in recent years , with the introduction of new technologies , dentistry has progressed 
 remarkably , developing and improving new materials . it has reached a stage where it is 
 possible to harmonize the color and reproduce the characteristics of natural teeth , 
 which gives everybody the opportunity to have a beautiful smile . due to these advances , 
 new techniques and materials a wide range 
 of composite resins is now available , which enables the choice for the material that is 
 best suited to each situation , and the correct use of either type of material is 
 indicative of successful treatment . in addition to composite resin restorations , another 
 aesthetic treatment option that has developed greatly is dental bleaching . some are performed 
 in the dental office ( in - office bleaching ) , others are performed by the patient under 
 the dentist 's supervision ( home bleaching ) , and others are associations of both that are 
 held part in office and part at home . the bleaching agents are peroxides , which 
 basically can be hydrogen or carbamide at different concentrations , the latter being 
 used more frequently . with all these resources and techniques , the dentist should also , 
 in addition to mastering the use of restorative materials , be aware of the interactions 
 of composite resins and bleaching agents . ( 2008 ) , when assessing 
 the tensile strength of the composite resin filtek z250 after exposure to the bleaching 
 agents whiteness hp ( 35% hydrogen peroxide ) and whiteness perfect ( 16% carbamide 
 peroxide ) , concluded that the whitening solutions did not affect the composite resin 's 
 tensile strength . cullen , nelson and sandrik ( 1993 ) also concluded that peroxide bleaching did not affect this 
 property . in the same year , bailey and swfit jr ( 1992 ) assessed the effects of bleaching agents on composite 
 resins ; by using scanning electron microscopy , they found that there were cracks on the 
 surfaces of the resins exposed to bleaching agents . ( 2002 ) who examined 
 this characteristic in the resins prodigy and silux plus before and after being exposed 
 to different concentrations of carbamide peroxide ( opalescence 20% - 3 h / day , 
 opalescence quick 35% - 1 h / day ) for 14 days . in this study ( 2006 ) investigated the effect of 10% and 35% carbamide 
 peroxide ( opalescence and opalescence quick ) on the surface roughness of two restorative 
 materials ( filtek - a110 and filtek - z250 ) , human enamel and a feldspathic porcelain . the 35% carbamide peroxide gel increased 
 the roughness , not only of the porcelain , but also of the resin filtek - z250 . polydorou , hellwig and auschill 
 ( 2006 ) assessed the effect of home - bleaching agents on the surface texture of different 
 restorative materials ( tetric ceram , tetric flow , enamel plus hfo , filtek supreme , 
 definite and vitablocs mark ii for cerec ) . the samples were divided into two groups ( one 
 polished with sof - lex sandpaper discs and the other group remained unpolished ) and both 
 were bleached with two bleaching agents ( 38% opalescence xtra boost and 15% opalescence 
 pf ) . the results showed that the polished samples were more stable when compared with 
 the unpolished ones , but bleaching did not severely affect the surface texture of the 
 studied materials . ( 2011 ) , a clinical study , that evaluated 
 the surface morphology of enamel and composite resin ( opallis - fgm ) after bleaching for 
 8 days with 16% carbamide peroxide by electron microscopy , only the enamel showed 
 morphological changes . gurgan and yalcin ( 2007 ) evaluated the effects of two bleaching agents ( crest 
 professional whitestrips - 6.5% hydrogen peroxide and vivastyle / vivadent -10% carbamide 
 peroxide ) in relation to surface roughness and microhardness of different restorative 
 materials ( definite , filtek - p60 and filtek flow ) . the results showed that both 
 bleaching agents affected the surface roughness and microhardness of all restorative 
 materials , although the hydrogen peroxide increased the surface roughness more than the 
 carbamide peroxide . ( 2006 ) also evaluated microhardness after immersing the samples in pigmented agents 
 ( wine and coffee ) and then bleaching them with the gels crest night effect , colgate 
 simply white night and opalescence quick . it was observed that the microhardness 
 decreased after immersion in bleaching agent , but with no significant difference between 
