material properties and technical approaches are two essential factors that have 
 developed together over time in order to allow for a better clinical performance of 
 composite resin restorations .
composite resins are so far the most esthetic restorative material applied in direct 
 restorations . filler and 
 organic matrix have been modified in an attempt to offer satisfactory mechanical and 
 esthetic characteristics , thus allowing its indication to posterior teeth . in this sense
, nanotechnology has been applied to dentistry , 
 permitting the incorporation of a larger amount of small - sized filler particles in a 
 more homogeneous distribution into organic matrix .
the decreasing filler size over the years resulted in some changes in commercial 
 composites , resulting in different implications to their adequate clinical use and 
 perspectives of success .
since the introduction of nanotechnology , these resins ( 0.1 - 100 
 m ) are classified as nanohybrid , nanomicrohybrid , microybrid , microfilled .
this scenario pointed out to the need 
 for investigating optical and mechanical properties of this new generation of composite 
 resins .
as fillers play a major role to reflect the irradiated light , enhanced esthetic 
 properties were previously verified .
a perspective of improved material is 
 also expected as high mechanical properties are attributed to filler load .
however , it should be highlighted that 
 the particles are not arranged in the same pattern to all nanotechnology materials . 

there are composites with nanofillers , nanoclusters and/or microhybrid particles that 
 are combined in different structures . additionally , a larger surface area of 
 particles with reduced filler size result in a material more prone to water uptake , 
 which can affect negatively its mechanical properties by degradation .
it is believed that as silane - based fillers are susceptible to 
 hydrolytic degradation , it may affect adversely their dynamic mechanical properties over 
 time .
surface roughness and wear tests after simulated toothbrushing have been indicated to 
 assess the mechanical features of restorative materials .
simulated toothbrushing can intentionally provoke a 
 stress in the organic matrix , fillers and their interfaces , and adhere to an assessment 
 of their resistance properties .
as fillers are incorporated into the organic matrix by a chemical treatment of their 
 surfaces , this interface can be stressed and be loosened from the matrix in different 
 patterns . through a three - body 
 abrasive action , toothbrushing provokes a mechanical challenge . in consequence , these 
 particles can be loosed , fractured or the organic matrix can be removed , exposing the 
 particles .
thus , roughness and wear readings can establish a comparison of the 
 performance of these materials .
the aim of this study was to compare mechanical performance of nanotechnology 
 high - density composite resins , according to their dimensions and distribution .
the null 
 hypothesis is that there is no difference of their performance on surface roughness and 
 wear assessments after simulated toothbrushing testing .
this in vitro study was performed involving two factors : material 
 ( in eight levels ) and time ( in two levels ) .
the quantitative response variables were 
 the surface roughness and wear analyzed by profilometry ( m ) .
information of tested composite resins all informations were supplied by the manufacturers not informed by manufactures bis - gma = bisphenol - a - glycidyl methacrylate ; bis - ema = bisphenol - a - ethoxylate 
 glycidyl methacrylate ; bis - pma = bisphenol - a - polyethylene glycoldiether 
 dimethacrylate ; tegdma = triethylene glycol dimethacrylate ; udma = urethane 
 dimethacrylate ten specimens of each material were prepared using a previously lubricated steel 
 stainless mold of 15 mm length x 4 mm in width x 5 mm in height placed over a glass 
 slab and polyester strip ( tdv dental ltda , pomerode , sc , brazil ) .
four individual 
 increments were inserted which were light - cured according to manufacturers ' 
 recommendations , using a halogen lamp vip ( vip , bisco inc , schaumburg , il , usa ) , with 
 irradiance of 600 mw / cm , as measured with a curing radiometer ( curing 
 radiometer - model 100p
the 
 final increment was pressed with a polyester strip ( tdv dental ltda , pomerode , sc , 
 brazil ) and glass slab under a constant axial load of 500 g for 30 s. regardless of 
 the recommended time , the last increment of all composite resins was light - cured for 
 40 s to standardize the surface .
the specimens were removed from the molds and the 
 excess was cut off with a # 12 bard - parker scalpel blade .
