The effect of additional enamel etching and a flowable composite to the interfacial integrity of Class II adhesive composite restorations.

This in vitro study evaluated the interfacial integrity of Class II resin composite restorations. The influence of a flowable composite and additional enamel etching was also evaluated. Deep, saucer-shaped Class II cavities were prepared in the mesial and distal proximal surfaces of 25 extracted human molars and assigned to five treatment groups. The gingival margins were extended to approximately 1 mm above the CEJ in 40 cavities and below the CEJ in 10 cavities. The prepared cavities were then restored with a self-etching primer system (Clearfil Liner Bond II) and a hybrid resin composite (Clearfil AP-X), with and without a flowable composite (Protect Liner F) and additional enamel etching with 37% phosphoric acid gel (K-etchant). After finishing, polishing and thermocycling (4 and 60 degrees C, x300), the samples were longitudinally sectioned through the restorations and resin-tooth interfaces were observed directly under a laser scanning microscope. Statistical analysis indicated that the use of a flowable composite produced significantly more (p = 0.04) gap-free resin-dentin interfaces than teeth restored without the flowable composite. However, both flowable composite and enamel etching could not prevent gap formation at enamel-resin interfaces and crack formation on enamel walls.

Dimensional changes of demineralized dentin treated with HEMA primers.

OBJECTIVES: The purpose of this study was to measure the dimensional changes of demineralized dentin before and after application of HEMA (2-hydroxyethyl methacrylate) by confocal laser scanning microscopy (CLSM). METHODS: The middle portion of bovine dentin was ground, polished, and covered with a vinyl tape with a 4-mm hole punched through it. A strip of polysiloxane impression material was then placed across the center of the dentin surface to preserve a strip of the original unetched surface. Dentin surfaces were etched with 32% phosphoric acid for 60 s and rinsed with water. The impression material was then removed and the following sequential steps were performed: the dentin surface was mildly air-dried, then strongly air-dried, then treated with either 35 wt.% HEMA/water or 100 wt.% HEMA and mildly air-dried, and then strongly dried again. The shrinkage of the demineralized dentin surface from the original unetched level was measured by CLSM in each step and results analyzed by one-way ANOVA. RESULTS: The dimensional changes of demineralized dentin after mild air drying were approximately -1 micron and, following strong air drying, resulted in -5 microns shrinkage. Following the application of 35 wt.% HEMA/water, the height of the demineralized dentin changed to a level of -3.3 microns, but then shrank to -4.8 microns after strong drying. ANOVA indicated that re-expansion of the shrunken etched dentin was significant (p < 0.05); however, the treated surface collapsed when it was strongly dried again (p < 0.05). 100% HEMA did not re-expand the shrunken demineralized dentin under any of the application on protocols (p > 0.05). SIGNIFICANCE: Thirty-five wt.% HEMA in water re-expanded the collapsed demineralized dentin matrix, however not to the original level. One hundred wt.% HEMA did not cause any re-expansion.

Effects of direct resin pulp capping techniques on short-term response of mechanically exposed pulps.

The aim of this in vivo study was to evaluate the effects of direct pulp capping techniques on the short-term response of mechanically exposed pulps using three commercially available adhesive resin systems. Class V cavities were prepared on the facial surface of 200 intact monkey teeth. Pulps were exposed with a carbide bur on the cavity floor. Each exposed pulp was capped with one of three commercially available adhesive resins or a hard-setting calcium hydroxide liner. All cavities were sealed with an adhesive resin, and were restored with hybrid resin composites. Inflammatory cell infiltration and dentine bridging of the exposed pulp and protrusion of the exposed pulp tissue into the cavities were evaluated histologically at 3, 7, 14, 30 and 60 days. A slight inflammatory cell infiltration was the principal reaction of the exposed pulp. The exposed area was occluded over time with dentine bridging in all groups. However, a protrusion of pulp tissue into the prepared cavity was observed at the periphery of the exposed area in all groups. These tissues communicated with the underlying pulp. The incidence of pulp tissue protrusion was ranked in order of increasing severity: Liner Bond II < Dycal < Bondwell LC = Super Bond C&B. Following pulp capping of the mechanical exposures, slight inflammation was the main reaction. Exposures became occluded with a dentine bridge over time. However, the protrusion of pulp tissue into cavities varied, depending on the materials used.

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.

Water sorption of several bonding resins.

