The bonding of an adhesive resin cement to single and combined adherends encountered in resin-bonded bridge work: an in vitro study.

Although resin-bonded bridges should ideally be bonded to enamel, abutment teeth may present with dentine or restorations at the bonding sites. This study assessed the influence of bonding to such adherends on bridge retention by using tensile bond strength measurements as the criteria for judgement. An adhesive resin cement (Panavia Ex) was bonded to single adherends of enamel, dentine, composite resin, glass ionomer or amalgam, and to combined adherends of enamel/dentine or enamel/restorative material. The bond strength to enamel (28 MPa) was comparable with that to composite resin (25 MPa), but significantly higher than to dentine (8 MPa), amalgam (8 MPa) and glass ionomer (13 MPa). When the bonding area was half enamel and half restorative material, the bond strength was only equivalent to that obtained when the entire bonding area consisted of restorative material, the less favourable adherend. A similar trend was observed with specimens of enamel/dentine. This indicated that the magnitude of the bond between the resin cement and combined adherends was limited by the strength of the bond to the less favourable adherend. It appears that extending a bridge retainer to cover exposed dentine, a glass-ionomer filling or an amalgam filling, could adversely affect the bridge retention.     

An In Vitro Investigation of a Comparison of Bond Strengths of Composite to Etched and Air-Abraded Human Enamel Surfaces

PURPOSE: The purposes of the study were to measure the tensile bond strength of composite resin to human enamel specimens that had been either etched or air-abraded, and to compare the quality of the marginal seal, through the assessment of microleakage, of composite resin to human enamel specimens that had been either etched or air-abraded. MATERIALS AND METHODS: Thirty mandibular molar teeth were decoronated and sectioned mesio-distally to produce six groups, each containing ten specimens that were embedded in acrylic resin using a jig. In each of the four treatment groups, the specimen surfaces were treated by either abrasion with 27 or 50 microm alumina at 4 mm or 20 mm distance, and a composite resin was bonded to the treated surfaces in a standardized manner. In the two control groups the specimens were treated with 15 seconds exposure to 36% phosphoric acid gel and then similarly treated before being stored in sterile water for 1 week. All specimens were then subjected to tensile bond strength testing at either 1 or 5 mm/min crosshead speed. For the microleakage study, the degree of dye penetration was measured 32 times for each treatment group, using a neutral methylene blue dye at the interface between composite and either 27 or 50 microm air-abraded tooth structure or etched enamel surfaces. RESULTS: The mean bond strength values recorded for Group 1 (phosphoric acid etch, 5 mm/min crosshead speed) was 25.4 MPa; Group 2 (phosphoric acid etch, 1 mm/min), 22.2 MPa; Group 3 (27 microm alumina at 4 mm distance), 16.8 MPa; Group 4 (50 microm alumina at 4 mm distance), 16.9 MPa; Group 5 (27 microm alumina at 20 mm distance), 4.2 MPa; and for Group 6 (50 microm alumina at 20 mm distance) 3.4 MPa. An analysis of variance (ANOVA) demonstrated significant differences among the groups, and a multiple comparison test (Tukey) demonstrated that conventionally etched specimens had a greater bond strength than air-abraded specimen groups. No significant difference in dye penetration could be demonstrated among the groups (p= 0.58). CONCLUSIONS: Composite resin applied to enamel surfaces prepared using an acid etch procedure exhibited higher bond strengths than those prepared with air abrasion technology. The abrasion particle size did not affect the bond strength produced, but the latter was adversely affected by the distance of the air abrasion nozzle from the enamel surface. The crosshead speed of the bond testing apparatus had no effect on the bond strengths recorded. The marginal seal of composite to prepared enamel was unaffected by the method of enamel preparation.     

