Do Fiber-Reinforced Composites Really Make Restorations Stronger?

A recent in vitro study from Kocaeli University, Turkey, has put a long-debated clinical question to test — does placing fiber-reinforced composites beneath nanoceramic CAD/CAM restorations actually improve fracture strength? The findings might surprise many restorative dentists who routinely use these fibers for reinforcement. ​In modern restorative dentistry, endodontically treated teeth often pose a biomechanical challenge. Loss of marginal ridges, deep MOD cavities, and subgingival margins all weaken tooth structure — in some cases reducing stiffness by as much as 63%. With adhesive systems and deep margin elevation (DME) techniques, clinicians can restore such compromised teeth more conservatively, preserving natural tissue and avoiding full crowns. Yet, whether adding a fiber-reinforced base truly boosts strength in these conservative restorations remains unclear. To clarify this, the Kocaeli University team compared different fiber-reinforced composites placed beneath nanoceramic CAD/CAM onlays (Cerasmart) — a popular material in today’s digital restorative workflows. ​Researchers selected 100 extracted human maxillary premolars and prepared standardized MOD cavities. The teeth were restored with Cerasmart CAD/CAM blocks of two different thicknesses — 2 mm and 3 mm — and divided into subgroups based on the type of base material used:

• Control: No fiber, only nanoceramic restoration
• Non-fiber composite: G-ænial Universal Flo
• Fiber-reinforced composites: Ribbond, EverStick NET, and EverX Flow

Each specimen underwent fracture strength (FS) testing, simulating occlusal forces using a universal testing machine. Statistical analysis (two-way ANOVA, p < 0.05) was then performed to compare differences between fiber types and material thicknesses. ​Only one material — Ribbond, made from ultra-high-molecular-weight polyethylene fibers — showed a statistically significant increase in fracture resistance compared to the control group (p = 0.047). However, EverStick NET and EverX Flow did not yield significant differences in FS values when compared to non-fiber or control groups. Interestingly, the study found that increasing the restoration thickness (from 2 mm to 3 mm) consistently improved fracture resistance across all groups (p < 0.001 for fiber-reinforced samples). In contrast, changes in remaining tooth height in the control group did not significantly affect outcomes (p = 0.078). In short: thickness mattered more than fibers. ​The findings suggest that while fibers are often used to reinforce restorations in teeth with significant coronal loss, their effect may not be as pronounced as once thought — at least when placed beneath modern nanoceramic CAD/CAM restorations. That said, fibers might still play a secondary role — possibly influencing fracture patterns (i.e., repairable vs. non-repairable failures), a point observed in previous studies and worth further exploration.