Mechanisms of early normal growth of the craniofacial skeleton Flashcards
Direction of growth of craniofacial skeleton
Grows forwards and downwards in rotational pattern
-this can affect vertical and horizontal relationships
Which growth patterns are more common?
Forward growth patterns more common than backward rotations -these can correct class 2 malocclusions or deepen an overbite
Interstitial growth
Occurs in soft tissues
Combination of hyperplasia and hypertrophy
In craniofacial skeleton, it occurs in cartilages, synchondroses and sutures
Endochondral ossification
Conversion of cartilage
Intramembranous ossification
Occurs only in embryo and is direct transformation of mesenchymal cells into osteoblasts
Direct growth
By surface apposition and resorption
In fully formed bone, growth activity can only occur in periosteum - periosteal surface remodelling (incl. surface depositio) is primary mechanism
Apposition and resorption
Apposition: bone being added on surface by osteoblasts
Resorption: bone being removed by osteoclasts
Mechanisms: genetic control
Must be factor, seen by similarities of facial form within families
Sutural directed growth theory
Sutural growth occurs in sutures
-sutures in membranous bones are growth centres
-expression of growth at these sites changes shape and, for example, causes forward translation of maxilla
NO: sutures are ‘sites’ of growth but not growth centres in themselves
What is growth of cranial vault determined by?
Pressure from growing neural tissues
Cartilage directed growth theory
Cartilages are primary factor in craniofacial growth
-in many areas, growing cartilage replaced by bone
-genetically determined
Possible cartilage growth sites: spheno-occipital and spheno-ethmoidal synchondroses, nasal septum and mandibular condyle
Evidence to support cartilage directed growth theory
Transplanted cartilages have an ‘intrinsic’ ability to grow
Removal of cartilages e.g. surgical removal of nasal septal cartilage decreases mid-face growth in a growing child
Cranial synchondroses as centre of skeletal growth
Synchondroses structurally resemble 2 epiphyseal cartilages placed back-to-back with common central zone of resting cells
Growth centres of the cranial base
They are epiphyseal cartilages of cranial base and are remnants of primary cartilagenous skeleton
Functional matrix theory
1960s, bone growth takes place in response to growth of surrounding tissues
2 matrices: Periosteal (muscles, nerves, glands, teeth) and capsular (neurocranial, orbital and phharyngeal fossae)
Evidence for functional matrix theory
Growth of calvarium: enlarges in response to growth of brain and eyes
Shape of coronoid process: only grows if subjected to functional forces from masseter and medial pterygoid muscles
Alveolar process only develops if teeth are present
What does functional matrix theory imply?
Ortho could be used to alter facial growth
Face proportions at birth
At birth, upper 1/3 of head-bearing cranium given priority (accommodates brain)
-face proportionally smaller than cranium at birth
Face proportion changes during growth
Change in proportion of face, face becomes bigger
Body proportion changes during growth
Head occupies 25% of body length at birth but 12% in adulthood
What dictates growth of head in early years?
