In endodontic therapy, overfilling of gutta-percha point in root canals sometimes occurs due to wrong measurement of working length and overextension of gutta-percha point. Although a slight overfilling to periapical tissues (within 2 mm past the apical foramen) is tolerable, marked overfilling should be checked by postoperative recheck radiographs and/or clinical symptoms. In this report, three clinical cases of marked overfilling are described and long-term radiographic observation (6-14 years) was continued. Overfilled gutta-percha points on the radiographic observation were 3.0 (case 1), 2.5 (case 2), and 3.5 mm (case 3) in the left maxillary molar of a 47-year-old woman, in the left mandibular molar of a 45-year-old woman, and in the left mandibular premolar of a 39-year-old woman, respectively. In case 1, an overfilled point was cut after 1.5 years and disappeared after 3.5 years, and then apical radiolucency was improved after 6 years. In case 2, overfilled points started to minimize after 3 years and disappeared after 14 years. In case 3, an overfilled point was minimized after 13 years accompanied with improvement of apical lesion. None of the cases showed any significant clinical symptoms after the overfilling. These observations are interesting to longitudinally evaluate the disappearance of overfilled gutta-percha and the improvement of apical lesion.

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Objective: This study examined the anti-plaque effects of a new fluoride-releasing adhesive system including S-PRG filler particles. Materials and Methods: The bonding agents evaluated were: Mega-Bond, G-Bond and SI-R20401, which is a new fluoride-releasing adhesive system that contains S-PRG filler particles. In vivo anti-plaque tests were carried out by using resin blocks that were coated with the bonding agents. The blocks were bonded on upper first molars of volunteers, debonded, and then observed with SEM. On the other hand, in vitro anti-bacteria tests were performed by immersing the resin blocks previously coated with mucin or albumin, in a solution of bacteria (radioactively labeled), for 24 hrs. The salivary proteins adsorbed by the resin blocks were analyzed (SDS-PAGE). Results: Large bacterial accumulation was observed in the resin blocks coated with Mega-Bond and G-Bond; however, almost no bacteria were observed in those blocks coated with SI-R20401. Singularity protein was found on the surface of SI-R20401 (18.2-95 kDa). Conclusions: SI-R20401 bonding agent presented appropriate characteristics and might be useful for caries treatment. Additionally, its anti-plaque quality suggests that application of this bonding agent could maintain the concept of minimal intervention.

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We have recently reported that antigen presenting cells, such as dendritic cells and macrophages, showed different ultrastructural characteristics in different regions of normal rat molar periodontal ligament (PDL). Such morphological heterogeneity may be caused, at least in part, by different maturation/activation statuses of these cells due to region-specific microenvironmental conditions. In order to further understand the regional differences in the maturation/activation statuses of antigen presenting cells, in this study we performed real-time PCR analysis of MHC class II, CD83 (predict), CD86 and Toll-like receptor 4 mRNAs in furcal, mesial, distal and periapical regions of normal rat molar PDL. The results demonstrated that all the mRNAs examined were detected in all the regions. Expression levels were high in the furcal region, the area closest to the oral environment, and low in the periapical region. These findings support the notion that different regions of the PDL contain antigen presenting cells of different maturation/activation statuses, depending on microenvironmental differences, such as the degree of bacterial challenge.

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Radiotherapy for oral cancer causes radiation caries. This study evaluated the effect of γ-ray irradiation on resin/dentin bond strength, dentin microhardness and elastic modulus. One group of bovine incisors was irradiated with 60 Gy γ-rays using a cobalt 60 therapeutic machine. The control group of bovine incisors was not irradiated with γ-rays. Flat dentin surfaces were prepared on the labial side. The teeth were treated with the Clearfil SE Bond adhesive system. Clearfil AP-X hybrid composite was built up to 3×4×3 mm. The resins were light cured with 600mW/cm² for 40s. After storage for 24h, the teeth were sectioned to about 1.0 mm thickness. The slabs were trimmed (ca. 1 mm²) at the adhesive-dentin interface for the micro-tensile bond strength test (μ-TBS). The trimmed specimens were mounted on a testing apparatus, and stressed to failure under tension at 1 mm/min in an EZ test machine. Nano-indentation hardness and elastic modulus on both dentin surfaces were measured using a nano-indentation tester. μ-TBS (n=10), nano hardness (n=20) and elastic modulus data (n=20) were analyzed using Fisher's PLSD test. There was no significant difference in μ-TBS between the intact group and irradiated group (p>0.05). Nano hardness and elastic modulus of the irradiated group were significantly lower than those of the intact group (p<0.05). Irradiation with 60 Gy γ-rays had no effect on resin/dentin bond strength. However, 60 Gy γ-ray irradiation significantly decreased the microhardness and elastic modulus of dentin.

