SARS-CoV-2 detection in pediatric dental clinic wastewater reflects the number of local COVID-19 cases in children under 10 years old.

This was the first longitudinal study to analyze dental clinic wastewater to estimate asymptomatic SARS-CoV-2 infection trends in children. We monitored wastewater over a 14-month period, spanning three major COVID-19 waves driven by the Alpha, Delta, and Omicron variants. Each Saturday, wastewater was sampled at the Pediatric Dental Clinic of the only dental hospital in Japan's Saitama Prefecture. The relationship between the weekly number of cases in Saitama Prefecture among residents aged < 10 years (exposure) and wastewater SARS-CoV-2 RNA detection (outcome) was examined. The number of cases was significantly associated with wastewater SARS-CoV-2 RNA positivity (risk ratio, 5.36; 95% confidence interval, 1.72-16.67; Fisher's exact test, p = 0.0005). A sample from Week 8 of 2022 harbored the Omicron variant. Compared to sporadic individual testing, this approach allows continuous population-level surveillance, which is less affected by healthcare seeking and test availability. Since wastewater from pediatric dental clinics originates from the oral cavities of asymptomatic children, such testing can provide important information regarding asymptomatic COVID-19 in children, complementing clinical pediatric data.

Determination of fracture toughness of human permanent and primary enamel using an indentation microfracture method.

The purpose of the present study was to examine the fracture toughness and Vickers microhardness number of permanent and primary human enamel using the indentation microfracture method. Crack resistance and a parameter indirectly related to fracture toughness were measured in 48 enamel specimens from 16 permanent teeth and 12 enamel specimens obtained from six primary teeth. The Vickers microhardness number of the middle portion was greater than the upper portion in primary enamel. The fracture toughness was highest in the middle portion of permanent enamel, because fracture toughness greatly depends upon microstructure. These findings suggest that primary teeth are not miniature permanent teeth but have specific and characteristic mechanical properties.

Evaluation of permanent and primary enamel and dentin mineral density using micro-computed tomography.

OBJECTIVES: The present study was performed to investigate the mineral density distribution in enamel and dentin for both permanent and primary teeth and to establish the standard density per tooth type using micro-computed tomography (CT). METHODS: Fifty-seven extracted human teeth (37 permanent, 20 primary) were evaluated in the present study. The enamel and dentin mineral densities in the extracted teeth were measured using micro-CT. Cubic regression curves were used to determine the mineral density distribution in the enamel and dentin for each tooth type. RESULTS: The mean values, distributions, and regression equations of the mineral densities were obtained. The mean mineral density values for permanent enamel and dentin were significantly higher than those for their primary counterparts for each tooth type. CONCLUSIONS: In the present study, we demonstrated the distribution of mineral density in sound enamel and dentin and attempted to determine the standard mineral density for each tooth type using micro-CT. The mineral density distributions found in this study contribute to our understanding of the mechanical properties of enamel and dentin. A positive correlation suggests that the systemic bone mineral density could be predicted based on the analysis of exfoliated teeth, such as in patients with hypophosphatasia. The present results may be useful in establishing a numerical standard for the mechanism involved in root fracture and for early detection of root fracture risk.

Two small linear marks on a mandible: collaborative networking between forensic experts.

A human male mandible was found under the eaves of a house. There were no associated items that allowed for personal identification. An anthropologist, who voluntarily joined our forensics team to give an expert opinion, found two small linear marks of 0.6 cm on the surface of the right condylar process. He thought these marks had been produced by a sharp object, and at the very least were not the result of bite marks by rodents or other animals. At first, the police did not appreciate the significance of the marks. One month later, however, other remains with similar marks were found near the scene, strongly suggesting that the case was a mutilation murder with a sharp weapon. After a vigorous search, the police obtained information that a young man in his twenties had gone missing in the area one year previously. After checking up on his relationships, a suspect was identified and arrested. The suspect subsequently confessed and was convicted as guilty of the crime. There are only a few forensic anthropologists in Japan. Consequently, almost all cases requiring bone examination have been handled by forensic pathologists, but it is hard for forensic pathologists to cover all fields comprehensively. The present case might have been solved without help from the anthropologist. However, we believe that forensic pathologists, especially less experienced ones, should seek advice from an expert in the field of forensic anthropology in order to carry a multidisciplinary forensic investigation. Given the current situation in, it is difficult in many institutes of forensics to obtain direct help from forensic anthropologists. The authors believe that collaborative networking via the Internet between forensic experts in each field cannot only obtain further information on complicated cases, but would also be helpful in training young forensic pathologists.

