Keiichi Hosaka

Durability of Resin-Dentin Bonds to Water- vs. Ethanol-saturated Dentin

Higher 24-hour resin-dentin bond strengths are created when ethanol is used to replace water during wet bonding. This in vitro study examined if ethanol-wet-bonding can increase the durability of resin-dentin bonds over longer times. Five increasingly hydrophilic experimental resin blends were bonded to acid-etched dentin saturated with water or ethanol. Following composite build-ups, the teeth were reduced into beams for 24-hour microtensile bond strength evaluation, and for water-aging at 37°C for 3, 6, or 12 months before additional bond strength measurements. Although most bonds made to water-saturated dentin did not change over time, those made to ethanol-saturated dentin exhibited higher bond strengths, and none of them fell over time. Decreased collagen fibrillar diameter and increased interfibrillar spacing were seen in hybrid layers created with ethanol-wet-bonding. Increases in bond strength and durability in ethanol-wet-bonding may be due to higher resin uptake and better resin sealing of the collagen matrix, thereby minimizing endogenous collagenolytic activities.

Long-term evaluation of water sorption and ultimate tensile strength of HEMA-containing/-free one-step self-etch adhesives

OBJECTIVE The objective of this study was to evaluate the water sorption (Wsp) and ultimate tensile strength (UTS) of HEMA-containing/free one-step self-etch adhesives after long-term water-storage. METHODS Three HEMA-containing one-step self-etch adhesives (Bond Force (BF), Clearfil S(3) Bond (S3) and OptiBond All-In-One (OP)), and one HEMA-free one-step self-etch adhesive, G Bond (GB) was used. After the solvents of each adhesive were evaporated, polymerised adhesive disks and dumbbell-shaped specimens of thirty-two each were prepared and divided into four groups of 14-, 90-, 180- and 360-day water-storage. After immersion in water for the designated storage periods, the disks were subjected to measurement of Wsp, and the dumbbell-shaped specimens were subjected to measurement of UTS. The data of Wsp and UTS were statistically analysed using a two-way ANOVA and Bonferroni test. RESULTS Wsp of BF, S3 and OP increased over time, whereas for GB, there were no significant differences in Wsp among all the storage periods. Wsp of GB was lower than those of BF, S3 and OP in each period. The UTS of BF, S3 and OP decreased over time, whereas for GB, there were no significant differences in UTS among all storage periods. The highest UTS was initially seen in BF>GB=S3=OP, and after 360-day water-storage, seen in BF=GB>OP=S3. CONCLUSIONS For the HEMA-containing adhesives, Wsp increased and UTS decreased over time. On the other hand, for the HEMA-free adhesive, Wsp and UTS did not significantly change even after 360-day water-storage.

Relationship between mechanical properties of one-step self-etch adhesives and water sorption

OBJECTIVES The purpose of this study was to evaluate the relationship between changes in the modulus of elasticity and ultimate tensile strength of one-step self-etch adhesives, and their degree of water sorption. METHODS Five one-step self-etch adhesives, Xeno IV (Dentsply Caulk), G Bond (GC Corp.), Clearfil S3 Bond (Kuraray Medical Inc.), Bond Force (Tokuyama Dental Corp.), and One-Up Bond F Plus (Tokuyama Dental Corp.) were used. Ten dumbelled-shaped polymers of each adhesive were used to obtain the modulus of elasticity by the three-point flexural bending test and the ultimate tensile strength by microtensile testing. The modulus of elasticity and the ultimate tensile strength were measured in both dry and wet conditions before/after immersion in water for 24h. Water sorption was measured, using a modification of the ISO-4049 standard. Each result of the modulus of elasticity and ultimate tensile strength was statistically analyzed using a two-way ANOVA and the result of water sorption was statistically analyzed using a one-way ANOVA. Regression analyses were used to determine the correlations between the modulus of elasticity and the ultimate tensile strength in dry or wet states, and also the percent decrease in these properties before/after immersion of water vs. water sorption. RESULTS In the dry state, the moduli of elasticity of the five adhesive polymers varied from 948 to 1530 MPa, while the ultimate tensile strengths varied from 24.4 to 61.5 MPa. The wet specimens gave much lower moduli of elasticity (from 584 to 1073 MPa) and ultimate tensile strengths (from 16.5 to 35.0 MPa). Water sorption varied from 32.1 to 105.8 g mm(-3). SIGNIFICANCE The moduli of elasticity and ultimate tensile strengths of the adhesives fell significantly after water-storage. Water sorption depended on the constituents of the adhesive systems. The percent decreases in the ultimate tensile strengths of the adhesives were related to water sorption, while the percent reductions in the moduli of elasticity of the adhesives were not related to water sorption.

