the use of bleaching materials both hydrogen peroxide and carbamide peroxide has become an attractive procedure in the dental clinic . furthermore , the use of fluoride - releasing glass ionomer as a dental restorative material has also become popular . the situation where these materials interact within the oral cavity during the bleaching process can occur frequently ; thus , understanding their reaction is important . the bleaching process is believed to occur through oxidation by hydroxyl radicals that are generated from the bleaching agent . with clinically favorable and safe aspects for patients , several studies have shown the effectiveness of bleaching agents on dental restorative materials and teeth with regard to surface hardness , or other modifications . during setting of glass ionomer , fluoride ions are produced from strong soluble aluminofluoride complexes like alf . when a fully set glass ionomer is exposed to neutral aqueous solutions , it absorbs water and releases ions such as sodium , silica , calcium , and fluoride . two processes occur during fluoride release : a fast elution process during the early periods , and a long - term diffusive process . it is also influenced by experimental factors , i.e. , storage media , frequency of change of the storage solution , composition and ph - value of saliva , plaque , and pellicle formation . in vitro , fluoride release increases in acidic media ; this was explained by the fact that decreasing ph increases the dissolution of the material leading to a higher fluoride level in acidic immersion . thereby , the proportion of free fluoride to bound fluoride was higher under acidic than under neutral conditions . when hydrogen peroxide is stored , an acidic ph must be maintained to extend the shelf life . they found that at home bleaching products have a ph range from 5.66 to 7.3 . while they found ph of in - office bleaching system were lower and ranged from 3.6 to 6.5 . when hydrogen peroxide interacts with dental materials , it decomposes to form hydroxyl radical intermediates and finally to form water and oxygen . also , carbamide peroxide will dissociate to h2o2 , co2 , urea and nh3 , and then h2o2 will decompose again to water and oxygen finally . those chemical ingredients may affect the fluoride release of glass ionomer restoratives . the purpose of this study was to evaluate the effect of vital bleaching on the fluoride release of various types of glass ionomer restorations . also , to compare the fluoride release of various types of glass ionomer restorations . two vital bleaching commercial products and three types of glass ionomer restorative materials were selected for this study . bleaching materials used were opalescence xtra boost ( 38%hydrogen peroxide with ph of 7 ) and opalescence quick ( 35%carbamide peroxide with ph of 6 ) both manufactured by ultradent ( inc . glass ionomer materials used were ketac fil ( conventional glass ionomer ) , photac fil ( resin modified glass ionomer ) , and f2000 ( poly acid modified composite resin ) manufactured by 3 m ( espe , st paul , usa ) . thirty disk shaped specimens ( 5 mm in diameter and 2 mm in thickness ) were prepared for each brand of glass ionomer . the mold was sandwiched between two glass plates to allow setting of glass ionomer under pressure . capsules of ketac fil were activated then triturated according to manufacturer instructions for 15 s , injected in the holes of the mold in one increment . the mold was filled to slight excess , the specimen 's top surface was covered by a mylar strip and a glass slide was secured to flatten the surface and pressed with standard load 500 mg over the mold then left for setting . capsules of both photac fil and f2000 were triturated according to manufacturer instructions for 15 s and injected into holes , covered with glass slide , and light cured for 40 s per each side using a light source ( pencure , j morita mfg corp . , each disk specimen was removed from the mold by separating its two halves and placed in a numerated plastic tube containing 5 ml of distilled water , tightly sealed with a cap . the specimens were incubated at 37c during the whole experimental period ( 3 months ) . after 24 h each group was further subdivided into three sub - groups , 10 samples for each group . the first sub group was a control group , the second sub group was bleached with opalescence xtra ( ox ) , and the last one was bleached with opalescence quick ( oq ) . second and third subgroups were bleached with the two bleaching agents ox and oq according to their manufacturer instructions , every sample was covered with 2 ml of the bleaching material and left for 1 h. disks were then washed thoroughly with distilled water , and then returned back to their tubes . control samples ( the first sub group ) returned back to the tubes after water in the tubes of all subgroups being changed with new 5 ml of distilled water . the measurements were performed after 1 week , 1 month , and 3 months and every time , samples were rinsed with distilled water and water in the tubes changed with new 5 ml of distilled water . fluoride release measurements were performed using specific ion electrode ( ph meter f-22  horiba  ) after adding total ionic strength adjustment buffer ( tisab ) solution . data were recorded and analyzed by using one - way analysis of variance ( anova ) followed by bonferroni multiple comparison post hoc test at the significance level of  = 0.05 . the analysis of variance was carried out considering the factors ( material , time , and interaction ) . data were recorded and analyzed by using one - way analysis of variance ( anova ) followed by bonferroni multiple comparison post hoc test at the significance level of  = 0.05 . the analysis of variance was carried out considering the factors ( material , time , and interaction ) . time had highly significant effect on fluoride released from all glass ionomer materials under test at p < 