however , some intrinsic characteristics from resin composite , for example , polymerization shrinkage and elastic modulus different of dental structure can produce several problems including postoperative sensitivity , secondary caries , pulp inflammation , tooth or restoration fractures , and marginal defects of the composite with the adjacent tooth structure .
the failure of such treatment is a public health problem which increases the cost of dental treatment and decreases dental health .
frequently , a range of experimental resins is launched on the market aiming to better physical and chemical properties , and consequently , an increase in the longevity of restorations .
thus , variations in the form and amount of inorganic particles in the polymeric matrix , in the photoinitiator system , handling , indications , among other factors , are increasingly frequent .
however , the characteristics and effects of these composites are not yet fully elucidated , especially in the short term ( early failure ) and associated a clinical performance , making it difficult to choose the ideal restorative material .
the measure of success of a restorative treatment appears to be strongly associated to its longevity .
although laboratory tests can provide relevant information on the restoration longevity , the long - term performance of these systems still depends on clinical evaluations .
however , clinical studies require a more effective approach and greater precision in the experimental design due to several variables which can influence the results such as : difficulty of patient compliance , difficulty of evaluating the restorations longevity as an objective factor ( operator , patient , and material ) , and difficulty to acquire a heterogenic group such as that present in clinical routine .
hence , several studies have used selective groups ( e.g. , dental students ) . however , these groups are not truly representative because they have distinguished prevention and hygiene practices .
therefore , all factors observed in several studies served as a base to the development of this study .
the purpose of this randomized and double - blind study was to assess the clinical performance of two composites for posterior tooth , in class i and ii restorations , using public health service system , during baseline , after 6- , 12- , and 24-months .
the null hypothesis tested was that there is no significant difference in clinical performance between z250 and p60 resin systems when using in posterior teeth .
a total of seventy restorations were placed in molar and premolars in thirty patients ( 14 females and 16 males ; 1840 years ) .
the following parameters were set for sample size calculation : the expected proportion was 0.8 , the relative standard error was of 10% , the power of the test was calculated to be 80% ( beta error ) , and the two - tailed alpha error of 5% was 2-sided . based on these data , a sample size of 25 subjects was found to be necessary . taking into consideration a possible loss during the study , a 20% increase in sample size was set totalizing 30 subjects .
all patients received dental treatment in a public health service system , allowing the formation of a heterogeneous sample , during 24-months .
the following criteria were used to select subjects to the study : good oral hygiene , low caries index , no periodontal disease neither parafunctional habits , the patients should have at least two posterior teeth ( molars and/or premolars ) with initial carious lesions to be treated , and/or teeth with unsatisfactory restorations which needed to be replaced .
patients committed to attend the annual recall by participating in the study , and they were divided into two study groups according to the tested materials [ table 1 ] .
the randomization process that has allocated the cavities and materials were performed by software spss - statistical package for social science , software version 12 , spss inc . ,
furthermore , aiming to secure a blind study , patients and examiners were unaware of any data from the randomization process .
groups , composition and lot of materials used in the study restorative procedures were carried out by an experienced clinician , who was submitted to a calibration process that consisted of performing 10 repeated restorations of each material under direct supervision of the project 's coordinator .
the operator 's questions were addressed , and consensus was obtained during the calibration session .
teeth were carefully cleaned with pumice / water slurry , rinsed with water , and air - dried .
amalgam and/or resin composite restorations considered unsatisfactory and cavity preparation were carried out with 245 carbide burs ( jet burs , beavers dental division of sybron , canada ) .
all internal angles were rounded , and dislodged enamel prisms at gingival wall were removed with a gingival margin trimmer .
the criteria used in the evaluation of unsatisfactory restorations were restoration failure , dentin or base was exposed , contact point was missing ( present periodontal inflammation ) , color and/or translucency beyond the normal range of tooth colors , marginal staining penetration in the direction of the pulp , marginal gap exhibiting the enamel 
dentin junction , fractured , loose filling that is missing partly or completely , and presence of caries ( associated with the filling ) .
every detail of cavity preparation such as cavity depth , enamel presence at the cervical margin , sclerotic dentin , possible pulp exposition , fissures and defects in the enamel , and cavity extension were recorded .
therefore , four teeth were covered with calcium hydroxide ( dycal dentsply ind e. com .
petrpolis , rj , brazil ) and resin - modified glass ionomer cement ( vitrebond ; 3 m dental products , st .
paul , mn , usa ) since the thickness of the remaining dentin was less than approximately 0.5 mm .
enamel was etched for 30 s and dentin for 15 s with 37% phosphoric acid gel ( scotchbond etchant ; 3 m dental products , st .
paul , mn , usa ) , washed for 30 s , and gently dried with air jet .
