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Optimum Force Magnitude for
Orthodontic Tooth Movement
- Review of Literature
Yijin Ren, Jaap C. Maltha.
The Angle Orthodo...
An optimal force system is important for
adequate biological response in the
periodontal ligament and magnitude of this
fo...
Schwarz (1932) proposed the first classic
concept of the optimal force.
He defined optimal continuous force as „„the
force...
This pressure in humans is about 15-20 mm
of Hg; and this comes to be 20 - 26 g for 1
sq.cm surface.
Based on this theory,...
According to Schwarz, forces well below the
optimal level cause no reaction in the
periodontal ligament.

Forces exceeding...
Schwarz‟s definition was slightly modified by
Oppenheim (1944) who advocated the use
of the lightest force capable of brin...
Reitan (1957) based on his histological
findings where he demonstrated cell-free
compressed areas within the pressure site...
Storey and smith (1952) proposed their
theory of “optimal force”.
Acc to this theory, there is optimal range of
force that...
This theory of „optimal force‟ was critically reviewed
by Boester and Johnston (1974).
They found in their study of 10 ind...
Hixon et al (1969) reported a more linear
relationship between force magnitude and
tooth movement, at least up to 300g of
...
The current concept of optimal force is based on
the hypothesis that a force of a certain magnitude
and temporal character...
Relationship between stress/strain and
amount of tooth movement
Force magnitude is a popular concept in
orthodontics. Howe...
The true mechanical parameter in tooth
movement is not the magnitude of the force
per se, but rather the magnitude of the
...
Compressive stress patterns in the periodontal ligament
under different force systems. A, Pure force applied at the
bracke...
Clinical interest in characterizing the nature
of the relation between the magnitudes of
applied force (i.e stress/strain)...
The assumption was that differential
movement of teeth, at first proposed by
Begg (1957), could be generally achieved
with...
In the last two decades, one of the central
questions raised about the exact
relationship of stress/strain pattern and
bio...
This question led to the classic study by
Quinn and Yoshikawa (1985) in which they
proposed four possible models for the
r...
HYPOTHESES OF THE STRESS-MOVEMENT
RELATIONSHIP
(Robert S. Quinn, and D. Ken Yoshikawa,
jco 1985)

The effect of periodonta...
Clinicians base their strategies for
controlling anchorage on their assumptions
about tooth movement.

Quinn and Yoshikawa...
Possible hypotheses of the relationship between
stress magnitude and the rate of tooth movement

www.indiandentalacademy.c...
Hypothesis 1 shows a constant relationship
between rate of movement and stress.
The rate of tooth movement does not
increa...
Acc to this hypothesis, anchorage control
does not obey concept of ‘differential
anchorage’.
Hence when elastics are used ...
Hypothesis 2 shows a linear increase in the rate of
tooth movement as the stress increases.
In this system, intra-arch anc...
This would distribute the stress over a larger
root surface, lowering the local stresses and
slowing the rate of tooth mov...
Hypothesis 3 depicts a relationship in which
increasing stress causes the rate of
movement to increase to a maximum.
Once ...
This hypothesis was originally proposed by
Smith and Storey (1952) and following
clinical strategies have evolved to take
...
Hypothesis 4 is a composite of some of the
foregoing concepts.
Here the relationship of rate of movement and
stress magnit...
EVALUATION OF HYPOTHESES
None of the studies in literature support
hypothesis 1 (constant relationship between
stress and ...
Hypothesis 3, the original Smith and Storey
proposal (1952), can no longer be
considered viable in light of subsequent
cli...
During canine retraction, canine moves
more than molar at both the high and low
force levels and more importantly, there i...
Evidence for 4th Hypothesis is more
compelling
Burstone and Groves, (1961), Hixon et al.
(1969) and Boester and Johnston (...
This study conclude that beyond an optimal
range, there is no effect of increased force
level on rate of tooth movement.

...
Both type (intermittent or continuous) and
level (magnitude) of force are important
factors in determining optimal force w...
