Evaluation of the Marginal Adaptation of a Pressable Ceramic System

Objectives: To evaluate the marginal adaptation of a pressable ceramic system to metallic and ceramic frameworks. Methods: A master model (Typodont) was prepared, 30 impressions were taken by an addition-silicon impression material, master dies were poured by type IV dental stone and wax patterns were produced. Two groups of specimens were manufactured; metallic frameworks from a Ni-Cr base alloy veneered with a pressable ceramic (Chemichl, group M), and all-ceramic crowns from the pressable ceramic (group C). The adaptation of each specimen to the abutment was assessed by measuring the marginal gap width at four locations around the margins (mid-buccal/b, -mesial/m, -lingual/l and –distal/d) employing a digital measuring microscope under 32X magnification. The specimens were then subjected to three repeated firings and the adaptation was evaluated again at the same locations. Statistical analysis was performed by three-way ANOVA using substrate type, location and firing treatment as discriminating variables (a=0.05). Results: The results of marginal adaptation were as follows (mean±SD): Group M/ Single Firing: 21±6(b), 19±7(m), 24±11(l) and 18±9(d) microns. Group M/Repeated Firings: 47±14(b), 53±25(m), 53±16(l) and 60±30 (d) microns. Group C/Single Firing: 18±8(b), 17±11(m), 21±10(l) and 24±12(d) microns. Group C/Repeated Firings: 19±7(b), 29±16(m), 27±13(l) and 31±18(d) microns. According to the statistical analysis, significant differences were found between the different levels of materials (p<0.0001) and repeated firings (p<0.0001), whilst no difference was found among locations (p=0.064). Conclusions: According to the results of the present study, the marginal gap width ranged from 17 to 60 microns. The marginal adaptation of the pressable ceramic system tested was independent of the marginal site and the material type used for framework fabrication. Repeated firings increased the marginal gap width in metal-ceramic specimens.