Growth and Development University of Maryland School of

Growth and Development University of Maryland School of Dentistry Department of Orthodontics

UNIT D 1 Later Stages of Development

Overview • Adolescence: The Early Permanent Dentition Years – Initiation of Adolescence – Timing of Puberty • Growth Patterns in the Dentofacial Complex – Dimensional Changes

Adolescence The Early Permanent Dentition Years • This period is particularly important in dental and orthodontic treatment, because the physical changes at adolescence affect the face and dentition • Major events: – Exchange from mixed to permanent dentition – Acceleration in the overall rate of facial growth – Differential growth of the jaws

Initiation of Adolescence • First events occur in the brain • Brain cells in hypothalamus begin to secrete substances called releasing factors • Pituitary portal system plays central role • The increasing level of sex hormones also causes other physiologic changes, including the acceleration in general body growth and shrinkage of lymphoid tissues seen in the classic growth curves • Neural growth is unaffected by the events of adolescence, since it is essentially complete by age 6

Diagrammatic representation of the cascade of endocrine signals controlling sexual development Copyright © 2007 Mosby, Inc. , an affiliate of Elsavier Inc.

Timing of Puberty • considerable individual variation • Adolescent growth spurt on average 2 years earlier in girls than in boys important impact on the timing of orthodontic treatment • Chronologic age only a crude indicator of where an individual stands developmentally • The stage of development on secondary sexual characteristics provides a physiologic calendar of adolescence that correlates with the individual’s physical growth status • Girls mature earlier on average, and finish their growth much sooner. • Timing of puberty affected by both genetic and environmental influences • Seasonal and cultural factors can affect the overall rate of physical growth

Growth curves for the maxilla and mandible show against background of Scammon’s curves. Copyright © 2007 Mosby, Inc. , an affiliate of Elsavier Inc.

Adolescence in girls • Stage 1: – Starts at beginning of physical growth spurt – The peak velocity of physical growth occurs about 1 year after the initiation (coincides with stage 2) • Stage 2: – Peak velocity of physical growth – Sexual characteristics develop (breast, pubic hair, axillary hair) • Stage 3: – Occurs 1 to 1. 5 years after stage 2 – Onset of menstruation – By this time growth spurt is complete

Adolescence in boys • Stage 1: – “fat spurt” – boy gains weight and becomes chubby (estrogen production by Leydig cells) • Stage 2: – About 1 year after stage 1 – Spurt in height just beginning – Decrease in subcutaneous fat, pubic hair begins to appear • Stage 3: – Occurs 8 – 12 months after stage 2 and coincides with peak velocity and gain in height – Axillary and facial hair – Muscles grow, more angular body form • Stage 4: – From 15 to 24 months after stage 3 (difficult to pinpoint) – Growth spurt in height ends – Facial hair on chin and upper lip, increase in muscular strength

Growth of the jaws • Usually correlates with physiologic events of puberty • There is an adolescent growth spurt in the length of the mandible, and modest increase in growth at the sutures of the maxilla • The cephalocaudal gradient of growth is evident in puberty • More growth in lower than upper jaw (differential growth) • Maturing face becomes less convex as the mandible and chin become more prominent as a result of the differential jaw growth

Growth Pattern in the Dentofacial Complex

Dimensional Changes 1. Growth of the Nasomaxillary Complex – Growth of this area produced by two basic mechanisms – (1) Passive displacement, created by growth in the cranial base that pushes the maxilla forward, and (2) active growth of the maxillary structures and nose Diagrammatic representation of a major mechanism for growth of the maxilla Copyright © 2007 Mosby, Inc. , an affiliate of Elsavier Inc.

2. Mandibular Growth – – – Growth continues at steady rate before puberty On average, ramus height increases 1 to 2 mm per year and body length increases 2 to 3 mm per year Accentuation of the prominence of the chin The increase in chin prominence with maturity results from a combination of forward translation of the chin as part of the overall growth pattern of the mandible and resorption above the chin that alters the bony contours Growth changes in the glenoid fossa are a source of variability in how much chin grows forward

3. Timing of Growth in Width, Length, and Height – For the three planes in space in both maxilla and mandible, there is a sequence in which growth is “completed” – Growth in width is completed first, then growth in length, and finally growth in height – Width of both jaws, including width of both dental arches, tends to be completed before the adolescent growth spurt – As the jaws grow in length posteriorly, they also grow wider. For the maxilla, this affects primarily the width across the second molars – Growth in length and height of jaws continues through puberty. In girls, maxilla grows slowly downward and forward to age 14 to 15 (2 to 3 years after menstruation), then tends to grow almost straight forward – In both sexes, growth in vertical height of face continues longer than growth in length, with the late vertical growth primarily in the mandible – Increase in facial height and concomitant eruption of teeth continue throughout life; (adult occlusal equilibrium)

Short face individuals: • • short anterior lower face height excessive forward rotation of the mandible during growth Nearly horizontal palatal plane and mandibular morphology of the “square jaw” type Deep bite malocclusion and crowded incisors

Long face individuals • Excessive lower anterior face height • Palatal plane rotates down posteriorly • Often creating a negative, rather than the normal positive inclination to the true horizontal • Mandible shows an opposite, backward rotation, with an increase in mandibular plane angel • Associated with anterior open bite malocclusion and mandibular deficiency (because chin rotates back as well as down)

Growth patterns Nomal hyperdivergent hypodivergent

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