Biology of Tooth Movement

Question 1

Periodontal Ligament

Answer 1

primarily made of collagenous fiber bundles

primary cells are fibroblasts which makes the collagen

the ligament is constantly remodeled: also by fibroblasts

Question 2

Cellular elements

Answer 2

principal cellular elements of PDL, are undifferentiated mesenchymal cells and their progent in the form of fibroblasts and osteoblasts

other cells include: osteoclasts, cementoclasts. they all proliferate at different stages of tooth movement

Question 3

Bone

Answer 3

adaptive and responsive character of bone is the main determinant in orthodontic tooth movement

tooth cannot move unless both bone apposition and resorption take place

structure: primarily collagen type I, hydroxyapatite

Question 4

Osteoblasts

Answer 4

originate from marrow stromal cell lineage

bone forming cells: they appear at bone remodeling sites where osteoclasts previously resorbed bone

participate in minerialization process

Question 5

Osteocytes

Answer 5

osteoblats that remian after bone formation stopped

occupy small lacunae w/in minerialized matrix of bone

Question 6

Osteoclasts

Answer 6

originate from hematopoietic mononuclear stem cells

multinucleated

resorb bone

Question 7

Alveolar bone proper

Answer 7

part of alveolar bone that lines the sockets

it is a thin lamella of compact bone in which periodontal fibers are embedded

specialized type of compact bone composed of bundle bone and haversian bone

referred to as bundle bone bc it incorporated Sharpey’s fibers of the perio ligament

Question 8

Bio-electric theory

Answer 8

relates tooth movement at least in part to changes in bone metabolism controlled by the electric signals that are produced when alveolar bone flexes and bends

first and second messengers stimulate cellular change

Question 9

Effects of Force Magnitude

Answer 9

There will be no tooth movement unless there is a force.

The response to sustained forces against the teeth is a function of force magnitude

Light continuous forces are compatible w/ the survival of cells w/in the PDL and a remodeling of the tooth socket by a relatively painless “frontal resorption” of the tooth socket

Question 10

Frontal Resorption

Answer 10

facilitates orthodontic tooth movement, whereas undermining resorption delays orthodontic tooth movement

Question 11

Optimal Pressure

Answer 11

minimal pressure causing maximal tooth movement. Varies for each tooth based on root surface

Question 12

Intrusion

Answer 12

10 - 20 gm

Question 13

Translation or bodily movement

Answer 13

70 to 120 g

Question 14

Force Types

Answer 14

Light, continuous forces - never declines to zero

interrupted forces - declines to zero

Intermittent forces - declines to zero (removable appliances)

Question 15

Force Duration

Answer 15

Threshold - 6 hrs per day

No tooth movement if forces are applied less than 6 hrs/day

From 6 to 24 hrs/day, the longer the force is applied, the more the teeth will move

Question 16

Anchorage

Answer 16

Newton’s Law: for every action, there is a reaction

defined: resistance to unwanted tooth movement

anchorage value: any tooth is roughly equivalent to its root surface area. Thus, molars and canines generally have higher anchorage values than incisors and bicuspids

Question 17

Reciprocal anchorage

Answer 17

both units move roughly equal distance

exemplified by closing a diastema between two central incisors

Question 18

Reinforced anchorage

Answer 18

Unit A has substantially more anchorage value than Unit B. Thus, Unit A moves little but Unit B moves a lot.

Exemplified by retracting anterior teeth to close an extraction space by using posterior teeth as a reinforced anchorage unit

Question 19

Stationary anchorage

Answer 19

bodily movement of the posterior teeth (needs larger force level vs. tipping of the anterior teeth.

posterior teeth do not move while anterior teeth move

Question 20

Cortical Anchorage

Answer 20

Loss of teeth leads to loss of alveolar bone and replaced with cortical bone and thus makes it harder to move the posterior teeth forward

Question 21

Skeletal Anchorage

Answer 21

head gear: not the best because it is not worn all the time

Question 22

Stationary anchorage: TAD (temporary anchorage device)

Answer 22

micro screws placed in the cortical bone can provide absolute anchorage

Question 23

potential complications of orthodontic tooth movement

Answer 23

the pulp

root resorption

alveolar bone height

Question 24

orthodontic effects on the pulp

Answer 24

rare if light, continous forces are applied

occasional loss of tooth vitality - history of previous trauma, excessive orthodontic forces, moving roots against cortical bone

endodontically treated teeth can be moved like natural teeth with proper management

Question 25

root resorption

Answer 25

more accurately, resorption of root cementum and dentin

normal ageing process in many individuals

likely occuring in many cases but not to the degree of clinical significance

root resorption induced by light orthodonttic forces is reversible (by regeneration and repair of cementum and/or dentin)

can lead to tooth mobility in severe cases

Question 26

generalized root resorption

Answer 26

affects most, if not all teeth: maxillary incisors more susceptible than other teeth

could be moderate or severe but commonly in the range of up to 2.5mm

etiology largely unknown but predisposing factors include conical roots with pointed apices, distorted tooth form, or a history of trauma

Question 27

Prostaglandin inhibitors

Answer 27

prolonged use of corticosteroids or NSAIDS such as aspirin, ibuprofen may affect tooth movement by inhibiting prostaglandin synthesis, a mediator of tooth movement