Evaluation of the Flexural Strength of Metal Frameworks Fabricated by Sintering-Based Computer-Aided Manufacturing Methods

Abstract

Statement of problem. Sintering-based computer-aided metal manufacturing strategies have been proposed as an alternative to hard metal milling. While these fabrication methods have been evaluated in terms of marginal and internal discrepancies and bond strength to porcelain, limited information on metal frameworks is available regarding their flexural yield strength. Purpose. The purpose of this in vitro study was to evaluate the flexural yield strength of 3-unit cobalt-chromium (Co-Cr) metal frameworks fabricated by hard metal milling (HMM), presintered soft metal milling (PSMM), and direct metal laser melting (DMLM) with 25-mu m and 50-mu m layer thicknesses. Material and methods. Three-unit master metal die models were prepared. A total of 40 metal frameworks (n=10) were fabricated by using HMM (group HM), PSMM (group PSM), and DMLM with 25-mu m (group LM25) and 50-mu m layer thicknesses (group LM50). Metal frameworks were cemented to the master die and then subjected to a 3-point bend test. The flexural yield force was used to calculate the flexural yield strength. The data were statistically analyzed (alpha=.05). One metal framework from each group was evaluated with scanning electron microscopy for microstructural analysis. Results. The group LM50 exhibited the lowest significant (P<.001) flexural yield strength values. The group HM exhibited higher flexural yield strength values than the other groups. No significant difference was found between the groups LM25 and PSM (P=.954) or between the groups PSM and HM (P=.111). Conclusions. The fabrication method significantly affected the flexural yield strength of metal frameworks. Metal frameworks fabricated by DMLM with a 50-mu m layer thickness exhibited considerably lower flexural yield strength values.