Dentin Adhesive Systems Research Articles

Effect of intrinsic wetness and regional difference on dentin bond strength

Objectives: The aim of this investigation was to determine the influence of intrinsic wetness on regional bond strengths of adhesive resins to dentin. Methods: Human caries-free third molars were randomly divided into three groups for bonding: Group 1—no pulpal pressure; Group 2—pulpal pressure of 15 cm H 2O; and Group 3—dentin dried overnight in a desiccator. Clearfil Liner Bond II (Kuraray) or One Step (Bisco) adhesive resins systems were applied to the flat dentin surfaces and the teeth were restored with APX resin composite (Kuraray). After 24 h in water at 37°C, the specimens were sectioned into 0.7 mm thick slabs and divided into three regional subgroups according to the remaining dentin thickness and visual criteria: pulp horn, center, and periphery. The slabs were then trimmed for the micro-tensile bond test and subjected to a tensile force and crosshead of 1 mm/min. The data were analyzed with ANOVA and Fisher's PLSD test at a confidence level of 95%. The fracture modes were determined under a scanning electron microscope (JXA-840, JEOL, Japan). Results: No significant regional difference was observed for the Group 1 and 2 specimens restored with Clearfil Liner Bond II ( p>0.05). However, bond strengths significantly decreased at the pulp horn region of the Group 1 and 2 specimens restored with One Step ( p<0.01). All bond strengths of Group 3 decreased significantly and regional differences were not evident ( p>0.05). Significance: The dentin adhesive system should be chosen according to the substrate and region to be bonded, since bond strengths can vary according to the intrinsic wetness, region, and the adhesive system.

The effects on pulp tissue of microleakage in resin composite restorations.

The purpose of this study was to evaluate histopathologically the effect on pulp tissue of microleakage in resin composite restorations. Seventy-two class V cavities were prepared on buccal surfaces of monkeys and divided into 3 groups, F, O, and S. Every cavity was etched with 37% phosphoric acid. In group F cavities, each cavity was restored with photo-curable composite without any dentin adhesives. In group O, the cavities were left unfilled. In group S, each cavity was treated with a dentin adhesive system and restored with a restorative composite. After 3, 30, or 90 days, animals were sacrificed and the subjected teeth were immediately removed, then fixed and decalcified. Following sectioning and staining with hematoxylin and eosin or Taylor's modified bacteria staining, each sample was examined with a light microscope. In most teeth with group S cavities, bacterial invasion was not found indicating excellent marginal sealing. The pulpal reaction was much less than that in other groups. In group F as well as in group O, bacteria were frequently observed in the cavity; however, bacteria penetrated into dentinal tubules more in group F than in group O at 30 and 90 days. A correlation between the presence of bacteria and pulpal inflammation was strongly indicated. It was suggested that a leaky restoration was more harmful to the pulp than an open prepared cavity without restoration.

Microhardness evaluations of resin-dentin bonding areas by nano-indentation.

The purpose of this experiment was to determine the hardness values of the hybrid layer and its surroundings through the continuous use of a microhardness measuring device. Black's Class V cavities were prepared in nine dog teeth. The cavities were divided into four groups according to the dentin adhesive system applied. The adhesive systems were: "Bond One System", "Liner Bond II sigma System", "One Step System", and "Single Bond System". The treated teeth were observed at seven days post-application. Specimens were cross-sectioned perpendicularly or horizontally to the resin-dentin interface and embedded in epoxy resin. Their surfaces were polished. The microhardness of the resin-dentin bonding area was measured with a nano-indentation tester. The hardness values at a point of 10 microns distant from the interface in the direction of the dentin differed between systems. It appeared that this was influenced by the presence of the decalcified dentin not impregnated by resin, differences in the chemistry forming the hybrid layer, and the composition of the bonding resin. The hardness of the dentin-bonding interface and its surroundings was determined, and these areas were observed using SEM. Three layers were confirmed the healthy dentin layer, the composite resin layer, and the hybrid layer, (in which decalcified dentin impregnated by resin and that not impregnated by resin are considered to be mix). In the hybrid layer, no impression was found by SEM although the hardness in the bonding interface was significantly different. These layers appear to be more elastic and softer than the healthy dentin.

