bleaching agents : opalescence 20% ( 20% carbamide peroxide gcsscorp , asia ) and clinex gel 35% ( 35% carbamide peroxide vishal dento care , india ) .
remineralizing agent : gc tooth mousse ( cpp - acp , gc crop , asia ) .
the extracted teeth were washed thoroughly under running tap water to remove blood , saliva , and other debris .
the teeth were stored in artificial saliva at room temperature till the experiment was started . 

0.053% tricalcium phosphate0.01 n hcl15 ml of sorbitol0.6 gm kcl0.42 gm nacl0.026 gm magnesium lactate0.05 m naoh5 ml of 0.2 m sodium phosphatedistilled water . 
 
0.053% tricalcium phosphate 0.026 gm magnesium lactate 5 ml of 0.2 m sodium phosphate 100 ml of 0.053% tricalcium phosphate in 0.01n hcl is mixed with 100 ml of a mixture containing 15 ml of sorbitol , 0.6 g kcl , 0.42 g nacl and 0.026 g magnesium lactate . after mixing the two at room temperature
the ph was adjusted to 7.4 by 0.05 m naoh and 5 ml of 0.2 m sodium phosphate , was added and made to volume 500 ml .
exact ph was verified using digital ph meter and the mixture was sterilized in an autoclave and stored at 4c .
the teeth were buccolingually sectioned with the help of double faced diamond disk mounted on micro motor with the straight handpiece .
the buccal surface portions of the crowns were mounted using cold - cure acrylic resin .
the specimen were subjected to polishing sequentially using 80 m , 100 m , 200 m , 400 m , grit size of sand papers and finally with diamond polishing paste .
baseline micro - hardness values were recorded and the blocks having the average surface micro - hardness 10% above and 10% below the overall average were discarded .
the specimens were randomly divided into three equal groups ; the grouping of specimens is as follows : 
 group a : ten specimens , exposed to 20% carbamide peroxide gel ( opalescence 20% , gc corp , asia ) for 2 h daily for 1-weekgroup b : ten specimens , exposed to 35% carbamide peroxide gel ( clinex gel 35% vishal dento care , india ) for 30 min daily for 1-weekgroup c : ( control group ) ten specimens , exposed to artificial salivagroup ar : postbleached specimens of group a treated with cpp - acp for 3 min daily for a period of 2 weeksgroup br : postbleached specimen of group b treated with cpp - acp for 3 min daily for a period of 2 weeks . 
 
group a : ten specimens , exposed to 20% carbamide peroxide gel ( opalescence 20% , gc corp , asia ) for 2 h daily for 1-week group b : ten specimens , exposed to 35% carbamide peroxide gel ( clinex gel 35% vishal dento care , india ) for 30 min daily for 1-week group c : ( control group ) ten specimens , exposed to artificial saliva group ar : postbleached specimens of group a treated with cpp - acp for 3 min daily for a period of 2 weeks group br : postbleached specimen of group b treated with cpp - acp for 3 min daily for a period of 2 weeks .
groups a and b were exposed to respective concentrations of carbamide peroxide gel daily for the time periods recommended by the manufacturer for 1-week .
after the recommendation time of exposure , daily the teeth were removed from bleaching gels , washed with de - ionized distilled water and placed in artificial saliva for the reminder of 24 h. the procedure was carried out for all specimens for a period of 1-week .
the control group teeth were kept in artificial saliva for the entire period of 1-week .
the micro - hardness test was done using leica vmht - mot micro - hardness tester with vicker 's diamond indenting tool after a period of 1-week under a load of 100 g for a period of 12 s per indentation .
three indentations were made for each specimen to get average micro - hardness value and mean and standard deviation ( mean  sd ) for each group was calculated .
gc tooth mousse was then applied to specimens of groups a and b according to manufacturers instructions for a period of 2 weeks .
after the recommended time period , 3 min daily , the teeth were removed from the solution washed with de - ionized distilled water and placed in artificial saliva for the reminder of the 24 h. after a period of 2 weeks micro - hardness tests were done , and the values were subjected to the variance of analysis of variance and paired t - test .
the extracted teeth were washed thoroughly under running tap water to remove blood , saliva , and other debris .
the teeth were stored in artificial saliva at room temperature till the experiment was started .

