Significant Reduction In Bond Strength Research Articles

Influence of Protease Inhibitors on Bond Degradation of Self-Etch Adhesive Systems to Caries-Affected Dentin: An <i>in Vitro</i> Study

Background: A decline in pH and dissolution of the inorganic content of the dental tissues are followed by exposure of the organic portion of the tooth, which, in dentin, is largely composed of collagen fibres. These unprotected fibres are then degraded by metalloproteinases and cysteine cathepsins, proteolytic enzymes present in dentin. We evaluated the influence of protease inhibitors on the bond strength of a self-etch adhesive system to caries-affected dentin. Eighty permanent third molars were selected for the study. Dentinal caries were induced artificially by the microbial method and the teeth were divided in four groups: G1—application of Clearfil SE Bond adhesive system (CL); G2—2% chlorhexidine (CLX) + CL; G3—sodium bicarbonate (BIC) + CL; G4—BI + CLX + CL. Bond strength was assessed immediately and at six months. During the six months, the specimens were stored in distilled water. Microtensile bond strength testing was performed. On immediate testing, there was no significant difference in bond strength across the control, BIC, and CLX groups. The combination of BIC + CLX, however, led to an immediate, significant reduction in bond strength. After six months, bond strength was reduced in all groups. The highest bond strength was obtained in the control group (P 0.05). Most fractures were adhesive, both immediately and at six months. We concluded that the cavity pretreatment with 2% CLX or 2% BIC did not have an immediate negative impact on bond strength of the Clearfil SE Bond system. After specimens were stored for six months in water, their bond strength of specimens was reduced in all groups. This reduction was the greatest in the groups exposed to the inhibitors.

Pretreatment with Sodium Fluoride Maintains Dentin Bond Strength of a Two-Step Self-Etch Adhesive after Thermal Stressing.

To evaluate the effect of sodium fluoride and chlorhexidine digluconate on the composite-dentin bond strength of a self-etch adhesive after thermocycling. Eighteen human third molars were prepared to expose a flat dentin surface and were divided into 3 groups (n = 6) according to the 3 cavity cleaning solutions: distilled water, 2% chlorhexidine digluconate (CHX), or 1.23% sodium fluoride (NaF). Solutions were rubbed onto dentin surfaces for 60 s, followed by bonding with Clearfil SE Bond, and a 5-mm-thick composite crown buildup. Bonded teeth were stored in distilled water for 24 h and then longitudinally sectioned to obtain bonded sticks. Half of the specimens were immediately tested in tension at 0.5 mm/min, while the remaining specimens were tested after 60,000 thermal cycles. Data were analyzed using two-way ANOVA and the Holm-Sidak method. There was no significant difference between the groups after 24 h (p > 0.05). Thermocycling resulted in significant bond strength reduction for distilled water and CHX (p < 0.05). When 24 h bond strengths were compared to the thermocycling group, NaF maintained its bond strength (p > 0.05), while significant reductions were observed for distilled water and CHX (p < 0.05). Pretreatment with NaF maintained the bond strength of Clearfil SE Bond to dentin after 60,000 thermal cycles, but pretreatment with CHX did not.

The effect of zoledronate-containing primer on dentin bonding of a universal adhesive.

To evaluate the bonding ability and nanoleakage of a universal adhesive applied to dentin pre-treated using a zoledronate-containing primer (zol-primer) before and after mechanical load cycling. Flat dentin surfaces obtained from human molars were assigned to one of the following adhesion procedures (n=6): 1-Single Bond Universal (SBU) applied in etch-and-rinse mode; 2- SBU applied as etch-and-rinse after the application of zol-primer; 3- SBU applied in self-etch strategy; 4- SBU applied as self-etch after the use of zol-primer. Half of the specimens were processed for microtensile bond strength test after 24h, while the other half part was submitted to 200,000 mechanical cycles. Further specimens were silver-impregnated and assessed for interface nanoleakage by SEM. Data were analyzed with two-way ANOVA and Tukey's test (p<0.05). At 24h evaluation, the four groups presented similar bond strengths, whilst both groups bonded with etch-and-rinse technique showed significant bond strength reduction after mechanical load (p<0.05), with the highest drop in bond strength for the specimens pre-treated with the zol-primer. No negative effects were found for self-etch strategy (p>0.05) in microtensile test. Lower nanoleakage expression was observed for etch-and-rinse specimens treated with zol-primer. However, noteworthy reduction of adhesive layer thickness was observed when combining the zol-primer with the self-etch bonding approach. It can be concluded that zol-primer should not be used along with a universal adhesive in etch-and-rinse mode, but its application before self-etch application may provide less degradation of the resin-dentin interface.