thereafter , the specimens were subjected to mechanical polishing in a metallographic 
 polishing machine ( arotec - apl 4 , arotec sa ind . com . , cotia , sp , brazil ) using the 
 sequence of # 600- , # 800- and # 1200-grit silicon - carbide abrasive papers under 
 water - cooling .
polishing was performed under a load of 172 g for 20 s for each 
 granulation .
all specimens were ultrasonically cleaned in deionized water for 10 min 
 and were identified and stored at 37c for 1 week . in order to allow wear analysis , each specimen had half of its surface protected with 
 two layers of nail polish that served as control ( with no abrasion ) .
baseline surface roughness of the specimens was analyzed by a profilometer ( hommel 
 tester t1000 , hommelwerke gmbh , villingen - schwenningen , germany ) accurate to 0.01 mm 
 and was expressed in mm as a ra value .
five records of each specimen were randomly 
 assessed . to record roughness measurements of the surfaces a device containing a 
 diamond needle affixed to the profilometer was used .
the average of five randomized 
 transversal readings was established as the baseline roughness value .
ra range was 
 previously adjusted at 0.01 to 0.8 mm at a cut - off of 0.25 mm .
it allowed 
 controlled performance using soft nylon bristle toothbrush heads ( colgate classic , 
 colgate - palmolive ind .
ltda , so paulo , sp , brazil ) under a load of 300 g and 
 temperature of 37c .
slurry was prepared according to iso specification # 14569 - 1 , 
 mixing 2:1 of deionized water and dentifrice ( colgate total 12 , colgate - palmolive 
 ind .
ltda , so paulo , sp , brazil ) and 0.4 ml amount was injected periodically to 
 renew for fresh slurry . for each specimen ,
a total of 100,000 strokes were performed 
 and toothbrushes were replaced after 50,000 strokes . at the end of the test , each 
 specimen was rinsed under running water and cleaning was completed by sonicating in 
 deionized water for 10 min .
the same 
 profilometer was used ; allowing a needle to run from the protected half ( control ) to 
 the abraded half .
parameters were adjusted to tolerances from 0 to 40 mm , length of 
 assessment at 4.8 mm and cut off of 0.25 mm .
random samples of each tested groups , before and after toothbrushing , were selected 
 for microscopic examination to illustrate possible events .
these specimens were 
 prepared and mounted on metal stubs , sputter coated with gold , and examined under a 
 scanning electron microscope ( jsm t220a , jeol ltd . , peabody , ma , usa ) at 500x 
 magnification .
the assumptions of equality of variances and normal distribution of errors were 
 checked for the tested response variables .
since the assumptions were satisfied , data 
 were subjected to one - way anova and tukey 's post - hoc test for the 
 comparison of initial and final roughness and wear among the materials .
paired t - test 
 was applied for roughness analysis considering a two - time evaluation ( p<0.05 ) .
this in vitro study was performed involving two factors : material 
 ( in eight levels ) and time ( in two levels ) .
the quantitative response variables were 
 the surface roughness and wear analyzed by profilometry ( m ) .
information of tested composite resins all informations were supplied by the manufacturers not informed by manufactures bis - gma = bisphenol - a - glycidyl methacrylate ; bis - ema = bisphenol - a - ethoxylate 
 glycidyl methacrylate ; bis - pma = bisphenol - a - polyethylene glycoldiether 
 dimethacrylate ; tegdma = triethylene glycol dimethacrylate ; udma = urethane 
 dimethacrylate ten specimens of each material were prepared using a previously lubricated steel 
 stainless mold of 15 mm length x 4 mm in width x 5 mm in height placed over a glass 
 slab and polyester strip ( tdv dental ltda , pomerode , sc , brazil ) .
four individual 
 increments were inserted which were light - cured according to manufacturers ' 
 recommendations , using a halogen lamp vip ( vip , bisco inc , schaumburg , il , usa ) , with 
 irradiance of 600 mw / cm , as measured with a curing radiometer ( curing 
 radiometer - model 100p
the 
 final increment was pressed with a polyester strip ( tdv dental ltda , pomerode , sc , 
 brazil ) and glass slab under a constant axial load of 500 g for 30 s. regardless of 
 the recommended time , the last increment of all composite resins was light - cured for 
 40 s to standardize the surface .
the specimens were removed from the molds and the 
 excess was cut off with a # 12 bard - parker scalpel blade .
