Investigation of Stress Distribution and Fatigue Performance in Restored Teeth Using Different Thicknesses of Adhesive Materials and Different Restorative Materials: 3D Finite Element Analysis (FEM)

<b>Background:</b> This study aimed to compare the stress distribution and fracture resistance of dental tissues and restorative materials with varying adhesive layer thicknesses and different restorative materials. <b>Methods:</b> A caries-free mandibular first molar (tooth #36) was scanned using CBCT. The scanned files were processed in Mimics 12 software for segmentation of enamel, dentin, and pulp tissues and then exported to STP format. Cavity preparations (DO, MO, MOD, and O) were designed in SolidWorks 2023. Bulk-fill composite, conventional composite, and hybrid composite were used for restorations with adhesive layers of 10, 15, and 20 μm thick. Stress distribution and fracture resistance were analyzed using 3D finite element analysis. <b>Results:</b> The highest stress values in enamel, dentin, and adhesive material were observed in models restored with bulk-fill composite, while the highest stress values within the restoration were found in models restored with hybrid composite. As the adhesive layer thickness decreased, stress accumulation within the restorative material increased. Enamel fractures occurred first in models with bulk-fill composite. Among restorative materials, fractures initiated first in models restored with hybrid composite, while the latest fracture onset was observed in models with bulk-fill composite. <b>Conclusions:</b> Restorative materials with low Young's modulus cause excessive stress accumulation in enamel and dentin, leading to early fracture of these tissues. In contrast, materials with a high Young's modulus transfer more stress to the restoration, causing premature fracture of the restorative material.