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This study was aimed to evaluate the effect of torsional preloads on the cyclic fatigue life of nickel-titanium (NiTi) instruments with different history of heat treatments by manufacturers. WaveOne (Primary) made of M-wire, K3XF (#30/0.06) of R-phase, and ProTaper (F2) of conventional NiTi alloy was used. Each file was preloaded at four conditions (nil, 25, 50, and 75% of their mean ultimate torsional strength) before fatigue testing. The torsional preloads 10-, 30-, or 50-times were applied by securing 5 mm of the file tip, rotating it until the preset torque was attained before returning to the origin. Then, the number of cycles to failure (NCF) was evaluated by rotational bending in a simulated canal. Data were analyzed using multiple linear regression analysis and two-way ANOVA. Fractured instruments were examined under scanning electron microscope (SEM). SEM showed that most WaveOne after 75% preloading, regardless of repetitions, showed some longitudinal cracks parallel to the long axis of the file, which were rare for K3XF. Regression analysis revealed that the brand of instrument was the most critical factor. At up to 75% preloading, ProTaper and K3XF did not show any significant decline in NCF. For 30-repetition groups of WaveOne, the 50 and 25% torsion preloaded groups showed a significantly higher NCF than the 0 and 75% groups. Within the limitations of this study, the alloy type of NiTi instrument have a significant effect on the phenomenon that a certain amount of torsional preload may improve the cyclic fatigue resistance of NiTi rotary instruments. SCANNING 37:172-178, 2015. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The aim was to evaluate the distribution and elimination of mercury in the tissues of rats exposed to powdered dental amalgam. The study comprised of three groups: the first (A) was an unexposed control, the second (B) was fed 8.3 mg of powdered amalgam weekly for 12 weeks, and the third (C) was fed 25.0 mg of powdered amalgam weekly for 4 weeks followed by either a 4- or 8-week period of non-exposure. The total amount of amalgam administered in each of the latter two groups was 0.1 g. Animals were killed at 4, 8 and 12 weeks, and their kidneys, liver and brains were removed. Mercury present in tissues from one side was analysed by cold-vapour atomic absorption spectrometry; tissues from the other side were stained autometallographically. No mercury was detected in any tissue of control group A. In group B, the mercury concentration in the kidneys was significantly higher than that of the control, whereas in group C, the mercury concentration in both the liver and kidneys decreased significantly during the period of non-exposure. Mercury was not detected in brain tissue from any group. The light-microscopic findings were in agreement with the quantitative results. Mercury grains were most common in the renal cortex, especially in the proximal tubule. Although there was some mercury accumulation in the tissues of the two experimental groups, no pathological reactions were noted. These data suggest that, in the rat, the ingestion of dental amalgam in small quantities for a limited period does not lead to morphological changes in the liver, brain or kidneys. It seems likely that mercury does not accumulate in brain tissue and that any accumulation in the kidneys and liver is at least partially reduced after ingestion ceases. [Copyright &y& Elsevier]

Objectives: Word-of-mouth (WOM) refers to communication among consumers, which greatly influences the marketing strategies of dental clinics. This study aimed to explore factors that affect use of WOM by dental patients and to analyse their pathways., Methods: The participants were 520 outpatients from four private dental clinics. Data were obtained from a survey using self-reported questionnaires, which included questions regarding seven latent variables: five exogenous variables, including medical service quality (physical environment, customer service, patient relationship quality) and individual characteristic variables (opinion leader tendency, social hub tendency); and two endogenous variables (intention to recommend, WOM experience). Statistical analysis was performed using structural equation modelling., Results: Significant associations were found in the pathways between relationship quality and intention to recommend, intention to recommend and WOM, and opinion leader tendency and WOM (P < 0.001). Higher patient relationship quality and higher intention to recommend were related to positive WOM, as was higher opinion leader tendency., Conclusions: Improving patient relationship quality can promote positive WOM for dental clinics. Strategies are needed to promote a positive perception of dental clinics by effectively responding to the views of patients with strong opinion leader tendencies., (© 2018 FDI World Dental Federation.)

