Facial Growth II Flashcards
What are the two forms of ossification?
- Intramembranous or endochondral
What are the two pre-exisitng cartilaginous skeletons for the face?
- Nasal capsule
- Meckel’s cartilage
What are the two pre-existing cartilaginous skeletons for face?
- Nasal capsule
- Meckel’s cartilage
How is the infant face different compared to the adult face?
- Face is small compared to adult cranium
- Eyes are large
- Ears low set
- Forehead upright and bulbous
- Face appears broad
- Nasal region vertically shallow
- Nasal floor close to inferior orbital rim
- In adult midface expands and nasal floor descends
What are the sites of facial growth?
- Sutures
- Synchondroses
- Surface deposition
What are sutures?
- Specialised fibrous joints situated between intramembranous bone
- Band of connective tissue which has osteogenic cells in centre (most peripheral provide new bone growth)
How does growth at sutures occur?
- Occurs in response to growing sutures separating the bone
- E.g. growth of calvarium in response to development of brain
- Where the bones are pushed apart new bones forms in suture
- Occurs in areas of tension
What happens to the sutures when facial growth is complete?
- Sutures fuse and become inactive
What are synchondroses?
- A cartilage based growth centre with growth occurring in both direction
Where are synchondroses found?
- Found in midline
- Exist between ethmoid, sphenoid and occipital bones
How is new cartilage formed at synchondroses?
- Bones either side of synchondrosis moved apart as growth takes places
- New cartilage formed in centre of synchondrosis
- Periphery transformed into bone
What is surface deposition?
- New bone deposited beneath periosteum over surfaces of both the cranial and facial bones
- Resorption also takes place as bones need to maintain their shape
What is the process of deposition and resorption known as?
- Remodelling
- Change in position of bone due to remodelling known as drift (cortical drift)
What is the cranial vault comprised of?
- Frontal
- Temporal
- Occipital
- Parietal
When does the cranial vault stop expanding?
- Expands in response to growing brain until 7years
When is the rate of growth the greatest in the cranial vault?
- Greatest first 3 years of life
What are the ways the cranial vault grows?
- Bone growth at sutures
- External and internal surfaces are remodelled through surface deposition and resorption to displace bones radially
Why does the forehead continue to enlarge even after neural growth has stopped?
- Continues to enlarger in response to expanding air sinuses (pneumatisation)
- More pronounced in males
How many fontanelles are present at birth and when do they close?
- 6 Fontanelles present at birth
- Close by 18months
What happens to the sutures when facial growth is complete?
- Sutures fuse
What bones is the cranial base made of?
- Frontal
- Ethmoid
- Sphenoid
- Temporal
- Occipital
What two ways does growth occur in the cranial base?
- Endochondral ossification
- Surface remodelling
When do the synchondrosis of the cranial base fuse?
- Spheno-ethmoidal synchondrosis fuses at 7years
- Spehno-occipital closes at 13-15 in females and 15-17 in males
- Spheno-occipital fuses at 20years
When does the growth of cranial base occur?
- Between 4 and 20years
- Causes overall increase in length of cranial base
How is the anterior cranial base used for orthodontists?
- Anterior cranial base relatively stable at 7 years
- Use for superimposition in cephalometric analysis
- Allows orthodontist to assess skeletal changes due to growth and/or treatment
How does the cranial base determine the relationship of maxilla and mandible?
- Shape or angle of cranial base affects jaw relationship
- Maxilla articulate with anterior cranial base
- Mandible with posterior cranial base and suspended beneath middle cranial fossa
What does a small angle in cranial base determine?
- Class III skeletal relationship
What does a large angle in cranial base determine?
- Class II skeletal pattern
What is included within the maxilla/ nasomaxillary complex?
- Orbits
- Nasal cavity
- Upper jaw
- Zygomatic processes
How is the maxilla displaced in relation to anterior cranial base?
- Downwards and forwards
What is meant by the term displaced in this context?
- When mass of bone moved relative to neighbours
- Brought about by forces exerted by soft tissues and intrinsic growth of bone
Where does sutural growth occur in maxilla/ nasomaxillary complex?
- At zygomatic and frontal bones
- Mid palatine suture
What surface remodelling occurs at maxilla/ nasomaxillary complex?
- Deposition on lower border of hard palate and alveolar process
- Resorption on floor of nasal cavity and floor or orbits
How does the mandible grow?
- Downwards and forward
Where does growth of the mandible occur?
- At condylar cartilage
- Adaptive growth not intrinsic
Where does surface remodelling occur in mandible?
- Resorption mainly anteriorly and lingually
- Deposition posteriorly and laterally
What are the results of surface remodelling in the mandible?
- Increase in height of ramus
- Increase in length of dental arch to accommodate permanent teeth
Why is forward displacement of maxillary complex important?
