Growth and Development
Saj Arora
Questions
- When do girls get their growth spurt? Boys?
- How quickly does the head grow in comparison to the body? What is the gradient called?
- How does the mandible get primarily displaced? Secondarily displaced?
- Where is the apposition and resorption of bone during the maxillary and mandibular development?
- What are the faults in Suture and Cartilage Theory?
Questions
- When harvesting Chondrocyte tissue which cephalic or caudal tissue has bone generation potential?
- Why is understanding growth theories important from a dental standpoint?
Growth
- Increase in Size and Capacity
- There is no such thing as Independent growth
- Well controlled growth = Functional and Structural equilibrium
- Development = Specialization and in turn, loss of differentiation potential
Bone Formation
- Bone Remodeling
- Bone Displacement
- Size Increase
- Surface Apposition (after mineralization)
Intramembranous Bone formation
-
Flat bones of the Cranial Vault
-
Mesenchymal Cells differentiate to Osteoblasts and lay down bone
Endochondral Ossification
-
Long bones base of skull
-
Base of skull
-
Cartilage first and then bone
Growth Mechanisms
- Endosteal/Periosteal (deposition/resorption)
- Thickness of bone remains constant
- Cortical Drift
- Unilateral deposition (increasing thickness)
- Over time resorption will have caused bone to shift
- Relocation/Remodeling
- Different position of the bone vs. physiologic changes to accommodate new functional loads
Displacement
- Primary Displacement
- Structure moves in opposite direction of appositional growth
- Secondary Displacement
- Structure grows in the direction of new bone formation
V-Principle
- New bone is formed on the lingual of the mandible
- Bone is resorbed from the anterior of the mandible
- Results in Horizontal Expansion
- V will enlarge and move away from the apex
Mandibular Growth
- V-Principle
- Primary Displacement
- Apposition at the condyles and at the posterior ramus
- Resorption at the angle of the mandible and the inside of the ramus
- Secondary Displacement
- Growth of temporal bone moves the condylar fossa shifting the mandible down and forward
Maxillary Growth
- V-Principle
- resorption on the anterior
- Primary Displacement
- Apposition on the oral cavity side
- Resorption on the nasal side
- Overall there is drift down (imbalance in deposition/resorption)
- Secondary Displacement
- Nasomaxillary Complex grows pushing the maxilla down and forward
Studying Bone Formation
- Longitudinal Studies
- Cross-sectional Studies
- Mixed Longitudinal Studies
- Know disadvantages and advantages for each
How to study Growth
- Anthropometric Studies
- Cephalometric Studies
- Craniometry
Growth Curves
- Distance Curves
- Function of age
- Cross-sectional and Longitudinal Studies
- Velocity Curves
- Rate of change over time
- Only Longitudinal Studies
- How?
- Vital Staining
- Radioactive Tracers
- Implant Radiology
Patterns of Growth
- Cephalocaudal gradient of Growth
- Scammon's Curves
Growth in Height
- Normal = 1 standard deviation around the mean
- between 16th and 84th percentile
- Girls spurt starts at the age of 12
- Boys spurt starts at 14
- Girls spurt begins 2-2.5 yrs before boys
- Girls menarche comes right after peak velocity of growth
Weight
More Variation in weight than height
Weight spurt lags by about 3 months
Timing
Most variations in growth are timing
Late bloomers grow slower but for a longer period
Maturity Indices
- Chronological Age -> Usually the worst
- Morphological Age
- Sexual Age
- Menarchy in girls
- Skeletal Age
- Cervical vertebrae and wrist bones
- Dental Age
- Eruption age
- Crown calcifications
Growth Theories
- Sutural Growth theory: False
- Sites of growth vs. Centers of Growth
- Suture transplanted do not form new bone
- Primary Cartilage Theory
- Cartilage contains growth information
- Everything else gets remodeled/displaced depending on the growth of cartilage
- Transplanting cartilage shows growth so it is a center of growth
- Removing it from the condyle doesn't affect other growth
- Removing it from the nasal septum affects growth
- Therefore, condyles are not centers of growth
Growth Theories
- Functional Matrix Theory: Best theory
- Growth occurs in response to functional needs
- Functional Matrix: includes teeth and muscles
- Skeletal Matrix: hard tissues
Bone Tissue Engineering
Sternal Chondrocytes
- Artificially created scaffold can generate new bone
- Harvest cartilage cells from bat place them in Chitosan
- Chitosan is the scaffold
- Bone is generated from Cephalic tissue and not from Caudal tissue
- Cephalic tissue can be induced by Vitamin A
- Caudal tissue is permanent cartilage
Early Treatment
- Remember Sutures react so if you apply force to separate them you will get bone formation
- Bases of distraction osteogenesis (Functional Matrix Theory)
- If the person is still pre-spurt you can get a lot of bone formation
- Palate Expanders and Head gear are amazing appliances to control growth
Narrow Arch
After Expander
Bite Modification
Bite Modification
Mandibular Bumper (crowding)
Growth and Development
By Saj Arora
