Vital tooth bleaching which is a routine treatment in modern dental practice is accomplished by either an at-home technique or in-office procedures with high-concentration bleaching agents [1,2]. Although the clinical effectiveness of tooth bleaching has been demonstrated extensively , there are some concerns about potential complications. Whitening agents have adverse effects on the dental pulp [4,5] may decrease micro-hardness of the bleached substrate , and have deleterious effect on bondstrength of the resin materials [7,8]. One of the theories regarding the deleterious effect of bleaching on the bondstrength of resin materials is related to the decrease in bondstrength with the free radicals from oxygen that remain in the dental tissues released by the bleaching agents. After an adhesive system application, the oxygen responds to the closures of the forming polymeric chains, finishing the polymeric extension, lessening the level of transformation of the adhesive system and resin composites and declining the bond quality . The use of bleaching techniques modified by a remineralizing agent called CPP-ACP (casein phosphopeptide amorphous calcium phosphate) has been suggested in an attempt to recover minerals that are lost during bleaching . A recent study revealed that the associative utilization of CPP- ACP and high concentration hydrogen peroxide may be a fruitful strategy for diminishing tooth sensitivity and restricting changes in the enamel morphology during in-office bleaching . Another modification is using fluoride with bleaching agents to prevent either hypersensitivity or demineralization accompanying tooth-whitening therapy. The addition of sodium fluoride to the bleaching agent was found to generate fluoridated hydroxyapatite and calcium fluoride crystals on the enamel surfaces, which potentially accelerated the remineralization of the bleachedenamel . But there is inadequate evidence on the influence of hydrogen peroxide and CPP-ACP on composite-enamel bonding. Additionally, despite profound scientific suggestions which support the remineralization capability of fluoride , the impact of fluoride on resin–enamel holding is dubious. Decreased resinbondstrength has been reported for fluoride-treated enamel, particularly
In the present study, green tea solution was used as an antioxidant at 5% concentrations for 10 minutes. Significant increase was observed in SBS of resin composite to 38% hydrogen peroxide bleachedenamel in group B2 (hydrogen peroxide + green tea), but there were no significant increase in SBS of resin composite to 15% carbamide peroxide bleachedenamel in group A2 (carbamide peroxide + green tea). In the study mentioned above, the different types, concentrations and application times of antioxidant used might explain the differences noticed in the results. In the present study, 15% carbamide peroxide and 38% hydrogen peroxide were used as a bleaching agents but in the above mentioned study, 17% carbamide peroxide was used. This difference, i.e., 17% carbamide peroxide with 38% hydrogen peroxide, might be the underlying reason for producing more peroxide molecules and hence this could be the reason for greater effectiveness of antioxidants on the SBS of resin composite to the bleachedenamel.
neutral and acidic pH . In the present study, ACP was added to Fuji Ortho LC glass ionomer powder in 1.55 wt%. The addition of ACP to Fuji Ortho LC glass ionomer probably increases the release of calcium, phosphate, and fluoride ions and decreases the risk of caries and demineralization of posterior teeth. Uysal et al  measured the SBS of brackets bonded with conventional and ACP-modified composites. Similar to our study, the addition of ACP to the bonding agent decreased the SBS . In their study, in contrast to ours, sandblasting was not performed to increase the SBS of the composite containing ACP to the enamel. Millett et al  bonded molar tubes and reported that RMGI cement yielded a higher SBS than Transbond XT; this finding was different from the results of the current study. This difference may be attributed to the use of molar tubes with different cross- sections, different storage times of the samples before SBS testing, and different methods of enamel surface preparation in the two studies. Millett et al  maintained the enamel surface moist after etching and before the application of Fuji Ortho LC glass ionomer, which was in contrast to our study.
Y Shimada et al  55 : conducted studies on ShearBondStrength 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-shearbond 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 shearbondstrength 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.
