Resin bonding using an all-etch or self-etch adhesive to enamel after carbamide peroxide and/or CPP-ACP treatment

BACKGROUND: Limited evidence exists regarding the effect of carbamide peroxide and casein phosphopeptide amorphous calcium phosphate (CPP-ACP) on composite-enamel bonding. Microshear bond strengths, using either a total-etch or self-etching adhesive, to enamel treated with carbamide peroxide and/or CPP-ACP were investigated. MATERIALS AND METHODS: Twenty-six extracted human third molars were sectioned into four parts, each being allocated into one of the four groups (n=26): bleach (Polanight, 16% carbamide peroxide), CPP-ACP (GC Tooth Mousse), bleach and then CPP-ACP, or untreated (control). The surfaces were bonded with a total-etch bonding system (Single Bond) or a self-etching primer system (Clearfil SE Bond) and tested using a microshear test. RESULTS: A significant difference in bond strength was found between bonding systems. SE Bond showed the highest bond strength to untreated enamel (p < 0.05). The microshear bond strength of SE Bond decreased when the enamel was treated with carbamide peroxide, CPP-ACP or both (p < 0.05). Only combined use of carbamide peroxide and CPP-ACP significantly affected microshear bond strength with Single Bond. CONCLUSION: These findings suggest the shear bond strength of resin to enamel using a self-etching priming adhesive may be affected if the enamel is treated with a bleaching agent or CPP-ACP.     

Effects of conditioners on microshear bond strength to enamel after carbamide peroxide bleaching and/or casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) treatment

OBJECTIVES: To evaluate (a) the enamel microshear bond strength (MSBS) of a universal adhesive and (b) the effects of conditioning with a self-etching primer adhesive with/without prior bleaching and/or casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) application. METHODS: Thirty-five molars were cut into four sections, assigned randomly to four groups (no treatment; 16% carbamide peroxide bleaching; CPP-ACP-containing paste (Tooth Mousse, TM); bleaching and TM) and treated accordingly. Specimens were divided into two for bonding with either a self-etching primer (Clearfil SE Bond, CSE) or a total-etch adhesive (Single Bond, SB). Specimens for CSE bonding were subdivided for one of four preconditioning treatments (no conditioning; 30-40% phosphoric acid (PA); 15% EDTA; 20% polyacrylic acid conditioner (Cavity conditioner, CC) and treated. The adhesives were applied and resin composite bonded to the enamel using microtubes (internal diameter 0.75mm). Bonds were stressed in shear until failure, mean MSBS calculated and data analysed using ANOVA with Tukey's HSD test (alpha=0.05). The modes of bond failure were assessed and classified. RESULTS: Two-way ANOVA revealed significant differences between treatments (P<0.0001), conditioners (P<0.0001) and a significant interaction between treatments and conditioners (P=0.001). One-way ANOVA revealed no significant differences in MSBS following any of the treatments for SB; following TM application for CSE without preconditioning; and significant differences in MSBS following bleaching with and without TM application for CSE. With preconditioning, applying PA before CSE post-bleaching and either PA or CC before CSE post-TM application, resulted in significant differences in MSBS (P<0.05). CONCLUSIONS: The use of conditioners prior to bonding with the self-etching primer adhesive system on treated enamel may significantly improve bond strengths.     

Influence of carbamide peroxide-based bleaching agents on the bond strength of resin-enamel/dentin interfaces

