Toru Nikaido

Evaluation of thermal cycling and mechanical loading on bond strength of a self-etching primer system to dentin

OBJECTIVE The aim of this study was to evaluate the in vitro durability and fracture modes of the tooth-resin interface following thermal cycling, fatigue load cycling (FLC) and micro-tensile bond strength testing (MTBS). METHODS Twenty-four human molars were divided into two groups. In group A, coronal dentin was ground flat with #600-grit SiC paper, Clearfil Linerbond.2V (LB.2V) adhesive was applied and a crown fabricated with Clearfil AP-X resin composite. Samples were loaded in the FLC simulator and thermal cycle device. In group B, Class I cavities were prepared with a diamond bur and the cavity restored with LB.2V/AP-X. Samples were simultaneously subjected to FLC and thermal cycling. After storage of the specimens in water for 1 week, MTBS tests were performed, and fracture modes examined by SEM. RESULTS For group A, MTBS were approximately 40 MPa with cohesive failures in the bonding resin of all specimens. Neither thermal nor mechanical stressing altered bond strengths on flat dentin surfaces. In group B, MTBS in the unstressed control group was 21 MPa with cohesive failures in the resin. As both thermal and mechanical stresses increased, there was a significant decrease in bond strength (16 MPa, P<0.05) and the fractures were seen in the resin-dentin interface and hybrid layer. SIGNIFICANCE Surface preparation, C-factor, cavity depth, the dentin substrate and character of the smear layer strongly influence the bond strength values after thermal and fatigue loading. The FLC simulator in combination with MTBS testing provides meaningful in vitro evaluation of dentin bonding durability.

The influence of storage solution on dentin bond durability of resin cement

OBJECTIVES This study was conducted to determine the influence of storage solution on the bond durability of three resin cements to bovine dentin over the period of 1 year. METHODS Ten bovine dentin specimens were tested for shear bond strength with each material (Panavia 21, Kuraray Co.; BISTITE, Tokuyama Co; MASA Bond, Sun Medical Co.) and storage mode, listed below. Four storage environments were studied as follows: water changed every day for 1 year; water unchanged for 1 year; Phosphate Buffered Saline (PBS) changed every week over 1 year; PBS unchanged for 1 year. Ten teeth were also tested for each material at 1 day as a control. The mode of failure was classified after fracture of the bonds by SEM observation. The means of the bond strengths were compared statistically by two-way ANOVA and Fishers PLSD test (p < 0.05). Results for the mode of fracture were analyzed using the Mann-Whitney U test. RESULTS Although there was no statistical difference in the mean bond strengths between the water and PBS storage solutions (p > 0.05) in all cements, the results for the shear bond strengths in the changed storage solution groups were significantly lower than those where the storage solution remained unchanged (p < 0.05). There were statistical differences between the 1 day results and the changed water groups among all cements (p < 0.05). SIGNIFICANCE The storage condition influenced the long-term durability of dentin bonding with resin cements.

Effect of primer treatment on bonding of resin cements to zirconia ceramic

OBJECTIVES To evaluate and compare bond strengths of different primers and resin cements to silica-based and zirconia ceramics. METHODS Silica-based and zirconia ceramic specimens were ground flat with #600-grit SiC paper. The ceramic surfaces were airborne-particle abraded and then divided into 11 groups of seven each: untreated (control); and conditioned with one of the six primers in combination with a resin cement from the same manufacturer as follows: Bistite II/Tokuso Ceramic Primer, Linkmax/GC Ceramic Primer, RelyX ARC/RelyX Ceramic Primer, Panavia F 2.0/Clearfil Ceramic Primer, and Resicem/Shofu Porcelain Primer and Resicem/AZ Primer. Stainless steel rods were bonded to the ceramic surfaces using one of the five resin cements. After 24-h water storage, the tensile bond strengths were tested using a universal testing machine and failure modes were examined. RESULTS Conditioning with primers containing a silane coupling agent (all the primers except AZ Primer) significantly enhanced bond strengths of resin cements to silica-based ceramic. For zirconia ceramic, Resicem/AZ Primer exhibited significantly higher bond strength than the other groups except Panavia F 2.0/Clearfil Ceramic Primer. The predominant failure mode of the groups conditioned with primers containing a phosphonic acid monomer (AZ Primer) or a phosphate ester monomer (Clearfil Ceramic Primer and Tokuso Ceramic Primer) was cohesive failure in cements whereas that with the other primers was adhesive failure at the zirconia surfaces. SIGNIFICANCE The use of primers containing a silane coupling agent improved resin bonding to silica-based ceramic. On the other hand, the use of primers containing a phosphonic acid monomer or a phosphate ester monomer improved resin bonding to zirconia ceramic.

