bonding to enamel is been considered satisfactory , but adhesion to dentin is much more complex due to the nature of the substrate . the best way to test the effectiveness of a biomaterial , as well as composite or luting cement or a bonding system , is in vivo experimentation in controlled trials .
however , it is quite impossible to distinguish by clinical evaluation and adhesion potential of a dentin - bonding system from many other parameters that influence either the quality or the longevity of a restoration .
theoretically , in vitro bonding tests would allow for measurement of the true strength of bonding of a given system to a dentinal substrate .
unfortunately , in vitro dentin adhesion testing has not been very successful in predicting in vivo effectiveness , probably because of the number of factors influencing test results and clinical relevance.[13 ] several authors have already studied the influence of some of these factors , such as the origin of the substrate , substrate storage , dentin depth , type of composite , testing mode , etc .
some previous reviews have listed most of the variables influencing dentin bond strength , but none has quantified their importance or defined their statistical significance . the purpose of this study is to evaluate the true factor that affects the bond strength of one - step and two - step self - etch adhesive .
this quantitative overview could be considered as a meta - analysis study performed under non - experimental conditions to assess the effects of certain clinical parameters on bond strength of adhesives .
potential papers were selected from articles published in 13 peer - reviewed journals using  pubmed data base  .
american journal of dentistry , journal of adhesive dentistry , british dental journal , dental materials , european journal of oral science , international dental journal , journal of dentistry , journal of dental research , journal of oral rehabilitation , journal of prosthetic dentistry , operative dentistry , quintessence international and journal of conservative dentistry . 

study with original data.paper published in english or translated to english.only studies measuring the bond strength of one - step and two - step self - etch dentin - bonding agents to be included.the bonding agents that are commercially available and tested by shear or tensile mode on sound dentin from permanent teeth.dentin-bonding agents involved in the analysis should have been tested in at least five different studies.the outcome measure had to be the dentin bond strength expressed in mpa / psi.light curing unit with intensity of 400 - 500 mw / cm.among the selected studies , some exclusion criteria applied.paper displaying only graphic data.dentin-bonding agents not used according to manufacturer 's instructions.dentin samples , which were contaminated or not treated under clinical conditions before application of the dentin - bonding agents , were excluded from the analysisstudy without data analysis . 
 
paper published in english or translated to english . only studies measuring the bond strength of one - step and two - step
the bonding agents that are commercially available and tested by shear or tensile mode on sound dentin from permanent teeth .
dentin - bonding agents involved in the analysis should have been tested in at least five different studies .
the outcome measure had to be the dentin bond strength expressed in mpa / psi .
light curing unit with intensity of 400 - 500 mw / cm . among the selected studies , some exclusion criteria applied .
dentin samples , which were contaminated or not treated under clinical conditions before application of the dentin - bonding agents , were excluded from the analysis study without data analysis .
we classified the parameters into four groups : group a - factors related to the dentin substrate ; group b - type of composite and dentin - bonding agents ; group c - bonding area and ; group d - thermocycling and testing mode .
selected studies were included in the meta - analysis the problem of bond - strength testing is that the materials were seldom compared with a standard .
rather , different materials were tested under various conditions and bond strengths are reported as point estimates and expressed in mpa .
it is difficult to compute a standard effect size for each study , as required in a classic meta - analysis .
thus , we decided to analyze directly the measures of bond strength from reports published in literature .
this quantitative overview was performed in non - experimental conditions since materials and conditions are not allocated randomly . from each report
means and standard deviations of bond strengths were extracted and tabulated with corresponding experimental conditions . the statistical analysis software system mix 2.0 professional ( biostat , englewood , nj ) was used to perform the statistical analysis .
potential papers were selected from articles published in 13 peer - reviewed journals using  pubmed data base  .
american journal of dentistry , journal of adhesive dentistry , british dental journal , dental materials , european journal of oral science , international dental journal , journal of dentistry , journal of dental research , journal of oral rehabilitation , journal of prosthetic dentistry , operative dentistry , quintessence international and journal of conservative dentistry .

 study with original data.paper published in english or translated to english.only studies measuring the bond strength of one - step and two - step self - etch dentin - bonding agents to be included.the bonding agents that are commercially available and tested by shear or tensile mode on sound dentin from permanent teeth.dentin-bonding agents involved in the analysis should have been tested in at least five different studies.the outcome measure had to be the dentin bond strength expressed in mpa / psi.light curing unit with intensity of 400 - 500 mw / cm.among the selected studies , some exclusion criteria applied.paper displaying only graphic data.dentin-bonding agents not used according to manufacturer 's instructions.dentin samples , which were contaminated or not treated under clinical conditions before application of the dentin - bonding agents , were excluded from the analysisstudy without data analysis . 
