the glass - ionomer cement ( gic ) was introduced by smith26 in the late 1960 's , resulting from the replacement of phosphoric acid by polyacrylic acid in zinc phosphate cements .
the original idea was to unite properties of the silica glass powder , such as high strength , hardness and the capacity to release fluoride , with the biocompatibility and adhesion ability of the polyacrylic acid liquid26 .
the anticariogenic property resulting from fluoride release turned out to be the most attractive aspect of this dental material .
in addition , gic adhesion mechanism to tooth structure , thermal compatibility with tooth enamel , biocompatibility and low cytotoxicity render to gic an interesting clinical option for restorative treatments30 . since the first commercial appearance of gic ( aspa , dentsply de trey ltd , weybridge , uk ) in 1976
, this material has undergone important modifications in composition to improve its tensile and fracture strengths , working time , chemical solubility , and polishing appearance4,27,28 .
therefore , new types of gics have been developed , such as the light - cured resin modified glass ionomer cement ( rmgic)1,27 . this material is obtained by adding a resin , usually the water - soluble polymerizable 2-hydroxyethyl methacrylate ( hema ) , to the liquid and its bonding process to tooth structure takes place by micromechanical retention , like in resin composites27 .
the setting reaction of rmgic follows two distinct mechanisms : resin polymerization and acid - base reaction .
the former can be initiated by either light exposure or redox reaction ( self - curing ) and is responsible for the immediate setting .
the advantages of this restorative material include longer working time and operator control over the setting reaction by light activation of the resin component and , consequently , an earlier development of higher bond strength , reduced brittleness , increase of tensile and flexural strengths , resistance to desiccation and acid attack , lower moisture sensitivity and solubility2,9,11,16,27,28 .
yet , the mechanical properties ( table 1 ) and esthetic appearance still limit its clinical use .
thus , the so - called sandwich restoration or " composite - laminated gic " technique has been used by clinicians to preserve the fluoride release mechanism and the chemical bond to tooth structure provided by the gic and rmgic , and to improve the esthetic and mechanical properties using a resin composite laminate .
microleakage studies are used to estimate the resistance of tooth - restoration interface to the passage of bacteria , fluids , chemical substances , molecules and ions3 .
the absence of a seal at restoration margins promotes tooth discoloration , adverse pulp response , postoperative sensitivity , and recurrent caries8 .
thus , some in vitro studies developed to predict the clinical marginal sealing ability of several restorative techniques found lesser microleakage when gic was used as a filling material beneath the composite resin10,14,23 . despite these enthusiastic results , the clinical performance of sandwich restorations does not seem to be very effective and some failures have been reported , mainly concerning the gic portion29 .
some authors have stated that this laminate restoration is an interesting alternative to amalgam , especially in high - caries risk patients7 .
other authors have suggested that the failures could be related to an inadequate selection of the gic- composite system , which should provide high tensile strength , a bonding agent with high wettability and a composite resin with small setting shrinkage17,18 .
the bonding mechanisms of restorative materials to tooth tissues are often explained in the literature7 .
yet , few studies have addressed aspects regarding the restorative materials used in sandwich techniques18,20 .
although enamel and dentin pre - treatment before the application of bonding systems and restorative materials is well established in the literature6 , the need for gic surface treatment before the placement of composite resin in sandwich restorations still remains debatable .
although acid etching of gic 's surface increases the tensile bond strength to resin composite12 , the influence of this conditioning step on microleakage has not been reported .
the purposes of this study were to evaluate the sealing ability of different gic materials used for the sandwich restoration technique , and to assess the effect of acid etching of gic surface on microleakage between the ionomer and composite materials .
the tested hypothesis was that acid etching of gic before placement of the composite resin does not increase the sealing between both restorative materials .
twenty extracted non - carious human permanent premolars with fully developed roots were selected for this study , which was approved by the local ethics in research committee .
the teeth were cleaned of calculus , soft tissue and other debris , and stored in 2% chloramine solution at 5c .
two window - like cavities were prepared on both proximal surfaces of each tooth using diamond burs ( no .
