Edge strength of indirect restorative materials

Objectives

To evaluate the edge strength and fracture patterns of different all-ceramic and indirect composite materials used in prosthodontic applications.

Methods

Fourteen rectangular-shaped samples (2–2.5 mm thick) were prepared of each of the following materials: BelleGlass NG (Kerr) (BG), fibre-reinforced BelleGlass/EverStick (Kerr/Stick Tech Ltd.) (BGES), Vita Mark II (Vita Zahnfabrik) (VMII), bilayered IPS e.max Ceram/CAD (Ivoclar-Vivadent) (Ceram/CAD), bilayered IPS e.max Ceram/ZirCAD (Ivoclar-Vivadent) (Ceram/ZirCAD) and unilayered IPS e.max CADLT (Ivoclar-Vivadent) (CADLT). Each group was further subdivided into seven subgroups (n = 2) corresponding to different edge distances at which samples were loaded. Samples were tested with an edge strength machine (CK10, Engineering Systems, Nottingham, UK) using a diamond Vickers indenter. The force-to-failure (N) was recorded and four readings were obtained per sample. The mode of failure was analysed microscopically. One-way ANOVA was used to detect differences in edge strength among the groups and correlation and regression analyses were used to detect the correlation between distance of loading and failure force.

Results

The mean values of edge strength (N) were 94.1 (11.2) for BG, 134.4 (10.9) for BGES, 50.5 (8.9) for VMII, 54.4 (7.5) for Ceram/CAD, 53.2 (8.4) for Ceram/ZirCAD and 69.1 (9.1) for CADLT. Significant (p < 0.05) strong positive linear correlations were found between the force-to-failure and edge distance among all groups. Three patterns of failure were identified: surface indentation without visible cracking, surface indentation with visible cracking and chipping.

Conclusions

Indirect composite materials had better edge fracture behaviour than all-ceramic materials. The addition of fibres enhanced the performance of the resin-composite material. Fracture strength increased as the distance from the edge increased. Edge fracture was restricted to the veneer material in bilayared systems and therefore a stronger veneer material is recommended.