Purpose: Dental pulp is involved in nutrient supply to the dentin and the maintenance of homeostasis, and plays a major role in reparative dentin formation. Dental pulp inflammation associated with the progression of dental caries facilitates the production of inflammatory cytokines such as interleukin-1β (IL-1β) and enzymes such as matrix metalloproteinases (MMPs) in the pulp tissue, resulting in tissue destruction. Elucidating the pathogenesis of pulpitis is important for dental pulp preservation. Thus, we investigated MMP-3 production by inflammatory cytokine IL-1β stimulation and extracellular signal-regulated kinase 1/2 (ERK1/2), an intracellular signal transducer, in human dental pulp fibroblast-like cells (HPFs).
 Methods: Under approval No. 070716 of the Ethics Committee of Osaka Dental University, HPFs from teeth extracted during orthodontic treatment were primarily cultured for three to ten generations to be used in the present study. HPFs were cultured in serum-free α-MEM, followed by the addition of IL-1β (0, 1, 2, 5, and 10 ng/ml) and an MEK inhibitor (U0126). MMP-3 production and ERK1/2 phosphorylation after the stimulation were examined by Western blotting using their detection antibodies. The supernatant was subjected to electrophoresis by SDS-PAGE using 1 mg/ml gelatin to be examined by gelatin zymography.
 Results: MMP-3 production in HPFs was enhanced by IL-1β stimulation. ERK1/2 phosphorylation was enhanced in an IL-1β concentration-dependent manner. Furthermore, the MEK1/2 inhibitor U0126 inhibited the ERK1/2 phosphorylation and MMP-3 production enhanced by IL-1β stimulation.
 Conclusion: The results of this experiment suggest that the MEK1/2 and ERK1/2 pathways are involved in MMP-3 production enhanced by IL-1β stimulation in HPFs.

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 Objective: Recently, the Er: YAG laser has been applied clinically and shown excellent effectiveness for the ablation of dental hard tissue. However, its ablation efficiency is significantly inferior to that of high-speed rotary ablation, and the longer treatment time has posed problems. To improve the ablation efficiency, attempts to increase the tip output and pulse repetition rate have been made, but various problems, including the effect on dental pulp, remain unresolved. Paying particular attention to the irrigation device, our study group prepared a test tip that sprays the irrigation fluid as a mist by modifying the conventional irrigation mechanism with the cooperation of J. Morita Mfg, and evaluated the ablation efficiency.
 Materials and Methods: Healthy human molar teeth, used as samples, were filed to the enamel and dentin using a model trimmer, polished using waterproof abrasive paper to #2000, and irradiated with a laser by operating the moving stage at 1 mm/s. Laser irradiation was performed by setting the distance to the sample at 0.5, 1.0, and 2.0 mm. The group in which laser irradiation was performed using C600F was regarded as a control group, and the group in which laser irradiation was performed using the test tip was regarded as the mist spray group. Each sample was examined under a laser microscope, and the cross-sectional area was calculated (n=5).
 Results: The cross-sectional area was significantly greater in the mist spray group than in the control group at an irradiation distance of 0.5 mm in enamel and at 0.5 and 1.0 mm in dentin (p<0.05).
 Conclusion: In laser ablation of dental hard tissue, spraying the irrigation fluid as a mist is considered to be effective for improving the ablation efficiency.

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 Purpose: We experimentally prepared a novel LED curing unit (MI-head) with a small tip (diameter: 2.1 mm) capable of irradiating light close to the gingival wall. In this study, we compared the MI-head and a conventional LED light curing unit, Pen Cure, to investigate the influence of the curing unit on adhesion to the gingival wall of class II cavities.
 Methods: Dentin adherend surfaces were prepared on extracted bovine teeth. Clearfil Mega Bond (MB) was applied to the surface, followed by light irradiation using Pen Cure or the MI-head at various irradiation distances and durations. Resin paste was then applied, and tensile bond strength (TBS) was measured after the specimens were placed in a 37°C water bath for 24 h. Class II cavities were prepared in extracted human teeth. After setting the matrix, MB was applied to the tooth surface, followed by light irradiation from the cuspal side using Pen Cure, or from the gingival wall side of the cavity using the MI-head. Resin paste was then incrementally filled and thermal stress was applied. Each sample was immersed in 5% basic fuchsin solution for 24 h, and marginal leakage was observed under an optical microscope. A class II cavity was prepared on the mesial side of the left first molar in an artificial mandibular model, and the light intensities of Pen Cure and the MI-head were measured under the same irradiation conditions as employed in the marginal leakage test.
 Results: Although TBS was significantly higher when irradiated with MI-head, marginal leakage could not be prevented. The light intensity of Pen Cure was significantly higher than that of the MI-head.
 Conclusion: The results of this study suggest that improvements in the irradiation method and prolonged irradiation are necessary to achieve adequate bond strength by the bonding agent applied to class II cavities using the MI-head.

