Effect of Internal Design Modification on the Mechanical Properties of Laser Sintered Cobalt-Chromium Multi-Unit Metal-Ceramic Frameworks.

Abstract

The purpose of the study was to assess the effect of internal design modifications on the mechanical properties of multi-unit Cobalt-Chromium (Co-Cr) metal-ceramic frameworks manufactured by direct metal laser sintering. Four-unit fixed partial denture metal-ceramic frameworks were digitally designed on a metal die model using 3D software. A total of 30 specimens were prepared using Co-Cr alloy powder with direct metal laser sintering (n = 10). The control group specimens were solid where the inside of the specimens was completely full. For the test groups, the internal design of the framework was modified. Leaving the outer shell thickness of the framework at 0.5 mm, two different internal designs with hollow geometries were created (1.5 mm and 2 mm inner bar distances) and a cross section area of the connector was calculated. The weights of the specimens were measured and subjected to a 3-point-bending test at 1 mm/min crosshead speed. Data were statistically analyzed using One-way ANOVA followed by Tukey (α = 0.05). There was a statistically significant difference among the groups in terms of weight of the specimens (p ≤ 0.05). However, no significant difference was observed among groups in term of both flexural strength and flexural modulus (p ≤ 0.05). Within the limitations of the study, it was concluded that changing the internal design of the metal frameworks decreases the weight of the framework, but does not affect the flexural strength and flexural modulus. Therefore, clinical applications of internally modified frameworks seem promising for metal-ceramic restorations.