Initial Strength of CAD CAM Veneered All-ceramic Posterior Restorations

Objectives: Lava™ DVS (3M ESPE) is the first commercially available CAD CAM veneering for zirconia restorations. The aim was to evaluate the initial strength of Lava™ DVS posterior crowns, compared to conventionally manufactured all-ceramic crowns.

Methods: Five different all-ceramic restorations were tested: an anatomical designed Lava™ zirconia coping veneered with Lava™ DVS (DVS), an anatomical designed Lava™ coping veneered with IPS e.max® ZirPress (Ivoclar) (ZP-A), a non anatomical designed Lava™ coping (uniform thickness of 0.5mm) veneered with IPS e.max® ZirPress (ZP-NA) and a monolithic IPS e.max® CAD (Ivoclar) crown (CA-1.2). All these crowns were designed with a minimum occlusion thickness of 1.2mm and an identical outer shape. IPS e.max® CAD crowns were also fabricated with a minimum occlusion thickness of 1.5mm to maintain the manufacturer instructions (CA-1.5). For each group 10 samples were fabricated according the manufacturers instructions. All crowns were cemented with Ketac™ Cem (3M ESPE) and loaded in a universal testing machine (Instron 5566) with a 10mm steel ball with a traverse speed of 0.5mm/min. The measurements were stopped if a decrease of force or a cracking noise occurred. The maximum fracture force was measured.

Results: Statistical analysis was performed using analysis of variance (ANOVA) and Fisher's least significant difference (LSD) test at a significance level of 5%. DVS (F = 3715 ± 623N) shows a high initial fracture force. There is no statistical difference between DVS and ZP-A: (F = 3368 ± 676N). To all other groups DVS shows a statistical higher fracture force (ZP-NA: F = 2808 ± 690N; CA-1.2: F = 1373 ± 250N and CA-1.5: F = 3147 ± 364N).

Conclusion: The results show that Lava™ DVS is expected to have a better mechanical performance compared to non anatomical designed zirconia restorations or lower strength framework crowns with the same crown thickness.