Effect of load cycling and in vitro degradation on resin-dentin bonds using a self-etching primer

The objective of this study was to evaluate the effect of in vitro degradation and mechanical loading on microtensile bond strength (MTBS) and microleakage (ML) of a resin composite to dentin using a self-etching primer adhesive [Clearfil SE Bond (SEB)] under two hydration statuses. Twenty-four flat dentin surfaces were divided in groups: 1) blot-dried, 2) air-dried. SEB was applied and resin buildups were performed with Tetric Ceram. Specimens were divided in four subgroups: a) sectioned into beams, b) load cycled, c) beams were immersed in NaOCl for 5 h, d) load cycled and immersed in NaOCl. Beams were tested in tension. For ML testing, 80 Class V cavities were prepared and molars divided in subgroups as described above (in group c and d, specimens were kept in distilled water for 1 year, instead of the 5-h NaOCl immersion). ML was assessed by dye penetration. Analysis of variance and multiple comparisons tests were used for MTBS. For ML, Mann-Whitney U and Wilcoxon matched pairs signed ranked were used (p<0.05). SEB applied to completely dehydrated dentin produced the highest MTBS, at 24-h evaluation. In vitro degradation always decreased MTBS, and fatigue loading only diminished MTBS on dehydrated dentin. Load cycling increased dye penetration on dentin margins. Degradation always increased ML in both enamel and dentin margins.     

Effect of cyclic loading on bonding of fiber posts to root canal dentin

This study evaluated the effect of mechanical loading on microtensile bond strength (MTBS) when luting fiber posts to root canal dentin. Forty maxillary premolars were endodontically treated, and the roots were prepared for post cementation using the FRC Postec system. A light-cured composite (Clearfil Photo Core, Kuraray) was used in combination with four adhesive systems: Single Bond (3M ESPE), Multilink Primer (Vivadent), Clearfil Photo Bond (Kuraray), and Clearfil New Bond (Kuraray). A composite build-up was performed around the root to provide adequate gripping during testing. For each experimental group, half of the specimens were load cycled under 90 N (5000 cycles, 3 cycles/s). Specimens were cut to obtain beams with the post in the center and with the radicular dentin overlaid by the composite build-up on each side. Microtensile testing was performed with a universal testing machine at a cross-head speed of 0.5 mm/min. The failure mode was classified under a stereomicroscope. ANOVA and Student-Newman-Keuls multiple comparison tests were performed. After 24 h, all adhesives performed similarly. When specimens were subjected to mechanical loading, decreases in MTBS were observed for Clearfil New Bond and Multilink Primer.     

Effects of a peripheral enamel bond on the long-term effectiveness of dentin bonding agents exposed to water in vitro

This study evaluated the effects of water exposure on the in vitro microtensile bond strength (muTBS) of etch-and-rinse and self-etching adhesives to human dentin over a 1-year storage period. Five adhesive systems used were as follows: a one-step self-etching adhesive (One-up Bond F-OB), two two-step self-etching primers (Clearfil SE Bond-SE and Clearfil Protect Bond-CP), and two etch-and-rinse adhesives (Single Bond-SB and Prime&Bond NT-PB). Dentin surfaces were bonded, restored, and assigned to four subgroups, according to the degree of water exposure: 24 h of peripheral water exposure (24 h-PE) (having circumferential enamel); and 1 year of peripheral exposure (1 yr-PE), direct exposure (1 yr-DE) (dentin directly water-exposed), or directly exposed to oil only (no water exposure) (1 yr-DOE). A composite-enamel bond adjacent to the restoration is determined if the water exposure was peripheral or direct. After storage periods, specimens were serially sectioned, trimmed to an hourglass shape with a cross-sectional area of 1 mm(2) at the interface, and tested in tension. Results were analyzed by two-way ANOVA and Tukey test (alpha = 0.05). No difference was found between 24 h-PE and 1 yr-PE for OB, CP, SB, and PB. However, muTBS values significantly dropped after 1 yr-DE for SE, CP, SB, and PB. A decreased muTBS was seen in SE after 1 yr-PE, but no differences existed between 1 yr-PE and 1 yr-DE. Similar or increased muTBS values were noted in 1 yr-DOE for all adhesives. Water-storage for 1 year significantly decreased muTBS for all adhesives. However, except for SE, the presence of a peripheral composite-enamel bond seemed to reduce the degradation rate in resin-dentin interfaces for all materials.     