paul , mn , usa ) and the resins composite were applied to the dental substrates in accordance with the manufacturer 's instructions . to provide the largest free surface area ,
each increment was light - cured for 40 s using a halogen curing light ( curing light xl 3000 , 3 m dental products , st .
paul , mn , usa ) , with minimum light intensity of 600 mw / cm and checked by a light - curing meter ( hilux dental curing light meter , benlioglu dental inc . , turkey ) .
class ii cavities , the proximal wall , was reconstructed to transform into a class i cavity , with the aid of polyester strip matrix ( k - dent quimidrol , joinville , santa catarina , brazil ) and dental interproximal wedges ( tdv dental ltda , pomerode , santa catarina , brazil ) .
resin insertion in the occlusal box was performed in cone - shaped increments according to progressive waxing technique .
the restorations were immediately finished by removing excess material , whereas the finishing and polishing were performed after 1 week , using a 12-fluted tungsten carbide burs ( jet burs , beavers dental division of sybron , canada ) , the enhance polishing system ( dentsply , rio de janeiro , brazil ) and sof - lex polishing discs ( 3 m dental products , st .
the restorations were evaluated by two calibrated examiners , and they were unaware of which material had been used .
the examiners were calibrated before the baseline evaluation using picture slides representing each condition to be assessed in the study , and any disagreements during evaluation were resolved by consensus among the examiners . modified us public health service ( usphs )
criteria [ table 2 ] were used to evaluate marginal discoloration , marginal integrity , surface texture , wear , postoperative sensitivity , and recurrent caries at baseline , after 6- , 12- , and 24-months . the data collection form used at baseline and
the restorations were classified and demonstrated by scores : alpha  ideal clinical situation , bravo  clinically acceptable , and charlie  clinically unacceptable situation . modified - usphs rating criteria interexaminer reliability was assessed using kappa index ( 0.90 ) .
comparisons of ratings for restorations and between baseline and follow - up examinations were analyzed by fisher 's and mcnemar 's chi - square tests for each category .
the value p  0.05 was set as the standard value considered to demonstrate statistically significant differences .
the statistical analyses were carried out with spss 16.0 ( spss inc . , chicago , il , usa ) .
a total of seventy restorations were placed in molar and premolars in thirty patients ( 14 females and 16 males ; 1840 years ) .
the following parameters were set for sample size calculation : the expected proportion was 0.8 , the relative standard error was of 10% , the power of the test was calculated to be 80% ( beta error ) , and the two - tailed alpha error of 5% was 2-sided . based on these data , a sample size of 25 subjects was found to be necessary . taking into consideration a possible loss during the study , a 20% increase in sample size was set totalizing 30 subjects .
all patients received dental treatment in a public health service system , allowing the formation of a heterogeneous sample , during 24-months .
the following criteria were used to select subjects to the study : good oral hygiene , low caries index , no periodontal disease neither parafunctional habits , the patients should have at least two posterior teeth ( molars and/or premolars ) with initial carious lesions to be treated , and/or teeth with unsatisfactory restorations which needed to be replaced .
patients committed to attend the annual recall by participating in the study , and they were divided into two study groups according to the tested materials [ table 1 ] .
the randomization process that has allocated the cavities and materials were performed by software spss - statistical package for social science , software version 12 , spss inc . ,
furthermore , aiming to secure a blind study , patients and examiners were unaware of any data from the randomization process .
restorative procedures were carried out by an experienced clinician , who was submitted to a calibration process that consisted of performing 10 repeated restorations of each material under direct supervision of the project 's coordinator .
the operator 's questions were addressed , and consensus was obtained during the calibration session .
teeth were carefully cleaned with pumice / water slurry , rinsed with water , and air - dried .
amalgam and/or resin composite restorations considered unsatisfactory and cavity preparation were carried out with 245 carbide burs ( jet burs , beavers dental division of sybron , canada ) .
all internal angles were rounded , and dislodged enamel prisms at gingival wall were removed with a gingival margin trimmer .
the criteria used in the evaluation of unsatisfactory restorations were restoration failure , dentin or base was exposed , contact point was missing ( present periodontal inflammation ) , color and/or translucency beyond the normal range of tooth colors , marginal staining penetration in the direction of the pulp , marginal gap exhibiting the enamel 
dentin junction , fractured , loose filling that is missing partly or completely , and presence of caries ( associated with the filling ) .
every detail of cavity preparation such as cavity depth , enamel presence at the cervical margin , sclerotic dentin , possible pulp exposition , fissures and defects in the enamel , and cavity extension were recorded .
therefore , four teeth were covered with calcium hydroxide ( dycal dentsply ind e. com .
ltda . , petrpolis , rj , brazil ) and resin - modified glass ionomer cement ( vitrebond ; 3 m dental products , st .