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.

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 CPP-ACP with sodium fluoride on inhibition of bovine enamel demineralization: A quantitative assessment using micro-computed tomography

OBJECTIVES The present study evaluated the effects of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and CPP-ACP with 900 ppm fluoride (CPP-ACPF) pastes on inhibition of enamel demineralization over time, using polychromatic micro-computed tomography (micro-CT). METHODS Enamel blocks were prepared from bovine teeth. The specimens were each treated by one of the following agents, 30 min daily for 7 days: deionized water (negative control); CPP-ACP paste; CPP-ACPF paste; and NaF solutions (positive controls) (90, 900, and 9000 ppm F). After treatment, the specimens were immersed in a demineralizing solution (pH 4.5) for 24, 72, and 120 h. Mean mineral loss (ML) and lesion depth (LD) after each period were determined from mineral density profiles obtained using micro-CT. RESULTS ML values in all the treatment groups were significantly smaller than those in the control group after 72 and 120 h of demineralization (p < 0.05, two-way ANOVA and t-test with Bonferroni correction). ML values in CPP-ACPF and NaF solution groups were significantly smaller compared to CPP-ACP group after 72 h (p < 0.05). LD values in the CPP-ACPF and all the NaF solutions groups were significantly smaller compared to the control group after 120 h (p < 0.05). The 9000 ppm F group showed the lowest nominal ML and LD values. CONCLUSIONS The application of CPP-ACP or CPP-ACPF pastes to sound enamel surfaces resulted in inhibition of enamel demineralization, and a better effect was noted for the latter paste. Quantitative assessment using polychromatic micro-CT demonstrated to be useful for detecting mineral density changes.

Shear bond strengths of three resin cements to dentine over 3 years in vitro

OBJECTIVES This study was conducted to evaluate the bond durability of three resin cements bonded to bovine dentine over a period of 3 years. METHODS Ten bovine dentine specimens were tested for shear bond strengths with each of the following materials: Panavia 21, BISTITE resin cement, and MASA Bond (experimental resin cement) at 1 day, 6 months, 1 and 3 years after cementation of a composite rod. All specimens were stressed in shear at a crosshead speed of 1mm min(-1) until failure. The means of the bond strengths were compared statistically by two-way ANOVA and Fishers PLSD test (P<0.05). The mode of failure was classified after fracture of the bonds by SEM observation. Results for the mode of fracture were analyzed using the Mann-Whitney U-test. RESULTS The shear bond strengths (MPa+/-SD) for different times (1 day, 6 months, 1 and 3 years) were: Panavia 21 (15.2+/-3.6, 9.3+/-3.2, 8.5+/-2.1, 6.8+/-2.4), BISTITE (15.6+/-2.8, 11.0+/-1.4, 10.4+/-2.2, 9.0+/-2.7) and MASA Bond (29.6+/-9.5, 17.5+/-4.6, 19.6+/-4.5, 16.1+/-5.4). Panavia 21 and BISTITE strengths were significantly lower (P<0.05) at all times compared with MASA Bond, and 1 day strengths for all three materials were significantly higher (P<0.05) than 3 year strengths. Regarding the fracture modes after bond testing, there were statistical differences between the 1 day and the 1 year results for all cements (P<0.05). Although no Panavia 21 specimen showed complete cohesive failure in the demineralized dentine during the experiment, several BISTITE and MASA Bond specimens showed cohesive fracture in the demineralized dentine. For BISTITE, partially or complete demineralized dentine cohesive failures increased over time. CONCLUSIONS The type of resin cement seemed to have an influence on the long-term durability of bonding to dentine.

Early Tensile Bond Strengths of Several Enamel and Dentin Bonding Systems

Tensile bond strength tests are commonly used for the evaluation of adhesive dental materials. The majority of these tests are carried out after 24 h of storage in water. However, determination of the early tensile bond strength could be more important, especially in relation to gap formation between the cavity surface and the restorative material. This study investigated the tensile bond strengths of five enamel/ dentin bonding systems and two experimental dentin bonding systems. Tensile bond strengths were obtained at one min, ten min, and 24 h after the resin composite was cured. Bond strengths at the early stages were always somewhat less than the 24-hour test results. For the enamel/dentin bonding systems, a significant difference was found between the enamel and dentin bond strengths at all time periods, except with Superbond D-liner and Liner Bond. The experimental group with glyceryl methacrylate as the primer produced a good 24-hour result (14.3 MPa), but the early bond strengths were no different from those in the non-primer-treated groups. It was concluded that this material may actually retard the polymerization of the bonding resin. Previous workers have suggested that a tensile bond strength in the order of 20 MPa is necessary for gap-free restorations to be obtained. Should this be the case, then all of the materials tested, from the aspect of early bond strength, lack the strength for prevention of gap formation, although Superbond D-liner and Liner Bond approached this hypothetical figure. These systems, Superbond D-liner and Liner Bond, also exhibit small differences between the enamel and dentin tensile bond strengths.

