The Carabelli trait and its association with maxillary molar crown base and cusp size was studied in a group of 128 Kwengo, a San-Negro hybrid community living in Western Caprivi, Namibia. The trait was classified according to a modification of the scheme put forward by Dahlberg and by Scott (In: Dental Anthropology, New York: Pergamon, 1963) (Hum. Biol. 52:63-78, 1980). Crown base areas were larger in trait-positive than in trait-negative molars, and this difference existed for all eight categories of the trait in the first molar and for most of the categories in the second and third molars. The degree of expressivity of the trait seems to be associated with molar size, but this is more apparent in the first than in the second and third molars.

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Implants of decalcified allogenic bone matrix (DABM) have been shown to induce the formation of bone when implanted in extraskeletal sites (Urist, M.R., et al. Sci. 150: 843, 1965). The purpose of this study was to investigate the bone induction effect of DABM on the cell population of organising haematomata in rats. Cylindrical silicone rubber chambers with perforated walls were filled with autologous blood and an implant of DABM and implanted on to the surfaces of the external oblique abdominal muscles in 15 Long Evans rats. Groups of 3 rats were killed at intervals of 1, 2, 3, 4 and 6 weeks after operation. The implanted chambers were recovered and the enclosed tissues were fixed in buffered formol saline, processed for histological sectioning. Transversely cut sections were prepared through the chambers and stained with haematoxylin and eosin.Granulation tissue grew into the clotted blood and surrounded the implants. At 3 weeks deposits of new bone and cartilage were present on the walls of excavation chambers which had formed in the implanted DABM. Increasing amounts of bone were present in the 4 and 6 week specimens. New bone only formed within the limits of the DABM implants and did not extend into the surrounding granulation tissue in the organising haematomata.Four cements of varying composition available for orthodontic band cementation were selected. These were: a composite cement, a carboxylate cement, a silico-phosphate cement and a zinc phosphate cement. The cements were evaluated for tensile bond strength to enamel and orthodontic band material. They were also subjected to tests for marginal leakage utilising a dye penetration technique. The composite cement had the highest mean tensile bond strength to enamel, 11,1 megapascals (SD 3,5) and also to band material, 2,5 megapascals (SD 0,5)The results indicated that there was a statistically significant difference between the tensile bond strengths to both human enamel and band material of the composite and carboxylate cements (P< 0,05). There was also a statistically significant difference between the tensile bond strength to enamel between the carboxylate and silico-phosphate cements. No marginal leakage occurred at the enamel/cement interface of either the composite or carboxylate cements. The scanning electron microscope was used to examine normal human enamel, areas of enamel decalcification on freshly extracted human teeth, enamel etched with the "conditioner" supplied with the composite cement, and the fitting surface of band material. Differences were shown between enamel etched with the "conditioner" and decalcified enamel areas on extracted human teeth. It is suggested that the most important interface, insofar as prevention of decalcification and caries formation are concerned, is the enamel/ cement interface. Failure at this interface could be an important cause of enamel decalcification beneath orthodontic bands. Electrical Resistance Measurements and other Physical Properties of Stressed and UnstressedBone.CH. ERIKSSON*. School of Dent...