Differential effect of in vitro degradation on resin-dentin bonds produced by self-etch versus total-etch adhesives

OBJECTIVE: To evaluate the effect of an in vitro challenge (NaOCl immersion) on microtensile bond strength (MTBS) of five adhesive systems to dentin. METHODS: Flat dentin surfaces from 40 molars were bonded with three total-etch adhesives (Single Bond, Prime&Bond NT and the experimental Prime&Bond XP), and two self-etching agents (Clearfil SE Bond and Etch&Prime 3.0). Composite build-ups were constructed with Tetric Ceram. Teeth were then sectioned into beams of 1.0 mm2 cross-sectional area. Half of the beams were immersed in 10% NaOCl aqueous solution for 5 h. Each beam was tested in tension in an Instron machine at 0.5 mm/min. Data were analyzed by 2-way ANOVA and multiple comparisons tests (p < 0.05). RESULTS: Clearfil SE Bond and Single Bond attained higher MTBS than the other three adhesives. Prime&Bond NT and Prime&Bond XP performed equally, and Etch&Prime resulted in the lowest MTBS. After NaOCl immersion, MTBS decreased in all groups. The highest MTBS values were obtained for Clearfil SE Bond and Prime&Bond XP. Scaning electron microscopy observation of debonded sticks evidenced dissolution and microstructural alterations of intertubular dentin, except when Clearfil SE Bond was used. CONCLUSIONS: Resin-dentin bonds are prone to chemical degradation. The extent of the resin degradation is adhesive system specific. Chemical degradation of the nonresin infiltrated collagen fibers does also exist in total-etch adhesives. Both processes may reduce long-term resin-dentin bond strength.     

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).     

The effect of six years of water storage on resin composite bonding to human dentin

The aim of this in vitro study was to evaluate dentin bond strength and marginal adaptation of direct resin composite fillings after different storage times. Three hundred sixty cavities were prepared in discs of freshly extracted human third molars and filled with resin composites. Multistep self-etching adhesives (Syntac Classic, A.R.T. Bond, both with and without total etching), three-step etch-and-rinse adhesives (Scotchbond Multi-Purpose Plus, EBS), and two-step etch-and-rinse adhesives (Prime and Bond 2.0, Syntac Single-Component) were used for bonding. After 1, 90, and 2190 days of water storage and 24 h thermocycling (1150 cycles), push-out testing was performed. From the 6-year group, replicas were made after 1 day, 90 days, and 1, 2, 3, 4, 5, and 6 years, and examined regarding marginal adaptation under an SEM (x 200 magnification). In all groups under investigation, push-out bond strengths remained stable after 90 days; however, the strengths significantly decreased after 6 years of water storage. The two-step systems exhibited lower bond strengths than three-step systems after 6 years. Marginal analysis revealed a significant loss regarding the percentage of perfect margins having been stable after 2 years for the three-step etch-and-rinse systems. Overall, the older three-step systems proved to be more effective than the simplified adhesives Syntac Single-Component and Prime and Bond 2.0 with regard to bond strength and marginal adaptation.     

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.     

Diffusion-induced water movement within resin-dentin bonds during bonding

It is thought that water-filled channels and nanovoids in resin-dentin bonds represent potential sites for degradation of bonds or hydrolysis of collagen or both. How water gains access to bonded interfaces is not clear. This study evaluated the diffusion-induced water uptake through resin-dentin interfaces during bonding. Two light-cured total-etch adhesive systems (Excite and One-Step Plus) and a chemical-cured adhesive (Amalgambond Plus) were used in this study. Dentin disks were placed in a split-chamber device, and the fluid movement across dentin was measured, with and without a physiological pressure, during bonding procedures and 24 h after bonding. For light-cured adhesives in the experimental groups, a 6 min interval of dark storage was conducted prior to light-curing, to evaluate the diffusion of water through the uncured resin monomers, and to test the effect of prolonged infiltration time of adhesives on water permeability of bonds. Prolonged adhesive infiltration reduced the water permeability of resin-dentin bonds for light-cured adhesives. Water gradients produced by bonding systems contribute to water movement across the dentin-adhesive interfaces during bonding procedures. Differences in chemical formulations for adhesive systems may lead to differences in the extent of diffusion-induced water movement and the amount of water within the resin-dentin bonds.     