- Creates space posteriorly for development of maxillary tuberosities
- Space for eruption of molar teeth
How much does the mandible increase in length for females and males?
- 26mm in males
- 20mm in females
- Between 4-20years
When is growth the most of the mandible?
- During pubertal growth spurt
When does growth of the mandible slow for females and males?
- 17 in females
- 19 in males
How much does the maxilla increase in length by for females and males?
- 8mm in males
- 5.5mm in females
- Between ages 4-20years
When does growth of the maxilla slow down significantly?
- 7 years
- Slows to adult levels at 12years
When will orthodontic treatment work best?
- Treatment that utilises growth of mandible Best during the pubertal growth spurt
- Treatment that utilises growth of maxilla work bet in early teenage years (before circumaxillary sutures and palates have fused)
What is the remodelling theory of craniofacial growth?
- Everything grows by process of deposition and reposition
- Sutures and cartilages don’t exert intrinsic force
- Historical theory
What is the sutural theory?
- Growth occurs at sutures and cartilages (genetically controlled)
- Growth at sutures is main factor for development of cranial vault and maxilla
- Historical theory
What is the cartilaginous theory?
- Cartilages like nasal septal cartilage and synchondrosis generate force
- Develops the bones in specific direction under genetic control
What is the functional matrix theory?
- Growth occurs in response to individual units that are developing to provide a function
- Each unit (functional matrix) composed of tissues, organs and spaces
- Force exerted by growing soft tissues determines direction and extent of growth
What are the most recent views on the control of growth?
- Combo of genetic and environmental factors
- Growth in one part of skull influences other
- Primary cartilages have intrinsic growth potential and exert genetic influence over growth
- Condylar (secondary) cartilage of mandible different
- Mandible responds to maxillary position changes to adapt growth?
How can growth be utilised by orthodontist to facilitate treatment outcome?
- Functional appliances
- Rapid maxillary expansion (RME)
- Protraction headgear
- Overbite reduction
When was a growth rotation originally described and who by?
- Bjork using implant studies in 1950’s and 60’s
Why does a growth rotation form?
- Imbalance in growth of anterior and posterior face heights
What does a forward rotation lead to?
- Short face
- Development of deep bite
What does a backwards rotation lead to?
- Long face
- Development of anterior open bite
What is adverse growth?
- Continued growth when there is significant growth rotation
- Can make malocclusion worse
What are the characteristics of adult facial growth?
- Very variable
- Continues slowly throughout life
- Length continues until 20 in males and late teens in females
- Increased overall length and prominence of nose and chin (forehead in males)
- Lips thinner and more retrusive
How can we measure facial growth changes?
- Casts of the face
- Cephalometry
- 3D laser scanning
- 3D photogrammetry
What are the indications for taking a lateral cephalogram?
- To aid diagnosis (vertical discrepancy or skeletal class)
- Treatment planning
- Progress monitoring
- Research projects
What is cephalometry?
- Analysis and interpretation of lateral cephalographs
- Need to be reproducible (patient positioned in cephalostat at set distance from cone and film)
How should the head be set up for a cephalograph?
- Frankfort plane horizontal
- Teeth in RCP
- Head kept steady by contacting soft tissues at nasion and bilaterally with ear rods in EAM
How can we analyse a lateral ceph?
- Identify any points/ landmarks / lines
- Measure lengths/ heights/ angles
Upon analysis what can a lateral ceph show us?
- Relationship between jaws and cranial base
- Relationship between the upper and lower jaw
- Position of teeth relative to the jaws
- Soft tissue profile
What are some reference landmarks?
Sella
- Nasion
- A Point
- B Point
- Anterior Nasal Spine
- Posterior Nasal Spine
- Pogonion
- Menton
- Gonion
- Porion
- Orbitale
What are some reference lines?
- Sella-nasion
- Frankfort plane
- Maxillary plane
- Occlusal line
- Mandibular plane
What are the angles measured in the Eastman Analysis?
- Antero-posterior pos of maxilla and mandible relative to base of skull (SNA, SNB)
- Position of mandible relative to maxilla (ANB = anteroposterior, MMPA or FMPA= vertical)
- Angulation of teeth to maxilla and mandible (UIMxP, LIMnp)
- Vertical facial proportions (LAFH/TAFH ratio)
What are the values of class I in ANB?
2-4°
What are the values for class II in ANB?
4->8°
What are the values for class III in ANB?
<3 - 2°
What is the value for average vertical discrepancy?
27°
What are some errors in cephalometry?
- Radiographic projection errors like magnification or distortion
- Errors within measuring system like non-linear fields
- Errors in landmark identification like quality of image, landmark definition and location
What are some stable structures that sequential lateral cephalograms can be superimposed?
- Anterior wall of sella
- Middle cranial fossa
- Anterior surface of zygomatic process
- Anterior border of chin
- Inner cortical plate mandibular symphysis
- Outline of mandibular canal
