PubMed · 13942053
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F G PAUTARD. 1961. An x-ray diffraction pattern from human enamel matrix.. https://doi.org/10.1016/0003-9969(61)90139-x
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Subsurface demineralization of dental enamel is a curious feature of both in vivo and in vitro lesion formation. Numerous explanations have been proposed to explain this. One general hypothesis is that subsurface demineralization in enamel and synthetic hydroxyapatite (HAP) aggregates may result from the phenomenon of coupled diffusion between the inward transport of acid and the outward transport of dissolution products. The aim of this study was to test the validity of this explanation. Inert electrolyte was added to demineralizing solutions in order to reduce electrostatic coupling between the diffusive flows that occur during lesion formation. Scanning microradiography (SMR) was used to examine surface layer formation, and to measure the rate of mineral loss at increasing ionic strengths. It was found that surface layer formation was significantly reduced as the concentration of inert electrolyte was increased. Further, the rate of mineral loss from the developing lesion increased as the concentration of inert electrolyte (and therefore the ionic strength) in the demineralizing solution increased. It is concluded that electrostatic coupling between counter diffusing acid and dissolution products during lesion formation can significantly influence the mineral concentration within the surface layer.
OBJECTIVES: The diagnosis of tooth wear is mostly based on visual scoring systems. Recently, methods measuring ultrasonic enamel thickness have been proposed. The aim of this study was to evaluate the reproducibility and evaluate factors affecting variation of ultrasonic enamel thickness measurements in an in vitro set up. METHODS: Four observers (1-4) in two institutes (G and S) performed ultrasonic enamel thickness measurements at buccal and palatal surfaces of extracted teeth placed in a phantom jaw. A Panametrics 25DL thickness gauge (Panametrics, Waltham MA, USA), with a 15 MHz transducer, covered by a plexi-glass delay line with a tip diameter of 2 mm was used, coupled to a laptop computer. After one week these measurements were repeated. Subsequently four selected teeth were measured 20 times at a fixed buccal site by one observer. Finally, two observers made ink marks with the instrument probe tip on the buccal and palatal surfaces of all teeth. This was repeated after one week. Digital images were made of the marked teeth and analysed to determine variation in positioning. The underlying enamel thickness variation was subsequently estimated. Results were analysed by calculating the 95% range of measurement variation (RMV, 4 x standard deviation) for each experiment. RESULTS: The main reproducibility experiment showed a 95% RMV of 0.79 mm (observer 1G), 0.64 mm (observer 2G), 0.63 mm (observer 3S), 0.71 mm (observer 4S), 0.51 mm (observer 1S). The repeatability experiment showed a mean 95% RMV of 0.26 mm. The probe position variation in the cervical-incisal direction resulted in an estimated thickness 95% RMV of 0.10 mm (1G) and 0.09 mm (2G). CONCLUSIONS: It was concluded that, due to measurement variation, thickness changes of less than 0.33 mm cannot be detected reliably. Probe positioning and a poor repeatability were responsible for only a small part of the total variation. Hence other factors influencing variation in enamel thickness are still to be identified.
OBJECTIVE: Eight commercially available resins, Epoxy Embedding Medium ("Epon"), Spurr, Epofix, Epo-Kwick, Epo-Thin, Technovit 9100 New, Unicryl, and Vestopal W, all intended for embedding specimens for microscopy, were tested and compared for binding and adaptation to the enamel surface of human third molar crowns that had been embedded in them. DESIGN: After sectioning, grinding and acid etching, the specimens were observed in the SEM. The presence or absence of a gap between enamel and resin was recorded together with the width of the gap, when present. RESULTS: A pilot study, where gaps were observed before and after etching, indicated that the etching did not widen the gap appreciably. The resins could be divided into three groups according to gap width: "Epon" and Spurr performed best with a mean gap width of only 0.6microm. Vestopal W, Epofix, Epo-Kwick, Epo-Thin, and Technovit 9100 New constituted a group of medium performance with mean gap widths of 2.3, 3.4, 3.8, 3.9 and 3.9microm, respectively. Less satisfactory performance was observed for Unicryl, with a mean gap width of 7.4microm. CONCLUSIONS: It is concluded that "Epon" and Spurr should be chosen for high quality embedding of undecalcified teeth, while Epo-Kwick is an acceptable alternative if a faster procedure is needed.