 0.053% tricalcium phosphate0.01 n hcl15 ml of sorbitol0.6 gm kcl0.42 gm nacl0.026 gm magnesium lactate0.05 m naoh5 ml of 0.2 m sodium phosphatedistilled water
. 
  0.053% tricalcium phosphate 0.026 gm magnesium lactate 5 ml of 0.2 m sodium phosphate 100 ml of 0.053% tricalcium phosphate in 0.01n hcl is mixed with 100 ml of a mixture containing 15 ml of sorbitol , 0.6 g kcl , 0.42 g nacl and 0.026 g magnesium lactate . after mixing the two at room temperature the ph was adjusted to 7.4 by 0.05 m naoh and 5 ml of 0.2 m sodium phosphate , was added and made to volume 500 ml .
exact ph was verified using digital ph meter and the mixture was sterilized in an autoclave and stored at 4c .
the teeth were buccolingually sectioned with the help of double faced diamond disk mounted on micro motor with the straight handpiece .
the buccal surface portions of the crowns were mounted using cold - cure acrylic resin .
the specimen were subjected to polishing sequentially using 80 m , 100 m , 200 m , 400 m , grit size of sand papers and finally with diamond polishing paste .
baseline micro - hardness values were recorded and the blocks having the average surface micro - hardness 10% above and 10% below the overall average were discarded .
the specimens were randomly divided into three equal groups ; the grouping of specimens is as follows : 
 group a : ten specimens , exposed to 20% carbamide peroxide gel ( opalescence 20% , gc corp , asia ) for 2 h daily for 1-weekgroup b : ten specimens , exposed to 35% carbamide peroxide gel ( clinex gel 35% vishal dento care , india ) for 30 min daily for 1-weekgroup c : ( control group ) ten specimens , exposed to artificial salivagroup ar : postbleached specimens of group a treated with cpp - acp for 3 min daily for a period of 2 weeksgroup br : postbleached specimen of group b treated with cpp - acp for 3 min daily for a period of 2 weeks . 
 
group a : ten specimens , exposed to 20% carbamide peroxide gel ( opalescence 20% , gc corp , asia ) for 2 h daily for 1-week group b : ten specimens , exposed to 35% carbamide peroxide gel ( clinex gel 35% vishal dento care , india ) for 30 min daily for 1-week group c : ( control group ) ten specimens , exposed to artificial saliva group ar : postbleached specimens of group a treated with cpp - acp for 3 min daily for a period of 2 weeks group br : postbleached specimen of group b treated with cpp - acp for 3 min daily for a period of 2 weeks .
groups a and b were exposed to respective concentrations of carbamide peroxide gel daily for the time periods recommended by the manufacturer for 1-week .
after the recommendation time of exposure , daily the teeth were removed from bleaching gels , washed with de - ionized distilled water and placed in artificial saliva for the reminder of 24 h. the procedure was carried out for all specimens for a period of 1-week .
the control group teeth were kept in artificial saliva for the entire period of 1-week .
the micro - hardness test was done using leica vmht - mot micro - hardness tester with vicker 's diamond indenting tool after a period of 1-week under a load of 100 g for a period of 12 s per indentation .
three indentations were made for each specimen to get average micro - hardness value and mean and standard deviation ( mean  sd ) for each group was calculated . percentage of micro - hardness change after the blocks being bleached was calculated .
gc tooth mousse was then applied to specimens of groups a and b according to manufacturers instructions for a period of 2 weeks .
after the recommended time period , 3 min daily , the teeth were removed from the solution washed with de - ionized distilled water and placed in artificial saliva for the reminder of the 24 h. after a period of 2 weeks micro - hardness tests were done , and the values were subjected to the variance of analysis of variance and paired t - test .

