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Biomedical subjects

A Demirjian

Publications and source records attributed to A Demirjian.

At least 19 recordsLinked to original sources
PubMed1992

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.

Adolescent↗
PubMed1991

A new teaching tool for dental and medical schools: multimedia CD-ROM on dental and skeletal development.

Multimedia teaching tools in Medicine are still very rare. Their presentation on a CD-ROM format is part of the emerging technologies in Medical Informatics. The Multimedia material presented here on Dental and Skeletal Development is mostly a Database and a Tutorial. The Database, which contains more than 2000 hand/wrist radiographs, is mostly intended for Pediatricians, Endocrinologists, Forensic Dentists and Physicians, as well as for Orthodontists and Pedodontists. The material is the result of 20-year of Longitudinal Growth study of children in Montreal. In this Multimedia CD-ROM, the research results are used for Medical teaching purposes.

Bone Development↗
PubMed1990

Mandibular growth prediction: mean growth increments versus mathematical models.

The aim of this study was to compare growth predictions obtained by adding mean annual velocities with predictions derived from a polynomial model of the population's growth curve. Given the child's previous measures at 11, 12 and/or 13 years of age, the cephalometric distance sella-gnathion at 15 years was estimated. Based on a sample of 223 boys and girls, the root mean square error decreased from 0.28 cm (males) and 0.18 cm (females) at 11 years, to 0.19 cm (males) and 0.12 cm (females) at 13 years. Root mean square errors were similar between methods, which was due to high correlations between measures across ages. Significantly, predictions based on mean increments were biased. They often over or underestimate growth for children who are larger and smaller than average. The observed bias was due to expected changes of variance associated with growth, which unconditional methods of prediction cannot control for. Predictions derived from growth models are conditional upon the child's size and are, therefore, unbiased.

Adolescent↗
PubMed1989

Modeling longitudinal mandibular growth: percentiles for gnathion from 6 to 15 years of age in girls.

Growth of the cephalometric landmark gnathion is modeled mathematically with multilevel statistical techniques. The findings, pertaining to a mixed longitudinal sample (N = 772) of 105 girls, 6 to 15 years of age, provide the most accurate descriptions of longitudinal mandibular growth presently available. Polar, rather than rectangular, coordinates are used to better distinguish between the amount and direction of growth. The velocity curve for sella-gnathion includes growth spurts during childhood (7.5 years) and adolescence (12.7 years). Growth direction of gnathion changes regularly throughout the age range, indicating a relative increase of vertical over horizontal growth. These reference standards serve as a basis for comparing and better understanding abnormal growth patterns.

Adolescent↗
PubMed1988

Pubertal growth of the cephalometric point gnathion: multilevel models for boys and girls.

Two-level polynomial models are used to summarize the amount Sella-Gnathion (S-Gn) and direction Nasion-Sella-Gnathion (N-S-Gn) of growth changes for the cephalometric landmark gnathion. Growth descriptions pertain to a mixed longitudinal sample of 209 French-Canadian children 10-15 years of age. The boy's growth curve attains mean minimum prepubertal velocity at 10.8 years and maximum pubertal velocity at 14.1 years. The girl's curve follows a cubic pattern, attaining maximum pubertal velocity at 12.1 years. Boys are larger than girls throughout the age range. Variation between-subjects increases with age in a curvilinear fashion. Growth direction of gnathion is more horizontally directed for girls than boys. Small but significant changes in growth direction occur between 10 and 15 years of age.

Adolescent↗
PubMed1986

Sexual dimorphism in the emergence of deciduous teeth: its relationship with growth components in height.

Sexual dimorphism in the emergence of the deciduous dentition of French-Canadian children may be explained by differences in recumbent length. Relative to the chronological age scale, boys are longer and their teeth emerge earlier than girls. Recumbent lengths attained at the exact age of emergence, as estimated by fifth-order polynomials fitted to each subject's serial data, are comparable between the sexes. Multi- and univariate analyses of variance show no significant sex differences in the lengths attained at the age of emergence of the deciduous teeth. These findings suggest that clinical standards for emergence of deciduous teeth scaled relative to length rather than chronological age are more accurate and efficient.

Age Factors↗
PubMed1986

Sexual dimorphism in mandibular growth of French-Canadian children 6 to 10 years of age.

Polynomial regression is used to model the mandibular growth of 28 girls and 26 boys who were followed longitudinally from 6 to 10 years of age. The pooled-within individual designs indicate that ramus height follows a linear pattern of size increase; corpus and total mandibular lengths display curvilineal, decelerating, patterns of growth over the age range. Multivariate analyses of variance reveal significant sex differences in size, favoring boys, for the two length measures at 6 years of age. Growth velocity for corpus length is also significantly greater in boys than in girls. Sexual dimorphism in the growth of total mandibular length is more complex, including differences in velocity and deceleration. Ramus height shows no significant pattern of variation between boys and girls for either size or growth velocity.

Aging↗
PubMed1986

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.

Adolescent↗
PubMed1985

Interrelationships among measures of somatic, skeletal, dental, and sexual maturity.

The interrelationships among five measures of physiologic maturity for 50 French-Canadian girls are evaluated--menarche, peak height velocity (PHV), 75% skeletal maturity, appearance of the ulnar sesamoid, and 90% dental development. The mean ages of occurrence of the events differed significantly (P less than 0.01). Menarche and 90% dental maturity showed the least variability. Ages of PHV, menarche, and 75% skeletal maturity were significantly correlated (P less than 0.05). Age of menarche was most closely associated with PHV. The appearance of the ulnar sesamoid was highly correlated with 75% skeletal maturity; both were equally related to the ages of PHV and menarche. The age at which French-Canadian girls attain 90% of their dental development showed no significant relationships with the other maturity indicators. The results imply that the mechanisms controlling dental development are independent of somatic and/or sexual maturity.

Adolescent↗
PubMed1985

Adjusting craniofacial correlations for technical error.

Reliability estimates provide a means of adjusting observed correlations for technical error. The results show that the true correlations among 11 craniofacial landmarks are consistently higher than observed values. Consequently, the regression slopes defining these relationships are also increased. The less reliable two measures are, and the closer their joint reliability approximates the observed correlation, the greater the expected change in true correlation. Adjusting craniofacial relationships for technical error may substantially increase the proportion of variation explained, and thereby alter statistical inferences drawn from results.

Cephalometry↗