Before glass fiber can be used in CAD/CAM resin composites, it needs fine tuning

CAD/CAM resin composites are opening up an exciting new area for materials research in dentistry.

Before glass fiber can be used in CAD/CAM polymer composites, it needs fine tuning

Endodontically treated teeth are more susceptible to fracture and often have a shorter lifespan compared to healthy teeth. The main problem is to prevent cracks below the cemento-enamel junction, which can lead to permanent root fractures. Although endocrowns and onlays have emerged as alternatives to traditional restorations, problems remain. A promising approach for reinforcing restorations is the use of fiber reinforced composites, especially glass fiber, and such reinforced composites have superior mechanical properties compared to particle filler composites.

In the study, the researchers sought to determine whether the presence and location of E-glass reinforcement affects the load-bearing capacity of the restoration, fatigue strength and failure mode. To do this, they created 90 samples consisting of a bidirectional fiber-reinforced composite layer between a surface layer of CAD/CAM resin composite of varying thicknesses and a particle-filled resin backing of varying thicknesses, with the CAD/CAM layer simulating a crown and the particle-filled composite simulating a composite pulp buildup. endodontically treated tooth. They used 30 samples of unreinforced CAD/CAM polymer composite as a control.

Half of the samples were subjected to compressive loading and the other half to cyclic loading. The first samples showed that they had the highest load at failure and that the breaking force decreased with decreasing thickness of the CAD/CAM polymer composite. Under compression, the CAD/CAM polymer composite exhibited high strength, especially when combined with a fiber layer that controlled lateral crack propagation. Cyclic loading has shown that cracks typically occur at stress levels lower than those defined by maximum strength. Notably, the thickness of the CAD/CAM resin composite layer played a significant role in the fatigue strength. Thicker layers had higher strength, but the location of the fiber layer affected the stress distribution. Specimens with balanced tensile and compressive stresses showed that the fiber layer deflected the crack, indicating the potential for reducing the number of unrepairable tooth fractures. Analysis of fracture surfaces using stereomicroscopy and scanning electron microscopy revealed the origin and direction of fractures.