Effects of sodium hypochlorite gel and sodium hypochlorite solution on dentin bond strength

The aim of this study was to determine the effect of 10% NaOCl gel and 10% NaOCl solution on dentin bond strengths of four adhesive systems. One hundred eighty bovine incisors were ground to achieve a flat polished surface, then divided into 12 groups: Gluma One Bond [G1-control; G2-NaOCl solution; G3-NaOCl gel]; Prime & Bond 2.1 [G4-control; G5-NaOCl solution; G6-NaOCl gel]; Single Bond [G7-control; G8-NaOCl solution; G9-NaOCl gel]; Prime & Bond NT [G10-control; G11-NaOCl solution; G12-NaOCl gel]. Dentin was etched, rinsed, and blot dried. For the experimental groups, after acid etching, 10% NaOCl solution or 10% NaOCl gel was applied for 60 s, rinsed, and blot dried. Composite resin was inserted and light cured. Shear bond strengths were tested with a crosshead speed of 0.5 mm/min. The mean values MPa (SD) were analyzed with two-way ANOVA and Tukey's tests (alpha < 0.01). Ten percent NaOCl solution significantly increased Gluma One Bond strength. No effect was observed for the other adhesives. The 10% NaOCl gel did not affect bond strengths. Ten percent NaOCl gel was less effective on collagen removal as compared to 10% NaOCl solution. The influence of collagen removal on bond strength is dependent on adhesive system, where both the solvent and the monomer can influence the results.     

Liquid photocurable biodegradable copolymers: in vivo degradation of photocured poly(epsilon-caprolactone-co-trimethylene carbonate)

The present investigation was designed to test cellular toxicity of modern dentin adhesives. With the use of the products Ariston Liner, Etch & Prime 3.0, Optibond Solo, Prime & Bond NT, Scotchbond 1, and Syntac Sprint, test specimens were prepared according to the manufacturers' instructions and transferred into a culture medium. Eluates were obtained and pipetted onto fibroblast cultures, incubated, and subsequently stained. The respective cell densities and the numbers of normal, altered, and dead cells were determined and compared with control cell cultures. Statistical analysis of the data showed that all materials caused cytotoxic effects. Scotchbond 1 displayed the highest number of dead cells. The difference was statistically significant compared to Etch" 3.0, Optibond Solo, Prime&Bond NT, and the control. The lowest cell density was found for Scotchbond 1 and Ariston Liner. The difference was also statistically significant in comparison with Etch" 3.0, Optibond Solo, Prime&Bond NT, and the control. To conclude, all tested dentin adhesives caused cytotoxic reactions. Taking the limitations of an in vitro experiment into consideration, Prime&Bond NT, Optibond Solo, and Etch" 3.0 appear to be the most recommendable products, and Scotchbond 1 and Ariston Liner the least.     

Micro-tensile bond strength of sound and caries-affected primary tooth dentin measured with original designed jig

To measure the micro-tensile bond strength (MTBS) on sound and caries-affected primary tooth dentin using an original designed jig that was developed for making symmetric and uniformly-sized specimens for the micro-tensile strength testing. The MTBS of dumbbell-shaped specimens and matchstick-shaped specimens were measured. Dumbbell-shaped specimens: The occlusal surfaces of 15 sound primary molars were ground with a water-cooled air turbine using a diamond bur. The adhesive systems and resin-based composites were Clearfil SE Bond and Clearfil AP-X (SE group) and Single Bond and Z250 (SB group). Matchstick-shaped specimens: Sixteen primary molars (5 sound and 11 carious) were used. The occlusal surfaces of sound teeth were ground with a water-cooled air turbine using a diamond bur. Infected dentin was determined by a caries detecting dye solution and removed with a round-shaped steel bur under water-cooling and with a hand instrument. SE was applied. Data was statistically analyzed using ANOVA and Fisher's PLSD at p < 0.05. The MTBSs (MPa) for the dumbbell-shaped specimens were 8.9 +/- 7.0 in the SE group and 10.3 +/- 5.8 in the SB group and that for the matchstick-shaped specimens were 9.0 +/- 6.3 in the sound-SE group and 9.2 +/- 5.8 in the carious-SE group. No significant difference was observed among them.     

