Scanning electron microscopy evaluation of enamel surfaces using different air-polishing powders in the orthodontic setting: an in vitro study.

Purpose: The aim of this in vitro study was to quantify and compare changes of the enamel surface caused by periodical use of different air-polishing powders during multibracket therapy.

Methods: Bovine high-gloss polished enamel specimens were air-polished using an AIR-FLOW® Master Piezon with maximum powder and water settings. Each specimen was blasted with sodium bicarbonate (AIR-FLOW® Powder Classic, Electro Medical Systems, Munich, Germany) and erythritol (AIR-FLOW® Powder Plus, Electro Medical Systems). Blasting duration was adapted to the powders' cleaning efficacy and corresponded to 25 air-polishing treatments in a patient with braces. A spindle apparatus ensured uniform guidance at a distance of 4 mm and a 90° angle. Qualitative and quantitative assessments were performed with the use of low vacuum scanning electron microscopy. Following external filtering and image processing, arithmetical square height (S_a) and root mean square height (S_q) were determined.

Results: Both prophy powders caused a significant increase in enamel roughness. Surfaces blasted with sodium bicarbonate (S_a = 64.35 ± 36.65 nm; S_q = 80.14 ± 44.80 nm) showed significantly (p < 0.001) higher roughness than samples treated with erythritol (S_a = 24.40 ± 7.42 nm; S_q = 30.86 ± 9.30 nm). The observed defects in enamel structure caused by sodium bicarbonate extended across prism boundaries. Prism structure remained intact after air-polishing with erythritol.

Conclusion: Both applied air-polishing powders led to surface alterations. Despite shorter treatment times, sodium bicarbonate was significantly more abrasive than erythritol. Clinicians must compromise between saving time and abrasively removing healthy enamel.