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Root canal treatment plays an essential role in the preservation of decayed teeth. Key requirements for successful root canal treatment are to control corrosion, to adequately remove sources of infection, to prevent root fractures, and to maintain the root canal seal for the long term. Vertical root fracture (VRF) is recognized as a major problem following root canal filling. VRF is found mostly in devitalized teeth and may lead to a rapid breakdown of the periodontal tissue along with the root fracture line, and often results in tooth extraction. One of the procedures for preserving VRF teeth is replantation of the tooth following adhesion of the fractured tooth outside the mouth using adhesive resins. However, risks of this method include fatal damage to the periodontal ligament resulting in tooth ankylosis and a prolonged time for healing. Recently, adhesive root canal sealers have been introduced to the market. Good results have been demonstrated when used for root canal filling, indicating that the materials could be used for VRF teeth. The aim of this study was to investigate the mechanical properties of adhesive root canal sealers to examine the possibility of using them for the treatment of VRF teeth. Twenty-four single rooted teeth extracted from patients for various reasons with sound root were used for this study. After root canal preparation using an Ni-Ti rotary file and chemical cleaning, the root canals were filled according to the single cone method using one of the following four combinations: 1) gutta-percha point with sealapex, 2) gutta-percha point with Accel primer, deintin activator and Superbond sealer, 3) gutta-percha point with Epiphany® and 4) gutta-percha point with AH Plus™. A novel microtensile test and SEM were used to evaluate the adhesive properties. The sealing capacity was evaluated by a fluid filtration system. The permeability test was also performed between Superbond C & B and Superbond sealer. The adhesive property and sealing capacity of Superbond sealer were significantly better than those of the other sealers (p<0.05). The permeability of Superbond sealer was also significantly higher(p<0.05). In SEM observations, a hybrid layer approximately 3-4 μm in thickness was observed at the interface between Superbond sealer and dentin. These findings suggest that Superbond sealer possesses adequate properties for sealing root fracture lines of VRF. Root canal filling of VRF teeth with Superbond sealer may be a useful methodin in view of its simplicity and longterm clinical success.

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Most sensations in the oral cavity are afferent sensory responses from the trigeminal nerve. We previously reported that persistent pain and inflammation in periapical periodontitis is associated not only with nerve fibers immunoreactive to calcitonin gene-related peptide (CGRP) in sensory nerve fibers of the periodontal ligament, but also with tyrosine hydroxylase (TH) as a rate-limiting enzyme for the synthesis of catecholamine as a representative marker of sympathetic nerve fibers. In this study, the influences of periapical periodontitis on the trigeminal ganglion were histologically evaluated. A rat periapical periodontitis model was produced. The rats were fixed by perfusion. The mandible and trigeminal ganglion were resected, and frozen serial sagittal sections were prepared and stained with hematoxylin eosin (HE) and immunohistologically stained with TH. HE staining of periapical tissue showing pulpal infection revealed an enlarged periodontal space and increased inflammatory cells, suggesting periapical periodontitis. The intensity of TH expression in the periodontal ligament was increased in rats with compared to controls without periapical periodontitis. With periapical periodontitis, the number of TH positive regins in the trigeminal ganglion was significantly higher compared with the control (p<0.05). These results suggest that the sympathetic nerves are involved in pain and inflammatory responses at the trigeminal ganglion level in periapical periodontitis.

