Factorial analysis of variables influencing stress in all-ceramic crowns

Objective. The objective of this investigation was to evaluate the relative contribution of variables in the crown–cement–tooth system that can influence magnitude of maximum principal stress in all-ceramic crowns. Methods. Factorial analysis was performed to calculate the coefficients of main and interactive effects of seven variables on maximum stress distribution in a series of finite element models of an axisymmetric stylized ceramic crown–cement–tooth system. Variables investigated at two levels were selected for their clinical relevance and included those relating to crown material and geometry (thickness and cuspal incline), cement modulus and thickness, supporting tooth core, and position at which the occlusal load was applied. Results. The average principal stress for all combinations of all variables was 135.1 MPa but stress magnitude ranged from 73.7 to 214.0 MPa. Crown material and thickness are of primary importance in stress magnitude but other variables (cement modulus, load position, and supporting tooth core) also contribute to the stress magnitude. Interactions between these variables can have an important influence, particularly since the stress in the crown is not necessarily sensitive to the same factors for all crown material systems. Significance. Comprehensive evaluation of stress in a crown of a crown–cement–tooth system must integrate the influence of single variables and their interactions.