Effect of Porcelain Firing on Marginal Adaptation of Three-Unit All-Ceramic Implant-Supported Restorations With Different Thicknesses of Zirconia Cores

Abstract

Introduction : In the last 20 years, growing patients demand for highly esthetic and natural appearing restorations has led to the development of new all ceramic materials. FPDs with zirconia ceramic frameworks are widely used for implant-supported FPDs, because of patient esthetic requirements. The marginal accuracy of a restoration is important for its longevity. Lack of adequate fit can damage tooth tissues and periodontal tissues around the tooth or implant. Factors influencing the marginal fit include finish line configuration, cement space, taper of preparation, manufacturing technique, cementation, porcelain veneering and firing cycles.

Materials and methods : In this study, two parallel fixture analogs and two straight implant abutments were used to make three-unit restorations in order to eliminate preparation errors and equalize the sample margins. The cast which the abutments were mounted on, was scanned with a scanner (3shape, E3, 1060 Copenhagen, Denmark / manufactured in Poland) and 20 three-unit zirconia cores in thicknesses of 0.6 mm and 0.8 mm were made by Milling machine (Imes-Icore, 350i, Germany) . The dimensions of the connector were considered 3 × 3 mm. The cores were divided into two groups; 0.6mm for group A and 0.8mm for group B, ten for each group. marginal adaptation (vertical) in each group was measured separately in 8 points (mid-mesial - mesio-buccal - mid-buccal - disto-buccal - mid-distal - disto-lingual - mid-lingual - mesio-lingual) around each abutment, under a stereo microscope (Nikon CDS, Tokyo, Japan) with a magnification of ×65 and a digital sight camera (Nikon, Tokyo, Japan), before porcelain firing and after porcelain firing. Due to the inconsiderable difference in firing temperature (about 10-15 ° C) in enamel porcelain powder and dentin porcelain powder, only one layer of dentin porcelain was used on zirconia cores, in order to reduce the error in matching the samples. The results were reported as descriptive statistic indicators. To compare the degree of marginal adaptation before and after porcelain firing, independent samples t-test was used. also two-way ANOVA was used to investigate the effect of core thickness on marginal adaptation. A probability of less than 5% was considered as a significant level. The analysis of the data was performed using SPSS version 17.

Results : Based on the results of our study, the marginal gap for group A was 22.03 ± 6.82 μm before porcelain firing and 71.48 ± 21.98 μm after porcelain firing , and for group B these figures were 16.17 ± 6.12 μm and 68.34 ± 14.59 μm .

Conclusion : It may be concluded that the porcelain firing cycle increases marginal gap in three-unit all-Ceramic implant-supported restorations. By increasing the zirconia core thickness, before porcelain firing, the marginal gap decreases; But there is no difference at the marginal adaptation between two groups, after porcelain firing. Thus, it is recommended to use minimum thickness in order to be conservative and obtain improved esthetics. The results showed that the marginal gap was clinically acceptable in the two groups.