Inokoshi S

Morphological Aspects of the Resin-Dentin Interdiffusion Zone with Different Dentin Adhesive Systems

Cross-sections of resin-dentin interfaces were etched with an argon-ion beam to make their substructure detectable by scanning electron microscopy. The dentin adhesive systems were categorized morphologically into three groups, and an attempt was made to clarify their adhesive mechanism. The first group of products removed the smear layer. The argon-ion bombardment clearly disclosed a hybrid or resin-impregnated dentin layer. It is hypothesized that conditioning with acidic or chelating agents demineralized the dentin surface-layer to a certain depth, leaving behind a collagen-rich mesh-work. Hydrophilic monomers are then believed to alter this collagen-fiber arrangement in a way that facilitates penetration of the adhesive resin, resulting in a mechanical, intermingled link between collagen and the adhesive resin. The second group preserved the smear layer. In this case, the dentinal tubules were obliterated with globular particles at their orifices and remained patent underneath these smear plugs. This type of adhesive system aims at the incorporation of the smear layer into the hydrophilic monomers, which have an affinity for the organic and/or inorganic components of the underlying dentin. Finally, a third, small group only partly dissolved the smear layer, creating a thin resin-impregnated dentin layer and a resin-impregnated smear plug. This study clearly showed that the application of recent adhesive systems induced structural changes in the dentin surface morphology, creating a retentive interface, called the interdiffusion zone, between the deep, untouched dentin layers and the composite filling material. This resin-dentin interdiffusion zone offers bonding sites for copolymerization with the resin composite and, concurrently, might have protective potential for the pulp tissues.

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.

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 Fishers 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.

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.

SEM and elemental analysis of composite resins

Twenty-four chemically cured, 21 light-cured anterior, three light-cured anterior/posterior, and 18 light-cured posterior composite resins were examined using scanning electron microscopy, and the elemental composition of their filler particles was analyzed with an energy dispersive electron probe microanalyzer. According to the results obtained, the composite resins were divided into five groups (traditional, microfilled type, submicrofilled type, hybrid type, and semihybrid), with two additional hypothetical categories (microfilled and hybrid). Characteristics of each type were described with clinical indications for selective guidance of respective composite resins for clinical use.

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.

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.

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.

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 Fishers 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.

Adhesive interface between resin and etched dentin of cervical erosion/abrasion lesions.

The interfacial structure between an adhesive composite resin and the dentinal walls of cervical erosion/abrasion lesions etched with 37% phosphoric acid gel for 60 seconds was investigated. Almost all dentinal tubules were occluded with rod-like structural depositions that remained undissolved even after acid conditioning. The hybrid layer between the adhesive resin and surface-demineralized dentin was found to be 0.3 to 3 microns, much thinner than that routinely found in either normal dentin or cariously affected dentin. The hybrid layer was thinnest at the occlusal walls of the cavity where the dentinal tubules run parallel to the cavity surface. The bond strength of adhesive resin to these areas may differ from that to intact normal dentin.