[Studies evaluating measurement accuracy of CMS-JAW, a jaw motion tracking device with six degrees of freedom using an ultrasonic recording system].

PURPOSE: For diagnoses of temporomandibular dysfunction, reports indicate the importance of analyzing jaw movements using a jaw motion tracking device with six degrees of freedom. However, such devices are not widely applied in clinical practice, due to difficulty of use. To determine whether CMS-JAW (a newly developed six degrees of freedom jaw motion tracking device that features easy analysis of jaw movements) offers the measurement accuracy required for clinical use, we evaluated the device by measuring condyle translation and rotation during jaw movement. METHODS: In this study, we evaluated measurement accuracy by comparing measurements of condyle movements obtained from the Win Jaw System, a comparable jaw motion tracking device with six degrees of freedom based on an ultrasonic recording system; the Gnathohexagraph II, a device based on a different measurement principle; and the CMS-JAW. In the experiment, we confirmed the condyle translations and rotations obtained by each device by measuring distances and angles, respectively, with a micro slider for three-dimensional measurements (to an accuracy of 0.01 mm and 0.02 mm) and a digital protractor (to an accuracy of 0.1 degrees). RESULTS: No significant distortions were observed in the space replicated based on the range of condyle translations obtained with CMS-JAW. Deviations from theoretical values were greatest along the z-axis, with a maximum error of 0.20 mm and root mean square (RMS) error of 0.10 mm. The maximum error for angles of condyle rotation was 0.50 degrees; RMS errors ranged from 0.05 to 0.30 degrees. CONCLUSION: Our analysis of condyle movement demonstrates that the CMS-JAW provides acceptable measurement accuracy for clinical applications.

Fracture of Ni-Ti superelastic alloy under sustained tensile load in physiological saline solution containing hydrogen peroxide.

The fracture of Ni-Ti superelastic alloy has been investigated by a sustained tensile-loading test in physiological saline solution containing hydrogen peroxide (0.15M NaCl + 0.3M H(2)O(2)). The fracture always occurs when the applied stress exceeds the critical stress for martensite transformation. In contrast, under a low applied stress, the fracture does not always occur within 1000 h. The fracture is probably mainly caused by localized corrosion associated with the preferential dissolution of nickel ions. In 0.3M H(2)O(2) solution without NaCl, the fracture does not occur even under a high applied stress. The results of the present study imply that one reason for the fracture of the Ni-Ti superelastic alloy in vivo is localized corrosion due to the synergistic effects of hydrogen peroxide and sodium chloride under applied stress.

Hydrogen absorption of titanium and nickel-titanium alloys during long-term immersion in neutral fluoride solution.

Hydrogen absorption of biomedical titanium and Ni-Ti alloys in a neutral fluoride (2.0% NaF) solution for up to 10,000 h at 37 degrees C has been evaluated by means of hydrogen thermal desorption analysis. For alpha titanium (commercial pure titanium), the amount of absorbed hydrogen was, at most, 10-30 mass ppm, and the corrosion product and hydride formation were revealed on the surface of the specimen by X-ray diffraction analysis. Ni-Ti superelastic alloy absorbed approximately 150 mass ppm of hydrogen, which was probably sufficient to result in the pronounced degradation of the mechanical properties, although corrosion was hardly observed. In contrast, hydrogen absorption of alpha-beta titanium (Ti-6Al-4V) and beta titanium (Ti-11.3Mo-6.6Zr-4.3Sn) alloys was negligible, although general corrosion was observed. The results of the present study indicate that the susceptibility of titanium and Ni-Ti alloys to hydrogen absorption in the neutral fluoride solution is different from that in the acidic fluoride solution reported previously.

Nondestructive Microcomputed Tomography Evaluation of Mineral Density in Exfoliated Teeth with Hypophosphatasia.

Most cases of hypophosphatasia (HPP) exhibit early loss of primary teeth. Results of microcomputed tomography (micro-CT) analysis of teeth with HPP have rarely been reported. The purpose of the present study was to describe the mineral density distribution and mapping of exfoliated teeth from an HPP patient using micro-CT. Four exfoliated teeth were obtained from a patient with HPP. Enamel and dentin mineral densities of exfoliated teeth were measured on micro-CT. The mean values of enamel and dentin mineral densities in mandibular primary central incisors with HPP were 1.61 and 0.98 g/cm3, respectively. The corresponding values in the mandibular primary lateral incisors were 1.60 and 0.98 g/cm3, respectively. Enamel hypoplasia was seen in the remaining teeth, both maxillary and mandibular primary canines and first and second molars. Micro-CT enables nondestructive, noninvasive evaluation and is useful for studying human hard tissues obtained from patients.