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In recent years, dental patients have demanded more esthetic restorations and the MI concept has been widely recognized in the dental industry. Therefore, composite resin restorations are often performed to satisfy these demands. Composite resins are esthetic restorative materials and are semitransparent to reproduce dentin colors. Composite restoration is known to be markedly affected by resin thickness and the color of underlying dentin at the cavity floor. Experiments were conducted in order to determine the ability of different composite resins to mask the color of stained dentin. The following four restorative materials were used: Solare (hybrid-type composite resin), EsteliteΣ (SFR composite resin), Clearfil Majesty (hybrid-type composite resin) and Beautifil II using S-PRG filler. Two shades that are common to all four resins were used: standard shade resin A3 and opaque shade resin A3. The following four samples were prepared: 1.5-mm standard shade resin; 1.5-mm opaque shade resin; 1.0-mm standard shade resin A3 overlapped with 0.5-mm opaque shade resin A3 (total thickness: 1.5 mm); and 0.5-mm standard shade A3 and 1.0-mm opaque shade resin A3 (total thickness: 1.5 mm). Spectrophotometric colorimetry was performed (background: white board, black board, mat water-based color charts with L* values of 75, 65, 55, 45 and 15) to determine XYZ and CIELAB values. The results showed that with a resin layer thickness of 1.5 mm, an opaque shade resin alone was not sufficient to mask background colors. These results suggest that when treating shallow and severely stained cavities, an opaque shade resin layer should be made as thick as possible to mask background colors. Of the four materials examined in the present study, BE using the S-PRG filler with light-diffusing properties was most effective in masking background colors, thus confirming that it is a suitable material for esthetic restoration of stained cavities.

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Curing units using blue light emitting diodes (LED) as a source of light are superior in energy efficiency with reduced heat generation. The curing units can be made compact, which is beneficial in clinical situations. Recently, high power density curing units which utilize blue LEDs whose spectral distributions fit those of photo-initiation have been used to polymerize visible light-cured restoratives. However, although new types of curing units using different LEDs have been available, little is known about their curing characteristics. The purpose of this study was to evaluate the curing irradiation characteristics of LED curing units in terms of curing depth, polymerization shrinkage, and Knoop hardness. The results were as follows: 1. Spectral distributions of the curing units were different and the peak wavelength was 453-465 nm for LED curing units, and 480 nm for halogen lamp curing units. 2. The power density of LED curing units ranged from 601 to 887 mW/cm², and was 832 mW/cm² for halogen lamp curing units. 3. The curing depth ranged from 1.93 to 2.87 mm for LED curing units, and from 1.92 to 2.47 mm for halogen lamp curing units. 4. Volumetric change ranged from 1.38 to 2.03% for LED curing units, and from 1.22 to 1.59% for halogen lamp curing units. 5. Knoop hardness number on the irradiated surface decreased as the distance from the center increased.

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The purpose of this study was to analyze the shaping ability of Mtwo® nickel-titanium (Ni-Ti) rotary instruments (VDW, Germany) in comparison with K3® (SybronEnd, USA) and ProTaper® (Dentsply-Maillefer, Switzerland). Simulated J-shaped and S-shaped canals in resin blocks (n=24, each) were prepared with Mtwo (10/04, 15/05, 20/06, 25/06) and ProTaper (S1, S2, F1, F2) instruments using a single-length technique, and with K3 (25/08, 30/04, 25/04, 25/06) instruments using a crown-down preparation technique (n=8, each). Using image analyzing software, pre -and post-instrumentation images were superimposed and material removal was measured for the outer and the inner sides. In J-shaped canals, measuring levels were set at 1, 2, 3 and 5 mm from the endpoint of preparation. In S-shaped canals, two measuring levels corresponding to the coronal and apical curvatures were set. The time required for canal preparation was also recorded. Data were analyzed by one-way ANOVA and Bonferroni-Dunn test. The results demonstrated that, in both J- and S-shaped canals, Mtwo instruments tended to remove more material from the inner side and less from the outer side compared to ProTaper and K3 instruments. Mtwo instruments were significantly faster than K3 instruments (p<0.05) in preparing S-shaped canals, although the three types of instruments showed no significant differences in the working time for J-shaped canals. These findings suggest that Mtwo instruments have the ability to cut inner canal walls of the apical curvature more efficiently than ProTaper and K3 instruments, which might facilitate efficient preparation of double-curved canals.