Influence of dentinal regions on bond strengths of different adhesive systems

This in vitro study assessed comparatively the shear bond strengths of three composite resins, 3M Valux Plus (3MVP), Herculite (H), Clearfil AP-X (CAP-X), a polyacid modified composite resin Dyract (D), and a resin modified glass-ionomer materials Vitremer (V), to cervical and buccal dentine regions of extracted human molar teeth. Four different bonding systems, 3M ScotchBond Multipurpose (SB), Clearfil Liner Bond 2 (LB2), Opti Bond (OB), and Prime & Bond 2.1 (PB 2.1) were used with the manufacturer's respective composite and compomer materials. One hundred freshly extracted mandibular molar teeth were selected for this study. Flat buccal dentine surfaces were created on 50 teeth and cylindrical rods of the five materials were bonded to the dentine surfaces. For assessment of cervical bond strengths, the materials were bonded to mesial and distal enamel bordered occlusal dentinal surfaces of the remaining 50 teeth. The five groups of restorative procedures were applied as follows; Group 1: SB + 3MVP, Group 2: LB2 + CAP-X, Group 3: OB + H, Group 4: PB2.1 + D, Group 5: Vitremer primer (VP) VP + V. Each restorative procedure thus had 20 specimens (10 buccal + 10 cervical). After 24 h of water storage (37 degrees C), the specimens were tested on a Universal Testing machine in shear with a cross head speed of 0.5 mm min-1. The bond strength values were calculated in MPa and the results were evaluated statistically using Kruskal-Wallis one-way/anova and Mann-Whitney U-tests. It was found that the bond strengths of SB + 3MVP, LB2 + CAP-X and VP + V to buccal dentine surfaces were significantly stronger (P < 0.05) than those to the occluso-cervical dentine floors. When the bond strengths to the occluso-cervical dentine and buccal dentine surface were compared, there was no significant difference between the materials (P > 0.05). Vitremer was found the least successful adhesive material in terms of shear bond strength on both buccal and occluso-cervical dentine surfaces.     

Shear bond strength of four orthodontic bonding systems

Recently new orthodontic bonding systems have been developed for attachment of brackets to the etched facial surfaces of teeth. Two of these new systems use bonding agents that contain solvents. It is claimed that this improves the polymerization of the unfilled resin primer and may increase bond strength. A new light-cured restorative enamel/dentin-bonding agent has also recently been introduced. Its value in orthodontic bonding has not been determined. The aim of this investigation was to evaluate the shear bond strengths of the three new bonding systems and to compare these with a conventional orthodontic bonding system. Forty-eight enamel specimens were prepared with 600-grit silicone carbide paper, acid etched with 37% phosphoric acid, and assigned to four enamel-bonding treatment groups: (A) Saga sealant; (B) Maximum Cure; (C) Scotchbond-2; and (D) Concise enamel bond. After enamel priming, the specimens were bonded to Concise orthodontic bonding resin. The bonded specimens were thermocycled (15 degrees C to 45 degrees C) and then stored in distilled water at 37 degrees C for 7 days. Shear bond strength was tested with an Instron testing machine at a strain rate of 0.02 in/min. The mean shear bond strengths and standard deviations reported in MN/m2 were (A) 20.34 (5.37); (B) 25.33 (5.96); (C) 14.59 (5.25); and (D) 20.13 (4.98). The mean shear bond strengths for groups A, B, and D were significantly greater (p less than 0.05) than that for group C. The addition of solvents to the new orthodontic bonding systems does not appear to have a clinically significant effect. The new restorative bonding resin does not provide comparable enamel bond strengths.     

The shear bond strength of bidirectional and random-oriented fibre-reinforced composite to tooth structure