Hydrogen embrittlement of work-hardened Ni-Ti alloy in fluoride solutions.

Hydrogen embrittlement of work-hardened Ni-Ti alloy has been examined in acidulated phosphate fluoride (APF) solutions. Upon immersion in a 2.0% APF solution with a pH of 5.0, tensile strength decreased markedly with immersion time. Moreover, the fracture mode changed from ductile to brittle due to brittle layer formation at the peripheral part of the cross section of the specimen. The amount of absorbed hydrogen increased linearly with immersion time, and it reached above 5000 mass ppm after 24 h. The hydrogen desorption temperature of the immersed specimens shifted from 450 degrees C to a lower temperature with immersion time. As the amount of absorbed hydrogen was larger than 500 mass ppm, the degradation of mechanical properties was recognized. Although the tensile properties and fracture mode scarcely change in a 0.2% APF solution, the slight reduction in hardness and hydrogen absorption of several hundreds mass ppm were observed. The results of the present study imply that work-hardened Ni-Ti alloy is less sensitive to hydrogen embrittlement compared with Ni-Ti superelastic alloy.

Development of phantom for quantitative analyses of human dentin mineral density.

The purpose of the present study was to develop a novel-designed phantom that could be scanned with a sample in the same image, that specialize for quantitative analyses of human dentin mineral density using the X-ray attenuation method. A further attempt was made to demonstrate the intracoronal dentin mineral density using this phantom in mandibular incisors. The phantom prepared with a 15 mm hole in the center of an acrylic resin bar having an outside diameter of 25 mm and 8 small holes (diameter, 3 mm) were made at equal intervals around the center. Liquid dipotassium hydrogen phosphate (K2HPO4) solutions were established at 0.4, 0.6, 0.8 and 1.0 g/cm3, and were arranged to these holes. The mean value of the intracoronal dentin mineral density was 1.486 ± 0.016 g/cm3 in the present study. As the results of the present study corresponded to previous reports, this new phantom was considered to be useful. This phantom enables the analysis of samples that are not readily available by conventional mechanical tests and may facilitate biomechanical investigations using X-ray images. It was suggested that this system is a simple, accurate and novel mineralization measuring system.

Hydrogen absorption behavior of beta titanium alloy in acid fluoride solutions.

Hydrogen absorption behavior of a beta titanium alloy in acid fluoride solutions has been analyzed by hydrogen thermal desorption. The amount of absorbed hydrogen increased with immersion time in a 2.0% acidulated phosphate fluoride (APF) solution. In the case of an immersion time of 60 h, the amount of absorbed hydrogen exceeded 10000 mass ppm. In contrast, the amount of hydrogen absorbed in the 0.2% APF solution was several times smaller than that in the 2.0% APF solution for the same immersion time. For immersion in a 0.2% APF solution, hydrogen absorption saturated after 48 h. The surface topography and corrosion products on the surface of the specimen immersed in the 2.0% APF solution were different from those in the 0.2% APF solution. During the later stage of immersion, the amount of absorbed hydrogen markedly increased under higher applied stress, although the applied stress did not enhance hydrogen absorption during the early stage of immersion. These results of hydrogen absorption behavior are consistent with the delayed fracture characteristics of the beta titanium alloy.

Delayed fracture of beta titanium orthodontic wire in fluoride aqueous solutions.

Hydrogen embrittlement of a beta titanium orthodontic wire has been examined by means of a delayed-fracture test in acid and neutral fluoride aqueous solutions and hydrogen thermal desorption analysis. The time to fracture increased with decreasing applied stress in 2.0% and 0.2% acidulated phosphate fluoride (APF) solutions. The fracture mode changed from ductile to brittle when the applied stress was lower than 500MPa in 2.0% APF solution. On the other hand, the delayed fracture did not occur within 1000h in neutral NaF solutions, although general corrosion was also observed similar to that in APF solutions. Hydrogen desorption of the delayed-fracture-tested specimens was observed with a peak at approximately 500 degrees C. The amount of absorbed hydrogen was 5000-6500 mass ppm under an applied stress in 2.0% APF solution for 24h. It is concluded that the immersion in fluoride solutions leads to the degradation of the mechanical properties and fracture of beta titanium alloy associated with hydrogen absorption.

