Characterisation and Performance of Fibre-Reinforced Composite Restorations

In the modern era of metal-free minimally-invasive dentistry, there is a growing tendency toward using metal-free restorative alternatives that provide not only excellent aesthetics but also enable superior durability. Fibre-reinforced composite (FRC) is one cost-effective alternative that fulfils the requirements of aesthetics and durability, and offers favourable physico-mechanical properties. Many FRC applications are well-documented in the literature, such as crowns and fixed partial dentures (FPD); however, their clinical implementation is still limited, owing to the lack of significant knowledge about their longevity, deterioration signs, optimum design and overall performance. This in-vitro research aimed to address these uncertainties by investigating the performance of FRC restorations, and the influence of fibre reinforcement on particular physcio-mechanical properties, including surface hardness, edge-strength, shear bond strength, fatigue and wear resistance.Basic testing models were used to investigate the effect of incorporating differently-oriented FRCs on the surface hardness, edge-strength and shear bond strength of particulate-reinforced composite (PRC). The results revealed that the incorporation of FRC significantly enhanced surface hardness (by 12 - 19 %) and edge-strength (by 27 -75 %). However, this incorporation significantly reduced the shear bond strength (SBS) between PRC and other restorative materials, including lithium disilicate ceramic (10.9�3.1 MPa) and Co-Cr metal alloy (12.8�2.3 MPa), compared to the control (15.2�3.6 MPa, 15.0�3.7 MPa). The orientation of FRC was also found to affect the efficiency of reinforcement as bidirectional FRCs exhibited significantly higher hardness (76.8�1.2 VHN), edge-strength (67.7�8.2 N) and SBS (14.1�3.9 MPa) values than unidirectional FRCs (72.4�1.2 VHN, 56.8�5.9 N, 9.8�2.3 MPa). Clinically-relevant testing models, employing accelerated aging techniques, were performed to investigate the fatigue and wear behaviours of anatomically-shaped FRC restorations in-vitro. Direct inlay-retained FRC-FPDs with two framework designs, were tested for their fatigue behaviour and load-bearing capacity. Type-I design (with an additional bidirectional FRC layer incorporated perpendicular to the loading direction) yielded significantly higher fatigue resistance (1144.0�270.9 N) and load-bearing capacity (1598.6�361.8) than Type-II design (with a woven FRC embedded around the pontic core) (716.6�72.1 N, 1125.8�278.2 N, respectively). However, Type-19II design exhibited fewer delamination failures. Both framework design and dynamic fatigue were found to have a significant influence (p<0.05) on the load-bearing capacity of FRC-FPDs.Additionally, the in-vitro fatigue and wear behaviours of FRC crowns, fabricated conventionally from bidirectional FRC and indirect PRC (Sinfony), were compared with those made of two CAD/CAM alternatives, namely Lava Zirconia (LZ) and Lava Ultimate (LU). A chewing simulator was employed to induce some fatigue wear in crowns, while an intraoral 3D scanner was used to quantify the resultant morphological changes. The results showed that FRC crowns had significantly lower mean cumulative wear (233.9�100.4 ? m) than LU crowns (348.2�52.0 ? m), but higher than LZ crowns (16.4�1.5 ? m). The mean load bearing-capacity after fatigue simulation was also the highest for LZ crowns (1997.8�260.2 N) compared with FRC (1386.5�258.4 N) and LU crowns (756.5�290.9 N). Accordingly, the incorporation of FRC in resin-composite restorations is advocated since it increases surface hardness and marginal integrity, improves fatigue and wear behaviours, and enhances load-bearing capacity and overall performance.