped)of residual roots in one-piece glass fiber post-core restoration.The results provide a theoretical basis for clinical selection of appropriate post-core materials for residual roots with different root canal morphologies.Methods: The study employs FEA to establish models of different root canal morphologies of residual roots repaired with post-core and crowns.A maxillary second premolar was selected to prepare the oversize root canal,a maxillary second premolar was selected to prepare the dumbbell-shaped root canal,and a mandibular second premolar was selected to prepare the normal root canal,all with complete dentin ferrule(2 mm in height and 1 mm in width).The three models were repaired using three different materials: one-piece glass fiber post-core(OGF),prefabricated glass fiber post and resin core(PGF),and cobalt-chromium integrated metal post-core(Co-Cr),followed by full zirconia crown repair.The second premolars in both the maxilla and mandible were loaded with a static force of 180 N in the direction of 45° along the tooth axis at the cingulum,while the maxillary central incisor was loaded with a static force of 100 N at the mid-third of the lingual surface in the same direction.The maximum equivalent Von Mises stress(EVM)and maximum principal stress(PM),stress distribution plots,and the peak of maximum displacement were calculated for dentin,post-core,crown,and the interface between the post-core and the crown adhesive.Results: The distribution of stress in the dentin for different post-core materials used for repairing different root canal morphologies of residual roots is similar and tends to be the highest for the PGF group in terms of EVM and PM,followed by the OGF group,while the Co-Cr group was in the lowest EVM and PM,located in the neck of the lingual dentin and the junction area with the alveolar bone.The size of the high stress distribution area is related to the root canal morphology and post-core material,with a significant difference in the high stress distribution area in the dumbbell-shaped root canal model,the most noticeable being the PGF.The stress distribution of the post-core shows significant differences among different root canal morphologies,with the OGF group being more uniform.In the normal root canal,the stress of the Co-Cr group is concentrated in the middle 1/3 of the post,while the stress of the OGF and PGF groups is biased towards the root 1/3.In the oversized and dumbbell-shaped root canals,the stress of the PGF group is concentrated in the neck 1/3 of the post,while that of the CoCr and OGF groups is located in the middle 1/3 of the post.The EVM,PM,and maximum displacement peak value of the PGF group at the post-dentin interface are far higher than those of the OGF group and higher than those of the Co-Cr group,particularly in the oversized and dumbbell-shaped root canals.At the same time,the PGF group has a larger high-stress distribution area in the oversized and dumbbellshaped root canals,with the EVM located at the neck 1/3 of the interface.Conclusion: From the perspective of FEA and biomechanics,it is recommended that in the selection of post-core material for post-core and crown restoration of residual roots:1.Without considering aesthetic factors,Co-Cr is a suitable choice compared to glass fiber material for post-core and crown restoration of residual roots with complete dentin ferrule,as it can bear more stress itself to reduce the stress of the dentin.2.When using PGF for post-core and crown restoration,the compatibility of PGF diameter and canal should be taken into account,and the bonding condition at 1/3 of the neck of the post and core should be specially taken into consideration in oversized and dumbbell-shaped root canals to reduce the risk of post and core debonding.3.Among the three different root canal morphologies of residual roots,the stress distribution of OGF is similar to that of Co-Cr and more uniform.The maximum stress at the post-dentin bonding interface is significantly lower than PGF in oversized and dumbbell-shaped root canals,making it suitable for improving repair results in these types of residual roots.