In this bond strength study, a bleaching agent containing 10% carbamide peroxide was applied over composite-teeth bonded interfaces of two adhesive systems applied to enamel and dentin. Sixteen human third molars were used for bonding procedures. Single Bond (SB) and Clearfil SE Bond (CB) were applied to enamel and dentin according to the manufacturers' instructions. A resin composite cube-like structure was incrementally built on the bonded surfaces. The restored teeth were sectioned into 0.7 mm thick slices that were trimmed at enamel or dentin bonded interfaces to an hourglass shape with a cross-sectional area of approximately 0.5 mm2. Specimens were assigned to 8 groups (n = 10) according to the following factors under study: dental substrate (enamel and dentin); adhesive system (SB and CB) and treatment (10% carbamide peroxide and not bleached/control). The bleaching gel (Opalescence) was applied at the bonded interfaces for 6 hours during 14 days and after daily treatment specimens were stored in artificial saliva. Unbleached specimens were stored in artificial saliva for 14 days. Specimens were tested for tension and the data were analyzed by three-way ANOVA and Tukey's test (p < 0.05). Enamel tensile bond strength of CB was reduced after carbamide peroxide application. The bleaching treatment did not alter dentin bond strength of both adhesives. The results suggest that bleaching significantly affects bond strength of CB to enamel, but no influence on bond strength to dentin was noted for both adhesive systems.     

Effect of carbamide peroxide bleaching on the shear bond strength of composite to dental bonding agent enhanced enamel

STATEMENT OF PROBLEM: Carbamide peroxide bleaching has been implicated in adversely affecting the bond strength of composite to enamel. PURPOSE: This in vitro study evaluated the effect of 3 dental bonding agents (OptiBond, All-Bond 2, One-Step) on the shear bond strength of a hybrid composite to enamel which was treated by a 10% carbamide peroxide bleaching system. MATERIAL AND METHODS: Cylinders of composite were bonded to carbamide peroxide-treated enamel on extracted human teeth using 3 dental bonding agents. After thermocycling, shear bond strengths were determined with a universal testing machine. RESULTS: OptiBond aided bond strengths were 23.7 +/- 5.6 MPa to bleached and 19.6 +/- 2.9 MPa to unbleached enamel. For All-Bond 2, bleached enamel exhibited bond strengths of 14.9 +/- 4.0 MPa and unbleached enamel exhibited a bond strength value of 20. 4 +/- 2.3 MPa. The composite bond strength for One-Step was 13.6 +/- 5.9 MPa to bleached and 23.0 +/- 3.9 MPa to unbleached enamel. There was no statistical difference between OptiBond (alcohol base) aided bond strengths for bleached and unbleached enamel; however, the bond strength of composite to bleached enamel with All-Bond 2 or One-Step (acetone base) was significantly lower than unbleached controls. CONCLUSION: The effect of bonding agent usage on composite bond strength to enamel bleached with a particular carbamide peroxide was dependent on the bonding agent used.     

The effect of enamel bleaching on the shear bond strengths of metal and ceramic brackets

The aim of this study was to evaluate the effects of bleaching and delayed bonding on the shear bond strengths of metal and ceramic brackets bonded with light and chemically cure composite resin to human enamel. One hundred and twenty extracted human premolar teeth were randomly divided into three groups of 40 each. The first two groups were bleached with 20 per cent carbamide peroxide (CP) at-home bleaching agent. No bleaching procedures were applied to the third group and served as control. The first two and control groups were divided into equal subgroups according to different adhesive-bracket combinations. Specimens in group 1 (n = 40) were bonded 24 hours after bleaching process was completed while the specimens in group 2 (n = 40) were bonded 14 days after. The specimens in all groups were debonded with a Universal testing machine while the modified adhesive remnant index was used to evaluate fracture properties. No statistically significant differences were found between the shear bond strengths of metal and ceramic brackets bonded to bleached enamel after 24 hours, 14 days, and unbleached enamel with light or chemical cure adhesives (P > 0.05). The mode of failure was mostly at the bracket/adhesive interface and cohesive failures within the resin were also observed. Our findings indicated that at-home bleaching agents that contain 20 per cent CP did not significantly affect the shear bond strength of metal and ceramic orthodontic brackets to enamel when bonding is performed 24 hours or 14 days after bleaching.     

