Acid Elution of Aluminum and Calcium from Human Deciduous Enamel in Relation to Dental Caries

Although aluminum itself was reported to prevent dental caries, previous in vitro studies reported that the aluminum level in the whole saliva of children was independent of caries prevalence. Purposes of this study were to compare the elution levels of aluminum and calcium from deciduous enamel into acidic artificial saliva, and determine whether the degree of aluminum elution reflects individual caries risk. One hundred and eleven extracted human deciduous teeth were collected. Concentrations of aluminum and calcium eluted from sound regions of enamel into artificial saliva (pH 6.2 or 5.5) were determined using atomic absorption spectrophotometry. One hundred and four and 108 available data samples were obtained for aluminum and calcium evaluation, respectively, and were compared based on the sex, tooth type, caries history, and the number of the donor’s carious teeth at each pH. Calcium elution was not affected by the sex;however, more aluminum was eluted from boys’ than from girls’ teeth at pH 5.5. The aluminum release depended on the tooth type, and was significantly higher in incisors than in molars at a pH of 5.5. In relation to the caries history, aluminum (at pH 5.5) and calcium (at pH 6.2) dissolved more from sound regions of the enamel of caries-experienced teeth than from the enamel of teeth without caries experience. Moreover, aluminum markedly dissolved from enamel in artificial saliva at both pH 6.2 and 5.5 when the donor had more carious teeth, regardless of the presence or absence of caries experience in the sampled teeth. There is a possibility that the rate of aluminum elution from enamel into acidic fluid reflects individual caries sensitivity.

Advantage of Introducing Quantitative Light-Induced Fluorescence in School Dental Checkups

Background: Caries detection in school oral examinations insufficient accuracy. Objective: To evaluate advantages of introducing quantitative light-induced fluorescence-digital (QLF-D) in school oral examinations. Methods: Experiment No. 1. Early demineralized lesions in the upper and lower incisors and canines were visually inspected by three dentists and by QLF-D. The numbers of tooth planes with early demineralized lesions were compared between the methods. Experiment No. 2. Approximal demineralized lesions in molars were assessed by visual inspection, x-ray imaging, and QLF-D. The numbers of tooth planes with demineralized lesions were compared among the methods. Experiment No. 3. Plaque distribution was evaluated by QLF-D and a traditional staining method. The ratio of the diameter of plaque to tooth crown in the tooth axis direction in each method was calculated. The results were evaluated by Pearson’s correlation coefficient analysis and Bland-Altman plot. Results: Experiment No. 1. The three dentists found 0.67 tooth planes on average. QLF-D found 22 tooth planes with early demineralized lesions in the same samples. Experiment No. 2. Fourteen approximal tooth planes of molars were found to have demineralized lesions by x-ray imaging. QLF-D detected 71.4% of the tooth planes out of the 14, whereas visual inspection found 7.1%. Experiment No. 3. The Pearson’s correlation coefficient for the evaluations of plaque distribution between the QLF-D and traditional staining methods was 0.77 (P Conclusion: The results support introduction of QLF-D for use in school dental examinations.

Effects of Zinc, Iron, and Copper on Bovine Enamel Erosion Evaluated Using Transverse Microradiography

Objective: This study aimed to clarify the effect of trace elements on enamel erosion due to citric acid eliminating other factors that can affect enamel erosion. Method: Forty enamel specimens were obtained by embedding bovine enamel blocks into a quick cure resin. Half of the enamel surface of the specimens was covered with nail varnish. The specimens were randomly divided into control (Ct), zinc (Zn), iron (Fe), and copper (Cu) groups and immersed in 1% citric acid solution, 1% citric acid solution with 10 mmol/L zinc, 1% citric acid solution with 10 mmol/L iron, or 1% citric acid solution with 10 mmol/L copper, respectively, at 37°C for 5 h. After immersion, the demineralized lesion depth was measured using transverse microradiography (TMR) and compared between groups using one-way analysis of variance and Tukey’s test. Results: The lesion depth was significantly higher in the Zn (218.9 ± 88.5 μm) group than that in the Ct group (116.3 ± 22.1 μm) (p < 0.01). Conclusion: It was suggested that zinc has decalcification properties when consumed with citric acid, while iron and copper don’t have such properties.

