AQ Bond Research Articles

Evaluation of Caries-Free Restorations Bonded with Various Adhesive Systems: In Vitro Study.

Purpose Secondary caries originate from a leakage pathway where oral acids can penetrate faster and demineralize the tooth substrate deeper which can be visualized by dye penetration. The ability to prevent secondary caries by contemporary adhesive systems was evaluated in this study. Dye penetration distance through leakage and into the tooth substrate adjacent to Class V restorations after artificial caries exposure was compared. Materials and Methods Previously frozen extracted human molars were used to prepare the Class V cavities at the CEJ on axial surfaces. All cavities were restored with either the resin-composite or amalgam with or without resin adhesives: dry bonding: Super-Bond D-Liner II Plus; moist bonding: All-Bond 2; and self-etch bonding: AQ Bond and Clearfil Protect Bond. Two subgroups of Super-Bond D-Liner II Plus were immersed for 14 days at 37°C either in artificial saliva (negative control) or the artificial caries solution. The other groups were soaked in the artificial caries solution. The distance of dye penetration into the adjacent enamel, cementum/dentin, and tooth-resin interfaces was measured after immersion in 0.5% basic fuchsin dye for 24 h. The tooth-resin interfacial layer was investigated using SEM. Results No dye penetration into the tooth-resin interface was found in Super-Bond D-Liner II Plus and AQ Bond groups which demonstrated a constant hybrid layer after a chemical challenge. The leakage distance at the cementum/dentin-resin interface of All-Bond 2, Clearfil Protect Bond, and non-adhesive amalgam (positive control) groups was significantly higher than the distance of dye penetration into the adjacent demineralized root surface (p < 0.05). Conclusion Caries associated with either amalgam or resin-composite restorations can be prevented using resin adhesives which can penetrate into the intact tooth substrate to form a stable hybrid layer. With caries-free restorations, tooth vitality may be conserved lifelong.

Polymerization kinetics of dual-curing adhesive systems when used solely or in conjunction with chemically-cured resin cement.

To investigate the chemical polymerization kinetics of commercial dual-curing adhesive systems when used solely or in conjunction with chemically-curing resin cement. Four adhesive systems comprising simplified-step adhesives and activators (Prime&Bond NT with Self Cure Activator, Excite DSC, AQ Bond Plus, All-Bond SE) were used. The pH values of the adhesives and adhesive/activator blends were measured. Differential scanning calorimetry (DSC) was used to investigate the extent of the chemical polymerization of the adhesives when used alone or directly intermixed with a chemically-cured resin cement (C&B Cement) for 60 min (n = 5). The data derived from the DSC analysis were statistically compared using one-way ANOVA and the Games-Howell post-hoc test (α = 0.05). All the adhesives were highly acidic; when they were blended with the respective activators, their pH values increased. Neither the adhesive/activator blends nor the adhesive alone/cement mixtures showed any detectable heat generation. The Prime&Bond NT/activator showed delayed heat generation only when intermixed with the catalyst/base paste. The other three adhesive systems produced similar exotherms when intermixed with the catalyst paste alone or with the catalyst/base paste (p > 0.05), but at significantly different maximum rates of polymerization (p < 0.05). Significantly shorter induction periods resulted when AQ Bond Plus and All- Bond SE were intermixed with the catalyst/base paste rather than with the catalyst paste alone (p = 0.004). The chemical polymerization occurring at the adhesive system/resin cement interface appears highly dependent on the adhesive system used and may be considerably delayed.