Effect of force level (magnitude) on
rate of tooth movement and root
resorption
Many studies have been performed to
invest...
A clinical inter-individual study was recently
carried out to investigate tooth movements
and adverse reactions of the too...
The results demonstrated that the rate of
tooth movement increased but
severity of root resorption (surface
extension and ...
An additional investigation was undertaken
by same authors to determine whether a
further substantial increase of force
ma...
The effects of a four-fold increased
orthodontic force magnitude on tooth
movement and root resorption.
- intra-individual...
This clinical and histological study was
designed as an intra-individual study to
investigate the effect of continuous for...
Subjects and methods

Experimental design and orthodontic
appliance
The maxillary first premolars bilaterally in
eight ind...
A fixed orthodontic appliance was inserted
the day the experimental period started and
consisted of molar bands on the fir...
A lingual arch with an
anterior acrylic bite
block was soldered to
the molar bands to
reduce the occlusal
forces on the te...
The buccally directed tooth movement was
performed with a sectional arch (Sentalloy
0.018” when 50g force was applied and
...
This continuous orthodontic force was
applied for 7 weeks (total duration of
study).
The force magnitude was controlled we...
The orthodontic force magnitude declined on
average from 50g to 41g (18 per cent) and
on average from 200 to 145g (28 per ...
Tooth movement registration
Alginate impressions were taken just before
start and at the end of the experiment.
With a sha...
The horizontal (buccal) tooth movement was
measured with a coordinate measuring
machine (Validator lOO@, TESA SA, Renens,
...
Radiographic registrations
Periapical radiographs using a long cone
parallel technique were taken within a week
before the...
Histological procedures
At the end of the experiment, the teeth
were extracted.
With the microtome set to 4 µm, the teeth
...
The sections were stained with haematoxylin
and eosin.
A light microscope with a micrometer fitted
into the eye-piece was ...
The surface extension
of resorption was
measured parallel to
the root surface.

www.indiandentalacademy.com
The depth of each
resorption lacuna was
measured at the
deepest point by using
the distance from the
bottom of the cavity
...
The mean value of root contour and root area were
calculated in order to describe the:
1 Resorbed root contour (%).
The su...
2 Resorbed root area (%).
The sum of the resorbed root area
(extension x depth of the resorption lacuna)
in the three long...
Results
Amount of tooth movement
After application of a continuous force of
50g for 7 weeks, the tooth displacements
varie...
This difference in horizontal tooth movement
was significant (P=0.02) with a 95 per cent
confidence interval.

www.indiand...
Root resorption
Root resorption was registered in all test
teeth and there were no significant
difference in number (n) or...
www.indiandentalacademy.com
Frequency and severity of root resorption showed
great individual variation, whether 50g or 200g force
was used.

200g for...
Discussion
A force of 50g has often been used and
recommended when buccal tipping of
premolars is desired.
The results of ...
One of the main findings in this
investigation was that the individual
variations in tooth movement as well as in
frequenc...
This finding indicate that the major source of
variation is probably not the magnitude of
force, but variation in metaboli...
In yet another hypothesis, it may be
speculated that a force magnitude of 200g
may be too large to express cellular
reacti...
Where adverse tissue reactions are concerned,
heavy force application may primarily prevent
cellular reactions on the root...
But this short term study of early tissue
reactions in adolescents can not answer this
assumption.

The experimental model...
It is therefore, necessary to utilize another
type of model, permitting tooth movement
along the alveolar ridge, if long-t...
Effect of type of force on rate of
tooth movement and root
resorption
Reitan (1957, 1970, 1985) advocated use
of intermitt...
Maltha and Dijkman (1996) reported more
resorption in dogs when using continuous rather
than intermittent forces.
Faltin e...
Constant versus dissipating forces in
orthodontics: the effect on initial tooth
movement and root resorption.
F. Weiland
E...
The aim of this clinical and laser scanning
microscopic study was to compare the
effects of two frequently used arch wires...
In a inter-individual comparison study
design, a total of 90 premolars in 27
individuals (10 boys, 17 girls, with a mean
a...
