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a satisfactory performance of esthetic restorative materials is dependent on their resistance to degradation in the oral environment . among the contributing factors are abrasion resulting from mastication , attrition , corrosion , erosion , and effects of hygiene procedures .
tooth brushing is an oral hygiene method that can increase the surface roughness of composite resins .
the american dental association ( ada ) notes that dentifrices are substances that help remove plaque during brushing .
they have basic component abrasives particles , humectants , binders , detergents , water , and desensitizing and therapeutic components , especially fluorides , which act on caries control .
biochemically , fluoride dentifrices can be considered colloidal suspensions that have an important action in reducing demineralization and enhancing re - mineralization of dental hard tissues and also act as a cleaning agent . the cleaning action is mainly promoted by the abrasive particles , which are insoluble minerals designed to disorganize the bacterial biofilm , removing microorganisms and stains , giving a whitened appearance .
the most common abrasive particles used in dentifrice formulations are softened silica ( hydrated silica ) , chalk ( calcium carbonate ) , and baking soda ( sodium bicarbonate ) .
other abrasives include hydrated alumina , calcium sulfate , sodium metaphosphate , and tricalcium phosphate .
each dentifrice has a relative dentin abrasivity ( rda ) , which is able to influence the surface roughness and wear of dental materials .
studies have shown that the use of whitening dentifrices results in higher tooth wear , and the dentin is eroded .
most whitening dentifrices are not formulated with bleaching agents , in fact , as their true action involves an extrinsic stain removal . similarly to dental hard tissues , when direct restorative materials such as resin composites are exposed to the tooth brushing abrasion process , an increase in surface roughness and loss of gloss occur . as a result , an accumulation of biofilm in this area
this negative effect is usually associated with the organic matrix of the composite resin . moreover , porous resin can promote biofilm accumulation and superficial degradation .
esthetically negative color changes in the composite resin can befall by penetration of coloring agents on the surface of the material and also from the physico - chemical formulation of the material when exposed to the oral environment .
even though the majority of studies have evaluated the effect of whitening dentifrices on surface roughness of composites after a long period of simulated use , usually 6 months to 1 year , this prolonged time may not be realistic for the whitening dentifrices ' indication .
in fact , a positive effect on tooth whitening can be reached after 2 weeks of dentifrice use , remaining stable for up to 12 weeks .
thus , there is still a need for studies to evaluate whitener dentifrices ' influence on esthetic composite resin restoration roughness over a short period .
the present study sought to investigate the effect of tooth brushing with different types of whitening dentifrices and with different rdas on the surface roughness of a nanohybrid composite resin .
the null hypothesis is that these substances are not able to significantly alter the surface roughness of this esthetic restorative material .
the surface roughness of a nanohybrid resin composite ( filtek z350 xt3m / espe , color a2e ) was evaluated ; its composition is described in table 1 .
thirty - two specimens were prepared by the incremental technique ( 1.5 mm ) from a silicone matrix with a 7.0 mm diameter and 3.0 mm depth and light cured for 40 s per increment ( radii - sdi led unit with 1200 mw / cm ) . for the last incremental polymerization ,
a transparent strip and a glass plate ( 0.2 mm thickness ) were placed on the composite resin .
nanohybrid composite resin ( filtek z350 xt ) composition the specimens were identified and stored in distilled water for 7 days at 37c .
afterward , finishing and polishing were made as follows : fine and ultrafine diamond points at high speed with abundant cooling water followed by silicone tips ( polidores siliconizados para compsitos ; dfl , rio de janeiro - rj , brazil ) with medium ( yellow ) and fine ( white ) granulation associated with diamond paste for finishing and prepolishing ( aci e acii ; fgm dentscare ltda , joinville - sc , brazil ) ; a final sequence using a felt disc with diamond polishing paste ( diamond excel ; fgm ) ; and finally , a new polishing with a dry - felt disc to obtain brightness .
then , a reference mark , using a carbide burn ( # 1 ) , was done at the lateral wall of the specimen .
it was done so that all future readings were performed in the same location and direction .
all samples were analyzed individually on a digital profilometer ( surface roughness tester model tr 200 , time group inc .