The influence of cross-sectional shape and surface area on the microtensile bond test

Objectives. The purpose of this study was to determine the effect of the cross-sectional area shape (cylindrical vs. rectangular) and the bonding surface area on the microtensile bond strengths and stress distribution of four dentin adhesive systems (Scotchbond MP Plus, OptiBond FL, OptiBond Solo, One-Step). In addition, finite element analysis (FEA) models were developed to investigate stress distributions. Methods. Extracted human molars were cut vertically and the occlusal enamel removed; one-half of the tooth was used for rectangular specimens, the other half for cylindrical specimens. The occlusal dentin was bonded according to the manufacturers' directions and covered with a block of resin composite. For the cylindrical specimens, the bonded dentin was shaped with a diamond bur on a lathe to produce specimens of area 1.1, 1.5 or 3.1 mm 2 at the bonded interface. The rectangular specimens were sectioned to obtain bar-shaped specimens, which were shaped to produce hour-glass shaped specimens with the same area as the round specimens. Bonds were stressed in tension at a speed of 1 mm min −1. The mean bond strengths were compared using two-way ANOVA, one-way ANOVA, LSD and Student's t tests. The fractured surfaces were examined by scanning electron microscopy, and the frequencies of the fracture modes were compared using the Kruskal–Wallis and Mann–Whitney U tests. FEA models were created simulating the cross-sectional areas for bonding to determine the stress distribution. Results. The 3.1 mm 2 bonding area groups showed significantly lower bond strengths than the 1.1 mm 2 bonding area groups ( p<0.05), except for the rectangular specimens using Scotchbond MP Plus and One-Step. Most cylindrical specimens of bonding area 1.1 or 1.5 mm 2 exhibited adhesive failure at the interface between the dentin and the adhesive resin. No differences were determined between cylindrical and rectangular specimens. The fracture mode matched the stress distribution patterns calculated from the FEA modeling. Significance. The results indicate that the test methods using small surface areas produce higher bond strengths than those using larger surface areas, and that cross-sectional shape has little effect. This is probably a result of fewer defects occurring in the small-area specimens.

Microtensile testing of dentin adhesives

Objectives. This study was conducted in order to compare the microtensile and shear bond strengths of five commercial dentin adhesive systems. Scotchbond Multipurpose with maleic acid (SM), Scotchbond Multipurpose with phosphoric acid (SP), Scotchbond Multipurpose Plus (SBP), Clearfil Liner Bond System (CL), and Prime and Bond (PB) were tested. Methods. Thirty extracted unerupted third molars, in groups of six teeth per adhesive system, were prepared for microtensile testing. The specimens were tested following a 24 h incubation at 37°C in normal saline. Shear bond testing was performed on 35 additional teeth, using seven teeth per adhesive system. After testing, the fracture sites were observed using light microscopy and a scanning electron microscope to determine the type of failure involved. Results. The microtensile test results (mean±SD) were SM, 24.6±7.2 MPa; SP, 28.8±11.8 MPa; SBP, 22.7±6.5 MPa; PB, 25.5±9.4 MPa; and CL, 36.8±10.0 MPa. A Bonferroni post-hoc test showed significantly ( p<0.05) greater strength for CL compared to SM, SP, SBP, and PB. The shear bond strength test results were SM, 19.4±4.4 MPa; SP, 24.5±8.4 MPa; SBP, 15.3±4.9 MPa; PB, 23.2±7.1 MPa; and CL, 24.8±3.5 MPa. No statistically significant differences were found among the shear bond strength test results. The shear bond test produced significantly more failures within dentin and composite than the microtensile method. Significance. It is concluded that the microtensile test produced a more definitive assessment of adhesive bond strength than the shear bond test. Microtensile testing showed CL to be significantly stronger than SM, SP, SBP, and PB ( p<0.05).