Objectives: Owing to its cost-effectiveness and operative convenience, dental amalgam remains in use as a restorative material for tooth caries in children in many countries. The aim of this study was to evaluate the relationship between dental amalgam exposure and urinary mercury (U-Hg) concentrations in children., Methods: In this longitudinal study, 463, 367 and 348 children, 8-11 years of age, were evaluated at baseline, and at the first and second follow-up visits, respectively. The interval between each survey was 6 months. For the oral examination and urine sample, the amalgam-filled tooth surface (TS), and U-Hg and creatinine concentrations of participants were determined, and the cumulative amalgam-filled TS and cumulative creatinine-adjusted U-Hg were calculated. To assess potential covariates, socio-demographic factors, oral health behaviour and dietary factors were surveyed by questionnaire. Data were analysed by the t-test, correlation analysis and mixed-model analysis. The statistical analyses were performed using SPSS 18.0., Results: Children with more than one amalgam-filled TS exhibited significantly higher creatinine-adjusted U-Hg concentrations than those without, in all three survey periods (P < 0.001). The results for the current and cumulative amalgam-filled TS significantly correlated with those for the current and cumulative creatinine-adjusted U-Hg concentration, respectively, in all surveys (P < 0.001). In the repeated-measures mixed model analysis, current and cumulative amalgam-filled TS was significantly related to current and cumulative creatinine-adjusted U-Hg concentration, respectively (P < 0.001)., Conclusions: Amalgam-filled TS was significantly correlated with U-Hg concentrations in children. Therefore, dental amalgam exposure can affect the systemic mercury concentration in children., (© 2016 FDI World Dental Federation.)

Purpose: This study aimed to investigate the efficacy of cleaning solutions on saliva-contaminated zirconia in comparison to air-abrasion in terms of resin bonding., Materials and Methods: For saliva-contaminated airabraded zirconia, seven cleaning methods)-no contamination (NC), water-spray rinsing (WS), additional airabrasion (AA), and cleaning with four solutions (Ivoclean [IC]; 1.0 wt% sodium dodecyl sulfate [SDS], 1.0 wt% hydrogen peroxide [HP], and 1.0 wt% sodium hypochlorite [SHC])-were tested. The zirconia surfaces for each group were characterized using various analytical techniques. Three bonded resin (Panavia F 2.0) cylinders (bonding area: 4.5 mm(2)) were made on one zirconia disk specimen using the Ultradent jig method [four disks (12 cylinders)/group; a total of 28 disks]. After 5,000 thermocycling, all specimens were subjected to a shear bond strength test with a crosshead speed of 1.0 mm/minute. The fractured surfaces were observed using an optical and scanning electron microscope (SEM)., Results: Contact angle measurements showed that groups NC, AA, IC, and SHC had hydrophilic surfaces. The X-ray photoelectron spectroscopy (XPS) analysis showed similar elemental distributions between group AA and groups IC and SHC. Groups IC and SHC showed statistically similar bond strengths to groups NC and AA (P>.05), but not groups SDS and HP (P<.05). For groups WS, SDS, and HP, blister-like bubble formations were observed on the surfaces under SEM., Conclusion: Within the limitations of this in vitro study, some of the cleaning solutions (IC or SHC) were effective in removing saliva contamination and enhancing the resin bond strength.

Objectives: Dentistry has been identified as one of the most stressful work environments. Knowledge of modifiable work-environment factors related to job stress could lead to a strategy and policy to provide a better work environment for dentists. The aims of this study were to examine the degree and distribution of burnout and to determine the factors associated with burnout subscale of Korean dentists., Methods: A cross-sectional survey of Korean dentists was conducted using a custom-designed and validated questionnaire that incorporated the Maslach Burnout Inventory Human Services Survey (MBI-HSS) as well as questions regarding sociodemographic and job-related characteristics. A random sample of 1,000 dentists was selected from 13,207 registered dentists in the Korean Dental Association. The MBI-HSS scores were summarised in the three dimensions of emotional exhaustion, depersonalisation, and personal sense of accomplishment. Bivariate and multivariate analyses were conducted to assess the prevalence of burnout and its related factors., Results: The adjusted response rate was 45.9% (444/967). In the subscales of burnout, 41.2%, 55.9%, and 41.4% of respondents scored highly in emotional exhaustion and depersonalisation and poorly for personal sense of accomplishment, respectively. High burnout seems to be more likely to occur in association with some of the sociodemographic and job-related characteristics, especially younger age, male gender, without occupational calling, and unwilling to reselect a dentistry as a job., Conclusions: This study suggests that burnout is a common problem in Korean dentists and that occupational calling and willing to reselect a dentistry as a job are important factors for managing burnout., (© 2014 FDI World Dental Federation.)

