Abstract
Purpose: The aim of the study was to evaluate the effect of simulated porcelain firing cycles and surface finishing on the marginal fit of commercially pure titanium (Cp Ti) copings.
Materials and Methods: A machined stainless steel die system with standard 0.5-m copings was fabricated. Wax patterns were prepared by pouring the molten wax on a two-part stainless steel die. Thirty specimens were cast in Cp Ti. These were divided into three groups with ten specimens in each group. Group 1 was treated with conventional cold working and later oxidized. Group 2 specimens were oxidized initially and then cold worked. Group 3 was heat treated in its original investment and later treated as in group 1. All specimens were later subjected to sequential simulated porcelain firing cycles, that is, oxidation, bonder, opaque, body, and glaze firing. Following the completion of each firing cycle, marginal discrepancy was measured in mu m using a traveling microscope. The obtained data were subjected to one-way analysis of variance (ANOVA) and Student's t-test. The statistical level of significance was set at 1%.
Results: The results showed that the mean and SD values (in mu m) were 55 +/- 2.6, 43 +/- 3.0, and 68 +/- 4.0 after oxidation for groups 1, 2, and 3, respectively. Mean and SD values (in mu m) after glaze firing were 76 +/- 3.9, 64 +/- 4.1, and 89 +/- 4.3 for groups 1, 2, and 3, respectively. The mean marginal opening was largest for group 3 specimens. One-way ANOVA showed the difference within the three groups was highly significant after oxidation (F-value 149.37 at p-value 0.0000) and glaze firing (F-value 82.43 at p-value 0.0000).
Conclusions: (1) The Student's t-test values demonstrated that increased marginal openings of the specimens resulted after the sequential simulated porcelain firing cycles. (2) Marginal discrepancy values improved when the specimens were thermocycled prior to cold working.