Spectral Characteristics of Light-curing Units and Dental Adhesives

Most manufacturers do not provide details about the photoinitiators contained in dental adhesives. Therefore, it is difficult to choose an optimal combination of dental adhesive and light-curing unit. The purpose of this study was therefore to investigate the spectral emission characteristics of several commercially available light-curing units and the spectral transmittance characteristics of contemporary dental adhesives. Spectral distributions of emitted lights were determined on a UV-vis-NIR spectrometer for three quartz-tungsten-halogen (QTH) light-curing units (Jetlite 3000, J. Morita; New Light VL-2, GC; D-Lux 2000, Dentrade) and three light-emitting diode (LED) light-curing units (Curenos, Shofu; G-Light Prima, GC; Bluephase, Ivoclar Vivadent). Spectral distributions of light transmittance in contemporary dental adhesives (Scotchbond Multi-Purpose, 3M ESPE; Adper Single Bond, 3M ESPE; One-Step, Bisco; AQ Bond Plus, Sun Medical; OptiBond All-in-One, Kerr; Clearfil S3 Bond, Kuraray Medical; G-Bond, GC; Tokuyama Bond Force, Tokuyama Dental; GBA 300 experimental, GC) were also determined. Each of the three QTH light-curing units had a wide emission range of 380-510 nm. A narrower emission range was observed in the LED light-curing units than in the QTH light-curing units. It was found that 2 LED light-curing units had dual peak wavelengths in both the blue and violet regions of the visible spectrum. There were some variations in light transmittance, and therefore the results suggested that some dental adhesives contain alternative photoinitiators besides camphorquinone. The selection of suitable light-curing units on the basis of the light absorption of dental adhesives and resin composites in dental clinics is of upmost importance.

Tensile Bond Strength of Single-Step Self-Etch Adhesives to Er:YAG Laser-Irradiated Dentin

The purpose of this study was to evaluate the influence of Er:YAG laser irradiation on the bond strength to dentine of three single-step adhesives (AQ Bond Plus, G-Bond, and Clearfil Tri-S Bond), and one two-step self-etch adhesive (Clearfil Megabond) as a control. The vast majority of the numerous reports on resin bonding to Er:YAG-lased dentine have concluded that Er:YAG laser irradiation is less effective in terms of bond strength, because of the sub-surface damage it produces. However, its effect in combination with single-step adhesives on bonding to dentine remains to be clarified. Eighty bovine incisors were ground with silicon carbide paper to obtain a flat dentine surface, which 40 were irradiated with an Er:YAG laser. Both lased and unlased dentine was bonded to a resin composite with each adhesive. Tensile bond strength was determined after 24 h of storage in water at 37 degrees C. Failure patterns after tensile bond testing was analyzed by scanning electron microscopy. The two-step self-etch adhesive (Clearfil Megabond) showed the highest bond strength to unlased dentine, but was significantly less effective on lased dentine than the three single-step adhesives. On the other hand, AQ Bond Plus produced an effective bond strength to both lased and unlased dentine, perhaps due to its low viscosity. The single-step adhesives tested in this study were as effective in combination with Er:YAG-lased dentine as the two-step self-etch adhesive.

Comparison of marginal microleakage between low and high flowable resins in class V cavity

The purpose of this study was to compare the microleakage of low and high viscosity flowable resins in class V cavities applied with 1-step adhesives. Forty Class V cavities were prepared on the cervices of buccal and lingual surfaces of extracted molar teeth and divided into four groups (n=8). Cavities were restored with AQ Bond Plus /Metafil Flo , G-Bond/ UniFil LoFlo Plus (Low flow groups), AQ Bond Plus/Metafil Flo and G-Bond/UniFil Flow (High flow group), respectively. Specimens were immersed in a 2% methylene blue solution for 24 hours, and bisected longitudinally. They were observed microleakages at the enamel and dentinal margins. In conclusion, the low viscosity flowable resins showed lower marginal microleakage than do the high vis cosity flowable resins in class V cavities.

Cytotoxicity of one‐step dentin‐bonding agents toward dental pulp and odontoblast‐like cells

