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2. Stress trajectories
History
Galileo (1638) & Monro(1776)
Mechanical implications of bone shape
Andre (1741)
Deformation could govern bone shape and that shape
could be changed through the application of mechanical
forces
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3. Julius Wolff –
“ Das Gesetz der Transformation der Knochen ”i.e.,
“The law of bone transformation”
Wolff’s law-
Bony trabeculae – delicate lace in
accordance to stress trajectories
In 1986, Maquet &Furlong
“The law of bone remodelling”
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4. Das Gesetz der Transformation der Knochen
Epoch making book
Researchers – form & function relation – not accurate
Inadequate understanding of histology & physiology
Wilhelm Roux
Uncovered the foundations of form-function interaction
In 1881, “Der Kampf der Theile im Organismus”
I.e.,(The struggle of the components with in organisms)
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5. The origin of Wolff’s law
In 1853, Meyer
Mechanics of the human skeleton
• Drawings
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7. In 1860, Meyer –
C.S of long bones
Trajectories cross at right angles
Cullmann -
Method of drawing trajectories
Wolf –
Added a crane type schema
Form –Trab organisation of bones involved the arrangement
of minm material to withstand maxm load
Law of orthogonality – definite mechanical mathematical laws
Interpritation of function was biased
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9. “Function can influence the overall pattern and
relationship of the structures”.
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10. Wolff’s biases –
His theory on interstitial bone growth
Role of heredity
Concept of function
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11. Interstitial bone growth-
Similar to soft tissue growth
Wolff’s statement-
• Each and every particle [of a bone]contributes
proportionally to the enlargement
Wegner & Koelliker –1872
• Remodelling
• Wegner’s statement
Wolff –1875
• Wegner’s expt – not fundamental
Baehr -1898
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12. Interstitial bone growth-
Hunter & Fluorens
Wolff –
Carried the incorrect notion
Remodeling – absent
Expts
His view – Trab architecture was not the result of
dynamic process, but was preexisting in the
compacta
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13. Heredity –
Trab –already existed in the compacta
Predesigned structure
Statements –1870
The initial architectonic configuration of bone is not the
result of static influences…but is preformed & inherited
from the parents
The appropriate architecture under normal conditions will
develop during the intrauterine period and is explained by
heredity
No dynamic interaction during development
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14. Function –
Static requirement/constraints to be met as in
engineering…(metaphors)
Good design above good repair capabilities
Roux –
• Loading & Unloading generated information for the
developing bone
Function –static role of bone .i.e.,support of body
weight
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15. Function-
Function –static role of bone .i.e.,support of body weight
A year before the book –
“The form of bone is exclusively determined by the
static load which it has to match, or- what is identical –
by its function”
Form – prerequisite for functioning
Ideal or normal form was defined by nature
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17. Conclusion
Author has won the battle against time
His law is an accepted phenomenon
The fact that he was wrong on all the biological
aspects concerning his law appears to be minor
concern
Roux only remembered in the historical section of a
good library
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18. Subsequent Research
Both Tension & Pressure - Loss of bone
tissue
Trabeculae cross at varying angles
Irregular & wavy
Vary from bone to bone
Function - Density
Function - Density
Ex ; Milwaukee Brace
Tooth c no opp Tooth
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19. Stress Trajectories of Force
Benninghoff made an exhaustive study of
the architecture of the cranial &facial
skeleton and so called “Stress Trajectories”
or “Lines of force” evolved.
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20. Benninghof –
Traj/Lines of Forces-
• Involve both compact & spongy bone
• In response to – local function
-epigenetic influences
• Obeyed no individual bone limits
• But rather demands of functional forces
• Head –2 Bones –Craniofacial skeleton
Mandible
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21. 3 main vertical pillars of stress trajectories
can be seen in the nasomaxillary region.
a.Canine pillar
b. Zygomatic pillar.
c.Pterygoid pillar
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26. Adolescent Growth Spurt
Adolescence
Imp period in dental & orthodontic treatment
2 years earlier in girls
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27. Timing of puberty-
Seasonal & Cultural factors
Genetic & Environmental influences
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28. For the 3 planes of space in both maxilla &
mandible – Definite sequence of growth
completion
WIDTH
LENGTH
HEIGHT
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29. Usually completed at the time of adolescent
growth spurt.
Narrow skeletal width --- Narrow palatal vault
Narrow dental arch
Cross bite
Transverse Growth of Maxilla
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33. Structure of the suture at different ages:
Infancy
Juvenile
Adulthoodwww.indiandentalacademy.com
34. R M E
• More skeletal changes
• Less dental changes
• Not used in preschool children
• 0.5-1mm/day
• 10-20 pounds
• Occlusal radiographs
• Clinical examination
• 3-4 months of retention
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36. Activation of RME.
Upto 15yrs of age 1800
(2 turns daily)
15-20yrs. of age 1800
(4 turns daily)
Over 20yrs. 900
(2 turns daily)
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37. How much to Expand?
Palatal cusps of upper maxillary teeth
should occlude with the lingual inclines of
the buccal cusps of the lower mandibular
teeth.
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38. Effects of RME:-
-Midpalatal suture opens anteroinferiorly.
-Midline diastema.
-Buccal flaring of posteriors.
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41. Ideal patients for RME treatment.
Full cusp cross bite with a skeletal
component
Some degree of dental as well as skeletal
constriction initially
No pre-existing dental expansion.
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42. Nasal hump & paranasal swelling.
Pain.
Buccal tipping of posteriors.
Root resorption.
Fenestration of roots
Adverse effects of RME:-
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45. Slow expansion
Less force
1mm/week
Reduced tissue damage
Reduced hemorrhage
2-4 pounds of force
More physiologic response
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47. Dental cross bites are corrected by
-Quad helix
-W arch
-Arch wire
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48. Skeletal & Dental changes in Expansion
Rapid Slow
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49. Anteroposterior growth of maxilla.
Maxillary excess:-For restriction of
maxillary growth in growing individuals
appliances like
1.Headgear
2.Functional appliances
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55. Cervical head gear:
used in patients with horizontal growth
pattern with reduced lower facial height.
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56. Occipital pull Head gear:-
Used in long face patients
with high mandibular
plane angle.
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57. Dental camouflage can be done for mild to
moderate skeletal problems.
For adult patients where growth is no longer
present surgical correction should be done.
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58. 3 major possibilities for correcting mandibular
defficiency
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69. Vertical excess of maxilla can be controlled
by inhibiting the descent of maxilla and
eruption of posterior teeth.
Vertical growth of maxilla
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81. Bibliography:-
Contemporary orthodontics
-William Proffit
Orthodontic principles &practice
-T.M.Graber
Essentials of facial growth
- Enlow
Factors affecting the growth of mid face
- James Mc Namara
Rapid maxillary expansion
- Donald J. Timms
Bone biodynamics in orthodontic and orthopedic treatment
- David S.Carlsonwww.indiandentalacademy.com