light - cured composite resins ( lccrs ) have been studied extensively in recent years . the 
 formulation proposed by bowen ( 1963 ) , 
 which is still in use today albeit with slight modifications , consists basically of a 
 resin matrix , filler particles , monomers and a photo absorbing compound . the latest development in this field has been the introduction of low shrinkage monomers 
 and nanofiller particles . lccr 
 ( polymerase chain reaction ) materials are present in filtec z350 ( 3m / espe , saint paul , 
 mn , usa ) , which combines nanometric particles and nanoclusters in a conventional resin 
 matrix , and in admira ( voco , cuxhaven , germany ) , whose resin matrix contains ormocer , an 
 organically modified ceramic . the light - curing units ( lcus ) equipped with a light - emitting diode ( led ) , which produces 
 cold light at 450 nm wavelength , is a promising device of costs and efficiency . however , 
 the lcu operating with a halogen lamp is still the first choice of clinicians and 
 extensive research has been dedicated to testing its efficiency . the present research focused on one of the important properties of lccrs - surface free 
 energy ( sfe ) , to study the interaction between the forces of cohesion and the forces of 
 adhesion that determine the occurrence of surface wetting . the wetting performance of etched enamel is important in all types of adhesive 
 restorations because of the close interaction between the surface free energy of the 
 etched enamel and the wettability of the luting and bonding material . the contact 
 angle measurement method is probably the most definite way to determine cell surface 
 hydrophobic . the angle is very high for water if substrata are hydrophobic . if the 
 surface is hydrophilic , the droplet quickly dissipates and the measured angle is low . contact angles values vary with surface topography , surface tension of the liquid , 
 surface energy of the substrate and the level of interaction between the liquid and 
 solid . hydrophobic materials 
 are more color - stable and stain - resistant than hydrophilic materials . gaps formed at the tooth / restoration interface may be caused by inadequate wetting of 
 the tooth surface by the restorative material along the preparation walls during 
 placement . surfaces with a low 
 surface free energy minimize plaque formation . to calculate de sfe , the first step consists of measuring the contact angle ( ca ) between 
 the solid under study and the test liquid , using a contact angle goniometer . the ca 
 which is the macroscopic expression of the micro and macroscopic phenomena occurring 
 between the solid , the test liquid . the acid - base theory involves the 
 multicomponent approach , whereby the sfe occurs through dispersive interactions or 
 lifshitz - van der waals ( lw ) and lewis acid - base ( ab ) interactions . the second approach 
 involves the equation - of - state theory , which is highly criticized from the thermodynamic 
 standpoint . although these theories are based on different concepts , they share the same 
 basic idea , i.e. , they attempt to express the reverse work of adhesion of some of the 
 components of the interfacial tension between liquids and solids . the aim of this work was to evaluate the variations in the surface energy of various 
 composite resins after curing by led and halogen curing devices , based on contact angles 
 and surface free energy . thirty - six test specimens of composite resins ( admira - voco , cuxhaven , germany ; filtec 
 z350 - 3m / espe , saint paul , mn , usa ; grandio - voco , cuxhaven , germany ) were prepared in 
 a 10 mm diameter , 2-mm thick articulated brass matrix . the specimens were finished 
 with sof - lex discs ( 3m / espe ) and polished with kota diamond paste ( kota dental 
 products , so paulo , brazil ) . the lcus employed were a led device ( elipar freelight ii -1000 mw / cm , 
 3m / espe ) and a halogen device ( vip tm 500 mw / cm and 600 
 mw / cm , bisco , inc . , schaumburg , il , usa ) . the light emission control was 
 preset with a radiometer ( demetron 100p / n ; demetron research corp . , the materials ( shade a2 ) were inserted into the matrix in two portions and pressed 
 with two microscope slides to achieve a smooth flat surface , after which they were 
 light - cured in the specimens center for 20 s on each side . twelve samples of each 
 composite were prepared , 6 were light - cured wit a led lcu and 6 with a halogen lamp . all specimens were stored in dark vials at 8c for 1 week , after which they were 
 finished and polished before testing . the static contact angles were measured with a goniometer ( ram - hart 100-fo , netcong , 
 nj , usa ) using deionized water and glycerol as test liquids ( table 1 ) . the 
