Effects of tooth whitening and orange juice on surface properties of dental enamel
By: Yan-Fang Ren,
Azadeh Amin, Hans Malmstrom
Introduction:
In this study they wanted to determine how 6% hydrogen peroxide (tooth whitening product) effected
the surface of enamel in comparison to orange juice. Whitening products contain
an oxidizing agents such as hydrogen peroxide which is thought to diffuse into
the enamel and dentin, oxidizing organic and inorganic colored compounds resulting
in change in tooth color (Ren et al., 2009).
The concern though is that it might causes chemical, structural and
mechanical changes in the enamel surface. Orange juice is a highly acidic drink
(pH less than 5.5) that initiates enamel demineralization. Microhardness
testing and surface 3D topography evaluations are used to determine and compare
the effects on the enamel.
Experimental procedure:
Enamel discs were
prepared using a slow speed diamond saw from freshly extracted human third
molars, which had been sterilized. Enamel surfaces were ground and polished to
obtain a smooth flat surface. A total of 40 enamel discs were used (15 for
whitening treatment, 15 for organic juice treatment and 10 for normal saline
controls) and they were stored in clarified human whole saliva at room
temperature until use. Prior to the experimental treatment of enamel discs
surface microhardness testing (Knoop indenter) and surface 3D topography
evaluations (3D focus variation scanning microscopy) were completed to obtain a
baseline.
The eBright Tooth Whitening Accelerator Home Edition LED
activated tooth whitening product was used which contained 6% hydrogen peroxide
at a pH of 5.5. In well culture plates enamel discs were treated with whitening
gel and submitted to LED light irradiation for 20minutes followed by washing
with distilled water for 30 seconds. This was repeated 4 more times to
stimulate 5 days of treatment. Between treatment cycles enamel discs were store
in fresh human whole saliva. For the orange juice challenge the enamel discs
were placed in the well culture plates containing 1.0 ml of orange juice at pH
of 3.8 (Minute Maid). Samples were placed in a rocking incubator for 20 minutes
to simulate sipping a drink followed by rinsing with distilled water for 30
seconds. Like the whitening products this was repeated 4 more times and stored
in saliva between treatments. The control enamel discs underwent the same
treatment as the orange juice except normal saline was used.
Microhardness and surface topography of the enamel discs
were evaluated again like before (baseline evaluation). Changes in surface
microhardness and surface topography were compared before and after treatment
using statistical analyses (StatView 5.0.1).
Results:
Comparing the surface microhardness results only the
treatment was orange juice showed a significant difference (p<0.0001) in
microhardness following treatment. The hardness for enamel discs treated with
orange juice decreased 84% from 287.3 to 45.3. For enamel discs treated with
the whitening product hardness decreased 5.6% from 279.4 to 260.7 and the
saline controls decreased 3.1% from 275.3 to 266.8. (Table 1). Although there was no significant
change in the hardness of the enamel for the whitening products and control
groups they noted that there was a significant variation in the change in
hardness for the individual specimens. 4
of the 15 whitening treatment and 2 of the 10 control group had a change in
microhardness greater than 10%.
For the 3D topography evaluations they looked at surface area roughness (Sa), surface maximum peak to valley distance (Sz)
and developed surface area ratio (Sdr). They found that the enamel surfaces after
the orange juice treatment were visibly rougher than those of the whitening gel
and normal saline and had more well developed peaks and valleys on surface (Ren
et al., 2009). Changes in the three
surface roughness and topographical measures
(Sa, Sz, and Sdr) were only significant for the treatment with orange
juice. An interesting note is the Sz and Sdr measures slightly decreased for
the whitening and control group in comparison with the orange juice, which
increased (Table 3 and 4).
The results show that the effects of the 6% hydrogen
peroxide whitening product on the enamel surfaces were not significant in
comparison to orange juice. The softer and rougher enamel makes teeth more
susceptible to the development of dental caries and non-carious lesions such as
abrasion (mechanical forces from daily activities such as toothbrushing) and
attrition (tooth grinding) (Ren et al., 2009).
Critique:
I thought this was an interesting paper that was easy to
follow and understand. I knew that acidic drinks such as orange juice were hard
on the enamel of teeth but I had no idea that it could cause that much of a harmful
effect. There have been many other papers published that look at the effect of
tooth whitening products on the enamel surface, but without having something to
compare your results to it is hard to get a clear picture on how harmful it
really is. I thought it was a great idea to compare it to the effects to that
of orange juice to give us a better perspective on the relative impact. The
methods section was concise but also detailed enough that if I wanted to repeat
their experiment I could. The figures in the results were easy to understand and clearly showed the different effects these products had on the enamel.