 0.053% tricalcium phosphate0.01 n hcl15 ml of sorbitol0.6 gm kcl0.42 gm nacl0.026 gm magnesium lactate0.05 m naoh5 ml of 0.2 m sodium phosphatedistilled water
. 
  0.053% tricalcium phosphate 0.026 gm magnesium lactate 5 ml of 0.2 m sodium phosphate
100 ml of 0.053% tricalcium phosphate in 0.01n hcl is mixed with 100 ml of a mixture containing 15 ml of sorbitol , 0.6 g kcl , 0.42 g nacl and 0.026 g magnesium lactate . after mixing the two at room temperature
the ph was adjusted to 7.4 by 0.05 m naoh and 5 ml of 0.2 m sodium phosphate , was added and made to volume 500 ml .
exact ph was verified using digital ph meter and the mixture was sterilized in an autoclave and stored at 4c .
the teeth were buccolingually sectioned with the help of double faced diamond disk mounted on micro motor with the straight handpiece .
the buccal surface portions of the crowns were mounted using cold - cure acrylic resin .
the specimen were subjected to polishing sequentially using 80 m , 100 m , 200 m , 400 m , grit size of sand papers and finally with diamond polishing paste .
baseline micro - hardness values were recorded and the blocks having the average surface micro - hardness 10% above and 10% below the overall average were discarded .
the specimens were randomly divided into three equal groups ; the grouping of specimens is as follows : 
 group a : ten specimens , exposed to 20% carbamide peroxide gel ( opalescence 20% , gc corp , asia ) for 2 h daily for 1-weekgroup b : ten specimens , exposed to 35% carbamide peroxide gel ( clinex gel 35% vishal dento care , india ) for 30 min daily for 1-weekgroup c : ( control group ) ten specimens , exposed to artificial salivagroup ar : postbleached specimens of group a treated with cpp - acp for 3 min daily for a period of 2 weeksgroup br : postbleached specimen of group b treated with cpp - acp for 3 min daily for a period of 2 weeks . 
 
group a : ten specimens , exposed to 20% carbamide peroxide gel ( opalescence 20% , gc corp , asia ) for 2 h daily for 1-week group b : ten specimens , exposed to 35% carbamide peroxide gel ( clinex gel 35% vishal dento care , india ) for 30 min daily for 1-week group c : ( control group ) ten specimens , exposed to artificial saliva group ar : postbleached specimens of group a treated with cpp - acp for 3 min daily for a period of 2 weeks group br : postbleached specimen of group b treated with cpp - acp for 3 min daily for a period of 2 weeks .
groups a and b were exposed to respective concentrations of carbamide peroxide gel daily for the time periods recommended by the manufacturer for 1-week .
after the recommendation time of exposure , daily the teeth were removed from bleaching gels , washed with de - ionized distilled water and placed in artificial saliva for the reminder of 24 h. the procedure was carried out for all specimens for a period of 1-week .
the control group teeth were kept in artificial saliva for the entire period of 1-week .
the micro - hardness test was done using leica vmht - mot micro - hardness tester with vicker 's diamond indenting tool after a period of 1-week under a load of 100 g for a period of 12 s per indentation .
three indentations were made for each specimen to get average micro - hardness value and mean and standard deviation ( mean  sd ) for each group was calculated . percentage of micro - hardness change after the blocks being bleached was calculated .
gc tooth mousse was then applied to specimens of groups a and b according to manufacturers instructions for a period of 2 weeks .
after the recommended time period , 3 min daily , the teeth were removed from the solution washed with de - ionized distilled water and placed in artificial saliva for the reminder of the 24 h. after a period of 2 weeks micro - hardness tests were done , and the values were subjected to the variance of analysis of variance and paired t - test .
the mean  sd value of control group c is 417.02  10.39 ; the mean  sd value of group a is 382.42  12.14 , the mean  sd value of group b is 346.65  30 .