 36 samples were divided into 12 groups of 6 test specimens each , and 6 drops of each 
 liquid were used for the measurements . the computer was set to record 10 contact 
 angle measurements of each drop , so 360 measurements were made for each group , making 
 a total of 4,320 measurements . =relative equilibrium pressure , =interface tension , 
 =interation forces ( london dispersive - debye dipole and 
 keeson dipole - dipole ) =acidic part -acceptor , =basic part - 
 donor the sfe was determined based on the harmonic mean method described by wu ( 1995 ) . because two test liquids are 
 required to calculate the sfe by this method , the samples were divided into 6 groups 
 of 6 test specimens each . a different lcu and test liquid the contact angle values determined for each group were stored in the computer , and 
 the surface energy was calculated using dropimage standard software , netcong , nj , 
 usa . the values were done by the soft but the calculations can be done by youngs 
 equation : 2=12+1 cos  and with the acid - base theory . statistical inter- and intra - group analyses of the data were made using anova and 
 tukey 's test at 0.05 significance level . thirty - six test specimens of composite resins ( admira - voco , cuxhaven , germany ; filtec 
 z350 - 3m / espe , saint paul , mn , usa ; grandio - voco , cuxhaven , germany ) were prepared in 
 a 10 mm diameter , 2-mm thick articulated brass matrix . the specimens were finished 
 with sof - lex discs ( 3m / espe ) and polished with kota diamond paste ( kota dental 
 products , so paulo , brazil ) . the lcus employed were a led device ( elipar freelight ii -1000 mw / cm , 
 3m / espe ) and a halogen device ( vip tm 500 mw / cm and 600 
 mw / cm , bisco , inc . , schaumburg , il , usa ) . the light emission control was 
 preset with a radiometer ( demetron 100p / n ; demetron research corp . , the materials ( shade a2 ) were inserted into the matrix in two portions and pressed 
 with two microscope slides to achieve a smooth flat surface , after which they were 
 light - cured in the specimens center for 20 s on each side . twelve samples of each 
 composite were prepared , 6 were light - cured wit a led lcu and 6 with a halogen lamp . all specimens were stored in dark vials at 8c for 1 week , after which they were 
 finished and polished before testing . the static contact angles were measured with a goniometer ( ram - hart 100-fo , netcong , 
 nj , usa ) using deionized water and glycerol as test liquids ( table 1 ) . the 
 36 samples were divided into 12 groups of 6 test specimens each , and 6 drops of each 
 liquid were used for the measurements . the computer was set to record 10 contact 
 angle measurements of each drop , so 360 measurements were made for each group , making 
 a total of 4,320 measurements . =relative equilibrium pressure , =interface tension , 
 =interation forces ( london dispersive - debye dipole and 
 keeson dipole - dipole ) =acidic part -acceptor , =basic part - 
 donor the sfe was determined based on the harmonic mean method described by wu ( 1995 ) . because two test liquids are 
 required to calculate the sfe by this method , the samples were divided into 6 groups 
 of 6 test specimens each . a different lcu and test liquid the contact angle values determined for each group were stored in the computer , and 
 the surface energy was calculated using dropimage standard software , netcong , nj , 
 usa . the values were done by the soft but the calculations can be done by youngs 
 equation : 2=12+1 cos  and with the acid - base theory . statistical inter- and intra - group analyses of the data were made using anova and 
 tukey 's test at 0.05 significance level . table 2 shows the mean values and standard 
 deviations of the interactions among the various types of lccrs , lcus , and test liquids , 
 as well as the statistically significant differences among the groups as indicated by 
 the tukey 's test . mean values of contact angles ( meansd ) tukey 's multiple comparisons- ( same letters = not statistically significant 
 p>0.05 ) sd = standard deviation the resin admira ( 74.45 ) , using glycerol as the test liquid and the halogen lamp as the 
 lcu , yielded the highest mean ca value , while grandio ( 59.19 ) resin tested with 
 glycerol , using led as the light source , yielded the lowest ca value . the inter- and intra - group ca values showed no significant difference ( p>0.05 ) for 
 the filtec z350 resin , but all values obtained for the resin grandio showed significant 
 differences ( p<0.05 ) . the sfe results listed in table 3 were subjected 
 to tukey 's test , which indicated the absence of statistically significant differences 