牙齿漂白剂对正畸托槽粘接强度的影响

目的:评价三种牙齿漂白剂对自酸蚀粘接系统粘接正畸托槽粘接强度的影响。方法:将100颗人前磨牙均分为四组:空白对照组(组1)、38%过氧化氢漂白组(组2)、10%过氧化脲漂白组(组3)和20%过氧化脲漂白组(组4),漂白牙齿后即刻使用自酸蚀正畸粘接系统Transbond Plus SEP将托槽粘接在牙面上,测量各组的抗剪切粘接强度,评价其剩余粘接剂指数,对结果进行统计学分析。结果:空白对照组的抗剪切粘接强度高于各漂白组,组2的抗剪切粘接强度高于组3和组4,而组4的抗剪切粘接强度最低,其差异均具有统计学意义(P<0.05)。各组的剩余粘接剂指数差异均有统计学意义(P<0.05),剩余粘接剂指数最低者为空白对照组,最高者为20%过氧化脲组。结论:在使用自酸蚀粘接系统粘接正畸托槽前应禁止使用过氧化物漂白牙齿,特别是高浓度的过氧化脲。     

Immediate bonding to bleached enamel

This research sought to determine the shear bond strength, degree of resin infiltration and failure mode when organic solvent-based adhesives (acetone or ethanol) were used in immediate bonding to enamel bleached with 10% carbamide peroxide or 38% hydrogen peroxide systems. Seventy-two non-carious bovine incisors were randomly assigned to three groups of 24 specimens each-control group (deionized water), 38% hydrogen peroxide bleach group and 10% carbamide peroxide bleach group. Each group was further subdivided into two subgroups of 12 specimens each according to the adhesive system used to bond the resin composite to enamel surfaces. The two adhesive systems used were Single Bond, an ethanol-based adhesive, and One Step, an acetone-based adhesive. The shear bond strengths of 38% hydrogen peroxide and 10% carbamide peroxide were significantly lower compared to the non-bleached controls. Fractography revealed an adhesive failure mode in all specimens. Qualitative comparisons of resin tags present in the bleached and unbleached specimens using scanning electron microscopy (SEM) revealed few, thin and fragmented resin tags when 38% hydrogen peroxide and 10% carbamide peroxide were used.     

The effect of nonvital bleaching on the shear bond strength of composite resin using three adhesive systems

PURPOSE: To evaluate the effect of nonvital bleaching on the shear bond strength of composite resin using three adhesive systems. MATERIALS AND METHODS: Two hundred seventy bovine teeth were assigned to 3 groups (n = 90): SP, paste of sodium perborate and water; CP, 37% carbamide peroxide; CO, control group (no treatment). After the bleaching treatment, the teeth in each group were cut into enamel (E) and dentin (D) sections. The teeth were embedded in polyester resin and polished in order to obtain a flat E or D surface. Each group was divided into 6 subgroups (n = 15) according to substrate (E and D) and adhesive system: SB, Single Bond (solvent: water/alcohol); PB, Prime & Bond NT (solvent: acetone); CLF, Clearfil SE Bond (solvent: water). The adhesive system was applied on each flat surface according to the manufacturer's instructions and a cylinder of composite resin Z-250 was overlaid. The specimens were stored in distilled water for 7 days at 37 degrees C. The SBS test was performed in a universal testing machine with crosshead speed of 0.5 mm/min. The data obtained (in MPa) were statistically analyzed with two-way ANOVA and Tukey's test (p < or = 0.05). RESULTS: The bleaching treatment influenced the SBS, regardless of the adhesive system used. On enamel, the SP and CP bleaching treatments reduced the SBS values. On dentin, the SP bleaching agent reduced the SBS values, but the CP bleaching did not. CONCLUSION: Nonvital bleaching treatment with sodium perborate may adversely affect shear bond strength of composite resin for both enamel and dentin. Similar effects can be expected from 37% carbamide peroxide bleaching agent on enamel but not dentin bonding strength. The use of water/alcohol and acetone-based adhesive systems cannot reverse the effects of bleaching treatments on bond strengths.     