 
paper published in english or translated to english . only studies measuring the bond strength of one - step and two - step
the bonding agents that are commercially available and tested by shear or tensile mode on sound dentin from permanent teeth .
dentin - bonding agents involved in the analysis should have been tested in at least five different studies .
the outcome measure had to be the dentin bond strength expressed in mpa / psi .
light curing unit with intensity of 400 - 500 mw / cm . among the selected studies , some exclusion criteria applied .
dentin samples , which were contaminated or not treated under clinical conditions before application of the dentin - bonding agents , were excluded from the analysis study without data analysis .
we classified the parameters into four groups : group a - factors related to the dentin substrate ; group b - type of composite and dentin - bonding agents ; group c - bonding area and ; group d - thermocycling and testing mode .
the problem of bond - strength testing is that the materials were seldom compared with a standard .
rather , different materials were tested under various conditions and bond strengths are reported as point estimates and expressed in mpa .
it is difficult to compute a standard effect size for each study , as required in a classic meta - analysis .
thus , we decided to analyze directly the measures of bond strength from reports published in literature .
this quantitative overview was performed in non - experimental conditions since materials and conditions are not allocated randomly . from each report means and standard deviations of bond strengths were extracted and tabulated with corresponding experimental conditions .
the statistical analysis software system mix 2.0 professional ( biostat , englewood , nj ) was used to perform the statistical analysis . differences between means were computed with analysis of variance .
tables 2 and 3 show descriptive statistics of different parameters tabulated from the selected studies according to the four groups described in materials and methods section . some parameters , such as tooth storage medium and dentin surface topography , were not included in the statistical analysis , due to their greater variability or lack of information .
it was noted that about one - third of the selected articles provided such information and that the distinction between the different failure modes was not always available and clearly identified .
one - way anova comparison between one - step and two - step self - etch adhesives is given in table 4 the p - values indicate the potential relation between each parameter and the bond strength .
their respective influences were given by the p - value at the significance level of 0.05( ) .
all the studied parameters showed no significant difference , except for dentin origin / site and bonding area .
in addition , statistical analysis done with anova showed statistical significance between the one - step and two - step self - etch adhesives .
descriptive statistics of the different parameters studied using one - step self - etch adhesives descriptive statistics of the different parameters studied using two - step self - etch adhesives comparison between one - step and two - step self - etch adhesives using anova
as quoted by dersimonian and laird ( 1986 )  meta - analysis is the statistical analysis of a collection of analytic results for the purpose of integrating the findings . 
the advantage of meta - analysis over the traditional literature review is the possibility of combining results from many studies and analyzing the factors that affect the bond strength of self - etch adhesives . in the studies
selected , the tensile or shear testing was done using a constant crosshead speed and the samples were continuously loaded such that the crack will propagate at increasing speed until separation . in a clinical situation ,
if these loads are high enough , small extensions of cracks ensure sub - critical crack growth in bonded area as explained by a. a. griffith .
according to griffith 's theory of brittle solid it is stated that the low fracture strength observed in experiments , as well as the size - dependence of strength , were due to the presence of microscopic flaws in the bulk material . in this practical situation ,
the crack speed is much lower than during tensile or shear forces , which is used to determine the adhesion potential of a dentin - bonding system .
the location of the initial flaw is unknown , and the stress concentration at the bonded interface is non - uniform and unpredictable .
moreover , the stress distribution is highly dependent on the test geometry , on the loading mode and on the material properties.[2729 ] our analysis revealed that the origin of dentin , site of bonding and bonding area had significant influence on bond strength of one - step and two - step self - etch adhesive .
the studies have also showed that there is a difference in bond strength between human teeth and bovine teeth .
this difference explains the fact that dentinal tubules are large in the coronal portion of bovine dentin , but one study by nakamichi et al , showed that there is no difference in bond strength between bovine and human dentin when only the superficial layers was used .
oilo and olsson showed that the tensile strength is higher on the buccal surface compared to the occlusal surface , which could be explained by the fact that the tubules are lower in number with less area percentage on the buccal surface than on the occlusal surface .
the analysis also showed a definite difference between enamel and dentin bonding which might be explained by various reasons .
dentin has a heterogeneous structure and different orientation of tubules with root dentin having smaller and more numerous branching of tubules when compared to crown dentin .
acidity of monomer also caused change in surface chemistry and morphology of dentin , which in turn can influence bonding .