there is significant reduction of micro - hardness values in both group a ( p = 0.001 ) and group b ( p = 0.001 ) after bleaching when compared to control group c. group b micro - hardness values are lower than group a. percentage of surface hardness in group a was 8.39% and for group b was 17.02% calculated by formula % surface hardness change = 100 ( base surface hardness - surface hardness)/base surface hardness . the mean  sd value of group ar is 386.45  10.43 ; the mean  sd value of group
there is significant increase in mean micro - hardness value in group br ( p = 0.03 ) when compared to postbleach ( group b ) and slight increase , but not significant in group ar ( p = 0.44 ) when compared to postbleach ( group a ) and the values after bleaching are remained less than control group c [ graph 1 ] .
comparison of micro - hardness of pre and postbleaching percentage of surface change is calculated .
the extent of remineralization for group br was more than the group ar [ table 1 ] denoting that the more demineralization , the more remineralization can occur after cpp - acp application [ graph 2 ] .
mean vhn values of microhardness postbleach and application of cpp - acp demineralization and remineralization after casein phosphopeptide - amorphous calcium phosphate application
the mean  sd value of control group c is 417.02  10.39 ; the mean  sd value of group a is 382.42  12.14 , the mean  sd value of group b is 346.65  30 .
there is significant reduction of micro - hardness values in both group a ( p = 0.001 ) and group b ( p = 0.001 ) after bleaching when compared to control group c. group b micro - hardness values are lower than group a. percentage of surface hardness in group a was 8.39% and for group b was 17.02% calculated by formula % surface hardness change = 100 ( base surface hardness - surface hardness)/base surface hardness .
the mean  sd value of group ar is 386.45  10.43 ; the mean  sd value of group br is 372.69  15.61 .
there is significant increase in mean micro - hardness value in group br ( p = 0.03 ) when compared to postbleach ( group b ) and slight increase , but not significant in group ar ( p = 0.44 ) when compared to postbleach ( group a ) and the values after bleaching are remained less than control group c [ graph 1 ] .
comparison of micro - hardness of pre and postbleaching percentage of surface change is calculated .
the extent of remineralization for group br was more than the group ar [ table 1 ] denoting that the more demineralization , the more remineralization can occur after cpp - acp application [ graph 2 ] .
mean vhn values of microhardness postbleach and application of cpp - acp demineralization and remineralization after casein phosphopeptide - amorphous calcium phosphate application
bleaching is an easy and conservative method for treating discolored teeth than veneers and laminations .
introduction of night guard vital bleaching has rekindled a resurgence of interest in tooth bleaching .
bleaching is a decolorization or whitening process that can occur in a solution or on the surface .
the color producing materials are typically organic compounds that possess extended conjugated chains of alternating single or double bonds and often include hetero atoms , carbonyl , and phenyl rings in the conjugated system and are often referred to as chromophore .
bleaching or decolorization of the chromophore can occur by destroying one or more of the double bonds in the conjugated chain or by oxidation of other chemical moieties in the conjugated chains .
carbamide peroxide is an adduct of urea and hydrogen peroxide which on contact with water breaks down to urea and hydrogen peroxide .
the chemistry of this agent is based primarily on its ability to generate free radicals in most solvents .
the hydroxyl radicals lack one electron , are extremely electrophilic and unstable and will attack most other organic molecules to achieve stability generating other radicals .
hydrogen peroxide bleaching can proceed via the perhydroxyl anion or free radicals depending on ph . as the peroxide diffuses into the tooth
, it can react with organic color materials found within the tooth structure leading to a reduction in color .
these oxidation reactions can cause alterations in the enamel structure , calcium and phosphate mineral loss , and pulpal sensitivity .
the results of these studies which are in accordance with the studies done by majeed et al .