 among the groups . mean , standard deviation and standard error for surface free energy 
 ( mj / m ) p>0.05 - not statistically significant the main controllable variables 
 involved in ca measurements are the light - curing process , the test liquids and the 
 chemical composition of the resin under study . all samples ( shade a2 ) were subjected to 40 s of light incidence upon the center of the 
 sample , which according to lindberg , peutzfeldt and van dijken ( 2004 ) is sufficient to cure the entire surface of such 
 samples . although the intensity of the vip tm ( bisco ) halogen lamp varied from 500 to 600 
 mw / cm , we do not believe this variation impaired the polymerization of 
 the test specimens of the 3 resins . the intensity of light emitted by a halogen lamp is 
 lower than that emitted by a led unit , but its values still exceed 280 to 300 mw / cm , according 
 to caughman , rueggeberg and curtis 
 ( 1995 ) . in view of the lack of information about the surface energy of these materials , 
 it is difficult to compare our results to those of other author . the test liquids used here had different polarities , in spite of similar 
 values which explains the mean 
 ca values ranging from 59.19 to 74.45 obtained in this study . the degree of purity and 
 the numerous measurements yielded reliable results and low standard deviations . although 
 zisman ( 1964 ) stated that the 
 volume of the drop does not influence ca values , this volume , as well as room 
 temperature and humidity , were standardized in this study in order to reduce the number 
 of variables . the organic matrix of admira resin is composed of ormocer , siloxane organic / inorganic 
 polymer , bis - gma , hema , udma , fe2o3 , tio and 4-tert - butylcatechol 
 ( tbc ) , and its inorganic matrix contains ba - al borosilicate , a silicon dioxide ( 0.04 - 0.7 
 m ) - 78% in weight and 56% in volume . the presence of these high surface energy 
 particles , which in some samples may have been located close to the surface , could cause 
 a decrease in measured ca values . light curing of the organic material , which closes the 
 carbon chains , also probably interferes in the expression of these particles even in the 
 deepest layers . the diameters of the inorganic particles of filtec z350 and grandio resins are 
 nanometric . wu ( 1973 ) argues that 
 the homogeneous dispersion of inorganic particles in the polymeric matrix is critical , a 
 statement confirmed by von werne and patten ( 2001 ) . hydrophobic polymers and inorganic hydrophilic particles 
 are physically difficult to mix , and phase separation or agglomeration is common in such 
 mixtures , resulting , according to the aforementioned author , in alterations in their 
 mechanical , optical and electrical properties . these particles can be treated chemically 
 used to produce a more hydrophobic or hydrophilic surface . as shown in table 2 , the ca values of the filtek 
 z350 resin showed no major variations in any of the combinations . in view of these 
 results , it is reasonable to assume that the components of the resin in these test 
 specimens were distributed more homogeneously . the ca values of the admira resin 
 revealed greater variations in the two test liquids and the two lcus . among the 3 resins 
 of this study , table 3 lists the mean values of the total sfe 
 calculated for each lccr with respective sd , indicating no significant differences among 
 the groups . the admira resin showed the highest sfe value when light - cured with the led 
 unit ( 40.17 mj / m ) , while the grandio resin displayed the lowest sfe when 
 photo - activated by the conventional halogen lamp ( 34.74 mj / m ) . the statistical analysis of the resins ' sfe data confirmed that the different types of 
 lcu employed to polymerize the resins did not influence these results . this finding is 
 congruent with that reported by glantz and larsson ( 1971 ) , although the resins tested by these authors belong to 
 another generation of composites , whose chemical compositions differ considerably from 
 those used in our study . milosevic ( 1992 ) who studied the 
 adhesion of saliva films on composite resins , stated that polymers are usually known as 
 low - sfe materials with values of about 40 mj / m , and that the particles of 
 their inorganic load have high sfe values . all the results obtained in the present 
 research ( table 3 ) are in agreement with those 
 of this author . the contact angles of the 3 polymers studied here did not 
 differ significantly , as did their wettability . the research recommends the material 
 that showed the highest contact angle ; 2 . polymerization with led or halogen units did 
 not alter the surface free energy of the composite resins .