What are the best materials to use for the first arch wire in orthodontic treatment?

Data sources Six electronic databases/registries including Medline, Cochrane Central Register of Controlled Trials (CENTRAL), Cochrane Oral Health's Trials Register, Embase, World Health Organization International Clinical Trials Registry Platform and The US National Institutes of Health Trials Registry (ClinicalTrials.gov) were searched up to October 2017. No restrictions of language or publication date were set.Study selection Only randomised controlled trials (RCTs) assessing the efficiency of initial arch wires to align teeth with fixed orthodontic braces in either or both upper and lower arches.Data extraction and synthesis Two reviewers abstracted data independently. Risk of bias was assessed using the Cochrane Collaboration Risk of Bias tool. Rate of alignment was considered the main outcome. Root resorption and pain level were considered adverse effects. Meta-analysis was performed when possible. Results Twelve RCTs involving 799 participants were included. Three studies were judged at high RoB, six were unclear and three were at low RoB. There was insufficient evidence to determine if there is a difference in the alignment rate between Multistrand stainless steel (MSS) and superelastic nickel-titanium (SNT) arch wires (mean difference (MD) -7.5 mm per month, 95% confidence interval (CI) -26.27 to 11.27; one study), between MSS and thermoplastic NiTi (TNT) arch wires, between conventional Niti (CNT) and TNT arch wires, between CNT and TNT arch wires and between SNT and TNT arch wires. In regards to pain level only two comparisons were assessed (MSS vs. SNT and SNT vs. TNT). The first one did not show meaningful differences while in the second insufficient evidence was identified. Conclusions In general terms there is insufficient evidence that any particular material is clinically superior to any other in regards to alignment rate, pain or root resorption.