Ceramic inlays: Is the inlay thickness an important factor influencing the fracture risk?

Abstract

ObjectivesIt is still unclear whether the inlay thickness is an important factor influencing the fracture risk of ceramic inlays. As high tensile stresses increase the fracture risk of ceramic inlays, the objective of the present finite element method (FEM) study was to biomechanically analyze the correlation between inlay thickness (T) and the induced first principal stress. MethodsFourteen ceramic inlay models with varying thickness (0.7–2.0mm) were generated. All inlays were combined with a CAD model of a first mandibular molar (tooth 46), including the PDL and a mandibular segment which was created by means of the CT data of an anatomical specimen. Two materials were defined for the ceramic inlays (e.max® or empress®) and an occlusal force of 100N was applied. The first principal stress was measured within each inlay and the peak values were considered and statistically analyzed. ResultsThe stress medians ranged from 20.7 to 22.1MPa in e.max® and from 27.6 to 29.2MPa in empress® inlays. A relevant correlation between the first principal stress and thickness (T) could not be detected, neither for e.max® (Spearman: r=0.028, p=0.001), nor for empress® (Spearman: r=0.010, p=0.221). In contrast, a very significant difference (p<0.001) between the two inlay materials (M) was verified. ConclusionsUnder the conditions of the present FEM study, the inlay thickness does not seem to be an important factor influencing the fracture risk of ceramic inlays. However, further studies are necessary to confirm this.