Experimental study on bond behavior between corrosion-cracked reinforced concrete and CFRP sheets

Bond behavior between corrosion damaged reinforced concrete and carbon fiber reinforced concrete polymer (CFRP) sheets was experimentally investigated. Forty ordinary strength concrete blocks (150 × 150 × 200 mm) were reinforced at one side across the 200-mm-dimension using three conventional ϕ12 mm steel bars at a spacing of (30, 40, and 50 mm) at a concrete clear cover of 15 mm. Thirty blocks were subjected to a cyclic treatment in 3% chloride solution until corrosion initiated and resulted in three different global cracking widths of up to 0.90 mm. Both control and corrosion damaged blocks were attached to CFRP sheets over their steel reinforced zone at bond lengths and widths ranging from (90 to 150 mm) and (50 to 150 mm), respectively, with CFRP bond length-to-bar spacing ratio kept constant at 1/3. Near-end pull-off tests were carried out using a special setup, mounted on a Universal Testing machine. Corrosion cracking caused significant reductions in bond strength, and slippage at ultimate stress at (41 and 68%), respectively. Other bond characteristics such as stress at first slippage, and bond stiffness and toughness were reduced, as well, by as high as (83, 44 and 67%) of those of control specimens, respectively. Corrosion cracks were more detrimental for smaller bond length and width values; especially after first and second corrosion stages, where bond failure was categorized by concrete skin peeling-off.

Effect of cavity disinfectants on antibacterial activity and microtensile bond strength in class I cavity.

This study was performed to compare the antibacterial activities of three cavity disinfectants [chlorhexidine (CHX), NaOCl, urushiol] and to evaluate their effect on the microtensile bond strength of Scotchbond Universal Adhesive (3M-ESPE, St. Paul, MN, USA) in class I cavities. In both experiments, class I cavities were prepared in dentin. After inoculation with Streptococcus mutans, the cavities of control group were rinsed and those of CHX, NaOCl and urushiol groups were treated with each disinfectant. Standardized amounts of dentin chips were collected and number of S. mutans was determined. Following the same cavity treatment, same adhesive was applied in etch-and-rinse mode. Then, microtensile bond strength was evaluated. The number of S. mutans was significantly reduced in the cavities treated with CHX, NaOCl, and urushiol compared with control group (p<0.05). However, there was a significant bond strength reduction in NaOCl group, which showed statistical difference compared to the other groups (p<0.05).

Effect of Fluoride and Simplified Adhesive Systems on the Bond Strength of Primary Molars and Incisors.

The aim of this study was evaluate in vitro the influence of simplified adhesive systems (etch-and-rinse and self-etching) and 1.23% acidulated phosphate fluoride (APF) on the microshear bond strength (μ-SBS) of composite resins on primary molars and incisors. Forty primary molars and forty incisors vestibular enamel was treated with either the self-etching Clearfil SE Bond (CSE, Kuraray) or etch-and-rinse Adper Single Bond 2 (SB2, 3M/ESPE) adhesive system. Each group was subdivided based on the prior treatment of the enamel with or without the topical application of 1.23% APF. Thereafter, matrices were positioned and filled with composite resin and light cured. After storage in distilled water at 37 ± 1°C for 24 h, the specimens were submitted to μ-SBS in a universal testing machine. Kruskal-Wallis and Mann-Whitney tests (p < 0.05) showed that the prior application of 1.23% APF led to a significant reduction in bond strength. The type of adhesive exerted no significant influence bond strength. In the inter-group analysis, however, significantly bond strength reduction was found for the incisors when CSE was employed with APF. Adhesive failure was the most common type of fracture. The bond strength was affected by the prior application of 1.23% APF and type of tooth.