Therefore, 84 teeth (maxilla/mandible) were
moved buccally with an experimental fixed
orthodontic appliance.
Impressions u...
Appliance design
A fixed orthodontic appliance was cemented
at the start of the experiment.
Appliance consisted of an acry...
A fixed orthodontic appliance was cemented at the start
of the experiment. It consisted of an acrylic splint
covering all ...
Brackets (0.018 inch slot) were bonded to
the experimental teeth.
The brackets were incorporated in the
splints in such a ...
Base of the slot of the „splint brackets‟ was
4.5 mm more buccally positioned than that
of the bracket on the experimental...
The contra lateral premolar was moved with
a super elastic wire (0.016 inch) with a
force plateau of 0.8–1 N.
(This wire h...
www.indiandentalacademy.com
At the end of the experimental period, tooth
displacement was studied threedimensionally on dental casts with a coordinate...
The depth, area, and volume of the
resorption lacunae were measured using
three-dimensional digital images made with
a con...
Result
Tooth movement
Teeth with the superelastic wire moved
significantly more (3.50 versus 2.30 mm)
and tipped buccally ...
Resorption
The number of resorptions on the roots of
the teeth moved with a super elastic wire
was significantly greater t...
www.indiandentalacademy.com
The amount of resorptive damage,
defined as the largest depth, perimeter,
area, and volume were compared between
these two...
www.indiandentalacademy.com
Conclusion
This study confirms earlier studies regarding
potential damage to tissues with use of
continuous force.
(Gibson...
It could not be confirmed that maxillary
teeth are at higher resorptive risk than
mandibular teeth, as has been stated in ...
The differing sensitivity is mostly explained
by the differing mechanical load of the
upper and lower teeth during treatme...
The amount of tooth movement and the amount of
resorptive activity were correlated. However, this
correlation was weak, th...
Individual variations have been reported to
be an important factor for both tooth
movement in both force systems.
(Hixon e...
Rygh and Brudvik (1993) stated :
„New wire qualities pose challenges for the
orthodontist who must try to avoid
continuous...
Thank you
For more details please visit
www.indiandentalacademy.com

www.indiandentalacademy.com
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Optimal force /certified fixed orthodontic courses by Indian dental academy

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Optimal force /certified fixed orthodontic courses by Indian dental academy

  1. 1. INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  2. 2. Optimum Force Magnitude for Orthodontic Tooth Movement - Review of Literature Yijin Ren, Jaap C. Maltha. The Angle Orthodontist 2003; 73, 86-92 www.indiandentalacademy.com
  3. 3. An optimal force system is important for adequate biological response in the periodontal ligament and magnitude of this force is related to the surface area of the root. www.indiandentalacademy.com
  4. 4. Schwarz (1932) proposed the first classic concept of the optimal force. He defined optimal continuous force as „„the force leading to a change in tissue pressure that approximated the capillary blood pressure, thus preventing their occlusion in the compressed periodontal ligament.‟‟ www.indiandentalacademy.com
  5. 5. This pressure in humans is about 15-20 mm of Hg; and this comes to be 20 - 26 g for 1 sq.cm surface. Based on this theory, Jepsen (1963) calculated optimal force for premolar with mean root surface area of 2.34 cm2, which comes to be 54g. www.indiandentalacademy.com
  6. 6. According to Schwarz, forces well below the optimal level cause no reaction in the periodontal ligament. Forces exceeding the optimal level would lead to areas of tissue necrosis, preventing frontal bone resorption. www.indiandentalacademy.com
  7. 7. Schwarz‟s definition was slightly modified by Oppenheim (1944) who advocated the use of the lightest force capable of bringing about tooth movement. www.indiandentalacademy.com
  8. 8. Reitan (1957) based on his histological findings where he demonstrated cell-free compressed areas within the pressure site, strongly advocated use of very light forces to maintain health of investing tissues. www.indiandentalacademy.com
  9. 9. Storey and smith (1952) proposed their theory of “optimal force”. Acc to this theory, there is optimal range of force that produce maximum tooth movement. When force is increased above this range, tooth movement slows down. www.indiandentalacademy.com
