Finishing protocols of orthodontic attachments determine surface roughness and susceptibility to microbial colonization in vitro

Abstract

To evaluate, in vitro, the microbiological contamination and surface roughness of orthodontic attachments finished using different excess-removal procedures. Thirty composite resin attachments were fabricated and allocated into three groups (n = 10/group): G1- no removal of excess resin; G2— excess removed using a No. 15 scalpel blade; and G3—excess removed using a 24-blade low-speed bur (Orthometric). All specimens underwent non-contact 3D profilometry to determine baseline surface roughness (Sa). Samples were then exposed for 24 h at 37 °C under microaerophilic conditions to a mixed inoculum (5 × 105 CFU/mL) consisting of Streptococcus mutans ATCC 25175, Lactobacillus casei ATCC 393 and Candida albicans ATCC 90028. Post-exposure assessments included biofilm acidogenicity, CFU quantification, and repeat 3D profilometry. There were no significant differences in pH values among G1, G2, and G3. CFU counts differed significantly among groups, with the highest microbial load in G1 (709.70 ± 221.8), followed by G2 (342.65 ± 84.8) and G3 (78.3 ± 38.7) (p < 0.05). Initial surface roughness showed similarity between G2 and G3, both significantly smoother than G1 (p < 0.05). After biofilm formation, G3 exhibited the lowest Sa values, G2 showed intermediate values, and G1 remained the roughest; all groups differed significantly (p < 0.05). Orthodontic attachment finishing protocols significantly affects surface roughness and subsequent microbial accumulation. Leaving excess resin increases roughness and biofilm formation, whereas finishing with a 24-blade low speed bur produces smoother surfaces and minimizes microbial contamination.