3145 and fg58l ; kg sorensen , so paulo , sp , brazil ) at high speed , as shown in figure 1 .
the tested materials included a conventional gic ( ci ) ( ketac fill plus , 3m - espe , st .
paul , mn , usa ; lot 178566 ) , a light - cured rmgic ( vitremer ; 3m - espe , st .
paul , mn , usa ; lot 4jp 2007 - 12 ) , an adhesive system ( as ) ( adper single bond ; 3m - espe , st .
paul , mn , usa ; lot 4bu 2007 - 11 ) and a composite resin ( cr ) ( filtek z250 ; 3m - espe , st .
all materials were handled at room temperature ( 23c ) following the manufacturers ' instructions .
the 40 cavities were randomly assigned to 4 groups ( n=10 ) and restored according to the sandwich technique18 .
the experimental groups were as follows : 
 group cie - ci was applied onto the axial and cervical cavity walls , allowed setting for 5 min and acid etched ( e ) along the cavity margins with 35% phosphoric acid for 15 s , washed with air - water spray for 30 s , and blotted with an absorbent sponge . the as was applied and light cured ( xl 3000 , 3m - espe , st .
paul , mn , usa ) for 10 s , completing the restoration with a layer of cr that was light cured for 40 s ; group cin - same procedures described for group cie , except for acid etching of the ci surface ; group : rme - same procedures described for group cie , but using the rmgic .
group rmn - same procedures described for group rme , except for acid etching of the rmgic surface .
all restorations were polished with sof - lex discs ( polishing discs , 3m - espe , st .
teeth were coated with 3 layers of nail varnish ( risqu , niasi s / a , taboo da serra , sp , brazil ; lot 331526 ) , except for a window area that included the restoration and 1 mm around it , and soaked in 1% methylene blue dye solution at 24c for 24 h , then rinsed under running water for 1 h. the teeth were adapted to an automatic cutting machine ( struers minitom , struers a / s , denmark ) with a water - cooled low - speed ( 250 rpm ) diamond wheel saw , and were bisected longitudinally to separate the mesial from the distal surfaces .
then , at least 2 approximately 1-mm - thick slices were obtained within the restored area . whenever more than 2 slices were obtained per restoration ,
only 2 of them were used in the study , being one slice above the cementoenamel junction ( cej ) and another below the cej .
therefore , 4 surfaces per restoration were examined in an optical microscope ( meiji emz - tr , meiji techno co ltd . ,
tokyo , japan ; magnification 10x-65x ) for marginal sealing and leakage ( 40 surfaces per group ) .
representative images were recorded from all specimens and maximum degree of dye penetration was registered according to the following scores ( iso / ts 11405 - 2003)13 : 0 = no dye penetration ; 1 = dye penetration into the enamel portion of the cavity wall ; 2 = dye penetration into the dentin portion of the cavity wall but not including the pulpal floor of the cavity ; 3 = dye penetration including the pulpal floor of the cavity .
results were statistically analyzed by kruskal - wallis at 5% significance level ( =0.05 ) and chi - square test for the two types of gic and for the acid - etching effect on both gics ( =0.05 ) .
the sample size , dye penetration scores , dye penetration score means and statistical grouping are summarized in table 2 .
group means followed by the same letter are not statistically different at p=0.05 no significant differences were found between groups cie and cin ( p>0.05 ) , and between groups rme and rmn ( p>0.05 ) regarding dye penetration means .
when both surface treatments ( e and n ) were considered , irrespectively of the materials ( ci and rmgic ) , no statistically significant differences were found ( p>0.05 ) .
however , significant differences were observed between the gics ( ci and rmgic ) , regardless the surface treatments , ci showing a significantly greater dye penetration score mean than that ofrmgic ( p<0.05 ) .
dye penetration at the gic - cr interface occurred in 4 teeth , being 3 in group cie and 1 in group cin .
whenever microleakage occurred , the maximum degree of dye penetration was always found within the slice obtained below the cej .
the polymerization shrinkage developed during the conversion of the monomer molecules into a polymer network is an undesirable resin composite phenomenon and can be considered one of the factors responsible by the lack of adaptation of the restoration to the cavity walls , increasing the susceptibility to caries especially in deep regions of the proximal box of class ii cavities7 .
the use of gic as an underfilling material in conventional sandwich restoration reduces considerably the bulk resin composite used , thus , the amount of polymerization shrinkage of the composite resin is decreased and the marginal adaptation may be improved . a further advantage of the sandwich technique is the fluoride - release property of gics , which is considered to have some inhibitory effect on caries formation and progression around the restoration27 .