Bonding performance of different adhesive systems to deproteinized dentin: microtensile bond strength and scanning electron microscopy

Deproteinization has been shown to optimize dentin bonding, but differences in adhesive composition should be considered. The objective of this study was to evaluate the effect of dentin deproteinization on microtensile bond strength (microTBS) of four total-etch adhesive systems (Single Bond/SB, Prime & Bond NT/PB, One Coat Bond/OC, and PQ1/PQ). The ultrastructure of the resin-dentin interfaces was also examined using scanning electron microscopy. Tukey's multiple-comparison tests indicated that PB and PQ produced significantly higher microTBS (p<0.05) after dentin deproteinization (PB=61.53 MPa, PQ=58.18 MPa). This treatment provided statistically lower results for SB (39.08 MPa), but the microTBS of OC to dentin was unaffected by dentin deproteinization. The bonding performance on deproteinized dentin surfaces depended on the characteristics of each adhesive system, as well as the adhesive dentin specificity to the oxidant effect of sodium hypochlorite. Incorporation of fillers in the adhesive, a possible self-etching action, and the presence of a volatile solvent (acetone) were the main factors for a better union between the adhesive system and deproteinized substrate.     

In vitro effect of nanoleakage expression on resin-dentin bond strengths analyzed by microtensile bond test, SEM/EDX and TEM

This study evaluated the effect of multiple consecutive adhesive resin coatings of adhesive bonded to human dentin on nanoleakage and resin-dentin bond strength. Resin bonded dentin specimens were prepared using a total-etch adhesive (One-Step Plus) applied as multiple consecutive coating, or using two self-etch adhesive systems (iBond or Fluoro Bond). For the total-etch adhesive, resin application and air evaporation were performed 1, 2, 3, or 4 times. The self-etch adhesives were applied according to manufacturers' instructions. Resin-dentin bonded beams were prepared and immersed in water (control) or ammoniacal silver nitrate. After storage, microtensile bond strengths were measured. The fractured surfaces were examined by scanning and transmission electron microscopy (SEM and TEM), and energy-dispersive X-ray spectrometry (EDX). No significant differences in bond strength were found between water and silver nitrate storage groups. Several types of silver depositions (spotted, reticular, or water trees) were found in adhesive joints. The bond strengths of the single coated specimens of the total-etch adhesive were significantly lower than those receiving 2-4 coatings. Single coats produced more nanoleakage than multiple coats. However, no correlation was found between the bond strengths and nanoleakage between the different adhesives (total-etch adhesive with different conditions or self-etch adhesives).     

Degradation patterns of different adhesives and bonding procedures

Various types of resin adhesives and procedures are available in the clinical field, so comprehensive understanding of degradation is required for each material and bonding procedure. The objective of this study was to investigate the bond durability for different adhesives and bonding procedures. Resin-dentin bonded beams were prepared with the use of two adhesives (One-Up Bond F/self-etching primer system and One Bond/total-etch adhesive) and two experimental groups for the bonding procedure (wet and dry bonding of the total-etch adhesive). Those samples were soaked in water for 24 h(control), 6 and 12 months. After the water immersion, the bond strengths were measured by the microtensile bond test, and subsequently fractography was performed with the use of SEM. Statistically significant reduction of the bond strength (p < 0.05) was apparent after 12 months of water exposure in the range 22-48% of the control. The bonding resin was eluted from the hybrid layer of the self-etching and the total-etch adhesives for the wet bonding. Micromorphological alterations were found due to the hydrolysis of collagen fibrils with the total-etch adhesive for the dry bonding mode. These pathologic alterations were in accord with the bond strength.     