paul , mn , usa ) since the thickness of the remaining dentin was less than approximately 0.5 mm .
enamel was etched for 30 s and dentin for 15 s with 37% phosphoric acid gel ( scotchbond etchant ; 3 m dental products , st .
paul , mn , usa ) , washed for 30 s , and gently dried with air jet .
paul , mn , usa ) and the resins composite were applied to the dental substrates in accordance with the manufacturer 's instructions . to provide the largest free surface area ,
each increment was light - cured for 40 s using a halogen curing light ( curing light xl 3000 , 3 m dental products , st .
paul , mn , usa ) , with minimum light intensity of 600 mw / cm and checked by a light - curing meter ( hilux dental curing light meter , benlioglu dental inc . , turkey ) .
class ii cavities , the proximal wall , was reconstructed to transform into a class i cavity , with the aid of polyester strip matrix ( k - dent quimidrol , joinville , santa catarina , brazil ) and dental interproximal wedges ( tdv dental ltda , pomerode , santa catarina , brazil ) .
resin insertion in the occlusal box was performed in cone - shaped increments according to progressive waxing technique .
the restorations were immediately finished by removing excess material , whereas the finishing and polishing were performed after 1 week , using a 12-fluted tungsten carbide burs ( jet burs , beavers dental division of sybron , canada ) , the enhance polishing system ( dentsply , rio de janeiro , brazil ) and sof - lex polishing discs ( 3 m dental products , st .
the restorations were evaluated by two calibrated examiners , and they were unaware of which material had been used .
the examiners were calibrated before the baseline evaluation using picture slides representing each condition to be assessed in the study , and any disagreements during evaluation were resolved by consensus among the examiners . modified us public health service ( usphs )
criteria [ table 2 ] were used to evaluate marginal discoloration , marginal integrity , surface texture , wear , postoperative sensitivity , and recurrent caries at baseline , after 6- , 12- , and 24-months . the data collection form used at baseline and
the restorations were classified and demonstrated by scores : alpha  ideal clinical situation , bravo  clinically acceptable , and charlie  clinically unacceptable situation .
comparisons of ratings for restorations and between baseline and follow - up examinations were analyzed by fisher 's and mcnemar 's chi - square tests for each category .
the value p  0.05 was set as the standard value considered to demonstrate statistically significant differences .
the sample ( 30 subjects , 14 females and 16 males , 1840 years ) , the number of restorations ( 35 per material ) , the distribution of restoration ( maximum of three pairs in the same patient ) , the relationship between class i and class ii ( 1:2 ) followed american dental association guidelines for new material testing .
the distribution of restorations and recall characteristics for both tested groups are described in table 3 .
the returns showed a collaboration rate of patients of 96.6% during 6 months , and after 24 months , 28 patients were examined , representing 93.3% .
distribution of restorations and recall characteristics for both tested groups the results of this study revealed an excellent quality of resin composite restorations , which showed no cases of nonacceptable restorations in any aspect .
no statistically significant differences between the two materials were found at 2 years with respect to evaluated criteria . the only criterion that presented a numerical , but not statistically , difference was marginal integrity .
thus , given the experimental conditions , our results demonstrated no material - time - dependency .
evaluation of the materials at baseline , 6 , 12 and 24 months ( alfa score percentage )
clinical evaluation of restorative procedures requires ( a ) choices of clinically relevant criteria , ( b ) assessment using simple nominal scales , ( c ) calibration of evaluators , ( d ) two independent evaluations , and ( e ) nonparametric statistical analysis that recognizes the patient ( and not the restoration ) as the independent variable .
furthermore , usphs evaluates only the degree of deviation from ideal restoration . however , there is still no complete and accurate method that can evaluate all these numerous variables .
problems in tooth restoration interface such as marginal integrity , marginal stain , and secondary caries are associated to materials physics and mechanics properties - elasticity modulus , thermal expansion coefficient , and curing shrinkage - and overall to enamel marginal finishing .
a low elasticity modulus determines a greater material deformation when force is applied , damaging adhesive bonding due to fatigue in tooth restoration interface .
tooth and restorative materials show different thermal expansion coefficient ; therefore , temperature change that takes place in oral cavity leads to stress in adhesive interface breaking hybridization bonding .
marginal integrity criteria showed distinct values ; nevertheless , there was no significant statistically difference .
both materials showed a slight degradation along the time , noticed through the changing in restoration scores from alpha to bravo along the 6 and 24 months . in the first 6 months
, group i ( single bond and filtek z250 ) showed 100% alpha score , after 12 months 97.1% and 2.9% bravo , and after 24 months showed 88.6% alpha score and 11.4% bravo score .
group ii ( single bond and filtek p60 ) showed after 6 months 6% bravo score , and after 12 and 24 months 91.4% to alpha score and 8.6% to bravo score .
