الفهرس | Only 14 pages are availabe for public view |
Abstract The present study was designed to evaluate the effect of different occlusal veneer preparation designs of CAD/CAM generated Zirconia reinforced Lithium Silicate (ZLS) , on fatigue resistance and stress distribution using Finite Element Analysis (FEA) method. A total of fifty four human mandibular molars were prepared to receive ZLS Occlusal veneers with three different preparation designs and accordingly were divided into three groups (n=18): group I (Conventional Design): Planar occlusal veneer preparation design. group II (Occlusal veneer with circumferential preparation): Modified occlusal veneer preparation design with circumferential finish line. group III (Occlusal veneer with intracoronal cavity extension): Modified occlusal veneer preparation design with intracoronal extension. All samples’ Occlusal veneers were constructed from Zirconia reinforced Lithium Silicate Ceramic blocks (Vita Suprinity) using the CEREC CAD/CAM system. All samples were subjected to Step Stress test on a universal testing machine to determine fatigue resistance. All the data were collected, tabulated and statistically analyzed. Microscopic examination of fractured samples was carried out using the stereomicroscope and the scanning electron microscope to determine modes of failure. Stress distribution was evaluated by 3D Finite element analysis test. 3D digital model was generated by CBCT scanning and Reverse engineering. The components of the model were assembled using Solidworks software and then imported in ANSYS software to carry out the analysis. The highest mean±SD values were recorded for group II (Circumferential Preparation) ; (890.57±211.53N) followed by group I (Planar Preparation) mean±SD values; (883.54±135.91 N) while the lowest mean±SD values were recorded for group III (Intracoronal Cavity extension) (875.57±143.52 N). The difference between groups was statistically non-significant as indicated by ANOVA test (p=0.9814<0.05). The results of 3D finite element analysis showed that the three preparation designs yielded low Von-Mises stresses within the factor of safety with enamel in cervical region being least safe when subjecting the models to average bite force of 500 N. The stress distribution among different layers of the model differed, where group I (Planar Occlusal veneer preparation) delivered equivalent stresses to the occlusal veneer as well as transferring stresses to the center of the tooth and cervical area concentrated towards lingual and distal areas with maximum stresses at center of occlusal veneer. While for group II (Circumferential occlusal veneer preparation design) the maximum stresses were developed at the occlusal veneer center and less stresses at lingual as well as distal halves of the tooth structure. In the meantime group III (Intracoronal extension occlusal veneer preparation design ) generated maximum amount of stresses among the three groups, where it delivered less stresses to the occlusal veneer and transferred larger stresses towards the center of the tooth and cervical area concentrated towards lingual and distal areas. |