Effect of light-cure time of adhesive resin on the thickness of the oxygen-inhibited layer and the microtensile bond strength to dentin

A thick oxygen-inhibited layer (OIL) on a cured adhesive layer (AL) is believed to result in both good adaptation of composite resin (CR) and high bond strength. A high degree of conversion (DC) of the AL is also needed for durable bonding. This study evaluated the hypothesis that increasing the DC by prolonging the light-curing time of adhesive bonding resin might decrease the bond strength of the adhesive to dentin because of the subsequent thinning of the OIL thickness. The OIL thickness and the DC of solvent-removed One Step and D/E bonding resin of All Bond 2 (Bisco, USA) were measured simultaneously with FT-NIR spectroscopy according to increasing light-cure times (10, 20, 30, and 60 s) so as to evaluate their effect on the microtensile bond strength. The bonded interfaces were evaluated using scanning electron microscopy. Excessive irradiation of light-curing adhesives increased the DC, but decreased the OIL thickness. When the OIL was significantly thin by curing the adhesives for 30 or 60 s, defects were observed at the interface between the AL and the CR, as well as at the interface between the AL and the hybrid layer. When the OIL was thick, free radicals from the overlying CR may have diffused into the unreacted monomer mixtures of the OIL, chemically connecting the cured AL and the newly curing composite. It was found that to obtain maximum dentin bond strength, light-curing adhesives should be cured for the irradiation time recommended by the manufacturer.     

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.     

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.     

Bonding characteristics of newly developed all-in-one adhesives

This study evaluated the microtensile bond strength and the interfacial morphology of newer adhesives. The occlusal surfaces of extracted teeth were ground flat for random allocation to four equal groups. Resin composite was bonded to each surface using either Clearfil SE Bond [SEB], Clearfil Protect Bond [PB], G-Bond [GB], or an experimental adhesive, SSB-200 [SSB]. After storage for 24 h in water at 37 degrees C, they were sectioned into beams (cross-sectional area 1 mm(2)) for microtensile bond strength testing (muTBS) at a crosshead speed of 1 mm/min. The load at failure of each was recorded; the data were analyzed by one-way ANOVA and Games Howell tests. The surfaces of the fractured specimens were observed using SEM. For the ultra-morphology of the interface, the occlusal surfaces of four more teeth were prepared as before and a thin layer of flowable resin composite was bonded to each surface using one of the four adhesives.The mean muTBS ranged from 39.68 MPa (GB) to 64.97 MPa (SEB). There were no statistical differences between SEB and SSB, or between PB and GB (p > 0.05). The muTBS of SEB and SSB were significantly greater than that of PB and GB (p < 0.05). SEMs of the fractured surfaces revealed a mixed (cohesive/interfacial) failure. TEM examination highlighted differences in the hybrid layer; SEB had a thicker layer than the others. In conclusion, the newer all-in-one adhesives produced a thin hybrid layer but varied in their bond strengths. The 2-step self-etching adhesives do not necessarily produce higher bond strengths than that of the all-in-one systems.     

Biomimetic remineralization as a progressive dehydration mechanism of collagen matrices – Implications in the aging of resin–dentin bonds

Biomineralization is a dehydration process in which water from the intrafibrillar compartments of collagen fibrils are progressively replaced by apatites. As water is an important element that induces a lack of durability of resin–dentin bonds, this study has examined the use of a biomimetic remineralization strategy as a progressive dehydration mechanism to preserve joint integrity and maintain adhesive strength after ageing. Human dentin surfaces were bonded with dentin adhesives, restored with resin composites and sectioned into sticks containing the adhesive joint. Experimental specimens were aged in a biomimetic analog-containing remineralizing medium and control specimens in simulated body fluid for up to 12 months. Specimens retrieved after the designated periods were examined by transmission electron microscopy for the presence of water-rich regions using a silver tracer and for collagen degradation within the adhesive joints. Tensile testing was performed to determine the potential loss of bond integrity after ageing. Control specimens exhibited severe collagen degradation within the adhesive joint after ageing. Remineralized specimens exhibited progressive dehydration, as manifested by silver tracer reduction and partial remineralization of water-filled microchannels within the adhesive joint, as well as intrafibrillar remineralization of collagen fibrils that were demineralized initially as part of the bonding procedure. Biomimetic remineralization as a progressive dehydration mechanism of water-rich, resin-sparse collagen matrices enables these adhesive joints to resist degradation over a 12-month ageing period, as verified by the conservation of their tensile bond strength. The ability of the proof of concept biomimetic remineralization strategy to prevent bond degradation warrants further development of clinically relevant delivery systems.     

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.     