Evaluation of some intracanal irrigants on push-out bond strength and mode of failure of resin and non resin cements to root canal dentin (in vitro comparative study)

Objectives: The purpose of this study was to evaluate the effects of five intracanal irrigants [distilled water, NaOCl, NaOCl + EDTA, ozonated water and NaOCl + ozonated water] on push-out bond strength of (zinc phosphate cement and Calibra® esthetic resin cement) and to determine the mode of failure. Materials and Methods: Seventy extracted single straight rooted teeth were selected. The crowns were sectioned at cemento-enamel junction. The sectioned roots were embedded vertically in clear acrylic resin. The root canals were prepared with K-files and Gates Glidden drills using step-back technique then the specimens were randomly assigned to five main groups according to the types of irrigant used and each main group were divided in to two subgroups and filled with zinc phosphate cement and Calibra® esthetic resin cement. The samples were sectioned horizontally to provide 4 millimeter dentin disc from coronal third of the roots. Each sectioned specimen was tested by using computerized universal testing machine. Finally each de-bonded specimens was examined under stereomicroscope to determine the mode of failure. Results: Two-way ANOVA tests showed that there was statistical significance difference between the two type of cement used in this study, also there was statistical significance difference between the types of irrigant; while the interaction between types of cement with types of irrigant was not statistically significant. Considering the dentine surface treatment, Paired T-test showed that irrigation with 5.25% NaOCl produce statistically significant reduction in bond strength to root canal dentin in comparison to control group, while irrigation with distilled water, 5.25 NaOCl plus 17% EDTA, 5.25% NaOCl plus 5gm/L ozonated water, 5gm/L ozonated water alone had no statistical significant affect on bond strength to root canal dentin. Comparing the cements, zinc Phosphate cement showed higher bond strength in comparison to Calibra® esthetic resin cement. Conclusions: NaOCl have negative effect on bond strength to root canal dentin, while distilled water, NaOCl plus EDTA, ozonated water alone or after NaOCl had no effect. Zinc phosphate cement had higher bond strength than Calibra® esthetic resin cement. The adhesive and mixed failures were higher than the cohesive failure for all groups in general.

Effect of rewetting suspensions of bioactive-glass on resin–dentin bond strength

Purpose: The aim of this study was to evaluate the effect of bioactive glass suspensions used to rewet dried demineralized dentinon the resultant immediate and3-monthbondstrength of one adhesive system to dentin. Methods and materials: The experimental bioactive glass was prepared by mixing different amounts of oxides (NbO5; (NH4)2HP4; CaO; Na2CO3). The average particle size, distribution and composition of the bioactive glass powder were determined by SEM and EDS. Sixty-five extracted human third molarswere used. Crowns fragmentswere embedded in transparent acrylic resin andpolished onwet #320-grit SiC paper for 20 s before bonding. The specimens were assigned into 5 different groups (n=13). The dentin surface was etched for 20 s with 34% phosphoric acid gel, rinsed with water for 20 s and air-dried with an oil free syringe for 30 s. The surface was then rewetted with either one of the four different concentrations of bioactive Nb/P suspension glasses (5%, 10%, 20%, 40%, w/v), or distilled water (control) brushed for 10 s and two consecutive layers of an adhesive system (One Step, Bisco, USA) were applied to dentin (20 s air-dried/20 cm distance) and polymerized for 10 s/1500mW/cm2. Two cylinders of composite resin were bonded to dentin and light polymerized for 40 s. The bonded samples were stored in a phosphate-calcium buffer solution (PBS) and tested in a shear mode at 0.5mm/min after 24h and 3 months. Failure modes were classified as adhesive, mixed and cohesive (resin). The data were analyzed by 2-way ANOVA and Holm–Sidak tests at a=5%. Results: There were no significant differences among the different concentrations of suspensions for both storage periods (F=0.26; p=0.9) and no significant interactions were observed (F=1.13; p=0.3). Storage time caused significant effects (F=14.1; p<0.001). Significant reductions in bond strength were observed after 3 months PBS storage for the Control and 5% suspension groups. No significant differences were observed for the higher concentrated suspensions. Values are MPa±SD. All groups showed a predominance of adhesive failure mode (Table 1).

