An In-vitro Evaluation of Mechanical Fatigue on Dental Resin-based Composites

Objectives: In the treatment of severe tooth wear patients, onlay restorations can be used including increased vertical dimension of occlusion. Strength of these restorations is depending on preparation design, adhesive technique, luting cement, composite material properties and thickness of the restoration. The aim of this in vitro study was to investigate the fatigue fracture strength of composite onlay restorations, made with different materials and in different restoration thickness.
Methods: 32 samples of two types of composite resin (Clearfil AP-X, Kuraray; Filtek Supreme XTE, 3M) 1 or 2 mm thick onlay shaped restorations were placed on flat bovine dentin surfaces using Clearfil SEBond (Kuraray) and divided over 4 aging groups for cyclic loading (n=8): A) Control, no aging, B) Rub&Roll device, 500,000 cycles, C) Rub&Roll device, 1.000,000 cycles and D) Bose Mouth Motion, 1.000.000 cycles. After fatigue testing, all specimens were subjected to a single-load-to-fracture test and fracture strengths were recorded in Newtons (N). Fracture strengths were analyzed using a linear regression model and independent T-tests (<0.05). Fractography was conducted on fragments after fracture.
Results: The initial strength of Clearfil AP-X (1,542.8 ± 551.2N) showed no significant difference compared to the initial strength of Filtek Supreme XTE (1,893.5 ± 756.7N). The Bose Mouth Motion technique showed a significant decrease on fracture strength (p=0.022), whereas both regimes of the Rub&Roll had no significant influence (p>0.05). Fracture strength of the restoration increased significantly for 2mm compared to 1mm thickness (p<0.001).
Conclusions: Cyclic loading by Bose Mouth Motion showed a decreased fracture strength of composite onlay restorations. Thicker restorations showed a higher fracture strength.