Post on 07-Apr-2018
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development of the skull
� at birth:
± frontal and parietal eminences are especially
prominent
± skull of a newborn infant is disproportionately
large compared with other parts of the
skeleton; however, the facial skeleton is small
compared with the calvaria� newborn: ~1/8
� adult: 1/3 of the skull
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� large size of the newborn's calvaria
± precocious growth & dev¶t of the brain
� smallness of the face ± rudimentary development of the maxillae,
mandible, & paranasal sinuses
± absence of erupted teeth
± small size of the nasal cavities
The rudimentary development of the face makes the orbits appear relatively large
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sutures and fontanelles
� sutures
± membranous tissue spaces separating the
bones of the skull in infants
� fontanelles
± areas where the major sutures intersect in the
anterior and posterior portions of the skull
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± anterior fontanelle� at birth = 4 cm to 6 cm in
diameter
� closes between 4 and 26
months of age
� 90% between 7±19 mos
± posterior fontanelle� at birth = 1 cm to 2 cm
� usually closes by 2 months
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� softness of the bones and their loose connections at the sutures
± enable the calvaria to undergo changes of shape (molding) during birth
during passage of the baby
through the birth canal
frontal bone becomes flat
occipital bone is drawn out
one parietal bone slightlyoverrides the other
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� Within a few days after birth, the shape of the
calvaria returns to normal.
� The resilience of the bones of the fetal skullallows it to resist forces that would produce a
fracture in adults.
� The fibrous sutures of the calvaria also permitthe skull to enlarge during infancy and
childhood.
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� increase in the size of the calvaria is
greatest during the first 2 years, the period
of most rapid brain development
� person's calvaria normally increases in
capacity until 15 or 16 years of age
after this, the calvaria usually increasesslightly in size for 3 to 4 years because of
bone thickening
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Age Changes in the Face
� mandible
±most dynamic of our bones
� its size and shape and the number of teeth itnormally bears undergo considerable change with
age
±newborn
� consists of two halves united in the median planeby a fibrous tissue joint, the mandibular symphysis
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� The mentalprotuberance (chin) begins to
develop in the 2nd year but is not fully
developed until after puberty.
� The two halves of the mandible begin to
fuse during the 1st year and are fused by
the end of the 2nd year.
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� body of the mandible in newborn infants ± mere shell lacking an alveolar process
± each half enclosing five primary (deciduous) teeth
± elongates, particularly posterior to the mental foramen, toaccommodate the development and then the bearing of eight
secondary (permanent) teeth, which begin to erupt during the 6th
year of life.
� teeth
± primary (deciduous) teeth� usually begin to erupt in infants of ~ 6 mos of age
± secondary (permanent) teeth
� begin to erupt during the 6th year of life
� not complete until early adulthood
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� Rapid growth of the face during infancy and early
childhood coincides with the eruption of primary teeth.
� Vertical growth of the upper face results mainly from
dentoalveolar development.
� These changes are more marked after the secondary
teeth erupt.
� Following complete loss of teeth in old age (or younger if
care is neglected), the alveoli begin to fill in with bone
and the alveolar processes begin to resorb.
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� Concurrent enlargement of the frontal and
facial regions is associated with the
increase in the size of the
paranasalsinuses.
� Most paranasal sinuses are rudimentary or
absent at birth.
� Growth of the paranasal sinuses is
important in altering the shape of the face
and in adding resonance to the voice.
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Craniosynostosis and Skull
Deformities� Premature closure of the sutures of the
skull (primary craniosynostosis) results in
several skull deformities. ± incidence ~ 1 per 2000 births
± cause unknown, but genetic factors appear to be
important
± prevailing hypothesis
� abnormal development of the cranial base creates
exaggerated forces on the dura mater (outer covering
membrane of the brain) that disrupt normal cranial suture
development
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± deformities are much more common in males
± often associated with other skeletal anomalies
± type of deformed skull that forms depends on
which sutures close prematurely
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� Scaphocephaly
± premature closure of the sagittal suture
± anterior fontanelle is small or absent ± long, narrow, and wedge-shaped skull
± ~ 1/2 the cases of craniosynostosis
± does not produce abnormal neurological
development
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� Plagiocephaly
± premature closure of the coronal or the
lambdoid suture
± occurs on one side only
± skull is twisted and asymmetrical
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� Oxycephaly or Turricephaly
± 30% of cases of skull deformity
± involve premature closure of the coronalsuture
± high, towerlike skull
± more common in females