 agents . ( 2008 ) also 
 reached this conclusion after assessing the composite resins filtek - z350 and filtek - 
 p60 were exposed to bleaching with 15% carbamide peroxide for 28 consecutive days . in 
 2007 , hannig , et al . assessed the 
 effect of different bleaching techniques on the microhardness of composite resins and 
 polyacid - modified composite resins ( tetric flow , tetric evoceram and compoglas ) . the 
 bleaching agents used were : vivastyle - 10% carbamide peroxide ( 1 h / day ) , whitestrips - 
 6.5% hydrogen peroxide ( 30 min / day ) , sodium perborate mixed with water ( once every 72 
 h ) , simply white - 5.9% hydrogen peroxide ( 1 h / day ) and opalescence xtraboost - 38% 
 hydrogen peroxide ( first and fifth day for 15 min ) . it was concluded that the agents 
 used reduced the microhardness . ( 2009 ) , who compared four different 
 techniques of tooth bleaching ( 7% hydrogen peroxide for 4 h daily for two weeks , 35% 
 hydrogen peroxide for 30 min , 10% carbamide peroxide for 4 h for 2 weeks and 35% 
 carbamide peroxide for 30 min ) with controls where samples of filtek supreme xt 
 ( 3m / espe ) were maintained in artificial saliva for 3 weeks . the fracture resistance of four nanoparticle composite resins ( filtek supreme plus , 
 tetric evoceram , premise and esthet - x ) after exposure to four different concentrations 
 of bleaching gels ( opalescence pf at 10% , 20% , 35% and 45% ) was tested by cho , et 
 al . those authors found 
 that bleaching had a significant effect on increasing the values of fracture resistance 
 for the resin filtek supreme plus , but not for the other resins . el - murr , ruel and 
 st - georges ( 2011 ) conducted a 
 review on the effects of external bleaching on restorative materials and found that when 
 it comes to composite resin , several studies have shown that bleaching agents have the 
 potential to alter the physical properties of the restorations , but not yet demonstrated 
 the clinical relevance that these changes may have . taking into account that a common clinical situation is the presence of composite resin 
 restorations in teeth that are exposed to the action of bleaching agents , this study is 
 justified and had the aim of investigating the effects of carbamide peroxide bleaching 
 agents on resin composition by the analysis of ion release . the possible hypotheses were 
 the null hypothesis that the bleaching agents do not affect the chemical integrity of 
 the evaluated composite resin , and the alternative hypothesis that the bleaching agents 
 cause the release of ions from the evaluated resin and thus lead to its chemical 
 degradation . in order to carry out this study , samples ( 4 mm in diameter and 2 mm thick ) of the 
 microhybrid composite resin filtek - z250 ( 3 m espe , st . two 10% carbamide peroxide bleaching agents were used : a 
 commercial product ( opalescence ; ultradent products inc . , south jordan , utah , usa ) and a 
 compounded bleaching agent obtained from a compounding pharmacy ( dermapele , santa maria , 
 rs , brazil ) ( figure 1 ) . after preparation , the samples were stored in glass jars 
 individually numbered and containing milli - q water for an initial period of 7 days and 
 then divided into three groups ( n=10 ) : group i : exposed to the commercial bleaching 
 agent , group ii : exposed to the compounded bleaching agent , and group iii ( control , 
 immersed in milli - q water without exposure to bleaching agents ) . after the initial 7 
 days in milli - q water , the samples of groups i and ii were exposed to the commercial and 
 compounded bleaching agents , respectively , in the same manner . one drop of bleaching 
 agent was delivered in each one of 10 numbered spots marked on a large petri dish and 
 one composite resin sample was placed on top of each drop . the samples were covered with 
 gauze slightly moistened with milli - q water and the petri dish was capped in order to 
 keep the samples moist , preventing dehydration and surface alterations , when placed in 
 an oven at 37c . after 8 h of daily treatment , the samples were cleaned with a soft 
 brush and water to remove the bleaching agents and were stored in their respective jars 
 containing milli - q water at 37c for 16 h. this protocol was repeated daily during 14 
 days . bleaching agent , composition and manufacturer analysis of ion release from resin was carried out by spectrophotometry before and after 
