Lecture 5

Question 1

The classic theory of tooth movement relies on ___ rather than ___ as the stimulus for _____ and ultimately tooth movement

Answer 1

Chemical signals

Electoral signals

Cellular differentiation

Question 2

What two things can cause the release of chemical messengers which in turn leads to remodeling of the alveolar bone and tooth movement?

Answer 2

Mechanical compression

Changes in blood flow

Question 3

True or false…

When a sustained force is placed on a tooth, the tooth shifts positions within the PDL space these compressing the ligament in all areas

Answer 3

False. It compresses in some areas but stretches in others

Question 4

The mechanical effects on the PDL causes the release of….

Answer 4

Chemical messengers such as cytokines and prostaglandins

Question 5

Blood flow is [decreased/increased] in the compressed PDL ares and [decreased/increased] under tension

Answer 5

Decreased

Increased (or maintained)

Question 6

Alterations in blood flow in the PDL causes changes in ____ levels

Answer 6

Oxygen/CO2

This alteration acts either directly or indirectly in stimulating the release of other biologically active agents that then stimulate cellular differentiation and activity

Question 7

When force is applied to a tooth the fluids are expressed out of the PDL space and the tooth moves in its socket. Then, the blood flow through the partially compressed PDL decreases and within a few hours the resulting change in the chemical environment produces an….

Answer 7

Increase in prostaglandins (especially prostaglandin E)

Increase in interleukin-1 beta levels which increases cAMP (which is an important second messenger for cellular differentiation

Question 8

Increase in interleukin-1beta levels increases ___ levels

Answer 8

CAMP

Question 9

True or false…

Prostaglandin release is a secondary response to pressure

Answer 9

False. It is a primary response

Question 10

True or false… prostaglandins stimulate both osteoclastic and osteoblastic activity

Answer 10

True

Question 11

The cAMP levels typically increase after ___ hours of sustained pressure. What is significant about this?

Answer 11

4-6

The amount of time to increase cAMP levels and produce cellular response correlates well with the philosophy that if a removable appliance is worn less than 6 hours per day, it will not have any orthodontic effects. Appliances worn above this threshold will produce tooth movement.

Question 12

What are the two thresholds for tooth movement?

Answer 12

5-10grams/cm^2

4-6 hours of sustained pressure (which is required for cAMP levels to increase to induce bone remodeling)

Question 13

True or false… the heavier the pressure that is placed on a tooth the greater the reduction in blood flow

Answer 13

True

Question 14

During a certain magnitude of continuous pressure, blood vessels are totally occluded and ___ occurs

Answer 14

Sterile necrosis of PDL tissue

AKA hyalinization

Question 15

What happens when the blood vessels in the PDL are totally occluded?

Answer 15

Differentiation of osteoclasts within the PDL space is no longer possible

After a delay of several days, osteoclasts within the adjacent marrow spaces attack the underside of the lamina dura in a process called undermining resorption

Question 16

During undermining resorption, tooth movement is delayed due to what two things?

Answer 16

A delay in the stimulation of the differentiation of the cells in the marrow spaces

Delayed due to the thickness of bone that must be removed from the underside of the areas before any tooth movement can take place

Question 17

What happens when a light continuous force is placed on a tooth so that the blood vessels are not totally occluded? (Frontal resorption)

Answer 17

Osteoclasts are activated from a local population of progenitor cells in the PDL and then a second wave of osteoclasts are brought in from distant areas via blood flow. These cells attack the adjacent lamina dura removing adjacent bone in a process called frontal resorption

Question 18

Soon after frontal resorption occurs, osteoblasts and osteoclasts recruited locally from progenitor PDL cells do what two things?

Answer 18

Form bone on the tension side

Begin remodeling on the pressure side

Question 19

Frontal resorption results in a smooth continuous tooth movement whereas undermining resorption causes a delay until the tooth jumps into space. Which is preferred?

Answer 19

Frontal resorption. Tooth movement is more effeicient where PDL necrosis is avoided and pain is lessened.

Question 20

True or false…

Even with light forces, in clinical orthodontics, small avascualr areas are likely to develop in the PDL which results in undermining resorption

Answer 20

True

(Smooth progression of tooth movement with light force may be unattainable in ideal clinical orthodontics. When continuous force is used in clinical practice, tooth movement usually proceeds in a more stepwise fashion because of the inevitable areas of undermining resorption)

Question 21

What is the rate limiting step in tooth movement?

Answer 21

Undermining resorption

Question 22

What is the max amount of tooth movement per month?

Answer 22

1mm