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 (R) Master Piezon with maximum powder and water settings. Each specimen was blasted with sodium bicarbonate (AIR-FLOW (R) Powder Classic, Electro Medical Systems, Munich, Germany) and erythritol (AIR-FLOW (R) 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 4mm and a 90 degrees 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 +/- 36.65nm; S-q=80.14 +/- 44.80nm) showed significantly (p<0.001) higher roughness than samples treated with erythritol (S-a=24.40 +/- 7.42nm; S-q=30.86 +/- 9.30nm). 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.