Mechanisms of early normal growth of the craniofacial skeleton Flashcards

1
Q

Direction of growth of craniofacial skeleton

A

Grows forwards and downwards in rotational pattern

-this can affect vertical and horizontal relationships

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2
Q

Which growth patterns are more common?

A
Forward growth patterns more common than backward rotations
-these can correct class 2 malocclusions or deepen an overbite
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3
Q

Interstitial growth

A

Occurs in soft tissues
Combination of hyperplasia and hypertrophy
In craniofacial skeleton, it occurs in cartilages, synchondroses and sutures

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4
Q

Endochondral ossification

A

Conversion of cartilage

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5
Q

Intramembranous ossification

A

Occurs only in embryo and is direct transformation of mesenchymal cells into osteoblasts

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6
Q

Direct growth

A

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

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7
Q

Apposition and resorption

A

Apposition: bone being added on surface by osteoblasts
Resorption: bone being removed by osteoclasts

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8
Q

Mechanisms: genetic control

A

Must be factor, seen by similarities of facial form within families

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9
Q

Sutural directed growth theory

A

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

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10
Q

What is growth of cranial vault determined by?

A

Pressure from growing neural tissues

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11
Q

Cartilage directed growth theory

A

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

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12
Q

Evidence to support cartilage directed growth theory

A

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

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13
Q

Cranial synchondroses as centre of skeletal growth

A

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

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14
Q

Functional matrix theory

A

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)

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15
Q

Evidence for functional matrix theory

A

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

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16
Q

What does functional matrix theory imply?

A

Ortho could be used to alter facial growth

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17
Q

Face proportions at birth

A

At birth, upper 1/3 of head-bearing cranium given priority (accommodates brain)
-face proportionally smaller than cranium at birth

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18
Q

Face proportion changes during growth

A

Change in proportion of face, face becomes bigger

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19
Q

Body proportion changes during growth

A

Head occupies 25% of body length at birth but 12% in adulthood

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20
Q

What dictates growth of head in early years?

A
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
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21
Q

Growth of sutures is a form of

A

Entirely a form of periosteal activity, hence sutures regarded as secondary growth centres

22
Q

Growth at sutures in early years

A
  • 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
23
Q

Function of sutures

A

Allow brain to expand whilst surface deposition and resorption create unique facial characteristics

24
Q

Anterior forehead

A

Remodelled under influence of frontal sinuses

-also an > in prominence of brows in later life, especially in males

25
Cranial base regions
Divided into anterior and posterior regions by spheno-occipital synchondrosis
26
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
27
Anterior section of cranial base
Spheno-ethmoidal synchondrosis in anterior section | Anterior cranial base follows neural pattern of growth and is stable by 8
28
Posterior section of cranial base
Including spheno-occipital synchondrosis | Follows somatic pattern of growth
29
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
30
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
31
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
32
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
33
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
34
Drift
Change in position of bony structure
35
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
36
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
37
Mandibular growth - resporption where?
Resorption from anterior surface and deposition on posterior surface
38
Mandibular growth - ages
Continues through puberty, ceasing in girls at 14-15 and in boys at 17-18
39
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
40
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
41
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
42
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
43
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 ```
44
Backward rotation of the mandible
Faces become longer with time Usually matrix rotation centred on condyle 1 in 5 cases
45
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
46
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
47
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
48
Improving posterior nasl obstruction (adenoidal facies)
Removing tonsillar tissue from posterior wall of pharynx | Weak evidence
49
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
50
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
51
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