The purpose of this study was to compare the cytotoxicity of five one-step dentin-bonding agents on human dental pulp and odontoblast-like cells (MDPC-23). Photopolymerized and unpolymerized samples of these dentin-bonding agents were prepared and incubated with dental pulp or MDPC-23 cells. After 24 or 72 h of incubation, the number of unstained cells with trypan blue was counted. The staining of cells with trypan blue stands for a cytotoxicity. The pulp cell and MDPC-23 cytotoxicity of polymerized sample treatment increased in the order of AQ Bond Plus (AQ)<Clearfil Tri-S Bond (TS)=G-bond (GB)<Absolute (AB)<Adper Prompt (AP) for 24 and 72 h. The pulp cell cytotoxicity of unpolymerized sample treatment for 24 h increased in the order of AQ<GB = AB<TS<AP. The MDPC-23 cytotoxicity of unpolymerized sample treatment for 24 h increased in the order of AQ<GB<TS = AB<AP. Whether polymerized or unpolymerized, AQ was the least cytotoxic agent, while AP was the strongest. All polymerized dentin-bonding agents exhibited lower cytotoxicity by 2-65% than their unpolymerized counterparts. The appearance of the cytotoxicity of dentin-bonding agents was time-dependent, and cell viability was lower at 72 h by 2-46% than at 24 h. The cytotoxicity to MDPC-23 cells was about 5-24% higher than that to pulp cells. These results indicate that one-step dentin-bonding agents differ markedly in their cytotoxicity. Differential cytotoxic effects of one-step dentin-bonding agents should be considered during clinical application of operative restoration.

The influence of cavity configuration on the microtensile bond strength between composite resin and dentin

This study was conducted to evaluate the influence of the C-factor on the bond strength of a 6th generation self-etching system by measuring the microtensile bond strength of four types of restorations classified by different C-factors with an identical depth of dentin. Eighty human molars were divided into four experimental groups, each of which had a C-factor of 0.25, 2, 3 or 4. Each group was then further divided into four subgroups based on the adhesive and composite resin used. The adhesives used for this study were AQ Bond Plus (Sun Medical, Japan) and XenoIII (DENTSPLY, Germany). And composite resins used were fantasists (Sun Medical, Japan) and Ceram-X mono (DENTSPLY, Germany). The results were then analyzed using one-way ANOVA, a Tukey's test, and a Pearson's correlation test and were as follows. 1. There was no significant difference among C-factor groups with the exception of groups of Xeno III and Ceram-X mono (p

Tensile Bond Strength of One-step Self-etch Adhesives to Er:YAG Laser-irradiated and Non-irradiated Enamel

This study determined the bond strengths to Er:YAG laser-irradiated and non-irradiated bovine enamel of three one-step self-etch adhesives (AQ Bond Plus (AQP), G-Bond (GB), and Clearfil Tri-S Bond (TS)) and one two-step self-etch adhesive (Clearfil Megabond (MB)). Eighty SiC paper-ground bovine enamel surfaces were used, of which half were laser-irradiated. The enamel surfaces were bonded to a resin composite with each adhesive, and tensile bond strengths were determined after 24 hours. For non-irradiated enamel groups, MB achieved greater bond strength to enamel than GB and TS (p < 0.05), but no significant difference was found between MB and AQP (p > 0.05). For laser-irradiated enamel groups, no significant differences were found among the four adhesives (p > 0.05). Additionally, for each adhesive, no significant differences were found between laser-irradiated and non-irradiated enamel. It was thus concluded that Er: YAG laser irradiation of enamel did not affect the tensile bond strength of one-step and two-step self-etch adhesives.

Microleakage of composite resin restoration according to the number of thermocycling

Present tooth bonding system can be categorized into total etching bonding system (TE) and self-etching boding system (SE) based on their way of smear layer treatment. The purposes of this study were to compare the effectiveness between these two systems and to evaluate the effect of number of themocycling on microleakage of class V composite resin restorations. Total forty class V cavities were prepared on the single-rooted bovine teeth and were randomly divided into four experimental groups: two kinds of bonding system and another two kinds of thermocycling groups. Half of the cavities were filled with Z250 follwing the use of TE system, Single Bond and another twenty cavities were filled with Metafil and AQ Bond, SE system. All composite restoratives were cured using light curing unit (XL2500, 3M ESPE, St. Paul, MN, USA) for 40 seconds with a light intensity of 600 ㎽/㎠. Teeth were stored in distilled water for one day at room temperature and were finished and polished with Sof-Lex system. Half of teeth were thermocycled 500 times and the other half were thermocycled 5,000 times between 5� C and 55� C for 30 second at each temperature. Teeth were isolated with two layers of nail varnish except the restoration surface and 1 mm surrounding margins. Electrical conductivity (㎂) was recorded in distilled water by electrochemical method. Microleakage scores were compared and analyzed using two-way ANOVA at 95% level. From this study, following results were obtained: There was no interaction between variables of bonding system and number of thermocycling (p = 0.485). Microleakage was not affected by the number of thermocycling either (p = 0.814). However, Composite restoration of Metafil and AQ Bond, SE bond system showed less microleakage than composite restoration of Z250 and Single Bond, TE bond system (p = 0.005).

