This study investigated the influence of the nanofiller loading level on the shear bond strength (SBS) fatigue limit of a methyl methacrylate (MMA)-based cement. A silver-palladium-copper-gold alloy disk was air-abraded and conditioned with a primer for noble metals. Hydrophobic fumed silica nanofillers (average particle size 7 nm) were added to 4-methacryloyloxyethyl trimellitate anhydride/MMA monomer in the following percentages (wt%): R0 = 0%; R1 = 1%; R3 = 3% and R5 = 5%. The monotonic SBS to the disk of the cement polymerized after mixing each monomer, polyMMA powder, and catalyst was determined after thermocycling. A conventional composite cement was used as a control (RelyX Unicem Clicker: RX). A staircase approach was used to determine the SBS fatigue limit of each material. After thermocycling, specimens were submitted to either 10,000 cycles (5 Hz) until adhesive failure, or until specimen fracture, and the minimum number of specimens tested for each material was 15. The SBSs of R3 and R5 were significantly lower than those of the other three cements, and the SBS fatigue limit of R5 was the lowest. The addition of more than 3 wt% of nanofiller to the monomer caused a significant deterioration in the SBS fatigue limit.

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The objectives of this study were to evaluate the ability to remove clinically produced dentin smear-layer and to investigate the relationship between the ability and the short-term bonding effectiveness, using six commercially available one-step adhesive systems. Two types of dentin surface produced using a regular-grit diamond bur or #2000 SiC paper were conditioned with one out of six adhesive systems, that is, G-Bond Plus (GP), Absolute 2 (AB), Bond Force (BF), BeautiBond (BB), Hybrid Coat II (HC), or Clearfil S3 Bond (TS) without light-curing, and rinsed with acetone and observed by scanning electron microscope (SEM). Moreover, the other specimens built up resin composites bonded with one out of the above six adhesives were subjected to micro-tensile bond strength (μTBS) testing. Additionally, the interfaces were observed by transmission electron microscope (TEM). According to the SEM and TEM images, AB showed a strong ability to remove the smear-layer, whereas the other adhesives could not dissolve the smear-layer and the smear-plugs. For GP, the μTBS to the regular-grit diamond bur ground surface was significantly higher than that to the #2000 surface, whereas the μTBSs to the #2000 surface were significantly higher than those to the regular-grit diamond bur ground surface for AB and TS. For BF, BB, and HC, the μTBSs to the regular-grit diamond bur ground surface and the #2000 surface were not statistically different. It is concluded that the relationship between the ability to remove the dentin smear-layer and the short-term bonding effectiveness differs according to the adhesives used.

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The purpose of this study was to examine the influence of light intensity on surface free energy characteristics and dentin bond strength of a dual-cure direct core build-up resin system. Bovine mandibular incisors were wet-ground on 600-grit SiC paper. Adhesives were applied and cured with light intensity of 0 (no irradiation), 200, 400, or 600 mW/cm2. The surface free energy of the adhesive was determined by measuring the contact angles of three test liquids placed on the cured adhesive. To determine the dentin bond strength, the core build-up resin pastes were condensed into the mold on the adhesive-treated dentin surfaces according to the manufacturer’s instructions. The resin paste was cured with the same light intensity as those used for the adhesive. Specimens were stored in water maintained at 37°C for 24 h, followed by shear testing at a crosshead speed of 1.0 mm/min in a universal testing machine. One-way ANOVA and Tukey HSD test were performed with the significance level set at 0.05. The surface free energy of the cured adhesive decreased with an increase in the light intensity of the curing unit. The greatest bond strengths were achieved when the resin pastes were cured with the strongest light intensity. The data suggest that the dentin bond strength of the core build-up system is affected by the light intensity, which is also influenced by the surface free energy of the adhesives.

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The purpose of this study was to evaluate the effect of opaque materials, abutment materials and luting materials on the fracture resistance of composite crowns for premolars. Abutment teeth were fabricated with either dental alloy (ME) or composite resin (CR). Composite crowns were fabricated with one of two opaque materials, namely a conventional material (Metacolor Prime Art Top Opaque: TO) and a fiber-premixed material (Metacolor Prime Art Jacket Opaque: JMO) at the internal layer. Two different luting materials, namely composite resin cement (Panavia F2.0: PA) and PMMA resin cement (Super-Bond C&B: SB) were used. A total of 48 specimens for eight groups (n=6) were subjected to 280-N cyclic impact loading at 1.0 Hz. The number of cycles which caused the composite crowns to fracture was defined as its fracture resistance. As a result of three-way ANOVA, a significant difference was observed in opaque materials (p<0.001, TO<JMO) and abutment materials (p<0.001, ME<CR), but no significant difference was observed in cement (p=0.92). Also, the JMO/CR group showed the highest resistance (PA group: an average of 1,174,625 times, SB group: an average of 1,067,541 times) in each luting material.

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To minimize the frequent visit to the clinic and chair occupation time, and to improve the predictability of the treatment, the so-called simultaneous treatment for root canal filling and core construction (STRC) for non-vital teeth was suggested by a core construction research task force of an adhesive dental clinical research working group in 2007. The key points of this treatment are to use: 1) a fiber post system, called i-TFC system with elastic modulus similar to that of root canal dentin, 2) and a highly biocompatible, excellent bonding resin cement, 4-META/MMA-TBB resin, to function as an adhesive sealer to carry out the root canal filling and the core construction simultaneously. The technique and procedure for STRC were established in our clinic in 2010. The clinical results of 55 cases (30 patients) more than 5 years after treatment are reported. The success ratio and the survival ratio of these 55 cases are 90.9% and 98.2%, respectively. These results show that STRC treatment is comparable to conventional treatments, minimizing the frequent visit to the clinic and chair occupation time.

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