the gic is still considered the only material with self - adherence to dental tissue6 and it has been previously shown that gic and composite resin can adhere effectively to each other9,12,15,17 , regardless of the limitations concerning this system18 .
the bond strength between these materials is influenced by , at least , four factors : 1 ) the tensile strength of gic , which is mostly dependent on the powder / liquid ratio ; 2 ) the viscosity of the bonding agent and its ability to wet the gic 's surface ; 3 ) the volumetric change in the composite resin during polymerization and ; 4 ) the difficulties in packing and adaptation of the composite resin to the gic without incorporation of voids18 .
it has been suggested that the acid etching of gic would allow a cleaned mildly roughened surface with high surface energy17 .
it has been assumed that this procedure would fulfill the requirements to a closer contact and a greater interlocked interface between gic and composite resin12,15 . in spite of these considerations ,
the results of the present study indicate that acid etching of ci and rmgic surfaces did not improve the sealing ability of sandwich restorations .
considering the tested gic materials , the sandwich restorations using rmgic showed significantly less dye penetration than those using ci , which is in agreement with the results of a previous report11 . in addition , no significant differences were found between the surface treatments ( e and n ) on same material .
these findings suggest that the accomplishment of acid etching for gic is not significantly relevant compared to the type of gic selected , which should be a material with improved mechanical properties and chemical composition ( table 1 ) .
previous studies have shown that the inability of conventional gics to produce an effective seal depends on two factors : 1 ) the material 's sensitivity to moisture during placement and early set ; and 2 ) the dehydration after setting , resulting in crazing and cracking5,16 . yet , it is assumed that the better sealing produced by rmgic is a result of the formation of resin tags into the dentinal tubules allied to the ion exchange process present in the interface between dentin and rmgic , as previously reported19,20,22 .
although some studies do not testify the presence of these resin tags or even the formation of an hybrid layer24,25 , this assumption stands to be the reason for the superior performance of the rmgic .
in addition , the presence of hema in the rmgic is responsible for the increased bond strengths to resin composite9 and should contribute to prevent dye penetration through the interface of these materials , as demonstrated by the results of the present study .
within the limitations of this study , the results suggest that phosphoric acid etching of gic prior to the placement of composite resin does not improve the sealing ability of sandwich restorations .
the resistance to dye penetration at the interfaces ( gic - composite resin - dentin ) seems to be primarily controlled by the type of gic , rmgic producing significantly less dye penetration than the conventional gic .
 the purposes of this study were to evaluate the sealing ability of different glass ionomer cements ( gics ) used for sandwich restorations and to assess the effect of acid etching of gic on microleakage at gic - resin composite interface . 
 forty cavities were prepared on the proximal surfaces of 20 permanent human premolars ( 2 cavities per tooth ) , assigned to 4 groups ( n=10 ) and restored as follows : group cie  conventional gic ( ci ) was applied onto the axial and cervical cavity walls , allowed setting for 5 min and acid etched ( e ) along the cavity margins with 35% phosphoric acid for 15 s , washed for 30 s and water was blotted ; the adhesive system was applied and light cured for 10 s , completing the restoration with composite resin light cured for 40 s ; group cin  same as group cie , except for acid etching of the ci surface ; group rme  same as cie , but using a resin modified gic ( rmgic ) ; group rmn  same as group rme , except for acid etching of the rmgic surface . 
 specimens were soaked in 1% methylene blue dye solution at 24c for 24 h , rinsed under running water for 1 h , bisected longitudinally and dye penetration was measured following the iso / ts 11405 - 2003 standard . 
 results were statistically analyzed by kruskal - wallis and chi - square tests ( =0.05 ) . 
 dye penetration scores were as follow : cie  2.5 ; cin  2.5 ; rme  0.9 ; and rmn  0.6 . 
 the results suggest that phosphoric acid etching of gic prior to the placement of composite resin does not improve the sealing ability of sandwich restorations . 
 the rmgic was more effective in preventing dye penetration at the gic - resin composite- dentin interfaces than ci . 
INTRODUCTION
MATERIAL AND METHOD
RESULTS
DISCUSSION
CONCLUSION