Amount of Calcium Elution and Eroded Lesion Depth in Bovine Enamel Derived from Single Short Time Immersion in Carbonated Soft Drink <i>in Vitro</i>

Erosion is one of serious oral health problems among Japanese children. Some dentists argue that brushing just after food/drink intake induces enamel abrasion. Objectives of this study were to evaluate amount of calcium elution from bovine enamel due to single and short immersion into carbonated soft drink, to calculate depth of the eroded lesion, and to determine when to brush teeth after carbonated soft drink intake from the view point of preventing enamel abrasion. Four enamel specimens were made from each of eight bovine teeth. The specimens were covered by quick-cure resin except for enamel surfaces. The four specimens from each bovine tooth were classified into three, six, nine, and 12 minutes immersion (IM3, IM6, IM9, and IM12) groups and immersed separately in five mL of carbonated soft drink. After the immersion, the calcium concentration of the original drink and the drink samples were evaluated using atomic absorption spectrophotometry. The dimension of each enamel specimen was calculated using a planimeter. The amount of eluted calcium per unit area of the enamel specimen into each drink sample was obtained. The depth of the demineralized lesion was obtained by dividing the amount of calcium elution per unit area by the concentration of calcium in enamel and the specific gravity of enamel. The lesion depth of the IM3 group was significantly lower than those in the IM6, IM9, and IM12 groups. The mean lesion depth in the IM12 group which showed the deepest lesion depth was 0.21 μm. As conclusions, the erosive lesion depth due to intake of carbonated soft drink was much shallower than remineralized enamel surface of a white spot lesion which can be repaired in plaque fluid in a short time, suggesting such erosion hardly causes tooth wear, hence it was suggested that brushing teeth just after the intake was recommended.

A prolonged granitoid formation in Saglek Block,Labrador:Zonal growth and crustal reworking of continental crust in the Eoarchean

The Archean continental crusts account for ca.20% of the present volume,but the thermal history of the Earths＇ mantle suggests much more continental crusts were formed in the early Archean.Because the Archean continental crust underwent severe metamorphism,it is important to avoid influence by the later thermal events.We carried out a comprehensive geochronological work of Cathodoluminescence（CL） observation and U-Pb dating of zircons from orthogneisses and supracrustal rocks over the Saglek Block to obtain their protolith ages.The zircons were classified into three domains of core,mantle and rims,and the cores were further classified into three groups of inherited,altered and zoned cores based on the zonation on the CL images.We estimated the protolith ages from Pb-Pb ages of the zoned-cores of zircons with low U contents.We made a detailed sketch of a small outcrop in St.John＇s Harbour South（SJHS） area,and classified the orthogneisses and mafic enclaves into seven generations based on the geologic occurrence.The first and second generations comprise mafic rocks and lack magmatic zircons.We conducted CL imaging and U-Pb dating of zircons from the third,sixth and seventh generation of the orthogneisses to estimate the protolith ages at 3902 L 25,3892 ± 33 and 3897 ± 33 Ma for each,supporting the presence of the over 3.9 Ca Iqaluk Gneiss.The geological occurrence that the mafic rocks occur as enclaves within the 3.9 Ga Iqaluk Gneiss indicates that they are the oldest supracrustal rocks in the world.Our geochronological and geological studies show the Uivak Gneiss is quite varied in lithology and age from 3.6 to 〉3.9 Ga,and tentatively classified into six groups based on their ages.The oldest Uivak Gneiss components including the Iqaluk Gneiss are present around the SJHS area,and the orthogneisses become young as it is away.The lines of evidence of overprinting of younger granitoid on older granitoid in small outcrops and geological-map scale as well as presence of inherited zircons even in the oldest suite suggests that crustal reworking played an important role on erasing the ancient crusts.