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 Purpose: We measured the hardness of demineralized dentin over time using the Cariotester to determine the effectiveness of several types of pulp-capping agent for IPC.
 Methods: Extracted human molars were used to prepare dentin samples with a diameter of 10 mm and thickness of 2 mm. Sound dentin samples were immersed in lactic acid solution and were regarded as demineralized when the value obtained using the Cariotester was approximately 20 KNH. HY-Bond Temporary Cement Soft (Shofu), Neodyne-α (Neo Dental Chemical Products), Dycal (Dentsply), and Calcipex Plain II (Nippon Shika Yakuhin) with a 60% calcium hydroxide mixture were used as the pulp-capping agents in the present study. Each pulp-capping agent was applied to the surface of demineralized dentin and covered with base cement. After the base cement solidified, pulp-capped dentin samples and controls were divided into two groups: those placed in a container with 100% humidity and those immersed in remineralization solution, and stored at 37°C in a thermostatic chamber for 1 and 3 months. The hardness of the capping agent-applied region was then measured. Data were analyzed using a one-way analysis of variance and Tukey's test (α=0.05). Pulp-capping agent-applied surfaces were also observed under SEM.
 Results: The hardness of demineralized dentin increased with the application of Dycal, Calcipex Plain II, and the 60% calcium hydroxide mixture, and mineralized substance-like aggregates were deposited on the surface of and between collagen fibrils. It was suggested that the remineralization of demineralized dentin depended on the calcium hydroxide concentration contained in a pulp-capping agent.
 Conclusion: The hardness of demineralized dentin increased and remineralization features were noted following the application of a pulp-capping agent containing over 27% calcium hydroxide.

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 Purpose: The solubility of synthesized organometallic compound silver methacrylate in pure water is very low. However, by liquefying silver-methacrylate in an aqueous solution which possesses a hydrophilic group, silver ions can react with even trace amounts of chloride ions to form silver chloride, which is insoluble in water and causes cloudiness. The application of this principle enables the amount of chloride ions in water to be determined. We have developed a new detection solution by synthesizing a particular silver methacrylate compound and adding it to various organic solvents, which can measure the content of chloride ions in electrolyzed strongly acidic water.
 Methods: To develop a system for determining the quantity of residual chloride in water, 0.01, 0.1, and 0.5 wt% silver methacrylate were dissolved in five water-soluble organic solvents (formaldehyde, acetonitrile, N, N-dimethylformamide, lactic acid, and acrylic acid) to produce a detection solution. The solution was poured into electrolyzed strongly acidic water. The acidic water was diluted using ultrapure water 0, 2, 4, 8, 16, 32, and 64 times. We measured the changes in the permeability of its cloudiness, based on the flux of light from an ultraviolet-visible spectrometer after 0, 30, and 60 min (mode:% transmission, 300 nm). The data (%T) were analyzed using four-way analysis of variables (ANOVA; Factor A: solvent, B: silver methacrylate content (wt%, as solute), C: reaction time from flooding, and D: dilution factor of electrolyzed acidic water). We identified the best conditions for practical applications. Next, using the same data, regression analysis was applied to the value of the residual chloride content (ppm) of the electrolyzed water at each dilution factor before flooding with the detection solution, and the corresponding transmission factor (%T) after flooding with the detection solution.
 Results: ANOVA showed significant differences among all the main effects and interactions. In three types of detection solution, the %T values of each acidic water hardly changed for reaction times exceeding 30 min. Additionally, their reactivities with chloride ions were excellent, and the changes in %T corresponded to the dilution factor of the electrolyzed acidic water. Regression analysis was significant in constructing a calibration curve for a detection solution consisting of N, N-dimethylformamide (purity: 99.5%) and 0.01 wt% silver methacrylate, for reaction times of 0, 30, and 60 min. A reaction time of 60 min gave y=−0.081x+97.031 (r=0.9605^**).
 Conclusion: These results show that our detection solution is suitable for practical applications, and can be used to determine the amount of residual chloride in electrolyzed acidic water in dentistry.

