بسم الله الرحمن الرحيم
Post natal growth of the mandible
THE MANDIBLE :
¨ THE MANDIBLE
¨ In contrast to maxilla,both endochondral and
periosteal activities are important in growth of the mandible.Cartilage covers
the surface of the mandibular condyle at the temporomandibular joint.All other
areas of the mandible are formed and grow by direct surface apposition.
¨ At birth the two rami of the mandible are quite short.
¨ Condylar development is mininmal and there is
practically no articular eminence in the glenoid fossa.Athin line of
fibrocartilage and connective tissue exist at the midline of the symphysis to
seprate right and left mandibular bodies.Between four
¨ months of age and the end of the first year ,the
symphyseal cartilage is replaced by bone.Although growth is quite general
during the first year of life ,with all surfaces showing bone apposition,there
is apparently no signification growth between the two halves before they
unite.During the first year of life ,appositional growth is specially active at
the alveolar border,at the distal and superior surface of the ramus ,at the
condyle ,along the lower border of the mandible and on its lateral surfaces
(Fig 4.8).
¨ After the first year of life the mandibular growth
becomes more selective.The condyle does show
¨ The condile does show aconsiderable growth there is
also agreater growtr at the body of the mandible and also at the alveolar
process . Cephalometric studies show that there is agrowth of the ramus without
changing the mandibular plane angle.
¨ resorptionalveolar border,and maintaining the
antero-poserior dimention of the ramus.Transverse dimensions ,after the first
year of life are mainly due to the growth at the posterior border in an
expanding "v" pattern(Fig. 4.9).
¨ scott divides the mandible into three basic type of
bone :basal,muscular and alveolar .the pasal portion is atube like central
foundation running from the condyle to the symphysis.The muscular portion
(gonial angle and coronoid process)is under the influence of the
master,internal pterygoid and temporalis muscle.Alveolar bone exists to hold
the teeth and it is gradually resorbedin the event of tooth loss.moss speaks of
the mandible as agroup of micro-skeletal units(Fig )
¨ The
coronoid process is one skeletal unite under the influnse of temporalis
.Thegonial angle is another skeletal unit under the influence of master and
internal pterygoid muscles.The alveolar process is under the influence of the
dentition.The basal tubular portion of the mandible server as protection for
the mandibular canal and apparently follows alogarithmic spiral in its downward
and forward movement from beneach the cranium.
Timing of growth :
¨ Timing of growth in width ,length,and height.
¨ Growth in width is completed first,the growth in
length, and finally growth in height. Growth in width of both jaws, including
the width of the dental arches, tends to be completed before the adolescent
growth spurt and is affected minimally if at all by adolescent growth changes.
Intercanine width is more likely to decrease than increase after age 12. There
is apartial exception to this rule, however. As the jaws grow in length
posteriorly , they also grow wider.
¨ For the mandible , both molar and bicondylar width
show small increases until the end of growth in length