In-vitro comparative study to evaluate bond strength of porcelain on metal sub-structure fabricated by selective laser melting (SLM) technique after application of different surface treatments

Introduction
Metal-ceramic bond strength is one of the essentials that must be studied due to recent develop­ments in dentistry.

Objectives
This study aimed to evaluate the ceramic bond strength with metallic sub-structure made of chromium-cobalt alloy and fabricated by selective laser melting (SLM) technique after applying different surface treatments.

Material and methods
40 metallic strips of Co-Cr alloy manufactured by SLM technique were divided into two main groups, A and B, which were again divided into 4 sub-groups as follows: A1 – natural surface roughness maintained (n = 10); A2 – natural roughness with a bonding agent application (n = 10); B1 – sandblasted surface (n = 10); B2 – sandblasted surface with a bonding agent application (n = 10). A surface roughness measuring test was carried out to obtain Ra-Rz values. Three-point bending test according to ISO 9693 standards was performed to determine the metal-ceramic bond strength in MPa. Fracture failure mode was determined by using an optical microscope.

Results
Student’s t-test was used to compare among the mean bond strengths of sub-groups, with a significant difference observed only between A1 and A2 and between A2 and B2 sub-groups. Mann-Whitney test was applied to compare among the mean ranks of the failure modes, with a significant difference noticed only between A1 and A2 sub-groups.

Conclusions
The bond strength in all the studied sub-groups exceeded the required minimum 25 MPa, according to ISO 9693 standards. The bonding agent had a minor effect when applied on sandblasted surfaces, while it had an important effect when applied on a natural surface roughness.