Evaluation of bond strength of silorane and methacrylate based restorative systems to dentin using different cavity models

ObjectiveThe aim of this in vitro study was to evaluate the microtensile bond strength (µTBS) to dentin of two different restorative systems: silorane-based (P90), and methacrylate-based (P60), using two cavity models.Material and MethodsOcclusal enamel of 40 human third molars was removed to expose flat dentin surface. Class I cavities with 4 mm mesial-distal width, 3 mm buccal-lingual width and 3 mm depth (C-factor=4.5) were prepared in 20 teeth, which were divided into two groups (n=10) restored with P60 and P90, bulk-filled after dentin treatment according to manufacturer's instructions. Flat buccal dentin surfaces were prepared in the 20 remaining teeth (C-factor=0.2) and restored with resin blocks measuring 4x3x3 mm using the two restorative systems (n=10). The teeth were sectioned into samples with area between 0.85 and 1.25 mm2 that were submitted to µTBS testing, using a universal testing machine (EMIC) at speed of 0.5 mm/min. Fractured specimens were analyzed under stereomicroscope and categorized according to fracture pattern. Data were analyzed using ANOVA and Tukey Kramer tests.ResultsFor flat surfaces, P60 obtained higher bond strength values compared with P90. However, for Class I cavities, P60 showed significant reduction in bond strength (p<0.05). No statistical difference between restorative systems was shown for Class I cavity model (p>0.05), or between Class I Cavity and Flat Surface group, considering P90 restorative system (p>0.05). Regarding fracture pattern, there was no statistical difference among groups (p=0.0713) and 56.3% of the fractures were adhesive.ConclusionIt was concluded that methacrylate-based composite µTBS was influenced by cavity models, and the use of silorane-based composite led to similar bond strength values compared to the methacrylate-based composite in cavities with high C-factor.

Effect of calcium hydroxide and endodontic irrigants on fibre post bond strength to root canal dentine

To analyse the effect of calcium hydroxide paste, endodontic irrigants and time of application on the bond strength of fibre posts to root canal dentine. Seventy bovine incisors were divided into 7 groups according to removal of calcium hydroxide and distilled water (CHW) (immediate - I; 21days - 21days; 6months - 6months) and endodontic irrigant (1% sodium hypochlorite - SH; 1% sodium hypochlorite+17% EDTA - SHE). Fibre posts were cemented (RelyX U100), after which the roots were serially sectioned and submitted to a micro-push-out test. Data were analysed using two-way anova followed by the Tukey's and the Dunnett's tests (α=0.05). The CHW groups were not significantly different from the control group in 13 of the 18 associated factors (P>0.05). There were significant reductions in bond strength in the cervical (P=0.0216) and middle (P=0.0017) thirds of the root at 6months in groups irrigated with SH. Irrigation with SHE reduced the bond strength significantly in the middle (P=0.0488) and apical (P=0.0252) thirds of the roots in the immediate groups and in the middle third (P=0.0287) in the 21-day group. Bond strength was greater in the cervical than in the apical thirds of all immediate and 21-day groups (P<0.05). Bond strength of groups that received CH paste was similar to that found in the control group in 13 of the 18 associated factors. EDTA and SH reduced bond strength in specimens in the immediate (middle and apical thirds) and 21-day (middle third) groups. There was a significant reduction in bond strength in the groups irrigated with SH and tested at 6months (cervical and middle thirds). There was a predominance of adhesive failures between resin cement and dentine in all groups.

Pre-treatment of radicular dentin by self-etch primer containing chlorhexidine can improve fiber post bond durability

We evaluated whether the pre-treatment of radicular dentin by ED Primer containing different concentrations of chlorhexidine can improve the bond durability of fiber post to radicular dentin. Experimental ED primers containing different concentrations of chlorhexidine (0%, 0.5% and 1.0%) were prepared. Thirty extracted maxillary anterior teeth were divided into 3 groups, each group corresponding to different chlorhexidine concentrations. Fiber posts were cemented in endodontically treated teeth with experimental ED primers and Panavia F. The bonded teeth were transversally sectioned into six slices and then were processed for thin slice push-out test 24 h later or after 18-months water storage. Eighteen-month storage resulted in significant bond strength reduction of all groups (p<0.05). The bond strength reduction of 1.0% group was significantly lower than that of control group and 0.5% group (p<0.05). In conclusion, the incorporation of 1.0% chlorhexidine into ED primer can extend the bond longevity of fiber post to radicular dentin.

