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Epidemiological studies have shown a positive association between selenium intake and dental caries. The purpose of this study was to determine quantitatively the selenium content of normal human enamel in a racial group with low caries prevalence. Each enamel sample was simultaneously irradiated with a reference standard containing 1 μg of selenium. The irradiations were done for three weeks in a nuclear reactor in a thermal neutron flux of 2 × 1013n cm−2 sec−1. After a cooling period of 3 weeks these samples were dissolved and quantitatively transferred, with selenium carrier, to a distillation apparatus. A selective distillation was carried out and each distillate made up to 25 ml and transferred to a standard plastic container. The gamma-ray activity of 75Se was measured with a 50cm3 coaxial Ge(Li) detector coupled to a fully transistorized 4000-channel analyser. The data were recorded on magnetic tape and afterwards computer-processed. The distillation technique gave a 98 per cent yield of selenium, which makes the method experimentally acceptable. The selenium content of the composite enamel samples was 0.08 ± 0.03 ppm.

A system using acidulated phosphate-fluoride solution (APF) was studied for the topical application of fluoride on acid-conditioned teeth and then coating with a cyanoacrylate varnish. Enamel biopsies for fluoride determination were taken from the six anterior teeth in both arches of 23 subjects, aged 19–23 years. The teeth were acid-conditioned and APF applied. The upper left and lower right segments were varnished while the contralatcral segments were left as controls. The teeth were re-biopsied in groups at 1, 2, 4, 12, 24 and 52 week intervals. At all intervals, fluoride levels after treatment were significantly higher (p < 0.001) regardless of whether they had been coated or not than those before treatment. There was no significant difference between coated and control teeth. When all the data were pooled, however, a significantly greater (p < 0.05) fluoride retention was found in the coated teeth.

The sample to be analysed and a standard of known composition were irradiated simultaneously and the induced radioactivity compared. The investigation was done with high resolution Ge (Li) detectors coupled to fully transistorized 400 and 4000 channel analysers. By varying the irradiation time and conditions, it was possible to employ a non-destructive analytical procedure. The concentration of 16 elements, namely, Mg, Na, Cl, Al, Ca, Cr, Ba, Sb, Ag, Zn, Co, Fe, Sr, Au, Br and Mn was determined in normal human enamel and dentine by instrumental activation analysis.

Sectioning of the inferior alveolar nerve in rats maintains the patency of the mandibular canal. If the inferior alveolar neurovascular bundle is avulsed, however, the mandibular canal becomes obliterated by bone within a short time. The connective tissue component of the degenerated nerve maintains the patency of the canal.