Biology of orthodontic tooth movement- Sun

Question 1

what is the pdl?

Answer 1

soft tissue connecting teeth to alveolar bone

approximately 0.5mm in width

Question 2

what are the constituents of pdl?

Answer 2

mainly parallel collagenous fibers
cells:fibroblasts, osteoblasts, mesenchymal stem cells, cells from vascular structures
blood vessels and nerve endings (unmyelinated, for perception of pain, pressure and position (proprioception)
tissue fluids- viscoelastic element, dampening effect

Question 3

when are osteoclast present in pdl?

Answer 3

when inflammation or bone resorption

Question 4

what is the pdl role in orthodontics?

Answer 4

pdl is constantly adapting and remodeling
pdl is adapted to resist short duration (Seconds) forces: the pdl fibers and tissue fluids act as a shock absorber system
prolong forced include a different response- remodeling of the pdl and adjacent bne

Question 5

what is important in inducing tooth movement?

Answer 5

force magnitude and duration- a force as low as 2 gm can induce tooth movement

Question 6

what needs to be remodeled for tooth movement?

Answer 6

pdl fibers (Especially sharpey's fibers)
remodleing conducted by fibroblast

Question 7

are fibroblast abundant in the pdl?

Answer 7

yes

Question 8

what is required for bone resorption?

Answer 8

osteoclast
multinucleated, produce acid and enzymes to remove bone
origin: hematopoietic stem cells>monocytes->osteoclasts
not normally available in the pdl- need to be recruited from blood vessels or bone marrow

Question 9

what is the bioelectric theory of orthodontic tooth movement

Answer 9

force induces piezoelectric signals

bioelectric potential changes cell activity

Question 10

what is the pressure tension theory

Answer 10

bone chnages caused by chemical signals
pressure and tension alter blood flow
formation and release of chemical messenger
chemical messengers change celll activities