Bleaching agents in varying concentrations (Carbamide peroxide 35% to 37% or Hydrogen peroxide 30% to 40%) have been used to achieve rapid aesthetic results . 5,6 When applied on tooth surface, hydrogen peroxide undergoes ionic dissociation and gives rise to the formation of free radicals -hydroxyl, nascent oxygen, and superoxide anions, which are the most potent free radicals. These are extremely reactive and therefore react with the rich regions of pigment within the tooth leading to dissociation of the larger pigmented molecules into smaller and less pigmented molecules . 5,6
pected to evaporate by air current. If these mate- rials are not fully removed from the bonding, they can cause reduction in bondstrength, through their negative effects on the polymerization process . By drying bonding layer of Clearfil S3 Bond, and removing solvents from the primer, the resin layer thins, and due to formation of air-inhibited layer after radiation of light, polymerization of re- sin may not be fully achieved. Under this condi- tion, the levels of non-polymerized acidic mono- mers increase. These agents attack the resin com- posite polymerization initiator system and interfere with its polymerization, which is followed by re- duced bondstrength. Also, unlike in Clearfil SE Bond, only one bonding layer is used in Clearfil S3 Bond. Here, again the protective effect of first layer (primer) in Clearfil SE bond that was ex- plained earlier is an issue. In Clearfil S3 Bond mo- nomer and acid are simultaneously exposed to ac- tivated oxygen, and thus, the oxide layer produced impedes resin polymerization and bondstrength is reduced. In a study by Chuang S.F et al in 2007, similar to present study 10% carbamide peroxide containing different percentages of fluoride were used and presented that enamel composite bond may be compromised due to reduced number of resin tags, which inhibits polymerization of bond- ing resin. A delay of one to two weeks in applica- tion of bonding improves bondstrength . Bar- cellos et al. in 2010 examined the effect of carba- mide peroxide gel 10%, 15%, and 20% on shearbondstrength of Z 350-filtech composite to tooth enamel and dentin, and the results were analyzed by one-way ANOVA and Tukey post hoc tests, with a conclusion that bondstrength of composite to bleachedenamel and dentin was influenced by different percentages of carbamide peroxide gel, which concurs with results obtained in this study . In a study by Faiz & Khoroushi et al. in 2011, the conclusion was that, using antioxidants as buf- fering agents after bleaching, and a delay of one week in application of composite bond, the bondstrength could be significantly improved . Ma- zaheri et al. in their 2011 study examined bondstrength of Z100 resin and reinforced glass iono-
In our study, 16% carbamide peroxide was used for external bleaching of teeth. In some studies 16%, 20% and 22% concentrations of carbamide peroxide have been used [5-7] and some others have suggested the use of 35% hydrogen peroxide . Since the solution containing sage was color- less, no discoloration was caused in the enamel. The present study was a preliminary study in this respect and we applied sage extract in the form of solution using the immersion technique. However, the hydrogel form is preferred over the solution due to easier control and handling. The hydrogel form is more suitable for clinical application and its efficacy should be compared with that of the solution form. Since antioxidants have short shelf lives and become inactive after some time, further studies are suggested on storage techniques of these materials.
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 Sodium ascorbate, 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 shearbondstrength. The data were evaluated using ANOVA and Tukey Post Hoc tests.
Several studies investigated the effect of adding different amounts and sizes of apatite powder to GIC for improving the physical property of this cement. [19-22] These studies demonstrated that GICs containing hy- droxyapatite exhibit better mechanical properties and higher bondstrength to dentin than the conventional GICs. A study reported that hydroxyapatite-reinforced glass-ionomer, 75wt% of glass-ionomer and 25wt% of hydroxyapatite, exhibited the highest bondstrength to dentin.  It has been demonstrated that adding nano- hydroxyapatite (nano-HA) to glass-ionomer shows higher bondstrength to tooth structure compared to mi- cro-hydroxyapatite (micro-HA). The decreased size of nano-HA particles, similar to that of the minerals in tooth, leads to increased surface area and higher solubil- ity, filling the enamel defects with higher performance ;this phenomenon occurs through releasing calcium and phosphate ions and by increasing the bondstrength be- tween the tooth and the restorative material. 
