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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.

1. The effects of frozen irradiated homogenous bone grafts on the healing of circumscribed defects in the mandibles and femora of forty albino rats have been studied. 2. The grafts were well tolerated by the host animals and did not appear in any way either to stimulate or to inhibit osteogenesis. The rate of healing of the defects containing the homografts compared favourably with that of the control defects.

A new composite restorative material, Enamelite, has recently been introduced for the conservative treatment of cervical erosion and hypoplastic enamel surfaces. The pulpal response elided by the restorative material was investigated in teeth of the vervet monkey and compared to a modified zinc oxide-eugenol cement. Buccal or labial Class V cavities were prepared in 128 teeth in six vervet monkeys. The teeth in contralateral segments were restored with the restorative and control materials, respectively. The experimental animals were killed at 4, 14 and 42 days. The restorative and control materials exhibited about the same minimal degree of cellular displacement and inflammatory response at each of the three postoperative time intervals. The percentage of specimens with reparative dentin increased progressively with time. At all three intervals the restorative material elicited a greater response than the control zinc oxide-eugenol cement. The results suggest that the clinical application of the restorative material on cervical eroded or hypoplastic enamel surfaces without a protective lining is a safe procedure.

The concentrations of magnesium, sodium, chlorine, aluminum, and calcium in pooled human dental calculus dried to constant weight at 105 C were determined by instrumental neutron activation analysis. Their mean concentrations were 0.50 ± 0.04%, 0.37 ± 0.03%, 0.09 ± 0.01%, 96.08 ± 14.63 ppm, and 28.04 ± 1.70%, respectively.

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.

The sample to be analysed, and a standard of known composition, were irradiated simultaneously in the poolside facility of a nuclear reactor for 130 hours in a thermal neutron flux of approximately 2×1013 n.cm−2. sec−1, and the induced radioactivity compared after a cooling period of four weeks. The investigation was done with a high resolution Ge(Li) detector coupled to a fully transistorized 4000 channel analyser. The concentration of five elements, namely Sb, Ag, Zn, Co and Fe, was determined in human dental calculus by instrumental activation analysis and found to be 0,68 ppm, 0,18 ppm, 174 ppm, 0,08 ppm and 54 ppm respectively.

Summary Conditioning of the enamel surface is an accepted procedure in several disciplines of dentistry to obtain increased bonding of dental materials to tooth surfaces. Three etching solutions commonly in use are 50% phosphoric acid, 50% phosphoric acid attenuated with 7% zinc oxide by weight and 50% citric acid. The effects of these solutions on the contact angle of an uncured epoxy resin on, and the bond strength of an epoxy resin formulation to polished enamel surfaces were investigated and compared with the results obtained on polished, unconditioned surfaces. In addition, the rates of etching of enamel surfaces by these acids were determined. The attenuated phosphoric acid produced the greatest reduction in contact angles and the most marked increase in bond strengths. 50% phosphoric acid etched the enamel surface to a greater extent than the other conditioning solutions.

The chemical treatment of tooth surfaces to improve bonding of dental materials to enamel and dentin is one of the approaches in overcoming the lack of adhesion of the available restorative materials to tooth structure. The acid etch technique is now an accepted procedure in restorative and preventive dentistry and for the direct bonding of orthodontic attachments. The pulpal response elicited by one of the conditioning agents, 50 % H3PO4 applied for 1 minute, was investigated in the teeth of the vervet monkey. The differences between most of the criteria used to evaluate the pulpal responses in acid-treated and control teeth at three time intervals, namely 4, 14 and 42 days, were statistically significant. These results suggest that a protective lining should be used to cover exposed dentin before etching adjacent enamel surfaces with 50 % H3PO4.

Summary None of the materials presently available to the dental profession truly dhere to enamel and dentine. Conditioning of the enamel surface with phosphoric acid greatly increases the bonding of dental materials to tooth structure and the etching technique is now an accepted and widely applied procedure in dentistry. During the development and laboratory evaluation of new dental materials, the resin-enamel bond strength is determined by means of tensile loading tests. The site of failure is often recorded as occurring within the test material; partly within the material; at the adhesive-enamel interface; within the enamel; or in a combination of these sites. An epoxy resin formulation developed for the direct bonding of orthodontic attachments was used as the adhesive and enamel etched with 50% phosphoric acid as the adherend surface. Experimental bonds were subjected to tensile stresses to failure and both the enamel and adhesive aspects of the fractured bonds examined by scanning electron microscopy. The results indicate that the sites of failure cannot be reliably classified by visual examination per se or under low magnification. A model is proposed to elucidate the characteristics of interfacial failures. This experimental model was tested by surface roughness profiles and atomic absorption spectrometry.

Conditioning with 50% phosphoric acid produces preferential etching of the enamel surface. Intimate interfacial contact is established between the adhesive and the etched enamel and tags of resin up to 50 μm in length project into the conditioned enamel surface. Etching increases the wettability of the enamel surface.

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.