Biomechanical behavior of fiber-reinforced and bulk-fill composites in extensive class II restorations: a...

Owing to the complexity of dental architecture and the ongoing development of restorative materials, the biomechanical behavior within restored dental structures is not yet fully understood.

This study aimed to evaluate and compare the stress distribution in extensive Class II restorations reinforced with different composite systems using 3D-Finite Element Analysis (FEA).

A sound human mandibular first molar was digitized to generate a 3D solid model. Five experimental groups with mesio-occluso-distal (MOD) restorations were simulated: G1, bulk-fill composite core; G2, short fiber-reinforced composite (SFRC) core; G3, ultra-high molecular weight polyethylene (UHMWPE) fiber-reinforced core; C-, conventional nanohybrid composite; and C+, intact sound tooth. All restored groups received an occlusal and proximal veneering layer of conventional nanohybrid resin. A vertical load of 600 N was applied, and von Mises and maximum principal stresses were calculated.

The UHMWPE group exhibited the most favorable stress distribution, demonstrating the lowest stress concentrations in the coronal tooth structure (353.5 MPa) and the adhesive interface (11.10 MPa). Conversely, the SFRC group presented the highest stress values in the remaining tooth structure (359.9 MPa), while the bulk-fill group recorded elevated stress peaks within the veneering material (21.29 MPa). Notably, the polyethylene core absorbed the highest internal stress (13.31 MPa) compared to the other experimental groups.

The type of structural reinforcement significantly dictates the biomechanics of Class II restorations. A core reinforced with polyethylene fibers (Ribbond THM) demonstrates a superior capacity to manage stress in high-load areas compared to SFRC (EverX Posterior) and bulk-fill composite (Tetric N-Ceram bulk fill).