thereafter , the specimens were subjected to mechanical polishing in a metallographic 
 polishing machine ( arotec - apl 4 , arotec sa ind . com . , cotia , sp , brazil ) using the 
 sequence of # 600- , # 800- and # 1200-grit silicon - carbide abrasive papers under 
 water - cooling .
polishing was performed under a load of 172 g for 20 s for each 
 granulation .
all specimens were ultrasonically cleaned in deionized water for 10 min 
 and were identified and stored at 37c for 1 week . in order to allow wear analysis , each specimen had half of its surface protected with 
 two layers of nail polish that served as control ( with no abrasion ) .
baseline surface roughness of the specimens was analyzed by a profilometer ( hommel 
 tester t1000 , hommelwerke gmbh , villingen - schwenningen , germany ) accurate to 0.01 mm 
 and was expressed in mm as a ra value .
five records of each specimen were randomly 
 assessed . to record roughness measurements of the surfaces a device containing a 
 diamond needle affixed to the profilometer was used .
the average of five randomized 
 transversal readings was established as the baseline roughness value .
ra range was 
 previously adjusted at 0.01 to 0.8 mm at a cut - off of 0.25 mm .
it allowed 
 controlled performance using soft nylon bristle toothbrush heads ( colgate classic , 
 colgate - palmolive ind .
ltda , so paulo , sp , brazil ) under a load of 300 g and 
 temperature of 37c .
slurry was prepared according to iso specification # 14569 - 1 , 
 mixing 2:1 of deionized water and dentifrice ( colgate total 12 , colgate - palmolive 
 ind .
ltda , so paulo , sp , brazil ) and 0.4 ml amount was injected periodically to 
 renew for fresh slurry . for each specimen ,
a total of 100,000 strokes were performed 
 and toothbrushes were replaced after 50,000 strokes . at the end of the test , each 
 specimen was rinsed under running water and cleaning was completed by sonicating in 
 deionized water for 10 min .
the same 
 profilometer was used ; allowing a needle to run from the protected half ( control ) to 
 the abraded half .
parameters were adjusted to tolerances from 0 to 40 mm , length of 
 assessment at 4.8 mm and cut off of 0.25 mm .
random samples of each tested groups , before and after toothbrushing , were selected 
 for microscopic examination to illustrate possible events .
these specimens were 
 prepared and mounted on metal stubs , sputter coated with gold , and examined under a 
 scanning electron microscope ( jsm t220a , jeol ltd . , peabody , ma , usa ) at 500x 
 magnification .
the assumptions of equality of variances and normal distribution of errors were 
 checked for the tested response variables .
since the assumptions were satisfied , data 
 were subjected to one - way anova and tukey 's post - hoc test for the 
 comparison of initial and final roughness and wear among the materials .
paired t - test 
 was applied for roughness analysis considering a two - time evaluation ( p<0.05 ) .
comparative roughness assessments and wear values after simulated toothbrushing are 
 presented in table 1 . for all composite resins , 

initial and final roughness was statistically different ( p<0.05 ) . mean and standard deviation of initial surface roughness ( ra ) , final surface 
 roughness ( ra ) and wear after simulated toothbrushing ( m )
different capital letters indicate differences between columns   different lower case letters indicate differences between rows   comparison among the tested materials regarding their initial roughness , showed that the 
 nanofilled resins , filtek z350 and concept advanced , as well as the microhybrid resins , 
 admira and estelite sigma , presented smoother surfaces while filtek z250 , tph3 , and 
 esthet x presented rougher surfaces . according to the final condition , roughness outcomes revealed a great variability of 
 performance after simulated toothbrushing .
admira , grandio , filtek z350 and tph3 were 
 less rougher than the other composite resins .
concept and esthet x were more susceptible 
 to abrasion , consequently , presented significantly higher roughness .
intermediate values 
 were found for filtek z250 and estelite sigma . according to the presented results , the 
 qualitative analysis of the sem micrographs of the resins , after the abrasion test , 
 showed more polished surface of the nanofilled and the nanohybrid resins than the 
 microhybrid resins , as seen in figure 2 .
