The Influence of Blade Type and Feeding Force during Resin Bonded Dentin Specimen Preparation on the Microtensile Bond Strength Test.

This paper presents the effect of blade type and feeding force during resin-bonded dentin specimen preparation on the microtensile bond strength (µTBS) test. Forty resin-bonded flat middle dentin specimens were divided into four groups. The specimens of each group were sectioned according to type of blade and feeding force as follows: fine grit/20 N, fine grit/40 N, medium grit/20 N, and medium grit/40 N to obtain resin-dentin sticks with a cross-sectional area of 1.0 mm2. Four sticks from the center of each tooth were subjected to the µTBS test. Five remaining sticks of each group were selected for surface topography observation under a scanning electron microscope (SEM). As a result, the bond strength of the medium-grit group was higher than that of the fine-grit group (p < 0.001), whereas the feeding force had no influence on bond strength values (p = 0.648). From the SEM, sticks prepared with the fine-grit blade showed a smoother surface integrity and fewer defects on the specimen edges in comparison with the sticks prepared with the medium-grit blade. The grit type of the blade is one of the considerable factors that may affect the bond strength and the surface integrity of resin-dentin specimens for microtensile testing.

The effect of phytic acid on enzymatic degradation of dentin.

We evaluated the effect of phytic acid on matrix metalloproteinase (MMP)- or cysteine cathepsin (CC)-mediated dentin degradation. Demineralized dentin beams were divided into five groups (n = 12) and treated with 1%, 2%, or 3% phytic acid or with 37% phosphoric acid. Untreated demineralized beams served as controls. After incubation for 1 or 3 wk, dry mass loss was determined and aliquots of incubation media were analysed for cross-linked telopeptide of type I collagen (ICTP) fragments for MMP-mediated and c-terminal telopeptide of type I collagen (CTX) for cathepsin-k-mediated degradation. The direct effect of phytic acid was evaluated using MMP activity assay. Data were analysed using repeated-measures anova. ICTP releases with 1% and 2% phytic acid treatment were statistically significantly lower than those following phosphoric acid treatment at 3 wk. The CTX release for phytic acid-treated beams at 3 wk was not significantly different from that of untreated control beams, but it was significantly lower than that of phosphoric acid-treated beams. Their MMP activities at 3 wk were not significantly different from those of the controls but they were significantly lower than those seen for phosphoric acid-treated beams. Compared to phosphoric acid, phytic acid treatment resulted in a reduced dentinal host-derived endogenous enzymatic activity and collagen degradation.

Assessment of current adhesives in class I cavity: Nondestructive imaging using optical coherence tomography and microtensile bond strength.

OBJECTIVES: To evaluate the sealing ability and the microtensile bond strength (MTBS) of different adhesive systems bonded to dentin in class I cavities. METHODS: Round tapered dentin cavities (3-mm diameter, 1.5-mm height) prepared in extracted human molars were restored using composite resin (Clearfil Majesty Posterior) with two-step etch-and-rinse adhesive system (Adper Single Bond 2: ASB2), two-step self-etch adhesive (Clearfil SE Bond: CSEB), all-in-one adhesives (G-Bond Plus: GBP; Tri-S Bond Plus: TSBP), or no adhesive (Control), or bonded using low-shrinkage composite with its proper adhesive (Filtek Silorane, Silorane Adhesive System: FSS). After 24-h water storage or 10,000 cycles of thermal stress, the specimens were immersed into a contrast agent. Two and three-dimensional images were obtained using optical coherence tomography (OCT). The mean percentage of high brightness (HB%) at the interfacial zone in cross-sectional images was calculated as an indicator of contrast agent or gap at the interface. The specimens were then sectioned into beams and the MTBS measured. RESULTS: The HB% (ASB2=TSBP=CSEBTSBP=GBP=FSS, ASB2>FSS) differed significantly among the adhesives. After aging, HB% increased for GBP and FSS specimens, and the MTBS decreased for FSS specimens (ANOVA, Tukey's post hoc, p<0.05). The HB% and MTBS were significantly and negatively correlated (p=0.002). Confocal laser scanning and scanning electron micrographs confirmed contrast agent infiltration within the gap. SIGNIFICANCE: There was a significant correlation between sealing performance and bond strength of the adhesives in the whole cavity. After aging, the two-step systems showed equal or superior performance to the all-in-one and Silorane systems.

Effect of a calcium-phosphate based desensitizer on dentin surface characteristics.

This study aimed to evaluate the ability of a newly developed calcium-phosphate desensitizer in dentin permeability reduction and its integration with dentin surface before and after immersion in artificial saliva (AS) under two different dentin surface characteristics; with or without the collagen exposure.Humandentin discs treated by EDTA to expose collagen fibrils or EDTA/NaOCl to expose plain dentin surface were subjected to a calcium-phosphate desensitizer (Teethmate Desensitizer; TMD), while non-desensitizer treatment served as control. TMD application showed the occlusion in dentinal tubules and reduction in dentin permeability up to 92%, regardless of dentin surface characteristics. After AS immersion, permeability reduction percent (PR%) significantly increased in EDTA/NaOCl pretreatment (p<0.05). Newly-formed crystallites were observed on desensitizer treated dentin and EDTA/NaOCl pretreatment control group, whereas the crystallites did not exist on EDTA pretreatment control group. Ultrasonication revealed the integration of the calcium-phosphate rich layer of desensitizer on dentin surface after AS immersion.

