Rare and Common Variants Conferring Risk of Tooth Agenesis.

We present association results from a large genome-wide association study of tooth agenesis (TA) as well as selective TA, including 1,944 subjects with congenitally missing teeth, excluding third molars, and 338,554 controls, all of European ancestry. We also tested the association of previously identified risk variants, for timing of tooth eruption and orofacial clefts, with TA. We report associations between TA and 9 novel risk variants. Five of these variants associate with selective TA, including a variant conferring risk of orofacial clefts. These results contribute to a deeper understanding of the genetic architecture of tooth development and disease. The few variants previously associated with TA were uncovered through candidate gene studies guided by mouse knockouts. Knowing the etiology and clinical features of TA is important for planning oral rehabilitation that often involves an interdisciplinary approach.

Emergence of permanent teeth and onset of dental stages in the population of Iceland.

The purpose of this investigation was to determine the mean ages at emergence of the permanent teeth of Icelandic children, as well as the mean ages at onset of the dental stages (DS). The material consisted of 1,941 randomly selected children, corresponding to 9.5% of the total primary and secondary school population of Reykjavik. The mean ages at emergence of the permanent teeth, along with the ages at commencement of DS 2, DS3, DS4 and DS M2, are given. Owing to the age distribution of the material, it was not possible to give mean ages at emergence of the first and third molars, or of the mandibular central incisors. A comparison of the emergence-ages in Icelandic children with those of Danish and Norwegian children showed close agreement.

Emergence of primary teeth and onset of dental stages in Icelandic children.

This study was undertaken to elucidate the mean ages at emergence of primary teeth and at the onset of dental stages DS 01 and DS 02 in Icelandic children. The material comprised 927 children (498 boys and 429 girls) aged 0-83 months who were presented for regular examinations in two Health Centers and children in three kindergartens in Reykjavík. Comparison of the mean ages at emergence of primary teeth in Icelandic, Finnish, Swedish, US, and Hungarian children disclosed a significantly earlier emergence in the Icelandic children, except that in Finnish children it was similar.

An epidemiologic study of occlusal anomalies in relation to development of the dentition in Icelandic children.

The purpose of the investigation was to determine the prevalence of occlusal anomalies in relation to dental stages (DS) in Icelandic schoolchildren, and to compare it with results from other Scandinavian countries and Ireland found on the basis of the same method. The material consisted of 1,641 randomly selected children, 791 boys and 850 girls, corresponding to 9.5% of the total primary and secondary school population of Reykjavík. A significant sex difference was only recorded in the frequencies of of two of the single morphologic traits of occlusal anomalies, the boys showing higher frequencies in deep bite and in scissors-bite. Significant differences in the occurrence of occlusal anomalies in Iceland and Denmark were only found in two out of 108 pairs of frequencies.

An epidemiologic study of dental space anomalies in Icelandic schoolchildren.

This study was performed mainly to determine the prevalence of space anomalies with regard to the various stages of dental development in Icelandic schoolchildren. The sample consisted of 1,641 randomly selected children (791 boys and 850 girls), making up 9.5% of the children attending all primary and secondary schools in Reykjavík during the school year 1972--73. In most of the frequencies of the different space anomalies boys showed a higher prevalence than girls. In both sexes there was often a significant difference from one stage of dental development to another. The results were compared with those reported for other ethnic groups.

Prevalence of hypodontia and malformations of permanent teeth in Iceland.

This study was performed to elucidate the prevalence of hypodontia and congenital malformations of permanent teeth in Iceland. Computer analysis was done on the basis of results from examining 1,116 children (521 boys and 595 girls), or about 9.5% of all schoolchildren in Reykjavík in stages DS 3 (canines and premolars erupting) and DS 4 (canines and premolars fully erupted) of dental development at the time of the study. The age range was mainly from 8-16 years. The prevalence of congenitally missing teeth (second and third molars excluded) was 6.7% in boys and somewhat higher, 8.9%, in girls, 7.9% for both sexes combined. On the average, each child was missing 1.9 teeth. In the girls, the most commonly absent teeth were the mandibular second premolar (55%), the maxillary second premolar (19%), and the maxillary lateral incisors (18%). In the boys the figures were 51%, 18%, and 10%, respectively. Malformation of permanent teeth, mainly in the form of pegshaped maxillary laterals, was also less common in the boys, 1.3% against 3.0% in the girls, and 2.2% for both sexes combined. Among Icelandic children hypodontia and/or congenital malformation of permanent teeth were found in 9.1%.