Purpose: This study aimed to investigate the effects of oral hygiene care by oral professionals on periodontal health in type 2 diabetes mellitus patients., Materials and Methods: Diabetic participants were recruited at a university hospital and matched at a 1:1 ratio by age and gender, and randomly allocated into intervention (40 people) and control groups (35 people). Tooth brushing instruction, oral health education, and supra-gingival scaling were implemented in all patients at baseline. This program was repeatedly conducted in intervention patients every month for 6 months, and twice at baseline and the sixth month in the control. Oral health was measured by decayed, missing, and filled teeth (DMFT), plaque index, calculus index, bleeding index, patient hygiene performance (PHP) index, tooth mobility, Russel's periodontal index, and community periodontal index (CPI). Diabetes-related factors, oral and general health behaviors, and sociodemographic factors were interviewed as other confounding factors. An analysis of covariance (ANCOVA) was used with SPSS for Windows 14.0., Results: At baseline, there were no significant differences between the two groups in average of periodontal health (calculus index, bleeding index, Russel's periodontal index, CPI, and tooth mobility), diabetes-related factors (fasting blood glucose, postprandial blood glucose, and HbA1c), and in distribution of sociodemographic factors and health behaviors. In intervention group, plaque index, dental calculus index, bleeding index, and PHP index were reduced fairly and steadily from the baseline. There were significant differences in plaque index, dental calculus index, bleeding index, PHP index, and Russel's periodontal index between the two groups at sixth month after adjusted for baseline status., Conclusion: Intensive oral hygiene care can persistently improve oral inflammation status and could slow periodontal deterioration.

Objective: Filtered 325-nm xenon light was used to test its effectiveness in the detection of incipient carious lesions on bovine enamel by measuring the fluorescence spectrum., Background Data: The combination of early detection with new interventional methodology and caries management will be the preferred dental practice in the future., Methods: Specimens of bovine tooth enamel were embedded in resin, polished, exposed to a lactate carbopol buffer system for 71 hours, and randomly divided into one control and three test groups of 10 specimens each, with Vickers hardness number (VHN) stratification. The surface changes were characterized by atomic force microscopy. All specimens were irradiated with xenon light, and a fluorescence spectrum was produced. Characteristics of fluorescence among the demineralized tooth groups were measured using an optical multichannel analyzer and a confocal laser scanning microscope., Results: The VHNs were significantly different among the four groups (p < 0.05). The fluorescence had a peak intensity of approximately 425 nm, and the slope value between 450 and 550 nm was significantly decreased in all test groups (groups II-IV) compared to the control group (group I), as the VHN decreased (p < 0.05). Demineralized lesion depth gradually increased to 30-40 microm in groups II-IV., Conclusions: The 325-nm xenon light resulted in high efficacy for detecting incipient carious lesions. By evaluating the highest peak and slope value, the incipient carious lesion may be detected.

Objective: To propose an efficient screening schedule for breast cancer among Korean women using the stochastic model in which the age-specific incidence rate was considered., Setting: Female breast cancer data in the Korea Central Cancer Registry 2002., Methods: The stochastic model was based on the threshold method, in which the schedule is determined by a pre-specified threshold value. The threshold value was defined as the probability of being in a preclinical state of breast cancer at age 40 years. The sensitivity of the mammography was specified as 0.7. Two models for mean sojourn time (MST) in the preclinical state were considered; MSTs for Model I were 2 (ages < 50 years), 3 (ages 50-59 years), and 4 years (ages > or = 60 years), and MSTs for Model II were 3, 4, and 5 years for the corresponding age groups., Results: The threshold method for Model I generated 19 examinations within the screening ages of 40-69 years. Each screening time was determined at ages 40.0, 41.6, 43.2, 44.8, 46.0, 47.2, 48.4, 49.6, 50.7, 51.7, 52.7, 53.7, 54.7, 56.2, 57.8, 59.4, 61.3, 63.1, and 64.9 years. The schedule sensitivity of Model I was 64.2%, which was higher than that (57.5%) of the biennial periodic schedule. Model II included 11 screenings between the ages of 40 and 69 years and also showed a higher schedule sensitivity, especially for women aged 40 years as compared with the biennial screening., Conclusions: This finding suggests that the threshold screening schedule for breast cancer increase the schedule sensitivity by reflecting the age-specific incidence rate of a population.