Initial adhesion of glass-fiber-reinforced composite to the surface of porcine calvarial bone

The aim of this preliminary study was to compare the initial bond strength of the glass-fiber-reinforced composite veil to the surface of the porcine calvarial compact bone using different adhesives. Fiber-reinforced composite (FRC) made of E-glass fiber veil with the BisGMA-PMMA resin system was used in the study. For the shear bond strength test, porcine calvarial bone cubes were mounted into resin matrix. FRC-veil discs were bonded to compact bone with different types of adhesives: (A) BisGMA-HEMA based (3M-ESPE Scotchbond Multi-Purpose Adhesive), (B) 4-META/UDMA/BisGMA based (Unifil Bond Bonding Agent) and MDP based (Clearfil Se Bond adhesive), (C) UDMA/BisGMA/PMMA-based experimental adhesive, and (D) silane-based (APS, ICS, MPS) experimental adhesives. The surface of the bone was mechanically roughened and was either used as such, treated with dental primers (Unifil Bond Self-etching Primer, Clearfil Se Bond Primer), or treated with an experimental silane mixture (APS, ICS, MPS), or with a mixture of the experimental silane liquid and Clearfil Se Bond Primer. The 3M-ESPE Scotchbond Multi-Purpose Adhesive and UDMA/BisGMA/PMMA experimental adhesive gave poor results in the shear bond test (0.58 and 0.40 MPa, respectively). Unifil Bond Bonding Agent and Clearfil Se Bond adhesive with respective primers markedly improved the shear bond strength; with Unifil the result was 3.40 MPa, and with Clearfil it was 6.19 MPa. When the bone surface was primed with a mixture of Clearfil Se Bond Primer and Clearfil Porcelain Bond Activator, the Clearfil Se Bond adhesive-impregnated FRC veil gave the best adhesion to the bone surface in this test: 9.50 MPa. The addition of bioactive glass granules between the veil and the bone lowered the shear bond strength in the test system described above to 6.72 MPa. The test systems with the silane mixture were also promising. In the SEM study, it was found that the mechanical treatment reveals the pores of the bone surface. Chemical treatments of the bone surface improved the adhesion of the FRC veil to the bone. The results showed that the adhesion of the FRC to the surface of the bone can be significantly improved with mechanical roughening and with special chemical treatments of the bone surface.     

Adhesive bond strength and compliance for denture soft lining materials.

Peel bond strength and tensile bond strength between three polyvinylsiloxane denture soft liners and a heat-cured acrylic resin denture base were measured using two adhesive systems. The soft lining materials differed only in regard of their filler content and compliance. The values of bond strength and mode of failure were explained in terms of the inherent strength of the bond and varying compliance and tear strength of the soft material. For tensile testing, when bond failure occurred through an adhesive debonding mechanism, materials of low compliance (stiffer materials) produced the greatest tensile bond strength. Conversely, when the same materials were subjected to peel testing a different trend emerged; the material with lowest compliance produced the lowest peel bond strength. When de-bonding occurs by tearing or snapping of the soft material, the measured value of bond strength was controlled by the tear strength of the soft material. The results could be explained by a consideration of stress concentrations at the soft-hard material interface during 180 degrees peel testing. Adhesives based on ethyl acetate solvents produced stronger bond strengths than equivalent toluene based adhesives, particularly for materials of low compliance. Bond failure for toluene based adhesives was predominantly adhesive, whereas that for ethyl acetate based adhesives was predominantly cohesive. Overall, the least resistance to peeling was exhibited by a material of low compliance (i.e. relatively stiff) bonded with a toluene based adhesive. When an ethyl acetate based adhesive was used, all materials exhibited a resistance to peeling with a predominantly cohesive mode of failure.     

Characterization of photopolymerization of dentin adhesives as a function of light source and irradiance

Manufacturers have attempted to address the limitations associated with dentin bonding by eliminating as many steps as possible in the bonding protocol. Theoretically, this approach increases the efficiency of the procedure and reduces technique sensitivity. These trends are reflected in the introduction of all-in one, single-step adhesive systems; the increased concentration of acidic resin monomers in these systems allows for simultaneous etching and priming of the prepared dentin surface. Ideally, the degree of monomer conversion would be high enough that the acidic reaction would be self-limiting. The purpose of this study was to investigate the effect of light irradiance and source on the photopolymerization of three commercial dental adhesives by monitoring the double bond conversion as a function of time during and after irradiation. The photopolymerization curing efficiency of the commercial adhesives investigated in this study varied as a function of light source and distance. The use of LED performed better than the halogen light in terms of polymerization rate and degree of conversion for the commercial single-step, sixth generation adhesive, Adper Prompt. In contrast, polymerization of commercial single-bottle, fifth generation adhesive, Single Bond and One-Up Bond F, was mainly a function of exposure time, irrespective of the two light units or intensities.     

The effects of three different desensitizing agents on the shear bond strength of composite resin bonding agents

The aim of this study was to evaluate the effects of three desensitizing agents on the shear bond strengths of four different bonding agents used to bond composite resin to dentin.A total of 160 extracted human molars were sectioned parallel to the occlusal plane under water cooling, polished and randomly divided into 4 groups of 40. Each group was treated with a different desensitizing agent (Tooth Mousse, Ultra-EZ, Cervitec Plus), except for an untreated control group. Each group was then randomly subdivided into 4 groups of 10, and a different dentin bonding agent (XP Bond, AdheSE, Adper Prompt L-pop, GBond) was applied to each group in order to bond the specimens to a resin composite (Gradia Direct) built up using a plastic apparatus. A Universal Testing Machine was used to measure the shear bond strength of each specimen. Statistical analysis was performed using one-way ANOVA and Tukey’s tests.With the exception of the Control/AdheSE and Ultra-EZ/XP Bond groups, no statistically significant differences were found in the shear bond strength values of the groups tested. These findings suggest that the use of different desensitizing agents does not affect the shear bond strength of various adhesive systems used to bond resin composite to dentin.     