  10. 10. This theory of „optimal force‟ was critically reviewed by Boester and Johnston (1974). They found in their study of 10 individuals that space closure after premolar extraction was about same after application of 140, 225 or 310g of force during 10 weeks. But space closure was significantly less when about 55g force was used. www.indiandentalacademy.com
  11. 11. Hixon et al (1969) reported a more linear relationship between force magnitude and tooth movement, at least up to 300g of force. www.indiandentalacademy.com
  12. 12. The current concept of optimal force is based on the hypothesis that a force of a certain magnitude and temporal characteristics (continuous vs intermittent, constant vs declining,etc ) would be capable of producing a maximum rate of tooth movement without tissue damage and with maximum patient comfort. The optimal force for tooth movement may differ for each individual. www.indiandentalacademy.com
  13. 13. Relationship between stress/strain and amount of tooth movement Force magnitude is a popular concept in orthodontics. However, it is an incomplete way to describe the forces delivered by an orthodontic appliance. www.indiandentalacademy.com
  14. 14. The true mechanical parameter in tooth movement is not the magnitude of the force per se, but rather the magnitude of the stress generated by the appliance in the surrounding periodontium. www.indiandentalacademy.com
  15. 15. Compressive stress patterns in the periodontal ligament under different force systems. A, Pure force applied at the bracket. B, Force and moment applied at the bracket Translation Tipping www.indiandentalacademy.com
  16. 16. Clinical interest in characterizing the nature of the relation between the magnitudes of applied force (i.e stress/strain) and the rate of orthodontic tooth movement determining the extent of anchorage loss began in the 1950s. www.indiandentalacademy.com
  17. 17. The assumption was that differential movement of teeth, at first proposed by Begg (1957), could be generally achieved with light force without any unwanted tooth movement. www.indiandentalacademy.com
  18. 18. In the last two decades, one of the central questions raised about the exact relationship of stress/strain pattern and biologic activity and thus rate of tooth movement, which may affect : - anchorage planning - efficiency of appliance in tooth movement www.indiandentalacademy.com
  19. 19. This question led to the classic study by Quinn and Yoshikawa (1985) in which they proposed four possible models for the relation between force magnitude and the rate of orthodontic tooth movement. www.indiandentalacademy.com
  20. 20. HYPOTHESES OF THE STRESS-MOVEMENT RELATIONSHIP (Robert S. Quinn, and D. Ken Yoshikawa, jco 1985) The effect of periodontal stress magnitude on the rate of tooth movement is an important issue in plans to control the displacement of posterior teeth. www.indiandentalacademy.com
  21. 21. Clinicians base their strategies for controlling anchorage on their assumptions about tooth movement. Quinn and Yoshikawa proposed four possible relationships between stress magnitude and rate of movement. www.indiandentalacademy.com
  22. 22. Possible hypotheses of the relationship between stress magnitude and the rate of tooth movement www.indiandentalacademy.com
  23. 23. Hypothesis 1 shows a constant relationship between rate of movement and stress. The rate of tooth movement does not increase as the stress level is increased. www.indiandentalacademy.com
  24. 24. Acc to this hypothesis, anchorage control does not obey concept of ‘differential anchorage’. Hence when elastics are used for retraction, only one size is necessary. Loop designs are not critical and can be simple and uncomplicated by helices. www.indiandentalacademy.com
  25. 25. Hypothesis 2 shows a linear increase in the rate of tooth movement as the stress increases. In this system, intra-arch anchorage could be manipulated by adding teeth (second molars) to the anchorage unit or moving the extraction site for example, second versus first premolars. www.indiandentalacademy.com
  26. 26. This would distribute the stress over a larger root surface, lowering the local stresses and slowing the rate of tooth movement. On the other hand, appliance that deliver higher stresses would close extraction sites most rapidly. (since large periodontal stressed will lead to faster tooth movement of both anterior and posterior teeth) www.indiandentalacademy.com
