E-glass fibres and CAD/CAM resin composits

Dental Tribune International

Fri. 8. December 2023

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GENEVA, Switzerland: Dental restorations often rely on CAD/CAM resin composites for their precision and reliability. However, ensuring the longevity and durability of these restorations remains a challenge. The integration of bidirectional E-glass fibres beneath the composites offers potential benefits in enhancing fracture resistance and directing crack propagation, thus potentially minimising catastrophic failures. A recent study has delved into understanding these dynamics further, finding that the exact placement of fibre layers under the composites needs consideration in order to balance resistance and risk of catastrophic failure.

Endodontically treated teeth are more prone to fractures and often have a reduced lifespan compared with non-treated teeth. The main challenge is preventing fractures below the cemento-enamel junction, which can cause unrepairable root fractures. While endocrowns and overlays have emerged as alternatives to traditional restorations, concerns remain. A promising approach to reinforcing restorations is the use of composites reinforced with fibre, especially glass fibre, and such reinforced composites possess superior mechanical properties compared with particulate-filled resins.

The researchers in the study sought to determine whether the presence and position of E-glass fibre reinforcement affects the restoration’s load-bearing capacity, fatigue resistance and fracture pattern. To do so, they created 90 specimens composed of a bidirectional fibre-reinforced composite layer between a superficial layer of a CAD/CAM resin composite of different thicknesses and a particulate-filled resin substructure of different thicknesses, the CAD/CAM layer simulating the coronal restoration and the particulate-filled resin simulating the resin composite core build-up of an endodontically treated tooth. They used 30 specimens of unreinforced CAD/CAM resin composite as control.

Half of the samples underwent compressive loading and the other half cyclic loading. The former showed that the control samples had the highest load at failure and that breaking force decreased with reducing CAD/CAM resin composite thickness. Under compressive loading, the CAD/CAM resin composite displayed high resistance, especially when integrated with a fibre layer, which directed crack propagation laterally. The cyclic loading showed that the fractures typically occurred at lower stress levels than those defined by maximum strength. Notably, the layer thickness of the CAD/CAM resin composite played a significant role in fatigue resistance. Thicker layers had higher resistance, but the positioning of the fibre layer had implications for stress distribution. Specimens with balanced tensile and compressive stresses showed that the fibre layer deviated the crack, indicating the potential for reducing non-restorable tooth fractures. Analysis of the fracture surfaces, using stereomicroscopy and scanning electron microscopy, elucidated fracture origins and directions.

The study, titled “Exploring the influence of placing bi-directional E-glass fibers as protective layer under a CAD-CAM resin composite on the fracture pattern”, was published online on 19 September 2023 in Dental Materials, ahead of inclusion in an issue.