Keywords bleaching - enamel hardness - CPP-ACPF - 5% NaF - remineralization
Introduction
Bleaching is one of the cosmetic dentistry treatments that is often done because it
is easy, efficient, and noninvasive to brighten discolored teeth.[1 ]
[2 ] Side effects of bleaching procedures such as tooth sensitivity, changes in enamel
structure, and pulp cell damage are of significant concern among dentists.[3 ] Some studies have shown that bleaching can also soften the hard tissues of teeth,
alter the morphology and mineral content of enamel, as well as a decrease the microhardness
of enamel.1.2
In-office bleaching techniques using high concentrations of hydrogen peroxide are
effective in brightening teeth; however, this material can weaken the surface structure
of enamel.[4 ] Some research results say that the use of high concentrations of hydrogen peroxide
can lead to changes in mineral composition, morphological changes, and a decrease
in the microhardness of enamel.[5 ] The application of remineralization materials either before or after bleaching can
minimize demineralization that has an impact on enamel hardness.[6 ]
Remineralization can either occur naturally or induced by remineralization agents
that precipitate into the dental structure.[7 ] In the early stages of white spot lesion, remineralizing agents that contain 5%
fluoride or casein phosphopeptide amorphous calcium phosphate fluoride (CPP-ACP) could
be used as noninvasive treatment.[8 ] Fluoride is one of the remineralization materials that has proven effective in the
prevention of dental caries. Fluoride will form fluorapatite crystals with the help
of calcium and phosphate ions on the enamel surface that will inhibit demineralization
and increase the microhardness value of enamel.[9 ] CPP-ACPF besides containing CPP-ACP also added 0.2% (900 ppm) sodium fluoride (NaF).
CPP-ACPF applications showed a higher increase in enamel hardness.[10 ] NaF is one type of topical fluoride that is often used in dentistry. The application
of fluoride will form a layer of calcium fluoride (CaF2 ) that then diffuses into the surface of the enamel to form fluorapatite. Thus, helping
to increase remineralization which can increase the hardness of the enamel.[9 ]
This study aimed to analyze whether there is an increase in enamel hardness post-external
bleaching after remineralized with CPP-ACPF and 5% NaF and the difference in increased
enamel hardness post-external bleaching between teeth remineralized with CPP-ACPF
and 5% NaF. The research hypothesis is that there is no difference in post-bleaching
enamel hardness remineralized with CPP-ACPF and 5% NaF.
Materials and Methods
An in vitro study used 30 samples of mandibular premolars extracted based on the central limit
theorem. The central limit theorem was a statistical theory where a sample was taken
randomly from a population (30 samples or more); then the average value of the sample
had a standard normal distribution.[11 ] The teeth were free of caries, fillings, erosion, and cracks, to obtain standard
enamel surfaces. The crowns were separated from the roots 2 mm from the cementoenamel
junction using a carborundum disc. The tooth fragments were positioned in an acrylic
resin cylinder with the labial surface exposed. The enamel surfaces were ground and
polished using #1200-grit silicon carbide paper.
The measurement of the enamel hardness value in the sample was performed using a Vickers
hardness tester with a load of 200 g for 10 seconds at three points of the central
labial surface of the tooth. The average value of the three points was used as the
hardness value of the sample. All samples were bleached using 40% hydrogen peroxide
(Opalescence Boost: Ultradent Product Inc., Lot #BL4SL) three times for 20 minutes.
The samples were randomly divided into three groups consisting of 10 samples each,
group I as a control without the application of remineralization material, group II
was given the application of CPP-ACPF (GC Tooth Mousse Plus: GC Europe, Lot #201130B)
3 minutes twice a day for 21 days, and group III was given the application of 5% NaF
(Clinpro White Varnish: 3M ESPE, Lot #NA62322) once and left for 4 hours. Then the
entire sample is rinsed and stored in artificial saliva that is replaced daily. Sample
hardness was measured before bleaching, after bleaching, and after remineralization
at 7, 14, and 21 days.
