Effect of Rhodium Coating on Surface and Mechanical Properties of NiTi Archwires: A Systematic Review and Meta-Analysis of In Vitro Studies

Abstract

Introduction: Orthodontic therapy, is effective when biomechanics and predictable treatment outcomes cause least discomfort for patients, for this selection of archwires is crucial. This study aimed to analyze the available literature on a comparative evaluation of surface roughness (SR), nanohardness (NH), load deflection property (LDP), and friction between rhodium-coated (RC), non-coated (NC), and other coated NiTi archwires. Materials and methods: An electronic search was conducted in PubMed, Scopus, Lilacs, and Web of Science for in vitro studies published in English from January 2000 to February 2024. The risk of Bias (RoB) was analyzed with the RoBDEMAT tool. Qualitative synthesis and meta-analysis of the included studies were performed only for the evaluation of SR among RC, NC, and other coated wires. Meta Analysis using the Random effects model (DerSimonian-Laird random effects pooling method) was carried out using RevMan Web for quantitative assessment of the included studies to assess surface roughness values among RC wires, non-coated, and other esthetic-coated wires. Results: A total of 12 studies were included, wherein RC, NC, and/or other coated wire archwires (EC, PC, FC, and OC) but from different brands were tested. The parameters in the included studies were assessed using a different experimental equipment. The RoB analysis revealed sufficient reporting in only one domain and inconsistent reporting in other domains for the included studies. Out of the nine studies reporting on SR, six studies reported a higher SR for RC than NC archwires and no significant difference in SR between RC and other coated archwires. In the eight studies included in the meta-analysis, a statistically significant pooled standard mean for the difference between RC and NC wires for SR was obtained (SMD = 1.30; P = 0.05; 95% CI = 0.00 to 2.59). Conclusion: The studies included in the systematic review showed varied methodological inconsistencies, and lacked protocols for sample size calculation. The available data are insufficient to report the effect of rhodium coating on properties such as load deflection rate, friction, and even flexural strength. However, the rhodium-coated wires had increased surface roughness and reduced nanohardness compared to non-coated wires.