the specimens were randomly divided into four groups ( n = 8) as follows : g1  specimens were brushed using distilled water ( control group ) ; g2  specimens were brushed using a dentifrice with a low rda value ( rda = 70 ; colgate total 12 professional clean , colgate palmolive industrial ltda ) ; g3  specimens were brushed using a dentifrice with a medium rda value ( rda = 104 ; sensodyne whitener extra fresh , glaxosmithkline consumer healthcare lp ) ; and g4  specimens were brushed using a dentifrice with a high rda value ( rda = 175 ; colgate luminous white , colgate palmolive industrial ltda ) . the composition and description of toothpastes are presented in table 2 .
dentifrice description used in the study the process of brushing included : three brushing cycles ( 2 min each cycle ) a day , totaling 90 cycles in a month .
each brush cycle was standardized by the use of a rechargeable electric toothbrush ( oral - b vitality handle and oral - b precision clean interchangeable brush head ) with oscillating and rotating technology ( 8800 strokes per min for 2 min ) .
the battery of the toothbrush was charged each 15 cycles , respecting the manufacturer 's instruction .
the amount of dentifrice used was a minimum possible volume to contact all the brush bristles . to avoid operator fatigue and overloads during brushing ,
the toothbrush was fixed on a device to standardize the pressure ( 30 g ) exerted by the brush bristles on the specimens .
after each brushing , the specimens were cleaned in an ultrasonic tank ( 10 min ) to remove debris and dentifrice remnants to avoid interference with the results . at the end of the brushing cycles ,
the average for each group was obtained in microns ( m ) . the statistical analysis considered the factor time ( before and after brushing ) and dentifrices ( colgate total 12 , sensodyne whitener extra fresh , and colgate luminous white ) . statistical analysis ( shapiro  wilk test ) was performed to verify the normality of the data , indicating that the distribution was not normal ( p = 0.0322 ) .
only the analysis of the values of   final  initial  had a normal distribution ( p = 0.0926 ) . therefore , the nonparametric kruskal 
wallis test and the dunn test were used for intergroup roughness comparison , showing no statistical difference between groups ( p > 0.05 ) . for intragroup comparison ,
the wilcoxon test was performed , which also showed no significant difference between the roughness values before and after brushing ( p > 0.05 ) . to compare the  final  initial ,
one - way anova was performed and found no significant difference between groups ( p > 0.05 ) .
surface roughness ( ra=m ) of a nanohybrid composite resin ( z350xt ) before and after tooth brushing
teeth restored with direct composite resin are constantly exposed to specific challenges of the oral cavity .
these challenges can modify the material properties and , when associated with daily brushing , eventually change its surface roughness , allowing bacterial growth and retention of extrinsic pigments . moreover , composite resins exhibit filler particles , which can be displaced during mastication and form cracks , exposing the organic matrix to the oral environment , facilitating abrasion . a study conducted by oliveira et al . evaluated the impact of the size and distribution of inorganic particles on the surface roughness and wear of composites after simulated tooth brushing in vitro , finding better results in the nanoparticle group ( filtek z350 ) .
the organic matrix of nanoparticle composites comprises urethane dimethacrylate ( udma ) , bisphenol a - glycidyl methacrylate ( bis - gma ) , and bisphenol a - methacrylate ( bis - ema ) .
according to barszczewska - rybarek , udma is less viscous and more flexible than bis - gma and has a greater amount of crosslinking and hardness . on the other hand ,
the bis - gma molecule is more rigid , with a small amount of double crosslinks and tends to be less stiff and has a higher water sorption .
bis - ema is a bis - gma analog molecule that allows more double coupling conversion while transforming the polymer into a more flexible and less rigid structure .
these above - mentioned aspects were taken into consideration when choosing the restorative material to be employed in the present study .
many studies have used simulated tooth brushing for in vitro studies , verifying the effects of dentifrices after long periods of use ( 6 months or more ) . in this study ,
the tooth brushing simulation corresponded to a short period ( 1 month ) because the positive effects of effective bleaching action dentifrices have been observed after 2 weeks of use , remaining stable up to 12 weeks . in the present study ,
because of these results , whitening dentifrices would be better indicated during an in - office dental bleaching technique , which involves three or four weekly treatments for positive esthetic results .
a study conducted by da costa et al . analyzed the surface roughness of different composite resins before and after simulated tooth brushing with different whitening dentifrices and also found no significant difference in results for the dentifrice factor , supporting the findings of our study .
