in the bleacheddentin even after SA application. The MMPs ’ activity of bleached and SA exposed group was similar to positive control (G1). The literature shows that the application of bleaching agents leads to denaturation of the dentin proteins by the oxidizing agents, 23 and may cause a modi ﬁ cation in the chemistry of the dental hard tissues, altering the ratio between organic and inorganic components. 24 Besides, oxidants may also inactivate the tissue inhibitors of metalloproteases. 11 In this sense, expo- sure of MMP-2 and − 9 to a low pH, followed by neutra- lization, has been shown to enhance the proteolytic activity of these enzymes. 25 Thus, the pH neutralization caused by SA may create a favourable environment for the activity of these proteases.
Y Shimada et al  55 : conducted studies on Shear BondStrength of Current Adhesive Systems to Enamel, Dentin and Dentin-Enamel Junction Region. This study investigated the bonding of current –reSuT adhesives to the region approximating the dentin-enamel junction (DEJ), where the etch pattern to enamel or dentin may be different. Three kinds of tooth substrates were chosen for testing: enamel, dentin and the DEJ region. A self-etching primer system (Clearfil SE Bond) and two total-etch wet bonding systems (Single Bond and One-Step) were used. Each tooth region was bonded with one of the adhesive systems, and a resin composite and was subjected to a micro-shear bond test. In addition, morphological observations were performed on debonded specimens and etched surfaces using confocal laser scanning microscopy (CLSM). CLSM observations showed that the DEJ region was etched more deeply by phosphoric acid gel than enamel or dentin, suggesting that the action of acid etch seemed to be more intense on the DEJ. However, no statistically significant differences of shear bondstrength values were observed between the DEJ region and enamel or dentin, or the adhesive systems used (p>0.05). Bonding to the DEJ was potentially as good as that of enamel or dentin.
Treatment of bleached teeth is challenging for dentists because they cannot immediately perform a resin restoration on bleached teeth due to the presence of oxygen or peroxide residues on the surface, since they prevent complete polymerization of adhesive resin . However, by postponing the composite restoration for two weeks following bleaching, no reduction in bondstrength would occur [5,15,17]. But, sometimes it is not possible for the patient to wait that long. Therefore, use of antioxidants like ascorbic acid or sodiumascorbate is one method to immediately increase the bondstrength of composite to bleached enamel [8,10]. It has been proven that application of sodiumascorbate can result in accumulation of Streptococcus mutants on bleached surfaces . Also, pH of sodiumascorbate is 1.8, which has adverse effects on tooth structure in clinical application. Short shelf life of sodiumascorbate solution or gel is another disadvantage of using it [26,27]. It has been demonstrated that use of herbal antioxidants such as green tea and grape seed is an effective alternative strategy for this purpose.
Since, there is a limited information available on the use of the newer natural antioxidant agents like Oligomeric Proanthocyanidin Complexes (OPCs) that they increases the bondstrength of composite resin to bleached enamel. OPCs present in natural antioxidants like grape seed extract and pine bark extract have free radical scavenging activity 4 ,36 . Hence, the aim of this in-vitro study was to evaluate and compare the effect of 10% SodiumAscorbate , 10 % pine bark extract, and Aloe vera leaf solution on the SBS of composite resin to bleached enamel.
still not clear, the reduced bondstrength of bleached enamel has been related to the presence of residual free radicals due to the breakdown of hydrogen peroxide [14, 18] and alter- ations in the enamel composition and structure [6, 19] fol- lowing the bleaching treatment. The residual oxygen in the interprismatic spaces can hamper resin infiltration and in- hibit resin polymerization . Moreover, morphological and compositional changes (e.g., porosity, loss of enamel prismatic form, loss of calcium, and changes in organic sub- stances) in the enamel may weaken the adhesive interface and compromise bondstrength [21, 22]. Therefore, bonding procedures should not be performed immediately after bleaching treatment . A waiting period of 1–3 weeks has been advocated by various researchers [21, 24, 25]. In addition to the delayed bonding procedure, the application of antioxidant agents (e.g., sodiumascorbate, sodium bi- carbonate, and grape seed extract) [18, 26, 27] and laser ir- radiation [28, 29] have been proposed to restore the compromised bondstrength of bleached enamel. By neu- tralizing residual free radicals  and promoting micro-retentions in the enamel surface , antioxidant agents and laser irradiation have been shown to reverse the reduced bondstrength between the composite resin and bleached enamel. However, it is important to point out that most of the above-mentioned studies measured the bondstrength without thermocycling [24–29]. Ther- mocycling is the in vitro process of subjecting a restor- ation and tooth to temperature limits similar to those experienced in the oral cavity . It would be of interest to investigate the effects of thermocycling on the bondstrength between the composite resins and the bleached enamel.