Fluoride-containing adhesive: durability on dentin bonding.

OBJECTIVES To evaluate (1) the influence of fluoride-containing adhesive on microtensile bond strength (microTBS) and (2) in vitro secondary caries inhibition at the resin-dentin interface after 24 h and 3 months water-storage and (3) the degree of conversion of different adhesives after 24h 1 month. METHODS Flat surfaces of human teeth were ground and randomly assigned to six groups: (SBMP-24) Scotchbond Multi-Purpose control [SBMP], 24 h; (SE-24) SBMP etch and primer+Clearfil SE Bond adhesive [SE], 24h; (PB-24) SBMP etch and primer+Clearfil Protect Bond adhesive [PB], 24h; (SBMP-3) SBMP, 3 months; (SE-3) SBMP+SE, 3 months; and (PB-3) SBMP+PB, 3 months. To evaluate the effect of the adhesive resin alone, all teeth were etched with 35% phosphoric acid and primed with SBMP primer prior to applying the adhesive resin. Bonded assemblies were prepared for microTBS and stored in distilled water at 37 degrees C for 24h and 3 months. Sections of restored teeth of each group were exposed to an acid challenge. The specimens were sectioned, polished, and then observed with polarized light microscopy (PLM). Also, the degree of conversion (DC) of the adhesives was measured using Fourier Transform-Infrared spectroscopy (FTIR) at 24 h and 1 month, after polymerization. RESULTS microTBS values obtained in MPa (24h/3m) were: (MP) 61.5+/-10.5/52.9+/-8.9, (SE) 55.5+/-11.8/55.6+/-13, and (PB) 50.3+/-9.9/61.0+/-13.6. For interface analysis by PLM, an inhibition zone (IZ) adjacent to the hybrid layer was created only when the fluoride-containing adhesive (PB) was used. The DC in percentage (24 h, 1 month) were: (MP) 60.5+/-2.8/61.3+/-0.6, (SE) 69.6+/-1.3/70.7+/-0.05, and (PB) 53.1+/-0.4/58.3+/-1.6. SIGNIFICANCE The fluoride-containing adhesive demonstrated significant increase of bond strength values after water-storage. This material was also able to create an acid inhibition zone in dentin. There was a significant increase of degree of conversion after 1 month only for PB.

Reinforcement of dentin in self-etch adhesive technology: A new concept

OBJECTIVE Characterize the ultramorphology and secondary caries inhibition potential of different dentin adhesive systems in order to find a satisfactory explanation resist to recurrent caries. METHODS Human premolar dentin was treated with one of the two self-etching adhesive systems, Clearfil SE Bond, Clearfil Protect Bond or an acid-etching adhesive system, Single Bond. The bonded interface was exposed to an artificial demineralizing solution (pH 4.5) for 90 min and then 5% sodium hypochlorite for 20 min. Transmission electron microscopic observation was performed at the adhesive-dentin interface. The width of the reinforced zone was measured and data were analyzed with univariate analysis of variance under general linear model. In order to identify type of crystallites in the reinforced zone selected area electron diffraction was performed. RESULTS An acid-base resistant zone (ABRZ) was found adjacent to the hybrid layer in the outer lesion front with only Clearfil SE Bond and Clearfil Protect Bond, while Single Bond was devoid of this protective zone. Crystallite arrangement and the ultramorphology were almost similar in the corresponding regions of Clearfil SE Bond and Clearfil Protect Bond. However, thickness of the ABRZ at the mid portion was 1159(+/-41.91)nm in Clearfil protect Bond, which was significantly thicker than that of Clearfil SE Bond (F=514.84, p<0.001). Selected area electron diffraction confirmed the crystallites in the zone as apatite. CONCLUSIONS The self-etching adhesive systems created a new reinforced acid resistant dentin under the hybrid layer. Difference in the thickness of the zone expressed a different potential for demineralization inhibition.