resin composites have been classified according to various characteristics , such as size , content , and filler type , and the physical and mechanical properties of the materials .
nanotechnology , known as molecular nanotechnology or molecular engineering , is the production of functional materials and structures , at a range of 0.1 - 100 nm , by various physical and chemical methods .
a nanohybrid is a hybrid resin composite with nanofiller in a prepolymerized filler form , whereas nanofill is a composite resin that is composed of both nanomers and nanoclusters .
the success of dental restorations depends on their compressive , diametral tensile and flexural strength , wear and fracture resistance , and polish retention .
moreover , the esthetics of restorative materials should mimic the appearance of natural teeth , which is directly related to color matching and color stability .
however , when exposed to the oral environment , restorative composites have a tendency to discolor .
intrinsic factors , such as the resin matrix of composites and incomplete polymerization , have a considerable influence on color stability .
this is usually attributed to chemical degeneration of the filler - resin bond and the solubility of the resin matrix .
extrinsic factors such as adsorption or absorption of extrinsic stains , on the other hand , are still a major problem with esthetic restorations .
the degree of color change is affected by a number of factors , including water sorption , chemical reactivity , dietary and smoking habits , bad oral hygiene , and surface smoothness of the restoration .
besides the composition of the materials , the characteristics of the particles and the finishing and polishing procedures have a direct effect on surface smoothness and susceptibility to extrinsic staining .
roughening of the surface caused by wear and chemical degradation may also affect the gloss and consequently increase extrinsic staining .
water sorption may cause softening of the resin matrix , degradation of resin , reduction of stain resistance , and changes in translucency .
the longevity and esthetic appearance of tooth - colored dental restorative materials greatly depend on the quality of the finishing and polishing techniques used .
high - quality finishing and polishing improve both the esthetics and the longevity of composite restorations , whereas rough , poorly polished surfaces contribute to staining , plaque accumulation , gingival irritation , recurrent caries , and discoloration of the restoration .
the aim of this in vitro study was to evaluate the effect of drinks on color stability and surface roughness of nanocomposites . in this context
, laboratory tests were performed to assess the performance of nanocomposites in direct contact with different substances that are part of the daily diet .
the null hypothesis is that the drinks ( red wine , grape juice , and acai juice ) have no effect on susceptibility to staining and the surface roughness of nanocomposites resins .
two commercially available resin composite products , chosen for their different types of filler particles , were used in this study [ table 1 ] . the commercial brand name , composition , and manufacturer of the materials used in the study forty circular samples were prepared 2.5 mm thick and 6 mm in diameter .
uncured resin composite samples were prepared by condensing them into a teflon ring mold in two increments according to the manufacturer 's instructions . after inserting the second increment of material into the mold ,
a polyester strip was pressed onto the surface of the mold with a glass plate in order to obtain a flat surface without bubble formation ; excess material was extruded by pressing a glass plate onto the mold with a 500-g weight on top over the resin composite / matrix ensemble , producing specimens with a smooth flat surface .
the specimens were light polymerized for 20 s on each increment using conventional quartz halogen tungsten light ( optilight plus / gnatus ) .
the distance between the light source and the specimen was standardized using a 1-mm glass slide .
the specimens were taken out of the mold immediately after the light - curing cycle and were stored in distilled water for 24 h. the specimens were finished and polished successively with the sof - lex system ( 3 m espe , st .
paul , mn , usa ) , color - coded from dark ( coarse ) to light ( superfine ) : coarse ( 5 s ) , medium ( 5 s ) , fine ( 20 s ) , and superfine ( 20 s ) . each disk was used twice in a low - speed hand piece ; they were rinsed briefly in distilled water ( 10 s ) and dried with paper towels between each grit .
the specimens were polished with felt discs ( fgm , joinville , sc , bra ) and diamond excel paste ( fgm , joinville , sc , bra ) for 20 s. the specimens were then washed with distilled water for 30 s , dried with paper towels and immersed in distilled water for 24 h at 37c .
specimens were randomized to four groups according to the storage solution : ( 1 ) distilled water ( control group ) ; ( 2 ) acai juice ; ( 3 ) grape juice ; and ( 4 ) red wine .
the ph of the solutions was verified using a ph meter ( pht ; t-1000 , tekna ind / com ltda , so bernardo do campo , sp , brazil ) , which indicated that the ph did not change during the period of treatment .
all the procedures were carried out by the same operator at room temperature ( 25c ) and relative humidity of 50% .
type , batch number , ph , and manufacturers of the immersion solutions after this treatment , the specimens were evaluated for surface roughness .