A challenge to the conventional wisdom that simultaneous etching and resin infiltration always occurs in self-etch adhesives

This study provided morphological evidence that discrepancies between the depth of demineralisation and the depth of resin infiltration can occur in some mild self-etch adhesives. Sound dentine specimens derived from extracted human third molars were bonded with 5 one-step and 5 two-step self-etch adhesives. One millimeter thick slabs containing the resin-dentine interfaces were immersed in 50 wt% aqueous ammoniacal silver nitrate and processed for TEM examination. A zone of partially etched but uninfiltrated dentine was identified beneath the hybrid layers in the milder versions of both one-step and two-step self-etch adhesives. This zone was characterised by the occurrence of silver deposits along the interfibrillar spaces of mineralised collagen fibrils. The silver infiltrated interfibrillar spaces were clearly identified from the one-step self-etch adhesives Xeno III, iBond, Brush&Bond and the experimental adhesive, and were thinner and only occasionally observed in the two-step self-etch adhesives Clearfil SE Bond and Clearfil Protect Bond. The more aggressive one-step and two-step adhesives that exhibit more abrupt transitions from completely demineralised to mineralised dentin were devoid of these silver-infiltrated interfibrillar spaces beneath the hybrid layers. Incomplete resin infiltration observed in some self-etch adhesives may be caused by the reduced etching potential of the acidic monomers toward the base of hybrid layers, or the presence of acidic but non-polymerisable hydrolytic adhesive components, creating potential sites for the degradation of the bonded created by these self-etch adhesives.     

Induction of cyclooxygenase-2 mRNA and protein expression by dentin bonding agents in human gingival fibroblasts

An ideal dentin bonding agent should be nonirritating to surrounding tissues. Unfortunately, all histological investigations have demonstrated that dentin bonding agents can induce mild to severe inflammatory alterations. However, there is little information on the precise mechanisms about dentin bonding agents-induced inflammatory reaction. Cyclooxygenase-2 (COX-2) is an inducible enzyme believed to be responsible for prostaglandin synthesis at the site of inflammation. The aim of the present study was to investigate the effects of three dentin bonding agents, Clearfil SE Bond, Prime & Bond NT, and Single Bond on the expression of COX-2 mRNA gene and protein in cultured human gingival fibroblasts. The exposure of quiescent human gingival fibroblasts to dentin bonding agents resulted in the induction of COX-2 mRNA expression. The investigations of the time-dependent on COX-2 mRNA expression in dentin bonding agent-treated human gingival fibroblasts revealed different patterns. The influence of COX-2 mRNA depended on the tested materials. In addition, all dentin bonding agents also induced COX-2 protein expression in human gingival fibroblasts. Taken together, the activation of COX-2 expression may be one of the potential mechanisms of dentin bonding agent-induced gingival inflammation.     

Changes in stiffness of resin-infiltrated demineralized dentin after remineralization by a bottom-up biomimetic approach

This study examined changes in elastic modulus, mineral density and ultrastructure of resin-infiltrated dentin after biomimetic remineralization. Sixty demineralized dentin beams were infiltrated with Clearfil Tri-S Bond, One-Step or Prime&Bond NT. They were immersed in simulated body fluid (SBF) for 1 week to maximize water sorption before determining the baseline elastic moduli. For each adhesive (N = 20) half of the beams remained immersed in SBF (control). The rest were immersed in a biomimetic remineralization medium. The elastic moduli were measured weekly for 15 additional weeks. Representative remineralized specimens were evaluated by X-ray microtomography and transmission electron microscopy (TEM). The elastic moduli of control resin-infiltrated dentin remained consistently low, while those immersed in the biomimetic remineralization medium increased by 55–118% after 4 months. X-ray microtomography of the remineralized specimens revealed decreases in mineral density from the beam surface to the beam core that were indicative of external mineral aggregation and internal mineral deposition. Interfibrillar and intrafibrillar remineralization of resin-sparse intertubular dentin were seen under TEM, together with remineralized peritubular dentin. Biomimetic remineralization occurs by diffusion of nanoprecursors and biomimetic analogs in completely demineralized resin-infiltrated dentin and proceeds without the contribution of materials released from a mineralized dentin base.     