  27. 27. Hypothesis 3 depicts a relationship in which increasing stress causes the rate of movement to increase to a maximum. Once this optimal level is reached, additional stress causes the rate of movement to decline. www.indiandentalacademy.com
  28. 28. This hypothesis was originally proposed by Smith and Storey (1952) and following clinical strategies have evolved to take advantage of its implications : - Use light forces to retract canines which will prevent anchorage loss, but using heavy forces to protract posterior teeth and "anchor" the canines. (differential anchorage) www.indiandentalacademy.com
  29. 29. Hypothesis 4 is a composite of some of the foregoing concepts. Here the relationship of rate of movement and stress magnitude is linear up to a point; after this point, an increase in stress causes no appreciable increase or decrease in tooth movement. Main difference between 3rd and 4th hypothesis is effect of force beyond optimal range. www.indiandentalacademy.com
  30. 30. EVALUATION OF HYPOTHESES None of the studies in literature support hypothesis 1 (constant relationship between stress and rate of movement). Hypothesis 2 (continuing linear relationship between stress level and amount of tooth movement) is also not substantiated well in literature. www.indiandentalacademy.com
  31. 31. Hypothesis 3, the original Smith and Storey proposal (1952), can no longer be considered viable in light of subsequent clinical experience. www.indiandentalacademy.com
  32. 32. During canine retraction, canine moves more than molar at both the high and low force levels and more importantly, there is no evidence for the rate of movement to suddenly reverse as the stress levels increase past a certain "optimum" value. www.indiandentalacademy.com
  33. 33. Evidence for 4th Hypothesis is more compelling Burstone and Groves, (1961), Hixon et al. (1969) and Boester and Johnston (1974) provide evidence that beyond a certain stress level, increasing stress no longer alters the rate of tooth movement. (no increase or decrease in rate of movement) www.indiandentalacademy.com
  34. 34. This study conclude that beyond an optimal range, there is no effect of increased force level on rate of tooth movement. But “what is the upper limit of this optimal range”? www.indiandentalacademy.com
  35. 35. Both type (intermittent or continuous) and level (magnitude) of force are important factors in determining optimal force which will preserve health of tissue. Any abnormal force will lead to adverse tissue reaction in form root resorption. www.indiandentalacademy.com
  36. 36. Effect of force level (magnitude) on rate of tooth movement and root resorption Many studies have been performed to investigate the relationship between magnitude of applied force and amount of tooth movement and root resorption. (Storey and Smith, 1952;Reitan, 1960; Burstone and Groves, 1961; Andreasen and Johnson, 1967; Hixon et aI., 1969, 1970; Boester and Johnston, 1974; Andreasen and Zwanziger, 1980; Maltha et al., 1993) www.indiandentalacademy.com
  37. 37. A clinical inter-individual study was recently carried out to investigate tooth movements and adverse reactions of the toothsupporting tissues when the applied continuous force was doubled from 50g to 100g for tipping movement of premolar tooth (Owman-Moll et al., 1995). Note – force of 50-55g is optimal for premolar tipping (acc. to Schwarz) www.indiandentalacademy.com
  38. 38. The results demonstrated that the rate of tooth movement increased but severity of root resorption (surface extension and depth of root resorption) showed no significant difference when force of 100g was applied and compared with 50g. www.indiandentalacademy.com
  39. 39. An additional investigation was undertaken by same authors to determine whether a further substantial increase of force magnitude would result in faster movement of the teeth without deleterious side effects. www.indiandentalacademy.com
  40. 40. The effects of a four-fold increased orthodontic force magnitude on tooth movement and root resorption. - intra-individual study in adolescents Owman-Moll, Juri Kurol and Dan Lundgren EJO 1996;18, 287-294 www.indiandentalacademy.com
  41. 41. This clinical and histological study was designed as an intra-individual study to investigate the effect of continuous force of 50g and 200g : - on tooth movements and - adverse tissue reactions (root resorption) www.indiandentalacademy.com