Another study showed that application of pome- granate peel extract, grape seed extract, green tea, and sodiumascorbate on enamel bleached with 40% hydro- gen peroxide neutralized the effect of residual oxygen molecules on the bleached enamel surface, and in- creased the SBS of composite resin.  The concentra- tion of antioxidants were similar to the current study, but we used 15% carbamide peroxide as the bleaching agent which is weaker than hydrogen peroxide and could produce less residual oxygen molecules. Appar- ently, the effect of antioxidant on the SBS would de- crease as the bleaching agent concentration decreases.
Aims: Residual peroxide on the enamel surface and in the interprismatic spaces decreases the shear bondstrength (SBS) of composite to bleached enamel. Evidence shows that 10% sodiumascorbate can efficiently neutralize the singlet oxygen generated by the bleaching agents. This study aimed to assess the effect of duration of application of sodiumascorbate on SBS of composite to bleached enamel. Materials and Methods: This in vitro experimental study was conducted on 30 sound human third molars, which were randomly divided into three groups (n=10). In group 1, the teeth were bleached for 45 minutes and were then subjected to immediate bonding and restoration with composite resin. In groups 2 and 3, the teeth were bleached, immersed in 10% sodiumascorbate solution for 5 (group 2) and 10 (group 3) minutes and were then bonded and restored with composite, and the SBS was then measured. Results: The highest SBS (14.02±8.6MPa) was noted in group 3 (immersion in 10% sodiumascorbate for 10 minutes before bonding). The lowest SBS was noted in group 1 (immediate bonding after bleaching) (p<0.05). The difference in SBS of groups 1 and 2 was not significant (p=0.4). Conclusion: Application of 10% sodiumascorbate for 10 minutes increases the SBS of composite to bleached enamel.
Materials and Methods: Forty flat enamel surfaces were prepared from freshly extracted human premolars using a low speed diamond saw. Then the specimens were divided into four random groups (n = 10). All the groups were treated with 30% H2O2. The specimens in Group I were bonded immediately after bleaching, whereas Group II, III and IV were treated with antioxidants Sodiumascorbate, Pomegranate peel extract and Grape seed extract respectively. After preparation, a standard shaped resin composite was applied to all specimens. The teeth were stored in deionized water for 24hrs at 37°C and a universal testing machine determined their shear bondstrength. The data were evaluated using ANOVA and Tukey Post Hoc tests.
molecules could be eventually displaced by competing cations derived from dentinal fluid or saliva and leach out of the denuded collagen matrix. For this reason, there is a prevailing notion that CHX binding to demineralized dentin merely postpones rather than permanently arrest bond degradation. Then again, for how long can CHX extend its protective effect is still a question that requires further research. Chlorhexidine proved to be beneficial only for etch-and-rinse adhesives, as it could not bind to the collagen matrix in the presence of an acidic environment as present in self-etch adhesives. 15
Self-etch adhesive systems are composed of various monomers, solvents, fillers, and initiators that make their molecular formulations quite complex. The intricate design involved in these systems has raised uncertainties regarding the long-term chemical stability of the components prior to clinical application. Therefore, this study aimed to investigate the effect of shelf-life simulation on the bondstrength of self-etch adhesives to dentin. Sound human teeth samples were used and restored using one of three different adhesives: AdheSE ? (Ivoclar Vivadent), Single Bond Universal ? (3 M ESPE), or Clearfil SE Bond ? (Kuraray); Filtek Z350 ? (3 M ESPE) was used as composite resin. The study (bondstrength testing) was conducted in two distinct parts: (1) without shelf-life simulation of adhesives; and (2) after storing the adhesives in a climate chamber at 40?C and 50% relative humidity (shelf-life simulation). Both groups were prepared for microtensile bondstrength ( μ TBS) testing; however, specimens from the first part of the study were evaluated after 24 h and 6 months of storage in distilled water, whereas specimens from the second part of the study were prepared and tested after 1, 2, and 3 months of shelf-life simulation of adhesives. The hybrid layer and fracture pattern of specimens were analyzed by scanning electron microscopy (SEM). Bondstrength data were analyzed using Kruskal-Wallis test and Tukey ? s test ( α = 5%). When no shelf-life simulation was applied, Single Bond Universal increased bondstrength after long-term water storage, whereas AdheSE and Clearfil SE Bond reduced bondstrength to dentin. However, the bonding ability of all three adhesive systems investigated was negatively influenced by the shelf-life simulation used.