a - 
 nanofilled ( esthet x ) ; b  nanohybrid ( tph3 ) ; c  microhybrid ( z250 ) comparing each system before and after toothbrushing simulation , except for grandio , all 
 materials became significantly rougher than their initial condition ( p<0.05 ) . the wear assessment values revealed that admira , grandio and filtek z350 were less 
 susceptible to wear after toothbrushing simulation , followed by tph3 , estelite sigma and 
 esthet x. concept and filtek z250 presented the least resistance to wear 
 ( p<0.05 ) .
enamel and dentin are directly affected by caries disease . when these tissues are 
 compromised
dentin 
 presents a mechanical property from a complex arrangement of collagen type - i - fibrils 
 reinforced with a nanocrystalline apatite mineral in the extra and intrafibrilar 
 spaces .
thus , when this natural complex 
 is changed , the restorative material needs to present properties that are able to 
 recover it an appropriate manner . in order to reach a satisfactory clinical performance , 

the composite resin is indicated as a hybrid material composed mainly by fillers and 
 organic matrix .
thus , mechanical properties are of great interest to allow composite 
 resins to be well indicated .
they are responsible for the 
 strength of the material and also protect organic matrix from wear .
nanotechnology provides incorporation 
 of well - distributed and larger amount of fillers compared with other 
 categories .
there have been several 
 investigations with the purpose to promote modifications to reach better 
 properties .
this balance of 
 organic matrix and fillers is responsible for the determination of long - term clinical 
 use .
therefore , the comparison of the performance of resin - based materials is an essential 
 parameter to aid clinical indication .
basically , it quantifies surface texture by means of randomized readings of the 
 amplitudes in mm , established as ra ( arithmetical roughness ) . according to the results of the present study , simulated toothbrushing was a mechanical 
 process able to modify the balance between organic matrix and filler since all composite 
 resins showed rougher surface after the abrasion challenge as shown in table 1 .
nanofilled materials have the ability to provide more 
 volume of filler in homogeneous distribution , which enables it to protect organic matrix 
 wear .
the 
 possible explanation relies on the fact that admira , even classified as a microhybrid 
 composite , is composed differently than other tested resins as its monomers are based on 
 ormocer , which is considered a resistant organic matrix .
long - term clinical studies have shown the superiority 
 of this matrix regardless of the size of filler . in occlusal 

stress - bearing cavities , the ormocer - based composite materials tested performed 
 comparably to conventional microhybrid bis - gma - based composites . this study reveals that 
 this organic matrix itself is more resistant than conventional monomers . on the other 
 hand ,
since the 
 variability between nano - sized materials also includes their distribution , it might 
 affect their performance in a not well - clarified manner .
filtek z250 , tph3 and grandio were the materials that exhibited rougher initial values . 

filtek z250 is a microhybrid resin while the manufacturers classify tph3 and grandio as 
 nanohybrid .
also , it is should be highlight that even filtek z250 and esthet x are both 
 microhybrid , they differed statistically from each other . despite this same 
 categorization
, it might vary in different levels that are not possible to precise , as 
 their manufacturers do not supply this information in details . in comparison with the 
 other tested materials ,
the distribution of the particles in hybrid resins is less 
 homogeneous , which allows this condition .
additionally , the range of fillers of 
 nanohybrid resins is large . when final roughness was analyzed , distinct performances were observed after simulated 
 toothbrush testing . except for grandio ,
all resins became rougher after toothbrushing , 
 but admira , grandio , filtek z350 and tph3 were less prone to be rougher .
once again , the 
 organic matrix composition of admira seemed to determine a good performance .
filtek z350 
 as nanofilled material attended the expectation of this technology , confirming previous 
 results .
likely , toothbrushing 
 abrasion caused a polishing effect on the surface , allowing smother surface compared 
 with other resins , even rougher than its initial condition .
concept and esthet x were 
 more susceptible to abrasion in terms of roughness as they presented the greatest values 
 after the test .
concept is categorized as a nanofilled composite resin and its organic 
 matrix is based on conventional bisgma .
limited information is supplied by its 
 manufacturer , and so , with the limitations of this study , we can not confirm precisely 
 the reason of this poor performance .
esthet x , on the other hand , as a microhybrid 
 resin , was rougher as expected , compared with nanosized resins .
