Abstract
Purpose – The purpose of this research paper is to compare corrosion data obtained from additive-manufactured heat-treated (HRx) and non-heat-treated (NHRx) cobalt-chromium (Co–Cr) alloys. Heat treatments are indicated as necessary in complex intra-oral framework production by additive manufacturing to remove accumulated thermal stresses. However, heat treatments have been linked to corrosion in cast dental alloys. Currently, there are few publications on this subject for laser-sintered dental alloys required for academic review. Design/methodology/approach – Five rectangular specimens (n = 5), each with a total surface area of 10.27 cm2, were fabricated for the two groups. Specimens were immersed in an artificial saliva solution suspended by a nylon thread for 42 days at 37°C. Readings for Co, Cr and molybdenum ions released into the solution were obtained using an atomic absorption spectrometer at 1-, 4-, 7-, 14-, 21-, 28-, 35- and 42-day intervals at a detection limit of one part per million. Test methods are in accordance with ISO 10271. Findings – Results showed a higher ion release in the HRx sample, statistically significant at 99 per cent confidence level (p < 0.01). A two-way ANOVA test conducted showed that there was a main effect of day and a main effect of finish, and there was also a significant interaction between these factors. Originality/value – The study concludes that, although ion release in both samples was within the safe level recommended by ISO for the three major alloying elements, heat treatment, indeed, contributed extensively to the reduced corrosion resistance in the laser-sintered Co–Cr alloy. Further biocompatibility tests are recommended.
Highlights
The construction of cobalt-chromium (Co-Cr) denture frameworks to carry artificial teeth in the mouth has for many years been restricted to the ‘lost wax’ process where molten alloys are caused to flow into heated hollow moulds formed by burnt-out wax patterns
There was a higher ion release (16.47 μg/L) in HRx sample compared to the small amount of 0.63μg/L released in NHRx sample after 42 days
A study by Alifui-Segbaya et al (2013) on the same HRx Co-Cr alloy used in this study showed a significantly larger corrosion resistance in polished and electrobrightened samples
Summary
The construction of cobalt-chromium (Co-Cr) denture frameworks to carry artificial teeth in the mouth has for many years been restricted to the ‘lost wax’ process where molten alloys are caused to flow into heated hollow moulds formed by burnt-out wax patterns. With the extensive advancement of computer aided technologies in dentistry, there is significant scope to replace the traditional casting technique with layer manufacturing techniques such as Additive Manufacturing (AM) in complex intra-oral framework production (Williams et al, 2006; Gao et al, 2009). Metal AM technology is a digitally driven process that uses either electron beams or laser beams to fuse metallic powders, in a layer-by-layer fashion into three dimensional (3D) objects. The laser manufacturing system have been routinely used to process many different alloys (Collins, 2012) including Co-Cr-Mo for denture frameworks. The few publications on the clinical performance of AM Co-Cr alloys claim they have the potential to further exhibit good corrosion resistance, biocompatibility and sustainable mechanical properties (Vandenbroucke and Kruth, 2007; Jevremović et al, 2011; Alifui-Segbaya et al, 2013)
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