Influence of light and laser activation of tooth bleaching systems on enamel microhardness and surface roughness JCD 2020

1. INFLUENCE OF LIGHT AND LASER ACTIVATION
OF TOOTH BLEACHING SYSTEMS ON ENAMEL
MICROHARDNESS AND SURFACE ROUGHNESS
ELEENA MOHD YUSOF, SITI AI'SHAH ABDULLAH, NOR HIMAZIAN MOHAMED
JOURNAL OF CONSERVATIVE DENTISTRY
DR.AJAY BABU GUTTI
DEPARTMENT OF CONS & ENDO
M.D.S IST YEAR

2. INTRODUCTION

3.  Tooth bleaching is a common sought-after dental treatment to enhance esthetics by improving tooth
color to a brighter shade.
 A study showed that 28% of adults in the United Kingdom were not satisfied with the appearance of
their teeth and 34% of adults in the United States of America were not satisfied with their existing
tooth color.
 Tooth bleaching is not considered a new technology. In 1848, the first nonvital tooth bleaching with
chloride of lime was practiced. Many different bleaching agents were also successfully used on
nonvital teeth including aluminum chloride, oxalic acid, pyroxene, hydrogen peroxide, sodium
peroxide, sodium hypophosphate, sulphurous acid, and potassium cyanide.
 By the 1860s, vital teeth were bleached externally using oxalic acid and later using hydrogen peroxide
or pyroxene. In the early 1900s, there was an addition of heated instruments or a light source to
accelerate the bleaching process.

4.  In-office bleaching uses a relatively high concentration of bleaching agent or gel for a shorter
period, while home-applied bleaching uses a low concentration of this agent.
 The concentration of an in-office bleaching agent that is normally used is between 25% and 35%
hydrogen peroxide or 35% carbamide peroxide. These are often used together with activating
agents such as light or laser.
 The in-office bleaching treatment used can result in significant whitening after only one visit but
may require multiple treatments for optimum result or can act as a boost therapy by initiating the
process and will be continued later by home-bleaching procedures.
 Peroxide bleaching systems are suspected of producing tooth whitening through the oxidation of
intrinsic or extrinsic chromogens on or within the tooth enamel. To do this, hydrogen peroxide must
be generated and/or diffuse to chromogenic materials on or within teeth. The delivery of effective
peroxide bleaching requires stabilized gel systems which are often formulated at low ph.

5.  Bleaching is a relatively safe procedure, but this treatment, through its mechanism of action,
produces some structural changes to the enamel that has raised concerns to general dentists and
dental researchers including mineral loss, loss of fluoride, increased surface roughness, reduced
enamel hardness, reduced fracture stability, and increased susceptibility to erosion or caries.
 Patients are often concerned about the unfavorable consequences of bleaching treatment
including tooth sensitivity and gingival irritation.
 There are limited studies available looking at the two tooth bleaching activation methods, light
and laser, and simultaneously compare the changes in the enamel microhardness and surface
roughness with time.
 This study aimed to compare the effects of light and laser activation of in-office tooth bleaching
systems on enamel microhardness and surface roughness at different time intervals. The null
hypotheses were a laser-activated in-office bleaching system producing the same amount of
reduction in enamel microhardness and a similar increase in surface roughness to a light-activated
bleaching system.

7. MATERIALS AND METHODS

8. Sound human premolar teeth, extracted for an orthodontic reason,
were embedded in epoxy resins to ease anchorage in preparing
enamel slabs.
Enamel slabs were prepared using a high-precision cutting machine
(IsoMet™ 2000, Buehler, Illinois, USA) to separate the buccal and
lingual surfaces
Two surfaces were further sectioned, separating the mesial and
distal parts.

9. Twenty-five enamel slabs were then randomly selected and embedded
in epoxy resins measuring 1 cm × 1 cm × 1 cm. The enamel surfaces
were then polished using 1200- grit silicon carbide paper in a polishing
unit with water irrigation to get a flat surface.
These specimens were then randomly divided into three treatment
groups
light-activated
bleaching
laser-activated
bleaching
control groups
Were stored in distilled water at 37°C.

10. Baseline data were collected for enamel microhardness
and surface roughness.
specimens were then applied with 35% hydrogen
peroxide activated with a light source for the light-
activated group and 35% hydrogen peroxide activated
with a laser source for the laser-activated group..
Both the specimen groups were tested again for
microhardness and surface roughness. This step was
repeated at 7 days and 28 days after the first bleaching.

