Purpose: Heat stress during restorative procedures can trigger damage to pulpodentin complex. It is universally known that dental pulp has tissue restoration ability. Odontoblast or odontoblast-like cells in dental pulp produce tertiary dentin in response to various irritations of pulpodentin as a defense reaction. However, the precise mechanism remains unclear. It is important to clarify this mechanism to save dental pulp and maintain healthy teeth. In the present study, we examined the effects of heat stress on dental pulp derived cells and the responses of the cells after heat stress. Materials and Methods: Viability and cell morphology of odontoblast-like cell line KN-3 were examined after exposure to heat stress at 43℃ for 45 minutes. The expression of several proteins (HSP25, HSP70, HSP90, Cyclin D1, Cyclin E, p21, p27, DSP and DMP-1) after heat stress was assessed by western blot analysis. Results: The viability of heat-stressed cells temporarily decreased and cells with nuclear fragmentation were observed at 12 hours after heat stress. The recovery of cell proliferation ability was observed at 1, 2 and 3 days after. Increase of the expression of HSP25, HSP70 and HSP90 was detected after heat stress. As for the expression of several proteins involving cell cycle, Cyclin D1 and Cyclin E increased at 6 and 24 hours after heat stress. However, expression of p21 and p27 peaked at 6 hours and decreased at 24 hours. The expression of odontoblast differentiation markers DSP and DMP-1 increased at 6 and 24 hours. Conclusion: After heat stress, the production of HSPs and transient cell-cycle arrest maintained the viability of KN-3 cells, and cell proliferation and differentiation into odontoblast-like cells were induced after heat stress.

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Purpose: There are many reports on the relationship between cardiovascular disease and periodontal disease in Europeans and Americans, but few such reports on the Japanese population. In this study, we investigated the status of cardiovascular disease and periodontal disease in the Tokai region based on the data of a health examination to clarify the relationship between these diseases in Japanese subjects. Methods: Five hundred forty-nine subjects who had received a dental examination and undergone a general health examination at the Heart Day Event in 2008 hosted by Toyohashi Heart Center were candidates for this study. Data on blood pressure, pulse, presence or absence of arteriosclerosis and/or arrhythmia, and history of angina pectoris or myocardial infarction or surgery were used for the survey of cardiovascular disease. As periodontal disease data, number of present teeth and Community Periodontal Index (CPI) were used. Statistical analysis was performed by comparing the presence or absence of cardiovascular disease with the index of periodontal disease. Results: The average age of the subjects was 61.7±13.6. The subjects were divided into two groups: the coronary heart disease (CHD) group (82 subjects) who had a history of either angina pectoris, myocardial infarction or surgery (percutaneous catheterization), and the non-CHD group (467 subjects). The number of present teeth for females in the CHD group was significantly smaller than that in the non-CHD group. In males, the odds ratio for a frequency of CPI code>3 who had a history of CHD was more than three times higher than that of CPI code<2, even after adjustment by some factors (i. e. diabetes, BMI, serum triglyceride, HDL, total cholesterol and age) related to CHD. Conclusion: These results suggest that there may be a relation between periodontal disease and CHD in the Japanese population.

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Purpose: In recent years, bleaching of teeth has become more common in dental clinics because of the increased desire for esthetic dentistry. However, it also has been pointed out that the bleaching treatment affects the mechanical properties of dentin. This study used Weibull analysis to investigate how the number of times of agent application and the type of surface to which the agent is applied during bleaching treatment affect the fracture mechanism in dentin. Method: Labial surfaces of bovine incisors were cut to obtain applied surfaces and 30% hydrogen peroxide solution was applied for 15 minutes with halogen lamp illumination during the last 10 minutes. The number of times of agent application was one or three and the applied surface was dentin. After agent application, dumbbell-shaped specimens were prepared from the dentin located 2.5-3.5 mm from the labial surface of the teeth, and used for the tensile test. In addition to the tensile strengths of the above dentin application, tensile strengths of enamel application and control obtained in a previous study (J Med Dent Sci 2008; 55: 175-180) were used following statistical analysis and a Weibull analysis. The effect of the number of bleaching treatments and the difference of applied surface on the dentin tensile strength was analyzed using 2-way ANOVA. In the Weibull analysis, the Weibull modulus was obtained from the Weibull plot for each condition. Results: The tensile strength decreased with the number of bleaching treatments, but there was no difference in tensile strength between enamel and dentin application. On the other hand, Weibull analysis demonstrated a difference in the Weibull plot between enamel and dentin application, resulting in a difference in Weibull modulus between dentin and enamel. We consider that this difference was because the region affected by reactive oxygen species was limited in the enamel application while the whole region was affected in the dentin application. Thus, the risk of strength deterioration would be less with enamel application than with dentin application from the standpoint of reliability. Conclusion: The number of times of bleaching agent application and the type of applied surface influence the tensile strength of the dentin of bleached teeth, suggesting the necessity of caution when providing bleaching treatment.

