Impact of Margin Type and Material Choice on Stress Distribution in Endocrown Restorations: A 3D Finite Element Study.

BACKGROUND Finite element analysis (FEA) for endocrown restorations (ER) on maxillary molars has rarely been investigated, despite its high incidence in gross decay and being treated endodontically. This study aimed to analyze the influence of various preparation features (margin type, pulp chamber extension, occlusal thickness) and restorative material (zirconia, lithium disilicate, nanoceramic resin) on the stress distribution pattern of maxillary first molar ER using three-dimensional FEA. MATERIAL AND METHODS Six three-dimensional finite element models (models A-F) were created for ER maxillary molars, considering preparation features - margins (flat butt, 20° bevel, shoulder), pulpal extension (2 mm/4 mm), and occlusal thickness (3 mm) - for 3 ER materials (zirconia, lithium disilicate, nanoceramic resin). The closing phase of mastication was loaded with 600 Newtons of functional load from an apple bolus. Von Mises Stress (VMS) was used to calculate tooth component and ER stress distributions. Standard criteria were used to calculate cement layer failure risk. RESULTS Resin nanoceramic shoulder margins with 2- and 4-mm PE (models E and F) had higher stress concentrations on the tooth preparation surface, cervical enamel, buccal roots, and ER intaglio surface. Higher elastic modulus (ME) materials had higher stress concentrations inside ER and less stress in the cement layer, facilitating tooth bonding. Resin nanoceramic distributed stresses more uniformly on ER/tooth tissues. CONCLUSIONS Different margin and pulpal extension preparation features and restorative materials cause varied ER stress distribution. Shoulder margin created considerably larger stresses in dental tissue and ER than flat butt margin, regardless of material type. Increased pulpal extension reduced tooth tissue stresses but increased ER.