 14 days of exposure to the agents . water was collected from the jars containing the 
 samples and taken for analysis in the hp 8453 spectrophotometer diode array . the nominal 
 values of ion release were recorded on spreadsheets and analyzed using spss ( statistical 
 package for social sciences , version 18.0 ; chicago , il , usa ) . normality of distribution 
 was verified with the shapiro - wilk and levene 's test for homoscedasticity . data 
 regarding ion release were ranked and compared between the 3 groups by anova and tukey 's 
 post - hoc test . the release of ions in each group was compared 
 between the two experimental periods ( baseline and after 14 days ) using paired t - tests . table 1 shows the values obtained after 
 statistical analysis of the groups at two experimental periods , i.e. before ( baseline ) 
 and after 14 days of exposure of the composite to different bleaching agents . it can be 
 observed that the ion release from composite resin did not differ among the three 
 treatments at baseline . however , when analyzed after 14 days of exposure , there was a 
 statistically significant difference between the group exposed to the compounded 
 bleaching agent ( group ii ) and group iii ( control ) and the group exposed to the 
 commercial bleaching agent ( group i ) . after 14 days , the group exposed to the compounded 
 bleaching agent presented a significantly greater ion release from composite resin 
 ( 0.023 ) than the control group ( 0.005 ) and the group exposed to opalescence ( 0.010 ) . the 
 release of ions from the composite resin in the control group was significantly higher 
 at the baseline ( 0.007 ) than at 14 days ( 0.005 ) , which means that it decreased over 
 time . in the group exposed to opalescence , ion release increased over time , but this was 
 not statistically significant . however , the release of ions from the composite resin 
 exposed to bleaching agent prepared at the compounding pharmacy increased significantly 
 comparing baseline values ( 0.001 ) and 14-day ( 0.023 ) values . analyses of the values of ion release from the composite resin according to the 
 exposure time for each row , lower case letters indicate a significant diference between 
 treatments within the same experimental period for each column , different capital letters indicate a significant diference 
 between the experimental periods while maintaining yhe same treatment ion release at baseline , where no sample had been exposed to bleaching agents , did not 
 have any statistically significant difference among the three groups . after 14 days , the 
 samples belonging to the non - bleached group ( control ) presented a statistically 
 significant decrease in ion release values . this can be explained by the fact that the 
 polymerization reaction of composite resins continues after the light source is removed . ( 1991 ) also showed that 
 residual monomers of bis - gma and tegdma remain attached to the matrix , even after 7 days 
 of immersion of the composite resin in water at 37c . during this period it is possible 
 to observe a certain amount of accumulation of inorganic portion of displaced material . anusavice ( 2003 ) stated that a 
 composite resin restoration that has just been cured and polished can still have more 
 than 50% of unreacted methacrylate groups , which may be released from the material . this 
 fact is in agreement with oysaed and ruyter ( 1986 ) who argued that during the first 3 months after curing , 
 the solubilization of a composite resin is more intense , decreasing gradually over 
 time . after 14 days of exposure to the bleaching treatments , the group in which an compounded 
 agent was used had a statistically significant increase in the amount of ion release 
 compared to baseline , and the group exposed to the commercial bleaching agent 
 ( opalescence ) had an increase , but it was not considered statistically significant . although no other studies assessing ion release from composite resins exposed to 
 bleaching agents were found , the results can be justified by the characteristics 
 inherent to the chemical formulation of whitening agents themselves . although the 
 chemical carbamide peroxide is the same in both bleaching agents , the characteristics of 
 each formulation and the more accurate quality control in manufacturing the commercial 
 product ( opalescence ) makes it safer or less aggressive , while the bleaching agent 