Adhesive performance of dentin bonding agents applied in vivo and in vitro. Effect of intrapulpal pressure and dentin depth

The purpose of this study was to evaluate the influence of intrapulpal pressure and dentin depth on bond strengths of an etch-and-rinse and a self-etching bonding agent to dentin in vitro and in vivo. Twenty-four pairs of premolars were randomly divided into four groups (n = 6) according to the dentin bonding agent, Single Bond and Clearfil SE Bond, and intrapulpal pressure, null or positive. Each tooth of the pair was further designated to be treated in vivo or in vitro. The intrapulpal pressure was controlled in vivo by the delivery of local anesthetics containing or not a vasoconstrictor, while in vitro, it was achieved by keeping the teeth under hydrostatic pressure. Class I cavities were prepared and the dentin bonding agents were applied followed by incremental resin restoration. For the teeth treated in vitro, the same restorative procedures were performed after a 6 month-storage period. Beams with 1 mm(2) cross-sectional area were prepared and microtensile tested. Clearfil SE Bond was not influenced by any of the variables of the study, while bond strengths produced in vitro were significantly higher for Single Bond. Overall, lower bond strengths were produced in deep dentin, which reached statistical significance when Single Bond was applied under physiological or simulated intrapulpal pressure. In conclusion, in vitro bonding may overestimate the immediate adhesive performance of more technique-sensitive dentin bonding systems. The impact of intrapulpal pressure on bond strength seems to be more adhesive dependent than dentin morphological characteristics related to depth.     

Effects of two multi-step self-etch primer/adhesives on apoptosis in human gingival fibroblasts in vitro

Various in vitro studies have shown induction of apoptosis by monomers incorporated to dental restorative materials and adhesive resins, while information regarding the effect of monomer combinations as commercially available products on apoptosis is limited. The aim of this study was to investigate the effects of two multi-step self-etch primer/adhesive systems on apoptosis of cultured primary human gingival fibroblasts. Cells were treated up to 48 h with Clearfil SE Bond (Kuraray, Japan) and FL Bond (Shofu, Japan) at 1:1000 v:v ratio to determine cell proliferation, using 0.02 mM staurosporine as positive control. Apoptosis was assessed using propidium iodide/acridine orange (PI/AO) staining, compared to nontreated controls. When compared to FL Bond, exposure of gingival fibroblasts to Clearfil SE Primer and Clearfil SE Bond resulted in a higher degree of cell proliferation. PI/AO staining revealed typical morphological features of apoptosis in FL Bond and Staurosporine groups, while some cells cultured in the presence of primer and adhesive components of Clearfil SE Bond showed nuclear fragmentation, indicative of early apoptosis. Our results indicate that apoptotic potential of the multi-step self-etch adhesives were material-dependent within the 48 h test period.     

In vitro microTBS of one-bottle adhesive systems: sound versus artificially-created caries-affected dentin

This in vitro study aimed to evaluate a pH-cycling model for simulation of caries-affected dentin (CAD) surfaces, by comparing the bond strength of etch-and-rinse adhesive systems on sound and artificially-created CAD. Dentin substrates with different mineral contents and morphological patterns were created by submitting buccal bovine dentin to the following treatments: (1) immersion in artificial saliva during the experimental period (sound dentin, SD), or (2) induction to a CAD condition by means of a dynamic pH-cycling model (8 cycles, demineralization for 3 h followed by mineralization for 45 h). The bond strength of Excite or Prime and Bond NT adhesive systems was assessed using the microtensile bond strength (microTBS) test. Dentin microhardness was determined by cross-sectional Knoop evaluations. Resin-dentin morphology after the treatments was examined by scanning electron microscopy. SD produced significantly higher microTBS than CAD for both adhesives evaluated, without differences between materials. CAD exhibited lower microhardness than SD. Morphological analysis showed marked distinctions between SD and CAD bonded interfaces. Under the conditions of this study, differences in morphological pattern and dentin mineral content may help to explain resin-dentin bond strengths. The proposed pH-cycling model may be a suitable method to simulate CAD surfaces for bonding evaluations.     

