Biomechanics and tooth movement

Question 1

Tooth movement

Answer 1

Physiological

Orthodontic

Question 2

Physiological tooth movement

Answer 2

Pre-eruptive
Eruptive
Post-eruptive

Question 3

Pre-eruptive tooth movements

Answer 3

Permanent teeth form lingually to primary teeth

Nearly always erupt lingually

Question 4

Eruptive movements

Answer 4

usually occurs at rate of 1mm per month

Question 5

Post-eruptive movement

Answer 5

Accomodate growing jaws
Compensate for occlusal wear
Compensate for interproximal wear - mesial drift
Infraocclusion due to ankylosis

Question 6

Growing jaws

Answer 6

Teeth move to adapt to gowth

Lower jaw tends to continue to grow anteriorly longer than the top jaw

Question 7

Occlusal wear

Answer 7

Thickening of cementum to account for occlusal wear

Question 8

Mesial drift

Answer 8

Even occurs if wisdom tooth is not there

Question 9

Orthodontic tooth movement

Answer 9

Vital PDL

-don’t need a vital pulp

Question 10

PDL

Answer 10

1. Cells
   - Obs!!!
   - Ocs!!!
   - fibroblasts
   - epithelial rests of Malassez
   - macrophages
   - undifferentiated mesenchymal cells
   - cementoblasts
2. Extracellular component
   - fibres (relevant to relapse and retention - about 3 months)
   - ground substance

Question 11

PDL fibres

Answer 11

1. Collagen fibre bundles
   - alveolar crest fibres
   - horizontal fibres
   - transseptal fibres
   - oblique fibres
   - apical fibres
   - interradicular fibres
2. Oxytalan fibres
   - elastic in nature
   - inserts into cementum and runs in 2 directions
   - function is thought to maintain the patency of blood vessels during occlusal loading

Question 12

Ground substance

Answer 12

1. Glycosaminoglycans
2. Glycoproteins
3. Glycolipids

Question 13

Resting forces

Answer 13

Very light forces
PDL metabolic activity 5-10g
PIC

Question 14

Ortho tooth movement

Answer 14

‘a pathological process from which the tooth usually recovers’

• bendy wires
• spring
• elastics

Question 15

Bone resorption removable appliance

Answer 15

PIC
Force, tension and pressure at different places
With removable appliance, just able to tip crown one way or other around point of rotation

Question 16

Pressure side of moving tooth

Answer 16

Differentiation of osteoclasts - bone resorption

Collagen fibre remodelling

Question 17

Tension side of moving tooth

Answer 17

Bone deposition

Collagen fibre remodelling

Question 18

Rate of movement

Answer 18

1. Initial compression
   - tooth moves through PDL
2. Delay phase (2-14 days)
   - loss of cells from area (no movement possible)
   - new cells move into area (osteoclasts, fibroblasts)
   - ->osteoclasts from vasculature system
   - collagen fibre remodelling
3. Tooth movement

Question 19

Duration of force (graph)

Answer 19

There is a threshold but we do not know what it is

This must be done ~6hrs/24 to have an effect

Question 20

Force levels

Answer 20

Optimum
-Graph
Excessive

Question 21

Optimum force levels graph

Answer 21

<1 s: PDL fluid incompressible, alveolar bone bends, piezoelectric signal generated
1-2s: PDL fluid expressed, tooth moves in PDL space
3-5s: BVs compressed on p side, dilated on tension side, PDL fibres and cells distorted
Minutes: blood flow altered, oxygen tension changes, chemicals released
Hours: Metabolic changes, cellular differentiation begins
2 days: tooth movement begins as Ocs/ Obs within PDL remodel bony socket

Question 22

Optimum force

Answer 22

Small cell-free zone - osteoclasts recruited from blood vessels in the PDL
Resorption from PDL side of socket

Question 23

Excessive force graph

Answer 23

<1s: PDL fluid incompressible, alveolar bine bends, piezoelectric signal generated
1-2s: PDL fluid expressed, tooth moves in PDL space
3-5s: BVs within PDL occluded on p side
Minutes: Blood flow cut off to compressed PDL area
Hours: cell death in compressed area
3-5 days: cell differentiation in adjacent narrow spaces, undermining resorption begins
7-14 days: undermining resorption removes lamina dura adjacent to compressed PDL, tooth movement occurs

Question 24

Excessive force

Answer 24

Complete loss of BVs in PDL
-Ocs recruited from endosteal surface of bone
Delay in tooth movement
Pain
Loss of viltality
Mobility
Root resorption
Loss of anchorage

Question 25

Optimum force depends on

Answer 25

``` Size of root Type of movement Continuous or intermittent better? 20-25g/cm^2 Anchorage also depends on force levels ```

Question 26

Heavy force

Answer 26

Canine does not move at first Molar moves forward -loss of anchorage

Question 27

Types of tooth movement

Answer 27

``` Tipping (removable) Bodily movement Rotation Torque Vertical movement -extrusion -intrusion ```

Question 28

Types of tooth movement

Answer 28

``` Tipping (removable) Bodily movement Rotation Torque Vertical movement -extrusion -intrusion ```

Question 29

Fully controlled movement

Answer 29

Need attachment to tooth - full 3D control

Question 30

Light force

Answer 30

``` Canine moves distally Anchor tooth (molar) moves forward only slightly ```

Question 31

Anchorage in orthodontics

Answer 31

Control of unwanted tooth movement Teeth respond to pressure Pressure = force per unit root area