group and four composite groups containing 1%, 2%, 5%, and 10% prpNPs were evaluated in this study. A laboratory scale (U.S. Solid, ND, USA) with a precision of 0.0001 g was used for weighing the composite and nanoparticles. The nanocomposites were stored in a dark environment at room temperature before bonding. Sixty sound bovine incisors without any enamel cracks, decay, erosions or fractures were collected. They were kept at 4°C in a solution of 0.5% Chloramine for four weeks. Afterwards, the samples were randomly divided into five groups (n=12): four groups for bonding with nanocomposites and one group for composite without prpNPs. The teeth were cleaned using a prophylaxis brush, then rinsed and finally dried. The buccal surfaces of the teeth were etched with 37% phosphoric acid gel (Ultra etch; Ultradent Products Inc., South Jordan, UT, USA) for 30 seconds, then washed with water for 30 seconds and dried with air without moisture or oil. A thin layer of bonding primer (3M Unitek, Monrovia, CA, USA) was placed uniformly on the etched surfaces of all teeth and exposed to a light-curing device (Demetron, Kerr, Orange, CA, USA) for 10 seconds.
Materials and Method: In this experimental study, 40 specimens (6×6mm) in 4 groups (n=10) were prepared in acrylic mold. Each specimen contained conventional GI ChemFil Superior with a height of 3mm, bonded to Z350 composite resin with a height measured 3mm. In order to bond the composite to the GI, the following adhe- sives were used, respectively: A: mild Clearfil SE Bond self-etch (pH=2), B: inter- mediate OptiBond self-etch (pH=1.4), C: strong Adper Prompt L-Pop (pH=1), and D: Adper Single Bond 2 total-etch (pH=7.2). The shearbondstrength was measured by using universal testing machine with a crosshead speed of 1mm/min. One-way ANOVA and Tukey’s test were used to analyze the data (p< 0.05).
Conventional caries removal using rotary in- struments often results in the removal of most of the caries-affected dentin leading to excessive loss of the tooth structure .This method also increases the thermal effect and pressure to the pulp ; that may be a greater problem in the primary teeth due to their large pulps and open dentin tubules. The fre- quent need for local anesthesia  and unpleasant vibrations felt by patients  may increase anxiety and fear of dental procedures. Thus, to reduce some of the factors, the application of the chemomechan- ical caries removal (CMCR) method , based on the non-invasive technique activity of a solution of monochloroaminobutyric acid (MAB) marketed as GK101E, was introduced in the late 1970s . The action of MAB involves disruption of collagen in the carious dentin, thus facilitating its removal.
fluoride ion release from a freshly mixed polyacid modifiedresin composite, or compomer (Dyract) and three resinmodified glass ionomer cements (Fuji II LC, Photac-Fil, and Vitremer) and to compare the use of 3 units for measuring fluoride release.Fluoride measurements were carried out using a fluoride ion-selective electrode connected to a pH ion-selective electrode meter. Fluoride ion release was measured in parts per million, micrograms per square centimeter, and micrograms per cubic millimeter. Showed Fuji II LC, Photac-Fil, and Vitremer showed high initial release values which decreased exponentially and then showed a slow decline during the ensuing time. Dyract released significantly less fluoride ions during the first 84 days than did the three resin – modified glass ionomer cements and maintained this low level of release throughout the study period. The amounts of fluoride ion release measured at any time interval varied with the units of measurements chosen but the pattern of release remained the same. They concluded that there was a wide variation in the amounts of fluoride ions released from related products, but the patterns of release were similar and unaffected by the units of measurements used.
Shearbondstrength is a simple and widely used test to assess the bonding performance of restorative material, particularly regarding the glass ionomer ce- ments, which present low bondstrength [20-21, 24, 26]. Recently, the µSBS test has become popularized as an alternative to the conventional shearbond test. In the µSBS test, the stress distribution is more concentrated at the interface compared with the conventional shearbond test. This would decrease the chance of cohesive failure in the material or enamel/dentin that does not display the true interfacial bondstrength [20-21, 27-28]. This method is an especially useful test for those sub- strates that are susceptible to the specimen preparation effects and micro tensile bondstrength testing condi- tions, such as glass ionomer or enamel [21, 28-29]. However, there are some questions concerning the in- terdependence of multiple specimens from the same tooth in micro test, which may exaggerate the statistical significance levels for comparison between materials. It is highly possible that the measurements originating from one tooth would be biased by the individual featur-
Since duration of application of sodium ascorbate after dental bleaching is still a matter of debate, this study aimed to compare the effect of 5 and 10 minutes application of 10% sodium ascorbate on SBS of composite to bleachedenamel. The results were also compared with the no-intervention control group. The results showed the highest SBS in group 3 (exposure for 10 minutes). For proper bonding to the enamel, 15 to 20MPa bondstrength is often required. ANOVA showed a significant difference in SBS of the three groups in our study (p<0.05).