11.  For the light-activated bleaching group, after the application of hydrogen peroxide gel of
about 2–3 mm thickness onto each specimen, they were cured with a halogen light source
at a wavelength of 480 nm for 10 min. Specimens were then cleaned with tissue paper
without washing before the same step was repeated.
 For the laser-activated bleaching group, after the application of hydrogen peroxide gel of
about 2–3 mm thickness onto each specimen, the agent was activated with a diode laser in
the range of 815 nm, 8 cycles, 10 s for each cycle. Specimens were then washed out of HP
before reapplication.
BLEACHING
TECHNIQUE

12.  Vickers hardness testing machine (HMV-FA, Shimadzu, Kyoto, Japan) was used to determine the
changes in enamel microhardness (Vickers microhardness [VMH]) after tooth bleaching.
 First, the pattern of indentation was set using the HMV software, three straight-line indentations
0.5 mm apart. The right lens was positioned into place before the specimen was being focused.
Upon focusing, three indentations were made with a load of 500 g for 15 s each. The depth of
indentation measures the hardness of the enamel.
MEASUREMENT
OF ENAMEL
MICROHARDNES
S

13.  After hardness testing, the surface texture was evaluated using an optical three-dimensional
measurement system.
 The surface roughness was measured as Sa and in the unit of the micrometer (μm). Using the
software, the specimens were put into focus under ×10 magnifications and a vertical resolution
was set at 195 nm.
 The surface was then evaluated, and three areas with measurement of 200 × 200 nm at the flat
surface and a mean value per specimen were calculated for baseline and after bleaching
treatment.
MEASUREMENT OF ENAMEL
SURFACE ROUGHNESS

14. The results of the enamel microhardness were statistically analyzed using Kruskal–Wallis and,
subsequently, Wilcoxon and Mann–Whitney tests. The mean of the surface roughness values was
analyzed using Kruskal–Wallis and Friedman tests, followed by the Wilcoxon test. SPSS® 10.1
software SPSS software (IBM SPSS Inc, Chicago, IL) was used for this purpose.
Statistical analysis

15. RESULTS

16.  The means of enamel surface microhardness values showed that there was a significant
difference for the light-activated bleaching group (P = 0.001). When comparing different
time intervals, it was found that there were no significant differences between the groups
except at day 28 (P = 0.005).
 At day 28, there was a significant difference between the light- and laser-activated
bleaching groups (P = 0.001) .The means of enamel surface roughness showed that there
were significant differences in the laser- (P = 0.033) and light-activated (P = 0.001)
bleaching groups from baseline to day 28.
 When comparing time intervals, it was found that there was no significant difference
between the three treatment groups.

17. DISCUSSION

18.  The negative impact of tooth bleaching on the integrity of organic enamel components such as protein
and collagen creates issues involving short-lasting whitening effect, rough surfaces, and softened
enamel.
 Softened and rough enamel surfaces may predispose the tooth to the development of dental caries and
non carious tooth surface loss such as abrasion and attrition.
 This study compared how light and laser activation of a bleaching agent caused alterations to enamel
microhardness and surface roughness.
 Results of this study indicated that the effects of hydrogen peroxide bleaching showed a significant
reduction in enamel microhardness at day 28 when the light was used to activate the bleaching agent as
compared to laser activation. A significant reduction in hardness was also observed between the time
intervals when light activation was used. Hence, the first null hypothesis was rejected.

19.  Findings of this study are in agreement with an earlier study that found a significant reduction in
enamel hardness by 13% after 5 min of exposure to 35% hydrogen peroxide activated by light, and this
was further reduced by 25% after 35 min of exposure.
 An increase in surface roughness and the subsequent ability of plaque and bacteria to adhere to the
enamel surface after a bleaching treatment had also been observed in previous studies. In this study,
the results showed an increase in enamel surface roughness between the time intervals when both
light and laser were used to activate the agents. There was, however, no significant difference in the
increase in surface roughness between the two activators. Thus, the second null hypothesis was
accepted.
 These findings correspond with the results of a study that observed an increase in roughness after
exposure to a similar concentration of hydrogen peroxide activated by light and laser.
 Lasers are utilized in tooth bleaching to catalyze the oxidation reaction of the bleaching gel. There are
numerous laser wavelengths available, and one of the most commonly used is themdiode laser. The
use of lasers provides much faster and effective bleaching than other conventional methods, and the
ability to control the generated heat ensures that the temperature is almost always optimal and
ultimately prevents pulpal overheating. In addition, it has been shown that patients undergoing
bleaching treatment with a higher laser wavelength exhibited less intensity of tooth sensitivity than
those treated with a lower wavelength.

20.  Light sources used for light-activated bleaching including quartz-tungsten-halogen lamps,
plasma arc lamps (used synonymously for xenon gas discharge or xenon short-arc
lamps), and laser sources (laser = light amplification by stimulated emission of radiation) of
a variety of different wavelengths as well as LED have been proposed for light activation of
bleaching products.
 Differences in the methodology may have affected the outcome of this study from the
others including the type of storage medium used, either stored in distilled water, artificial
saliva, or human saliva.
 The present study used distilled water as a storage medium that may not simulate the
clinical condition, however, the outcome from this study provides a basis on the degree of
acid dissolution of the enamel surface upon bleaching agent application irradiated by two
different activators, light and laser. For this reason, dental practitioners should practice the
use of remineralizing agents immediately after tooth bleaching procedures to promote
remineralization.

