tooth color is considered as the most important aspect to assess patient 's perception to dental attractiveness .
it has been observed that most of the people are dissatisfied with their tooth color , thereby demanding for information regarding the efficacy of various procedures available to enhance tooth color such as micro / macro abrasion , bleaching , veneers , crowns , and composite restoration .
careful diagnosis and treatment planning can lighten teeth in challenging situation , with bleaching considered to be the simplest , less invasive , and economic approach .
harlan , in 1884 , published what is believed to be the first report of hydrogen peroxide which he called hydrogen dioxide . since then , many manufacturing companies are mixing various chemical solutions along with hydrogen peroxide to speed up in - office bleaching .
attempts are even being made to speed up the bleaching process in the office by using an electric current , ultra - violet rays , and other heating instruments and lights .
hydrogen peroxide being unstable splits into hydroxyl ( ho ) , perhydroxyl radicals ( ho2 ) superoxide anions ( o2 ) , and reactive oxygen molecules ( o ) that attack the long and strongly colored molecules to achieve stability , thereby generating other radicals .
the longer chain molecules then split in shorter chains which reflect light differently than its precursors and thus the tooth appears lighter .
dissociation of hydrogen peroxide to obtain free radicals can be accelerated using chemical , heat , or light to reduce the treatment time .
tooth color is determined visually using a set of color tabs / shades called shade guides such as vita - classic , vitapan-3d master , whereas objective method for measuring shade encourages the use of electronic devices such as spectrophotometer , colorimeter , or rgb system .
shadestar is a digital shade - taking device , which gives reliable and reproducible objective results in multiple shade standards such as vita - classic , vitapan 3d - master , ceram - x mono , and ceram - x duo .
therefore , the aim of this in vitro study is to evaluate the role of light and laser sources in the bleaching ability of 37.5% h2 o2 on extracted human teeth .
about 30 extracted human maxillary central incisors were visually examined for the absence of caries , cracks , restorations , or other surface defects .
specimens were then analyzed using an ultrasonic scaler and polished with pumice - water paste .
samples were then prepared by sectioning crown of each specimen which was sectioned at a distance of 7 mm from the cemento - enamel junction ( cej ) while the roots were sectioned at a distance of 4 mm from the cej followed by mesio - distal sectioning , parallel to the long axis of the tooth .
the labial half of each tooth was used for the study and the lingual half was discarded . for staining the samples ,
samples were immersed in 200 ml of a freshly prepared coffee solution ( nescafe classic ) , as reported earlier by sulieman et al . and stored in a bacteriologic oven for 7 days at a temperature of 37c .
the specimens were then washed under running tap water and embedded in a customized putty mold , covering its labial surface .
a circular , measured preselected area of 7 mm diameter was cut through the putty mold on the labial surface of specimen to suit the measuring tip diameter of shadestar , to prevent external light interferences , and to standardize color - gauging .
the vita classic values registered at this stage with shadestar were recorded as baseline values .
specimens were randomly divided into three different experimental groups of 10 specimens each . a 2 mm thick layer of 37.5% hydrogen peroxide gel ( pola office+ ) was applied on the specimens at 3 intervals for 8 min each with a waiting period of 3 min between each bleaching session , as per manufacturer 's instructions .
the gel was removed with a suction tip , tooth was later washed under running water , and then the shade was measured in the predetermined area . a 2 mm thick layer of 37.5%
hydrogen peroxide gel was applied and each specimen was photoactivated at 3 intervals for 8 min each with a waiting period of 3 min between each bleaching session , using halogen light ( beyond , stafford , tx , usa ) with power density of 150 w and high - intensity blue light ( 480 - 520 nm ) , kept at a distance of 15 mm from the tooth surface .
water - saturated gauze pad was placed under each specimen during bleaching procedure to prevent dehydration . a 2 mm thick layer of 37.5%
hydrogen peroxide bleaching gel was applied and activated using picasso diode laser ( gaalas ) with a wavelength of 810 nm and it was preset into pulsed mode # 4 of 7 w power with duration of 9.9 s and an interval of 1.5 s. the bleaching hand piece of picasso diode laser was held to cover 2 teeth at a time , for a period of 30 s. the procedure was repeated 6 times giving a total activation period of 3 min per cycle followed by a holding period of 4 min .
the whole procedure was repeated 4 times , with the total laser bleaching time being 28 min as per the manufacturer 's instructions .