PURPOSES: To determine, over the period of 1 month, (a) the degree of water sorption, and (b) the change in dimension, of four bonding resins and one low viscosity resin. MATERIALS AND METHODS: Six specimens of bonding resin (Prisma Universal Bond 3, All-Bond 2, Bondwell LC, and LB Bond from the Clearfil Liner Bond II system) and a low viscosity resin (Protect Liner F) measuring 5 mm long, 5 mm wide and 3 mm thick were made. Each specimen was weighed immediately after curing and placed in distilled water at 37 degrees C. Weights at 1, 2, 3, 7 days and 2, 3 and 4 weeks were obtained. Specimens were measured initially and at the above times. After 4 weeks, specimens were dried for 2 weeks and remeasured for size and weight. Then, the specimens were placed in a vacuum for approximately 4 hours and the weights and dimensions were remeasured. Values were converted to a mean percentage of the original dry weight and dimension and analyzed using one-way ANOVA and Fisher's PLSD test. RESULTS: All materials absorbed most water in the first week. Prisma Universal Bond 3 stabilized within 2 days, LB Bond stabilized within the first week, whereas the remaining materials showed statistical increases in weight for 2-3 weeks (P < 0.05). After 4 weeks, LB Bond and All-Bond 2 resins demonstrated an approximate 8% weight increase, and the least increase was observed for Protect Liner F and Prisma Universal Bond 3 at about 3%. After desiccation, Protect Liner F and All-Bond 2 returned close to their original weight, and the remainder weighed less than initially. Dimensional changes were similar to changes in weight; LB Bond showed the greatest dimensional change over the 4 weeks (5%) and Protect Liner F the least change.

Demineralizing effect of dental cements on human dentin.

OBJECTIVE: This study was undertaken to verify the hypothesis that dentin surfaces are demineralized during placement of four kinds of chemically setting cements (zinc phosphate cement, luting glass-ionomer cement, restorative glass-ionomer cement, and zinc polycarboxylate cement). METHOD AND MATERIALS: Sixty cemented dentin disks were observed under scanning electron microscopy and with confocal laser scanning microscopy after use of an argon-ion etching technique. To determine the surface effects of the cements, 30 dentin surfaces were treated with 1 of 6 freshly mixed cements (5 per group) for 60 seconds. The disks were subjected to rinsing with a water spray and ultrasonic washing prior to scanning electron microscopic observation. RESULTS: Observation of cemented dentin specimens revealed that the dentin was not completely demineralized at the interface formed by the cement and dentin and that the extent and depth of demineralization along the interface tended to be nonuniform. Zinc phosphate cement caused the greatest demineralization of dentin, followed by luting glass-ionomer cement. The extent of demineralization with restorative glass-ionomer cement or zinc polycarboxylate cement was less discernible. Confocal laser scanning microscopy generally confirmed scanning electron microscopic observations and revealed that most of the specimens showed close adaptation of the cements to the dentin surfaces. CONCLUSION: Acid-containing cements have self-etching properties that are effective, to various degrees, in removing the smear layer and promoting close adaptation to dentin surfaces.

Selective caries removal with air abrasion.

The purpose of this study was to evaluate selective caries removal using an air-abrasive technique. Alumina powders, glass beads, crushed glass powders, and crushed powders of polycarbonate resin were applied to intact human enamel, dentin, and artificially demineralized dentin (caries-model dentin). Furthermore, the effect of the particle size of abrasives and air pressures on the abraded depths was examined. When alumina powders and glass beads were used, the abraded depths of enamel, dentin, and caries model increased as the particle size and air pressure increased. Alumina powders and crushed glass powders abraded intact enamel and dentin more than the caries-model dentin, whereas glass beads abraded the caries-model dentin more than the intact enamel and dentin. Only crushed powders of polycarbonate resin abraded the caries-model dentin without reducing intact enamel and dentin. With hard particles, such as alumina powders, glass beads, or crushed glass powders, selective caries removal by the air-abrasive technique appeared to be difficult to achieve, even if the particle size and the air pressure were changed. Crushed powders of polycarbonate resin that reduced only the caries-model dentin are harder than caries-model dentin, but softer than intact enamel and dentin. This study elucidated the possibility of selective carious dentin removal with the air-abrasive technique.

Short-term reaction of exposed monkey pulp beneath adhesive resins.

Monkey pulpal responses to four adhesive resin systems used as direct pulp capping agents were histopathologically evaluated at 3, 7, 14, 30, and 60 days after operation. No serious inflammatory reaction of the pulp, such as necrosis or abscess formation, was observed. Slight inflammatory cell infiltration was the main inflammatory reaction of the exposed pulp, and the exposed area became occluded with dentin bridging as the observation period increased. Healing of exposed dental pulp beneath adhesive resin capping slightly differed depending on the materials used.