the average surface roughness ( ra , m ) was measured with a surface profilometer ( surftest sj-301 , mitutoyo , japan ) using a tracing length of 1.25 mm and a cutoff of 0.25 mm to maximize filtration surface waviness , and a measuring speed of 0.5 mm / s using tools 301 , mitutoyo , japan .
each specimen was measured 3 times at different locations and in different directions near the center of the specimen , and the average roughness , ra , was derived from these readings .
a calibration block was used periodically to check the performance of the profilometer , and all test procedures were performed by only one operator .
color values were recorded in sequence using a digital spectrophotometer ( vita easyshade , vita zahnfabrik , bad sckingen , germany ) .
the spectrophotometer measured the tooth color based on the ciel*a*b * color space system , which allows the color to be determined in three - dimensional space .
l * represents the value ( lightness or darkness ) . the a * value is a measure of redness ( positive a * ) or greenness ( negative a * ) .
the b * value is a measure of yellowness ( positive b * ) or blueness ( negative b * ) .
the color difference ( e ) between the color coordinates was calculated by applying the formula e * = [ ( l * ) + ( a * ) + ( b * ) ] in order to compare values before and after the storage treatment .
three measurements were taken with the active point of the spectrophotometer in the center of each specimen , and thus the instrument automatically averaged the three readings for each specimen , which was then used for the overall data analysis .
the roughness and the color were measured before ( baseline ) and 1 , 2 , 4 , 8 , and 12 weeks after storage in the different liquids , and after repolishing . for each group ,
the specimens were kept immersed in the respective solutions for 4 h daily over a period of 12 weeks .
these solutions were renewed daily and after the immersion period , the specimens were washed and stored in distilled water . at the end of the periods of immersion ,
the values of the optical properties and surface roughness were tabulated and subjected to statistical analysis ( spss for windows , version 13.0 ; spss inc . , chicago , il , usa ) using the paired t - test , one - way analysis of variance , and the tukey test and the independent sample t - test ( p < 0.05 ) .
for filtek z350 xt , when each group was compared over time , acai juice ( p = 0.003 ) , grape juice ( p = 0.03 ) , and red wine ( p = 0.003 ) presented statistically significant changes in the color of the resin from the 2 week ; distilled water did not show a significant change ( p > 0.05 ) .
the specimens in distilled water did present differences after 8 weeks of immersion ( p = 0.002 ) .
a decrease in staining was observed after repolishing in all groups ( acai juice , p = 0.001 ; grape juice , p = 0.000 ; wine , p = 0.007 ) , except the distilled water group ( p > 0.05 ) ; the average staining for the distilled water group was much lower than that in the other groups throughout the experiment .
when the filtek z350 xt groups were compared at each time point , there was no statistically significant difference between the distilled water group and the acai juice group ( p = 0.17 ) , although there are numerical differences in the averages ; these groups showed less staining compared with the other groups .
there was also no significant difference between the grape juice and red wine groups ( p = 0.51 ) , however , they presented a statistically significant difference compared with the distilled water and acai juice groups ( p = 0.000 ) , which stained less .
after repolishing , there was a decrease in the mean staining at 12 weeks , although the pattern of the differences between the groups remained ( p = 0.000 ) [ table 3 ] ; water and acai juice stained less and grape juice and red wine stained more .
after repolishing , the staining was similar to the reading at the 2 week for the distilled water and acai groups . for grape juice and red wine ,
means and standard deviations for the color difference ( e ) between the specimens immersed in different beverages for evolu - x , acai juice ( p = 0.008 ) , grape juice ( p = 0.003 ) , and red wine ( p = 0.003 ) presented statistically significant changes in the color of the resin from the 2 week ; there was no change in the control group ( p > 0.05 ) .
the color for the distilled water group changed after 12 weeks ( p = 0.016 ) .
there was a decrease in the staining after repolishing for the grape juice ( p = 0.001 ) and red wine groups ( p = 0.000 ) , however , the distilled water and acai juice groups did not have a statistically significant decrease in staining ( p > 0.05 ) , even though the average value of staining in these groups was much less than in others .
there was no significant difference between the grape juice and red wine groups in the first 4 weeks ( p > 0.05 ) ; however , the difference was statistically significant compared with the distilled water and acai juice groups ( p = 0.000 ) . from week 8 , the red wine group showed more staining than the grape juice group ( p = 0.000 ) .
however , there was no significant difference between the distilled water and acai juice groups ( p > 0.05 ) and they showed less staining than the other groups .