Effects of curing mode and moisture on nanoindentation mechanical properties and bonding of a self-adhesive resin cement to pulp chamber floor.

OBJECTIVE: This study aimed to investigate the effect of dentin surface moisture and curing mode on microtensile bond strength (MTBS) and nanoindentation characteristics of a self-adhesive resin cement. METHODS: Forty-four extracted human molars were distributed into four groups according to dentin surface moisture (dry or wet) and curing mode of the resin cement (light or chemical). Clearfil SA Cement (Kuraray Noritake Dental, Japan) was used for cementation of composite cores to the pulp chamber dentin. The specimens were sectioned into beams for MTBS test at the pulpal floor. Nanoindentation hardness and creep of the cement layer were measured under 100 mN load with 30s hold segment. Data were statistically analyzed using two-way ANOVA and Weibull distribution of MTBS (α=0.05). RESULTS: Moisture, curing mode or their interaction did not significantly affect mean MTBS values that ranged 17.6-22.6 MPa (p>0.05); however, the lowest characteristic strength was found in moist chemically cured group. Hardness ranged 437-512 MPa, and was not affected by the experimental factors (p>0.05). Nanoindentation creep ranged 9.3-10.9% with the chemically cured groups showing the highest values, indicating lower cross-linking and deformation resistance of their polymer network. SIGNIFICANCE: Additional moisture on dentin surface did not contribute to adhesion of the anhydrous self-adhesive resin cement to dentin. Light-curing, despite attenuation through the composite core, was beneficial and improved nanoindentation creep resistance of the cement. The difference was not, however, reflected in the mean bond strength or hardness values.

Effect of waiting interval on chemical activation mode of dual-cure one-step self-etching adhesives on bonding to root canal dentin.

OBJECTIVES: The purpose of this study was to evaluate the effect of waiting interval on the chemical activation of dual-cure one-step self-etching adhesives before placing resin core materials on the regional bond strength to root canal dentin. MATERIALS AND METHODS: Forty-eight post spaces prepared in human lower premolars were applied with four dual-cure one-step self-etching adhesives Estelite Core Quick: ECB/ECQ, Clearfil DC Core Automix: CDB/CDC, Unifil Core EM: UNB/UNC, BeautiCore: BTB/BTC as the manufacturers' instructions. These adhesives were cured with light activation for 10 s, or chemical activation with 0, 10, and 30 s waiting intervals prior to placing resin core material. Resin core materials were then placed into the post space and light-cured for 60 s. After 24h water storage, each specimen was serially sliced into 8, 0.6 mm × 0.6 mm thick beams for the µTBS test. The regional µTBS data were analyzed using three-way ANOVA and Dunnett's T3 test (p < 0.05). RESULTS: For the chemical activation with 10 and 30 s waiting intervals, ECB and CDB exhibited significantly improved µTBS, whereas for UNB and BTB, the µTBS were not significantly different but increased with waiting interval. On the other hand, light-activation of all the adhesives produced significantly higher µTBS to root canal dentin than chemical activation (p < 0.05), except for the UNB group. CONCLUSIONS: For the chemical activation of dual-cure one-step self-etching adhesives, a waiting interval prior to placing resin core material improved µTBS to root canal dentin. Polymerising the adhesives before polymerisation reaction of resin core material would be effective for bonding to root canal dentin. CLINICAL RELEVANCE: For chemical activation mode as well as light activation mode, pre-curing of adhesive layer before proceeding polymerisation of resin filling material would produce higher bonding performance to dentin in the cavity.

Effect of air-drying dentin surfaces on dentin bond strength of a solvent-free one-step adhesive.

The purpose was to evaluate the effect of air-drying dentin surfaces on the microtensile bond strength (µTBS) of a solvent-free onestep adhesive (Bond 1 SF). Twelve human molars were ground with 600-grit SiC paper. Before applying bonding agent, the dentin surface was rinsed with distilled water and blot-dried with tissue paper, followed by air-drying for 0, 3, 30, and 60 s using with a dental air syringe. After applying and curing Bond 1 SF, resin composite was incrementally built up. Specimens were then stored in distilled water for 24 h and then µTBSs were measured at a cross-head speed of 1 mm/min. Higher µTBS were observed when the dentin surface was air-dried for 3 s (33.2±6.8MPa)>0 s (26.7±4.5MPa)>30 s (22.6±5.5MPa)=60 s (20.4±5.0MPa). The results suggested that prolonged air-drying of the dentin surface removed water and decreased the bond strengths of Bond 1 SF.