Changes in microtopography across polished resin-dentin interfaces.

PURPOSE: To investigate the resistance of the hybrid layer to polishing and argon-ion etching by measuring the microprofile along the resin-dentin interface. MATERIALS AND METHODS: Mid-coronal human dentin disks were treated with one of three commercially available dentin bonding systems (All-Bond 2, Clearfil Liner Bond II, Scotchbond Multi-Purpose Plus), and bonded together so as to prepare three pairs of specimens. The bonded assemblies were sectioned perpendicular to the adhesive interface and embedded in epoxy resin. The polished interfaces were argon-ion etched through a grid square mesh placed on the interface. A profile of the hybrid layer in the ion-etched and non-etched areas was taken using a surface analyzing scanning electron microscope. RESULTS: The normal mineralized dentin showed no reduction after argon-ion etching. The hybrid layer was reduced more than the adhesive resins during argon-ion etching. Reduction of the hybrid layer by argon-ion etching was greater with phosphoric acid-treated groups than with a self-etching-treated group (P < 0.05). The surface profiles of the non-etched, polished hybrid layer showed a slight concavity, with the deepest point in the middle of the hybrid layer. Argon-ion etching created non-uniform reduction of the hybrid layer, producing the deepest point close to the top of the hybrid layer in all systems.

Adhesion of resin-modified glass ionomer cements using resin bonding systems.

OBJECTIVES: To compare the in vitro shear bond strength of two commercially available resin-modified glass ionomer cements (RmGIC) to bovine dentine, with and without the use of adhesive bonding systems. METHODS: Ninety-six flat bovine dentine surfaces were divided into eight groups for bonding procedures. Fuji II LC and Vitremer were bonded to dentine that had been treated with and without Clearfil Photo Bond, Clearfil Liner Bond, or Clearfil Liner Bond II. The control group consisted of specimens that were treated as recommended by the manufacturer of each resin-modified glass ionomer cement. The bonded assemblies were stored in tap water for 24 h at 37 degrees C, and shear bond strengths measured using a universal-testing machine at a crosshead speed of 1 mm/min. RESULTS: For the control group, shear bond strength of Fuji II LC was significantly greater than Vitremer (P < 0.005). However, when any of the resin bonding systems was applied, no statistical difference between Fuji II LC and Vitremer was determined (P > 0.05). The Clearfil PhotoBond and Liner Bond groups showed similar bond strengths (P > 0.05), but were significantly less than Liner Bond II (P < 0.001). CONCLUSIONS: A recent bonding system combined with the RmGICs exhibited the greatest shear bond strength to dentine, irrespective of chemical differences that may exist between the two RmGICs.

In vitro secondary caries inhibition around fluoride releasing materials.

Objectives of the study were to compare the capacity of fluoride releasing materials to inhibit in vitro caries formation and to measure the width and height of the inhibition zones. Box-shaped cavities were prepared on bovine root dentine and restored with Fuji II, Fuji II LC. Vitremer, or Clearfil Liner Bond II system with a fluoride releasing composite. After immersion in a buffered demineralizing solution of 50 mmol/L acetic acid adjusted to pH 4.5 for 3 days, longitudinal sections were cut and imbibed in quinoline for analysis under a polarized light microscope (PLM). The contours of the lesions and inhibition zones were traced and their depth, width and height calculated. The data were analyzed by one-way ANOVA and Fisher's PLSD test at 95% level of confidence. The polarized light microscopy results showed a distinct inhibition zone adjacent to both conventional and resin-modified glass ionomer cements; however, it was not observed around the adhesive resin system. The width and height of this inhibition zone were significantly greater for Fuji II than for Fuji II LC and Vitremer. An inhibition zone was not observed adjacent to the adhesive resin system with fluoride releasing composite. The resin-modified glass ionomer cements produced less protection against in vitro secondary caries formation than the conventional glass ionomer cement. The recent bonding system that releases fluoride failed to produce an inhibition zone along the cavity wall adjacent to the restoration.

Monkey pulpal responses to conventional and adhesive luting cements.

Monkey pulpal responses to metal inlays luted with a combination of an adhesive resin and luting composite and conventional dental cements were histopathologically evaluated. Initial pulpal responses caused by re-exposure of the cut dentin surfaces and luting procedure under hydraulic pressure subsided at 90 days after final cementation. There was no significant difference among pulpal reactions to conventional dental cements and a combination of an adhesive resin and luting composite. The adhesive resin coating of freshly cut dentinal walls/floors immediately after cavity preparation seems to provide protection for the dentin and pulp in indirect restorations requiring temporary sealing.

