esthetic restorative materials have been widely used in dentistry in both anterior and posterior restorations . currently , four types of direct esthetic restorations are commonly used in dentistry which includes - resin composites , poly - acid modified resin composites ( copolymer ) , glass - ionomers and resin - modified glass - ionomers . resin composites were introduced in the early 1970s and are widely used as direct esthetic restorations.1 however , composite restorations have several significant disadvantages despite their continuous improvements.2 despite the fact that composites are currently the most preferred material for restorations , the polymerization shrinkage of 2.6 - 7.1% prompting microleakage is one of the most often observed issues.3 - 14 microleakage is one of major drawbacks of composites which lead to the development of recurrent caries , post - operative sensitivity , enamel fracture , marginal staining , and eventual failure of restorations.4 studies have reported several ways to decrease this problem such as slowing down the composite polymerization rate , utilizing an incremental build - up technique or placement of low modulus in - between layer , and reducing the c factor ( the ratio of bonded to non - bonded restoration surfaces).5 silorane - based dental resin composite materials introduced to clinical dentistry with an intention to reduce the polymerization shrinkage . its matrix consists of siloxanes and oxiranes , which differ from the conventional methacrylate ( bis - gma ) composite matrix . manufactures claimed that the silorane - based composites produce low - polymerization shrinkage of < 1% volume by using archimedes method . silorane - based composites polymerize by open ring polymerization reaction minimizing polymerization shrinkage and polymerization stress . thus , it provided a high - performance bond to the tooth with significantly lower shrinkage than other methacrylate composites.6,7 moreover , oxirane and siloxane were hydrophobic in nature making silorane based composites chemically stable in aqueous solution with less water sorption . additionally , silorane - based dental resin composites showed less microleakage and cusp deflection compared to other bis - gma composite materials.8 - 11 by utilizing bis - gma based technology , nontraditional these contained sub - micrometer particles ( nano fillers ) to further improve the physical and optical properties of the resins . nanohybrid composites with bis - gma base has been recommended for both anterior and posterior restorations . further , it has been improved to overcome composite drawbacks of recurrent caries , post - operative sensitivity , enamel fracture , marginal staining , microleakage and eventual failure of restorations . to the best of our knowledge , there is a lack of reported studies on the comparative evaluation of microleakage of methacrylate based nanohybrid and microhybrid composite materials with that of silorane based microhybrid composite materials . hence , the present study is aimed to evaluate the microleakage of silorane based ( filtek p90 , using two - step self - etching prime and bond adhesive system ) composite material with that of methacrylate based ( filtek z250 using single bond universal total etching technique , and filtek z250 xt using single bond universal self - etching technique ) composite materials in class i restorations by using stereomicroscope . sixty extracted intact upper premolar teeth were collected , and removal of calculus and debris was carried out by hand scaling . teeth were kept in 5% sodium chloride solution at 37c for the duration of 1-month . teeth were prepared approximately 4 mm in length mesio - distally , 2 mm bucco - palatally in width and 3 mm in depth to receive standardized class i restoration by using prefabricated polyvinylsiloxane mold of 2 mm  4 mm . the corresponding depth of the cavity was obtained with a diamond bur marked 3 mm from the tip of the bur . marking on the bur was carried out by using carborundom disk ( b&d technologies co , nanyi street , qiaonan , panyu , guangzhou , 511400 china ) . all the class i cavities was prepared by using high - speed hand piece ( nsk , avtec dental , mount pleasant , sc , u.s.a . ) , under constant water irrigation . 90 cavosurface margins were prepared , and the dimensions of the cavities were checked with a boley gauge . later teeth were randomly divided into three ( n = 20 ) groups to receive restorative materials . paul , mn , usa ) with single universal bond ( 3 m espe , st . paul , mn , usa ) was used as per the manufacturer s instructions . a phosphoric acid etching gel 35% ( scotchbond universal etchant , 3 m espe , st . paul , mn , usa ) was applied to the prepared tooth structure for 15 s. rinsed with water and dried carefully without incorporating oil or water . then , the bonding agent applied with a scrubbing motion for 20 s and exposed to the gentle stream of air for 5 s , followed by light curing for 10 s. filtek z250 was placed in a cavity in two increments with each increment of 2 mm size as per the manufacturer s instructions and light cured for 40 s. filtek z250 xt resin composite shade a2 ( 3 m espe , st . paul , mn , usa ) with single bond universal self - etch ( 3 m espe , st . the bonding agent was applied with a scrubbing motion for 20 s and the gentle air stream was passed for 5 s before it could be light - cured for 10 s. composite filtek z250 xt was placed by using the same protocol as described in group a. low shrinkage resin composite filtek p90 shade a2 ( 3 m espe , st . paul , mn , usa ) with ls system adhesive primer and bond ( 3 m espe , st . the p90 primer was applied by using a micro brush