a significantly thicker hybrid layer was noted in areas with perpendicular tubule orientation than in areas with parallel tubule orientation surface area significantly affects the bond strength in one - step and two - step self - etch adhesives .
bond strength is calculated as the load at failure divided by the cross - sectional area of the bonded surface .
an inverse relationship between bond strength and bonded surface area has been recently shown , confirming previous studies .
these authors explain the lower strengths of large bonded samples by the greater number of defects within the adhesive joint .
burrow mf et al , stated that clearfil se bond showed no statistical difference to g - bond .
do amaral rc et al , suggested application of bonding agents with agitation on the dentin surface to improving the resin - dentin bond strength of one - step self - etch adhesives . when bonded to dentin
, the adhesives with simplified application procedures ( in particular , one - step self - etch adhesives ) still underperform as compared to conventional three - step adhesives . 
mild  two - step self - etch adhesives that provide additional chemical bonding , appear to most optimally combine bonding effectiveness with a simplified application protocol our analysis has showed that two - step self - etch adhesive system showed a superior in vitro performance in comparison to one - step self - etch system .
these results are in accordance with those of other studies . the bonding ability of the all - in - one adhesives depends on their specific composition . in light of the low in vitro bond strengths and high rate of spontaneous failures of some all - in - one
adhesives compared to those of the two - step adhesives , the newest adhesives should be screened more strictly before they are recommended for clinical use .
one - step self - etch adhesives showed higher bond strengths on ground enamel and no reductions in resin - enamel bonds were observed after 12 months of water storage .
marginal adaptation was significantly better for clearfil s3 bond than for adper prompt l - pop .
serious limitation of all - in - one adhesives are as follows : incomplete polymerization and continued demineralization of the adjacent dentin structure in the tubules . for all - in - one adhesives to be acidic ,
studies have shown that this water acts as a major interfering factor in polymerization which leads to unpolymerized acidic and aggressive monomers to continue etching the dentin , thereby leading to a detrimental impact on the bond .
other factor leading to low bond strength and failure of resin - based adhesives in vivo are harsh conditions of the oral environment , such as intraoral temperature , moisture contact , fatigue of bond due to tooth flexure and bacterial enzymes . the shelf life of one - component self - etching adhesives is determined by their chemical composition . in conventional methacrylate - based adhesives
( adhese ) , the inherently acidic environment of such formulations leads to monomer degradation due to hydrolysis .
in contrast , methacrylamide - based adhesives are stable to aqueous acid and exhibit much superior storage stability without monomer degradation - related losses in adhesion performance .
intermediary strong self - etch adhesives ( adhese and xeno iii ) exhibited significantly superior shear bond strength values compared to both 
strong ( prompt - l - pop ) and  weak ( clearfil se bond ) self - etch systems , which implies that ph of the adhesive has a significant effect on the bond strength .
suzuki and finger found a linear relationship between the remaining dentin thickness to the pulp and the shear bond strengths of three different adhesives , an observation subsequently confirmed by other authors the analysis surprisingly showed that type of composite and thermocycling did not significantly affect bond strength . nevertheless , three studies reported a decrease in adherence after thermocycling whereas other studies reported an increase , depending on the adhesive system tested .
from this meta - analysis study , we have analyzed that two - step self - etch adhesive showed better bonding ability than one - step self - etch adhesives .
thereby , several clinical parameters among which dentin origin , site and area of bonding have shown a significant influence on mean bond strength of adhesive system .
thus , our study suggests , that the practitioners can easily control these parameters by using standardized protocol for the clinical success of self - etch adhesive systems .
 aim : the purpose of this study is to critically evaluate the factors that affect the bond strength of one - step and two - step self - etch adhesives by using meta-analysis.materials and methods : potential papers that were selected according to inclusion and exclusion criteria from articles were published in 13 peer - reviewed journals using  
 pubmed data base  . from each report , means and standard deviations of bond strengths were extracted and tabulated with corresponding experimental conditions.results:all the studied parameters showed no significant difference , except for dentin origin / site and bonding area . 
 in addition , statistical analysis done with anova showed statistical significance between the one - step and two - step self - etch adhesives.conclusions:our analysis has showed that two - step self - etch adhesive system showed a superior in vitro performance in comparison to one - step self - etch system . 
 nevertheless , certain factors such as dentin origin , site and area of bonding affect the bond strength of adhesives . 
INTRODUCTION
MATERIALS AND METHODS
Data collection
Inclusion criteria
Statistical analysis
RESULTS
DISCUSSION
CONCLUSION