the development of bleaching agents containing hydrogen peroxide or its precursor , carbamide peroxide , in varying concentrations , ranging from 10 to 38% , has made in - office bleaching effective . although effective bleaching has been achieved in terms of esthetics , the deleterious effects of bleaching agents on the tooth surface have been an area of concern . various scientific reports have demonstrated that changes occur in the surface texture , composition , and microhardness of the enamel , when teeth are bleached with hydrogen peroxide . any attempt to achieve high efficiency dental bleaching with less or no deleterious effects on enamel is a welcome change in dentistry . one such attempt is the addition of vegetative enzymes to the bleaching agent that may promote and accelerate the dissociation of the latter . the present study aims at providing a tooth bleaching formulation containing vegetative enzyme extract obtained from plant tubers . sweet potato ( ipomoea batatas l ) is one such plant tuber , which has a high content of enzymes such as polyphenol peroxidase ( po ) , catalase ( cat ) , and superoxide dismutase ( sod ) . hence , the aim of this in vitro study is to evaluate the color change in teeth bleached with two different concentrations of hydrogen peroxide , using sweet potato extract as an additive , with the help of a spectrophotometer , and furthermore , to evaluate the surface changes in the enamel post bleaching , using a scanning electron microscope ( sem ) . two hundred grams of sweet potato , with purple color flesh , were cleaned , peeled , and cut into cubes . the cubes were smashed to a concentrate with 25 ml of deionized water in a blender and the concentrate was filtered out . one hundred milliliters of the filtered sweet potato concentrate was centrifuged at 2000 rpm for two minutes at a temperature of 4c . twenty - four maxillary central incisor teeth , extracted due to periodontal disease , and free of visible cracks , caries , defects , or decalcification were collected for the study . the teeth were cleaned of calculus and the remaining soft tissue using an ultrasonic scaler ( satelec / acteon suprasson newtron ultrasonic scaler , new jersey , usa ) . the teeth were stored in 0.2% thymol and refrigerated under 4c until use . a tea bag ( 2 g ) ( ranfer tea , colombo , sri lanka ) was suspended in 100 ml of boiling deionized water for five minutes , and the solution was cooled to room temperature . after 24 hours , the teeth were washed and stored under 100% humidity at 37c , until use . the baseline color values of the specimens were measured over a white background using a reflectance spectrophotometer ( x - rite gretag macbeth , berlin , germany ) , which recorded the color variables l , a , b according to the cielfab color system . the teeth were randomly divided into two groups of 12 teeth each , based on the concentration of hydrogen peroxide , as follows : group i ( n = 12 ) - 35% ( h2o2 ) group ii ( n = 12 ) - 10% ( h2o2 ) the roots of all the teeth were sectioned at the cementoenamel junction using a rotating diamond disk under water cooling . then the crowns were sectioned labio - palatally to obtain equal mesial and distal halves . each half was mounted on a self - curing acrylic resin block , leaving the labial surface exposed . one - half of the tooth was bleached with hydrogen peroxide alone ( subgroup a ) and the other half of the same tooth was bleached with a combination of hydrogen peroxide and sweet potato extract ( subgroup b ) , as follows : group ia : ( n = 12 ) 35% hydrogen peroxide solution . group ib : ( n = 12 ) 1 ml of sweet potato extract was blended with 28 ml of ( 100 mm ) phosphate buffered saline ( pbs ) and 1 ml of 35% ( 1 m ) hydrogen peroxide to prepare a solution of 30 ml . group iib : ( n = 12 ) 1 ml of sweet potato extract was blended with 28 ml of pbs ( 100 mm ) and 1 ml of 10% hydrogen peroxide ( 1 m ) to prepare a solution of 30 ml . the specimens in each subgroup were covered with a piece of gauze , saturated with 3 ml of the experimental solution , for a period of 30 minutes , with the bleaching agent being changed every 10 minutes . this bleaching procedure was repeated twice , with a one - week interval , during which time the specimens were stored in artificial saliva at 37c . after carrying out the bleaching protocols , the teeth were rinsed and stored in artificial saliva at 37c for 24 hours . the color of the bleached specimens were then measured over a white background employing a spectrophotometer , which recorded the color variables l , a , b according to the cielab color system . the color change ( e ) was calculated from the l , a , and b values employing the following formula : e = [ ( l ) + ( a ) + ( b ) ] the color change before and after bleaching was taken as an index to evaluate the whiteness after bleaching . data pertaining to color change was analyzed using the student 's t test at a 5% significance level . to evaluate the effect of bleaching solutions on the surface morphology of enamel , all the samples were subjected to scanning electron microscopic analysis ( sem jeol model , jse-5610 lv ) . the specimens were vacuum desiccated first in alcohol and subsequently in acetone , followed by sputter - coating with gold . the entire exposed labial surface was scanned and the most critical areas were selected for sem photomicrographs . two hundred grams of sweet potato , with purple color flesh , were cleaned , peeled , and cut into cubes . the cubes were smashed to a concentrate with 25 ml of deionized water in a blender and the concentrate was filtered out . one hundred milliliters of the filtered sweet potato concentrate was centrifuged at 2000 rpm for two minutes at a temperature of 4c . twenty - four maxillary central incisor teeth , extracted due to periodontal disease , and free of visible cracks , caries , defects , or decalcification were collected for the study . the teeth were cleaned of calculus and the remaining soft tissue using an ultrasonic scaler ( satelec / acteon suprasson newtron ultrasonic scaler , new jersey , usa ) . artificial staining of the teeth as established by suleiman m et al . , was followed in this study . a tea bag ( 2 g ) ( ranfer tea , colombo , sri lanka ) was suspended in 100 ml of boiling deionized water for five minutes , and the solution was cooled to room temperature . the teeth were then immersed in tea solution for 24 hours . after 24 hours , the teeth were washed and stored under 100% humidity at 37c , until use . the baseline color values of the specimens were measured over a white background using a reflectance spectrophotometer ( x - rite gretag macbeth , berlin , germany ) , which recorded the color variables l , a , b according to the cielfab color system . the teeth were randomly divided into two groups of 12 teeth each , based on the concentration of hydrogen peroxide , as follows : group i ( n = 12 ) - 35% ( h2o2 ) group ii ( n = 12 ) - 10% ( h2o2 ) the roots of all the teeth were sectioned at the cementoenamel junction using a rotating diamond disk under water cooling . then the crowns were sectioned labio - palatally to obtain equal mesial and distal halves . each half was mounted on a self - curing acrylic resin block , leaving the labial surface exposed . one - half of the tooth was bleached with hydrogen peroxide alone ( subgroup a ) and the other half of the same tooth was bleached with a combination of hydrogen peroxide and sweet potato extract ( subgroup b ) , as follows : group ia : ( n = 12 ) 35% hydrogen peroxide solution . group ib : ( n = 12 ) 1 ml of sweet potato extract was blended with 28 ml of ( 100 mm ) phosphate buffered saline ( pbs ) and 1 ml of 35% ( 1 m ) hydrogen peroxide to prepare a solution of 30 ml . group iib : ( n = 12 ) 1 ml of sweet potato extract was blended with 28 ml of pbs ( 100 mm ) and 1 ml of 10% hydrogen peroxide ( 1 m ) to prepare a solution of 30 ml . the specimens in each subgroup were covered with a piece of gauze , saturated with 3 ml of the experimental solution , for a period of 30 minutes , with the bleaching agent being changed every 10 minutes . this bleaching procedure was repeated twice , with a one - week interval , during which time the specimens were stored in artificial saliva at 37c . after carrying out the bleaching protocols , the color of the bleached specimens were then measured over a white background employing a spectrophotometer , which recorded the color variables l , a , b according to the cielab color system . the color change ( e ) was calculated from the l , a , and b values employing the following formula : e = [ ( l ) + ( a ) + ( b ) ] the color change before and after bleaching was taken as an index to evaluate the whiteness after bleaching . data pertaining to color change was analyzed using the student 's t test at a 5% significance level . to evaluate the effect of bleaching solutions on the surface morphology of enamel , all the samples were subjected to scanning electron microscopic analysis ( sem jeol model , jse-5610 lv ) . the specimens were vacuum desiccated first in alcohol and subsequently in acetone , followed by sputter - coating with gold . the entire exposed labial surface was scanned and the most critical