Tensile bond strengths and adhesive interfaces of ten dentin bonding systems.

Tensile bond strength measurements and scanning electron microscopic observations have been performed to evaluate the adhesive properties of new dentin bonding systems. To date, however, it was impossible to compare previously reported data among researchers, because there was no standardization of in vitro test methods. There have also been few reports about the correlation among tensile bond strengths (TBS) and morphological features of the adhesive interfaces of recent systems. Therefore, the purpose of this study was to investigate the relationship between TBS to bovine dentin, following the guidelines documented by the International Organization for Standardization (ISO), and the morphology of resin/dentin interfaces of nine commercially available and one experimental bonding systems. The nine recent bonding systems used in this study showed significantly higher mean TBS (ranging from 25.0 to 14.8 MPa) than did a system (PhB) marketed ten years ago (9.3 MPa). However, morphological features of the resin/dentin interface varied among the systems, and no statistically significant correlation was found between TBS and width of the hybrid layer (p = 0.62). In order to evaluate the quality of the resin/dentin interface, quantitative analyses are needed to clarify the saturation and polymerization of resin in the hybrid layer.

Microhardness of in vitro caries inhibition zone adjacent to conventional and resin-modified glass ionomer cements.

OBJECTIVE: This study was conducted to correlate Knoop and triangular hardness numbers by measuring the microhardness of in vitro caries-inhibited and -demineralized dentin adjacent to a conventional and two resin-modified glass ionomer cements. METHODS: Box-shaped cavities were prepared on bovine root dentin and restored with either Fuji II, Fuji II LC, or Vitremer. The teeth were then decalcified in an acid buffered solution of 50 mmol l-1 acetic acid adjusted to pH = 4.5 for 3 days. Knoop and triangular microhardness indentations were performed perpendicular to the surface and parallel to the cavity wall, in the demineralized lesion and inhibition zone. Calcium and phosphorous contents of the outer lesions and inhibition zones were compared using energy-dispersive X-ray spectrometry (EDS). The correlation between Knoop and triangular hardness was analyzed by correlation coefficient. The statistical significance of hardness data was analyzed by one-way ANOVA and Fisher's PLSD test (p < 0.05). RESULTS: Triangular hardness (HT) correlated well with Knoop hardness number (KHN) (r2 = 0.81, p < 0.05). The microhardness of the inhibition zone created by Fuji II was of 59.2 +/- 3.8 HT and was statistically significantly higher than the zone produced by Fuji II LC and Vitremer. Fuji II LC and Vitremer produced inhibition zones with similar microhardness [48.3 +/- 3.5 HT and 44.0 +/- 7.6 HT, respectively (p > 0.05)]. Calcium and Phosphorous were present in the inhibition zone, but did not exist in the demineralized lesion. SIGNIFICANCE: Knoop and triangular hardness numbers correlated significantly (p < 0.05), and the latter seems to be a promising alternative method for measuring very narrow surfaces. Despite the fact that all glass ionomer materials used in this study were effective in producing an acid-resistant layer, microhardness and intensity of these layers were material dependent.

[Dental pulp reactions and pulp protection: traditional underlayers versus dentin adhesive lacquer]. / Pulpareacties en pulpabescherming: traditionele onderlagen versus dentinehechtlakken.

The dental pulp possesses an intrinsic healing capacity, by which pulpal reactions remain initially localised; they are often completely reversible. The younger and healthier the pulp is, the greater its healing capacity will be. Only in case of bacterial infection will the sterile pulpal inflammation convert into a local necrosis of the pulpal tissue that gradually will expand apically until the whole pulp is contaminated. The profit-effect of pulpal protection by means of traditional calcium hydroxide medicaments is compared with a more modern adhesive dentin sealing. Potential pulpal response to restorative materials and procedures are reviewed. Finally, clinical guidelines for optimal pulpal protection and dentinal sealing are formulated.

Bond strengths of resin to enamel and dentin treated with low-pressure air abrasion.

The effect of low-pressure (41.8 psi) air abrasion with alumina and glass beads on bonding to tooth substrates was evaluated. Tensile bond strengths of a bonding resin to air-abraded bovine enamel and dentin were measured. Scanning electron microscopy was used to observe (1) air-abraded surfaces, (2) fractured surfaces after the tensile bond test, and (3) interfaces of bonded specimens. Air abrasion with glass beads significantly decreased the bond strengths to enamel and dentin, whereas air abrasion with alumina decreased adhesion to enamel but not to dentin. The air-abraded enamel and dentin surfaces were irregularly roughened, and smear layers were created by air abrasion. Hybrid layers were observed at the interface between the bonding resin and the air-abraded dentin. The SEM photographs suggested that air abrasion may weaken the tooth surfaces, which could account for the decrease of the bond strengths.