, flaitz and hicks showed clearly that the application of carbamide peroxide bleaching gel lowered the micro - hardness of the enamel and also showed the changes in enamel are directly proportional to concentration of bleaching agent which are in similar to the studies done by hegedus et al .
the oral environment can naturally rebuild enamel through a process called as remineralization , to some extent on its own , but the extent of remineralization is controlled by ph and the amount and availability of calcium and phosphate ions .
the minimum thermodynamic requirement for remineralization to occur is simply that the ion activity product is greater than the solubility product constant for tooth mineral .
solubility constraints limit the level of supersaturation and forms calcium phosphate mineral , therefore , limit mineral ion concentration in remineralizing solutions to a relatively low level
. a considerably large volume of remineralizing solution is required to supply the needed mineral ions , suggesting that remineralization in vivo is a relatively slow kinetic reaction .
casein phosphopeptides are multi phosphorylated from an enzymatic digest of the bovine milk protein casein .
these peptides have remarkable ability to stabilize the calcium phosphate in solution as amorphous calcium phosphate ( acp ) , through their multi phosphoryl residues cpp bind to forming nanoclusters of acp in metastable solution , preventing their growth to critical size required for nucleation and phase transformation .
cpp - acp nanoclusters have shown to localize at the tooth surface , which buffers free calcium and phosphate ion activities by helping to maintain a state of supersaturation with respect to tooth enamel depressing demineralization and enhancing remineralization .
the results of this study showed that there was a definitive increase in microhardness when compared to the postbleach hardness even after the specimens are maintained in artificial saliva . at normal oral ph and temperature
, the addition of acp components to the salivary system can cause the hydrolysis of acp into apatite within a few minutes , which is roughly 20,000 times faster than normal .
the susceptibility of bleached enamel to caries is still a topic of study , but precautions should be taken as remineralization is a slow process in vivo .
the advanced whitening technologies containing cpp - acp as component are marketed , but the efficacy of the agents has to be determined .
milk protein casein can cause allergic reactions in sensitive people , so judicial use of this material is recommended keeping this matter of concern in view .
higher concentrations of carbamide peroxide bleaching gels had a definite effect of reducing the surface micro - hardness of sound enamel to significant levels .
the enhancing potential of cpp - acp is in direct correlation with a degree of demineralization of enamel .
the importance of bleaching as a conservative treatment option for the discolored teeth when compared to veneers and laminates can not be undervalued , but must be used with caution and postbleaching regimen with cpp - acp are worth consideration .
further research for the better remineralizing material should be done as the micro - harness values had not reached the baseline values .
 objective : the aim of this study was to evaluate the potential of casein phosphopeptide - amorphous calcium phosphate ( cpp - acp ) in remineralizing the bleached enamel surface using micro-hardness.materials and methods : thirty human enamel slabs were randomly divided into three groups ( n = 10 ) . groups a and b were exposed to 20% carbamide peroxide and 35% carbamide peroxide gel , respectively . after the exposure to the bleaching agent , the slabs were kept in artificial saliva for 1-week . 
 group c ( control group ) were kept in artificial saliva for 1-week . 
 vickers micro - hardness test was performed by leica vmht - mot micro - hardness tester . 
 cpp - acp ( gc tooth mousse , melbourne , australia ) was then applied to specimens of groups a and b for 3 min for 2 weeks . 
 micro - hardness values of postbleach group a ( ar ) and group b ( br ) were recorded and statistically analyzed by paired t - test and one - way analysis of variance at the significance level of  = 0.05.results:there was a significant decrease in micro - hardness of enamel in carbamide peroxide bleached groups . 
 however , there was a significant increase in micro - hardness after the remineralization by cpp - acp and the extent of remineralization is more for the group b.conclusions:that bleaching agents reduced enamel micro - hardness and the use of cpp - acp after bleaching can significantly enhance the micro - hardness of bleached enamel . 
Materials and Methods
Specimen preparation
Preparation of artificial saliva
Composition
Preparation
Procedure
Results
Postbleaching
After remineralization of bleached tooth
Discussion
Conclusions
Financial support and sponsorship
Conflicts of interest