Effect of 10% sodium ascorbate on the shear bond strength of composite resin to bleached bovine enamel

The purpose of this study was to comparatively investigate the effect of antioxidant treatment and delayed bonding after bleaching with three different concentrations of carbamide peroxide (CP) on the shear bond strength of composite resin to enamel. One hundred flat buccal enamel surfaces obtained from bovine incisors were divided into three bleaching groups of 10, 16 and 22% CP (n = 30) and a control group. Each bleaching group was then divided into three subgroups (n = 10). Group 1 consisted of specimens bonded immediately after bleaching. Group 2 specimens were treated with antioxidant agent, 10% sodium ascorbate, while Group 3 specimens were immersed in artificial saliva for 1 week after bleaching. Specimens in the control group were not bleached. After the specimens were bonded with Clearfil SE Bond and Clearfil AP-X, they were thermocycled and tested in shear until failure. Fracture analysis of the bonded enamel surface was performed using scanning electron microscope. The shear bond strength data was subjected to one-way analysis of variance followed by Duncan's multiple range test at a significance level of P < 0.05. Shear bond strength of composite resin to enamel that was bonded immediately after bleaching with 10, 16 and 22% CP was significantly lower than that of unbleached enamel (P < 0.05). For all three bleaching groups, when the antioxidant-treated and delayed bonding (1 week) subgroups were compared with the control group, no statistically significant differences in shear bond strength were noted (P < 0.05).     

The shear bond strength of acetone and ethanol-based bonding agents to bleached teeth

PURPOSE: The purpose of this in vitro study was to evaluate the: (1) shear bond strength (SBS) of acetone and ethanol-based bonding agents to composite resin 24 hours after being bleached with 35% hydrogen peroxide; and (2) interface morphology and mode of fracture (IMMF) between composite resin and enamel. METHODS: Forty extracted teeth were randomly assigned into 4 groups: (1) group 1: 35% H2O2 + acetone; (2) group 2: H2O2 + ethanol; (3) group 3: acetone; (4) group 4: ethanol. All teeth were acid etched, bonding agents were applied, and a composite resin stub was bonded and stored again in saline for 24 hours. SBS was determined, and scanning electron microscopy (SEM) was used for IMMF evaluation. RESULTS: SBS was significantly lower in bleached than unbleached teeth (P < .001), but SBS did not differ between the acetone-based or ethanol-based adhesives (P = .55) and bleaching did not interact with adhesive treatment (P = .39). IMMF analysis of the unbleached teeth showed a continuous interface between the resin and enamel. By contrast, bleached teeth showed sparse contact between the resin and enamel and the resin was poorly infiltrated into the enamel surface. CONCLUSION: Morphologic changes in human tooth enamel, 24 hours after bleaching, were associated with a reduction in the shear bond strength of adhesives.     

Effect of bleaching on shear bond strength to dentin of etch-and-rinse and self-etching primer adhesives

This study evaluated in vitro the influence of enamel bleaching on bond strength to dentin. One hundred and twenty bovine incisors were divided into 12 groups (n = 10), according to adhesive system: Adper Single Bond 2 (ASB2), Prime & Bond 2.1 (PB), Adhese (AD) and Clearfil SE Bond (SE). The experimental groups were exposed to 10% carbamide peroxide for 4 hours a day over a period of 10 days. After the bleaching, they remained stored in artificial saliva for a further 24 hours or 7 days. The control groups were stored in artificial saliva for 24 hs. Resin composite (Z250) cylinders were made, and the specimens were stored in distilled water (37 degrees C/24 h), until the shear strength test was performed. The results were statistically analyzed using ANOVA 3-way and Turkey's test (a < 0.05). The highest mean value of experimental groups was obtained for ASB2 (7 d) and the lowest for PB (24 h). Significant differences were observed for bleaching and adhesive system, but not for storage time. Moreover, the interaction between the factors under study was shown to be significant. Statistical differences were observed between the tested adhesives for the different bleaching situations and storage times. It may be concluded that dental enamel bleaching and storage time in artificial saliva interfered with the bond strength to subjacent dentin provided by the Prime & Bond 2.1 and Clearfil SE Bond.     

Bonding to enamel and dentin using self-etching adhesive systems.