  42. 42. Subjects and methods Experimental design and orthodontic appliance The maxillary first premolars bilaterally in eight individuals, six boys and two girls aged 12.1-13.6 years (mean age 13.0 years), formed test teeth. www.indiandentalacademy.com
  43. 43. A fixed orthodontic appliance was inserted the day the experimental period started and consisted of molar bands on the first maxillary molars joined with a half round transpalatal bar for reinforcement of the anchorage. www.indiandentalacademy.com
  44. 44. A lingual arch with an anterior acrylic bite block was soldered to the molar bands to reduce the occlusal forces on the test teeth. www.indiandentalacademy.com
  45. 45. The buccally directed tooth movement was performed with a sectional arch (Sentalloy 0.018” when 50g force was applied and Australian wire 0.018” when 200g force was applied). These wires were attached to the molar band and ligated to a bonded 0.018” bracket on the test teeth. www.indiandentalacademy.com
  46. 46. This continuous orthodontic force was applied for 7 weeks (total duration of study). The force magnitude was controlled weekly and reactivated to 50g and 200g, and was measured to the nearest 1g with a strain gauge (Haldex'E Halmstad, Sweden). www.indiandentalacademy.com
  47. 47. The orthodontic force magnitude declined on average from 50g to 41g (18 per cent) and on average from 200 to 145g (28 per cent) during each week of appliance reactivation. www.indiandentalacademy.com
  48. 48. Tooth movement registration Alginate impressions were taken just before start and at the end of the experiment. With a sharp pencil, a point on each of the buccal and palatal cusps of the test and control teeth was marked on the cast. www.indiandentalacademy.com
  49. 49. The horizontal (buccal) tooth movement was measured with a coordinate measuring machine (Validator lOO@, TESA SA, Renens, Switzerland) to the nearest 0.01 mm. www.indiandentalacademy.com
  50. 50. Radiographic registrations Periapical radiographs using a long cone parallel technique were taken within a week before the start of the tooth movement and immediately before extraction of the teeth. www.indiandentalacademy.com
  51. 51. Histological procedures At the end of the experiment, the teeth were extracted. With the microtome set to 4 µm, the teeth were serially sectioned parallel to the long axis in a bucco--palatal direction from the mesial surface to the middle of the root (with total 3 levels). www.indiandentalacademy.com
  52. 52. The sections were stained with haematoxylin and eosin. A light microscope with a micrometer fitted into the eye-piece was used to measure surface extension and depth of root resorption. www.indiandentalacademy.com
  53. 53. The surface extension of resorption was measured parallel to the root surface. www.indiandentalacademy.com
  54. 54. The depth of each resorption lacuna was measured at the deepest point by using the distance from the bottom of the cavity perpendicular to the tangent passing through the borders of the resorption lacuna on the root surface. www.indiandentalacademy.com
  55. 55. The mean value of root contour and root area were calculated in order to describe the: 1 Resorbed root contour (%). The sum of the extension of the resorption along the root surface in the three longitudinal and bucco-palatally directed histological sections of each tooth was registered and a mean was calculated and related to a registered mean root contour. www.indiandentalacademy.com
  56. 56. 2 Resorbed root area (%). The sum of the resorbed root area (extension x depth of the resorption lacuna) in the three longitudinal and bucco-palatally directed histological sections of each tooth was registered and a mean was calculated and related to a registered mean root area. www.indiandentalacademy.com
  57. 57. Results Amount of tooth movement After application of a continuous force of 50g for 7 weeks, the tooth displacements varied between 1.5 and 5.9 mm (mean 3.5 +/- 1.2 mm). When a continuous force of 200g was applied, the movements varied between 1.9 and 7.9 mm (mean 5.1 +/- 1.9 mm). www.indiandentalacademy.com
  58. 58. This difference in horizontal tooth movement was significant (P=0.02) with a 95 per cent confidence interval. www.indiandentalacademy.com