Results
Analysis of the data used was an analysis of variance (ANOVA) test to assess differences
in the increase in enamel hardness between groups and paired t -tests to determine differences in enamel hardness in each group. Enamel hardness
after bleaching treatment decreased significantly compared with before bleaching treatment
in all three groups (control, CPP-ACPF, and 5% NaF). The results of enamel hardness
testing before and after bleaching treatment can be seen in [Table 1 ].
Table 1
Results of the enamel hardness before and after bleaching
Treatment
n
Mean
SD
Before bleaching
After bleaching
Before bleaching
After bleaching
Control
10
411.10
333.00
11.350
25.924
CPP-ACPF
10
411.40
357.45
11.735
12.716
5% NaF
10
400.00
353.05
8.580
17.574
Total
30
407.50
347.83
11.605
21.720
Abbreviations: CPP-ACPF, casein phosphopeptide amorphous calcium phosphate fluoride;
5% NaF, 5% sodium fluoride; SD, standard deviation.
Enamel hardness has increased significantly after remineralization treatment. The
results of the enamel hardness testing after 7,14, and 21 days of remineralization
in the CPP-ACPF and 5% NaF group can be seen in [Table 2 ].
Table 2
Results of enamel hardness after remineralization treatment at 7, 14, and 21 days
Treatment
Days
Mean
n
SD
CPP-ACPF
7
415.45
10
9.335
14
420.20
10
6.197
21
422.00
10
5.715
5% NaF
7
413.05
10
7.448
14
415.65
10
5.056
21
421.65
10
6.334
Abbreviations: CPP-ACPF, casein phosphopeptide amorphous calcium phosphate fluoride;
5% NaF, 5% sodium fluoride; SD, standard deviation.
Furthermore, a follow-up test was performed using paired t -test to determine the difference in enamel hardness in the CPP-ACPF and 5% NaF groups
after remineralization treatment for 7, 14, and 21 days. The results of the paired
t -test analysis can be seen in [Table 3 ].
Table 3
Results of paired t -test analysis of enamel hardness after remineralization treatment at 7, 14, and 21
days
5% NaF
(7 days)
5% NaF
(7 days)
5% NaF
(7 days)
5% NaF
(7 days)
5% NaF (7 days)
5% NaF
(7 days)
413.05
415.45
415.65
420.20
421.65
422.00
5% NaF
(7 days)
413.05
CPP-ACPF
(7 days)
415.45
0.4350
5% NaF
(14 days)
415.65
0.3980
0.9480
CPP-ACPF
(14 days)
420.20
0.0228
0.1254
0.1418
5% NaF
(21 days)
421.65
0.0067
0.0471
0.0544
0.6366
CPP-ACPF
(21 days)
422.00
0.0049
0.0363
0.0422
0.5577
0.9091
Abbreviations: CPP-ACPF, casein phosphopeptide amorphous calcium phosphate fluoride;
5% NaF, 5% sodium fluoride.
The difference in the increase of enamel hardness between the control group and the
remineralized group with CPP-ACPF and 5% NaF can be seen in [Fig. 1 ].
Fig. 1 Diagram of differences in increased enamel hardness after remineralization treatment
in control, casein phosphopeptide amorphous calcium phosphate fluoride (CPP-ACPF),
and 5% sodium fluoride (5% NaF) groups. The results of the study showed that the increase
in post-bleaching enamel hardness in the CPP-ACPF group was higher than the 5% NaF
group, although there was no statistically significant difference.
