Surface modification of orthodontic elastomers to overcome biofilm formation

Introduction: One of the major problems for patients undergoing treatment with fixed orthodontic appliances is the development of oral biofilm-related disease. One way to potentially reduce biofilm formation is to modify the appliance surface characteristics to make it less adherent to bacteria. The aim of this study was to create a superhydrophobic surface on orthodontic elastomeric chain material to reduce bacterial adhesion. Materials and Methods: Orthodontic elastomeric material was modified with sandpaper of various grit sizes. Custom made jigs were used to stretch the elastomers to 150% and 200% of initial length. Surface characteristics were assessed quantitatively with confocal microscopy and qualitatively with scanning electron microscopy. Contact angles were measured using a goniometer. Bacterial adhesion was measured after incubating saliva coated elastomers with Streptococcus gordonii ATCC10558 for 30 minutes, by counting colony forming units on Columbia sheep blood agar plates. Results: Abrasion with sandpaper of grit size 80-600 produced elastomers with surface roughness (Ra) of 2-12 µm. The effect of extending these elastomers on roughness was variable. Contact angles were found to follow a quadratic trend with a maximum contact angle of 104°at an Ra of 7-9 µm. Maximum contact angles, when viewed perpendicular to stretch, were found to decrease from 104° to 95° when the extension was increased from 100 to 200% and increased from 102° to 105° when viewed parallel to the stretch. Bacterial adhesion increased exponentially as roughness increased and this effect was more pronounced with elastomer extension. Conclusions: It was not possible to obtain a superhydrophobic surface, with an advancing contact angle >150° and contact angle hysteresis ≤ 4, using sandpaper abrasion. All surface modifications increased bacterial adhesion to the elastomer