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Ortho > Lecture 5 > Flashcards

Lecture 5 Flashcards

1
Q

orthodontic treatment is based on the principle that if ___ is applied to a tooth, tooth movement will occur

A
  • prolonged pressure

- this happens as the bone around the tooth remodels, by selectively being removed in some areas and added in others

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2
Q

because the bony response of prolonged pressure is mediated by the ___, tooth movement is primarily a ___ phenomenon

A
  • PDL

- PDL

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3
Q

because tooth movement is primarily a PDL phenomenon, what might happen if the cementum of the tooth and the alveolar bone come into contact without a healthy PDL?

A

the tooth may become ankylosed

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4
Q

under normal circumstances, the PDL occupies a space approximately ___mm in width

A

0.5mm

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5
Q

the PDL contains a network of __parallel/perpendicular__ collagenous fibers, which insert into the cementum of the root and alveolar bone

A

parallel

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6
Q

the PDL space contains what 5 cellular elements?

A
  • mesenchymal cells - multipotent stromal cells that can differentiate into a variety of cell types
  • fibroblasts
  • osteoblasts
  • vascular and neural elements
  • the PDL space also contains tissue fluids
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7
Q

the collagen of the PDL is constantly being remodeled and renewed during normal function by what two cell types?

A

fibroblasts and fibroclasts

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8
Q

remodeling and recontouring of the bony socket and the cementum of the root is constantly being carried out by what two cells?

A

osteoclasts (bony socket) and cementoclasts (cementum)

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9
Q

what are the nerve endings found within the PDL?

A
  • unmyelinated free endings associated with perception of pain
  • complex receptors associated with pressure and positional information (proprioception)
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10
Q

the PDL space is filled with fluid, which is the same fluid found in ___ and is derived from the ___

A
  • all other tissues

- the vascular system

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11
Q

what is the function of the fluid filled chamber in the PDL space?

A

it acts like a shock absorber for the tooth during normal function

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12
Q

describe PDL fluid compression and tooth movement

A
  • during the first second of pressure on a tooth, very little fluid is squeezed out of the PDL space (shock absorber)
  • if the pressure is maintained, the fluid is rapidly expressed, and the tooth displaced within the PDL space, compressing the PDL against the adjacent bone, which causes pain (usually takes between 3-5 seconds of pressure)
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13
Q

what other light prolonged forces also have the same potential to move teeth as orthodontic forces created by braces?

A

forces in the natural environment, from lips, cheeks, and tongue

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14
Q

T or F:

resting pressures from the lips, cheeks, and tongue are usually balanced

A
  • false
  • for example, in the mandibular anterior area, tongue pressure is greater than lip pressure
  • in the maxillary incisor region, lip pressure is greater
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15
Q

because resting pressures from the cheeks, lips, and tongue are not in balance, there must be a mechanism that creates a threshold of force that must be reached before tooth movement can occur. where is this mechanism found?

A

the PDL

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16
Q

___ produced by ___ probably explains why teeth are stable in the presence of imbalanced pressures that would otherwise cause tooth movement

A
  • active stabilization produced by metabolic effects in the PDL
  • *active stabilization of the PDL implies that there is a threshold for orthodontic force
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17
Q

what is the threshold for orthodontic force provided by active stabilization of the PDL?

A

5-10g/cm^2

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18
Q

what is the envelope of stability, and how does it relate to orthodontic retention and relapse?

A
  • teeth occupy a position in the oral cavity where the pressures placed against them are in equilibrium
  • if the pressure equilibrium is not in balance, the tooth will move to the position of least resistance and occupy that space, which places these forces back into balance
  • this is important in understanding orthodontic retention and relapse
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19
Q

what is a lip bumper?

A
  • a removable appliance used in growing children to create and save the space necessary to accommodate the adult teeth without extraction
  • it harnesses the natural forces of the muscles surrounding the lower teeth to broaden and lengthen the dental arch
  • it keeps the lip pressure away from the teeth, while simultaneously allowing the tongue to put pressure on the lingual surfaces of the incisors
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20
Q

after a tooth emerges into the mouth, further eruption depends on what metabolic events within the PDL?

A

formation of cross-linkages and maturational shortening of collagen fibers

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21
Q

what is the piezoelectric current theory of bone remodeling during tooth movement?

A
  • during normal function, forces on the teeth can be quite high, but only last for 1 second or less
  • under a heavy load, quick displacement of the tooth within the PDL space is prevented by the incompressible tissue fluid, which transfers the force to the alveolar bone, which bends in response
  • bone bending in response to normal function generates piezoelectric currently that appear to be an important stimulus to skeletal regeneration and repair; this is the mechanism by which bony architecture is adapted to functional demands
22
Q

what is a piezoelectric current?

A

-in many crystalline materials, like hydroxyapatite in bone, a deformation of the crystal structure produces a flow of electric current, as electrons are displaced from one part of the crystal lattice to another

23
Q

piezoelectric signals have which two unusual characteristics? what are these characteristics caused by?

A
  • a quick decay rate - the signal quickly dies away to zero even though the force on the bone is maintained
  • the production of an equivalent signal, opposite in direction when the force is released
  • they are caused by the migration of electrons from one location to another when the crystal structure is deformed, causing an electric current flow to be observed
24
Q

in piezoelectric currents, as long as the force is maintained, the crystal structure is stable, and no further ___ are observed; when the force is released, the crystal returns to its original shape and the ___ flow of electrons is seen

A
  • electrical events

- reverse

25
Q

in piezoelectric currents, ions in the fluids that bathe living bone interact with the complex electric field generated when bone bends, causing ___ signals in the form of ___ and ___

A
  • electric signals
  • volts and temperature changes
  • *these small voltages observed in the fluid ions are called a streaming potential
26
Q

what is streaming potential?

