Fracture risk of lithium-disilicate ceramic inlays: a finite element analysis

In the present study, lithium-disilicate ceramic inlays should be analyzed biomechanically according to their thickness and dimension, and it should be clarified as to whether there is a significant relationship between the inlay volume and the induced tensile stress level.

Using a new parametric CAD modeling procedure, 27 lithium-disilicate ceramic inlays with various parameters of "depth", "width", "angle" and restoration volume were generated. These inlays were integrated into the CAD model of a lower molar created from the CT data of an anatomical preparation. The resulting CAD models were, finally, three-dimensionally cross-linked to FEM models. After applying a compressive force of 200 N, Principal Tensile Stresses (PTSs) could be measured in the inlay. The values were subject to statistical analysis afterwards.

The volume of the inlay restorations varied between 35.7 mm(3) and 82.5mm(3). The maximum PTS values (n=10) only showed a slight negative correlation with the inlay volume. The correlation coefficient according to Spearman was -0.082 (p ≤ 0.001). If the highest 1000 PTS values of each inlay were considered (n=1000), the correlation coefficient was further reduced to +0.068 (p ≤ 0.001). No significant correlation between the inlay volume and the induced PTS level could be detected.

Under the conditions and limitations of the present FEM study, the inlay volume did not significantly influence the tensile stress level of ceramic inlays. The results may support the thesis that volume-reduced all-ceramic inlays might not have an increased fracture risk. Further studies are needed to confirm this.