  59. 59. Root resorption Root resorption was registered in all test teeth and there were no significant difference in number (n) or severity of root resorption (i.e. resorbed root contour (%) and resorbed root area (%)) after application of a 50g compared with a 200g force. www.indiandentalacademy.com
  60. 60. www.indiandentalacademy.com
  61. 61. Frequency and severity of root resorption showed great individual variation, whether 50g or 200g force was used. 200g force 50g force www.indiandentalacademy.com
  62. 62. Discussion A force of 50g has often been used and recommended when buccal tipping of premolars is desired. The results of this study showed that when applied continuous force increased four fold, (200g) tooth movement increased 50 % without any significant increase in root resorption. www.indiandentalacademy.com
  63. 63. One of the main findings in this investigation was that the individual variations in tooth movement as well as in frequency and severity of root resorption were large, irrespective of amount of force. www.indiandentalacademy.com
  64. 64. This finding indicate that the major source of variation is probably not the magnitude of force, but variation in metabolic response. It is well known that prostaglandins play a major role in resorption processes. (Klein and Raisz, 1970; Somjen et a/., 1980; Ngan et al., 1988; Brudvik and Rygh, 1991). www.indiandentalacademy.com
  65. 65. In yet another hypothesis, it may be speculated that a force magnitude of 200g may be too large to express cellular reactions close to the root surface and that tooth movement may take place mainly by undermining resorption of the alveolar bone. (as proposed by Reitan, 1985). www.indiandentalacademy.com
  66. 66. Where adverse tissue reactions are concerned, heavy force application may primarily prevent cellular reactions on the root surface. But still, in a longer perspective, when the force is reduced due to tooth movement, extensive root resorption may take place. (as in this study also, higher forces have influenced the root surface) www.indiandentalacademy.com
  67. 67. But this short term study of early tissue reactions in adolescents can not answer this assumption. The experimental model used in this study does not allow long-term investigations due to the limited bucco-lingual extension of the alveolar process. www.indiandentalacademy.com
  68. 68. It is therefore, necessary to utilize another type of model, permitting tooth movement along the alveolar ridge, if long-term results are to be studied. www.indiandentalacademy.com
  69. 69. Effect of type of force on rate of tooth movement and root resorption Reitan (1957, 1970, 1985) advocated use of intermittent forces to prevent the development of root resorption by enabling reparative processes to occur during periods with little or no force. www.indiandentalacademy.com
  70. 70. Maltha and Dijkman (1996) reported more resorption in dogs when using continuous rather than intermittent forces. Faltin et al. (2001) confirmed that a reduction of continuous force magnitude should be considered to preserve the integrity of the tissues. www.indiandentalacademy.com
  71. 71. Constant versus dissipating forces in orthodontics: the effect on initial tooth movement and root resorption. F. Weiland EJO 2003; 25, 335-342 www.indiandentalacademy.com
  72. 72. The aim of this clinical and laser scanning microscopic study was to compare the effects of two frequently used arch wires on tooth movement and root resorption. www.indiandentalacademy.com
  73. 73. In a inter-individual comparison study design, a total of 90 premolars in 27 individuals (10 boys, 17 girls, with a mean age of 12.5 years) were used in study. Out of these 90 teeth, 6 teeth served as control. www.indiandentalacademy.com
  74. 74. Therefore, 84 teeth (maxilla/mandible) were moved buccally with an experimental fixed orthodontic appliance. Impressions using alginate were taken immediately before insertion of the experimental appliance. www.indiandentalacademy.com
  75. 75. Appliance design A fixed orthodontic appliance was cemented at the start of the experiment. Appliance consisted of an acrylic splint covering all but the experimental teeth. www.indiandentalacademy.com
  76. 76. A fixed orthodontic appliance was cemented at the start of the experiment. It consisted of an acrylic splint covering all but the experimental teeth in one arch. www.indiandentalacademy.com
