Purpose: It is well known that intracanal fractured instruments make it difficult to disinfect the entire root canal system, and that hasty removal attempts may lead to overenlargement and perforation of the root canal wall. In this study at the Clinic of Operative Dentistry and Endodontics in Kyushu Dental College Hospital, we surveyed how many fractured instruments found in root canals were successfully removed. Methods: The research covered 35 root canals involving fractured instruments within a 3-year period (2008-2010). Ultrasonic instruments were used to remove the fractured instrument under a dental microscope. The referral rate from other clinics, tooth types, numbers, and locations of fractured instruments in a canal, and the rate of successful removal of the fractured instrument, were analyzed. Results: The referral rate from other clinics for the purpose of removing fractured instruments was 63 %. Fractured instruments were most frequently found in the mesial root of lower molars. The maximum number of fractured instruments found in a root canal was 3. The fractured instruments were mostly located in the apical and middle portions of the root canal. The overall rate of successful removal was 89 %, and the functional recovery of the tooth was also achieved. Conclusion: The rate of successful removal of fractured endodontic instruments by ultrasonic instrument under a dental microscope is higher than that by the conventional method, suggesting that this method may be useful for removing fractured intracanal instruments.

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Purpose: Carbamide peroxide is included in medical whitening agents, especially for home-use whitening agents. As its mechanism of action, carbamide peroxide is known to dissociate into urea and hydrogen peroxide. Subsequently, it extracts active oxygen, which affects and bleaches out various substances that discolor or otherwise affect teeth, thereby whitening them. Both hydrogen peroxide and carbamide peroxide, which were originally used as oral bactericides, not for whitening, are considered to be safe agents without toxic consequences or side effects. On the issue of whether urea hydrogen peroxide, which is frequently used for home whitening, can prevent caries or not, we researched its antibacterial action using in vitro experiments. Methods: Using Streptococcus mutans PS-14 strains, Streptococcus sobrinus 6715 strains, and Actinomyces naeslundii ATCC19246 strains, we measured the minimum growth-inhibitory density with the 10-times serial dilution method. Furthermore, we examined their antibacterial action against resting cells in terms of changes in concentration and over time. In addition, we took the measured value of GTF activity as a WIG production inhibition test. Results: 1. The minimum inhibitory concentration against S. mutans was found to be 250 μg/ml. 2. The minimum inhibitory concentration against S. sobrinus was found to be 300 μg/ml. 3. The minimum inhibitory concentration against A. naeslundii was found to be 300 μg/ml. 4. The antibacterial activities were found to be a bactericidal effect against resting cells of S. mutans, S. sobrinus and A. naeslundii. 5. Carbamide peroxide considerably inhibited the sucrose-dependent water insoluble glucan synthesis activity of crude glucosyltransferase produced by S. mutans PS-14 and S. sobrinus 6715. Conclusions: From the above results, carbamide peroxide was found to have a prominent bactericidal effect against cariogenic bacteria, suggesting that it has an anticariogenic effect.

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Purpose: Reciproc nickel-titanium instruments are designed specifically to prepare root canals using one single instrument under reciprocating movement. This study aimed to determine the shaping ability of Reciproc instruments in comparison with twisted file (TF) instruments, with regard to the working time and post-instrumentation canal shape in simulated curved canals. The influence of prior glide path preparation on the shaping ability of Reciproc instruments was also investigated. Methods: Simulated canals with a 30-degree curvature in resin blocks were divided into 4 groups (n=8, each) and prepared using the following instruments: Group 1, Reciproc R25 (25/.08); Group 2, RaCe (10/.04; for glide path preparation) followed by Reciproc R25; Group 3, RaCe (10/.06) followed by Reciproc R25; and Group 4, TF (25/.08). The time required for instrumentation was recorded. After preparation of the canal, the increase in canal width at the inner and outer sides of the curvature was measured by digital image analysis at 1-, 2-, 3-, 4-, 5-, 7-, 9- and 12-mm levels from the apical foramen. Canal centering ratios were then calculated. Data were analyzed by one-way analysis of variance and Bonferroni-Dunn test at the significance level of 5 %. Results: Group 4 exhibited significantly smaller canal width increases at 1- to 4-mm levels of the inner side and significantly larger increases at 7- to 12-mm levels of the outer side, compared with the other groups. Group 4 also showed significantly smaller centering ratios at 1-, 2-, 7-, and 9-mm levels, compared with any of the other groups. Total instrumentation time in Group 1 was significantly longer than that in the other groups. The time taken for Reciproc instrumentation was significantly shorter in Groups 2 and 3 compared with that in Group 1. Conclusion: Under the present experimental conditions, Reciproc instruments, regardless of prior glide path preparation, produced less canal deviation in the apical and coronal regions compared with TF instruments. When the canal preparation was performed with one single file, Reciproc instrumentation required significantly longer time than TF instrumentation. Following prior glide path preparation, however, the time taken for Reciproc instrumentation was significantly reduced and the total instrumentation time was similar to that required for TF instrumentation.

