Surface-engineered and AgNPs-fortified dental archwires: Structural and microbiological assessments

• Fixed orthodontic archwires affect oral hygiene leading to microbial infections. • We enriched hydrothermally etched archwires with silver nanoparticles. • The resultant surfaces possess better antibacterial and antifungal properties. • The cytocompatibility of most of the archwire types was not compromised. Treatment with fixed orthodontic appliances is associated with increased difficulty in maintaining oral hygiene. Orthodontic appliances result in specific changes in the oral environment, including a reduction in pH and an elevation of cariogenic flora levels in saliva and biofilm. This also entails a risk of gingival and cariogenic lesions. This tendency can be favored or hindered by using different materials. Recently, considerable interest has grown considering the usage of ions or nanoparticles to increase the antimicrobial affinity of biomaterials used for orthodontic appliances. Therefore, in this study we explored the possibilities of improving the surface characteristics and biofunctionality of the orthodontic materials used in clinical dental practice. Hereby, seven commonly used commercial archwires , belonging compositionally to four alloys: stainless-steel, β-titanium alloy, nickel-titanium alloy, and titanium-niobium alloy were surface-treated, through hydrothermal etching using an aqueous phosphate solution, before being coated with silver. All samples were analyzed structurally and microbiologically. The structural assessment was performed pre- and post-etching and post-silver deposition using scanning electron microscopy (SEM) and high-resolution and scanning transmission electron microscopy (HRTEM and STEM), all combined with energy dispersive X-ray spectroscopy (EDX). This assessment confirmed the successful etching process and the growth of two types of titanium phosphate phases on most of the titanium-containing alloys. Furthermore, microscopic inspection revealed that the obtained silver coating on all alloys is in the form of silver nanoparticles (AgNPs). Microbiologically, the bacterial and fungal affinity of the blank and treated archwires were assessed, besides their cytotoxicity. Overall, the surface treatment of most of the alloys succeeded in improving their antimicrobial effectiveness, without much compromise to their cytocompatibility for at least half of the treated archwires.