Mechanisms of early normal growth of the craniofacial skeleton

Question 1

Direction of growth of craniofacial skeleton

Answer 1

Grows forwards and downwards in rotational pattern

-this can affect vertical and horizontal relationships

Question 2

Which growth patterns are more common?

Answer 2

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

Question 3

Interstitial growth

Answer 3

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

Question 4

Endochondral ossification

Answer 4

Conversion of cartilage

Question 5

Intramembranous ossification

Answer 5

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

Question 6

Direct growth

Answer 6

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

Question 7

Apposition and resorption

Answer 7

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

Question 8

Mechanisms: genetic control

Answer 8

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

Question 9

Sutural directed growth theory

Answer 9

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

Question 10

What is growth of cranial vault determined by?

Answer 10

Pressure from growing neural tissues

Question 11

Cartilage directed growth theory

Answer 11

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

Question 12

Evidence to support cartilage directed growth theory

Answer 12

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

Question 13

Cranial synchondroses as centre of skeletal growth

Answer 13

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

Question 14

Functional matrix theory

Answer 14

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)

Question 15

Evidence for functional matrix theory

Answer 15

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

Question 16

What does functional matrix theory imply?

Answer 16

Ortho could be used to alter facial growth

Question 17

Face proportions at birth

Answer 17

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

Question 18

Face proportion changes during growth

Answer 18

Change in proportion of face, face becomes bigger

Question 19

Body proportion changes during growth

Answer 19

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

Question 20

What dictates growth of head in early years?

Answer 20

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

Question 21

Growth of sutures is a form of

Answer 21

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

Question 22

Growth at sutures in early years

Answer 22

• 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

Question 23

Function of sutures

Answer 23

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

Question 24

Anterior forehead

Answer 24

Remodelled under influence of frontal sinuses

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

Question 25

Cranial base regions

Answer 25

Divided into anterior and posterior regions by spheno-occipital synchondrosis

Question 26

Growth and changes of cranial base

Answer 26

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

Question 27

Anterior section of cranial base

Answer 27

Spheno-ethmoidal synchondrosis in anterior section

Anterior cranial base follows neural pattern of growth and is stable by 8

Question 28

Posterior section of cranial base

Answer 28

Including spheno-occipital synchondrosis

Follows somatic pattern of growth

Question 29

Cranial base: the early years

Answer 29

Facial changes in early years are closely related to synchondroses
Facial bones continue to enlarge to accommodate airway and masticatory growth and function

Question 30

Cranial base: the adolescent years

Answer 30

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

Question 31

Growth of maxilla

Answer 31

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

Question 32

Maxillary palatal growth and remodelling of palatal vault

Answer 32

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

Question 33

Growth translation and remodelling

Answer 33

Work together
Surface remodelling of bone in opposite direction to which bone is being translated
-reshaping of face as bone moves downwards and forwards

Question 34

Drift

Answer 34

Change in position of bony structure

Question 35

Mandibular growth - length

Answer 35

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

Question 36

Mandibular growth - ramus

Answer 36

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

Question 37

Mandibular growth - resporption where?

Answer 37

Resorption from anterior surface and deposition on posterior surface

Question 38

Mandibular growth - ages

Answer 38

Continues through puberty, ceasing in girls at 14-15 and in boys at 17-18

Question 39

Mandibular growth - height

Answer 39

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

Question 40

Condylar cartilage

Answer 40

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

Question 41

Bjoerk’s research

Answer 41

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

Question 42

Internal rotation of mandible

Answer 42

-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

Question 43

Forward rotation of the mandible

Answer 43

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

Question 44

Backward rotation of the mandible

Answer 44

Faces become longer with time
Usually matrix rotation centred on condyle
1 in 5 cases

Question 45

Features of long face individuals

Answer 45

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

Question 46

Features of short face individuals

Answer 46

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

Question 47

Adenoidal facies

Answer 47

Children with difficulties in nasal breathing
Increases in both lower and total face height
Narrow upper arches
Retroclined incisors
Some normalisation with time

Question 48

Improving posterior nasl obstruction (adenoidal facies)

Answer 48

Removing tonsillar tissue from posterior wall of pharynx

Weak evidence

Question 49

Growth of the nose

Answer 49

Downward and forward growth of the nose
Vertical growth is more than antero-posterior
Growth of nose is independent of skeletal classification

Question 50

Growth of the lips

Answer 50

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

Question 51

Growth of the chin

Answer 51

> chin projection in males during growth due to mandibular growth
Gender difference in soft tissue thickness during growth, males later growth and greater