Characterisation of resin-dentine interfaces by compressive cyclic loading

The aims of this in vitro study were to evaluate the ultra-morphological changes in resin-dentine interfaces after different amounts of thermomechanical load (TML), and to determine the corresponding microtensile bond strengths (microTBS). Enamel/dentine discs with a thickness of 2 mm were cut from 24 human third molars and bonded with four adhesives involving different adhesion approaches: Syntac (Ivoclar Vivadent; used as multi-step etch-and-rinse adhesive), Clearfil SE Bond (Kuraray; two-step self-etch adhesive), Xeno III (Dentsply DeTrey; mixed all-in-one self-etch primer adhesive system), and iBond (Heraeus Kulzer; non-mixed all-in-one self-etch adhesive). The resin-dentine discs were cut into beams (width 2 mm; 2 mm dentine, 2 mm resin composite) and subsequently subjected to cyclic TML using ascending amounts of mechanical/thermal cycles (20 N at 0.5 Hz of mechanical load and 5-55 degrees C of thermal cycles: for 0/0, 100/3, 1,000/25, 10,000/250, 100,000/2,500 cycles). Loaded specimens were either cut perpendicularly in order to measure microTBS (n=20; crosshead speed: 1 mm/min) or were immersed in an aqueous tracer solution consisting of 50 wt% ammoniacal silver nitrate and processed for ultra-morphological nanoleakage examination using transmission electron microscopy (TEM). microTBS were significantly decreased by increasing amounts of TML for all adhesives (p<0.05). Bond strengths after 0 vs. 100,000 thermomechanical cycles were: Syntac: 41.3/30.1 MPa; Clearfil SE Bond 44.8/32.5 MPa; Xeno III 27.5/13.7 MPa; iBond 27.0/6.2 MPa. Relatively early, a certain amount of nanoleakage was observed in all groups by TEM, which was more pronounced for Xeno III and iBond. The incidence of nanoleakage remained stable or was even reduced with increasing load cycles for all adhesives except iBond, where exact failure origins were detected within the adhesive and at the top of the hybrid layer.     

Ultramorphological analysis of resin-dentin interfaces produced with water-based single-step and two-step adhesives: nanoleakage expression

This study evaluated the nanoleakage patterns in bonded interfaces using two single-step, self-etching adhesives (Adper Prompt-AD, and One-up Bond F-OB), two two-step, self-etching primers (Clearfil SE Bond-CF, and Unifil Bond-UB), and one two-step, total-etch adhesive (Single Bond-SB). Dentin surfaces were bonded with the adhesive systems and stored in water at 37 degrees C for 1 week and 6 months. After storage periods, teeth were sectioned into 0.8 mm-thick slabs, coated with nail varnish except for the bonded interfaces, and immersed in ammoniacal AgNO(3) for 24 h. After immersion in photodeveloping solution, bonded sections were prepared and observed under a SEM using the backscattered electron mode. Undemineralized, unstained, epoxy resin-embedded sections were prepared for TEM. Nanoleakage patterns were qualitatively compared between periods. Nanoleakage was observed in all bonded specimens at both periods. CF and UB presented silver deposits predominantly restricted to the thin (0.5 microm) hybrid layer (HL) at both periods. Although no evident differences were observed in the nanoleakage pattern of UB at 7 days and 6 months, CF presented enlarged areas of silver impregnation after 6 months. SB presented accumulation of silver particles mostly within the HL at 7 days, which was intensified after 6 months. AD and OB presented massive silver accumulation within the HL and the overlying adhesive layer. No evident differences were noticed between storage periods. Silver impregnation increased for all adhesive systems from 7 days to 6 months, except for UB.     

