Edge strength of indirect aesthetic restorative materials

Objectives: The aim of this study was to evaluate the edge strength of different all-ceramic and resin-composite materials used in prosthodontic applications. Methods: 14 disc samples (14 mm x 2.5 mm) were prepared of each of the following materials; BelleGlass (BG) (Kerr, CA, USA), fibre-reinforced BelleGlass/EverStick (BGES) (Kerr, CA, USA /Stick Tech Ltd Oy, Turku, Finland ), Vita Mark II (VM) (VITA Zahnfabrik, Bad Sackingen, Germany) and bilayered IPS e.max Ceram/CAD (IPS) (Ivoclar-Vivadent, Schaan, Liechtenstein). Each group of materials was further subdivided into 7 sub-groups (n=2) corresponding to different edge-distances (0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 mm). Samples were tested using an edge strength measurement device (CK10, N Engineering Systems, Nottingham, UK) with a diamond Vickers indenter and the force (N)-to-fracture was recorded. 5 readings per sample were obtained. One-way ANOVA test was used to detect statistically significant differences among the different materials while regression and correlation analyses were performed to detect correlations between the fracture strength and the distance of loading. Results: The force (N)-to-fracture at a distance of 0.5 mm from the edge was defined as the Edge Strength. The mean force values of edge strength (N) for the different materials were: 103.8 (37.8) for BG, 188.2 (47.8) for BGES, 52.5 (14.6) for VM and 119.2 (28.0) for IPS. These values were significantly different at p<0.05 apart from BG and IPS. Strong correlations between the failure-forces to fracture and edge-distance were found for BG (r²=0.905) and BGES (r2=0.906) while weaker ones were noticed for the other 2 groups (r2= 0.545) for VM and (r2=0.687) for IPS. Conclusions: The addition of fibres enhanced the performance of the resin-composite material. Fracture strength has generally increased within the groups as the distance from the edge increased.