An in Vitro comparison of the effects of various air polishing powders on enamel and selected esthetic restorative materials

Objective: The purpose of this study was to investigate the effects of each of the commercially available air polishing powders on the surface characterization of human enamel, hybrid composite, and glass ionomer using a highly standardized protocol. The air polishing powders utilized in the study included aluminum trihydroxide, calcium carbonate, calcium sodium phosphosilicate, glycine, and sodium bicarbonate. Methods: The hybrid composite and glass ionomer cement were mixed and photo light-cured for 40 seconds according to manufacturer's directions, and formed in a specially prepared mold that was coated using a Teflon® aerosolized spray. The enamel samples were prepared by removing sections of human enamel from extracted unerupted third molars using a water-cooled, slow-speed diamond rotary saw. The enamel sections were approximately one centimeter in diameter and 3 mm thick. The enamel sections were flattened using a series of silicon carbide grit papers (600, 800, and 1200 grit) mounted on a rotating polishing wheel. A flat polished enamel surface, at least 5 mm in size, was produced and embedded in the hybrid composite material used for testing purposes, resulting in a sample approximately 10 mm in diameter and 2 mm thick. The restorative material samples were wet-polished to produce a uniform smooth surface and to remove the resin-rich surface layer, using the same series of silicon carbide grit papers used on the enamel (600, 800, and 1200 grit). The 1200 grit abrasive paper used is equivalent to a dental polishing disc commonly used to finish dental restorations. All samples were stored in distilled water at 37°C prior to testing. Each of the three types of samples was treated with each air polishing powder for one, two, and five seconds. A test group of five samples each of hybrid composite, glass ionomer cement, and enamel was fabricated for each of the six types of abrasive powder and three-time exposures for the air polishing treatment, resulting in a total of 270 samples. The treatment samples were exposed to the air polishing powders for the three periods of time using a custom mounting jig and shutter device that was fabricated to standardize the air polishing treatments. The air polishing handpiece was placed in a mounting jig that positioned the tip of the handpiece at an 80° angle from the sample surface. The exposure to the air polishing air, water, and polishing powder was regulated by an articulated metal plate positioned between the tip and the test sample. The holder for the test sample kept the sample in a constant circular motion to simulate clinical use of the air polishing handpiece. A custom computer program was developed to activate a stepper motor that rotated the metal plate away from the sample for the controlled exposure times of one, two, and five seconds before the plate moved back to intercept the polishing spray mixture. Results: The effect of the air polishing application on the surfaces of the tooth enamel and restorative materials was evaluated for changes in surface roughness and surface topography. The average surface roughness value was evaluated with a contact profilometer prior to and after the air polishing treatment. Changes in the surface characterization of each sample due to air polishing treatment were recorded using scanning electron microscopy. Epoxy resin replicas of representative test samples were made for evaluating under the scanning electron microscope. Samples were sputter-coated with gold palladium and the scanning electron photomicrographs were taken at a magnification of 25X and at a 45 angle. Based on evaluation with the contact profilometer, there were statistically significant interactions between the type of powder and material, type of power and time, and type of material and time. The SEM photomicrographs were used to evaluate the clinical significance of the effects of the air polishing on each type of material. The SEM photomicrographs provided a visual quantitative analysis of the effects of air polishing powders on the restorative materials and the enamel. Any disruption of the surface characterization was considered to be clinically significant and represented volumetric loss and violation of the integrity of the restorative materials and/or enamel. Conclusions: Based on the results of this study, the air polishing powders that are compatible with use on hybrid composite and glass ionomer cements are EMS glycine and EMS sodium bicarbonate. The air polishing powders that are compatible for use on enamel include EMS glycine, Dentsply sodium bicarbonate, and EMS sodium bicarbonate.