 prepared at the compounding pharmacy had more chance of variations related to the 
 production process , resulting in deleterious effects of various magnitudes . a study by bailey and swift junior 
 ( 1992 ) showed that the action of bleaching agents produced cracks in the surface of the 
 composite resins . ( 2006 ) , polydorou , hellwig and auschill ( 2006 ) and gurgan and yalcin ( 2007 ) showed that the resins are degraded when exposed to 10% 
 carbamide peroxide bleaching agents , which can be evidenced by the increased surface 
 roughness of resin composites when exposed to bleaching treatments . ( 2002 ) indicated 
 that the surface roughness remained constant before and after bleaching with hydrogen 
 peroxide . several authors evaluated the 
 microhardness of composite resins exposed to bleaching agents and found statistically 
 significant decreases in relation to this property . ( 2009 ) did not achieve the same result , 
 as the bleaching treatments did not alter the microhardness of the direct restorative 
 material . ( 2009 ) found 
 that the values of fracture resistance of various composites increased after exposure to 
 different concentrations of a bleaching agent . this shows that so far there is no 
 consensus about whether there are deleterious effects of carbamide peroxide bleaching 
 agents on composite resins but there is a strong trend indicating that they are not 
 harmless . this study found that after 14 days of exposure of the composite resin tested 
 led to the intensification of ion release of this material , which can accelerate 
 chemical degradation . the clinical relevance of the results of this study is the fact 
 that , as chemicals , both bleaching agents showed effects related to chemical degradation 
 of the composite resin , which , when added to other chemical and physical exposures , can 
 often lead to the premature failure of composite resin aesthetics . this leads the 
 authors to suggest avoidance of excessive and indiscriminate exposure of composite 
 resins restorations to 10% carbamide peroxide bleaching agents , especially when the 
 origin and manufacturing process are not strictly controlled . further studies should be 
 carried out to assess the impact that these findings may have on the long - term 
 performance of these materials considering that resins are widely used in adhesive 
 restorative dentistry . from the results of this in vitro study , it was concluded that : after 14 days of treatment , a statistically significant increase occurred in the amount 
 of ions released from the composite resin exposed to the compounded bleaching agent 
 compared with the control and the commercial product , which demonstrates its more 
 aggressive effect on the restorative material . the result leads us to reject the null hypothesis because the bleaching agents affected 
 the chemical integrity of the composite and leads us to partially confirm the 
 alternative hypothesis because significant difference was observed only for the 
 compounded bleaching agent .
objectivethis in vitro study evaluated the influence of two 10% carbamide 
 peroxide bleaching agents - a commercial product ( opalescence pf ; ultradent 
 products , inc . ) and a bleaching agent prepared in a compounding pharmacy - on the 
 chemical degradation of a light - activated composite resin by determining its 
 release of ions before and after exposure to the agents . 
 material and methodsthirty composite resin ( filtek z250 ; 3m / espe ) samples were divided into three 
 groups : group i ( exposed to opalescence pf commercial bleaching agent ) , group ii 
 ( exposed to a compounded bleaching agent ) and group iii ( control - milli - q water ) . 
 after 14 days of exposure , with a protocol of 8 h of daily exposure to the 
 bleaching agents and 16 h of immersion in milli - q water , the analysis of ion 
 release was carried out using a hp 8453 spectrophotometer . 
 the values were 
 analyzed statistically by anova , tukey 's test and the paired t - tests . 
 the 
 significance level was set at 5% . 
 resultsafter 14 days of the experiment , statistically significant difference was found 
 between group ii and groups i and iii , with greater ion release from the composite 
 resin in group ii . 
 conclusionsthe compounded bleaching agent had a more aggressive effect on the composite resin 
 after 14 days of exposure than the commercial product and the control ( no 
 bleaching ) .