Objectives: The purposes of this study were to propose a screening schedule for the early detection of breast cancer among Korean women, as based on the statistical model, and to compare the efficacy of the proposed screening schedule with the current recommendations., Methods: The development of the screening schedule for breast cancer closely followed the work of Lee and Zelen (1998). We calculated the age-specific breast cancer incidence rate from the Korea Central Cancer Registry (2003), and then we estimated the scheduling of periodic examinations for the early detection of breast cancer, using mammography, and based on the threshold method. The efficacy of the derived screening schedule was evaluated by the schedule sensitivity., Results: For estimating the screening schedule threshold method, we set the threshold value as the probability of being in the preclinical stage at age 35, the sensitivity of mammography as 0.9 and the mean sojourn time in the preclinical stage as 4 years. This method generated 14 examinations within the age interval [40, 69] of 40.0, 41.3, 42.7, 44.1, 45.4, 46.7, 48.0, 49.3, 51.0, 53.2, 55.3, 57.1, 59.0 and 63.6 years, and the schedule sensitivity was 75.4%. The proposed screening schedule detected 85.2% (74.5/87.4) of the cases that could have been detected by annual screening, but it required only about 48.7% (14.0/30.0) of the total number of examinations. We also examined the threshold screening schedules for a range of sensitivities of mammography and the mean sojourn time in the preclinical stage., Conclusions: The proposed screening schedule for breast cancer with using the threshold method will be helpful to provide guidelines for a public health program for choosing an effective screening schedule for breast cancer among Korean women.

Objective: A 325-nm ultraviolet (UV) laser was tested for effectiveness in the detection of incipient carious lesions on teeth., Background Data: The combination of early detection with new intervention methods and caries management will be the preferred dentistry of the future., Methods: Carious lesions from extracted teeth or from demineralized teeth were irradiated by UV laser, and the fluorescence spectrum was measured. The peak ratio between two peak intensities in the spectrum was determined., Results: Fluorescence peak intensity of approximately 425 nm was gradually decreased as carious lesions formed, whereas the change 625 nm was less significant. The peak ratio change between peak intensities of approximately 425 and at 625 nm was observed after 30 min of demineralization. Morphological changes were barely observable in this range., Conclusions: A 325-nm UV laser showed high efficacy in the detection of incipient carious lesions. By evaluating peak ratio, the incipient carious lesions could be detected.

Aim: To investigate the use of polyol-containing chewing gums in a day-care centre (kindergarten) setting as a means to affect the growth of mutans streptococci and dental plaque., Design: Over a period of six months, 123 five-year-old children chewed xylitol (X group), sorbitol (G group), or did not chew gum (C group). Consumption of xylitol, and sorbitol was 4.5 to 5.0 g per day and subjects consumed in five supervised daily chewing episodes four at the day-care centres and one at home., Methods: Interproximal dental plaque was sampled at baseline and after six months for a laboratory study of mutans streptococci counts. The Quigley & Hein plaque index procedure was used. Interviews and questionnaires elucidated the acceptability of the programme., Results: Parents and kindergarten personnel regarded the programme as an important, additional procedure to promote better oral health. The children regarded the use of chewing gum as a pleasurable experience. Compared with groups G and C, there was a statistically significant reduction of mutans streptococci in the interproximal plaque in the X group. The Quigley & Hein plaque index scores tended to decrease in the X group, while no such trend was observed in the G group., Conclusions: Habitual use of relatively small daily quantities of polyol-containing chewing gum by young children may be regarded as an important additional caries-preventive procedure in a combined day-care centre and home setting. Especially xylitol-containing chewing gum may significantly reduce the growth of mutans streptococci and dental plaque which may be associated with dental caries.

Background: The purposes of this study were to compare patient expectation before periodontal surgical treatment with their level of satisfaction afterward on the basis of a self-reported questionnaire, and to analyze the relationship between various satisfaction factors and periodontal surgical treatment., Methods: Information was obtained from 33 patients initially diagnosed with chronic periodontitis. The survey was completed twice by each patient, once before and once after modified Widman flap surgery., Results: The satisfaction scores of items related to patient expectation of treatment outcome decreased significantly following surgery. The patients also expressed great dissatisfaction with items regarding disease prevention such as "desire for knowledge of periodontal disease prevention" and "desire for knowledge of recurrence control methods." However, some items such as "dental pain during treatment," "dental fear of treatment," and "cost of treatment" increased significantly after treatment. The total mean score of general satisfaction before treatment was 2.65, decreasing to 2.60 after treatment., Conclusions: Among the 5 subscales, any increase in patient satisfaction related to the treatment factors is difficult to achieve, but we should be able to raise the satisfaction level of our patients through improvement of the preventive measure factors.