Effect of cross-sectional surface area on bond strengths between resin and dentin

Objectives. This study was conducted to determine the effect of the bonding area on the micro-shear and micro-tensile bond strengths of four dentin adhesive systems (Scotchbond MP Plus, 3M Dental Products, St. Paul, MN; OptiBond FL, Kerr Corp., Orange, CA; OptiBond Solo, Kerr Corp., Orange, CA; One-Step, Bisco, Inc., Itasca, IL). Methods. Sixty extracted human molars were cut vertically and occlusal enamel removed, one half of the tooth was used for tensile testing and one half for shear. The occlusal dentin was bonded according to manufacturers directions with a resin composite block and sectioned to obtain up to three square bar-shaped specimens, which were shaped with a high speed diamond bur on a lathe to produce cylindrical specimens of 1.2, 1.4 or 2.0 mm diameter at the bonded interface. The bonds were stressed in shear or tension at a crosshead speed of 1 mm min −1. The mean bond strengths were compared using one-way ANOVA, two-way ANOVA and student's t-test. The fractured surfaces were examined under a scanning electron microscope and the frequency of fracture modes was compared using the Kruskal–Wallis and Mann–Whitney U tests. Results. For all materials, the 2.0 mm diameter group showed significantly lower bond strengths than the 1.2 mm diameter group in both shear and tensile tests ( p<0.05). Most specimens of 1.2 mm or 1.4 mm diameter exhibited adhesive failure at the interface between the dentin and the adhesive resin. Significance. The results indicate that small surface areas of test specimens are associated with higher bond strengths and that the effect on tensile and shear values is similar.

The effect of fissure morphology and pretreatment of the enamel surface on penetration and adhesion of fissure sealants.

Fissure sealants have been used successfully as a means of preventing fissure caries. This effectiveness is directly related to sealant retention and retention is dependent upon a meticulous method of application. The aims of this study were to determine if sealant adhesion and penetration were affected by the variation in preparation of the enamel surface, or by pretreatment of the enamel surface with dentine adhesive systems, in fissures of varying morphology. Non-carious posterior teeth were visually examined and sorted according to fissure type, classified as shallow, deep or intermediate. Occlusal fissures were sealed using one of six methods, thermocycled for 200 cycles between 5 and 55 degrees C, in artificial saliva, then placed in a 1.5% procion orange dye for 3 min. Teeth were sectioned bucco-lingually and examined with a light microscope for (i) penetration of the sealant into the fissure pattern and (ii) adhesion of the sealant. All sealant techniques employed in this study adapted well to the enamel surface as the 1.5% procion Reactive orange dye failed to penetrate any of the sealed tooth sections. Shallow fissures were well obturated in both lateral and vertical dimensions. Sealants adapted well to the vertical walls at the orifice of deep fissures but generally failed to penetrate into the deeper aspects. Reducing the etching period with 37% phosphoric acid resulted in increased voids between the sealant and enamel surface and poorer adaptation to the vertical walls. The addition of dentine adhesive systems, Scotchbond Multi-Purpose and All-Bond 2, enhanced the vertical penetration of the sealant, particularly in deep fissures. It is proposed that the dentine adhesive systems may improve the retention rate of sealants in deep fissures particularly if the fissure is not completely dry prior to resin placement.

The effect of fissure morphology and pretreatment of the enamel surface on penetration and adhesion of fissure sealants

summary Fissure sealants have been used successfully as a means of preventing fissure caries. This effectiveness is directly related to sealant retention and retention is dependent upon a meticulous method of application. The aims of this study were to determine if sealant adhesion and penetration were affected by the variation in preparation of the enamel surface, or by pretreatment of the enamel surface with dentine adhesive systems, in fissures of varying morphology. Non‐carious posterior teeth were visually examined and sorted according to fissure type, classified as shallow, deep or intermediate. Occlusal fissures were sealed using one of six methods, thermocycled for 200 cycles between 5 and 55°C, in artificial saliva, then placed in a 1.5% procion orange dye for 3 min. Teeth were sectioned bucco‐lingually and examined with a light microscope for (i) penetration of the sealant into the fissure pattern and (ii) adhesion of the sealant. All sealant techniques employed in this study adapted well to the enamel surface as the 1.5% procion Reactive orange dye failed to penetrate any of the sealed tooth sections. Shallow fissures were well obturated in both lateral and vertical dimensions. Sealants adapted well to the vertical walls at the orifice of deep fissures but generally failed to penetrate into the deeper aspects. Reducing the etching period with 37% phosphoric acid resulted in increased voids between the sealant and enamel surface and poorer adaptation to the vertical walls. The addition of dentine adhesive systems, Scotchbond Multi‐Purpose and All‐Bond 2, enhanced the vertical penetration of the sealant, particularly in deep fissures. It is proposed that the dentine adhesive systems may improve the retention rate of sealants in deep fissures particularly if the fissure is not completely dry prior to resin placement.