Discussion
Based on the results of the analysis using the ANOVA test, there was a significant
decrease in the enamel hardness value after bleaching with 40% hydrogen peroxide compared
with the initial hardness. This decrease in hardness was caused by changes in mineral
content in the form of demineralization in the enamel structure. The enamel demineralization
process after bleaching is related to the composition and concentration of the bleaching
material, the contact time and the method of application of the bleaching material
to the teeth, the pH value, and the type of solution in the bleaching material.[12 ]
[13 ]
Hydroxyapatite crystals are the components that makeup enamel hardness composed of
the main inorganic matrix in the form of calcium and phosphate.[14 ] Bleaching treatment with high concentrations of hydrogen peroxide detaches calcium
and phosphate ions of the enamel surface, thereby reducing the microhardness of the
enamel. Mondelli et al research on the side effects of hydrogen peroxide bleaching
material on enamel shows that the higher the concentration of bleaching material,
the higher the demineralization of enamel that occurs.[15 ] Oxidation–reduction reactions of bleaching materials produce hydrogen ions (H+ ) that can create an acidic environment and cause the dissolution of organic and inorganic
enamel matrices.[16 ]
Remineralization using fluoride after bleaching has been shown to restore the microhardness
of the enamel surface. Fluoride compounds can restore damaged tooth microstructure
through the absorption and sedimentation of salivary components such as calcium and
phosphates.[17 ] The formed calcium fluoride (CaF2 ) layer deposited on the surface of the enamel crystals forming fluorapatite.[18 ]
In the control group, the enamel hardness did not increase compared with the initial
hardness after 7 days in artificial saliva, but on day 21 it returned to the initial
hardness. Saliva plays a role in returning calcium and phosphate ions to the demineralized
enamel surface, thereby increasing remineralization.[19 ] Although artificial saliva was used in this study, it was not able to restore the
initial enamel hardness in a short time due to the limited amount of minerals. Remineralization
materials are still needed to prevent side effects of post-bleaching demineralization
such as sensitivity, changes in morphological structure, and enamel hardness.16.19
In the CPP-ACPF group, the enamel hardness increased beyond the initial hardness after
CPP-ACPF application for 7 days, then increased further on day 14 and experienced
a slight increase on day 21. CPP-ACPF contains calcium, phosphate ions, and 0.2% (900 ppm)
NaF. CPP are able to stabilize calcium, phosphate, and fluoride ions in nanocomplexes
of ACPF solutions.[16 ] CPP-ACPF acts as a reservoir of calcium and phosphate ions available in natural
saliva and maintains the solution in a supersaturation state, thereby increasing the
remineralization and enamel crystal hardness.[20 ] Aras et al research found that CPP-ACPF remineralization was effective in increasing
enamel surface hardness in artificial enamel caries.[21 ] Llena et al and Heshmat et al research showed that the use of CPP-ACPF for 2 weeks
post-bleaching can increase remineralization and restore enamel hardness.16.22
In the 5% NaF (3M Clinpro White Varnish) group, the enamel hardness increased beyond
the initial hardness after 5% NaF application for 7 days, slightly increased at 14
days, and further increased at 21 days. Clinpro White Varnish contains tricalcium
phosphate and 5% (22,600 ppm) NaF.[22 ] Dionysopoulos et al concluded that topical application of fluoride during and after
bleaching treatment significantly increased the surface microhardness of the enamel.[23 ] Topical application of high concentrations of fluoride will form a layer of calcium
fluoride (CaF2 ) on the enamel surface to inhibit demineralization or decrease in enamel hardness.[24 ]
Conclusion
Based on the results of the study, it can be concluded that there was an increase
in the enamel hardness after external bleaching that was remineralized with CPP-ACPF
and 5% NaF. There was a difference in the increased enamel hardness between teeth
remineralized with CPP-ACPF and 5% NaF. CPP-ACPF showed a higher enamel hardness value
than 5% NaF. The limitation of this study was used Vickers hardness tester only. Further
experimental research is needed to determine the remineralization of enamel hardness.
From the results of this study, it is suggested that patients should be given the
application of a remineralizing agent using CPP-ACPF or 5% NaF after bleaching treatment.