Translucency, opalescence and light transmission characteristics of light-cured resin composites.

OBJECTIVES To evaluate the translucency, opalescence and light transmission characteristics of resin composites with different thicknesses. METHODS Disks of three resin composites (Estelite∑, Beautifil II, Clearfil Majesty) of A2 shade were prepared in diameter of 10mm with various thicknesses (0.5mm, 1.0mm and 2.0mm). Color was measured according to CIELAB color scale on a reflection spectrophotometer and a color haze meter, and translucency parameter (TP) and opalescence parameter (OP) were calculated. Using the distribution graphs of transmitted light intensity on a goniophotometer, diffusion factor (DF) as an indicator for a diffuse transmission property and peak gain (G0) for a straight-line transmission property were calculated. RESULTS The TP and G0 values significantly decreased in the order: 0.5mm>1.0mm>2.0mm thickness (p<0.05). The OP value increased as the thickness of resin composite increased from 1.0mm to 2.0mm (p<0.05), while was similar for the 0.5mm- and 1.0mm-thick groups. The DF value increased from 0.5mm to 1.0mm, but was similar for the 1.0mm- and 2.0mm-thick groups. There was a significant correlation between TP and DF (R(2)=0.96, p<0.001). On the other hand, there was a weak correlation between OP and DF (R(2)=0.21, p<0.005), however within the values of the 0.5mm-thick group, OP was highly correlated with DF (R(2)=0.84, p<0.001). SIGNIFICANCE At the 0.5mm thickness, the translucency (TP) and opalescence (OP) of resin composites had a significant correlation with a diffuse transmission property (DF). When more than 1.0mm thickness of resin composites, translucency and opalescence were influenced by the thickness, in which translucency significantly decreased and opalescence significantly increased.

Influences of composite-composite join on light transmission characteristics of layered resin composites

OBJECTIVES The purposes of this study were: (1) to determine the light transmission characteristics (straight-line and diffusion transmission) of bulk-filled and layered resin composites, and (2) to evaluate the effect of layering filling on translucency and color appearance of resin composites. METHODS Three light-cured resin composites (EsteliteΣ, Tokuyama Dental; Beautifil II, Shofu and Clearfil Majesty, Kuraray Medical) in A2 and OA2 shades were used in this study. 2 mm-thick resin composite discs were prepared by two methods; bulk filling technique (2 mm filling at one time), layering technique (two layers each 1 mm thickness). The transmitted light intensity of each resin composite disc was measured using a goniophotometer, and diffusion factor (DF), an indicator for diffuse transmission property, and peak gain (G0) for straight-line transmission were calculated from the light distribution graphs. Color was measured according to the CIELAB color scale on a spectrophotometer, and the translucency parameter (TP) and color difference (ΔE(*)) between bulk-filled and layered specimens were calculated. The data were statistically analyzed using three-way ANOVA, and Dunnetts T3 and t-test for post-hoc test. RESULTS Three-way ANOVA revealed that the layered specimens had significantly lower G0 values and higher DF values than the bulk-filled specimens, and significantly reduced TP values. The color differences (ΔE(*)) ranged from 1.07 to 1.85 between the bulk-filled and layered specimens. SIGNIFICANCE Resin composite placed in layers exhibited reduced straight-line light transmission and increased diffusion transmission compared with bulk-filled resin composite. The layering technique affected the translucency and color rendition of resin composite.

