Design features of a three-dimensional molar crown and related maximum principal stress. A finite element model study

Abstract

Objective-To evaluate the effects of clinically relevant variables on the maximum principal stress (MPS) in the veneer layer of an anatomically correct veneer-core-cement-tooth model. Methods-The average dimensions of a mandibular first molar crown were imported into CAD software; a tooth preparation was modeled by reducing the proximal walls by 1.5 mm and the occlusal surface by 2.0 mm. 'Crown systems' were composed by varying characteristics of a cement layer, structural core, and veneer solid, all designed to fit the tooth preparation. The main and interacting effects of proximal wall height reduction, core material, core thickness, cement modulus, cement thickness, and load position on the maximum stress distribution were derived from a series of nite element models and analyzed in a factorial analysis of variance.Results-The average MPS in the veneer layer over the 64 models was 488 MPa (range= 248 to 840 MPa). MPS increased significantly with the addition of horizontal load components and with increasing cement thickness. In addition, MPS levels varied as a function of interactions between: proximal wall height reduction and load position; load position and cement thickness; core thickness and cement thickness; cement thickness and proximal wall height reduction; and core thickness, cement thickness and proximal wall height reduction.Conclusion-Rational design of veneered structural ceramics must consider the complex geometry of the crown-tooth system and integrate the in uence of both the main effects and interactions among design parameters.

The Effect of Marginal Preparation Type on an All-Ceramic Anterior Crown: A Finite Element Study

“…All-ceramic crowns' stress distributions were evaluated on posterior tooth in previous studies. 1,9,[12][13][14]16,18 Among these studies the results of the marginal preparation type comparison studies reported that chamfer preparation type shows more uniform stress distribution than shoulder preparation types in accordance with our results. 9,12,13 In addition our results revealed that Von Mises stresses decreased from the ceramic layers to the tooth structure.…”

“…All ceramic crowns mimic the original color and translucency of the tooth and demonstrate higher biocompatibility compared to metallic structures. 1,2 When single crowns are indicated, mechanical properties (such as flexure strength, modulus of elasticity, and fracture toughness), marginal adaptation, and esthetic appearance are essential factors for determining which system to use, but the functional aspect should be considered first. 3,4 Increased fracture resistance of ceramic systems when metal reinforcement was eliminated has been obtained by the addition of chemical components such as aluminum oxide, leucite, and lithium disilicate.…”

“…The importance of anatomically correct model to give clinically relevant results is well documented. 1,11,13,16 It is known that the design of the finishing line is one of the factors that influence marginal adaptation 20,21 and fracture resistance 22 of crowns. Chamfer and rounded shoulder marginal preparation designs are mostly preferred for all ceramic restorations and reported to transfer a minimum of masticatory stress from the coping into the veneering porcelain.…”

“…2,9 In vitro laboratory testing of anatomically correct all ceramic crowns is costly and time consuming. 1,10,11 However, Finite Element Analysis (FEA) allows investigation of stress distributions through model simulations, could be used to examining the role of design variations. 9,[12][13][14][15][16][17][18][19] Most model simulations were simplified and ignored the behavior of components of the tooth-crown systems.…”

“…Chamfer and rounded shoulder marginal preparation designs are mostly preferred for all ceramic restorations and reported to transfer a minimum of masticatory stress from the coping into the veneering porcelain. 20,21 Preparation design of restorations have been studied either on posterior tooth 1,9,[12][13][14]16,18 or on porcelain laminate veneers 15,17,19 by three dimensional (3D) FEA. However, there is not enough evidence to decide which design offers better stress distribution within all ceramic restoration of an anterior tooth.…”