The effect of layer thickness on the porcelain bond strength of laser-sintered metal frameworks.

STATEMENT OF PROBLEM: Laser sintering has become a common manufacturing technique in the fabrication of metal-ceramic restorations. The layer thickness of the sintering process may affect the surface morphology and hence the porcelain bond strength. However, limited information is available on the effect of layer thickness on porcelain bond strength. PURPOSE: The purpose of this in vitro study was to evaluate the porcelain bond strength of direct metal laser-melted (DMLM) cobalt-chromium (Co-Cr) metal frameworks sintered with 25-mum and 50-mum layer thicknesses. MATERIAL AND METHODS: Thirty metal frameworks (n=10) were fabricated by using the lost-wax technique (group C [control]), DMLM with a 25-mum layer thickness (group L25), and DMLM with a 50-mum layer thickness (group L50) according to the International Organization for Standardization (ISO) 9693-1. The surface roughness of 1 metal specimen from each group was analyzed by atomic force microscopy. After porcelain firing, a 3-point bend test was applied to each metal-ceramic specimen as in ISO 9693-1. In addition, 1 metal framework from each group was prepared and examined by scanning electron microscopy to evaluate surface morphology. Data were analyzed statistically by using 1-way analysis of variance and the Tukey honestly significant difference tests (alpha=.05). RESULTS: Group C and group L25 showed significantly higher (P<.001) mean porcelain bond strength values than group L50, and no significant bond strength difference was found between groups C and L25. All groups generally exhibited an adhesive type of failure. CONCLUSIONS: The results indicate that layer thickness may affect the porcelain bond strength of DMLM metal frameworks.