Dentin bonding durability of two-step self-etch adhesives with improved of degree of conversion of adhesive resins

PURPOSE To evaluate (1) the initial and long-term microtensile bond strengths of two-step self-etch adhesives with different degrees of conversion (DC); (2) the elastic modulus of the respective adhesive resins; (3) the water sorption of the respective adhesive resins. MATERIALS AND METHODS Two two-step self-etch adhesives, Clearfil SE Bond (CSE) and Clearfil SE Bond 2 (CSE2) were used in this study. The DC was determined using ATR/FT-IR with a time-based spectrum analysis. Midcoronal flat dentin surfaces of 24 human molars were prepared with 600-grit SiC paper for microtensile bond strength (µTBS) testing. CSE and CSE2 were applied to the dentin surfaces according to the manufacturers instructions, followed by composite buildups. The µTBS was measured after water storage for 24 h, 6 months, and 1 year. The elastic modulus (before and after 1 month of water immersion) was determined by the three-point flexural bending test and water sorption values by the water sorption test. RESULTS CSE2 showed significantly higher DC than CSE. The µTBS of CSE2 was significantly higher than that of CSE in all water storage periods. One-year water storage decreased the µTBS of CSE; however, it did not decrease that of CSE2. Regarding the polymerized adhesive resins, the elastic modulus of CSE2 was significantly higher than that of CSE before and after water immersion (p < 0.001), and the water sorption of CSE was higher than that of CSE2. CONCLUSIONS The higher DC of adhesive resins of two-step self-etch adhesives resists water aging and improves the initial bond strengths and durability of the resin-dentin bond.

The effect of five kinds of surface treatment agents on the bond strength to various ceramics with thermocycle aging

This study evaluated the effects of ceramic surface treatment agents on shear bond strengths to ceramic materials with and without thermocycling. Ceramic plates were prepared from feldspathic ceramic; AAA, lithium disilicate ceramic material; IPS e.max Press, zirconia ceramic; Lava. Ceramic surfaces were pretreated with one of five surface treatment agents (Clearfil PhotoBond mixed with Porcelainbond activator (PB), Clearfil SE One mixed with Porcelainbond activator (SO), Ceramic Primer (CP), Universal Primer (UP), Scotchbond Universal (SU)), and then a resin cement (Clapearl DC) was filled. After 0, 5,000, and 10,000 thermocycles, micro-shear bond strengths between ceramic-cement interfaces were determined. SU exhibited significantly lower initial bond strength to AAA and e.max than PB, SO, CP, and UP. For Lava, PB, SO, CP and SU exhibited higher initial bond strengths than UP. Thermocycles reduced bond strengths to all the ceramic materials with any surface treatment.

Color shifting at the border of resin composite restorations in human tooth cavity.

