Stress distribution on molars with endocrown: Finite element analysis

Objective: To evaluate the influence of sequential dental structure reduction on stress distribution of second mandibular left molar restored with endocrown by 3D finite element analysis (FEA). Methods: Intact mandibular molar was selected and scanned using computed tomography scanner (I-CAT, Xoran Technologies, Ann Arbor, USA). The 3D-stereolithography files obtained were exported to the SolidWorks software (Solidworks Corporation, Dassault Systemes, France) to create periodontal-ligament, bones, cavity preparations without [Wo] and with [W] cusp coverage, ceramic restorations (IPS e.max Press Ivoclar Vivadent, Schaan, Lichtenstein) and luting layer. The experimental models were analyzed by the FEA software package Ansys Workbench V12. (Ansys Inc., Canonsburg, PA, USA). The Poisson ratio and the elastic modulus of the ceramic specimens were obtained by tensile and flexural tests. Linear-static-isotropic models were created. The experimental groups were: intact tooth (IT); occlusal-distal extension (WoOD); mesio-occlusal-distal extension (WoMOD); with buccal cusp coverage (WV); with lingual cusps coverage (WL); with coverage of all cusps (WT); residual tissue 2 mm above of the cement-enamel junction (Rn). A 200N-loading was applied on buccal and lingual cusps. The stress distribution was analyzed by Rankine principal stress criterious.Results: "None" experimental group simulated stress distribution as the "IT". "WoOD" showed lowest stress levels at the internal angles. Stress levels were higher at internal angles for "W" and "WoMOD". No difference was observed between the other groups when compared to "Wo" and "W" with "MOD" extension. Conclusion: The reduction of dental structure promotes stress concentration at the cavity angles. The presence of a proximal wall is an important biomechanic factor of the remaining dental tissue and the coverage of the cusps did not improve the prognosis when compared to the more conservative cavity preparations.