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Purpose: The purpose of this study was to evaluate the efficacy of sonic and ultrasonic irrigation on calcium hydroxide (Ca(OH)₂) paste removal and to measure the volume of remaining Ca(OH)₂ paste in the root canal with micro-computed tomography scanning (micro-CT). Methods: Twenty-one root canal models (D-mec) were used. These models had two orifices and one apical foramen with two isthmuses positioned 5 and 9 mm from the apex, respectively. All root canal models were filled with Ca(OH)₂ paste (Calcipex II, Nihon Shika Yakuhin). After 7 days, the root canal models were randomly divided into one control group (n=7) and two experimental groups (n=7 each). Groups A, B and C were irrigated using a conventional syringe (3.0 ml syringe, Terumo) with a needle (Blunt®, Nipro), a sonic Sally (Yoshida), and an ultrasonic Grand Piezo (Yoshida), respectively. After irrigation (Group A: 30 sec, Groups B and C: 15 sec , the root canal models were scanned using micro-CT (InspeXio SMX100CT®, Shimadzu), and the volume of remaining Ca(OH)₂ paste was measured. One-way ANOVA and Tukey-Kramer were used for statistical analysis (p<0.05). Results: No techniques removed the Ca(OH)₂ paste completely from the root canal. Although more remnants of Ca(OH)₂ paste remained in Group A (control) than in Groups B and C (p<0.05), there was no significant difference in the volume of Ca(OH)₂ paste remnants between Groups B and C. Conclusion: The results indicated that sonic and ultrasonic irrigation were significantly more effective for removing Ca(OH)₂ paste from the root canal than manual irrigation. No significant difference was found between Group B (sonic irrigation) and Group C (ultrasonic irrigation).

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Purpose: The purpose of this study was to examine the influence of tooth-surface moisture conditions on optical coherence tomography (OCT) imaging. Methods: Emitted light was coupled in a single-mode fiber-optic Michelson interferometer, and delivered to a sample and reference mirror mounted on a linearly translating galvanometer driven by a triangular voltage waveform at a fringe-modulation frequency of 1 kHz. Backscattered light from the sample was coupled back to the system, digitized and used to create two-dimensional images together with beam scanning. OCT imaging of the surfaces of extracted human teeth was performed soon after mounting ('wet' condition), immediately after air blowing for 10 sec ('air-blow' condition), and at 1-, 5- and 10-min intervals thereafter. Results: For the wet condition, three distinct peaks indicated the water surface, tooth surface and dentino-enamel junction. Backscattered light was detected at levels above noise, possibly causing grainy OCT images. By contrast, two distinct peaks indicating the tooth surface and dentino-enamel junction were observed for the air-blow and 10-min conditions, with greater signal intensities for the latter. The intensity was higher for the air-blow condition than the wet condition. The signal intensities increased during storage in air at room temperature. Conclusion: Tooth-substrate moisture conditions appeared to influence OCT imaging, and water irrigation followed by 10-sec air-blowing might be a suitable procedure for the OCT examination.

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Purpose: The current study monitored the polymerization processes of resin cements using an ultrasound device, and investigated the influence of the power density of the curing unit, and the application of the self-etching primer, on the polymerization behavior of dual-cured resin cements. Methods: The dual-cured resin cements used in this study were Bistite II (Tokuyama Dental), Linkmax (GC), and ResiCem (Shofu). The propagation time of longitudinal ultrasound waves was measured by a Pulser-Receiver (MODEL 5900, Panametrics). Resin cements were mixed and inserted into a transparent mold, and specimens were placed on the sample stage, onto which the primer, if used, was also applied. Power densities of 0 (no irradiation), 200 or 600 mW/cm² were used for curing. The transit time through the cement disk was divided by the specimen thickness to obtain the longitudinal sound velocity. Six specimens per group were used for each condition, and Tukey HSD tests were done at a significance level of 0.05. Results: When resin cements were light-irradiated, each curve displayed an initial plateau of -1,500 m/s, which rapidly increased to a second plateau of 2,300-2,900 m/s. The increase rate of sound velocity increase was slower when the cements were light-irradiated at lower power densities, and increased when the primer was applied. Conclusion: The ultrasound device monitored the setting processes of dual-cured resin cements accurately based on the longitudinal ultrasound velocity. The polymerization behavior of dual-cured resin cements was therefore shown to be affected by the power density of the curing unit and the application of self-etching primer, of which the degree of influence varied among the resin cements tested.

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