In comparison with composite resins, RMGICs self-adhere to hard tissue, thanks to the micromechanical interlocking of their constituents. Moreover, their mechanism of attachment to dentin is somewhat different; so that they attach to the dentin through a chelation reaction, followed by metal ion exchange, and formation of a layer between the GI and tooth structure. [15-17] Yet, it is still unclear how CHX may affect the quality of GI-tooth structure interactions. In a study on Vitremer, 2% CHX did not interfere with the microtensile bondstrength of RMGI to the primary tooth dentin.  Few studies on Fuji II LC restorative material showed that disinfection with CHX had no negative effect on its bondstrength to permanent tooth dentin after 24 hours. [19- 20] Yet, the long-term bondstrength between this material and dentin was reported to have significantly decreased. 
a decrease in the micromechanical interaction between resins and NaOCl-treated dentin. On the other hand, chlorhexidine a cationic bisguanide, was used as a final flush in G3 (Fig. 4). It shows optimal antimicrobial activity over the pH range from 5.5 to 7.0, and acts by adsorbing onto the cell walls of microorganisms and causing breakdown of intracellular components . Erdemir et al.  reported that endodontic irrigation with CHX solution significantly increased bondstrength to root dentin. This was found to be in agreement with our study. These authors suggested that adsorption of CHX by dentin may favor the resin infiltration into dentinal tubules, which explains the high bondstrength values obtained in G3. Also, CHX increases the wettability of endodontic sealers on dentin, which can be explained by the presence of surface surfactant in CHX, increasing the surface energy and promoting higher wetting ability to dentin. Additionally, this substance has a broad-spectrum MMP-inhibitory effect that improves the resin-dentinbond stability .
microtensile bondstrength ìn the total-etching groups (G2 and G4). The great dem- ineralization caused by acid etching exposes a large amount of collagen fibrils and the air-abrasion with Bioglass 45S5 for 1 min may cause the collapse of the demineralized collagen fibers, jeopardizing the adhesion between adhesive and dentin decreasing the bondstrength. Further studies should be performed to confirm this hypothesis. The self-etching with air-abrasion Bioglass 45S5 (G3) not improve the microtensile bondstrength. The presence of the functional monomer 10-MDP may have compete with Bio- glass 45S5, since this monomer shows a phosphate group attached to carbon chain . In water this monomer ionizes creating covalent bonds with Ca +2 and PO 4 ions pre-
U200, GIC and RMGIC). Duraphat is a varnish with 2.3% F and has been established that it has effective desensitization. Some scholars have suggested that the application of Du- raphat could form a spherical calcium fluoride (CaF 2 ) on the dentin surface [6, 13]. Bifluorid 12 contains 5.6% F, and sodium fluoride parti- cles penetrate into tubules to prevent hyper- sensitivity and CaF 2 or CaF 2 -like deposits on the dentin surface which decrease the dentin permeability [7, 13]. A previous study indicat- ed that the application of Bifluorid 12 prior to cementation prevented the forming of a stable hybrid layer resulting in a bondstrength reduc- tion . Prime & Bond NT possesses a favor- able penetrability and adhesiveness quality, and it exposes dentin tubules by acid-etching, then resin penetrates into tubules, a polymer- izing resin tag to block tubules mechanically .