Influence of organic acids present in the oral biofilm on the microtensile bond strength of adhesive systems to human dentin

This study evaluated the influence of organic acids present in the oral biofilm on the microtensile bond strength (μTBS) of adhesive systems to human dentin. Sixty occlusal dentin surfaces were wet ground with 600 grit SiC abrasive paper and divided into four groups according to the adhesive systems: Scotchbond Multipurpose (SMP), Adper Single Bond 2, Adper Scotchbond SE (ASE), and Clearfill SE Bond (CSE). After the adhesive systems were applied, a block of resin composite was built up on the dentin surfaces. After 24 h storage in distilled water at 37°C, the teeth were perpendicularly cut to obtain beams (1 mm(2)). For each adhesive system, the beams were divided into three groups according to storage media: artificial saliva (AS); propionic acid (PA), and lactic acid (LA). After 7 days storage at 37°C, the beams were submitted to μTBS testing. The μTBS ranged from 36.0 ± 1.6 (ASE-PA) to 52.5 ± 1.2 (CSE-AS). For all adhesive systems, the μTBS values after storage in PA were lower than those in AS. Except for the SMP, the values of μTBS after storage in LA were lower than those in AS. The adhesive ASE presented the lowest values of μTBs in the three media. The acids present in the oral biofilm may affect the bond strength of adhesive systems to human dentin.     

Evaluation of the fatigue behavior of the resin-dentin bond with the use of different methods

The clinical performance of directly bonded resin composites is fundamentally dependent on durable adhesion to prevent gap formation over time. The goal of this investigation was to evaluate the effectiveness of various dentin adhesives by means of quasistatic and dynamic dentin bond strengths, and also to determine marginal and internal gap formation after loading in an artificial oral environment. Three hundred thirty human third molars were used within four weeks of extraction. Adhesives used were A.R.T. Bond, OptiBond FL, Scotchbond Multi-Purpose Plus, Single Bond, Prime & Bond NT, and One Up Bond F for bonding of one resin composite (Z 250). Buccal and lingual aspects of 90 teeth were ground flat to expose dentin, then resin composite cylinders were bonded. Initial bond strengths (n = 10) and adhesive fatigue limits (n = 20) were determined with the use of a shear test apparatus. One hundred eighty conical cavities were prepared into dentin discs and filled with the same materials. After 21 days of storage, initial push-out bond strengths (n = 10) and adhesive fatigue limits (n = 20) were measured. Sixty molars with MO cavities (n = 10) with margins below the cement-enamel junction were filled. Before and after thermomechanical loading (100000 x 50 N and 2500 x thermocycling between + 5 and + 55 degrees C), marginal gap formation and internal adaptation (only after loading) were analyzed under a SEM (x 200). The one-bottle systems showed higher shear bond strengths when evaluated statically and dynamically. However, cyclic fatigue push-out bond strengths resulted in higher values for older multistep systems. Marginal and internal gap analysis confirmed the results, in favor of older adhesive systems (p <.05; Mann-Whitney U test).     

Nanoleakage and microshear bond strength in deproteinized human dentin

This study evaluated the influence of dentin deproteinization with NaOCl on the microshear bond strength (microSBS) and the nanoleakage patterns of three dentin bonding systems (DBS). Occlusal dentin surfaces, obtained from extracted noncarious human molars, were divided into two experimental groups, according to dentin surface treatment: Group I-37% H(3)PO(4)/15s and Group II-37% H(3)PO(4)/15s + 10% NaOCl/1 min. The dentin surfaces were bonded with one of the following DBS: Scotchbond Multipurpose-SBMP, Prime & Bond NT-PB and Clearfil SE Bond-SE. After 1 week storage in water at 37 degrees C, the specimens were subjected to the microSBS test. The data were analyzed by two-way ANOVA and Student-Newman-Keuls' test (p = 0.05). The nanoleakage was evaluated using scanning electron microscopy (SEM) in backscattered electron imaging regime. No significant difference in microSBS between dentin treatments was found for SBMP. For PB, microSBS increased after NaOCl dentin treatment. SE showed a reduction in microSBS in deproteinized specimens. SEM analysis showed different nanoleakage patterns for each DBS. Irrespective of dentin treatments, all SBMP specimens showed nanoleakage. SE did not show nanoleakage with the two dentin treatments. PB showed nanoleakage within the hybrid layer only in acid-etched specimens. The influence of dentin deproteinization was dependent on the dentin bonding system formulation.