Shigeru Uno

Effects of mechanical properties of adhesive resins on bond strength to dentin.

OBJECTIVES The purpose of this study was to evaluate the relationship between the micro-tensile bond strength to dentin and mechanical properties of the cured adhesive resins. METHODS Coronal dentin surfaces of extracted human teeth were treated with four commercial self-etching priming systems (Clearfil SE Bond; UniFil Bond; Tokuso Mac-Bond II; and Imperva Fluoro Bond) and bonded with a resin composite. After 24h storage in water at 37 degrees C, the bonded specimens were trimmed and subjected to micro-tensile bond strength testing at a cross-head speed of 1mm/min. Debonded surfaces were observed under a FE-SEM. For testing mechanical properties, 0.7-mm thick slabs of each adhesive resin were prepared, light-cured, and stored dry at the room temperature for 24h. After trimming, ultimate micro-tensile strength was measured. The nano-hardness and Youngs modulus were also evaluated using cured adhesives that were prepared in the same manner as described above. RESULTS The micro-tensile bond strengths to dentin and ultimate micro-tensile strengths of the resins were not significantly different among all systems (P>0.05). However, the nano-hardness and Youngs modulus of Clearfil SE Bond and Imperva Fluoro Bond adhesive resins were significantly higher than those of UniFil Bond and Tokuso Mac-Bond II resins (P<0.05). The micro-tensile bond strength significantly correlated with the ultimate micro-tensile strength of the resins (r(2)=0.77; P<0.05), but was not correlated with the nano-hardness or Youngs modulus (P>0.05). SEM observation of the debonded surfaces revealed a mixed type of fracture with a combination of interfacial and cohesive failure within the adhesive resin. SIGNIFICANCE The four self-etching priming systems exhibited similar dentin bond strengths, which also correlates with the ultimate strength of the adhesive resins.

Long-term mechanical characteristics of resin-modified glass ionomer restorative materials.

OBJECTIVES The purpose of this study was to compare the effects of long-term water storage on the mechanical characteristics of four resin-modified glass ionomer restorative materials with those of a conventional glass ionomer cement and a resin composite material. METHODS Cylindrical specimens were prepared and stored in water for 1 h, 24 h, 1 wk, 1 mon, 3 mon and 6 mon prior to determination of diametral tensile strength (DTS) and depth of surface indentation both under 1 N load and after removal of the load. RESULTS Diametral tensile strength was lowest for the conventional glass ionomer cement and highest for the composite; the resin-modified glass ionomer cements were intermediate between the reference materials. Water storage reduced DTS between 24 h and 1 wk or 1 mon but then remained unaffected until the final measurements after 6 mon. The materials showed a trend toward a slight increase in the depth of indentation both under load and after removal of the load with increasing storage time. These mechanical properties indicate the position of four resin-modified glass ionomer cements on a continuum with conventional glass ionomer cement and resin composite as the end points. SIGNIFICANCE The mechanical properties of resin-modified glass ionomers show that this group of materials is weaker than resin composite but stronger than conventional glass ionomer cement. Water storage for 6 mon has little adverse effect on the mechanical properties.

Resin-modified glass ionomer cements: bonding to enamel and dentin.

OBJECTIVES This study was designed to investigate the effect of storage in water on bonding efficacy to enamel and dentin of four resin-modified (Dyract, De Trey Dentsply; Fuji II LC, GC Dental Corp.; Photac Fil, ESPE; Vitremer, 3M Dental Products), one conventional glass ionomer filling material (Ketac Fil, ESPE) and a resin composite system (Pekafill/Gluma bonding system, Bayer). The hypothesis was that water storage would lead to an adverse effect on bond strength of resin-modified glass ionomer cements to enamel and dentin. METHODS The shear bond strength of each material was determined after storage periods of 24 h, 1 wk, 1 mon, 3 mon and 6 mon. The data were subjected to one-way ANOVA. Significant differences were determined by multiple comparison testing (significance level 5%). The failure modes of the debonded specimens were analyzed with a dissecting microscope. RESULTS Shear bond strengths to enamel for Dyract, Photac Fil and Pekafill were 5.2 +/- 1.3, 9.9 +/- 1.6 and 17.0 +/- 2.3 MPa, irrespective of storage time (p > 0.05). For Ketac Fil, the average shear bond strength between 1 wk and 6 mon was 4.5 +/- 1.7 MPa, the mean value for Fuji II LC between 24 h and 3 mon was 10.3 +/- 3.9 MPa and after 6 mon was 19.8 +/- 4.4 MPa, while Vitremer showed increasing shear bond strengths between 24 h (2.4 +/- 0.8 MPa) and 1,3 and 6 mon (13.8 +/- 4.3 MPa). Shear bond strengths to dentin were not adversely affected by storage throughout the 6 mon for Dyract (13.0 +/- 2.6 MPa), Fuji II LC (12.7 +/- 1.7 MPa) and Pekafill (14.6 +/- 3.1 MPa), when tested by ANOVA (p > 0.05). Ketac Fil showed 4.9 +/- 1.2 MPa between 1 wk and 6 mon and lower shear bond strength after 24 h. The average shear bond strengths up to 1 mon for Vitremer were 5.4 +/- 2.5 MPa (p > 0.05). However, at 3 and 6 mon immersion in water, three specimens had loosened spontaneously. With Photac Fil, no adhesion to dentin was registered. Most samples showed cohesive failure patterns in the restorative materials. Adhesive or mixed failures were registered only for Vitremer on dentin and enamel up to 1 wk and for Dyract on enamel. SIGNIFICANCE Long-term water storage generally had no adverse effect on bonding efficacy of resin-modified glass ionomer cements to dentin and enamel.