Effects of Dentin Bonding Agents on Bonding Durability of a Flowable Composite to Dentin

The present study evaluated the bonding durability of a flowable composite on bovine dentin using dentin bonding agents with different numbers of application steps: Scotchbond Multipurpose (three steps), Prime & Bond NT and One-Step (two steps), AQ Bond and Prompt L-Pop (one step). Shear bond strength tests were performed, and resin-dentin interface and fracture mode were observed. There were no significant differences in bond strength among the specimens within 37 degrees C storage group (p > 0.05) and post-thermocycling group, except between Prompt L-Pop and Scotchbond Multipurpose (p < 0.05) in the post-thermocycling group. Further, Scotchbond Multipurpose and One-Step showed significantly lower bond strengths after thermocycling (p < 0.05). It was thus shown that the use of simplified bonding agents did not necessarily improve the bonding strength of flowable composites.

Effect of Polymerization Accelerator on Dentin Bonding of One-step Bonding Agent

The aim of this study was to enhance the bond strength of one-step bonding agents to dentin. In particular, the focus was on using Catabrush the applicator system of AQ Bond Plus. Catabrush was supplemented with N-phenylglycine and aromatic sulfinate as polymerization accelerators, as N-phenylglycine was reportedly beneficial in improving the bond strength to dentin. The results indicated that the bond strength to dentin was significantly augmented and the photo-polymerization as well as the chemical polymerization were both improved even in the moistened dentin when 1.0 wt% N-phenylglycine was added to AQ Bond Plus agent, hence implying significantly higher bond strength to dentin. It was therefore concluded that N-phenylglycine is useful as a polymerization accelerator to be adopted in the applicator system for one-step bonding agents.

Comparative enamel bond strength between light- and dual-cured composites bonded by self-etching adhesives

This study compared the microshear bond strength () of light-cured and dual-cured composites to enamel bonded with three self-etching adhesives. Crown segments of extracted human molars were cut mesiodistally, and 1 mm thickness of specimen was made. They were assigned to three groups by used adhesives: Xeno group (Xeno III), Adper group (Adper Prompt L-Pop), and AQ group (AQ Bond). Each adhesive was applied to cut enamel surface as per manufacturer's instruction. Light-cured (Filtek Z 250) or dual-cured composite (Luxacore) was bonded to enamel of each specimen using Tygon tube. After storage in distilled water for 24 hours, the bonded specimens were subjected to testing with a crosshead speed of 1 mm/minute. The mean (n = 20 for each group) was statistically compared using two-way ANOVA, Tukey HSD, and t test at the 0.05 probability level, The results of this study were as follows ; 1. The of light-cured composite was significantly higher than that of dual-cured composite when same adhesive was applied to enamel. 2. For Z 250, the of AQ group () to enamel was significantly higher than that of Adper soup (), but not significantly different with Xeno group (). 3. For Luxacore, the of Xeno group () to enamel was significantly higher than that of Adper group (), but not significantly different with AQ group ().