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 Purpose: Ni-Ti orifice openers were designed to prepare the coronal and middle third of canals. The purpose of this study was to compare the generated cutting torque after 10 continuous uses at two rotational speeds.
 Methods: EndoWave .08 Ni-Ti rotary instruments (EW; J. Morita) and standardized straight root canal models were used in this study. The root canal model made of resin, which has a cut feeling similar to that of dentin, was used. A computer controlled torque testing device was used for this experiment. Instruments were inserted to a depth of 8 mm into the root canal. The rotational speed was fixed at 300 rpm and 600 rpm, respectively. The insertion speed into the root canal was set at 0.01 mm/sec. The torque generated under each experimental condition was recorded. The cutting blade was cleaned with a toothbrush after each use and was subjected to ultrasonic cleaning for five minutes. The same cutting procedure was repeated 10 times. Five root canal models were used for each experimental condition. The cutting efficacy was analyzed based on the torque-insertion distance and the variation in torque (ΔT) was calculated. The file was observed morphologically after the final cutting.
 Results: The torque generated in root canal orifice enlargement was found to increase as the instrument was inserted further into the root canal. As shown by the torque-insertion distance curve of EW, the cutting torque increased with the number of cutting times. At both rotational speeds, ΔT tended to increase and cutting efficiency tended to decrease as the cutting time was increased. From observations of the cross section of the cutting part, wear was observed in the cutting edge after the final cutting, and this wear indicates increased ΔT.
 Conclusion: These results suggested that prolonged use of EW .08 taper Ni-Ti rotary instruments significantly reduces their cutting efficiency.

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 Purpose: The purpose of this study was to evaluate the effect of remaining tooth thickness (RTT) on resin composite bond strength to the mesial wall and distal wall when using two-step and one-step self-etching adhesive systems.
 Methods: The occlusal enamel was ground to expose flat superficial dentin surfaces of human molars. Box-form occlusal cavities of 3 mm long×5 mm wide were prepared to a depth of 4 mm below the flat dentin surfaces. The buccal and lingual walls of cavities were removed to make flat surfaces (mesial wall and distal wall) for bonding. Each specimen was restored with one of two adhesives: the one-step self-etching system Clearfil tri-S Bond (Kuraray Noritake Dental, TS) ; or the two-step self-etching system Clearfil SE Bond (Kuraray Noritake Dental, SE) ; followed by buildup using Z100 resin composite (3M ESPE). After 600 mW/cm² light-curing for 40 s, teeth were stored for 24 hours in water. The teeth were sectioned perpendicularly to the flat mesial and distal wall dentin to obtain approximately 1 mm² beams. RTT from the resin-dentin bond to the tooth surface was measured in each slab using a digital caliper.
 The micro-tensile bond strength (μTBS, MPa) was determined. Data (n=6) were analyzed using Bonferroni's test.
 Results: TS showed significantly lower μTBS for the RTT<2 mm substrates compared with that of the RTT≥2 mm group (p<0.05). However, there was no significantly different μTBS between the RTT<2 mm group and RTT≥2 mm group using SE (p>0.05).
 Conclusions: Bonding to wall dentin was affected by remaining tooth thickness when using the one-step self-etching system Clearfil tri-S Bond. However, for the two-step self-etching system Clearfil SE Bond, bond strength to wall dentin was not affected by the remaining tooth thickness.

