Establishment And Preliminary Application Of Simulated Mechanical Model Of Maxillary Central Incisors Restored With Cast Post-Core-Crown

Objective:To select an artificial substitute with similar mechanical properties to dentin and study the effect of loading location and loading angulation on fracture resistance of maxillary central incisors restored with cast post-core and crowns by establishing a simulated mechanical model in vitro.Methods and Results:Experiment 1:PEEK,PLA,SLA UV curable resin,nylon fiber with glass microbeads,which were manufactured by rapid prototyping technology,and melamine which were manufactured by injection molding technology,were prepared into mechanical test samples.Each material was divided into 3 groups with 5 parallel samples in each.The compression,tensile and bending strength of the samples were tested respectively.The compressive strength of the five materials were 45.33±2.92,30.40±1.15,49.18±5.08,41.68±2.12,311.70±3.25MPa.The tensile strength were 54.77±1.99,34.25±0.78,50.76±5.16,36.28±1.08,60.63±3.79MPa.The flexural strength were 130.17±23.62,47.38±10.62,74.68±5.08,36.31±3.77,157.03±31.72MPa,respectively.The mechanical properties of melamine were similar to dentin.Experiment 2:Forty-eight standardized analogues made of melamine simulating tooth preparations of cast post-core restored maxillary central incisors were randomly divided into 2 main groups,Groups A and B.The angles between the loading direction and the long axis of specimens in both groups were 45° and 60°respectively.Each group was then randomly divided into 3 subgroups marked as 1,2 and 3,with 8 specimens in each.All the specimens were embedded in acrylic resin and surrounded by silicone impression material to simulate periodontal ligament.The loading locations were 3mm,5mm and 7mm below the incisal edge on lingual surface,respectively.After standardized restorative procedure,all the samples were mounted on the universal testing machine.Static load at the cross-head speed of lmm/min was applied until the specimen fracture occurred and force at fracture as well as fracture mode was recorded.SPSS26.0 was used for statistical analysis.The mean fracture load of six groups were as follows:754.82±94.75N for Group A1,556.12±35.90N for Group B1,1228.56±162.11N for Group A2,817.11±135.81N for Group B2,1682.34±251.96N for Group A3,1097.00±156.89N for Group B3.Loading location and loading angulation both have a significant effect on the fracture resistance of the specimens,and there was an interaction between them(P<0.05).All the specimens showed unrestorable fracture pattern,with crack lines under the embedded acrylic resin,but no significant difference was found in the fracture mode among all groups(P>0.05).Conclusion:1.It is feasible to substitute melamine material for natural teeth in the biomechanical experiment of post-core-crown restoration in vitro.2.Loading location and angulation may have an impact on the fracture resistance of cast post and core restored maxillary central incisors under static load.There is a significant interaction between them,but no significant influence is found on fracture mode with different loading conditions.3.Occlusal contact may affect the long-term prognosis of maxillary central incisors restored with cast post-core-crown.