this could probably be due to small fracture of the cavosurface margin and material . according to marginal discoloration ,
both materials showed similar score , showing after 12 months 100% alpha score and after 24 months 97.1% alpha score .
concerning secondary caries both materials showed identical clinical behavior after 24 months which was 100% alpha score .
those results matched the findings from trkn and oguz , leinfelder , cenci et al .
analyzing the results for postoperative sensitivity , it was noticed that both materials ( group i and group ii ) showed 100% alpha score in all evaluated periods .
all cavity margins had enamel present which increases significantly the restorative adhesive system sealing capacity , decreasing possibility of marginal microleakage , and its consequences such as postoperative sensitivity .
nevertheless , there was a numerical difference ( percentage ) to marginal integrity in group i , which is presented in table 4 .
the resins composite are both indicated for posterior restorations but differ in terms of handling characteristics . however , the lack of difference occurred due to similarities in the chemical composition of the composites used [ table 1 ] .
p60 is filled to 61% by volume with zirconia / silica filler particles having a size range of from 0.01 to 3.5 m , contain a greater number of smaller particles and the total load is approximately to 84% for weight .
z250 is filled to 60% by volume with zirconia / silica particles having a size range of 0.013.5 m and an average size of 0.6 m , contains also a greater number of smaller particles and the total load is approximately to 78% for weight .
since materials were distributed likewise in the same patient , the variable patient factor can not be used as a cause of greater wear .
it was observed no wear after 12 months , only notice after 24 months , which matched the results from trkn and oguz , gianordoli neto et al . that happened because the improving of composites physic properties .
new formulations decreasing tremendously the average size of particles have been developed over the last decade . besides that , the incremental technique favored better clinical results , once lower increments decreased inner porosity and improved composite conversion rate , which reduced the observed wear .
the polishing consists of making the restoration surface look as enamel . after evaluation of superficial texture in different periods ( baseline , 6 , 12 , and 24 months ) , filtek z250 ( group i ) restorations showed 100% after 12 months and 94.3% alpha score after 24 months and filtek p60 ( group ii ) showed after the same period 97.1% and 94.3% .
both restorative adhesive systems used are hybrid and have as inorganic phase extremely small silica and zircon particles .
it is associated to resin matrix with components ( triethylene glycol dimethacrylate ) increasing the molecular bonding and a higher conversion rate of double linking during curing process , which leads to a great resistant organic matrix . according to anusavise and leinfelder , decreasing size , changing composition , and increasing quantity of particles made nowadays composites 1015 times superior than the previous ones in wear resistance and surface texture maintenance . in accordance with the results of the present study
all restorations after 24 months appeared to be clinically acceptable but are important to follow - up these restorations for a longer period to analyze the clinical performance of the resin composite systems .
long - term clinical trials are certainly needed because they remain the ultimate way to collect scientific evidence on the clinical effectiveness of restorative treatments .
on the basis of the results and despite the limitations of this study , it seems reasonable to conclude that all direct resin composite restorations were clinically satisfactory and no significant differences were found among them over an evaluation period of two years .
 background : clinical evaluations as fundamental method to prove the efficiency of restorative materials.aim:this study evaluated the clinical performance of restorative systems during 2 years of clinical service.materials and methods : this study assessed the clinical performance of restorative systems ( filtek z250 and p60 ) , during 2 years of clinical service , using the us public health service system . 
 the randomized and double - blind study comprising thirty volunteers . 
 the restorations were evaluated at baseline , 6 , 12 , and 24 months . 
 it was used the following criteria : marginal discoloration ( md ) , marginal integrity ( mi ) , superficial texture ( st ) , wear ( w ) , postoperative sensitivity ( ps ) and recurrent caries ( rc).results : statistic analysis was performed using fisher 's and mcnemar 's exact tests and pearsons 's chi - square in a significance level of 5% . 
 the results at baseline and 24 months for group i were : md  100 , 100% ; mi  100 , 88.6% ; st  100 , 94.3% ; w  100 , 94.3% ; ps  100 , 100% ; rc  100 , 100% , of alpha scores ; group ii : md  100 , 97.1% ; mi  100 , 91.4% ; st  100 , 94.3% ; w  100 , 91.4% ; ps  100 , 100% ; rc  100 , 100% , of alpha scores . 
 it was observed no statistical difference in the evaluated criteria and period.conclusions:after 24 months of evaluation , both restorative systems exhibited acceptable clinical performance . 
INTRODUCTION
MATERIALS AND METHODS
Patient selection and description of the groups
Clinical procedures
Clinical evaluation
Statistical analysis
RESULTS
DISCUSSION
CONCLUSIONS
Financial support and sponsorship
Conflicts of interest