Tissue Reactions to Orthodontics

Question 1

Tooth movement

Answer 1

osteoblast is pivotal cell
excessive ortho forces can cause inefficient tooth movement and adverse tissue reactions

Question 2

Bioelectric Theory

Answer 2

tooth movement changes in bone metabolism controlled by electrical signals that are produced when the alveolar bone and collagen flex and bend
stress-generated electric signals do not fully explain tooth movement, electric and electromagnetic influences can modify the bone remodelling on which tooth movement depends

Question 3

Piezoelectric potentials

Answer 3

phenomenon observed in many crystal structures in which the deformation of the crystal structure (due to applied force) produces a flow of electric current, as electrons are displaced from one part of the crystal to another

Question 4

Bioelectric potentials

Answer 4

observed in bone that is not being stressed
metabolically active bone or connective tissue cells in areas of active growth or remodelling produce electronegative charges that are generally proportional to how active they are.

Question 5

Pressure-Tension theory

Answer 5

Tooth movement to changes in bone metabolism controlled by chemical rather than electric signals:
- Alteration in blood flow associated with pressure within the PDL
- Formation and/or release of chemical messengers
- Activation of cells

Question 6

Impact of blood compression

Answer 6

alteration in blood flow quickly create changes in the chemical environment. These chemical changes, acting either directly or by stimulating the release of other biologically active agents, then stimulate cellular differentiation and activity.

Question 7

Changes in the PDL following orthodontic loading?

Answer 7

Compression side
- compression of bv
- attraction of osteoclasts
- resorption of bone (Howship’s lacunae)
- production of fibrous tissue in Howship’s lacunae

Tension side
- stretching of PDL fibres
- stimulation of osteoblasts
- deposition of bone

Question 8

Osteoblasts

Answer 8

derived from mesenchymal/stromal cells (CT cells found in bone marrow)
- construct ECM of bone
- demonstrate inc levels of intracellular messenger Camp when stimulated
- control osteoclast function

Question 9

Osteoclasts

Answer 9

large multinucleated cells, of the monocyte-macrophage lineage
- adhere to the bone surface and secrete acid/hydrolytic enzymes into it
- found in well-defined pits known as ‘howship’s lacunae’

Question 10

What is bone remodelling controlled by?

Answer 10

Systemic hormones - parathyroid
local factors - prostaglandins

Question 11

How do osteoblasts control osteoclasts?

Answer 11

RANK Ligand and OPG
Factors (e.g., PTH) induce the expression of RANK ligand on osteoblasts
RANK ligand in combination with other factors (M-CSF and VEGF) induce the differentiation of osteoclasts from their precursors
Osteoblasts secrete OPG which opposes the effects of RANK ligand
RANK ligand is a member of the TNF superfamily and is expressed on the cell surface of osteoblasts. It binds to a receptor (RANK) on the osteoclast.
Opposing its actions is OPG, a soluble member of the TNF superfamily that is secreted by osteoblasts.
Osteoclastogenic molecules stimulate expression of RANK ligand and blunt production of OPG.