0.05 [ table 1 ] . ketac fil showed initial burst in fluoride release in the first week ( t1 ) of 58.6 ppm , then concentration of fluoride decreased sharply after 1 month ( t2 ) of 10.94 ppm . after 3 months ( t3 ) , the concentration of fluoride decreased again of 5.94 ppm [ figure 1 ] . for photac fil , time had only a significant effect on fluoride release [ figure 2 ] . fluoride release of f2000 was also affected by time and this was highly significant [ figure 3 ] . effect of time on fluoride release for three types of glass ionomer materials mean fluoride concentration of ketac fil as affected by time . studying fluoride release as affected by the type of glass ionomer material regardless the type of bleaching and time ; the result was highly significant at p < 0.01 . comparing the three brands ; there was no significant difference at p > 0.05 in fluoride release considering only the type of bleaching regardless type of glass ionomer and time . a significant increase in the mean fluoride released from ketac fil bleached with opalescence xtra compared to the untreated control group and the group bleached with opalescence quick . for photac fil , opalescence xtra caused slight increase in fluoride release while no significant differences in fluoride release were found after bleaching f2000 . according to the type of bleaching and the time , highly significant difference was found between the tested materials at p < 0.01 . the use of hydrogen peroxide or peroxide releasing agents , such as carbamide peroxide or sodium perborate for brightening discolored teeth has become a popular treatment modality . glass ionomers are often used for restoration of cervical lesions because of bonding to tooth structure and releasing fluoride . the influence of various bleaching agents on physical properties , surface morphology , and color of different restorative materials has been investigated in several in vitro studies simulating the clinical situation as closely as possible . in our study , it was found that the effect of bleaching on fluoride release of glass ionomer is material dependent depends on the type of bleaching material and the type of glass ionomer . moreover , time factor was found to have an essential role . the high initial fluoride effect was only observed with ketac fil and photac fil after 1 week and dropped sharply by the second period after 1 month . this finding is in agreement with previous studies which may be attributed to the high instability and erosion of glass ionomer during the early setting period . those studies have shown that the cumulative amount of fluoride ions released from glass ionomer cements , after a short period of time , is diffusion controlled and follows a decreasing gradient , which is linear to the square root of time . thereby , the initial high amounts of fluoride rapidly decrease after 24 - 72 h and plateaued to a nearly constant level within 10 - 20 days . in contrast significant difference in fluoride release was found between both ketac fil , photac fil , and f2000 but no significant difference was found between ketac fil and photac fil . ranking the three brands according to their fluoride release at the first period of the test ; ketac fill was the material with the greatest rate of fluoride release , followed by photac fill then f2000 . this difference can be explained by the composition of the compomer brands , which exhibited higher fluoride content and contained smaller fillers , which might lead to a better reactivity due to the greater size of the specific surface . however , it was material dependent and depended on the type of bleaching , type of glass ionomer , and time . this effect was highly significant by the first week and did not prolong to other periods of the test . , 1997 who stated that the main daily release of fluoride did not differ significantly between bleaching agent and control . the reason for the contrasting results between the two studies may be attributed to different concentrations of bleaching agents used in both studies . opalescence quick has no significant effect on the fluoride release of the three materials . excluding the ph factor ( as both bleaching materials are close to neutral ) , this can be attributed to that : carbamide peroxide degrades into approximately one - third hydrogen peroxide and two - thirds urea , and hydrogen peroxide can be considered its active ingredient . the hydrogen peroxide content in opalescence quick is therefore much lower than that in opalescence xtra . also opalescence quick has more complicated steps of break down to free radicals than opalescence xtra . this result was in agreement with lee , et al . , 2002 who concluded that hydrogen peroxide has a similar effect on the fluoride release from compomers compared to the case of distilled water . opalescence xtra ( ox ) increased fluoride release from conventional and resin - modified glass ionomers in the first week while the effect faded by time . opalescence quick ( oq ) had no significant effect on the fluoride release of the three materials .
objective : this study was designed to evaluate the effect of two bleaching agents on the fluoride release of three types of glass ionomer materials.materials and methods : a total of 90 specimens of the tested materials ( ketac fil , photac fil and f2000 ) were prepared by a split teflon ring with an internal diameter of 5 mm and thickness of 2 mm . 
 the tested materials were applied and bleached according to manufacturer instructions . 
 fluoride release measurements were made by using specific ion electrode.results:results revealed that bleaching with opalescence xtra caused little increase in fluoride release from ketac fil and photac fil but has no effect on f2000 . 
 however , opalescence quick had no significant effect on the three tested materials.conclusions:bleaching effect on fluoride release is material dependent and time has a significant role on fluoride release .