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Purpose: It is generally accepted that mirror skill is essential for dental treatment. In the present study, we compared the effects of different training methods for cavity preparation of upper teeth using a newly developed training instrument on the acquisition of preparation skills with a dental mirror. Methods: The content of training was MO cavity preparation for the upper jaw left side first molar with a dental mirror. The examinees were fifth-grade dental students, who were randomly assigned to two groups: group 1 that prepared the MO cavity in a dental mannequin simulator after specific training using the newly developed training instrument, and group 2 that prepared the MO cavity in the simulator without specific training. The training period was 7 days, and the two different methods were interchanged between the two groups on the fourth day of training during the period. The cavity preparation time, cavity preparation form, evaluation by evaluators, and self-evaluation by examinees were evaluated. The cavity preparation time was also evaluated by analysis of variance (p<0.05). Results: Compared with the first training day, the cavity preparation time on the seventh training day was shorter in both groups. The cavity preparation form in both groups improved in a time-dependent manner, especially in group 1. In the self-evaluation, there were differences in the handling of instruments and the cavity preparation form between the two groups after the fifth training day. The sense of accomplishment in the self-evaluation in both groups remarkably increased on the first day of specific training using the newly developed instrument. Conclusion: These results suggest that the specific training using the newly developed instrument may be effective for the acquisition of preparation skills with a dental mirror, and that early exposure to the specific training may achieve short-term improvement of the skills as well as their sense of accomplishment.

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Purpose: Some reports have described the physical and chemical analyses of enamel subsurface lesions and remineralized enamel subsurface lesions. However, there have been few reports on the changes in characteristics of redemineralized enamel subsurface lesions after remineralization. The present study was designed to investigate the characteristic changes of both enamel surface and adjacent subsurface and deeper layer following demineralization of remineralized enamel subsurface lesions. Methods: Bovine enamel subsurface lesions were created using a lactic acid gel system at pH 4.6 for a ten-day period. The enamel lesions were remineralized under conditions of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) containing paste or acidulated phosphate fluoride (APF) gel for one week. These remineralized enamel lesions were again demineralized with an artificial decalcifying solution containing acetic acid for six days. The surface structures of enamel subsurface lesions after various treatments were observed by scanning electron microscope. Thin specimens were cut from subsurface lesions, remineralized lesions or re-demineralized remineralized-lesions, and then contact microradiograms (CMR) were taken using these sections. The mineral profiles were analyzed using the CMR technique, and the degree of remineralization was evaluated by the changes in lesion depth and mineral loss values. Micromorphology of the longitudinal section of each specimen and the distribution of Ca and P were also analyzed by field emission-electron probe microanalyzer. Results: The acid-etching pattern with preferentially removed prism peripheries could be found on the re-demineralized remineralized-lesions without any enamel erosion. This particular study revealed that CPP-ACP and APF could induce remineralization of the subsurface layer, showing acid resistance. However, remineralization was hardly induced in the deeper layer where the mineral value is equivalent to that of sound enamel. Furthermore, re-demineralization after remineralization caused more invasive acid attack in the adjacent deeper layer under the enamel sub-surface lesion, which produced preferential and severe mineral loss in enamel rods exhibiting an etching pattern with distinct hollowing of prism cores and relatively intact prism peripheries. Conclusion: Based on the results of these analyses, both the enamel surface and adjacent subsurface layer following demineralization of remineralized enamel subsurface lesions demonstrated acid resistance, while the adjacent deeper layer suffered more invasive acid attack, exhibiting preferential and severe demineralization of the enamel prism cores.

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Purpose: The hypothesis of this study was that CO₂ laser irradiation with different wavelengths produces different characteristic changes even with the same degree of laser absorption in minerals of tooth substance. The study was designed to examine the characteristic changes of CO₂-lased dentin with different wavelengths (λ: 9.3 and 10.6 μm) to investigate the effects of the difference of the degree of laser absorption in dentin. Methods: Specimens prepared from extracted human dentin were irradiated by CO₂ lasers with a wavelength of 9.3 μm (9.3 μm-laser, an experimental apparatus by Takara Belmont) and with a wavelength of 10.6 μm (10.6 μm-laser, Bel-Luxar, Takara Belmont). The morphological changes of the 9.3 μm- and 10.6 μm-lased dentin were examined using a scanning electron microscope (SEM). The crystallographic changes were analyzed by micro-X-ray diffractometry (micro-XRD) and micro-Fourier transform infrared reflection spectroscopy (micro-FT-IR). The acid-resistance effects of CO₂ laser irradiation were also examined by measurement of dissolved Ca (atomic absorption spectrophotometer). Results: Under the SEM observation, cracks on the 9.3 μm-lased dentin were limited to within the irradiated area, while cracks on the 10.6 μm-lased dentin were created beyond the irradiated area. More micro-melts and occluded orifices of dentinal tubules were produced on the 9.3 μm-lased dentin. The micro-XRD and micro-FT-IR revealed that the 9.3 μm-laser irradiation increased the crystallinity of dentin. The laser irradiation increased the acid resistance of human dentin. Conclusion: It was suggested that the 9.3 μm-laser irradiation demonstrated different characteristic changes from those of 10.6 μm-laser irradiation even with the same degree of laser absorption in dentin. These effects may be due to the difference of the degree of laser absorption and/or the energy uptake efficiency in lased dentin.

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Purpose: This case report illustrates the exploration, diagnosis and treatment plan for the simultaneous occurrence both of myofascial pain syndrome-induced non-odontogenic toothache in masticatory muscle and periapical inflammation and fenestration-induced odontogenic toothache. Case and result: At the first visit, the patient complained not only of pain at the maxillary lateral incisor on the left side but also irradiation pain on the ipsilateral orofacial region. After several assessments, the disease was diagnosed as myofascial pain syndrome in masticatory muscle in association with periapical inflammation and fenestration on the ipsilateral maxillary lateral incisor. After root canal therapy, cognitive-behavioral intervention and physical therapy, the patient showed a good prognosis. Discussion and conclusion: It is important that clinicians identify the symptom as odontogenic or non-odontogenic toothache at the initial visit, and then to perform priority treatment for effective and better healing. This case report indicates that proper examination, diagnosis and adequate treatment led to better prognosis.

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