OBJECTIVES: The objective of this study was to evaluate the bond strength and fracture pattern of fibre-reinforced composite (FRC) with two different fibre orientations and matrix compositions to dentine and enamel. MATERIALS AND METHODS: Extracted human molars were used as substrates (enamel and dentine) with a standard acid-etch technique. Light-polymerizable FRC with two different interpenetrating polymer network matrices and random or bidirectional fibre orientations was applied to the substrate, together with the adhesive resin. As a control, particulate filler composite resin was bonded to the substrates. The substrate-composite specimens (n=10) were either stored in water for 24h or additionally thermocycled for 6000 cycles. The shear bond strength of composite to substrate was measured and the fracture surfaces were evaluated visually and with SEM. RESULTS: Three-way factorial analysis of variance highlighted significant differences according to the substrate type, storage condition and composite material (p<0.05). Dentine specimens showed a significantly lower range of bond strength values (8.8-15.0 MPa), compared with enamel specimens (14.0-23.0 MPa). The highest mean bond strength in dentine was 15.0 MPa obtained with bidirectional FRC, whereas the highest bond strength in enamel was 23.0 MPa obtained with random-oriented FRC. Thermocycling did not identify a significant effect on the dentine bond strength, but did identify a significant decrease in enamel bond strength values (p<0.05). Several cohesive failures were observed in the tooth structure with the control material, whereas no cohesive bulk fracture of the tooth was observed when a thin layer of FRC was placed at the interface. CONCLUSIONS: The addition of bidirectional or random continuous fibres did not show any significant improvement in bond strength values compared to control of particulate filler. However, the difference in the fracture patterns observed may have implications for clinical applications.     

Bonding of a composite restorative material to etched glass ionomer cement

The tensile bond strengths of a composite restorative material to phosphoric acid etched restorative glass ionomer cement were examined as a function of cement brand, time after mixing at which etching was performed, thickness of film on enamel and dentine and extent of exposure to water during cement maturation. Optimum bond strengths were obtained with mature cements isolated from water during maturation. Bond strengths were similar to or greater than tensile strengths of cements and many currently available dentine bonding agents for composites. Bonding to etched cement occurs by micromechanical interlocking and the zone of bond failure in tension was in the surface layer of the cement.     

三种牙本质粘接系统微拉伸粘接强度的比较

目的　用微拉伸粘接强度检测法评价 3种不同类型的牙本质粘接系统与正常牙本质的粘接强度 ,用扫描电镜分析其断裂类型。方法　选择 15颗正畸治疗拔除的健康前磨牙 ,去除面釉质层 ,随机均分为 3组。选用 3种牙本质粘接系统All Bond 2 (AB2 组 ) ,Fluoro Bond (FB组 )和XenoⅢ (Xeno组 ) ,分别按厂商说明书要求用于暴露的表层牙本质面上 ,再用蓝色复合树脂恢复牙冠至要求高度。用低速锯将牙齿片切为横截面积约 0 81mm2 的长方体状样本 ,用微拉伸测试仪检测其粘接强度 ,加载速度为 1mm/min。用扫描电镜观察样本断端形态 ,对微拉伸粘接强度测试值和断裂类型进行统计学分析。结果　 3种牙本质粘接系统的微拉伸粘接强度分别为AB2 组 :( 2 9 5 6± 5 4 7)MPa ,Xeno组 :( 15 81± 7 6 7)MPa,FB组 :( 14 6 1± 4 5 0 )MPa。AB2 组的微拉伸粘接强度高于Xeno组和FB组 (P <0 0 1) ,后两者的测值间差异无显著性 (P >0 0 5 )。扫描电镜观察结果显示 ,绝大部分样本的断裂类型都是粘接面型断裂。结论　 3种牙本质粘接系统与正常牙本质的粘接强度存在差异 ,All Bond 2的粘接强度最高 ,但临床操作复杂 ,技术要求较高 ;Fluoro Bond和XenoⅢ使用方法较简单 ,对牙髓的影响可能较小。     

Shear bond strength of Mirage Bond to enamel and dentin.

This study determined the shear bond strength of resin composite to bovine enamel etched with Mirage Bond primer containing 2.5% nitric acid. These results were compared with 37% orthophosphoric acid gel. In addition, the bond strength of resin composite to dentin was determined following treatment with the same primer. Resin composite was applied with and without an intermediary unfilled resin, and the specimens were stored for 1 week and then thermocycled prior to testing. The bond strength to enamel was substantially greater than to dentin (P less than 0.001). The results for enamel revealed that there was no significant difference between the etchant regimes (P greater than 0.05) but the intermediary resin significantly improved bond strengths (P less than 0.05). The presence of an intermediary resin also significantly improved the bond strength to dentin (P greater than 0.05).     

