John Silness

Periodontal Disease in Pregnancy I. Prevalence and Severity

(1963). Periodontal Disease in Pregnancy I. Prevalence and Severity. Acta Odontologica Scandinavica: Vol. 21, No. 6, pp. 533-551.

Longitudinal relationship between incisal occlusion and incisal tooth wear

The purpose of the study was to evaluate the longitudinal relationship between incisal wear of central incisors and the size of vertical overbite (OB) and horizontal overjet (OJ). Stone casts of 51 subjects were used for the determinations. Casts were obtained when the subjects were 15 and 27 years old. Statistical analysis was performed with the t test for paired samples, the chi-square test of association. Pearsons product moment correlation coefficient, and Spearmans rank correlation coefficient. Both overbite and overjet diminished after 12 years, and incisal wear increased. It was concluded that increase in age, incisal wear, vertical overbite and incisal occlusion (OB/OJ) are clinical predictors of wear of maxillary and mandibular central incisors in adolescents.

The Structure and Mineralization of the Carapace of the Crab (Cancer pagurus L.)

Hegdahl, T., Silness, J. & Gustavsen, F. 1977. The structure and mineralization of the carapace of the crab (Cancer pagurus L.). 1. The endocuticle. Zool. Scr. 6: 89-99. The endocuticle of the dorsal carapace of Cancer pagurus in the intermoult condition was studied by means of light microscopic, electron microscopic, microradiographic, X-ray diffraction, and electron probe techniques. Within the lamellae the fibrils and the long axes of the calcite crystals were parallel and ran horizontally. The cuticle appeared lamellar for two reasons: (1) an alternation in the direction of the fibrils as well as the long axes of the calcite crystals in various vertical levels gave rise to the lamellar appearance; (2) in a zone subjacent to the exocuticle differences in the degree of mineralization often brought about a marked layering of the endocuticle. The fibrils were contained in tubes made up by the inorganic crystals. In undecalcified preparations the pore canals were elliptic in cross section. They contained filamentous material in which very small crystals were indicated. The walls of the pore canals did not possess any structurally differentiated lining. At diametrically opposite ends of the pore canal cross sections very large crystals occurred. Results of measurements of dimensions of fibrils, inorganic tubes, pore canals, and crystals in various sites are presented. Trond Hegdahl, John Silness & Finn Gustavsen, School of Dentistry, University of Bergen, Arstadveien 17, N-5000 Bergen, Norway.

Distribution of corrosion products in teeth restored with metal crowns retained by stainless steel posts.

The nature and distribution of corrosion products in teeth restored with metal crowns retained by stainless steel posts were examined by means of energy-dispersive X-ray microanalysis, microradiography, and electron microscopy. The corrosion products consisted of calcium, phosphorous, iron, chromium, nickel, zinc, stannum and other elements. A possible root fracturing mechanism is discussed.

The Structure and Mineralization of the Carapace of the Crab (Cancer pagurus L.) 2. The exocuticle

Decalcified and undecalcified preparations of the crab Cancer pagurus in the intermoult condition were studied to examine the mineralization and structure of the epicuticle, using light microscopic, electron microscopic, and microradiographic methods. The epicuticle was found to be composed of two layers, one superficial membrane, and one thicker layer, measuring 1‐2 μm. From the base layer spines or microtrichia projected. These were approximately 18 μm long and built like the remainder of the epicuticle. The spines and the base layer of the epicuticle contained vertical canals which in undecalcified sections accomodated columns of crystals. These canals were the only location in which minerals occurred in the epicuticle. In decalcified preparations filamentous strands were observed in the canals. Elsewhere in the epicuticular tissue no fibrillar structure was observed. The canals and their contents seemed to extend across the junctional zone between the epicuticle and the exocuticle.

Prevalence, pattern, and severity of incisal wear in dental students

This paper describes the prevalence, pattern, and severity of incisal wear of anterior teeth in 64 dental students at an average age of 23 +/- 1.7 years with a high number of permanent teeth present. The index used to assess wear on stone casts (IwI) was shown to have good reproducibility. The results indicated that about 98% of the anterior teeth had been worn to various degrees. In both jaws central incisors were most commonly affected by incisal wear, canines followed next in order, and lateral incisors were least commonly affected. Wear of identical teeth on the right and left side tended to be bilaterally symmetrical in both jaws. The results of these initial observations suggest that data from re-examination of this study group will lend themselves to detecting possible changes of the pattern and severity of incisal wear of permanent anterior teeth.

Distribution of artificial crowns and fixed partial dentures

Since its inception six years ago, students at this institution have fabricated single artificial crowns for 743 women and 396 men. In addition, 363 women and 241 men received fixed partial dentures. Most of the patients were between 20 and 70 years of age. The youngest was 14 years of age, and the oldest 81 years. The students recorded all details of treatment which provided the data for this report.

A 2-year follow-up study of incisai tooth wear in dental students

This report was derived from cross-sectional and longitudinal analyses of prevalence, pattern, and severity of incisal wear in 64 dental students who had virtually complete dentitions at the first examination and unchanged dentitions at the re-examination. They were first examined in 1991 and re-examined after 24 months in 1993. The average age of the students in 1991 was 23 +/- 1.7 years. Assessment of incisal wear was made on stone casts based on silicone impression material in accordance with the Incisal wear Index (IwI). The results showed that the prevalence of incisal wear had not changed during the observation period. The severity of incisal wear for maxillary and mandibular central and lateral incisors had remained essentially the same, whereas the severity of wear of maxillary and mandibular canines had increased during the observation period. There was no statistically significant relationship between age and IwI. The wear pattern found for anterior teeth is discussed in relation to the cuspid protection and the group function theories of occlusion.

Area of the organic-inorganic interface of dental enamel

The area of the organic-inorganic interface of several kinds of dental enamel was determined by examining on a computer images based on electron micrographs of decalcified sections. The mean values varied between 0.1363 m2/mm3 and 0.2229 m2/mm3. Assuming a specific gravity for dental enamel of 3.15 the corresponding values were 43 m2/g and 71 m2/g, respectively. The possibility that fluoride may influence the area of the organic-inorganic interface was discussed.

Re-examination of incisal tooth wear in children and adolescents.

The material presented in this report was derived from a longitudinal study of the development and progress of incisal tooth wear in children and adolescents. The study group was established in 1991-1992 (baseline examination) and consisted of participants between 8 and 15 years of age. They were re-examined in 1993 (interim examination) and in 1994 (final examination). In all, 77 school children (30 females and 47 males) participated in the three examinations. The timespan between baseline and interim was on average 15 months and the period between interim and final examination averaged 16 months. The total observation period was approximately 32 months. Assessments of incisal wear was made on stone casts using the incisal wear index which was shown to have good reproducibility. The results demonstrated that the prevalence and severity of incisal wear had increased significantly with age. In general the rate of incisal wear progression was higher between baseline and interim than between interim and final examination. In this respect certain differences between the tooth types seemed to exist. At baseline the relationship between age and incisal wear was positive and statistically significant for all tooth types. At the final examination the strength of this relationship had decreased for maxillary and mandibular central and lateral incisors. For canine teeth of both jaws the relationship between age and incisal wear was no longer statistically significant at the final examination.