# Effects of Additive Manufacturing Techniques for Cobalt-Chromium Alloys on Opposing Enamel Wear

## TL;DR

This study compares how different manufacturing methods for cobalt-chromium dental alloys affect wear on human enamel.

## Contribution

The study evaluates the enamel wear caused by additive manufacturing versus conventional methods for cobalt-chromium alloys.

## Key findings

- SLM Co-Cr alloys caused similar enamel wear as conventional casting methods.
- Heat treatment improved hardness of SLM alloys without increasing enamel wear.
- Ni-Cr alloys caused less enamel wear compared to Co-Cr alloys regardless of manufacturing method.

## Abstract

This study aimed to examine the wear on opposing enamel caused by additive manufacturing techniques for cobalt-chromium (Co-Cr) alloys. Selective laser melting (SLM) techniques were compared with conventional methods. Cast nickel-chromium (Ni-Cr) alloys were also included for comparison.

Four groups of dental alloys were examined (
n
 = 10/group): as-built SLM Co-Cr (CS), heat-treated SLM Co-Cr (CS-H), cast Co-Cr (CC), and cast Ni-Cr (NC) alloys. Surface roughness and hardness of these alloys were initially assessed. Wear test was conducted against human enamel cusps using a chewing simulator (49-N load, 1.6-Hz frequency). Volumetric and vertical enamel wear were measured at 60,000, 120,000, and 240,000 chewing cycles using an intraoral scanner combined with open-source 3D software.

Enamel wear was analyzed using a generalized estimating equation (α = 0.05).

Alloy hardness varied among the groups. NC exhibited the lowest hardness, followed by CS, CC, and CS-H. Throughout the entire test, no significant differences in enamel wear were observed among CS, CS-H, and CC. However, NC caused lower enamel wear than the other groups, with a more pronounced difference observed after 120,000 chewing cycles.

SLM is a promising alternative for manufacturing Co-Cr alloys used in fixed dental prostheses, as it exhibited comparable enamel wear to conventional casting. Moreover, optimized heat treatment enhanced the hardness of SLM-fabricated alloys without increasing enamel wear. However, it is noteworthy that Co-Cr alloys fabricated by any techniques resulted in higher enamel wear than Ni-Cr alloys.