OBJECTIVES: This study investigated the effectiveness of three different dentin adhesive systems on the adhesion of resin composite to both dentin and enamel. METHOD AND MATERIALS: The flat dentin and enamel surfaces of 60 extracted human molar teeth were exposed by wet grinding with 600-grit silicon carbide paper. One total-etch self-priming adhesive system (Prime & Bond NT), one two-step self-etching primer adhesive system (Clearfil SE Bond), and one "all-in-one" self-etching adhesive system (Prompt L-Pop) were evaluated. Each bonding system was applied according to the manufacturer's instructions and followed by composite (TPH Spectrum) application. Twenty-four hours after bonding, the teeth were subjected to shear testing. There were 10 replicates for each group. RESULTS: Prompt L-Pop exhibited significantly higher bond strength values to enamel (27 +/- 4.2 MPa) than all other groups. There were no statistically significant differences for shear bond strength to dentin among adhesives. Prompt L-Pop showed the statistically significantly higher bond strength to enamel than dentin. There were no statistically significant differences between the enamel and dentin bond strengths of Clearfil SE Bond and Prime & Bond NT. CONCLUSIONS: The self-etching adhesive systems produced high bond strengths to human coronal dentin and ground enamel surfaces. These materials seem to be very promising for further clinical applications, and the results are very encouraging for the clinical success of these simplified adhesive systems. The self-etching adhesive systems produced even better bond strengths to both enamel and dentin than conventional total-etch systems, especially the "all-in-one" system, which produced the highest bond strength to enamel.     

Effect of antioxidant treatment on bond strength of a luting resin to bleached enamel

PURPOSE: The aim of this study was to comparatively investigate the effect of antioxidant treatment and delayed bonding after bleaching with carbamide peroxide on the shear bond strength (SBS) of a luting resin to enamel. MATERIALS AND METHODS: Forty flat enamel surfaces were prepared from freshly extracted human molars using a low speed diamond saw, then divided into three bleaching groups (n=10/group) and a control group (n=10). Group 1 consisted of specimens bonded immediately after bleaching. Group 2 specimens were treated with an antioxidant agent, 10% sodium ascorbate, while Group 3 specimens were immersed in artificial saliva for 1 week after bleaching. Specimens in Group 4 were not bleached, but immersed in artificial saliva for 1 week before bonding. Forty ceramic blocks (Empress 2, Ivoclar) were prepared and luted to teeth using a dual-curing resin cement (Variolink II, Ivoclar). The specimens were thermocycled and the SBS tests were performed using a universal testing machine (crosshead speed: 0.5mm/min). Fracture analysis of the bonded surfaces was done using a scanning electron microscope. Statistical analysis was carried out by Kruskall-Wallis and Mann-Whitney U-tests. RESULTS: While the samples that were immediately bonded after bleaching (Group I) demonstrated significantly lower shear bond strengths and 10% sodium ascorbate group (Group II) demonstrated significantly higher bond strengths than control group samples (p<0.05), no significant differences were found among delayed bonded group and control group (p>0.05). CONCLUSION: Using sodium ascorbate with a concentration of 10% may be reliable for reversing the compromised bond strength.     

Reversal of compromised bonding in bleached enamel

Oxygen inhibits polymerization of resin-based materials. We hypothesized that compromised bonding to bleached enamel can be reversed with sodium ascorbate, an anti-oxidant. Sandblasted human enamel specimens were treated with distilled water (control) and 10% carbamide peroxide gel with or without further treatment with 10% sodium ascorbate. They were bonded with Single Bond (3M-ESPE) or Prime&Bond NT (Dentsply DeTrey) and restored with a composite. Specimens were prepared for microtensile bond testing and transmission electron microscopy after immersion in ammoniacal silver nitrate for nanoleakage evaluation. Bond strengths of both adhesives were reduced after bleaching but were reversed following sodium ascorbate treatment (P < 0.001). Resin-enamel interfaces in bleached enamel exhibited more extensive nanoleakage in the form of isolated silver grains and bubble-like silver deposits. Reduction of resin-enamel bond strength in bleached etched enamel is likely to be caused by a delayed release of oxygen that affects the polymerization of resin components.     

