Biomechanical performance of chitosan-nanoparticle-modified bulk-fill and conventional resin composites: a combined finite element and in-vitro study

This study aimed to evaluate and compare the stress distribution of chitosan-modified and unmodified Bulk-fill and conventional composite resins using finite element analysis (FEA) and in-vitro fracture resistance testing. A three-dimensional (3D) FEA model of a maxillary premolar (34,253 nodes; 17,851 tetrahedral elements) with a Class II mesio-occluso-distal (MOD) cavity was subjected to 900 N vertical occlusal loading to record von Mises stress, total deformation, and XY-plane shear stress. The groups analyzed were: Sound Tooth Control; Unmodified/Plain Conventional: Tetric N-Ceram 2 composite; Chitosan-Modified Conventional: Tetric N-Ceram 2 composite; Unmodified/Plain Bulk-Fill: Tetric PowerFill composite; and Chitosan-Modified Bulk-Fill: Tetric PowerFill composite. In parallel, fifty extracted premolars (restored according to the same grouping) underwent in-vitro fracture resistance testing after thermocycling (5–55 °C, 10,000 cycles). Data was analyzed using Two-Way Analysis of Variance (ANOVA) test and Bonferroni Post hoc analysis. A 95% confidence range was used to determine statistical significance for p ≤ 0.05. Intact enamel produced von Mises stress of 66.69 MPa with minimal deformation (0.0039 mm). Intact dentin showed comparable stress (66.89 MPa) but 4.4-fold higher deformation (0.0175 mm). Among restorative groups, modified Bulk-fill demonstrated lowest deformation (0.0069 mm), highest calculated shear stress (32.4 MPa), and highest fracture resistance (107.55 MPa). The maximum von Mises stresses were 78.26 MPa for Bulk-fill, 104.6 MPa for Tetric N-Ceram 2 (highest), 101.3 MPa for modified Bulk-fill, and 75.4 MPa for modified Tetric N-Ceram 2, indicating material-dependent stress distributions following chitosan modification. Chitosan modification altered the modeled biomechanical response and was associated with favorable numerical trends, particularly in Bulk-fill, but a significant independent chitosan effect on fracture resistance was not demonstrated. Not applicable.