The effect of thermocycling on the adhesion of self-etching adhesives on dental enamel and dentin

AIM: The aim of the present study was to investigate the effectiveness of one total-etch self-priming adhesive and two one-step self-etching adhesive systems on the adhesion of a resin composite to both dentin and enamel. The effect of thermocycling on the adhesion was also investigated. The null hypothesis tested was thermocycling would not affect bond strengths to enamel and dentin treated with self-etching adhesives or a total-etch adhesive. METHODS AND MATERIALS: Two single-step self-etching adhesives [Xeno III (XE3) and Prompt L-Pop (PP)] and one two-step total-etch adhesive system (Prime & Bond NT) (P&B NT) were used in this study. Thirty caries-free unrestored human third molars were used to make specimens of enamel and dentin. Different adhesives were applied on enamel and dentin surfaces according to the manufacturer's instructions then hybrid composite restorative material was condensed on the surface using a mold. The bonded specimens were stored in distilled water at 37 masculineC for 24 hours before being tested. Half of the bonded specimens were tested for shear bond strength without thermocycling. The other half of the test specimens were thermocycled using a thermocycling apparatus in water baths held at 5 masculineC and 55 masculineC with a dwell time of one minute each for 10,000 cycles prior to shear testing. The mean shear bond strength before and after thermocycling was calculated, and the results were subjected to two-way analysis of variance (ANOVA) and repeated measure design to show the interaction between different materials and different times. RESULTS: The results showed shear bond strength on both enamel and dentin of the total-etch adhesive and the self-etching adhesives decreased after the specimens were subjected to thermocycling. CONCLUSIONS: The null hypothesis tested "thermocycling would not affect bond strengths treated with self-etching adhesives" was rejected. Furthermore, the study revealed the following: 1. The shear bond strength to both enamel and dentin of the total-etch adhesive and the self-etching adhesives decreased after the specimens were subjected to thermocycling. 2. XE3 achieved the highest bond strength to both enamel and dentin (26.994+/-1.17 and 25.22+/-1.26, respectively). 3. XE3 showed even better bonding after thermocycling to enamel and dentin than the total-etching system or PP. 4. Although PP bonded to enamel showed lower shear bond strength value than XE3, it has durable bond strength even after thermocycling.     

In vitro testing of all-in-one adhesives as fissure sealants

PURPOSE: To evaluate the clinical efficacy of all-in-one adhesives as fissure sealants. METHODS: Resin-enamel bonded specimens were fabricated between polished and ground enamel surfaces using two all-in-one adhesives (One-Up Bond F and Xeno CF Bond) and two resin sealants (Teethmate F-1 and Helioseal F). Specimen beams were prepared and microtensile bond tests were performed at a crosshead speed of 1 mm/minute. The bond strengths obtained were subjected to one-way ANOVA and Scheffe's F test (P < 0.05: n=12 for each group). To evaluate the etching effect of phosphoric acid and the all-in-one adhesives, the treated enamel surfaces (37% phosphoric acid, 40% phosphoric acid, or all-in-one adhesives) were examined by FE-SEM. RESULTS: The bond strengths of the two all-in-one adhesives tested to the polished enamel surface were significantly lower (P < 0.05) than to ground enamel. However, no significant differences (P > 0.05) were found between the polished and ground enamel surfaces for resin sealants using phosphoric acid. Under SEM examination, 37% or 40% phosphoric acid etched the enamel surface more than all-in-one adhesives.     

Relationship between composite fracture toughness and bond strengths to enamel and dentine

Background: This study aimed to evaluate the association between the fracture toughness of two nanofilled‐hybrid resin composites (Clearfil Majesty Esthetic [CME], Kuraray Medical, Japan; Estelite Σ [ES], Tokuyama, Japan) and their bond strengths to enamel and dentine mediated by a self‐etching primer system (Clearfil SE Bond [CSE]; Kuraray). Methods: Twenty‐four permanent human molars were sectioned into enamel and dentine specimens and finished with 600‐grit silicon carbide paper, bonded with CSE and either CME or ES, for μ‐shear bond strength (μSBS) and μ‐tensile bond strength (μTBS). The specimens were tested until failure at a cross‐head speed of 1 mm/min, failure loads recorded, bond strengths calculated and results analysed using independent samples t‐tests. Eight single‐notched bar‐shaped specimens, 30 mm × 5.2 mm × 2.2 mm, were prepared for each resin composite and fracture toughness measured using four‐point bending at a cross‐head speed of 0.5 mm/min. Results were analysed using independent samples t‐tests. Results: For μSBS and μTBS, there was no significant difference between the resin composites for enamel or dentine. The fracture toughness of CME was significantly higher than that of ES. Conclusions: For both enamel and dentine, resin composite fracture toughness affected neither μTBS nor μSBS to enamel or dentine.     