for 15 s , mildly air - dried and finally light - cured for 10 s. the p90 bond was applied , and a gentle stream of air was passed and light - cured for 10 s. p90 was placed by using the same protocol as described in group a according to the manufacturer s instructions and light cured for 40 s. all the specimens were polished with a series of coarse , medium , fine and superfine polishing discs ( sof - lex ; 3m / espe , st . paul , mn , usa ) with an electric handpiece ( k10 ; kavo , leutkirch , germany ) at 15,000 rpm for 15 s. all composite increments were light - cured using elipar s10 led curing unit ( 3 m espe , seefeld , germany ) at a power density of 1000 mw / cm for 40 s in a soft start mode , whereas adhesive systems were light - cured using the same light - curing unit with power density for 10 s. the integrated radiometer was utilized to continuous monitoring of the light intensity . teeth were then subjected to thermocycling , according to the international organization for standardization standard 11405 for 500 cycles at 5c-55c with a 30-s dwell time . before the evaluation of the microleakage , the root apices of the teeth were completely sealed with sticky wax and two coats of nail varnish was applied over the crown root surfaces except for 1 mm around the restoration margins . teeth were then drenched in 2% methylene blue dye ( ph = 7 ) ( merck specialties private ltd , mumbai , india ) at 37c for 24 h,13 washed and dried . later on , teeth were embedded in the acrylic resin block sectioned longitudinally in bucco - lingual direction with a diamond saw mounted on a cutting machine ( isomet 1000 ; buehler 41 waukegan road lake bluff , illinois usa ) . stereomicroscopic ( motic microscopes , china ) examination was carried out to determine the extent of dye penetration at 40 magnification based on five - point scale . 0 = no dye penetration;1 = dye penetration limited to outer half of the axial wall;2 = dye penetration limited to inner half of the axial wall;3 = dye penetration reach the pulpal wall;4 = dye penetration beyond the pulpal wall . 
  0 = no dye penetration ; 1 = dye penetration limited to outer half of the axial wall ; 2 = dye penetration limited to inner half of the axial wall ; 3 = dye penetration reach the pulpal wall ; 4 = dye penetration beyond the pulpal wall . whitney test were executed at a 95% significance level to evaluate any significant differences among the composite materials . all the statistical analysis was performed using the spss 11.0 program ( spss inc . , paul , mn , usa ) with single universal bond ( 3 m espe , st . paul , mn , usa ) was used as per the manufacturer s instructions . a phosphoric acid etching gel 35% ( scotchbond universal etchant , 3 m espe , st . paul , mn , usa ) was applied to the prepared tooth structure for 15 s. rinsed with water and dried carefully without incorporating oil or water . then , the bonding agent applied with a scrubbing motion for 20 s and exposed to the gentle stream of air for 5 s , followed by light curing for 10 s. filtek z250 was placed in a cavity in two increments with each increment of 2 mm size as per the manufacturer s instructions and light cured for 40 s. paul , mn , usa ) with single bond universal self - etch ( 3 m espe , st . the bonding agent was applied with a scrubbing motion for 20 s and the gentle air stream was passed for 5 s before it could be light - cured for 10 s. composite filtek z250 xt was placed by using the same protocol as described in group a. paul , mn , usa ) with ls system adhesive primer and bond ( 3 m espe , st . the p90 primer was applied by using a micro brush for 15 s , mildly air - dried and finally light - cured for 10 s. the p90 bond was applied , and a gentle stream of air was passed and light - cured for 10 s. p90 was placed by using the same protocol as described in group a according to the manufacturer s instructions and light cured for 40 s. all the specimens were polished with a series of coarse , medium , fine and superfine polishing discs ( sof - lex ; 3m / espe , st . paul , mn , usa ) with an electric handpiece ( k10 ; kavo , leutkirch , germany ) at 15,000 rpm for 15 s. all composite increments were light - cured using elipar s10 led curing unit ( 3 m espe , seefeld , germany ) at a power density of 1000 mw / cm for 40 s in a soft start mode , whereas adhesive systems were light - cured using the same light - curing unit with power density for 10 s. the integrated radiometer was utilized to continuous monitoring of the light intensity . teeth were then subjected to thermocycling , according to the international organization for standardization standard 11405 for 500 cycles at 5c-55c with a 30-s dwell time . before the evaluation of the microleakage , the root apices of the teeth were completely sealed with sticky wax and two coats of nail varnish was applied over the crown root surfaces except for 1 mm around the restoration margins . teeth were then drenched in 2% methylene blue dye ( ph = 7 ) ( merck specialties private ltd , mumbai , india ) at 37c for 24 h,13 washed and dried . later on , teeth were embedded in the acrylic resin block sectioned longitudinally in bucco - lingual direction with a diamond saw mounted on a cutting machine ( isomet 1000 ; buehler 41 waukegan road lake bluff , illinois usa ) . stereomicroscopic ( motic microscopes , china ) examination was carried out to determine the extent of dye penetration at 40 magnification based on five - point scale . 
 0 = no dye penetration;1 = dye penetration limited to outer half of the axial wall;2 = dye penetration limited to inner half of the axial wall;3 = dye penetration reach the pulpal wall;4 = dye penetration beyond the pulpal wall . 