The influence of the energy density and other clinical parameters on bond strength of Er:YAG-conditioned dentin compared to conventional dentin adhesion

The aim of this in vitro study was to optimise clinical parameters and the energy density of Er:YAG laser-conditioned dentin for class V fillings. Shear tests in three test series were conducted with 24 freshly extracted human third molars as samples for each series. For every sample, two orofacial and two approximal dentin surfaces were prepared. The study design included different laser energies, a thin vs a thick bond layer, the influence of adhesives as well as one-time- vs two-time treatment. The best results with Er:YAG-conditioned dentin were obtained with fluences just above the ablation threshold (5.3 J/cm(2)) in combination with a self-etch adhesive, a thin bond layer and when bond and composite were two-time cured. Dentin conditioned this way reached an averaged bond strength of 23.32 MPa (SD 5.3) and 24.37 MPa (SD 6.06) for two independent test surfaces while showing no statistical significance to conventional dentin adhesion and two-time treatment with averaged bond strength of 24.93 MPa (SD 11.51). Significant reduction of bond strength with Er:YAG-conditioned dentin was obtained when using either a thick bond layer, twice the laser energy (fluence 10.6 J/cm(2)) or with no dentin adhesive. The discussion showed clearly that in altered (sclerotic) dentin, e.g. for class V fillings of elderly patients, bond strengths in conventional dentin adhesion are constantly reduced due to the change of the responsibles, bond giving dentin structures, whereas for Er:YAG-conditioned dentin, the only way to get an optimal microretentive bond pattern is a laser fluence just above the ablation threshold of sclerotic dentin.

Fusion sputtering for bonding to zirconia-based materials.

To evaluate the influence of fusion sputtering on zirconia-resin microtensile bond strength after 6 months of water storage. Zirconia disks received one of the following surface treatments: particle abrasion with 50-µm aluminum oxide particles or fusion sputtering, while as-sintered specimens served as a control. The prepared zirconia disks (Lava Zirconia) were bonded to pre-aged composite disks (Filtek Z250) using a phosphatemonomer- containing resin cement (RelyX Unicem), and the bonded specimens were sectioned into micro-bars (1 x 1 x 6 mm) which were either immediately tested or after 6 months of water storage (n = 25). Scanning electron microscopy (SEM) and surface roughness were performed for the prepared specimens. Data were analyzed using two-way ANOVA (α = 0.05). Particle abrasion (33.1 MPa) and fusion sputtering (42.5 MPa) produced significantly higher MTBS values and resisted degradation after 6 months of water storage, while as-sintered specimens (12.4 MPa) demonstrated a significant reduction in bond strength after water storage (2.9 MPa). SEM examination indicated that fusion sputtering resulted in the creation of retentive zirconia beads on the treated surface, which enhanced micromechanical retention with adhesive resin and prevented interfacial failure. Fusion sputtering is a new and a simple method suitable for enhancing the bond strength of adhesive resins to zirconia-based frameworks.

Effect of chlorhexidine incorporation into dental adhesive resin on durability of resin-dentin bond.

This study evaluated the effect of chlorhexidine (CHX) incorporation into experimental dentin adhesives with different hydrophilicities on the microtensile bond strength (µTBS) to dentin. Flat, deep dentin surfaces were prepared from 60 extracted human third molars. Three ethanol-solvated (50 wt% ethanol/50 wt% comonomers) experimental adhesives with varying degrees of hydrophilicity were prepared for the CHX-free groups. For the CHX-containing groups, chlorhexidine diacetate was further added to the ethanol-solvated adhesives to form a concentration of 2.0 wt% CHX. Dentin surfaces were etched with 37% phosphoric acid for 15 s, rinsed and blot dried before bonding. The adhesives were generously applied to dentin with a microbrush for 15 s. A second application of fresh adhesive was made and light cured for 20 s (600 mW/cm2) after solvent evaporation. Composite buildups were made using Filtek Z250 (3M ESPE). The bonded teeth were sectioned into 0.9 mm x 0.9 mm beams and stressed to failure at a crosshead speed of 1 mm/min. Testing was performed 24 h after specimen preparation and 12 months after storage in artificial saliva. The µTBS data were analyzed using three-way ANOVA and Tukey's multiple comparison tests. Fractographic analysis was performed by SEM. Significant differences were observed for the three factors "adhesive hydrophilicity" (p < 0.001), "CHX incorporation" (p = 0.001), and "storage time" (p < 0.001). Interaction among these three factors was also significant (p < 0.001). Incorporation of CHX had no effect on the immediate bond strength of the three experimental adhesives (p > 0.05). After storage in artificial saliva, significant reduction in bond strength was observed in all adhesive groups, except for CHX-containing adhesive I (p < 0.001). The µTBS of the CHX-containing experimental adhesive III was significantly higher than the corresponding CHX-free adhesive (p < 0.001) after aging. When incorporated into hydrophilic dental adhesives, chlorhexidine can partially reduce the degradation of the resin-dentin bonds.