Skeletal maturation of the hand in Iceland.

The mean time at onset of the stages of skeletal maturation of the hand, PP2=, MP3=, S, MP3cap, DP3u, PP3u, and MP3u, in a cross-sectional sample of Icelandic school chidren in Reykjavík, a total of 1426 (690 boys and 736 girls), was assessed on radiographs of the hand and compared with results published from Denmark and Greenland. On the whole, the Icelandic children were most ahead, while S appeared at about the same time in all three nations. Otherwise, the mutual relationship between the skeletal stages was very similar. Girls reached all stages significantly sooner than boys, and this agrees with the findings in Denmark and in Greenland. The sex difference was most marked in the Icelandic material. The accidental error due to method in assessing the differences in skeletal maturation proved to be less than 5%, similar to that reported by others.

Hypodontia, hyperodontia, and double formation of primary teeth in Iceland. An epidemiological study.

The aim of this study was to determine the prevalence of hypodontia, hyperodontia, and double formation of primary teeth in Icelandic children in the dental stage DS 02 (primary dentition complete). The study group comprised 927 children (498 boys and 429 girls). This was about 9% of all children aged 0-83 months in Reykjavik at the time of the registration of these anomalies, during the winter of 1978-1979. The children included those presenting for regular examinations in two health centers, children from three kindergartens, and seven pre-school classes from two schools in Reykjavik. Of these children 61.9% were selected for this study as they proved to be in dental stage DS 02 (primary teeth fully erupted). The prevalences were hypodontia, 0.5%; hyperodontia, 0.5%; and double formation, 0.7%. Comparison was made with earlier results from Iceland and with results from several other nations.

Prevalence of gingivitis in 6-year-olds in Reykjavik, Iceland.

As part of a wider investigation of malocclusion, the aim of this study was to determine the prevalence of gingivitis in 6-year-olds in Reykjavik. Parents and guardians of the 401 children in 8 schools were invited by letter to have their children take part. There were 230 positive replies (57%). The Gingival Bleeding Index was used to determine the condition of the gingiva on mesiobuccal and buccal surfaces of 6 selected teeth (totaling 12 surfaces). The results showed that 26% had healthy gingivae, 23% showed bleeding from one surface, 20% from two, 17% from three, and 15% from four to eight surfaces. There were no statistically significant differences in the number of bleeding surfaces between boys and girls. The mean GBI for the whole group was 16%. Gingivitis in this group was therefore prevalent but usually slight.

Prevalence of malocclusion in 6-year-old Icelandic children.

The prevalence of different malocclusion features was investigated in 396 6-year-old Icelandic children, using the epidemiologic registration method described by Björk et al. in 1964. Girls were ahead of boys with regard to dental stage (P < 0.01). One or more permanent teeth were congenitally missing in 5% of the children. Postnormal occlusion was found in 27% of the boys and in 31% of the girls, and prenormal occlusion was found in 6% and 5%, respectively. Straight terminal plane at the second deciduous molars was found in individuals with either normal or postnormal occlusion. Thus, it can be misleading to use the relation of the terminal planes as a measurement of the sagittal relation between the jaws. The prevalence of hypodontia was much lower than has been reported previously for Icelandic children.

Craniofacial morphology in 6-year-old Icelandic children.

The purpose of the study was to describe the craniofacial characteristics of 6-year-old Icelandic children, make a normative standard for children with an Angle Class I molar relationship, and compare them to those with an Angle Class II molar relationship. The material consisted of the radiographs of 363 children, 184 (50.7 per cent) boys and 179 (49.3 per cent) girls with a mean age of 6 years 7 months (range: 5 years 7 months-7 years 8 months). Twenty-two reference points were digitized and processed by standard methods with the Dentofacial Planner computer software program. The 33 variables calculated included both angular and linear. Two sample t-tests were used to study the differences between different groups. Only minimal differences could be noted between sexes in sagittal and vertical angular measurements. Linear measurements, on the other hand, were usually larger for the boys. When compared with Norwegian material of the same age group, similar trends were observed between sexes in both studies, but the Icelandic children showed slightly more mandibular prognathism and a lower mandibular plane angle. When compared with children with an Angle Class I molar relationship, children with an Angle Class II molar relationship did not have a different maxillary prognathism nor a different mandibular length. Cranial base dimensions were all significantly greater and the cranial base flexure was also significantly more obtuse in the distal group.