Discussion
This in-vitro micro-computed tomography study was designed to assess the effect of an air-polishing device using three different powders on the enamel and root surface at two different power settings. Defect depth, defect volume, demineralization depth, and TMD were also evaluated. To our knowledge, this is the first study in the literature that has assessed demineralization depth and TMD change after air polishing and evaluate the effect of erythritol air polishing on the root surface.
The first hypothesis for defect depth was supported by results on the enamel surface at two different power settings. It was found that all powders caused defects on the enamel surface at both power settings. There was a statistically significant difference between the mean defect depths of the three powders. The sodium bicarbonate group had significantly the greatest mean defect depth.
The abrasive property of the powder is determined by particle diameter, shape, and hardness. Particle shape and hardness are the main factors affecting the abrasive property. Data on particle sizes are contradictory. Some studies reported that abrasive powders with small particle sizes cause more abrasion, as well as studies showing the opposite. According to the results of the present study, the fact that sodium bicarbonate powder had the highest mean defect depth can be explained by having a greater Mohs hadness value and particle size than erythritol and glycine powders. It was thought that the difference between the mean defect depths is less because the Mohs hardness values of the erythritol and glycine powders are the same and their particle sizes are close to each other.
Some of the studies reported that sodium bicarbonate air polishing causes abrasion and roughness on the enamel surface, while others reported that it does not cause changes on the intact enamel surface and is safe and efficient to remove stains. In the present study, in line with other previous studies, it has been also shown that sodium bicarbonate-based powder cause defects on the enamel surface. Barnes et al. reported that sodium bicarbonate and glycine-based abrasive powders showed statistically significant abrasive properties on the enamel surface, however, no difference between their abrasive properties was seen. In the present study, it was observed that the defect depth and defect volume caused by sodium bicarbonate powder on the enamel surface were significantly higher than the defect depth and defect volume created by glycine powder. The sodium bicarbonate powder used in the study by Barnes et al. has the same particle size as the powder used in our study, however, the particle size of the glycine-based powder is larger than the glycine powder used in our study. Barnes et al. evaluated the roughness caused by polishing with profilometry. Our study evaluated defect depth, defect volume, and demineralization depth using a micro-CT device. The different materials and methods of the studies may have caused differences between the results.
Camboni and Donnet evaluated the effect of erythritol air polishing on the enamel surface by SEM and reported that erythritol air polishing did not create a microscopically visible defect on the enamel surface. Considering the results of our study, erythritol-based abrasive powder causes defects and demineralization on the enamel surface. Camboni and Donnet made an application with a water setting of 11 LED and a power setting of 6 LED for 10 seconds. In our study, the applications were made for 5 seconds with a power setting of 9 and 17 LED and a water setting of 6 LED. As the air pressure increases, the efficacy of the instrument increases. The higher power settings in our study may have caused defects on the enamel surface.
The results regarding the mean defect depth and defect volume on the cementum surface did not support our first hypothesis. The findings in the present study showed that sodium bicarbonate air polishing caused the highest mean defect depth on cementum as caused by enamel at both power settings. At the maximum power setting, no significant differences were found between the mean defect depth of erythritol and glycine groups on the cementum. At both power settings, no significant differences were detected between the mean defect volume on cementum surfaces in the erythritol and glycine groups and the glycine and sodium bicarbonate groups. The erythritol group had significantly less mean defect volume than the sodium bicarbonate group.
Although many studies in the literature evaluating the effect of sodium bicarbonate and glycine air polishing on the root surface there are no studies evaluate the changes caused by erythritol air polishing on the root surface. Studies have reported that sodium bicarbonate air polishing causes severe defects and is not safe to use on the root surface. Some studies reported that glycine powder shows less abrasive properties on the root surface compared to sodium bicarbonate, while other studies reported that there is no statistically significant difference between the mean defect depths and defect volumes of glycine powder and sodium bicarbonate. It is thought that there may be differences in the particle size and shape of the powders used in the studies, the manufacturers of the powders and devices, the application time, angle, application method, and the analysis method of the post-instrumentation defect may be revealed differences between the studies.
The first hypothesis could not be confirmed. At both power settings, no significant differences were observed between the mean demineralization depth on enamel surfaces in between the powders. At a medium power setting, no significant differences were seen between the mean demineralization depth on cementum surfaces in between the powders. At the maximum power setting, the mean demineralization depth on the cementum surface in the sodium bicarbonate group was greater than the other two groups. The similarity of demineralization depth averages can be explained by the close pH values to each other. pH values of sodium bicarbonate, glycine, and erythritol-based powders are 8.1, 6, and 7, respectively. The second hypothesis could not be confirmed too. There were statistically significant differences between the mean TMD values before and after the application in all groups. After the application, the average TMD was found to be lower. Berkstein et al. reported that the meantime to remove the stain by the air-polishing device was 3.23 seconds per root surface. Petersilka et al. assumed that the time required to clean the surface is 2.5 seconds since the device is in a stationary position in vitro study. They reported that a time of 20 seconds would represent approximately the time spent on root surface instrumentation within 2 years. In our study, a total of 10 seconds was air polishing to the enamel and cementum surface. This represents the time spent during 1-year supportive periodontal treatment, and 4 times in a year. During the time required for one-year supportive treatment, all powders caused a reduction in tooth mineral density.
The third hypothesis was confirmed. Power setting has been shown to high impact on substance removal. An increase in power setting will cause an increase in instrument efficacy. The results of our study also support this information. At the maximum power settings, defect depth, defect volume, and demineralization depth were found significantly higher than at medium power settings in all groups.
The higher the hardness of the surface to be instrumented, the smaller the amount of substance removed from the surface. Enamel is the hardest tissue in the body of a vertebrate. Enamel has a Mohs hardness value of 5, while cementum has a Mohs hardness value of 2.5 - 3. The results of our study are also parallel to those reported results. All powders showed more abrasive properties on exposed cementum surfaces, especially at the maximum power setting.
One of the strengths of the present in vitro study is, the tooth surfaces were evaluated with a micro-CT device and the measurements were made by superimposing 3-D images before and after the examination. The biggest advantage of micro-CT examinations on the tooth surface is that high-resolution images can be obtained directly by scanning the tooth surface without requiring any surface preparation or invasive processing before imaging.
Atkinson et al. reported that due to the tendency of the exposed root surface to be hypermineralized, the amount of tissue removed by air polishing may be less than the root surface that was not exposed to the oral cavity. The differences in the cementum structure, which is not exposed to the oral environment, and which has become exposed because of periodontal pathologies, suggest that the effects of applications with air-polishing systems may also differ. For this reason, in our study, we attempted to imitate the clinical situation by air polishing the root surface exposed to the oral cavity.
It is recommended to move the handpiece during clinical use of air-polishing systems. In in vitro studies, it is difficult to imitate clinical practice by moving the handpiece and standardizing this mobility. Although the application angle and distance in our study were determined by the manufacturer’s recommendations, the handpiece and the sample were fixed to ensure standardization and comparison. This may have prevented the results of our study from fully demonstrating clinical effects and this may assume as one of the limitations.