Opacity and color changes of tooth-colored restorative materials.

Internal opacity and color changes of several esthetic direct restorative materials were determined using an accelerated test proposed by Asmussen (1981). Five chemically cured composites, seven light-cured composites, and three resin-modified glass-ionomer cements were placed in acrylic rings. After curing, they were left at 37 degrees C for 1 week before baseline measurement, and then stored in 60 degrees C distilled water up to 4 weeks. Color change was determined by a color analyzer, and contrast ratio representing opacity was calculated. All chemically cured composites tested discolored to dark yellow or dark brown after 4 weeks. Opacity decreased for two macrofilled composites. Light-cured composites discolored slightly, but their opacity change was negligible. All resin-modified glass-ionomer cements tested showed an abrupt decrease of opacity at the initial stage, with accompanying darkening of the materials. Opacity decrease was found to be a factor of discoloration for some tooth-colored restorative materials, and might be caused by a refractive index change of the matrix phase of the materials.

Clinical and semiquantitative marginal analysis of four tooth-coloured inlay systems at 3 years.

OBJECTIVES: The marginal quality of four tooth-coloured inlay systems was clinically investigated and subjected to computer-aided semiquantitative marginal analysis under scanning electron microscopy (SEM) after 3 years of clinical service. METHODS: Three of the restoration types were made using the Cerec CAD-CAM apparatus: one was milled from preformed glass ceramic blocks, and the two other inlay types were milled from preformed porcelain blocks. The fourth system was based on an experimental indirect resin composite inlay system. Each inlay type was luted with a different luting resin composite. The clinical evaluation was performed with a mirror and explorer by two clinicians separately, and the marginal analysis was conducted microscopically on replicas (SEM x 200). RESULTS: After 3 years in situ, all the restorations were clinically acceptable. No recurrent caries was observed. Marginal analysis under SEM detected a high percentage of submargination for all four systems, which suggests that their respective resin composite luting agents were all subject to wear. The percentage of marginal fractures on the enamel side as well as on the inlay side did not increase dramatically compared to the 6-month results. CONCLUSION: The first recall after 6 months of clinical service indicated how tooth-coloured inlays behave at their margins. The 3-year results confirmed the early findings, indicating that wear of resin composite lutes is important and present in all systems. The two ceramic materials showed a similar behaviour at the margins. The resin composite inlay performed better at the inlay site than at the enamel site.

In vivo adhesive interface between resin and dentin.

V-shaped cervical cavities prepared in monkey teeth were restored with several dentin bonding systems, and the in vivo resin-dentin interfacial structures were observed under the scanning electron microscope using an argon-ion etching technique. The hybrid layer could be clearly observed; its depth was dependent on the conditioner/primer used and tended to be thinner at the deep part of the cavity. Resin tags were also clearly observed, and their structure at the inner part was noted to be rougher than that closer to the tubule orifices. When 37% phosphoric acid gel was used, the tags in the deeper parts of the cavity were much rougher. Hemispherical and spherical roughened structures were observed directly above the tubule orifices, which were thought to be a mixture of dentinal fluid and bonding resin that had flowed out from the tubules. The acidic primer containing maleic acid and HEMA could not remove the smear plugs, and undissolved smear particles were observed in the tubules.

Shear and tensile bond testing for resin cement evaluation.

OBJECTIVES: The aim of this study was to compare the tensile and shear bond strengths of one experimental and four commercially available resin cements following the ISO document TR 110405 for bond measurement. METHODS: Tensile and shear bond tests were performed using bovine enamel and dentin as the tooth substrate with each of the resin cements. Resin composite rods were cemented to the prepared tooth surfaces. The bond strengths were obtained 24 h after cementation, and mode of failure was classified after fracture of the bonds, both visually and by SEM observation. RESULTS: Significant differences existed between the two bond test methods for all materials with enamel and three of the five cements when bonded to dentin. The shear test results were always the higher of the two test methods. Mode of fracture varied little for the visual classification, but the morphology from SEM observations showed considerable differences. SIGNIFICANCE: Although there are deficiencies in the current test methods these may be outweighed by substrate variables. A test model should be designed to determine which stresses, tensile or shear, are the greatest for different types of restorations. With this information, the type of test selected could provide appropriate information before clinical trials are commenced.