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.     

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).     

In vitro degradation of resin-dentin bonds analyzed by microtensile bond test,scanning and transmission electron microscopy

Our knowledge of the mechanisms responsible for the degradation of resin-dentin bonds are poorly understood. This study investigated the degradation of resin-dentin bonds after 1 year immersion in water. Resin-dentin beams (adhesive area: 0.9mm(2)) were made by bonding using a resin adhesive, to extracted human teeth. The experimental beams were stored in water for 1 year. Beams that had been stored in water for 24h were used as controls. After water storage, the beams were subjected to microtensile bond testing. The dentin side of the fractured surface was observed using FE-SEM. Subsequently, these fractured beams were embedded in epoxy resin and examined by TEM. The bond strength of the control specimens (40.3+/-15.1MPa) decreased significantly (p<0.01) after 1 year of water exposure (13.3+/-5.6MPa). Loss of resin was observed within fractured hybrid layers in the 1 year specimens but not in the controls. Transmission electron microscopic examination revealed the presence of micromorphological alterations in the collagen fibrils after 1 year of water storage. These micromorphological changes (resin elution and alteration of the collagen fibrils) seem to be responsible for the bond degradation leading to bond strength reduction.     

Adhesion to chondroitinase ABC treated dentin

Dentin bonding relies on complete resin impregnation throughout the demineralised hydrophilic collagen mesh. Chondroitin sulphate-glycosaminoglycans are claimed to regulate the three-dimensional arrangement of the dentin organic matrix and its hydrophilicity. The aim of this study was to investigate bond strength of two etch-and-rinse adhesives to chondroitinase ABC treated dentin. Human extracted molars were treated with chondroitinase ABC and a double labeling immunohistochemical technique was applied to reveal type I collagen and chondroitin 4/6 sulphate distribution under field emission in-lens scanning electron microscope. The immunohistochemical technique confirmed the effective removal of chondroitin 4/6 sulphate after the enzymatic treatment. Dentin surfaces exposed to chondroitinase ABC and untreated specimens prepared on untreated acid-etched dentin were bonded with Adper Scotchbond Multi-Purpose or Prime and Bond NT. Bonded specimens were submitted to microtensile testing and nanoleakage interfacial analysis under transmission electron microscope. Increased mean values of microtensile bond strength and reduced nanoleakage expression were found for both adhesives after chondroitinase ABC treatment of the dentin surface. Adper Scotchbond Multi-Purpose increased its bond strength about 28%, while bonding made with Prime and Bond NT almost doubled (92% increase) compared to untreated specimens. This study supports the hypothesis that adhesion can be enhanced by removal of chondroitin 4/6 sulphate and dermatan sulphate, probably due to a reduced amount of water content and enlarged interfibrillar spaces. Further studies should validate this hypothesis investigating the stability of chondroitin 4/6 and dermatan sulphate-depleted dentin bonded interface over time.     

Light-curing efficiency of dental adhesives by gallium nitride violet-laser diode determined in terms of ultimate micro-tensile strength

The purpose of this study was to evaluate whether violet-laser diode (VLD) can be used as light-curing source. The ultimate (micro-)tensile strength (μTS) of three adhesives was determined when cured by VLD in comparison with curing by two different types of commercial LED light-curing units. One VLD (VLM 500) and two LED units (Curenos and G-Light Prima) were used to cure the adhesive resin of the two-step self-etch adhesives Clearfil SE Bond, Tokuso Mac Bond II, and FL-Bond II. A 0.6-mm thick acrylic mould was filled with adhesive resin and cured for 60 s. After 24-h water storage, specimens were trimmed into an hourglass shape with a width of 1.2 mm at the narrowest part, after which the μTS was determined (n=10). In addition, the light transmittance of each adhesive was characterized using a UV-vis-NIR spectrometer. No significant difference in curing efficiency between VLD and LED were observed for both Tokuso Mac Bond II and FL-Bond II (p>0.05). For Clearfil SE Bond, the μTS of VLD-cured specimens was higher than that of the specimens cured by the LED Curenos unit (p<0.05). Spectrometry revealed that this marked difference must be attributed to a different light transmittance of Clearfil SE Bond for visible blue light versus for the lower area of UV and visible violet light. In conclusion, A GaN-based violet laser diode can be used as light-curing source to initiate polymerization of dental resins.