Rix et al. (2001) reported higher bondstrength values for Transbond XT specimens; although adequate bondstrength of brackets to the enamel was noted in their study when bonding with Assure indry and wet conditions (10.74 MPa and 10.99 MPa); similar to our findings . They showed that bondstrength of the Assure adhesive was not significantly affected by dry orwet conditions. In contrast to our results, Oztoprak et al. (2007) showed that saliva (10.66 MPa versus 16.4 MPa) and blood contamination (6.83 MPa versus 16.4 MPa) significantly decreased bondstrength values compared to dry conditions . Furthermore, Webster et al. (2001) reported the Assure system to show more tolerance against saliva contamination similar to our study results . Again, Schane- weldt et al. (2002) concluded that the bondstrength of Assure and MIP primers are not af- fected by saliva contamination . Similarly, Nemeth et al. (2006) reported that bondstrength of Assure to enamel contaminated with saliva is bet- ter than other materials . It seems that bonding to bothdry and wet enamel surfaces depends on the material itself and sufficientbond strengths to wet and saliva-contaminated enamel surfaces can be achieved using appropriate materials.
After the shearbondstrength tests, the predominant type of fracture in CO, SB, TXT and TP was cohesive in resin, corroborating the studies of Penido et al.  and Buyukyilmaz et al. . However, in in vivo studies, these authors verified that the bond failure occurred at the cement/bracket interface, and that this type of fracture is frequently found in clinical practice. It is the most desirable type, since facture at this interface may cause damage to the enamel, due to strangulation of the resin that remains between the bracket mesh, making this area more fragile . Two samples from CO presented enamel fracture, a result similar to that found by Penido et al. . Only FMO presented mostly adhesive fractures. Also, there were mixed fractures in all groups that might be the result of mechanical retention of the bracket base or chemical bonding between the enamel and adhesive. Bond failure at any of the mentioned interfaces has its own advantages and disadvantages. For instance, bond failure at the bracket-adhesive interface is advantageous because it leaves an intact enamel surface; however removing residual adhesive is time consuming and imposes the risk of enamel damage. On the other hand, bond failure at the enamel-adhesive interface leaves less residual adhesive remnants but the risk of enamel surface damage is increased. Bond failure at the enamel-adhesive interface leaves less adhesive remnants on the enamel surface and therefore decreases the risk of enamel damage during adhesive removal but imposes a higher risk of enamel damage during debonding . Because of the higher bondstrength of CO composite, the risk of enamel damage during debonding is high as well.
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. 
It is a light curable GIC which has smaller glass particles which allow greater density and assures a smoother and glossier finish. The resin components in the liquid assume a key role in the improvement of the physical properties of the RMGICs. After initial setting, these cement allow the passage of the pulpal fluid through an absorption layer, formed near the dentinal tubules. This layer can make up for the polymerization shrinkage of the resin agent, maintaining the marginal seal of the restoration. Moreover, the polymerization stresses developed by RMGICs are much lower than the ones produced by composite resin, due to their slow setting reaction, and smaller resin content in the material. 
These superficial oxides play an important role in surface wettability and formation of a chemical bond with resin cement. Panavia resin cement also contains 10-MDP active monomer and forms a covalent bond with the oxide layer present at the surface of base metal alloys . SEM micrographs of the Ni-Cr alloy revealed that in the pattern of etching by Nano Met Etch, rate of irregularities and surface porosities was greater than that in the sandblasted specimens. Consequently, the resin cement bond to the surface treated with Nano Met Etch was greater than that to the sandblasted surface (Figs. 1A and 1b). Another point worth noting is that overall porosities due to the understudy chemical etchant were more uniform that those due to sandblas- ting, which results in higher surface wettability in etched surfaces and lower wettability in sandblasted specimens. Other studies also confirm that acid etching causes a uniformly etched surface . As observed, no adhesive failure occurred in the Ni-Cr alloys which means that the bondstrength between the Nano Met etched surface of alloy and cement was higher than the cohesive strength of the resin cement; whereas, in the sandblasted specimens of this alloy three cases of adhesive failures (35% of