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 Purpose: It is widely recognized that removal of the smear layer by etching and penetration of resin into decalcified dentin and its polymerization and curing by priming and bonding are necessary to acquire favorable adhesion to dentin. However, these treatments take time and the procedure is complex and technique-sensitive, and thus a simple clinical procedure for composite resin restoration is strongly desired. Self-adhesive composite resin requiring no tooth surface treatment for adhesion would be optimal and particularly useful for the elderly and children; this is a new approach to composite resin restoration.
 Considering that it may be clinically applicable as a liner, we prepared trial self-adhesive flowable composite resins using existing flowable composite resins and one-step bonding agents, and evaluated their adhesiveness to human dentin.
 Methods: The experimental self-adhesive flowable composite resins were bonded to grinding human dentin and to smear-free dentin, and subjected to micro-vibration. The specimens were stored for 24 hours in distilled water (37°C), then their tensile bond strength was measured. The means and standard deviations were determined for each trial self-adhesive flowable composite resin group.
 Results: The mean adhesive strength of self-adhesive flowable composite resin prepared by mixing an existing flowable composite resin (Beautifil Flow F02; 80 wt%, 90 wt%) and solvent-removed one-step bonding agent (BeautiBond; 20 wt%, 10 wt%) was very low (2 MPa or lower), whereas that of self-adhesive flowable composite resin (trial 6) prepared by mixing self-adhesive composite resin with a solvent-removed one-step bonding agent Bond Force at 50 wt% and 50 wt% inorganic filler was 5.26 MPa, similar to that (5.62 MPa) of Fusio Liquid Dentin sold in the U.S., and the pH of these in contact with moisture was less than 3.0. In addition, the adhesive strength of various trial self-adhesive resins after removal of the smear layer from the adhered surface tended to increase, and that of Bond Force at 50 wt% and 50 wt% inorganic filler was 6.49 MPa. Furthermore, when micro-vibration was added to the mixing self-adhesive composite resin with a solvent-removed Clearfil Tri-s Bond at 50 wt% and 50 wt% inorganic filler, the mean adhesive strength was 6.55 MPa.
 Conclusion: It is suggested that the adhesive strength of trial self-adhesive flowable composite resins prepared with two commercial one-step bonding agents (Bond Force and Clearfil Tri-s Bond) is sufficient for clinical application as a liner.

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 Purpose: Every patient would like minimally invasive and aesthetic dental treatment; hybrid ceramic restoration is one treatment that can satisfy such desires. This study examined the effect of dynamic load simulating mastication on the microleakage of MODB hybrid ceramic onlay restorations.
 Methods: The standardized MODB onlay cavity was prepared in 32 extracted human lower molars using a cavity duplicator with a master cavity. The dentin surfaces of duplicated cavities were pretreated with an all-in-one adhesive system (Crearfil Tri-S Bond, Kuraray Noritake Dental) and were sealed with a low-viscosity resin composite (Clearfil Protect Liner, Kuraray Noritake Dental). Impressions of immediate sealed cavities were taken and were poured with a high-strength dental stone. MODB onlays were fabricated on the stone dies with a hybrid ceramic material (Estenia C & B, Kuraray Noritake Dental). The onlays were bonded with a dual-cure resin luting cement (Clearfil Esthethic Cement, Kuraray Noritake Dental). Restored specimens were divided into two groups (n=16) : a group with dynamic load stress (S+) simulating mastication, and a group without stress (S−, control). For the S+ group, dynamic load stress (16.0 kgf×3×10⁵ times) was applied to the restored specimens in circulated water at 37°C. For the S− group, no stress was applied. The restored specimens with and without dynamic load stress were immersed in 1% methylene blue solution at 37°C for 60 min. Each specimen was sectioned mesiodistal-vertically to obtain two slabs of 1.0-mm thickness. The slabs were polished with a series of SiC papers up to 2,000 grid. Microleakage in the lingual (L) and gingival (G) walls of each slab was evaluated by a graded criterion. The data of microleakage were examined using the Kruskal-Wallis test.
 Results: Microleakage of L (S+) was significantly greater than that of L (S−) at p<0.01, although no difference was found between the microleakage of G (S+) and G (S−). The leakage of L (S+) was significantly greater than that of G (S+) at p<0.05, but the leakage of L (S−) was statistically similar to that of G (S−).
 Conclusion: The dynamic load significantly increased the microleakage in the lingual wall of the MODB hybrid ceramic onlay restoration. However, the leakage in the gingival wall did not vary with the stress. The difference in the microleakage between lingual and gingival walls was recognized only under the dynamic load condition.

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