OBJECTIVES The purposes of this study were to evaluate color shifting at the boarder of resin composite restorations after placement in human tooth cavities in vitro. METHODS Twenty extracted human premolars with an A2 shade were used in this study. Cylindrical shaped cavities (3.0mm or 1.5mm depth; 2.0mm diameter) were prepared in the center of the crowns. One of four resin composites of A2 shade (Clearfil AP-X, AP; Clearfil Majesty, MA; Tetric N Ceram, TNC; Ceram X mono, CX) was placed in the cavity, and the color was measured at four points (0.4mm × 0.4mm) on the restored teeth (area 1: tooth area 1.0mm away from the border of resin composite restoration; area 2: tooth border area 0.3mm away from margin of resin composite restoration; area 3: resin composite border area 0.3mm away from margin of resin composite restoration; area 4: resin composite area at the center of resin composite restoration) using a spectrophotometer (Crystaleye). The color of each area was determined according to the CIELAB color scale. Color differences (ΔE*) between the areas of 1 and 2, 2 and 3, 3 and 4, and 1 and 4 were calculated, and also the ratio of ΔE*23 to ΔE*14 as a parameter of the color shifting at the border of resin composite restoration, was determined. The data were statistically analyzed using two-way ANOVA, and Dunnetts T3 and t-test for the post hoc test. RESULTS For all materials, the Δ*23 were significantly lower than ΔE*14, in which ΔE*23 were significantly influenced by the materials although there were no significant differences in the ΔE*14 between the materials. Additionally, ΔE*12 were significantly higher than ΔE*34. For the 3.0mm cavity depth group, the lowest ΔE*23/14 ratio was seen in CX = <TNC<AP. For the 1.5mm cavity depth group, TNC dramatically reduced the ΔE*23/14 ratio, and the lowest ratio was seen in TNC = CX<MJ<AP. SIGNIFICANCE All resin composite restorations in the tooth cavities produced the color shifting of resin composite and tooth at the border. For deep cavity, resin composites with higher diffused light transmission property showed higher color shifting at the border, while for shallow cavity, the straight-line as well as diffused light transmission of resin composite affected the color shifting at the border. Clinically, diffused light transmission property of resin composites may contribute to the color shifting at the border of resin composite restoration regardless of cavity depth, resulting in better color matching.

Influence of water immersion on the mechanical properties of fiber posts

PURPOSE The purpose of this study was to evaluate the influence of water immersion on the mechanical properties of three kinds of glass fiber posts and the fracture resistance of structures using resin composites with glass fiber posts. METHODS Each post was divided into three groups; a control group and two water immersion groups (30 and 90 days). Flexural strength was determined by three-point bending test. Each structure was divided into two groups; a control group and a water immersion group for 30 days. The fracture strength of structures was determined by a static loading test. RESULTS In the flexural strength, two kinds of post in water immersion groups showed lower values than control groups. In the fracture strength, two kinds of structures in water immersion group showed lower values than control groups. CONCLUSION The prefabricated glass fiber posts and structures using resin composites with glass fiber posts were affected by water immersion.

Smear layer-deproteinizing improves bonding of one-step self-etch adhesives to dentin

OBJECTIVES Smear layer deproteinizing was proved to reduce the organic phase of smear layer covered on dentin surface. It was shown to eliminate hybridized smear layer and nanoleakage expression in resin-dentin bonding interface of two-step self-etch adhesive. This study aimed to investigate those effects on various one-step self-etch adhesives. METHODS Four different one-step self-etch adhesives were used in this study; SE One (SE), Scotchbond™ Universal (SU), BeautiBond Multi (BB), and Bond Force (BF). Flat human dentin surfaces with standardized smear layer were prepared. Smear layer deproteinizing was carried out by the application of 50ppm hypochlorous acid (HOCl) on dentin surface for 15s followed by Accel® (p-toluenesulfinic acid salt) for 5s prior to adhesive application. No surface pretreatment was used as control. Microtensile bond strength (μTBS) and nanoleakage under TEM observation were investigated. The data were analyzed by two-way ANOVA and Tukeys post-hoc test and t-test at the significant level of 0.05. RESULTS Smear layer deproteinizing significantly improved μTBS of SE, SU, and BB (p<0.001). Hybridized smear layer observed in control groups of SE, BB, and BF, and reticular nanoleakage presented throughout the hybridized complex in control groups of BB and BF were eliminated upon the smear layer deproteinizing. SIGNIFICANCE Smear layer deproteinizing by HOCl and Accel® application could enhance the quality of dentin for bonding to one-step self-etch adhesives, resulting in the improving μTBS, eliminating hybridized smear layer and preventing reticular nanoleakage formation in resin-dentin bonding interface.