postnatal growth and development Flashcards
postnatal growth and development of the mandible
- it appears as tho there is forward and downward growth (vital staining studies), and one could suppose that mandible enlarges by growth at the anterior end
- growth mainly happens in a posterior direction, with forwards and downwards displacement (primary displacement)
resultant changes due to growth
mandibular growth results in increase in height, length and width
growth sites of the mandible
- Limited growth takes place at
the symphysis menti until
fusion occurs (1 year after
birth) = width - At the condylar cartilage
(major site of growth) = height - The posterior border of ramus
= length - Alveolar ridges = height
according to moss - functional matrix theory
the mandible is a makroskeletal unit made up of micro skeletal units:
- condyle
- coronoid process
- chin
- angular
- alveolus
- basal
what is each mikroskeletal unit influenced by
it is influenced by a functional matrix that acts upon each bone
teeth
acts as a functional matrix for the alveolar unit
temporalis
influences the coronoid process
the masseter and medial pterygois
has some influence on the gonoil angle
condylar cartilage
serves as a growth cartilage that acts as a functional matrix to stretch the periosteum inducing lengthened periosteum to form intramembranous bone beneath it
alveolar bone - mikroskeletal unit under the influence of teeth - functional matrix
- teeth are also a functional matrices (periostea matrix)
- most orthodontic therapy is based on the fact that when this functional matrix grows or is moved, the skeletal unit (the alveolar bone) responds appropriately to this morphorgenetically primary demand
e.g. when teeth are moves with the use of a NiTi arch wire, the alveolar bone expands by laying down more bone in the direction of the applied force
“V” principle of enlow
- most of the facial bones has a “V” shaped configuration = mandible +cornoid process
- bone deposition on the inner side and resorption of the outer surface
- deposition also also occurs at the end of the two arms of the “V” resulting in it’s widening
“V” - principle of Enlow - growth of the coronoid process
- the coronoid processes become larger and higher
- they grow farther apart at their apices by additions on the lingual surface with contralateral removal from the buccal side
- lingual deposition brings their bases towards each other
summary: growth of the mandible primarily involves
bone remodelling
cortical drift
bone remodelling
involves independent sites of resorption and formation that change the size and shape of a bone
cortisol drift
combination of bone deposition and resorption resulting in north movement towards the deposition surface. contributes to the lengthening of the alveolar bone posteriorly to accommodate posterior teeth
- if resorption and deposition occurs at the same times, the thickness of the bone remains constant
- if in case more bone is deposited on one side and less bone is resorbed on the opposite side then thickness of bone increases
growth timing
growth of width of the mandible is completed first: then growth in length and finally height
growth of the nano-maxillary process is produced by three mechanisms
displacement
growth at sutures
surface remodelling
displacement
physical movement of the whole bone as a unit
types secondary and primary
primary displacement (translation)
movement of the bone due to its own growth
growth of the maxilla at tuberosity region results in pushing of the maxilla against the cranial base which results in displacement of the maxilla in forward and downward direction
secondary displacement
of the naso-maxillary complex occurs in a downward and forward direction as cranial base grows
if bone gets displaced because of growth and enlargement of an adjacent bone
growth of the cranial base causes forward and downward displacement of the maxilla
growth of the maxillary tuberosity
the maxillary tuberosity grows in three directions by bone position on the external surface
posteriorly
laterally: by deposition on the buccal surface
downward: by deposition of bone along the alveolar ridges
growth at the sutures
- the maxilla is converted to the cranium and the cranial base by several sutures
- these sutures are all oblique and parallel to each other
- this allow the downward and forward positioning of the maxilla as growth occurs at these sutures
- as the connective tissue within the sutures proliferate, the maxilla Is carried downward and forward
this leads to opening of space at the sutural attachments - new bone is formed on either side of the suture
- thus, the overall size of the bones increase on either side
cartilaginous theory (Scott) nasal septum
- growth of the nasal septum thrust the nasa-maxillary process anteriorly
- evidence: removal of the nasal septum results in mid face deficiency
surface remodelling
remodelling occurs by bone deposition and resorption to bring about:
1. increase in size
2. change in shape
3. change in functional relationship
summary - postnatal growth of the mass-maxillary complex
growth in height - vertical
growth in width - transverse
growth in length - A-P (Anteroposterior) - sagittal
growth of the maxilla in width
- growth in the mid palatine suture
- remodelling at the lateral surfaces of the alveolar processes
growth in the vertical dimension - height
primary displacement - at the maxillary tuberosity
patatal remodelling - “V” theory of Scott
eruption of teeth - functional matrix theory of moss
growth in the A-P dimension (length)
palatomaxillary suture
