Biomechanics and tooth movement Flashcards
What are the types of tooth movement?
Physiological and orthodontic
Physiological tooth movement types?
Pre-eruptive = permanent teeth form
Eruptive
Post-eruptive
What is the rate of eruptive movement? (physiological)
Occur at rate of 1mm per month
Why does posteruptive movement occur? (physiological)
Accommodate growing jaws - teeth move to adapt to growth
Compensate for occlusal wear
Compensate for interproximal wear - mesial drift
What is needed for orthodontic tooth movement?
Vital periodontal ligament
Name the cells of the periodontal ligament
Osteoblasts Osteoclasts Fibroblasts Epithelial cell rests of malassez Macrophages Undifferentiated mesenchymal cells Cementoblasts
Name the extracellular compartments of the periodontal ligament
Fibres - collagen
Ground substance - glycosaminoglycans, glycoproteins, glycolipids
Define orthodontic tooth movement
A pathological process from which the tooth usually recovers
How does bone resorption occur in ortho?
Spring applied to mesial aspect of canine tips it backwards = pressure and tension at root apex
Pressure side of moving tooth;
= Differentiation of osteoclasts - bone resorption
= Collagen fibres remodelling
Tension side of moving tooth;
= Bone deposition and collagen fibre remodelling
Rate of ortho movement?
Initial compression = tooth moved through PDL
Delay phase (2-14 days);
- Loss of cells from area - no movement possible
New cells move into area
Tooth movement;
- PDL populated by new cells - osteoclasts from vascular system
- Bone resorption
- Collagen fibre remodelling
How long does force have to be applied to achieve tooth movement?
Threshold is 6hrs of force a day
Optimum force timeline?
<1 second = PDL fluid incompressible, alveolar bone bends
1-2 secs = PDL fluid expressed, tooth moves in PDL space
3-5 secs = BVs compressed on pressure side, dilated on tension side, PDL fibres and cells distorted
Minutes = Blood flow altered, oxygen tension changes, chemicals released
Hours = metabolic changes, cellular diff begins
2 days = Tooth movement begins as osteoclats/blasts within the PDL remodel bony socket
Excessive force timeline?
<1 second = PDL fluid incompressible, alveolar bone bends
1-2 secs = PDL fluid expressed, tooth moves in PDL space
3-5 secs = BVs in PDL occlude on pressure side
Minutes = Blood flow cut off to compressed PDL area
Hours = Cell death in compressed area
3-5 days = cell diff in adjacent narrow spaces, undermining resorption begins
7-14 days = undermiding resorption removes lamina dura adjacent to compressed PDL, tooth movement occurs
What occurs with excessive ortho force?
Complete loss of BVs in PDL - osteoclasts recurited from edosteal surface of bone Delay in tooth movement Pain Loss of vitality Mobility Root resorption Loss of anchorage
What does the optimum force depend on?
Size of root
Type of movement
Continuous or intermittent?
20-25g/cm2