after repolishing , the mean amount of staining decreased compared with the values at 12 weeks , although the pattern of the differences between the groups remained the same ( p = 0.000 ) [ table 3 ] ; water and acai juice stained less and grape juice and red wine stained more .
after repolishing , the staining pattern for the acai juice group was similar to that of the 1 week .
for the distilled water , grape juice and red wine groups , the staining pattern was similar to that at the 2 week . comparing the two resins , from the 1 week
it was found that the evolu - x specimens immersed in grape juice stained less than the filtek z350 xt specimens ( p = 0.014 ) .
this pattern continued in weeks 2 ( p = 0.020 ) , 4 ( p = 0.024 ) , 8 ( p = 0.017 ) , and 12 ( p = 0.011 ) and after repolishing ( p = 0.002 ) . samples of evolu - x resin immersed in red wine differed from the filtek z350 xt samples after 2 weeks ( p = 0.026 ) and after repolishing ( p = 0.002 ) . for the acai juice group ,
there was a difference between the composites ( p = 0.000 ) after week 12 and after repolishing ( p = 0.011 ) .
the filtek z350 xt specimens showed a difference in the roughness of the red wine group after 12 weeks of immersion ( p = 0.009 ) , but this difference was reversed after repolishing .
after 8 weeks of immersion , there was no difference in the roughness of the samples immersed in different media ( p > 0.05 ) .
after 12 weeks , the samples immersed in red wine had greater roughness than the samples immersed in grape juice ( p = 0.005 ) , and this difference was reversed after repolishing [ table 4 ] .
means and standard deviations for surface roughness measurements for the specimens immersed in different beverages for evolu - x , there was a statistically significant increase in the roughness of the red wine group from the 1 week ( p = 0.03 ) and the acai juice group from the 2 week of immersion ( p = 0.039 ) .
after 2 weeks of immersion , there was a difference in roughness when the different groups were compared ( p = 0.001 ) .
however , there was no significant difference between the distilled water and grape juice groups ; the acai juice and red wine groups also did not show a statistically significant difference ( p > 0.05 ) .
comparing the surface roughness of the two resins , evolu - x had lower roughness than filtek z350 xt ( initial , p = 0.002 ; 1 week after , p = 0.08 ; 12 weeks after , p = 0.025 ) when immersed in distilled water . in the acai juice group ,
the roughness of filtek z350 xt was lower than evolu - x after repolishing ( p = 0.000 ) .
in the grape juice group , filtek z350 xt was less rough in the 4 week ( p = 0.02 ) .
in the red wine group , filtek z350 xt was less rough in the 1 week ( p = 0.007 ) and at week 8 ( p = 0.000 ) .
there were statistical differences on staining susceptibility and the surface roughness of nanocomposites resins . according to color differences in esthetic restorations ,
three different intervals were used to distinguish changes in color values : e < 1 , imperceptible by the human eye ; 1.0 < e < 3.3 , appreciated only by a skilled person , clinically acceptable ; and e > 3.3 , easily observed , not clinically acceptable . the filtek z350 xt and evolu - x resins immersed in distilled water showed clinically acceptable color changes throughout the study .
this observation confirms that water sorption itself did not alter the color of composites to a significant extent because distilled water has no colorant components .
however , both the filtek z350 xt and evolu - x resins immersed in distilled water showed statistically significant changes in color in weeks 8 and 12 , respectively .
the filtek z350 xt samples immersed in acai juice showed clinically acceptable color changes in the first 8 weeks , but at week 12 the color changes were not clinically acceptable .
the evolu - x samples immersed in acai juice showed clinically acceptable staining detectable only by a skilled person ( 1.0 < e < 3.3 ) .
both resins immersed in grape juice and red wine showed clinically unacceptable color changes from week 1 . even after repolishing , both resins showed e > 3.3 for grape juice and red wine ; when these color changes are easily observed , they are not clinically acceptable and replacement of restorations is required .
many studies have demonstrated that resin - based composites are susceptible to staining by common beverages , especially red wine and grape juice . in our study ,
red wine caused the highest discoloration of the restorative materials , followed by grape juice , acai juice , and distilled water .
foods that are rich in anthocyanins , such as blueberries , red grapes , red wine , and acai juice have a strong color .
anthocyanins are water - soluble vacuolar pigments that may appear red , purple , or blue , according to the ph .
it has been reported previously that alcohol causes some degradation on the surface properties of resin composites .
a rougher , degraded surface provides an extensive surface area for adsorption of pigments , thereby leading to more staining .