a water - saturated gauze pad was placed under each specimen during bleaching procedure to prevent dehydration .
vita classic shade guide readings of each specimen were measured and recorded immediately postbleaching , over respective intervals of 1 , 2 , and 3 weeks of storage in normal saline , using shadestar .
the obtained readings were scored according to value - oriented vita classic shade guide readings as used by pohjola et al . and leonard et al .
all the statistical analyses were done using spss version 17 ( spss inc , iii , chicago , usa ) .
friedman test was done for intragroup comparison ( p < 0.01 ) and kruskal - wallis anova was done for intergroup comparison ( p < 0.017 ) .
a 2 mm thick layer of 37.5% hydrogen peroxide gel ( pola office+ ) was applied on the specimens at 3 intervals for 8 min each with a waiting period of 3 min between each bleaching session , as per manufacturer 's instructions .
the gel was removed with a suction tip , tooth was later washed under running water , and then the shade was measured in the predetermined area .
a 2 mm thick layer of 37.5% hydrogen peroxide gel was applied and each specimen was photoactivated at 3 intervals for 8 min each with a waiting period of 3 min between each bleaching session , using halogen light ( beyond , stafford , tx , usa ) with power density of 150 w and high - intensity blue light ( 480 - 520 nm ) , kept at a distance of 15 mm from the tooth surface .
water - saturated gauze pad was placed under each specimen during bleaching procedure to prevent dehydration .
a 2 mm thick layer of 37.5% hydrogen peroxide bleaching gel was applied and activated using picasso diode laser ( gaalas ) with a wavelength of 810 nm and it was preset into pulsed mode # 4 of 7 w power with duration of 9.9 s and an interval of 1.5 s. the bleaching hand piece of picasso diode laser was held to cover 2 teeth at a time , for a period of 30 s. the procedure was repeated 6 times giving a total activation period of 3 min per cycle followed by a holding period of 4 min .
the whole procedure was repeated 4 times , with the total laser bleaching time being 28 min as per the manufacturer 's instructions .
a water - saturated gauze pad was placed under each specimen during bleaching procedure to prevent dehydration .
vita classic shade guide readings of each specimen were measured and recorded immediately postbleaching , over respective intervals of 1 , 2 , and 3 weeks of storage in normal saline , using shadestar .
the obtained readings were scored according to value - oriented vita classic shade guide readings as used by pohjola et al . and leonard et al .
all the statistical analyses were done using spss version 17 ( spss inc , iii , chicago , usa ) .
friedman test was done for intragroup comparison ( p < 0.01 ) and kruskal - wallis anova was done for intergroup comparison ( p < 0.017 ) .
at baseline , no statistically significant difference in the mean shade values is found among the three experimental groups .
all the groups produced significant increase in lightness from baseline following bleaching , with the group ii showing comparatively lighter teeth followed by group iii and i. there was statistically significant difference in mean shade values immediately postbleaching and over a period of 1 , 2 , and 3 weeks postbleaching between group i and ii and between group i and iii .
however , no statistically significant difference in the degree of lightness was observed between groups ii and iii as shown in table 1 .
intra- and inter - group mean shade values comparison the mean shade change values from baseline immediately postbleaching was found to be highest for group ii , followed by group iii and i. the difference in mean shade change values from baseline was found to be significant between group i and ii at duration of 1 , 2 , and 3 weeks postbleaching . however , no statistically significant difference was observed between group i and iii ; group ii and iii as shown in table 2 .
intra- and inter - group mean shade change value comparison statistically significant increase in lightness from baseline shade values was observed immediately postbleaching in all the three groups . in groups
group i showed an increase in value - oriented scores , with no statistically significant difference from their baseline values at 2 weeks postbleaching .
tooth whitening , also referred to as bleaching , is considered to be the most conservative method to manage a discolored tooth when compared to all the above - mentioned treatment modalities .
diffusion of peroxide into the organic matter of tooth structure depends on the diffusion coefficient , duration of application , and concentration of active bleaching agent .
hence , in the present study , 37.5% hydrogen peroxide is used as a bleaching agent .
photocatalytic interactions accelerate the dissociation of hydrogen peroxide by heating up the bleaching agent , thereby increasing the interaction between reactive oxygen and pigmented molecules , leading to enhanced bleaching efficiency . in the present study ,
shadestar , a digital shade measuring device , is used to evaluate the shade during the trial as it gives quick and reliable readings .