Adhesion of Indirect MOD Resin Composite Inlays Luted With Self-adhesive and Self-etching Resin Cements

This study investigated the effect of loading on the bond strength to dentin and microleakage of MOD indirect composite restorations bonded with self-adhesive and self-etching resin cements with or without acid etching of the proximal enamel margins. Class II MOD cavities were prepared in 48 molar teeth into dentin and divided into three groups of 16 teeth. Impressions were taken and indirect composite inlays fabricated (Estenia C & B). The enamel margins of the proximal boxes of half the specimens were phosphoric acid etched, and the inlays were cemented with one of three cements (Panavia F 2.0, SA Cement, or Rely X Unicem). After luting, eight teeth in each cement group were mechanically loaded at 2.5 cycles/s for 250,000 cycles. Unloaded teeth acted as controls. Teeth were stored in Rhodamine B solution for 24 hours, sectioned buccolingually at the proximal boxes to examine microleakage using confocal microscopy, and further sectioned for μTBS testing of the resin-dentin interface. Analysis of variance was performed to assess the effect of loading and acid etching on microleakage and bond strength. Acid etching had no effect on microleakage. No significant difference in the dentin bond strengths between the three cements existed after loading. Panavia F 2.0 exhibited a significant reduction in bond strength. With regard to microleakage at the proximal boxes, loading had no effect on dye penetration at the cavity floor. However, at the axial walls, loading had a significant deleterious effect on Panavia F 2.0. No difference in microleakage existed between the three cements at both sites before and after loading. In conclusion, the two tested self-adhesive cements exhibited similar bond strengths before and after loading to the self-etching resin cement. Loading reduced dentin bond strengths and increased microleakage at the resin-dentin interface. However, acid etching of the enamel margins had no significant effect on microleakage in the approximal regions of the bonded inlays.

Effect of contamination and decontamination on adhesion of a resin-modified glass-ionomer cement to bovine dentin.

To determine the adhesion of resin-modified glass-ionomer cement to bovine dentin under contaminated and decontaminated conditions. Forty-five bovine mandibular incisors were used. The surfaces of bovine dentin specimens were subjected to Temp-bond, dental handpiece lubricant (contamination), Hibiscrub, chlorhexidine or pumice (decontamination), as well as contamination followed by decontamination. From these, 14 test groups were created to investigate the effects of these variables on the microtensile bond strength of a resin-modified glassionomer cement to dentin. In addition, scanning electron microscopy was performed to examine the effects of contamination and decontamination procedures on the dentin surfaces. The data were analyzed by one-way ANOVA, Kruskal-Wallis, and Mann-Whitney tests. SEM examination showed visible differences between the control group and dentin contaminated with Temp-bond or handpiece lubricant. All the contamination and decontamination test agents when used alone - except Hibiscrub - showed significant reductions in bond strength when compared to the control (p < 0.001). All the test groups subjected to contamination followed by decontamination showed a significantly reduced bond strength (p < 0.001) when compared to the control, with the exception of the handpiece lubricant/Hibiscrub combination. Under the conditions tested, Temp-bond, handpiece lubricant, chlorhexidine, and pumice may have an adverse effect on the bonding of resin-modified glass ionomer to dentin. Hibiscrub was effective in decontaminating handpiece lubricant but not Temp-bond.