in addition , it is likely that the lower ph of the grape juice affected the surface of the composite resin , increasing absorption of pigment . throughout the study ,
evolu - x resin showed less staining at the various times and in different immersion media compared with filtek z350 xt .
the susceptibility of the resins to staining may be attributed to the composition of the materials and the characteristics of the particles .
the hydrophilicity and degree of water sorption of a resin matrix could affect the staining susceptibility of resin composites .
if the resin composite can absorb water , then it can also absorb other fluids , which results in discoloration .
water sorption occurs mainly by direct absorption into the resin matrix , whereas glass filler particles do not absorb water into the bulk of the material , but can adsorb water onto the surface .
water sorption of the resin composite may decrease the life of the restoration by expanding and plasticizing the resin component , hydrolyzing the silane , and causing the formation of microcracks .
these microcracks or interfacial gaps at the interface between filler and matrix , allow stains to penetrate and cause discoloration . in this study
, the advantages of nanofills did not seem to render them more stain resistant as described in other studies .
however , studies have shown that nanofill resins stain more than nanohybrid resins and microhybrid resins .
the type of resin matrix used can be a major contributor to the discoloration of the resin composite .
it was found that water uptake in bisphenol - a glycidyl dimethacrylate - based resins increased from 3% to 6% as the proportion of triethylene glycol dimethacrylate ( tegdma ) increased from 0% to 1% , respectively .
this study demonstrated that filtek z350 xt , which includes tegdma , was the most susceptible to staining .
absorption of alcohol molecules contained in beverages into the resin matrix could result in softening of the surface of the composite .
this explains the change in surface roughness of the resin when immersed in red wine .
despite the statistically significant increase in roughness at some points during this study , studies by berger et al . and antonson et al .
showed that the average surface roughness of a resin nanoparticulate after polishing using the sof - lex system was 0.1 and 0.08 , respectively .
yeh et al . showed that the surface roughness of a nanohybrid resin when immersed in distilled water was 0.1 .
thus , with the knowledge that roughness values between 0.06 and 0.1 are within the standard range for these composites , the change in roughness observed in this study does not seem to be relevant .
there is a hypothesis that staining occurs in the most superficial layer of the composite .
thus , repolishing can possibly removing discoloration , and prevent premature replacement of the restoration . in the current study ,
repolishing reduced the discoloration caused by immersion in colored beverages , but was not sufficient to remove the discoloration .
they concluded that staining caused by coffee and red wine was superficial and 20-m wear was sufficient to remove the discoloration .
the solutions tested in this study do not represent all the substances to which restorative materials may be exposed in the oral environment , therefore additional studies are necessary to investigate the color stability of composite resin - based materials .
according to study , it was concluded that : colored drinks promoted color change of filtek z350 xt and evolu - x composites during the studyboth filtek z350 xt and evolu - x resins showed clinically unacceptable color change after immersion in grape juice and red wine , even after repolishing , indicating a need for replacement of the restorationrepolishing was effective in reducing the color change of the composites under study , although always to a clinically acceptable levelin general , evolu - x composite showed less color change than filtek z350 xt composite in the period evaluated and after repolishingthe increase in roughness was reversed after repolishing .
colored drinks promoted color change of filtek z350 xt and evolu - x composites during the study both filtek z350 xt and evolu - x resins showed clinically unacceptable color change after immersion in grape juice and red wine , even after repolishing , indicating a need for replacement of the restoration repolishing was effective in reducing the color change of the composites under study , although always to a clinically acceptable level in general , evolu - x composite showed less color change than filtek z350 xt composite in the period evaluated and after repolishing the increase in roughness was reversed after repolishing .
 objective : the aim was to evaluate the color and surface roughness of nanoparticle ( c1 ) and nanohybrid ( c2 ) composites after immersion in distilled water , acai juice , grape juice and red wine and repolishing.materials and methods : after recording the initial surface roughness and color , the specimens were divided into four groups according to the storage solution . 
 the specimens were reassessed after immersion for 1 , 2 , 4 , 8 , and 12 weeks and after repolishing.results:the results showed that after 2 weeks , there were statistically significant changes in color of both resins in all groups , with the exception of the specimens stored in distilled water ( p > 0.05 ) . 
 only 12 weeks of immersion in red wine changed the roughness of composite c1 ( p = 0.009).conclusions : red wine produced the greatest color change in nanocomposites , followed by grape juice . 
 acai juice made the color unacceptable clinically only after 12 weeks . 
 repolishing reduced the color change in all groups . 
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
CONCLUSION