Effectiveness of all-in-one adhesive systems tested by thermocycling following short and long-term water storage

To evaluate and compare the marginal integrity of in vitro Class V restorations made with all-in-one adhesive systems by thermocycling after different periods of water storage, to provide an analysis of static and quasi-dynamic deterioration in water. Standardized Class V cavities (17 groups, 8 specimens each) were prepared in extracted human caries-free anterior teeth. The cavities were filled using 14 all-in-one adhesive systems/composite resin combinations in addition to the multi-bottle adhesive systems Syntac and OptiBond FL (etch-and-rinse technique) and Clearfil SE Bond (self-etching) as controls. The samples were thermocycled after water storage for 21 days, after 1 year and again after 3 years (2000 cycles between 5 and 55 degrees C) and replicas were made before and after each thermocycling treatment (TC) for quantitative marginal analysis in the SEM. In dentin, marginal adaptation showed no significant differences between all groups after the first TC. After one year of water storage and a second TC, the results for Prompt L-Pop (1999), Adper Prompt L-Pop/Tetric Ceram, and One-up Bond F Plus showed a statistically significant decrease of margin quality 1 (MQ1) score compared to the reference groups. When the all-in-one adhesives G-Bond, AQ-Bond, Hybrid Bond, and One-up Bond F Plus were used, the enamel margins of restorations showed lower percentages of "continuous margins" (p < 0.05) after 1 year of water storage and TC. Of the materials tested after 3 years of water storage and TC, only AQ Bond had a significantly lower MQ1 score. While all materials exhibited deterioration in the MQ1 quality score, the rate of deterioration varied, and the results show that different materials have different deterioration rates after initial vs long-term water storage. The deterioration along margins in dentin was not as extensive as predicted from other studies; however, the results from the enamel margins show that one-bottle all-in-one adhesives seem to be significantly affected by water storage. The results of this study suggest that the all-in-one adhesive group members perform very differently from each other: thus, data need to be explored further at the level of each different adhesive product.

New concept of resin‐dentin interfacial adhesion: The nanointeraction zone

The purpose of this study was to evaluate the morphological appearance of resin-dentin interface produced by 1-step adhesive systems in order to classify them, using TEM. It was hypothesized that all interfaces produced by each 1-step adhesive show characteristics similar to that produced by the conventional self-etching system rather than that produced by etch-and-rinse system. The flattened dentin surfaces were subjected to bonding treatment using either a 2-step adhesive: single bond, mega bond, unifil bond; or a 1-step adhesive: Prompt L-Pop, absolute, xeno CF, AQ bond, one-up bond F, G bond, and SSB-200. A flowable resin was then applied to these surfaces. The results revealed that resin-dentin interfaces produced by 1-step systems were classified into three categories. Additionally, the interface produced by G bond and SSB-200 showed a different morphological appearance from that of the others. The interface produced by these adhesives was thinner and less demineralized, with the presence of hydroxyapatite-coated collagen fibrils. It is proposed that "Nanointeraction Zone (NIZ)" is a new complementary classification for partially demineralized resin-dentin interdiffusion zones. Thus, one-step self-etching adhesive systems can be classified into three categories, etch-and-rinse type, mild self-etching type, and NIZ type, by their morphological appearance of the interface.

Shear Bond Strengths of Self-etching Adhesives to Caries-affected Dentin on the Gingival Wall

The purpose of this study was to evaluate the bonding ability of five current self-etching adhesives to caries-affected dentin on the gingival wall. Seventy extracted human molars with approximal dentin caries were employed in this study. In order to obtain caries-affected dentin on the gingival wall, grinding was performed under running water. Following which, specimens mounted in acrylic blocks and composite resins of the bonding systems were bonded to dentin with plastic rings and then debonded by shear bond strength. With Clearfil SE Bond, bonding to caries-affected dentin showed the highest bond strength. With Optibond Solo Plus Self-Etch, bonding to caries-affected dentin showed higher shear bond strength than AQ Bond, Tyrian SPE & One-Step Plus, and Prompt-L-Pop (p<0.05). Further, the bond strengths of Clearfil SE Bond and Optibond Solo Plus Self-Etch to sound dentin were higher than those of Prompt-L-Pop, AQ Bond, and Tyrian SPE & One-Step Plus (p<0.05). In conclusion, besides micromechanical interlocking through hybrid layer formation, bond strength of self-etch adhesives to dentin may be increased from additional chemical interaction between the functional monomer and residual hydroxyapatite. The results of this study confirmed that differences in bond strength among self-etching adhesives to both caries-affected and sound dentin were due to chemical composition rather than acidity.

