A. Demirjian

New systems for dental maturity based on seven and four teeth

An updated system for estimating dental maturity is presented. It extends the original system (Demirjian et al., 1973) based on radiographs of 7 teeth by including two extra stages, and by enlarging the standardizing sample to include 2407 boys and 2349 girls. Percentile standards from ages 2-5 to 17-0 years are presented separately for boys and girls. Scoring systems and percentile standards are presented for two different sets of 4 teeth and a comparison of all three systems is made. It is suggested that these systems may measure somewhat different aspects of dental maturity.

Sexual Differences in Dental Development and Prediction of Emergence

The dental development of a genetically homogeneous French-Canadian group of children ranging in age from 2.5 to 19 years was evaluated from 5,437 panoramic radiographs by the method of Demirjian et al. 8 The maturity of each mandibular tooth was evaluated individually. For each stage of each tooth, the developmental curves of boys and girls were compared. A common pattern was found for each tooth, namely the chronological similarity -between boys and girls in the early stages of development and the advancement of girls over boys for the later stages. Developmental scores were given to the seven mandibular teeth. Up to five to six years of age, no difference was found in the timing of dental development between boys and girls, in contrast to the older ages where girls were always more developed than boys. When the emergence curve was plotted with developmental curves, a close relation was established between the stage of formation of all teeth and their emergence, hence the predictive value of the use of dental maturity curves in clinics.

Sexual Dimorphism in the Development, Emergence, and Agenesis of the Mandibular Third Molar

The development, alveolar emergence, and agenesis of the mandibular third molars, in a homogeneous group of French-Canadian children and young adults ranging in age from seven to 25 yr, were evaluated from 4640 panoramic radiographs using the method of Demirjian et al. 8 Clinical emergence was recorded from dental casts of children between 15 and 19 yr. The occurrence of bilateral agenesis was about 9%, without significant sexual difference. The left and right third molars had the same pattern of crown and root development and emergence. Girls were ahead of boys up to the second half of crown formation, but this sexual difference disappeared at the first stage of root formation. The root development course was faster in males than in females. At the apex closure, the sexual difference was much more marked for retarded cases (about 2.7 yr) than for median (1.5 yr) or advanced cases (0.4 yr). For alveolar and clinical emergence, males were about six mo ahead of females at the median level.

The pattern of facial growth before and during puberty, as shown by French-Canadian girls.

The results are reported for an analysis of longitudinal sequences of lateral head X-rays of 50 Montreal girls, taken annually between the ages of 6 and 15 years. Mean size changes for distances within the cranial base, the maxilla and the mandible, as well as those outlining the facial polygon, are displayed on a common proportional scale based on mean sizes at 15 years old. Mean growth velocities are displayed on both a chronological age scale and on one relative to the individual age of peak growth velocity in stature. A distinct facial pattern of growth is established, In terms of the proportion of final size achieved during childhood, it is below the cranial pattern, but above the general skeletal one. This facial pattern shows a pubertal peak in growth, but one quantitatively less important than that for stature. The timing of the two peaks is closely aligned, although the evidence favours a slightly later development for the face. The mandibular ramus provided the sole exception to this common facial pattern, though some questions on maxillary growth remain open.

A polynomial approach to craniofacial growth: Description and comparison of adolescent males with normal occlusion and those with untreated Class II malocclusion

Orthogonal polynomials are used to model the craniofacial growth of adolescent boys, aged 11 through 14 years, and to evaluate variation between normal occlusion and untreated Class II malocclusion. The results show linear growth (velocity) for the maxillary measures; their angular relationships to the cranial base remain stable throughout the age range. Mandibular measures show growth velocity and acceleration, indicating the adolescent growth spurt. For the majority (80%) of measures, boys with normal occlusion and those with Class II malocclusion were not significantly different. Mean growth velocity of basion-nasion is significantly greater for subjects with Class II, Division 1 malocclusion. Total mandibular length and the ANB angle display significant mean size (constant) differences between boys with normal occlusion and boys with untreated Class II malocclusion. The groups are comparable in growth velocity and acceleration, indicating that the size differences are established before 11 years of age and maintained during adolescence.

Sexual Dimorphism in the Emergence of the Deciduous Teeth

Exact ages of emergence of the twenty deciduous teeth have been investigated on a longitudinal sample of 195 French-Canadian children (113 boys and 82 girls). A multivariate analysis of variance yielded a significant overall sex difference (p<O. 0001). It has been found that the emergence of the deciduous dentition in boys is more precocious than that in girls by about one month; this difference is present at the emergence of the upper central incisor and is maintained henceforth. The only notable exception to this pattern is the emergence of the first molars. Results of the present study, combined with those of previous research, suggest that sexual dimorphism in the emergence of the deciduous teeth could be mediated through ethnic factors.

The Inter-examiner Variation in Rating Dental Formation from Radiographs

Six examiners evaluated dental formation on 191 radiographs, using an eight-stage system. Discrepancies between these examiners are generally of the order of ± one stage, in about 20 to 25% of the cases. The authors thus suggest the use of reference radiographs, for the double purpose of ensuring a homogeneous rating by two examiners or more, as well as the assessment of eventual differences between populations.

Childhood and pubertal growth changes of the human symphysis.

Longitudinal growth changes of the human symphysis were evaluated for 75 children (37 males and 38 females) between 6 and 15 years old. Childhood growth was described by mean yearly rates of change between 6 and 10 years for females and between 7 and 11 years for males; pubertal changes pertain to growth between 10 and 14 for females and between 11 and 15 for males. Cephalometric tracings of the mandible were superimposed using stable reference structures. Vertical growth changes, particularly for landmarks located in the upper 20% of the symphysis, were most pronounced. Annual rates of vertical growth ranged between 0.9 mm/yr for the lingual incisor contact point to -0.2 mm/yr for gnathion. Males showed significantly greater rates of vertical growth than females, especially for the upper half of the symphysis. Vertical growth rates were also greater during puberty than during childhood. The horizontal growth changes indicated lingual movement of most symphyseal landmarks. Annual rates of growth were greatest for landmarks located in the upper half of the symphysis. B-point showed the greatest lingual drift. During puberty, the mandibular incisors in females moved lingually as the upper anterior half of the symphysis remodeled; in males, the incisors maintained their horizontal position as the labial sulcus developed.

Cephalometric reliability. A full ANOVA model for the estimation of true and error variance.

A detailed description of sampling designs for assessing the reliability of cephalometric measurements, emphasizing distinctions between true and observed variance, random and systemic components of variance, and complete and minimal models for evaluating measurement error.

Age at menarche in French Canadian urban girls

SummaryIn 1969–1970, a random sample of 1002 girls aged 10·5 to 15·0 from different socio-economic strata were interviewed in Montreal schools. The mean age at menarche of these urban girls was 13·08±0·04 years (S.D. 1·10) from probit analysis. French Canadian girls today commence menarche at about the same age as British girls and about 8 months earlier than Montreal girls three decades ago. Contrary to findings in most other populations (with a different level and way of life), French Canadian girls from upper socio-economic groups mature later than girls from lower socio-economic groups.Girls from large families or with more linear physique were older at menarche than others. Family size and the type of physique were independent factors. There was a close relation between social class and family size, and we consider family size to be one of the most important factors contributing to the different onset of sexual maturation of girls in different socio-economic strata.