according to the ada , each dentifrice has a rda , which is able to influence the surface roughness of restorative materials .
however , during tooth brushing , ions and specific proteins present in saliva dilute and minimize this effect .
the rda value depends on the size and surface structure of the abrasive particles present in the dentifrice ; high values indicate more abrasivity .
the dentifrices ' rdas in this study were 70 m ( colgate total 12 ) , 104 m ( sensodyne whitener extra fresh ) , and 175 m ( colgate luminous white ) , and they were all below the ada 's limit ( 180 m ) .
hydrated silica and titanium oxide were the abrasive agents of the dentifrices used in this study [ table 2 ] .
hydrated silica is formed by mineral compounds with different physico - chemical properties and is considered a good cleaning agent with high abrasive capacity ; it is compatible with most fluorinated compounds .
however , titanium dioxide is able to temporarily modify the enamel shade by its impregnation onto surface irregularities of the tissue .
therefore , the user of these products is led to believe that teeth are whiter ; however , both the tooth and the restorative material surfaces have increased their roughness , becoming prone to future staining .
in addition , salivary properties can reduce the effects of roughness of a composite , as the fluid provides the sliding surface attenuating wear .
however , the saliva role in this process was not simulated in our study , and the composite resin wear can be lowered clinically . the brushing pressure applied to the specimens can also influence the wear on surfaces ( tooth / restoration ) .
for this reason , a dental electric toothbrush with a 30 g pressure was set on a device to avoid overloading and operator fatigue during brushing .
however , it can be observed that even with the use of such device , a trend of increasing surface roughness of the composite resin was observed , confirming the findings of other authors .
another important aspect is the correlation between the use of whitening dentifrices and the type of brush used by the patient .
thus , dentifrices with extremely high rda values ( i.e. , more abrasive ) should be used in combination with soft bristles . the electric toothbrush used in the present study
had soft bristles and worked with oscillating and rotating movements ( 8800 strokes per min ) .
a toothbrush with extra - soft bristles eventually boosts a dentifrice 's abrasive action and shortens the toothbrush life .
therefore , the professional dentist must know the characteristics and composition of whitening dentifrices to propose a more correct usage during a dental bleaching treatment .
the results have appointed to a safe use of whitening dentifrices in a short period .
the results of this study support the conclusion that none of the whitening dentifrices evaluated were able to significantly increase the surface roughness of the nanohybrid composite resin in a short period ( 1 month ) , confirming the null hypothesis of the present study .
thus , dental professionals should be alert to indicate the safe use of these whitening dentifrices for a few weeks , only aiming for stain removal .
this study was financed by the funding agency of the amazon state ( fapeam ) , through the edictal paic / sisproj , process # 20151 .
this study was financed by the funding agency of the amazon state ( fapeam ) , through the edictal paic / sisproj , process # 20151 .
objectives : the present study verified the influence of whitening dentifrices on the surface roughness of a nanohybrid composite resin.materials and methods : thirty - two specimens were prepared with filtek z350 xt ( 3m / espe ) and randomly divided into four groups ( n = 08 ) that were subjected to brushing simulation equivalent to the period of 1 month . the groups assessed were a control group with distilled water ( g1 ) , colgate total 12 professional clean ( g2 ) , sensodyne extra whitener extra fresh ( g3 ) , and colgate luminous white ( g4 ) . a sequence of 90 cycles was performed for all the samples . 
 the initial roughness of each group was analyzed by the surface roughness tester ( tr 200-time group inc . 
 , ca , usa ) . after the brushing period 
 , the final roughness was measured , and the results were statistically analyzed using nonparametric kruskal  
 wallis and dunn tests for intergroup roughness comparison in the time factor . for intragroup and 
   final  initial  comparisons , the wilcoxon test and ( one - way ) anova were , respectively , performed (  = 0.05).results : the roughness mean values before and after brushing showed no statistically significant difference when the different dentifrices were used . 
 none of the dentifrices analyzed increased significantly the nanohybrid composite resin surface roughness in a 1 month of tooth brushing simulation.conclusions:these results suggest that no hazardous effect on the roughness of nanohybrid composite resin can be expected when whitening dentifrices are used for a short period . 
 similar studies should be conducted to analyze other esthetic composite materials .