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Residual roots of teeth often have large amounts of softened dentin in the root canals, making the construction of an abutment impossible. Moreover, because removal of the softened dentin leaves only a thin layer of healthy dentin, the tooth is usually extracted. In my first report I examined the rehardening or recalcification of softened dentin using nano-hydroxy-apatite (HA) as the experimental material. I artificially softened all the dentin in a tooth, and found that with active penetration of nano-HA to deep within the dentin, the artificially softened dentin could be rehardened to nearly the hardness of intact dentin. It was then necessary to investigate the bonding properties of rehardened root canal dentin, which is necessary for conducting prosthetic procedures. Metal and resin materials are used in constructing abutments. It is reported that with resin the bonding strength is consolidated through direct bonding with HA. Therefore, in this study I investigated the bonding properties of soft root canal dentin that had been rehardened. The bonding strength of the resin filling the root canals was measured using a "punch through" method. The results showed that the bonding strength of artificially softened root canal dentin, which had been rehardened by using nano-HA, was approximately 35% of the bonding strength of intact root canal dentin. After nano-HA had been used to improve the bonding strength, 35% HEMA solution dentin primer was applied. As a result, bonding strength increased to 64%. The basic structure of dentin was seen and residual resin tags were observed in the dental tubules under SEM, confirming that hardening occurred through the action of nano-HA. Furthermore, after hardening, adhesive properties appeared. Bonding strength increased with taper angle in the root canals. It was also found that bonding strength increased with the amount of nano-HA. The results of this and my previous report indicate that softened dentin can be preserved, abutments constructed, and crown prosthesis procedures conducted without extracting the tooth. These findings highlight the possibility of more reliable treatment in the future.

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Objectives: We aimed to establish a new method for determining the hardness of human carious dentin without extraction. Method: We produced a handy indentation device (weight: 80 g) with a conical sapphire indenter (0.5 mm φ-48°-0.7mil). Operating load for indentation was set at 150gw. The carious dentin of an extracted human tooth was ground with a series of emery papers. The sapphire indenter was pressed into various places of the remaining carious dentin. The diameter (μm) of each indentation was measured under a microscope attached to a hardness tester (MHT-1, Matsuzawa). Then Knoop hardness number (KHN) was determined with the hardness tester at the site of 25 μm from the margin of each indentation. The data of the diameter and the KHN were plotted on a graph, and the relation between the diameter of indentation produced by our device and the hardness determined with the hardness tester was examined. Results: We revealed a correlation between the diameter of indentation and the KHN, enabling us to convert the diameter into the KHN. Therefore, it seems reasonable to suppose that if we indent carious dentin using the device and take an impression with a silicone impression material clinically, and then measure the diameter of indentation on the replica model, we can determine the KHN of the dentin without extraction. Conclusion: The new method using the handy indentation device might allow us to determine the hardness (KHN) of human carious dentin under clinical conditions.

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It is widely known that most bacteria produce exopolysaccharide and exist in the form of communities, commonly referred to as biofilm. Since the ability of bacteria to form biofilm is considered an important factor in persistent infections, it is important to isolate these bacteria from lesions and study their mechanism of biofilm formation. The screening of biofilm-forming bacteria is difficult because it requires the measurement of viscosity of culture supernatants and scanning electron microscopic (SEM) observation of cell surface structures. We used Congo red agar (CRA) plates to screen biofilm-forming bacteria from the oral cavity. Whole saliva from five healthy volunteers was diluted to 10^-4 to 10^-6 and used to inoculate CRA plates. The bacterial cultures were incubated aerobically at 37℃ for 24 hours. Using a stereoscopic microscope, the colonies were divided into four groups: black colonies with rough periphery (RB), lucent or red colonies with rough periphery (RL), black colonies with smooth periphery (SB) and lucent or red colonies with smooth periphery (SL). The cell surface structures of the bacterial strains obtained from arbitrarily selected colonies in each group (RB: 24; SB: 24; RL: 8; SL: 13) were further studied by SEM, and each strain was identified by 16S rRNA gene sequencing. Bacterial strains that formed rough periphery colonies (RB and RL types) on CRA under aerobic conditions expressed dense fibrillar structures, which is a typical phenotype for biofilm-forming bacteria. On the other hand, more than 90% of bacterial strains that formed colonies with smooth periphery (SB and SL types) showed biofilm-negative cell surfaces. In addition to Congo red reaction, the reaction of bacteria obtained from each colony type to calcofluor white (CFW), which binds to β1-3 and β1-4 carbohydrate linkages and fluoresces under long-wavelength UV light, was examined. CFW reaction did not correspond to biofilm phenotype. These results suggest that oral bacteria that form colonies with rough periphery cultured under aerobic conditions on CRA have the capacity to form biofilm. We also found that CRA can be applied as a simple method for screening oral biofilm-forming bacteria.

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