  77. 77. Brackets (0.018 inch slot) were bonded to the experimental teeth. The brackets were incorporated in the splints in such a way that a normal interbracket distance (5mm) existed between the brackets on the splint and the bracket on the experimental tooth www.indiandentalacademy.com
  78. 78. Base of the slot of the „splint brackets‟ was 4.5 mm more buccally positioned than that of the bracket on the experimental tooth in the middle. The premolar on one side was activated with a stainless steel wire (0.016 inch) with a buccal offset of 1 mm, which was reactivated every four weeks. www.indiandentalacademy.com
  79. 79. The contra lateral premolar was moved with a super elastic wire (0.016 inch) with a force plateau of 0.8–1 N. (This wire had an initial activation of 4.5 mm and was not reactivated during the 12 week experimental period). www.indiandentalacademy.com
  80. 80. www.indiandentalacademy.com
  81. 81. At the end of the experimental period, tooth displacement was studied threedimensionally on dental casts with a coordinate measuring machine. Teeth were then extracted. Six premolars were used as control teeth and were extracted before the experiment started. www.indiandentalacademy.com
  82. 82. The depth, area, and volume of the resorption lacunae were measured using three-dimensional digital images made with a confocal laser scanning microscope (CLSM). www.indiandentalacademy.com
  83. 83. Result Tooth movement Teeth with the superelastic wire moved significantly more (3.50 versus 2.30 mm) and tipped buccally to a larger degree (9.26° versus 7.81°) during the 12-week experimental period than those moved with the stainless steel wire. www.indiandentalacademy.com
  84. 84. Resorption The number of resorptions on the roots of the teeth moved with a super elastic wire was significantly greater than those moved with a stainless steel wire (22 versus 16, P < 0.001). www.indiandentalacademy.com
  85. 85. www.indiandentalacademy.com
  86. 86. The amount of resorptive damage, defined as the largest depth, perimeter, area, and volume were compared between these two groups. The teeth moved with the super elastic wire showed significantly more resorptive damage regarding all these parameters. www.indiandentalacademy.com
  87. 87. www.indiandentalacademy.com
  88. 88. Conclusion This study confirms earlier studies regarding potential damage to tissues with use of continuous force. (Gibson et al. 1992; Owman-Moll et al. 1995; Daskalogiannakis and McLachlan. 1996; Darendeliler et al., 1997 and Faltin et al. 2001) www.indiandentalacademy.com
  89. 89. It could not be confirmed that maxillary teeth are at higher resorptive risk than mandibular teeth, as has been stated in the literature (Ketcham, 1927, 1929;Massler and Malone, 1954; Massler and Perreault, 1954;Phillips, 1955; McFadden et al., 1989). www.indiandentalacademy.com
  90. 90. The differing sensitivity is mostly explained by the differing mechanical load of the upper and lower teeth during treatment or differing amounts of tooth movement during orthodontic therapy. In this investigation, the force system used in the maxilla and mandible was the same. www.indiandentalacademy.com
  91. 91. The amount of tooth movement and the amount of resorptive activity were correlated. However, this correlation was weak, the correlation coefficient (r) being 0.35 This confirms data from the literature (Stuteville, 1937, 1938; Morse, 1971; Von der Ahe, 1973; Hollender et al., 1980; Sharpe et al., 1987; Kelley et al., 1993; Beck and Harris, 1994; Baumrind et al., 1996; Costopoulos and Nanda, 1996). www.indiandentalacademy.com
  92. 92. Individual variations have been reported to be an important factor for both tooth movement in both force systems. (Hixon et al., 1970; Maltha et al., 1993; Lundgren et al., 1996) and root resorption (Henry and Weinman, 1951; Massler and Malone, 1954; Kvam, 1972; Reitan, 1974; Zachrisson, 1976; Linge and Linge, 1983). This clinical study confirms these findings. www.indiandentalacademy.com
  93. 93. Rygh and Brudvik (1993) stated : „New wire qualities pose challenges for the orthodontist who must try to avoid continuous forces that are heavy enough to lead to necrosis of the periodontal ligament, and last long enough to prevent the root from recovering from damage inflicted on its surface‟. www.indiandentalacademy.com
  94. 94. Thank you For more details please visit www.indiandentalacademy.com www.indiandentalacademy.com

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