Effect of slow-curing on cavity wall adaptation using a new intensity-changeable light source

OBJECTIVE The purpose of the study was to investigate the effects of a new intensity-changeable light source Curetron 7 (CT-7) devised for the slow-curing on cavity wall adaptation in the adhesive composite restorations, as well as the microhardness of the cured composite. METHODS Microhardness of both top and bottom surfaces was measured by an indentation method for 2mm thick cylindrical specimens, and cavity adaptation was evaluated in cylindrical dentin cavities (slashed circle 3.5x1.5mm(2)) of human extracted molars bonded to a hybrid resin composite. The irradiation was done with CT-7, VIP or Candelux (CDX) under the following five conditions: CT1, 600mW/cm(2)x30s (CT-7); CT2, 230mW/cm(2)x20s+600mW/cm(2)x20s (CT-7); CT3, 230mW/cm(2)x20s+pause x 10s+600mW/cm(2)x20s (CT-7); VIP, 300mW/cm(2)x3s+pause x 3min+600mW/cm(2)x30s (VIP); CDX, 200mW/cm(2)x10s+600mW/cm(2)x30s. RESULTS Five irradiation conditions had no influence on the microhardness for either top or bottom surface (Scheffe, p>0.05). In conditions CT3, VIP and CDX, top surfaces were harder than bottom surfaces (Students t-test, p<0.05). The statistical analysis revealed no difference in adaptation among the locations along the cavity walls for each irradiation conditions (Kruskal-Wallis, p>0.05). In comparison of poled data for each condition, the best adaptation was seen in condition CT3, and the second in condition VIP (Kruskal-Wallis, p<0.05). SIGNIFICANCE These results proved the efficacy of the slow-curing method combined with the interval between two irradiations with low intensity and high intensity. CT-7 could be useful for the adhesive composite restorations.

Short- and long-term in vitro study of the bonding of eight commercial adhesives to normal and deproteinized dentin.

Objective. The aims of this study were to investigate the influence of deproteinization of dentin on the shear bond strength (SBS) mediated by eight dentin adhesives, and to evaluate the long-term durability of the SBSs. The hypotheses were that deproteinization of dentin would not affect the capacity for adherence, and that in contrast to the SBSs to collagen-rich surfaces, the SBSs to deproteinized surfaces would be stable during a 1-year period of storage in water. Material and Methods. Ground surfaces of human dentin were either rinsed with water (normal dentin) or treated with sodium hypochlorite (deproteinized dentin). The dentin surfaces were analyzed by Fourier transform-infrared spectroscopy (FT-IR) using horizontal attenuated total reflectance (HATR). In addition, the SBS to normal and deproteinized dentin treated with the adhesives was measured after 24 h or 1 year of storage in water. Results. The IR absorption peaks at approximately 1,640, 1,560, and 1,240 cm−1 were assigned to the collagen matrix and peaks at about 1,000 cm−1 were assigned to the phosphate group in hydroxyapatite. From the relative magnitude of the peaks, it was determined that the utilized deproteinization method was effective. Furthermore, the normal dentin group showed SBS values ranging from 10 to 39 MPa and the deproteinized dentin group showed SBS values ranging from 13 to 30 MPa. Conclusions. According to the statistical analysis, the results only partly supported the hypotheses: it was found that the influence on bond strength of deproteinization of dentin surfaces and the effect of 1 year of storage in water depended on the composition of the dentin adhesive.

Effect on bonding of curing through dentin

The aim of this study was to investigate the effect of the thickness of dentin (1, 2, or 3 mm) placed between the light guide and the composite resin on the shear bond strength to dentin treated with a simplified Gluma system. The effects of the thickness of composite resin (2 or 3 mm), irradiation time (20, 40, or 60 sec), and shade (universal or brown) were also examined. The results showed that the thickness of dentin influenced bonding and interacted with the other three variables. It is suggested that dentin located between the light guide and composite resin may attenuate the light aimed at the bonding interface in the same manner as a layer of composite resin.

Effect of 2-hydroxyethyl methacrylate in an Al2Ox3/glycine solution used as primer for dentin bonding.

The aim of this study was to investigate the effect of 2-hydroxyethyl methacrylate (HEMA) in an Al2Ox3/glycine solution used as primer for dentin bonding in combination with an experimental BISGMA-HEMA-based adhesive resin. With various amounts of HEMA in the Al2Ox3/glycine solution, a shear bond test showed a maximum strength at 50 wt% of HEMA. In this case, scanning electron microscopy examination showed a HEMA-infiltrated surface layer of the dentin along the interface between dentin and the adhesive resin. It is suggested that HEMA in Al2Ox3/glycine solutions may facilitate penetration of HEMA into etched or primed dentin.