Influence of Veneer Thickness, Coping Thickness and Veneer-Coping Ratio on the Fracture Toughness of Ceramic Layered Metal and Zirconium Crowns

摘要

The aim was to investigate the influence of veneer thickness, coping thickness and veneer coping ratio (V/C ratio) on the fracture toughness (K-IC) of implant retained metal ceramic crowns (MCC) and zirconia ceramic crowns (ZCC). Seventy copings each of metal and zirconia were fabricated using the CAD-CAM technique. Veneering ceramic was applied using hot-pressing technique for both MCC and ZCC specimens. The groups within each material (ZCC and MCC) were based on different coping thickness (0.5, 0.7 and 1.0 mm) and overall sample (2.0, 2.3 and 2.5 mm) thickness. Specimens in each group were assessed for fracture toughness using micro-indenter. Crack lengths for specimens were evaluated to calculate K-IC (fracture toughness). Results were analyzed using ANOVA. Among MCC specimens, increasing V/C ratio showed higher K-IC (p = 0.019). Increasing veneer thickness from 1.3 mm to 1.8 mm improved (p 0.006) K-IC, however K-IC values were comparable (p = 0.086) with different coping thickness for MCC specimens. For ZCC specimens, V/C ratio (p = 0.0444), veneer thickness (p = 0.035) and coping thickness (p = 0.032), all showed significant influence on K-IC. Overall MCC showed higher K-IC compared to ZCC specimens. Coping thickness, veneer thickness and V/C ratio showed significant influence on fracture toughness of bilayered ZCC and MCC specimens.