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.