Brain -reaches 50% of total weight at age 1 -75% by 3 -90% age 7 Full development by 11 -surrounding cranium expands to accommodate it
Growth of sutures is a form of
Entirely a form of periosteal activity, hence sutures regarded as secondary growth centres
Growth at sutures in early years
- Much of growth activity is in sutures
- Fast rate of growth in sutures
- Sutures begin to fuse at age 7
- Sutural growth slows down during puberty until all have fused by age 17
Function of sutures
Allow brain to expand whilst surface deposition and resorption create unique facial characteristics
Anterior forehead
Remodelled under influence of frontal sinuses
-also an > in prominence of brows in later life, especially in males
Cranial base regions
Divided into anterior and posterior regions by spheno-occipital synchondrosis
Growth and changes of cranial base
Formed in cartilage and later transformed by endochondral ossification
After first year, synchondroses account for much growth of width and height
-spheno-occipital: active until 16
-spheno-ethmoidal: active until 8
Anterior section of cranial base
Spheno-ethmoidal synchondrosis in anterior section
Anterior cranial base follows neural pattern of growth and is stable by 8
Posterior section of cranial base
Including spheno-occipital synchondrosis
Follows somatic pattern of growth
Cranial base: the early years
Facial changes in early years are closely related to synchondroses
Facial bones continue to enlarge to accommodate airway and masticatory growth and function
Cranial base: the adolescent years
Dramatic physical changes during puberty (up to 2 years earlier in girls)
Dramatic development in lower 2/3 face
-forward growth of upper and lower jaws
-forward elongation of nose
-backward shift of orbits
-posterior movement of zygoma
-posterior extension of dental arches in tuberosity of maxilla
Growth of maxilla
Postnatal growth of maxilla occurs by surface and sutural deposition
- as maxilla grows down and forward, new bone added on both sides of sutures
- sutures appear merely to be responding as result of separating forces caused by soft tissue growth
Maxillary palatal growth and remodelling of palatal vault
As maxilla is translated down and forwards bone is added to tuberosity area
Remodelling continues on bone surface, maxilla translated down and forwards
While floor of nose is resorbing and bone being added to floor of mouth
Sagitally, this accounts for fact that maxilla appears to move down more than forwards
Growth translation and remodelling
Work together
Surface remodelling of bone in opposite direction to which bone is being translated
-reshaping of face as bone moves downwards and forwards
Drift
Change in position of bony structure
Mandibular growth - length
Grows at steady rate before puberty
Growth in length occurs by cartilage replacement in secondary growth cartilage at condylar head
Resorption and deposition at condylar neck
Variability of mandibular position depends upon glenoid fossa
As mandible grows in length and upwards, condylar head is remodelled
Mandibular growth - ramus
As mandible grows in height and length, ramus is remodelled
Bone at tip of condyle at early age can be found on anterior ramus some years later
Mandibular growth - resporption where?
Resorption from anterior surface and deposition on posterior surface
Mandibular growth - ages
Continues through puberty, ceasing in girls at 14-15 and in boys at 17-18
Mandibular growth - height
Growth in height continues longer than length
Slow increase throughout life of alveolar bone
Slows to almost nothing in girls at 17-18 and boys at 20-21
Condylar cartilage
Not a true cartilage
Cells of proliferative zone differentiate into chondroblasts of condylar cartilage
These cells after do not divide, so they are appositional in character and cells are not organised into parallel columns
Bjoerk’s research
Growth rotations
Placed implants: showed that there are existing stable structures
1. around inner cortex of mandibular symphysis
2. around inferior dental canal
3. in retromolar region of mandible adjacent to 3rd molar tooth germs
Remodels over time - less change to the Frankfurt plane
Internal rotation of mandible
-relative to cranial base
-masked by surface apposition and resorption
-can only be seen to full extent by superimposing serial radiographs with implants
2 types: matrix rotation around condyle, intra-matrix rotation within body of mandible
Forward rotation of the mandible
Occurs in most people Av person from 4 - adult: -15 degrees true rotation -25% matrix rotation, 75% intra -mandibular plane angle < by 2-4 degrees -most rotation masked by resorption and apposition Faces become shorter with time
Backward rotation of the mandible
Faces become longer with time
Usually matrix rotation centred on condyle
1 in 5 cases
Features of long face individuals
As mandible moves down & back, anterior face height increases and usually anterior open bite
Incisors thrust forwards relative to mandible
Skeletal anterior open bite can occur later in life, up until ~ 30
Pxs become more class 2 as mandible moves posteriorly
Features of short face individuals
Short anterior face height
Excessive forward rotation of mandible
Increase in normal internal rotation and decrease in external compensation
Deep bite and crowded incisors common
Adenoidal facies
Children with difficulties in nasal breathing
Increases in both lower and total face height
Narrow upper arches
Retroclined incisors
Some normalisation with time
Improving posterior nasl obstruction (adenoidal facies)
Removing tonsillar tissue from posterior wall of pharynx
Weak evidence
Growth of the nose
Downward and forward growth of the nose
Vertical growth is more than antero-posterior
Growth of nose is independent of skeletal classification
Growth of the lips
Uppler lips > in length from 1-3 rapidly, then reduce from 3-6, slow > thereafter
Maxillary lip complete in females by ~14 and males at ~18
Mandibular lip length growth persists longer than maxillary length, not complete in most males by 18
Growth of the chin
> chin projection in males during growth due to mandibular growth
Gender difference in soft tissue thickness during growth, males later growth and greater