areas were selected for sem photomicrographs . there was no significant difference between the mean e values of group ia ( 35% h2o2 - 65.24  1.02 ) and group iia ( 10% h2o2 - 64.19  1.88 ) ( p > 0.05 ) . the mean e values of group ib ( 35% h2o2 + sweet potato extract - 72.52  2.03 ) and group iib ( 10% h2o2 + sweet potato extract - 71.50  1.81 ) were significantly higher compared to their respective baseline values ( p < 0.001 ) . the mean e values of groups ib and iib were significantly higher than those of groups ia ( 35% h2o2 - 65.24  1.02 ) and iia ( 10% h2o2 - 64.19  1.88 ) , respectively , ( p < 0.05 ) . there was no statistically significant difference between the mean e values of groups ib and group iib ( p > 0.05 ) . mean e values and standard deviation of the study groups the sem micrographs of group ia [ figure 1a ] and group iia [ figure 1c ] showed a roughened enamel surface , with loss of aprismatic enamel . the sem micrographs of group ib [ figure 1b ] and group iib [ figure 1d ] showed a lesser number of morphological surface irregularities , with an absence of cracks and craters . loss of the aprismatic layer , presence of crater and surface irregularities , ( b ) sem micrograph of group ib ( 35% h2o2 + sweet potato extract ) . lesser number of surface irregularities , with absence of craters and cracks , ( c ) sem micrograph of group iia ( 10% h2o2 ) . loss of aprismatic layer , surface irregularities , cracks and depressions , ( d ) sem micrograph of group iib ( 10% h2o2 + sweet potato extract ) . treatment of discoloration varies from bleaching to even a full coverage restoration , depending on the severity of the stains , with bleaching serving as a more conservative , cost - effective and time - saving procedure . the theory of bleaching involves the release of free radicals from the dissociation of the bleaching agent , which attacks the organic molecules ( stains ) in the teeth to achieve stability . this is followed by a further release of free radicals , which in turn react with the unsaturated bonds of the stains , disrupting the electron conjugation and providing a change in the absorption energy of the organic molecules in the enamel . these disrupted molecules reflect less light , thus making the tooth appear lighter in shade . hydrogen peroxide readily decomposes when it encounters substances with which it can react and results in the release of free radicals . if the bleaching procedure is continued beyond the saturation point , in the course of decomposition , hydrogen peroxide also interacts with the organic components of the tooth , such as proteins and lipids , resulting in their removal . hydrogen peroxide also dissolves the inorganic components of enamel by penetrating the intra- and interprismatic regions . an increased exposure to hydrogen peroxide leads to an increase in its penetration into the enamel . hence , this in vitro study aims at achieving high efficiency dental bleaching , with less or no deleterious effects on the enamel surface . sweet potato contains a plurality of antioxidant molecules , which are either enzymatic or non - enzymatic in nature such as catalase ( cat ) , superoxide dismutase ( sod ) , carotenoids , phenolic compounds , and ascorbic acid . several studies in the field of food chemistry have indicated that these phytochemicals have a high free - radical scavenging activity . in the present study , the cie lab values were used to assess the color change of the bleached enamel . in 1976 , cie recommended the cie lab color scale for use . this scale defined the color more closely to human perception , and thus , provided a standard scale for comparison of color values . a spectrophotometer was selected for the study over a calorimeter , as the latter was designed to measure the color of flat surfaces of objects rather than tooth surfaces , which were not usually flat . also the inter - instrument repeatability with a calorimeter was comparatively poor when compared with intra - instrument repeatability . ( 1998 ) and tung et al . , ( 2002 ) inferred that the colors assessed by the colorimeter and the shade guides were inconsistent . on the other hand , the spectrophotometer not only demonstrated high accuracy and reproducibility similar to the colorimeter , it even performed better than the shade guide assessment . the results of this in vitro study indicated that there was no significant difference in the mean e values of group ia and group iia . leonard et al . , in 1998 , and matis et al . , in 2000 , showed that lower concentrations of carbamide peroxide achieved the same result in whitening teeth , as compared to the higher concentrations , when shade assessment was done after a period of two to six weeks . the addition of sweet potato extract to both 35% ( group ib ) and 10% ( group iib ) of hydrogen peroxide yields significantly higher mean e values , when compared to groups ia and iia , in which no sweet potato extract is added . this can be attributed to the enzymatic action of the catalase present in sweet potato , which , when added to hydrogen peroxide , reduces its high activation energy and increases the rate of release of the free radicals . activation energy is critical to any intended chemical reaction . in order to initiate the reaction , this minimum energy barrier has to be overcome by the reactant molecules , so that the reaction can be activated , whereby , subsequent reaction products can be produced . certain enzymes , when added to the reactant molecules , can reduce the needed level of activation energy and increase the efficiency or rate of the chemical reaction . when catalase is added to hydrogen peroxide in specific concentrations , the enzyme catalase combines temporarily with the hydrogen peroxide molecule forming a catalase - hydrogen peroxide complex . this combination places added stress on the intermolecular bonds holding the substrate molecules together , thereby lowering the activation energy ( 21 kj / mol ) needed to initiate the chemical reaction . owing to this , large quantities of free radicals of hydrogen peroxide are released within a shorter period of time . this in turn reduces the time the bleaching agent is in contact with the tooth , and thus , lessens the possibility of creating grooves or micropores across the surface of the bleached enamel . the effectiveness of bleaching is directly related to exposure time and concentration of the active ingredient . with an increase in the exposure time and concentration , the oxidative process becomes stronger , and hence , the resultant complications become greater  the most common being weakening of the enamel . the sem micrographs of group ib [ figure 1b ] and group iib [ figure 1d ] show lesser number of surface irregularities , with absence of cracks and craters , when compared to group ia [ figure 1a ] and group iia [ figure 1c ] . the lesser enamel surface changes in groups ib and iib may be attributed to the presence of enzymatic and non - enzymatic antioxidants in sweet potato , which exert a scavenging action on free radicals , thus limiting their deleterious effects on the enamel . achieving a smooth enamel surface post bleaching reduces the possibility of stain or pigment deposition within a certain period of time , after bleaching , and the addition of sweet potato extract to hydrogen peroxide enables one to achieve the same . under the limitations of this in vitro study , it can be concluded that the use of hydrogen peroxide ( both 35 and 10% ) containing sweet potato extract , as a bleaching agent , not only results in the restoration of natural tooth color , but also decreases the effects of bleaching on the enamel morphology , compared to the use of hydrogen peroxide alone .
objectives : to evaluate the color change in teeth bleached with two different concentrations of hydrogen peroxide , containing sweet potato extract as an additive , using a spectrophotometer , and to evaluate the surface changes in enamel using a scanning electron microscope ( sem).materials and methods : baseline color values of 24 artificially stained incisors were obtained using a spectrophotometer . 
 the specimens were divided into two groups of 12 teeth , each based on the concentration of hydrogen peroxide ( h2o2 ) as follows : group i  35% h2o2 and group ii  10% h2o2 . 
 one - half of the tooth was bleached with h2o2 alone ( subgroup a ) and the other half was bleached with a combination of h2o2 and sweet potato extract ( subgroup b ) . 
 post bleaching the commission internationale de l eclairage l * , a * , b * ( ciel*a*b * ) values were obtained and e was calculated . 
 the surfaces of the samples were examined using sem.results:the mean e values of groups ib ( 72.52  2.03 ) and iib ( 71.50  1.81 ) were significantly higher than those of groups ia ( 65.24  1.02 ) and iia ( 64.19  1.88 ) , respectively , ( p < 0.05 ) . 
 the sem images of groups ib and iib showed lesser surface irregularities and morphological alterations in enamel.conclusion:the addition of sweet potato extract to hydrogen peroxide not only resulted in the restoration of the natural tooth color , but also decreased the effects of bleaching on the enamel morphology , compared to the use of hydrogen peroxide alone .