Mapping of Nanomechanical Properties of Enamel Surfaces Due to Orthodontic Treatment by AFM Method

Background: Atomic force microscopy imaging was used to study the structural topography of enamel crystals in healthy and affected enamel. The correlation of topographic images with nanomechanical properties allows for the assessment of morphology and properties at the micro- and nano-meter level in three dimensions simultaneously. Methods: A total of 60 premolars were treated like teeth during orthodontic bonding and debonding procedures. Every stage was observed in AFM. Surface roughness, image surface area difference, mean Young’s modulus, and mean adhesion force (the force of attraction between the scanning blade and the surface averaged over the image) were determined for the following areas: the central part of the surface, responsible for load transmission; the top of the surface, subject to the most abrasive wear; the lower part of the surface, responsible for the transport of fluids. Results: The highest roughness occurred on the etched surface—average 63 nm, followed by the intact enamel—8.3 nm, cleaned enamel—7.0 nm, and the resin-coated surface—5.4 nm. Conclusion: Etching increases enamel roughness and reduces hardness. Resin reduces roughness of the etched surface and increases hardness. The intact enamel has the highest hardness. The enamel smoothness is greater after polishing than in the intact enamel.