considering the reliability and accuracy of vita classic shade guide , in the present study , value - oriented vita classic shade guide scale was used to calculate shade change from baseline .
laser being monochromatic , coherent , and collimated is a differentiated source of energy , when irradiated on a bleaching agent , the chromophores present in the gel absorb the light and thus activate the molecule , thereby improving tooth whitening ability .
few studies showed enhanced bleaching results on using laser , while other studies showed no significant improvement . in the present study , laser activation produced comparatively enhanced bleaching efficacy with hydrogen peroxide gel when compared to nonactivation group , which is in correlation with the results obtained by calatayud et al .
halogen light , one of the most common light sources used in power bleaching , transmits higher temperatures without causing discomfort to the patients
. results of the present study demonstrated greater average shade change values following bleaching for halogen - activated group than nonactivation and laser activation groups .
this might be because of difference in the power density of both the activation sources , leading to variation in the degree of heat produced in the bleaching gel which in turn enhances the decomposition of hydrogen peroxide .
the results obtained were in accordance with the study conducted by patel et al . where halogen light provided comparatively enhanced tooth whitening than diode laser and plasma arc light .
durability of bleaching results was found to be maintained throughout the trial period of 3 weeks for halogen - activated group .
however , for laser - activated group , the effect of bleaching therapy diminished over a period of 2 weeks and for no - light bleaching group , the effect lasted no longer than a week after bleaching . though the exact mechanism of samples retaining the shade is not clearly understood , it was observed earlier that depending on the degree of porosity in the enamel and dentin , oxygen gets entrapped in the tooth structure and facilitates further bleaching .
heating of bleaching gel further increases the penetration of peroxide into the organic matter of tooth structure , and continuous oxidation takes place over time .
however , this is an in vitro study , whereas in clinical situations , teeth are constantly exposed to various staining substances causing variations in the response to bleaching , this could be a limitation .
furthermore , future studies can be done with larger sample size and different activation modes for bleaching .
on the basis of results obtained from the present study , following conclusions can be drawn : 
 all the groups produced significant increase in lightness from baseline following bleaching .
halogen and laser light activation group showed increased lightness than nonlight - activated group with no statistically significant differencehalogen and laser light activation group maintained the shade obtained for 3 weeks postbleaching ; whereas no - light activation group presented with shade rebound after 2 weeks postbleaching . 
 
halogen and laser light activation group showed increased lightness than nonlight - activated group with no statistically significant difference halogen and laser light activation group maintained the shade obtained for 3 weeks postbleaching ; whereas no - light activation group presented with shade rebound after 2 weeks postbleaching .
 introduction : the aim of this in vitro study is to evaluate the role of light and laser sources in the bleaching ability of 37.5% h2 o2 on extracted human teeth.materials and methods : about 30 caries - free single - rooted maxillary central incisors were used for the study . 
 specimens were prepared by sectioning the crown portion of teeth mesiodistally , and labial surface was used for the study . 
 specimens were then immersed in coffee solution for staining . 
 color of each tooth was analyzed using shadestar , a digital shademeter . 
 specimens were then divided into three groups of 10 each and were subjected to bleaching with 37.5% h2 o2 , 37.5% h2 o2 + light activation , and 37.5% h2 o2 + laser activation , respectively . 
 postbleaching , the color was analyzed for all the specimens immediately and then after 1 , 2 , and 3 weeks intervals , respectively.results:all the statistical analyses were done using spss version 17 . 
 intra- and inter - group comparisons were done with friedman test and kruskal  wallis anova , respectively . 
 statistical analysis concluded with a significant improvement in their shade values from baseline in all the three groups . 
 halogen light activation and laser - activated groups showed comparatively enhanced bleaching results over no - activation group , though the difference was not statistically significant.conclusion:the results of the present study show that bleaching assisted with halogen light and laser showed increased lightness than nonlight activated group . 
 durability of bleaching results obtained postbleaching was maintained throughout the experimental trail period of 3 weeks for both halogen light and laser activation group , whereas no - light activation group presented with shade rebound after 2 weeks postbleaching . 
INTRODUCTION
MATERIALS AND METHODS
Group I
Group II
Group III (with laser activation)
RESULTS
DISCUSSION
CONCLUSION
Financial support and sponsorship
Conflicts of interest