Quantitative Analysis of the Dentin Adhesive Interface by Auger Spectroscopy

The ultimate success of a dentin adhesive bond is dependent in large part on specific conditions at the interface between the tooth and the adhesive. Most current dentin adhesive systems use some sort of pre-treatment to demineralize the first few microns of the dentin surface, leaving a meshwork of collagen into which the adhesive resin can penetrate, infiltrate, and polymerize. The general hypothesis tested in this experiment was that the penetration and distribution of adhesive resin into the demineralized zone are a function of the conditioner used as a pre-treatment for the adhesive application. Four commercially available adhesive systems were modified to incorporate hydroxyethylthiomethacrylate (HETMA), a sulfur-substituted, traceable analogue of 2-hydroxyethylmethacrylate (HEMA), thereby allowing for a qualitative measurement of the amount and distribution of monomer in the treated dentin substrate by energy-dispersive x-ray spectroscopy (EDS) and a quantitative measurement by Auger electron spectroscopy (AES). The dentin pre-treatments investigated were: (1) 10% citric acid/3% ferric chloride, (2) 10% maleic acid, (3) 2.5% nitric acid, and (4) an alcoholic solution of HEMA with a phosphorus acid ester. These pre-treatments were applied to freshly extracted teeth that had been sectioned to expose the dentin and ground to simulate the smeared layer. After the appropriate pre-treatment was applied, a 10% (v/v) solution of HETMA in acetone was applied to the surface, followed by the corresponding adhesive resin, which was then polymerized. The samples were then processed for observation by scanning transmission electron microscopy (STEM), AES, and STEM/EDS analysis. The results indicated significant differences in the ability of HETMA to penetrate the dentin surface conditioned by the four pretreatments investigated here. This study also demonstrated that AES and STEM/EDS could be used in a correlative fashion to determine the distribution of HETMA within or adjacent to the treated dentin surface.

Scanning Transmission Electron Microscopy/Energy-dispersive Spectroscopy Analysis of the Dentin Adhesive Interface Using a Labeled 2-Hydroxyethylmethacrylate Analogue

In an attempt to compare the morphology of the dentin adhesive interface and the wetting and penetration of the adhesive in relation to the dentin surface, we studied four dentin adhesive systems using scanning transmission electron microscopy (STEM) and energy-dispersive spectroscopy (EDS). 2-Hydroxyethylmethacrylate (HEMA), a monomer common to many commercial dentin adhesive systems, was altered to produce a thiolated analogue (HETMA). Sulfur, traceable by EDS and STEM, was substituted for the oxygen atom in the backbone of the HEMA molecule. The resulting analogue, with solubility parameters and other wetting and physical properties very similar to those of HEMA, was applied to four sets of tooth specimens, each pre-treated with a different primer or etchant. Three separate pre-treatments--nitric acid, maleic acid, and citric acid/ferric chloride--created a demineralized zone approximately 1 to 3 microns thick at the dentin surface. The HETMA was found to permeate freely into this zone when either of the latter two pre-treatments was used. However, the band of dentin that was demineralized by the nitric acid pre-treatment appeared impermeable to the HETMA. The fourth pre-treatment, an alcohol-based solution including the phosphorus acid ester PENTA and HEMA, modified the smear layer of the tooth slightly and did not appear to demineralize the dentin. HETMA applied to the specimens pre-treated with PENTA and HEMA was clearly in intimate contact with the dentin or modified smear layer; however, it did not penetrate or diffuse into these areas. It did flow into the dentinal tubules, as was also evident with each of the other systems. It was concluded that the acid pre-treatment of the dentin greatly influenced the wetting behavior of the dentin adhesive and thus could substantially affect the resultant bond strength of the dentin adhesive systems.