In contrast, other established methods for assessing push out bondstrength involve the canal preparation, obturation and analysis of the different root sections of extracted teeth [20, 29]. These techniques have a disad- vantage of causing inconsistent baseline measurements due to lack of proper standardization of the root canal anatomy. Moreover, according to the recent evolution in the methodological aspect recommended by Scelza et al.  and Silva et al. , this study used single dental slices each with three standardized holes to test the push out bondstrength of three different sealers . This was done to eliminate the complicating ele- ments such as age of tooth, canal shape, scleroses, and micro-hardness in order to maintain a standardization of the comparisons. Additionally, a distance of 1 mm was maintained between any two holes, external ce- mentum and the root canal surface to avoid fracture of the dental slice . Standardized artificial holes of 0.8 mm in diameter were created to replicate the internal root canal anatomy . With regard to the plunger tip size, Chen et al.  proposed that the size of the plun- ger tip should be 0.85 times smaller than the size of the filling material. Further, this researcher proposed that the position of the plunger tip must be closer to the diameter of the sealer. This allowed the plunger tip to concentrate the stress closer to the sealer dentine inter- face. Phosphate based solution (PBS) had been used as
(Pentron Clinical) using oblique incremental technique, or restored directly with Fusio™ Liquid Dentin self-adhesive flowable composite (Pentron Clinical) (Group 3), accord- ing to manufacturers’ instructions. After restoration of the cavities, each group was further subdivided into three equal subgroups (n = 10): Subgroup 1 – control, Subgroup 2 – subjected to occlusal cyclic loading (90N for 5,000 cycles), and Subgroup 3 – subjected to occlusal cyclic loading (90N for 10,000 cycles) (Table 2).
Based on the results of the present study, we can conclude that there is no one factor responsible for bond degradation. The μ SBS values obtained during an experiment are a direct function of the combination of: 1- A suitable surface treatment method and the use of and MDP-based primer (that will dictate the quality of the resin-zirconia bond), and 2- The type of aging treat- ment used is paramount for the validity of in-vitro test- ing. It is noteworthy that thermocycling at 10,000 cycles did not degrade the bond. Further research using higher cycles values should be done to prove or disprove the effect of thermocycling on μ SBS values. 3-A minimum of one year in storage medium should be used during aging tests. Further studies should be performed to con- ﬁ rm that fact.
Polymerization is important in terms of physico- mechanical strength of the adhesive . In simplified adhesives, the degree of conversion was shown to be low . This can cause low mechanical properties, higher permeability , more water sorption , more nanoleakage , degradation of the bonding interface , more leaching out of residual unpolymerized mon- omers and lower biocompatibility . Polymerization is inhibited by several factors such as the presence of oxygen , presence of intrinsic water from dentin and solvents . Another reason postulated for incomplete conversion of SEAs is the interaction of acidic monom- ers with amines of the photoinitiator system .
a dry state; the molecules are arranged more compactly. This is because extra-fibrillar spaces in hydrated type I collagen are filled with water, while dried collagen has fewer extra-fibrillar spaces open for the penetration of the monomers included in the adhesive systems (Sasaki, 1996). Aggressive water removal (i.e. over-dry) may also permit additional hydrogen bonds to form between collagen molecules that were previously bonded to water molecules, leaving no inter-fibrillar spaces. During air-drying, water that occupies the inter-fibrillar spaces previously filled with hydroxyapatite crystals is lost by evaporation, resulting in a decrease of the volume of the collagen network to approximately one third of its original volume (Rosenblatt et al., 1994). Both previously mentioned studies are in agreement with our results that revealed higher mean shear bondstrength values in case of moist dentin than in case of dry dentin especially with the use of ethanol based adhesive (moist: 20.79 +/- 4.91 and dry: 14.13 +/- 4.65) and acetone based adhesive (moist: 8.05 +/- 2.08 and dry: 5.45 +/- 1.49) with exception of water/ethanol adhesive that gave a reversed result to the other two adhesives i.e. dry dentin gave higher mean shear bondstrength values than in case of moist dentin (dry: 18.11 +/- 3.50 and moist: 15.73 +/- 4.13). On the other hand, results of Gwinnett in his study, revealed that the bondstrength values of Gluma bonding agent (acetone based) were compromised by the presence of moisture. He stated that while Gluma is hydrophilic and acetone containing, it does not appear to possess the same behavioral characteristics embodied in the other systems as evidenced from lack of a bond to moist dentin (Reinhardt, 1997).
In order to avoid dentin contamination and the resulting problems, the dual bond- ing or immediate dentin sealing technique has been proposed [4, 5]. In this procedure a dentin bonding agent is applied to the fresh cut dentin prior to the placement of the provisional restoration. Immediate dentin sealing requires hybridization of the exposed dentin surface immediately after tooth preparation and during final luting procedures [6, 7]. The technique prevents the bacterial invasion and dentin sensitivity during the provisional phase, and it is concerned with increased bondstrength . Another advan- tage is that the thickness of dentin bonding agent is considered before tooth preparation impression . The technique could be used with a 3-step etch-and-rinse dentinbond- ing agent, leading to increased microtensile bondstrength compared to delayed dentin sealing. General protocol suggests the use of two step total-etch systems and two-steps self-etch systems as well .