The effect of hydrogel and solution of sodium ascorbate on bond strength in bleached enamel

Compromised bonding to bleached enamel can be reversed with sodium ascorbate as an antioxidant. This study evaluated the effect of hydrogel and solution of sodium ascorbate on enamel-resin composite shear bond strength after bleaching. Sixty buccal enamel surfaces obtained from human, sound third molars were randomly divided into 4 groups (n=15). Enamel surfaces were subjected to different treatments: 1) bleaching (10% carbamide peroxide gel); 2) bleaching + 10% sodium ascorbate solution; 3) bleaching + 10% sodium ascorbate hydrogel and 4) bleaching + 20% sodium ascorbate hydrogel. The specimens were bonded with Single Bond and restored with a composite. The specimens were prepared for shear bond testing. The data was evaluated using ANOVA and Tukey tests. Bond strengths were significantly increased following hydrogel and solution of sodium ascorbate treatments (p<0.05). Also, there was no significant difference among the different forms of sodium ascorbate preparations.     

Bond strength of different adhesive systems to dental hard tissues

This study compared the shear bond strengths of different adhesive systems to enamel and dentin of different depths. The adhesive systems used were: Single Bond one-bottle total-etch; AQ Bond one-step self-etching, Clearfil SE Bond two-step self-etching and Tyrian SPE/One-step Plus two-step self-etching. Eighty extracted non-carious human mandibular molars were mounted in self-curing resin and the occlusal surfaces were ground with a mechanical grinder to obtain flat occlusal enamel surfaces. After applying the adhesive systems, a plastic tube was attached to the enamel surfaces. The tube was filled with a universal hybrid resin composite, which was then polymerized. The specimens were stored in water at 37 degrees C for 24 hours. Shear bond testing was carried out using an Instron Universal testing machine with a crosshead speed of 1 mm/minute. The occlusal enamel of the 80 teeth was removed to determine the bond strengths of the adhesives to superficial dentin. To obtain deep dentin, the same teeth were ground deep towards the pulp, with the remaining dentin thickness approximately 0.7 mm. The adhesives and restorative material were then applied to the prepared dentin surfaces following the methodology described above. For occlusal enamel surfaces, the bond strength of Single Bond was significantly higher than the other adhesives. Single Bond, Clearfil SE Bond and Tyrian SPE/One-step Plus performed equally when bonded to superficial dentin; the lowest bond strength was obtained with AQ Bond. On deep dentin, the highest bond strengths were obtained with Clearfil SE Bond. For each adhesive system, shear bond strength to enamel was statistically higher than it was to either superficial or deep dentin. There were no significant differences between shear bond strengths to superficial versus deep dentin, regardless of adhesive.     

Effect of composite resin contamination with powdered and unpowdered latex gloves on its shear bond strength to bovine dentin

SUMMARY The aim of the present study was to evaluate the effect of composite resin contamination with powdered and unpowdered latex gloves on the shear bond strength of etch-and-rinse and two-step self-etch adhesive systems. Standard flat dentin surfaces were prepared on the facial aspect of 120 bovine incisors and randomly assigned into two (n=60) groups: group 1: Single Bond (SB), group 2: Clearfil SE Bond (CSE). Furthermore, each group was randomly subdivided into three (n=20) based on the type of composite contamination (without contamination, contamination with powdered latex gloves, and contamination with unpowdered latex gloves). The adhesives were applied and resin composite bonded to the dentin. After thermocycling, the specimens were subjected to a shear bond strength test. Two-way analysis of variance (ANOVA) and a post hoc Bonferroni test were used for statistical analysis. One-way ANOVA was used to compare shear bond strength values in each group. Statistical significance was set at p < 0.02. Two-way ANOVA showed that the shear bond strength was significantly influenced by the type of composite surface contamination (p=0.001). In the SB group there were no significant differences between different surface treatments (p=0.08). In the CSE group a significant difference was observed between the subgroup without contamination and the subgroup with powdered latex glove contamination (p=0.01); however, no significant differences were observed between the other subgroups.     

The effect of elapsed time following bleaching on enamel bond strength of resin composite.