Bond Strength of Total-Etch Dentin Adhesive Systems on Peripheral and Central Dentinal Tissue: A Microtensile Bond Strength Test

The purpose of this study was to evaluate the microtensile bond strength (mu TBS) of four total-etch adhesives [Excite (EB), Prime&Bond NT (PBNT), Single Bond (SB), and One Coat Bond (OCB)] by comparing them to five self-etching adhesives (Clearfil SE Bond (CSEB), Xeno III (X III), Prompt L-Pop (PLP), AQ Bond (AQB), and Tyrian/One Step plus (TOSP)] at different dentinal areas. In addition the interface between the adhesive resins and dentin was examined using scanning electron microscopy (SEM). Superficial occlusal dentin of extracted human molars was exposed and finished with wet 800-grit silicon carbide paper. A block of composite resin was then bonded to the molar samples with the above adhesives according to the manufacturers' instructions. After 24 hours in water at 37 degrees C, the specimens were sectioned into 1 mm thick slices and divided into two regional subgroups according to their relationship to pulp tissue using visual criteria: pulp center and pulp periphery. The slices were then trimmed for the microtensile bond test and subjected to a tensile force and crosshead speed of 1 mm/min. Two-way analysis of variance was performed for statistical analyses. In addition the bond strengths for nine adhesive systems for each dentinal area were compared using the Post-Hoc test. The resin-dentin interfaces for each adhesive system were observed under a SEM. Mean mu TBS ranged from (25.2 MPa) for TOSP to (48.9 MPa) for PBNT. The bond strengths of total-etch adhesive systems were not significantly different, and were higher than self-etch adhesive systems, except for CSEB (p<0.05). No significant regional difference was observed for all of the nine adhesive systems (p>0.05). SEM observation showed there is not a standard hybridization for adhesive systems. Different dentinal areas may not exhibit as great an influence on bond strengths using new adhesive systems.

Shear Bond Strengths of Two Composite Core Materials After Using All‐in‐One and Single‐Bottle Dentin Adhesives

The purpose of this study was to compare the shear bond strengths of 2 composite core materials after using all-in-one and single-bottle dentin bonding materials. The occlusal surfaces of 100 extracted, intact human third molars were ground to expose a flattened area of dentin and polished with 600-grit silicon carbide paper. Specimens were divided into 5 main groups (n= 20). Three all-in-one (AQ Bond, One-Up Bond, Xeno-CF Bond) and 2 single-bottle adhesives (Single Bond, One-Step Plus) were used. Each group was further divided into 2 subgroups. Ti-Core and Built-it F.R. core materials were applied using a translucent plastic ring (diameter: 3 mm, height: 5 mm). After storage in 37 degrees C water for 24 hours, shear bond strengths were measured using a Universal testing machine with a crosshead speed of 0.5 mm/min. Debonded dentin surfaces were examined with SEM. Two-way analysis of variance (ANOVA) and multiple comparison (Tukey) tests were used for statistical analysis of data. Two-way ANOVA revealed that the type of core material did not significantly influence the shear bond strength (p > 0.05), whereas there were significant differences in shear bond strength among the types of bonding agents (p < 0.0001). Shear bond strengths for single-bottle adhesive systems were significantly higher than those for all-in-one adhesive systems (p < 0.05). Furthermore, the interaction of these 2 parameters was not significant (p > 0.05). The fracture modes were predominantly adhesive for all-in-one adhesives and cohesive for single-bottle adhesives. Bonding of composite core materials with the newly developed all-in-one dentin adhesives produced lower shear bond strengths as compared with single-bottle adhesives.