Resin-modified glass ionomers for luting posterior ceramic restorations

Objectives. Until recently, esthetic inlay restorations in posterior teeth have been limited to cavities surrounded by enamel. Dentin adhesive systems in combination with luting composites and light-cured resin-modified glass ionomer cements offer a possibility for bonding ceramic inlays to cavities when the cervical margin is in dentin. This study was designed to compare in vitro marginal integrity of ceramic inlays bonded to dentin to restorations placed in cavities with margins located entirely in the enamel. Methods. In the present in vitro study, the sealing abilities of a dentin bonding agent/luting composite combination (Syntac/Dual Cement, Vivadent) and resin-modified glass ionomers (Photac Fil, Photac Bond, ESPE; Dyract, De Trey Dentsply; Fuji II LC, GC Dental Industrial Corp.; and Vitremer, 3M Dental Products) used as luting agents in cavities extending beyond the cemento-enamel junction, were compared to the sealing abilities of a conventional luting composite (Vita Cerec Duo Cement, Vita) in cavities within sound enamel. SEM analysis and dye penetration were performed to evaluate marginal integrity at the cervical cavity margins. Results. The dentin bonding agent/luting composite combination (Syntac/ Dual Cement) rendered a marginal seal within the dentin similar to the quality obtained with the conventional luting procedures within sound enamel. When three out of the five resin-modified glass ionomers were used as luting agents (Dyract, Fuji II LC and Vitremer), the results were comparable to those reported for the dentin bonding agents and the conventional method. Significance. Light-cured resin-modified glass ionomer cements may be considered as an alternative to dentin bonding agents when the cavity margins of ceramic inlay restorations are within the dentin. However, further studies, e.g., wear resistance, must be performed.

Demonstration of a focused ion-beam cross-sectioning technique for ultrastructural examination of resin-dentin interfaces

Objectives. Focused ion-beam (FIB) etching, commonly used as a cross-sectioning technique for failure analysis of semiconductor devices, has recently been applied to biological tissues to expose their ultrastructure for examination. It was the aim of this investigation to determine the practical utility of FIB to cross-section resin-dentin interfaces in order to morphologically evaluate the completeness of resin penetration into the exposed collagen scaffold at the resin-dentin bond interface. Methods. Two representative commercially available dentin adhesive systems were bonded to mid-coronal dentin. After appropriate fixation and dehydration of the resin-bonded dentin samples, a scanned focused ion-beam of a few tens of nano-meters in diameter was used to cross-section the resin-dentin interface. Examination of the interfacial ultrastructure was accomplished using a field-emission SEM. Results. Results indicate possible artifact production at the cross-sectioned interface, hiding its actual ultrastructure, probably due to a heat-effect with possible recrystallization. Further studies of FIB are needed to optimize its usefulness for resin-dentin interface examinations and other biological tissue applications. Significance. Complete resin saturation of the demineralized dentin surface-layer has been claimed to be the key factor for a long-lasting resin-dentin bond. A “clean” artifact-free micro-cross-sectioning technique may provide indisputable ultra-structural information about the depth of resin penetration into the demineralized zone. Such a test would be useful in the development of dentin adhesive systems.

Antibacterial activity of several proprietary dentine adhesive systems after curing

Antibacterial activity of several proprietary dentine adhesive systems after curing

Clinical Status of Ten Dentin Adhesive Systems

Laboratory testing of dentin adhesive systems still requires corroboration by long-term clinical trials for their ultimate clinical effectiveness to be validated. The objective of this clinical investigation was to evaluate, retrospectively, the clinical effectiveness of earlier-investigated dentin adhesive systems (Scotchbond, Gluma, Clearfil New Bond, Scotchbond 2, Tenure, and Tripton), and to compare their clinical results with those obtained with four modern total-etch adhesive systems (Bayer exp. 1 and 2, Clearfil Liner Bond System, and Scotchbond Multi-Purpose). In total, 1177 Class V cervical lesions in the teeth of 346 patients were restored following two cavity designs: In Group A, enamel was neither beveled nor intentionally etched, as per ADA guidelines; in Group B, adjacent enamel was beveled and conditioned. Clinical retention rates definitely indicated the improved clinical efficacy of the newest dentin adhesives over the earlier systems. With regard to adhesion strategy, adhesive systems that removed the smear layer and concurrently demineralized the dentin surface layer performed clinically better than systems that modified the disorderly layer of smear debris without complete removal. Hybridization by resin interdiffusion into the exposed dentinal collagen layer, combined with attachment of resin tags into the opened dentin tubules, appeared to be essential for reliable dentin bonding but might be insufficient by itself. The additional formation of an elastic bonding area as a polymerization shrinkage absorber and the use of a microfine restorative composite apparently guaranteed an efficient clinical result. The perfect one-year retention recorded for Clearfil Liner Bond System and Scotchbond Multi-Purpose must be confirmed at later recalls.

