Bone Development Flashcards
What kind of bone ossification is suture growth
Intramembranous. Bone formation by secretion of bone matrix directly within connective tissue with no intermediate formation of cartilage.
Describe mechanism of suture growth
Secondary and adaptive. Growth of brain causes bone to separate. Osteogenic cells from inner osteogenic layer of periosteum fill in bone. Dura mater secretes soluble factors in response to expanding brain, maintaining suture patency and preventing interdigitation so that there is continued growth
What kind of growth does cranial base undergo
Bipolar cartilaginous growth. Cranial base synchondroses
What are the growth movements resulting from bone surface remodelling
Cortical drift:
Deposition on one surface and resorption on the other. Movement occurs secondary to bone remodelling
Primary displacement:
Displacement of bone due to growth of surrounding soft tissue. Stimulate enlargement and remodelling of condyle and rami parallel to displacement. Bone growth backwards and upwards by amount that equals displacement of mandible.
Secondary displacement
Movement of bone not directly related to own engagement. Eg growth by middle cranial fossa displaces maxilla anteriorly and inferiorly
How did we prove that bone is not primary determinant of growth
Suture transplant does not lead to growth. Suture growth responsive to external influences
Compare growth site and growth centre
Growth site is where growth occurs while growth centre is where independent growth occurs. Growth at growth site responds to extrinsic factors while growth centre more intrinsically regulated. Growth site has no tissue separating capabilities, while growth centre able to separate tissues for growth
What type of ossification does cranial vault undergo
Intramembranous ossification: bone matrix secreted directly onto connective tissue, no intermediate formation of cartilage
Cranial vault growth
Mainly via suture growth (growth site). At birth, major sutural fibrous articulations and fontanelles present to allow continued growth via suture growth. Dependent on brain for development. Suture synostosis starts at 20 years old; sagittal suture cease at 25 years, coronal suture cease at 27 years. Periosteal activity along exterior surface continues throughout life, increasing thickness
What kind of ossification does cranial base undergo
Endochondral ossification: cartilage proliferation followed by displacement, hypertrophy and displacement of maturing cartilage cells
Intramembranous ossification: tympanic bone, greater wing of sphenoid, pterygoid process of sphenoid bone
How does cranial base grow?
Synchondroses growth anteroposteriorly ie via temporary cartilaginous joints of endochondral ossification (cranial base derived from hyaline cartilage, primary chondrocytes present) Bipolar synchondroses. Growth centre regulated by intrinsic growth factors. Intramembranous ossification of pterygoid process and greater wing of sphenoid and tympanic bone
Intersphenoid synchondroses fuses around birth. Sphenoethmoidal synchondroses fuses around 7yo. Sphenooccipital sunchondroses fuse shortly after puberty
Surface remodelling occurs where periosteum is present
How does mid face and mandible ossify
Intramembranous ossification: bone matrix deposited directly on connective tissue, no cartilage intermediate
Development of the midface
All bones except nasal septum and inferior turbinate formed by intramembranous ossification. Late embryonic, fetal period, growth of brain and cranial cavity affects growth of midface which is connected to neurocranium by circum maxillary suture, septum, vomer, nasal capsule. Nasal septum growth contributes most significantly until age 7. From 7 years old, soft tissue growth and expansion of oronasal capsule result in downward and forward growth.
What are the mechanisms of growth of midface
Endochondral ossification except for inferior turbinate and nasal septum. After age 7, significant downward and forward growth mainly due to soft tissue growth and expansion of oronasal capsule.
3 mechanisms
- Suture growth
- circum-maxillary and intra maxillary suture: downward and forward growth due to displacement of midface as a results of soft tissue pulling midface in different directions
- transverse plane: sagittal suture growth due to expansion of brain - Extensive surface remodelling
- anteroposterior and vertical plane
- anteroposterior: deposition at posterior margin of maxillary tuberosity, resorption at anterior surface of maxilla; increase length of dental arch and maxilla anteroposteriorly
- vertical: apposition on orbital floor (superior drift) & apposition on palatal surface (inferior drift) + resorption of roof and floor of nasal cavity —> enlargement of nasal cavity and sinus with age (corticol drift) - Passive displacement due to cranial base growth, no actual enlargement of midface
Other growth:
- vertical: thicker due to development of dentition and alveolar bone, eruption of teeth bring alveolar bone along
- vertical: by primary displacement, soft tissue pull anteriorly and inferiorly
How does mandible ossify
intramembranous ossification except mandibular condyle ** membrane derived secondary cartilage **. Endochondral proliferation at condyle for growth of mandible
Characteristics of mandibular condylar cartilage
Growth site. Cartilage originates from periosteum ie arises within skeletogenic membrane. Has characteristics of both intramembranous bone and histological and functional features of hyaline growth cartilage