Microtensile bond strength of single step adhesives to dentin

This study compared the microtensile bond strength (μ TBS) of three single step adhesives to dentin. Occlusal superficial dentin was exposed in fifteen human molars. They were assigned to three groups by used adhesives: Xeno group (Xeno III), Prompt group (Adper Prompt L-Pop), AQ group (AQ Bond). Each adhesive was applied to dentin surface, and composite of same manufacturer was constructed. The bonded specimens were sectioned into sticks with an interface area approximately 1 ㎟, and subjected to μ TBS testing with a crosshead speed of 1 ㎜/minute. The results of this study were as follows; 1. The μ TBS to dentin was 48.78 ± 9.83 ㎫ for Xeno III, 30.22 ± 4.52 ㎫ for Adper Prompt L-Pop, and 26.31 ± 7.07 ㎫ for AQ Bond. 2. The mean μ TBS of Xeno group was significantly higher than that of Prompt group and AQ group (p <

Micro-shear Bond Strength of Five Single-step Adhesives to Dentin

The micro-shear bond strengths (MSBSs) of five single-step self-etch adhesives (Adper Prompt L-Pop [APL], AQ Bond plus [AQP], OBF-2 [OB2], Reactmer Bond [RB], and Xeno III [XIII]) were compared with that of a two-step self-etch adhesive, Clearfil SE Bond [SE]. The adhesives were applied on dentin surfaces, according to manufacturers' instructions, for bonding of resin composite to dentin. After 24 hours, a micro-shear bond test was carried out and the data were analyzed by one-way ANOVA and Bonferroni test (p<0.05). The mean MSBSs in MPa were APL: 22.8, AQP: 37.4, OB2: 34.7, RB: 28.3, XIII: 30.3, and SE: 47.2. Among the single-step adhesives, the MSBS of AQP and OB2 were significantly higher than APL (p<0.05). In conclusion, the single-step adhesives used in this study, apart from AQP, produced significantly lower MSBS than the two-step adhesive (p<0.05).

Single-step adhesives are permeable membranes

Objectives. This study tested the hypotheses that micro-tensile bond strengths of all currently available single-step adhesives to dentine are adversely affected by delayed activation of a light-cured composite, and that such a phenomenon only occurs in the presence of water from the substrate side of the bonded interface. Methods. In experiment I, a control three-step adhesive (All-Bond 2, Bisco) and six single-step adhesives (One-Up Bond F, Tokuyama; Etch&Prime 3.0, Degussa; Xeno CF Bond, Sankin; AQ Bond, Sun Medical; Reactmer Bond, Shofu and Prompt L-Pop, 3M ESPE) were bonded to sound, hydrated dentine. A microfilled composite was placed over the cured adhesive and was either light-activated immediately, or after leaving the composite in the dark for 20 min. In experiment II, three single-step adhesives (Etch&Prime 3.0, Xeno CF Bond and AQ Bond) were similarly bonded to completely dehydrated dentine using the same delayed light-activation protocol. In experiment III, a piece of processed composite was used as the bonding substrate for the same three single-step adhesives. The microfilled composite was applied to the cured adhesives using the same immediate and delayed light-activation protocols. Bonded specimens were sectioned for micro-tensile bond strength evaluation. Fractographic analysis of the specimens was performed using SEM. Stained, undemineralised sections of unstressed, bonded specimens were also examined by TEM. Results. When bonded to hydrated dentine, delayed light-activation had no effect on the control three-step adhesive, but significantly lowered the bond strengths of all the single-step adhesives ( p<0.05). This adverse effect of delayed light-activation was not observed in the three single-step adhesives that were bonded to either dehydrated dentine or processed composite. Morphological manifestations of delayed light-activation of composite in the hydrated dentine bonding substrate were exclusively located along the composite–adhesive interface, and were present as large voids, resin globules and honeycomb structures that formed partitions around a myriad of small blisters along the fractured interfaces. Conclusion. These features resembled the ‘overwet phenomenon’ that was previously reported along the dentine–adhesive interfaces of some acetone-based three-step adhesives. The cured adhesive layer in single-step adhesives may act as semi-permeable membranes that allow water diffusion from the bonded hydrated dentine to the intermixed zone between the adhesive and the uncured composite. Osmotic blistering of water droplets along the surface of the cured adhesive layer and emulsion polymerisation of immiscible resin components probably account for the compromised bond strength in single-step adhesives after delayed activation of light-cured composites.