Bond strength and microleakage of current dentin adhesives

Objectives. The purpose of this in vitro study was to evaluate shear bond strengths and microleakage of seven current-generation dentin adhesive systems. Methods. Standard box-type Class V cavity preparations were made at the cemento-enamel junction on the buccal surfaces of eighty extracted human molars. These preparations were restored using a microfill composite following application of either All-Bond 2 (Bisco), Clearfill Liner Bond (Kuraray), Gluma 2000 (Miles), Imperva Bond (Shofu), OptiBond (Kerr), Prisma Universal Bond 3 (Caulk), Scotchbond Multi-Purpose (3M), or Scotchbond Dual-Cure (3M) (control). Lingual dentin of these same teeth was exposed and polished to 600-grit. Adhesives were applied and composite was bonded to the dentin using a gelatin capsule technique. Specimens were thermocycled 500 times. Shear bond strengths were determined using a universal testing machine, and microleakage was evaluated using a standard silver nitrate staining technique. Results. Clearfil Liner Bond and OptiBond, adhesive systems that include low-viscosity, low-modulus intermediate resins, had the highest shear bond strengths (13.3 ± 2.3 MPa and 12.9 ± 1.5 MPa, respectively). Along with Prisma Universal Bond 3, they also had the least microleakage at dentin margins of Class V restorations. Significance. No statistically significant correlation between shear bond strength and microleakage was observed in this study. Adhesive systems that include a low-viscosity intermediate resin produced the high bond strengths and low microleakage. Similarly, two materials with bond strengths in the intermediate range had significantly increased microleakage, and one material with a bond strength in the low end of the spectrum exhibited microleakage that was statistically greater. Thus, despite the lack of statistical correlation, there were observable trends.

Morphologic aspects of the resin-dentin interdiffusion zone with five different dentin adhesive systems tested in vivo

The new generation of enamel dentin adhesive materials provides removal of the smear layer, inducing structural changes in the dentinal surface and creating a retentive interdiffusion zone or hybrid layer between the two substrates. Some studies have demonstrated hybrid layer formation in in vitro samples, but few articles have described it in in vivo specimens. The hybrid layer forms in peritubular and intertubular treated dentin and improves adhesion between tooth surface and adhesive resins. This in vivo study investigated the formation of a hybrid layer by use of five different enamel dentin adhesive systems. The dentin adhesives systems were tested on flat dentin preparations made on vestibular surfaces of periodontally compromised teeth. The sample teeth were extracted immediately after the resin was cured. Half of the samples were used to visualize the hybrid layer and the other half to observe the morphology of the resin tags by use of scanning electron microscopy. All the tested products formed a hybrid layer. In many areas of samples of Gluma 2000, Scotchbond Multipurpose, All Bond 2, and Super Bond D Liner systems, characteristic reverse cone-shaped tags were visible. Resin tags produced by Clearfil Liner Bond adhesive were narrower at the apertures of tubules than those of the other four adhesive materials. Morphology of the hybrid layer and of the resin tags of these samples were similar to in vitro samples observed in other studies.

Chemical characterization of the resin-dentin interface by micro-Raman spectroscopy.

The chemical nature of the interface between dentin and adhesive resin materials was characterized by micro-Raman spectroscopy. The resulting chemical profiles were correlated with photomicrographs obtained by SEM after an argon-ion-beam etching treatment of the sample surface. Two commercially available dentin adhesive systems, of which one was also applied with a different conditioning agent, were investigated. Raman spectra, which were recorded along line scans across the interface with a step increment of 1 micron, revealed that resin effectively penetrated 4 to 6 microns deep into the superficially decalcified dentin zone. Across the interface, a gradual transition from resin to dentin over the interdiffusion zone with a mixed contribution of both substances was noticed. Finally, resin appeared to penetrate to the entire decalcification depth of dentin regardless of the aggressiveness of the conditioning procedure.