The discussion was informative but they didn’t directly suggest explanations for the findings. They referenced many papers to help explain the results but they never clearly stated why the orange juice was more harmful than the whitening product. I just had to assume it was due to differences in pH. They also didn't mention any ideas on why the mean maximum peak to valley distance (Sz) and developed surface area ratio (Sdr) decreased for the whitening and control groups but increased for the orange juice group. Since the microhardness decreased for all three I would figure both of those measures should have increased for all of the groups as well. The section on the effect of fluoride treatment was interesting but I thought it was out of place as they did not use any fluoride treatment within their experiment. It was odd that they were using their results from this paper to support why fluoride treatment is more effective following whitening treatment than from soft drink/ acid erosion. Another complaint I have is that in the introduction they talk about how consumption of soft drinks has increased and that many studies has shown that these can cause surface enamel erosions, but the effect of whitening treatment relative to that of soft drinks on dental hard tissue is not known (Ren et al, 2009). I’m not sure why they would just switch to compare the whitening treatment to orange juice. Results were definitely interesting with the orange juice but I was a bit confused that they mentioned the soft drinks so extensively in the introduction. One last critical observation is that their references were not organized in alphabetical order. For a published paper I would not expect to see these types of errors. Overall I thought this was a good study with interesting results but the paper could have been written better. To end on a positive note, I liked that they mentioned the consequences of this decrease in surface microhardness and surface topography (roughness). It was a good way to clue up the paper.
The discussion was informative but they didn’t directly suggest explanations for the findings. They referenced many papers to help explain the results but they never clearly stated why the orange juice was more harmful than the whitening product. I just had to assume it was due to differences in pH. They also didn't mention any ideas on why the mean maximum peak to valley distance (Sz) and developed surface area ratio (Sdr) decreased for the whitening and control groups but increased for the orange juice group. Since the microhardness decreased for all three I would figure both of those measures should have increased for all of the groups as well. The section on the effect of fluoride treatment was interesting but I thought it was out of place as they did not use any fluoride treatment within their experiment. It was odd that they were using their results from this paper to support why fluoride treatment is more effective following whitening treatment than from soft drink/ acid erosion. Another complaint I have is that in the introduction they talk about how consumption of soft drinks has increased and that many studies has shown that these can cause surface enamel erosions, but the effect of whitening treatment relative to that of soft drinks on dental hard tissue is not known (Ren et al, 2009). I’m not sure why they would just switch to compare the whitening treatment to orange juice. Results were definitely interesting with the orange juice but I was a bit confused that they mentioned the soft drinks so extensively in the introduction. One last critical observation is that their references were not organized in alphabetical order. For a published paper I would not expect to see these types of errors. Overall I thought this was a good study with interesting results but the paper could have been written better. To end on a positive note, I liked that they mentioned the consequences of this decrease in surface microhardness and surface topography (roughness). It was a good way to clue up the paper.
Future research:
I noted from reading the discussion that
saliva could contribute to the protection of the enamel surface through its
remineralization effect so it would be interesting to see how it differs from
distilled water. In a future study you could use distilled water instead of saliva as the storing medium and compare the change in microhardness and roughness to give an idea of how much of a protective effect saliva has. Based on what I
have read I would predict that there would be a greater change in the surface
microhardness and surface topography. Also since they noted that the mean
surface microhardness change varied significantly within the whitening treated and
control groups I would suggest using a larger sample size to ensure a more
accurate result. Variation is to be expected since these were extracted teeth
and they should not all be identical in strength and composition (variation
exists between individuals). The larger sample would help control for these variations. One last suggestion I would have for a future
experiment is to see the effects of fluoride treatment follow whitening and
orange juice treatment. In the discussion the authors touched on the effects of
fluoride treatment through referencing other papers. They mention that fluoride
might be more effective following whitening treatment than following the orange
juice erosion. It would be interesting to see results to go along with these statements.
Ren, Y., Amin, A., Malmstrom, H. (2009) Effects of tooth whitening and orange juice on surface properties of dental enamel. Journal of Dentistry. 37:424-431.
