Transcript GROW – Unit D1 Slides

Growth and
Development
University of Maryland School of Dentistry
Department of Orthodontics
UNIT D1
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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