Evaluation of the bonding of cervical restorative materials

Variable results have been reported for the bonding of cervical lesion restorative materials to enamel and dentine. The effect of surface condition on bond strength was studied for two glass ionomer and one polycarboxylate cements and one composite resin material. Flat surfaces of human enamel and dentine, prepared by wet grinding on 600 grit silicon carbide paper, were treated respectively with water, phosphoric acid, citric acid, EDTA and/or remineralizing solution. Using an improved bonding device the cements and the composite resin were bonded to the prepared enamel and dentine surfaces. After 24 h in water at 37°C a tensile bond strength was determined. The bond fracture surfaces were examined in the scanning electron microscope. The results showed good bonding of the materials to enamel after the recommended surface treatments with cohesive failure and values 60–120 kg/cm² Bonding to dentine was more variable and was critically dependent on surface preparation. Caulk-ASPA bond strengths that were obtained after various treatments ranged from 34 kg/cm² (untreated dentine) to 54 kg/cm² (citric acid treatment). Fuji ionomer bond strengths that were obtained after various treatments ranged from 42 kg/cm² (citric acid treated dentine) to 56 kg/cm² (EDTA treated). Durelon bond strengths that were obtained after various treatments ranged from 24 kg/cm² (citric acid treated dentine), to 69 kg/cm2 (remineralizing solution treated dentine). The bond strengths that were obtained with Cervident after various treatments ranged from 0 kg/cm² (untreated dentine) to 30 kg/cm² (phosphoric acid treated dentine plus the adhesion promoter). SEM examination showed micromechanical bonding through penetration into dentinal tubules for all materials.     

An investigation of the composite resin/porcelain interface.

Failures at composite resin/porcelain interfaces under shear-like loading were examined. Porcelain surfaces were treated with hydrofluoric acid and/or one of two silane coupling agents, using two different composite resin cements. The results showed that after seven days storage, bond strengths of specimens which had undergone porcelain surface treatment were greater than the cohesive strength of the porcelain itself, resulting in brittle fracture of the porcelain. The diluted restorative composite resin performed as well as the commercial composite resin cement. Silane pretreatment of porcelain was important as the bond strength of etched/silane primed specimens was significantly higher than the etched only specimens. However, one primer appeared to be more efficient than the other in bond promotion. Some explanations for the differences in bond strengths are offered.     

Factors affecting shear bond strength of composite resin to fluorosed human enamel

The aim of this work was to determine the effects of age, severity of fluorosis, and etching time on the shear bond strength of direct composite resin to human enamel. A total of 117 teeth, freshly extracted from patients in areas of Saudi Arabia endemic for dental fluorosis, were classified according to age (< 40 years and 40+ years) and severity of fluorosis, using the Thylstrup and Fejerskov index, TFI: TFI = 0, TFI = 1-3, and TFI = 4-6. Cylindrical composite resin specimens 5 mm in diameter and 3 mm high were bonded to the flattened midlabial enamel surfaces etched for 60 or 120 seconds and shear bond strength measured, using the Instron Universal Testing Machine at a crosshead speed of 0.5 mm/minute. Shear bond strength of the resin varied between 11.2 +/- 3.6 and 21.6 +/- 4.1 MPa. Three-way analysis of variance and Sheffé's multiple range test showed that the severity of fluorosis had no statistically significant effect on shear bond strength (p > 0.05). However, the bond was significantly stronger in teeth from patients < 40 years old than from those 40+ years old. Furthermore, at age < 40 years, shear bond strength was significantly higher in teeth etched for 120 seconds than those etched for 60 seconds (p < 0.05), but this was not the case in teeth from the older patients. In teeth with TFI = 1-3, the mode of bond failure was predominantly mixed, but at TFI = 4-6, the bond failure was mostly cohesive in enamel at all ages and etching times. It is, therefore, concluded that both age and etching time affect the shear bond strength of composite resin to fluorosed human enamel.     