intermediate final 
 roughness values were detected in filtek z250 , tph3 and estelite sigma .
as these 
 materials are classified as micro or nanohybrid materials , their performances are 
 similar according to a previous study , which stated that they are both resistant 
 materials . according to wear values ,
the specific performance of this ormocer - based material seems to confirm the 
 relevance of organic matrix as well as fillers .
grandio and filtek z350 did not differ significantly from admira . once again , nanofilled 
 materials also attest to the relevance of a combination of reduced size with homogeneous 
 distribution of filler to reach satisfactory performance . in sequence ,
concept and filtek z250 were the 
 resins that had the high level of wear .
as also stated , the poor results and lack of 
 information about the organic matrix composition of concept makes this resin less 
 reliable .
manufacturers have produced composites with different filler sizes ( ranging from 5 to 
 100 nm ) and distributions , in order to enhance performance .
the mechanical properties 
 like high flexural strength , low abrasion , low polymerization shrinkage and resistance 
 to fracture are attributed to the high - filler load of these materials because of the 
 small size the fillers possess .
an 
 explanation for the improvement of the wear resistance with the smaller particles is 
 that the mean distance between neighboring particles was smaller than that with the 
 coarsest filler particles .
this size 
 and distribution is favorable to protect organic matrix against wear , resulting in 
 greater durability . from the observations of admira
, it can be stated that the 
 ormocer - based composite is relevant to resist wearing and roughness changes , which is 
 comparable to the performance of the nanofilled composite resins compared with the other 
 tested materials .
comparison of 
 different categories of direct composite resins revealed that all materials became 
 rougher after simulated toothbrushing .
in general , nanofilled systems and the ormocer - based resin 
 showed better performance than the microhybrid and conventional organic matrix 
 composites . this comparison can be helpful to predict the performance of these materials 
 under clinical service .
this study was performed by g.u.o . as fulfillment of her master s degree research 
 that was supported by grant 136375/2006 - 5 from cnpq ( conselho nacional de 
 desenvolvimento cientfico e tecnolgico ) , brazil .
authors are also thankful for 3 m 
 espe , voco , dentsply , tokuyama dental corporation and vigodent s / a produtos e 
 comrcio for donation of the tested products .
 objectivesnanofilled composite resins are claimed to provide superior mechanical properties 
 compared with microhybrid resins . 
 thus , the aim of this study was to compare 
 nanofilled with microhybrid composite resins . 
 the null hypothesis was that the 
 size and the distribution of fillers do not influence the mechanical properties of 
 surface roughness and wear after simulated toothbrushing test . 
 material and methodsten rectangular specimens ( 15 mm x 5 mm x 4 mm ) of filtek z250 ( fz2 ) , admira ( a ) , 
 tph3 ( t),esthet - x ( ex ) , estelite sigma ( es ) , concept advanced ( c ) , grandio ( g ) and 
 filtek z350 ( f ) were prepared according to manufacturer 's instructions . 
 half of 
 each top surface was protected with nail polish as control surface ( not brushed ) 
 while the other half was assessed with five random readings using a roughness 
 tester ( ra ) . 
 following , the specimens were abraded by simulated toothbrushing with 
 soft toothbrushes and slurry comprised of 2:1 water and dentifrice ( w / w ) . 
 100,000 
 strokes were performed and the brushed surfaces were re - analyzed . 
 nail polish 
 layers were removed from the specimens so that the roughness ( ra ) and the wear 
 could be assessed with three random readings ( m ) . 
 data were analyzed by anova and 
 tukey 's multiple - comparison test ( =0.05 ) . 
 resultsoverall outcomes indicated that composite resins showed a significant increase in 
 roughness after simulated toothbrushing , except for grandio , which presented a 
 smoother surface . 
 generally , wear of nanofilled resins was significantly lower 
 compared with microhybrid resins . 
 conclusionsas restorative materials suffer alterations under mechanical challenges , such as 
 toothbrushing , the use of nanofilled materials seem to be more resistant than 
 microhybrid composite resins , being less prone to be rougher and worn . 
INTRODUCTION
MATERIAL AND METHODS
Experimental design
RESULTS
DISCUSSION
CONCLUSIONS
ACKNOWLEDGMENTS