Fracture associated with hydrogen absorption of sustained tensile-loaded titanium in acid and neutral fluoride solutions.

The fracture of commercial pure titanium in acid and neutral fluoride solutions has been examined by a sustained tensile-loading test and hydrogen thermal desorption analysis. It was found that the fracture of titanium occurred in neutral 2.0% NaF solution as well as in 2.0% acidulated phosphate fluoride (APF) solution. The time to fracture decreased with increasing applied stress in both 2.0% APF and 2.0% NaF solutions. In the case of the same applied stress, the time to fracture in the 2.0% APF solution was shorter than that in the 2.0% NaF solution. General corrosion was exhibited on the side surface of the tested specimens. The formation of sodium titanium fluoride was observed on the surface of the immersed specimens in the 2.0% APF solution. Hydrogen desorption of the tested specimen in the 2.0% APF solution was observed with a peak at approximately 600 degrees C. The amount of absorbed hydrogen was >300 mass ppm in the 2.0% APF solution under an applied stress for 24 h. The results of the present study imply that applying stress to titanium by immersing in fluoride solutions leads to the degradation of its mechanical properties.

Hydrogen embrittlement of Ni-Ti superelastic alloy in fluoride solution.

Hydrogen embrittlement of Ni-Ti superelastic alloy in a fluoride solution (0.2% APF) has been investigated by means of a tensile test (after immersion) and hydrogen thermal desorption analysis. Upon immersion, the tensile strength of the alloy decreased to the critical stress level of martensite transformation. Hydrogen desorption of the immersed specimens appeared with a peak at around 500 degrees C. The amount of absorbed hydrogen in the alloy ranged from 100 to 1000 mass ppm when immersed in the fluoride solution for 2 to 24 h. The immersion in the fluoride solution led to the degradation of mechanical properties due to hydrogen embrittlement. The results of the present study imply that one reason that Ti and its alloys fracture in the oral cavity is the fact that hydrogen is absorbed in a fluoride solution, such as prophylactic agents.

Degradation in performance of orthodontic wires caused by hydrogen absorption during short-term immersion in 2.0% acidulated phosphate fluoride solution.

The purpose of this study was to investigate the degradation in performance of four major alloys of orthodontic wires, namely nickel-titanium, beta titanium, stainless steel, and cobalt-chromium-nickel, caused by hydrogen absorption during short-term immersion in an acid fluoride solutions. The hydrogen-related degradation of orthodontic wires after immersion in 2.0% acidulated phosphate fluoride solution at 37 degrees C for 60 minutes was evaluated by a tensile test, scanning electron microscope observation, and hydrogen thermal desorption analysis. Upon immersion, the tensile strengths of the nickel-titanium and beta titanium wires decreased. Particularly, the nickel-titanium wire fractured before yielding, and the fracture mode changed from ductile to brittle. The amounts of absorbed hydrogen in the nickel-titanium and beta titanium wires were 200 and 100 mass ppm, respectively. On the other hand, the tensile strengths of the stainless steel and cobalt-chromium-nickel wires were only slightly affected by immersion. The results of this study suggest that degradation in performance of orthodontic wires of titanium alloys occurs because of hydrogen absorption even after a short-term immersion in fluoride solutions.

Inhibition of hydrogen embrittlement of Ni-Ti superelastic alloy in acid fluoride solution by hydrogen peroxide addition.

Inhibition of the hydrogen embrittlement of Ni-Ti superelastic alloy in an acidulated phosphate fluoride (APF) solution has been attempted by adding various amounts of H(2)O(2). In a 0.2% APF solution, hydrogen absorption is markedly inhibited by adding H(2)O(2), although corrosion is slightly enhanced by increasing the amount of added H(2)O(2). By adding a small amount of H(2)O(2) (0.001 M), in the early stage of immersion, hydrogen embrittlement is inhibited and corrosion is only slightly enhanced. Upon adding H(2)O(2), it appears that the dominant cathodic reactions change from hydrogen evolution to H(2)O(2) reduction reactions, or the surface conditions of the alloy are changed by H(2)O(2) with a high oxidation capability, thereby inhibiting hydrogen absorption. The present study clearly indicates that infinitesimal addition of H(2)O(2) into acid fluoride solutions is effective for the inhibition of the hydrogen embrittlement of the alloy.