Assessment by nano-indentation of the hardness and elasticity of the resin-dentin bonding area.

The hardness and Young's modulus of the successive layers across a resin-dentin bonding area were determined by nano-indentation for four commercially-available dentin adhesive systems, of which two were also applied with a different conditioning agent. With a computer-controlled nano-indentation technique, minute triangular indentations were made within a small area of a few micrometers' diameter at a load of a few milli-Newtons. The load and displacement of the indenter were continuously monitored during the loading-unloading sequence, so hardness and Young's modulus could be computed as a function of the indenter geometry and the applied load. The hardness of the resin-dentin interdiffusion zone was significantly lower than that of unaltered dentin. A gradient of moduli of elasticity was observed from the rather stiff dentin over a more elastic resin-dentin interdiffusion zone and adhesive resin layer to the restorative composite. That gradient was more substantial in those systems that produced relatively thick adhesive resin layers or supplementally provided a filled low-viscosity resin as an intermediate layer between the adhesive resin and the bulk restorative composite. Such an elastic bonding area might have a strain capacity sufficient to relieve stresses between the shrinking composite restoration and the rigid dentin substrate, thereby improving the conservation of the dentin bond and, as a consequence, the marginal integrity and retention of the restoration.

Two-year clinical evaluation of two dentine-adhesive systems in cervical lesions

Two commercially available dentine-adhesive systems, Tenure and Tripton, were tested in two different cavity designs by placing 132 Class V composite restorations in cervical lesions of 35 patients. In Group A, the cervical restorations were placed totally in dentine without any intentional enamel involvement. In Group B, they were placed in dentine with adjacent enamel margins bevelled and acid etched. The retention rate, the evidence of clinical microleakage, and the marginal integrity were monitored over a 2-year period. The results of this clinical investigation indicate a high failure rate when only dentinal bonding was involved. A loss rate of 30% for Tenure and 55% for Tripton was noted in Group A after 2 years of clinical service. However, both adhesive systems used in combination with micromechanical retention on the enamel border (Group B) performed extremely well with only one restoration each having debonded over the 2-year period. Identically, marginal integrity and evidence of clinical microleakage more severely deteriorated with time for the Group A restorations in comparison with their Group B counterparts. In summary, the overall results were more positive for Tenure than for Tripton. It is concluded that micromechanical retention by acid etching of the enamel margin is still indispensable for the clinical success of cervical Class V composite restorations, primarily for retention and clinical microleakage and also, but to a lesser degree, for marginal adaptation. adaptation.

Comparative SEM and TEM examination of the ultrastructure of the resin-dentin interdiffusion zone.

The resin-dentin interdiffusion zone produced by a dentin-adhesive system that removes the smear layer and concurrently decalcifies superficial dentin was morphologically examined by both scanning and transmission electron microscopy. Cross-sectioned resin-bonded dentin discs were etched with an argon-ion beam to make the resin-dentin interface observable by SEM. For the TEM examination, the sections were partly decalcified by an aqueous EDTA solution to facilitate ultramicrotomy and to disclose the ultrastructure of the interdiffusion zone. Both SEM and TEM confirmed the presence of the resin-dentin interdiffusion zone as the junction between the deep unaltered dentin structure and the restorative resin. Within the interdiffusion zone, three sublayers with characteristic ultrastructure and staining were identified by TEM. An upper diffuse black layer contained few structural features. Underneath, partially-altered collagen fibrils were closely packed, mostly running parallel with the interface and perpendicular to the dentinal tubules. Their outline was electron-dense, forming tunnel-like structures. At the base of the upper layer, several stained projections were found to bulge out into the underlying collagen network and appeared to be confined by obstructive, parallel-running collagen fibrils. Finally, the third dense layer, containing hydroxyapatite crystals, demarcated the superficially demineralized dentin layer from the deeper unaltered dentin. Resin diffusion into the decalcified dentin surface layer was evident, but diminished with depth, presumably reducing deeper resin impregnation into the interfibrillar spaces. The citric acid dentin-pretreatment probably caused denaturation of the superficial collagen fibrils. Its decalcifying effect gradually weakened with depth, leaving behind hydroxyapatite crystals at the base of the interdiffusion zone.(ABSTRACT TRUNCATED AT 250 WORDS)