Effect of cement spacer on fit accuracy and fracture strength of 3-unit and 4-unit zirconia frameworks.

Background: Cement spacer is essential for compensating deformation of zirconia restoration after sintering shrinkage, allowing proper seating and better fracture resistance of the restoration. Studies assessing the effect of cement spacer on fit accuracy and fracture strength of zirconia frameworks are missing in the literature. Therefore, the aim of this study was to evaluate the effect of different cement spacer settings on fit accuracy and fracture strength of 3-unit and 4-unit zirconia frameworks.

Methods: Sixty standardized stainless-steel master dies were manufactured with 2 prepared abutments for fabricating 3-unit and 4-unit zirconia frameworks. The frameworks were assigned into 6 groups (n = 10) according to cement spacer setting (30 μm, 50 μm, and 80 μm) as follows: 3-unit frameworks; 3u-30, 3u-50, 3u-80, and 4-unit frameworks; 4u-30, 4u-50, and 4u-80. The frameworks were assessed for fit accuracy with the replica method. The specimens were cemented to their corresponding dies, and the fracture strength was measured in a universal testing machine. The Weibull parameters were calculated for the study groups and fractured specimens were inspected for failure mode. Two-Way ANOVA followed by Tukey test for pairwise comparison between study groups (α = 0.05).

Results: The cement spacer had a significant effect on both fit accuracy and fracture strength for 3-unit and 4-unit frameworks. The 50 μm spacer had significantly better fit accuracy followed by 80 μm, and 30 μm spacers. Both 50 μm and 80 μm spacers had similar fracture strength, and both had significantly better strength than 30 μm spacer.

Conclusions: For both 3-unit and 4-unit zirconia frameworks, 50 μm cement spacer can be recommended over 30 μm and 80 μm spacers for significantly better fit accuracy and adequate fracture strength.