Influence of porcelain firing on changes in the marginal fit of metal-ceramic fixed partial dental prostheses fabricated with laser sintering: An in vivo study.

BACKGROUND: Marginal fit is the most important criterion in the evaluation of the clinical acceptability of fixed restorations. Due to cement solubility and plaque retention, marginal gaps are potentially harmful to both the teeth and the periodontal tissues. OBJECTIVES: The aim of the study was to investigate the accuracy of the fit of dental metal-ceramic bridges manufactured with the use of direct metal laser sintering (DMLS), and to explore the effects of porcelain firing on the marginal, axial and occlusal fit of metal-ceramic frameworks. MATERIAL AND METHODS: The study involved 10 patients with 3-unit metal-ceramic restorations produced using the DMLS technique. Using the silicone replica technique, we examined the marginal, axial and occlusal fit of the dental bridges before and after ceramic firing. The Shapiro-Wilks normality test and Student's paired t‑test were implemented to analyze the mean differences in the marginal, axial and occlusal fit of the restorations before and after ceramic firing. A 95% confidence interval (CI) and discrepancy values at the level of 1% and 0.1% (p > 0.05) were applied. RESULTS: All the mean values of the measurements of marginal (156.08 mum), axial (95.75 mum) and occlusal (252.83 mum) gaps were lower before ceramic veneering than after ceramic veneering, when the mean value for the marginal gap was 178.17 mum, for the axial gap - 106.75 mum and for the occlusal gap - 266.00 mum. CONCLUSIONS: Porcelain firing caused no statistically significant differences in the discrepancy values of marginal, axial and occlusal fit. For clinical application, further improvement of the DMLS system is highly recommended. Marginal gaps in DLSM bridges significantly exceed the permissible inaccuracy values of 100-120 mum for prosthetic restorations.