Recent studies have concluded that carbamide peroxide bleaching agents significantly affect the bond strength of composite to bleached enamel. This study evaluated the effects of bleaching regimen with different carbamide peroxide concentrations and post-treatment times on composite bond strength to enamel. Two hundred and four flat buccal and lingual enamel surfaces obtained from erupted sound third molars were randomly divided into 17 groups (n = 12). Sixteen experimental groups comprised the evaluation of four carbamide peroxide home bleaching agents (Opalescence 10%-20% and Whiteness 10%-16%) and four time intervals after bleaching (one day, one, two and three weeks). Specimens of control group were not submitted to bleaching and were stored in artificial saliva at 37 degrees C for 10 days. The specimens of experimental groups were exposed to one daily application of carbamide peroxide for six hours for 10 consecutive days. After each daily treatment and post-bleaching, the specimens were stored in artificial saliva solution. Bonds were formed with Scotchbond MP and Z-100 composite resin, and shear bond test was carried out 24 hours after adhesive-composite application. Two-way ANOVA showed that the bond strengths were significantly different (p < 0.05). For the first two weeks post-bleaching, the bond strengths of resin to enamel were low. After a lapse of three weeks, the bond strength returned to that of the untreated control group. Increased concentration did not prolong the time needed prior to bonding.     

Can previously bleached teeth be bonded safely?

The purpose of our study was to determine the effect of a 35% hydrogen peroxide bleaching agent on the shear bond strength of metallic orthodontic brackets. Sixty premolars were randomly divided into 3 groups of 20 each. Teeth in group A were etched with 37% phosphoric acid before bonding metallic premolar brackets. Teeth in the other 2 groups were bleached with a 35% hydrogen peroxide in-office bleaching agent according to the manufacturer's recommendations. Twenty bleached teeth (group B) were bonded immediately, and the other 20 (group C) were stored in artificial saliva for 30 days before bonding. Shear bond strength of these brackets was measured on a universal testing machine and recorded in MPa. Adhesive remnant index (ARI) scores were determined after the brackets failed. Data were analyzed with analysis of variance (ANOVA) and chi-square tests. The shear bond strength values of groups A, B, and C were 12.9 +/- 3.4, 12.0 +/- 4.6, and 14.8 +/- 4.0 MPa, respectively. Results of ANOVA showed no statistically significant differences in shear bond strengths between groups (P >.05). ARI scores were significantly different in all groups. The unbleached group's failures were primarily at the bracket/adhesive interface, whereas the bleached groups either showed cohesive failures within the adhesive or failed at the adhesive/enamel interface. The results of this study suggest that office bleaching with hydrogen peroxide does not adversely affect the bond strengths of brackets bonded immediately after bleaching or 30 days after bleaching, even though bleaching can result in differences in the failure site.     

Influence of prolonged light-curing time on the shear bonding strength of resin to bleached enamel

This study evaluated the effect of prolonged light-curing time using a light-emitting diode unit (LED) on the shear bond strength of a resin composite to enamel immediately after bleaching. The enamel surfaces of human molars were divided into four groups: one control and three bleaching groups. One bleaching group (CP) was exposed to a 10% carbamide peroxide bleaching agent and bonded after 24 hours. The other two bleaching groups (HP) were bleached with a 38% hydrogen peroxide bleaching agent, then bonded either within one hour (HPA) or after 24 hours (HPB). All groups were subdivided into two subgroups and cured for two different times (20 or 40 seconds) with an LED unit. Shear bond strength (SBS) was tested with a universal-testing machine and the data were analyzed by ANOVA and post-hoc tests. Scanning electron micrographs of representative specimens were taken. A significant difference was seen between the control and HPA groups for both curing times (p = 0.000). However, neither the CP nor HPB groups showed any significant differences compared with the control groups (p > 0.05). Two-way ANOVA showed that a significant effect of the curing time factor was recorded for all groups (p = 0.000). Prolonged curing time, using an LED unit with a light intensity of 500 mW/cm2, increased resin-enamel bonding strengths for the control and bleached groups when bonding was performed after 24 hours of immersion in deionized water. However, the SBS was still compromised when bonding was performed immediately to enamel bleached with 38% HP.