Bonding durability of HEMA-free and HEMA-containing one-step adhesives to dentine surrounded by bonded enamel

OBJECTIVE: To evaluate the bonding durability of HEMA-free and HEMA-containing one-step adhesives to dentine surrounded by bonded enamel after 1-year storage in water. MATERIAL AND METHOD: Flat coronal dentine surfaces of extracted human molars were prepared, leaving the surrounding enamel. Two one-step self-etch adhesive systems: HEMA-containing Tri-S Bond (TSB; Kuraray Medical Inc., Tokyo, Japan) and HEMA-free G Bond (GB; GC Co., Tokyo, Japan), were applied to both dentine and the surrounding enamel surfaces according to manufacturers' instructions. Following resin composite crown (Clearfil AP-X, Kuraray Medical Inc., Tokyo, Japan) build-ups, the bonded specimens were stored in 37 degrees C water for 24h (control group), 3 months, 6 months and 1 year. After the designated periods of water storage, the specimens were serially sectioned perpendicular to the adhesive interface into 0.7 mm thick slabs, and then trimmed to form hour-glass configurations with a 1mm2 cross-sectional area. The micro-tensile bond strength (muTBS) test was carried out at a crosshead speed of 1.0mm/min. The muTBS data were statistically analyzed using two-way ANOVA, t test, and Tukey's HSD post hoc multiple comparison tests (alpha=0.05). RESULTS: After 1 year water of storage, the bond strength of TSB to dentine was significantly lower compared with the 1-day, 3-month and 6-month groups (p<0.05). On the other hand, the muTBS of GB decreased over time, but there was no significant difference between the experimental periods (p>0.05). CLINICAL SIGNIFICANCE: Bonded enamel margins may not maintain the integrity of the resin-dentine interface created by HEMA-free and HEMA-containing one-step adhesives.     

Is a low viscosity bonding resin necessary?

Low viscosity bonding resins have been introduced for use on etched enamel surfaces prior to the application of the viscous composite resins. In this in vitro study the effects of a low viscosity bonding resin on the bond strength, adaptation and microleakage of a composite resin to etched enamel were evaluated. The low viscosity bonding resin did not improve the tensile bond strength of a composite resin to etched enamel, did not increase resin penetration into etched enamel and did not decrease marginal leakage at the composite resin/etched enamel interface. The continued use of low viscosity bonding resins in clinical dentistry is questioned.     

Adhesion to enamel of light-cured poly-acid dental materials

The purpose of this study was to determine the tensile bond strengths of a resin-modified glass ionomer cement and a poly-acid modified resin composite to enamel. Three different enamel surface preparations (unetched enamel; enamel treated with 10 per cent polyacrylic acid; enamel etched with 35 per cent phosphoric acid), were used. On etched enamel, the glass ionomer cement (15.0 MPa) and the resin composite (14.3 MPa) had significantly higher bond strengths than the other groups tested, but were not significantly different from each other. In the acid treated groups, cohesive failure within the material occurred in all specimens, while in the other groups, all specimens failed adhesively. Further investigation is required to test the clinical efficacy of these restorative materials.     

Adaptation to the cavity floor of the light-cured glass ionomer cement base under a composite restoration

The study attempted to assess methods of prevention of the formation of a contraction gap in a cylindrical enamel and dentine cavity. The influence has been investigated of the tensile bond strength of cement/dentine and cement/composite resin and the direct tensile strength during setting of light-cured glass-ionomer cements. The interface between composite resin/cement and cement/dentine were viewed and photographed by replica techniques under an SEM (Scanning Electron Microscope). The most noticeable finding was that an enamel and dentine cavity applicated with light- and auto-cured glass-ionomer cement generally presented with a small construction gap at the tooth restoration interface. However, the light-cured glass-ionomer base (Vitrabond) exhibited significantly better tensile bond strength to dentine and resin performance than the conventional glass-ionomer tested. This study revealed that there was no clear relationship between the adhesion to dentine and the adaptation to the dentine cavity floor.     