  0 = no dye penetration ; 1 = dye penetration limited to outer half of the axial wall ; 2 = dye penetration limited to inner half of the axial wall ; 3 = dye penetration whitney test were executed at a 95% significance level to evaluate any significant differences among the composite materials . all the statistical analysis was performed using the spss 11.0 program ( spss inc . , descriptive statistics of mean , standard deviations , minimum and maximum scores for dye penetration test as shown in table 1 . it is evident that silorane - based composite material filtek p90 showed a highest mean score of 2.45  0.89 , as compared to methacrylate based composite materials filtek z250 and filtek z250 xt . number of teeth showing dye penetration reaching the pulpal wall of the cavity was highest ( n = 14 ) with filtek p90 ( silorane ) composite material as compared to the other two composite materials ( graph 1 ) . dye penetration test . a highest mean rank of 33.65was observed with filtek p90 ( silorane ) , followed by 30.55 and 27.30 filtek z250 xt ( methacrylate ) and filtek z250 ( methacrylate ) , respectively . wallis test revealed no significant differences ( p > 0.05 ) ( table 2 ) . microleakage of composite restorations occurs because of stresses encountered along the tooth / restoration margin from polymerization shrinkage , temperature variation in the oral environment , and mechanical fatigue through repetitive masticatory loading.15 the most likely cause for this phenomenon is polymerization contraction , which is toward the   stronger enamel composite joint and the light source.4 - 10 various methods to detect microleakage have been suggested including dye leakage method , the use of color producing microorganisms , radioactive isotopes , the air pressure method , neutron activation analysis , electrochemical studies , scanning electron microscopy , thermal and mechanical cycling , and chemical tracers.16 a newer silorane - based composite resin system was designed to overcome polymerization contraction issue.6,17 the present study investigated the microleakage of a new low - shrinkage resin composite and clinically successful methacrylate resin composites in class i restorations . these class i cavities was chosen due to the high c - factor that leads to greater polymerization stresses,18 as a result of confined contraction by number of bonded surfaces . we did not observe any significant differences in microleakage among the three composite resin systems . this could be due to the use of high intensity light in a continuous mode , self - etch hydrophilic adhesive systems , the increased c - factor of class i cavity and the relatively excess concentration of methylene blue dye used in this study . the results of this study showed that the novel low - shrink composite restorative material filtek p90 showed microleakage score very similar to z250 with total etch single universal bond and z250 xt with self - etch systems after thermocycling . assumption that microleakage of the cavities restored with the filtek p90 ( silorane ) compared to the other resin - based composite materials was due to the innate ring - opening polymerization reaction of the silorane monomers , which make - up the volumetric reduction as the molecules approximate each other . however , radical polymerization of the other resin based composites is obvious with a decrease in polymerization shrinkage stresses at the tooth / restoration border . therefore , methacrylate based composite resins better withstand thermocycling fatigue at the tooth / restoration interface . our study is in agreement with the study reported by ernst , who presented no differences in microleakage of teeth restored with silorane and methacrylate composite ( tetric ceram ) with adhesive ( clearfil se bond ) system.13 this finding was due to the fact that author used an all - in - one ( 7 generation ) experimental bond of silorane before produced by the company . whereas in the present study new bond produced with silorane composite system consisting of two - step and two components ( 6 generation ) was utilized . however , we disagree with study results of palin et al . , who have reported that the microleakage of silorane based composite material was lesser than that of methacrylate based composite after occlusal loading forces.19 - 21 within the limitation of this study , we conclude that all the restorative systems tested in this study exhibited microleakage . however , silorane based technology ( filtek p90 ) showed higher microleakage scores compared with the clinically successful methacrylate - based composite materials ( filtek z250 and filtek z250 xt ) .
background : to evaluate the microleakage of silorane - based composite material ( filtek p90 ) with that of two homologous methacrylate - based composites materials ( filtek z250 and filtek z250 xt ) , by using two different bonding techniques.materials and methods : sixty extracted human maxillary first premolars prepared for standardized class i cavities ( 4 mm  2 mm  2 mm ) were randomly divided into three groups . 
 group a ( n = 20 ) was filled with filtek z250 ( methacrylate ) using single bond universal total etching technique , group b ( n = 20 ) was filled with filtek z250 xt ( methacrylate ) using single bond universal self - etching technique and group c ( n = 20 ) restored with filtek p90 ( silorane ) with dedicated two - step self - etching prime and bond adhesive system ( p90 system adhesive ) . 
 teeth were subjected to thermocycling regime ( 500 , 5 - 55c ) , and dye penetration by immersing in 2% methylene blue for 24 h. tooth sectioning was performed , and extent of the dye penetration was scored based on dye penetration scale to evaluate the microleakage . statistical analysis included descriptive statistics and inferential statistics of kruskal  wallis test to compare the mean ranks between groups.results:there was no significant difference observed for microleakage among the three composite materials tested in the present study . 
 however , the cavities restored with silorane ( filtek p90 ) based composite displayed higher microleakage than the filtek z250 , z250 xt.conclusion:all the restorative systems tested in this study exhibited microleakage , but the silorane technology showed more microleakage when compared to the methacrylate - based composite systems .