A
  • small voltages observed in fluid ions
  • like piezoelectric currents, a streaming potential has a rapid onset and alteration as changing stresses are placed on the bone
27
Q

what happens to bone mineral without stress-generated signals (i.e. when signals generated by the bending of alveolar bone, from chewing for example, are not present)?

A

-the bone mineral is lost, and general skeletal atrophy ensues

28
Q

T or F:
the sustained force of the type used to induce orthodontic tooth movement produces prominent cyclic stress generated signals

A
  • false

- in orthodontic force, as long as the force is sustained, piezoelectric currents are NOT produced

29
Q

are vibrating applications of pressure (like from the acceledent appliance) advantageous in orthodontic tooth movement? why or why not?

A

no, because the stress-generated signals from cyclic stress do not produce bone remodeling

30
Q

the PDL pressure-tension theory of tooth movement relies on ___ signals rather than ___ signals as the stimulus for cellular differentiation and ultimately tooth movement

A
  • chemical

- electrical

31
Q

chemical messengers are important in the PDL pressure-tension theory of tooth movement and bone remodeling. what two events can cause the release of chemical messengers?

A
  • mechanical compression of tissues

- changes in blood flow

32
Q

how does the PDL pressure-tension theory work?

A
  • when a sustained force is placed on a tooth, the tooth shifts positions within the PDL space, compressing the ligament in some areas, while stretching it in others
  • chemical messengers are released
  • alterations in blood flow quickly create changes in oxygen/carbon dioxide levels, which stimulates the release of other biologically active agents which stimulate cellular differentiation and activity
33
Q

what are some of the chemical messengers released in the PDL pressure-tension theory?

A

cytokines, prostaglandins, and other chemical messengers

34
Q

describe blood flow changes in the PDL pressure-tension theory

A

-blood flow is decreased in the compressed PDL area, while it is maintained or increased where the PDL is under tension

35
Q

what are the effects of force on a tooth with respect to the PDL pressure-tension theory?

A
  • 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 increase in prostaglandin E and IL-1beta levels, which increase cyclic adenosine monophosphate (cAMP), an important second messenger for cellular differentiation
36
Q

what is the effect of prostaglandins on tooth movement? is prostaglandin release a primary or secondary response to pressure?

A
  • prostaglandins stimulate osteoclastic and osteoblastic activity, making prostaglandins particularly suitable as a mediator of tooth movement
  • primary response
37
Q

during tooth movement, cAMP levels typically increase after how many hours of sustained pressure? what philosophy does this correlate with?

A
  • 4-6 hours
  • correlates with the philosophy that if a removable appliance is worn less than 6 hours per day, it will not have any orthodontic effects, but appliances worn above this threshold will produce some tooth movement
38
Q

what are the two thresholds of tooth movement?

A
  • amount of force

- amount of time

39
Q

what is the force threshold for tooth movement?

A

between 5-10 grams/square cm

40
Q

what is the time threshold for tooth movement?

A

4-6 hours of sustained pressure is required for the cAMP levels to typically increase, which must occur to induce bone remodeling, which will then allow tooth movement to occur

41
Q

the heavier the pressure that is placed on a tooth, the ___ the reduction in blood flow

A

greater

42
Q

at a certain magnitude of continuous pressure, blood vessels are totally occluded and ___ ensues; what is this referred to as?

A
  • a sterile necrosis of PDL tissue
  • it is referred to as hyalinization or sterile necrosis because the area appears to be absent of any cells, due to the inevitable loss of all the cells when the blood supply is lost
43
Q

what happens when the PDL is compressed to the point that blood flow is totally cut off?

A
  • 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
44
Q

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

A
  • a delay in the stimulation of the differentiation of the cells within 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
45
Q

what happens when a light continuous force is applied to a tooth?

A
  • the PDL is compressed but blood flow to the area is not completely occluded
  • 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
  • frontal resorption occurs as these cells attack the adjacent lamina dura and remove adjacent bone, allowing tooth movement to occur
  • osteoclasts and osteoblasts recruited locally from progenitor cells in the PDL form bone on the tension side, and begin remodeling activity of the pressure side
46
Q

describe the difference between frontal resorption and undermining resorption

A
  • frontal resorption - a steady attack on the outer surface of the lamina dura results in smooth continuous tooth movement
  • undermining resorption - there is a delay until the bone adjacent to the tooth can be removed (at this point, the tooth fills in the new position, and if the heavy force is maintained, there will be another delay until a second round of undermining resorption can occur)
47
Q

not only is ___ more efficient when an area of PDL necrosis is avoided, but ___ is also lessened

A
  • tooth movement

- pain

48
Q

even with light forces, small avascular areas are likely to develop in the PDL even with the lightest of wires. what affect does this have on tooth movement?

A

it will be delayed until these areas can be removed by undermining resorption

49
Q

is a smooth progression of tooth movement with light force always attainable in ideal clinical orthodontics?

A

not always

50
Q

what happens to tooth movement when continuous force is used in clinical practice?

A

it usually proceeds in a more stepwise fashion because of the inevitable areas of undermining resorption that will occur

51
Q

in clinical practice, an individual tooth’s movement will typically include areas of frontal and undermining resorption, with ___ being the rate limiting step in the tooth’s movement

A

undermining

Ortho (15 decks)

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