Ten‐years degradation of resin–dentin bonds

The purpose of this study was to evaluate the durability of resin-dentin bonds in 10-yr water-storage testing. Resin-dentin bonded bulk specimens were prepared using six commercially available resin adhesives. The resin-dentin bonded specimens were stored in water for 24 h (control group) or for 10 yr (experimental groups). After each storage period, the specimens were sectioned to make specimen beams and then subjected to a microtensile bond test. After the bond test, fractured surfaces were examined by scanning electron microscopy (SEM). In addition, interfacial observation of silver nanoleakage was performed using the backscatter electron mode of SEM. The bond strengths of four of the six adhesive systems tested decreased significantly after 10 yr. However, no significant bond-strength reduction was recorded for the other two systems. The interfacial observations showed water tree propagation in the bonding resin layer as a typical morphological change after aging for five of the six adhesives tested. Water tree propagation may be a symptom of degradation in the resin bonding layer of resin-dentin bonds.

The influence of rotating fatigue on the bond strength of zirconia-composite interfaces

Objectives To evaluate the effect of cyclic loading on the bond strength of resin composite to zirconia framework material. Methods Bar shaped zirconia/composite specimens (2 mm × 2 mm × 25 mm) were prepared using three different resin cements and placed in a four-point bending test setup. The flexure strength ( F s) was calculated by placing the bars ( n = 10) fixed between the four supports (at 10 and 20 mm) with the interface centered between the inner rollers and subsequently loaded (1 mm/min crosshead speed) until fracture. Rotating fatigue resistance (RFR) was determined in a rotating bending cantilever test setup (104, 1.2 Hz) with the highest stress located at the interface ( n = 20). The RFR was determined by the staircase method and the mean RFR was calculated using logistic regression analysis. Results Resin cement composition had no significant influence on the bond strength value obtained by both F s ( F = 0.6, P ≥ 0.5) and RFR ( F = 1.1, P ≥ 0.3) tests. However, after rotating fatigue testing there was a significant reduction in bond strength between 46 and 50% of the three resin cements. Conclusion Zirconia resin bond strength is liable to deterioration under the influence of fatigue.

Effect of Contamination on Reinforcing Bar-Concrete Bond

Current specifications require the removal of reinforcing bar contaminants that reduce bond prior to placing concrete. This study focused on the interactions of contaminant type, bar size, epoxy coating, concrete strength, and test method (beam and direct pullout). The majority of the beam tests showed the bond strength was not significantly affected, with certain exceptions. However, the direct pullout tests revealed a significant reduction of bond strength in most situations. Although the bond strength was still greater than that required by code, it is recommended that specifications for removal of contaminants should not be relaxed until further study is performed.

The incorporation of chlorhexidine in a two-step self-etching adhesive preserves dentin bond in vitro

Objectives To investigate whether the incorporation of chlorhexidine in a two-step self-etching adhesive can preserve dentin bond strengths. Methods Different amounts of 20% chlorhexidine digluconate were added directly to the primer of Clearfil SE Bond to prepare mixtures of four different concentrations of chlorhexidine: 0.05%, 0.1%, 0.5% and 1.0%. Sixteen extracted third molars were randomly divided into 4 groups. Each group corresponded to one of the four chlorhexidine concentrations. Each of the 16 teeth was sectioned into two halves. One half was bonded with Clearfil SE Bond without chlorhexidine, and the other half was bonded with Clearfil SE Bond containing different concentrations of chlorhexidine. Specimens were stored in 0.9% NaCl containing 0.02% sodium azide at 37 °C. Microtensile bond strengths were tested 24 h after specimen preparation or 12 months later. The modes of fractures were examined under a stereomicroscope. Results Twelve-month storage resulted in significant bond strength reduction of all control groups ( p < 0.05). When incorporated in SE Bond primer, chlorhexidine preserved dentin bond in the 0.1%, 0.5% and 1.0% chlorhexidine group ( p < 0.05); in the 0.05% group, there is no statistical difference of bond strength between control group and experimental group tested at the 12-month period ( p > 0.05). Conclusions When incorporated in the primer of Clearfil SE Bond, chlorhexidine can preserve dentin bond as long as the concentration of chlorhexidine in the primer is higher than or equal to 0.1%.