21.  Fluoridated hydrogen peroxide bleaching gels can reduce microhardness and accelerate
microhardness recovery in the posttreatment phase to a better extent than nonfluorinated
bleaching gels. This may be attributable to the fluoride component of bleaching gels that
support the repair of the microstructure defects by absorption and precipitation of salivary
components such as calcium and phosphate.
 The use of a high-concentration fluoride dentifrice (5000 parts per million) postbleaching
has also been shown to increase the enamel microhardness and decrease the surface
roughness.
 Although fluoride therapy could enhance the remineralization process, the effect would not
occur if the mineral contents of the enamel are lost as there would be no mineral substrate
upon which the fluoride ions can act on.
 Type of microhardness testing could also play a factor in the outcome of a study.In a past
study, it was proven that the usage of human saliva and the Vickers hardness test instead
of the Knoop hardness test was associated with a less frequency of microhardness
reductions as the indentation shape produced by the two varies.

22.  One of the strengths of this study is a comparison of the effect of vital bleaching on the
enamel surface between different time intervals were made.
 In a clinical situation, a bleaching procedure may need to be repeated to achieve the
intended results. Although this study revealed that the reduction in microhardness and the
increase in surface roughness became more prominent with time, the storage medium
used limits the knowledge on the duration required for the remineralization process to
take place.
 Recommendations for future studies would include increasing the duration from one
bleaching treatment to another to better understand the length of time required before the
next bleaching procedure and the use of human saliva as a storage medium to best
mimic a clinical condition.

23. CONCLUSION

24.  Within the limitations of the present study, it can be concluded that the activation of a
bleaching agent with light caused a significant reduction in enamel microhardness and
an increase in surface roughness after a month when compared to activation with
lasers that caused minimal or no significant alterations.
 This study provides a foundation that the use of lasers as an activator in a bleaching
treatment is better in maintaining the integrity of the enamel structures.

25. Effect of fluoride containing bleaching agents on enamel surface properties
Hui-Ping Chen , Chih-Han Chang, Jia-Kuang Liu, Shu-Fen Chuang, Jin-Yi Yang
 Objectives: To evaluate the effects of fluoridated bleaching agents and post-bleaching
fluoridation treatment on the whitening efficiency and microhardness of bovine enamel.
 Methods: Twenty five freshly extracted bovine incisors were cut into halves, embedded
and then divided into the following five groups: Group 1, untreated controls; Group 2,
treatment with 10% carbamide peroxide (CP) bleaching agent; Group 3, treatment with
10% CP followed by a 0.9% sodium fluoride gel application, Group 4, treatment with 10%
CP containing 0.11% fluoride; Group 5, treatment with an experimental bleaching agent
consisting of 10% CP and 0.37% fluoride. Groups 2-5 were treated 8h per day for 14
days then immersed in saliva for 2 weeks. Enamel morphology changes were evaluated
under SEM on Day 14. Changes in enamel color and microhardness were evaluated on
Days 7 and 14, and compared with the baseline data. Additionally, microhardness was
determined on post-bleaching Days 21 and 28.
 Results: After 2 weeks, an erosion pattern was noted on the specimens in Groups 2 and
3. Groups 4 and 5 showed a milder demineralized pattern. All the bleached enamel
specimens revealed increased whiteness and overall color value. Groups 2 and 3
showed significantly decreased enamel microhardness compared to their baseline data.
The specimens treated with fluoridated bleaching agents showed relatively less
reduction in enamel microhardness than those treated with nonfluoridated agents during
the bleaching treatment.
 Conclusions: The fluoridated bleaching agents produced less demineralization of

26. Influence of study design on the impact of bleaching agents on dental enamel microhardness: a
review
Thomas Attin , Patrick R Schmidlin, Florian Wegehaupt, Annette Wiegand
 Objective: Numerous studies investigated the impact of bleaching procedures on enamel
microhardness. The outcomes of these studies reveal inconsistencies regarding the fact
whether a microhardness reduction due to bleaching occurs or not. Aim of the present review
was to summarize the existing literature of external bleaching therapies, which used
microhardness tests for evaluation of possible effects on enamel and to weigh up different
parameters of the study designs with respect to the outcome of these studies.
 Methods: The data from original scientific full papers listed in PubMed or ISI Web of Science
(search term: enamel and (bleaching or peroxide) and (hardness or microhardness or Knoop or
Vickers)) and received by additional hand-search meeting the inclusion criteria were included
in the review. Influences of different parameters on the outcome of the bleaching treatments
were analyzed with the Fisher's-exact-test.
 Results: A total of 55 studies were identified with 166 hardness measurements conducted
directly after bleaching and 69 measurements performed after a post-treatment episode.
Directly after bleaching, 84 (51%) treatments showed microhardness reduction compared to
baseline, whereas 82 (49%) did not yield microhardness reduction. After the post-treatment
episode, 20 (29%) treatments showed hardness reduction and 49 (71%) did not. A significant
higher number of bleaching treatments resulting in enamel microhardness reduction were
observed, when artificial instead of human saliva was used for storage of the enamel samples
in the intervals between the bleaching applications and when no fluoridation measures were
applied during or after the bleaching phase.
 Significance: The review shows that in those studies, which simulated the intraoral conditions
as closely as possible, the risk of enamel microhardness decrease due to bleaching treatments
seems to be reduced. Nevertheless more in situ- and in vivo-studies are needed to verify this
observation.