Micro-tensile bond strengths of bonding agents to pulpal floor dentine

AIM: The purpose of this study was to characterize the dentine surface of the pulpal floor and to determine the micro-tensile bond strengths of two dentine adhesive systems used in conjunction with a resin composite core material to pulpal floor dentine. METHODOLOGY: Thirty-six extracted human molars were cut horizontally with a slow-speed diamond saw to expose the pulp chamber and the pulp tissue was removed. Eight teeth were used to investigate characteristics of untreated and etched dentine surfaces of the pulpal floor using SEM. Twenty-eight teeth were randomly allocated to two groups, each of 14 teeth. In group 1, a 'one-bottle' system (Prime & Bond NT) was used as dentine bonding agent and in group 2, a self-etching-priming system (Clearfil SE Bond) was applied. Pulp chambers of both groups were then filled with resin composite core buildup (FluoroCore) and kept moist in tap water at 37 degrees C for 24 h. Samples were prepared for micro-tensile bond testing by sectioning each tooth vertically in the mid-pulpal floor region and shaped to an hour-glass form of 1 +/- 0.2 mm(2) area at the bonded interface. Micro-tensile bond strengths were determined using a universal testing machine at a crosshead speed of 1 mm min-1. Fractured surfaces were examined by SEM. RESULTS: The intact pulpal floor showed numerous calcospherites with variable tubule density and few accessory canals. Etching the pulpal floor with 34% phosphoric acid gel resulted in an irregular surface with patent dentinal tubules and the dome-shaped calcospherites mostly lost. With self-etching primer, the superficial dentine surface was less demineralized and little peritubular dentine matrix was removed. Mean bond strength for the self-etching-priming (Clearfil SE Bond) specimens was significantly greater than for 'one-bottle' (Prime & Bond NT) specimens (P< 0.05, Student's t-test). The fracture mode of Clearfil SE Bond specimens was mostly partial cohesive failure within dentine, whilst Prime & Bond NT specimens mostly showed partial cohesive failure in bonding resin/composite. CONCLUSIONS: Despite an irregular surface morphology and absence of a smear layer, bonding to pulpal floor dentine was weaker than previously reported for cut coronal dentine. The self-etching-priming system bonded more strongly than the 'one-bottle' system.     

Tensile bond strength of brackets after antioxidant treatment on bleached teeth

Various studies have reported a significant reduction in tensile bond strength of brackets when bonding is carried out immediately after bleaching. The purpose of this investigation was to determine the effect of an antioxidant agent on the tensile bond strength values of metal brackets bonded with composite resin to human enamel after bleaching with carbamide peroxide (CP). A total of 80 extracted premolar teeth were randomly divided into three bleaching groups of 10 per cent CP and an unbleached control group. The specimens in group 1 were bonded immediately after bleaching; group 2 were stored in an artificial saliva solution for 7 days after bleaching; group 3 were treated with 10 per cent sodium ascorbate, immediately before bonding, whereas the unbleached specimens in group 4 had no treatment before bonding. Tensile bond strengths were established in MPa. To evaluate the amount of resin left on the enamel surfaces after debonding, the adhesive remnant index (ARI) scores were used. The tensile bond strength data were analyzed with the Kruskal-Wallis test and pairwise comparisons were made by the Mann-Whitney U test at a significance level of P < 0.05. The brackets bonded immediately after bleaching revealed significantly lower tensile bond strengths than those of unbleached enamel (P = 0.000). No statistically significant differences in tensile bond strength were noted when the delayed-bonding (P = 6.000) and antioxidant-treated (P = 0.2757) groups were compared with the control group. The antioxidant treatment immediately after bleaching was effective in reversing the tensile bond strength of brackets.