This slide gives a ideas about basic bio mechanics and bio mechanics consideration in anchorage, bio mechanical consideration in friction in orthodontics . This power point includes V bend mechanics,Step bends,Biomechanical considerations of anchorage,Various method to save augmented anchorage Anchorage requirement in the use of edgewise /PAE appliance Biomechanics related to friction,Factors affecting friction Conclusion

1. Basic
Biomechanics
By
Dr Gejo johns

2.  V bend mechanics
 Step bends
 Biomechanical considerations of anchorage
 Various method to save augmented anchorage
 Anchorage requirement in the use of edgewise /PAE
appliance
 Biomechanics related to friction
 Factors affecting friction
 Conclusion
 Reference
CONTENTS

3. V bend mechanics
 The force system produced by the v bend is a two couple
system when both the ends are engaged in edge wise
bracket .
 Moments are created at both the brackets due to bracket
slot- arch wire relationship
 The magnitude of moment depend on the angle of entry or
how steep the wire respect to the slot orientation.

4. Centered v bend
 A standard edge wise bracket on cuspid labelled as ‘B’ and on molar labelled as ‘A’
. Both are perfectly aligned means the slots are parallel to each other and are
placed on a common interbracket axis .let us assume they are separated by a
distance ‘L’ and that V bend is located exactly at the center of distance ‘L’ . Since
the angle of entry at the two bracket are identical but facing in opposite direction
the moment created at the brackets are equal magnitude but opposite direction
the sum total of moment is zero and there is no force

5. Off-centered V bends
 If we shift the bend slightly towards the molar the bracket ‘A’ will
experience a greater moment than bracket ‘B’ because angle of
entry in bracket ’A’ has increased while that in bracket ‘B’ has
reduced . The two moments are acting in opposite direction their
sum total cannot become zero but have a residual moment in
order to establish equilibrium another moment that is equal in
magnitude but opposite in direction needs to be created

6.  As the bend shift more and more towards bracket ‘A’
the moment within it will continue to increase and the
moment at bracket ‘B’ will continue to reduce. The
sum total of the moment at the two bracket will leave a
residual moment of increasing magnitude. The vertical
force will also continue to increase in magnitude
because they have to balance the residual moment.

7.  It has been experimentally found by Burstone and Koenig
that when the bend reaches 1/3 of the distance between the
two brackets, the moment at the bracket B becomes zero
V bend at 1/3 of the distance

9. How the moment at B bracket reduce to
zero
 As the bend is shifted more and more towards bracket A the
wire segment entering to bracket A keeps on shortening and
the wire segments entering B bracket keeps on getting longer
both the wire have to flex to enter into their respective
attachments but the longer segment being more flexible .
When the bend is at 1/3 position the longer segment assumes
a parallel to the bracket slot therefore the moment at bracket
B become zero

10.  Two symmetrically placed off- centered bends will also have
the same effect of a centered bend

11.  If the bend is off center their will be a long segment and a
short segment . When the short segment is engaged into
bracket or tube , the long segment will point in the
direction of the force produced on the tooth that will
receive the long segment
Mulligan TF. Common sense mechanics part 1 Clin Orthod 1979,Nov ;13(11):676-683

12. Step bends
 A step bend may be intentionally given in an arch wire , or
it may develop on account of the arch wire bracket
relationship

13. Intentionally given step bend A step bend that develops due to wire
bracket relation

14.  Step bend may be given purposely to change the
angulations of teeth , which is caused by faulty bracket
angulations; or it may develop due to difference in
angulations of two teeth
Intentional or unintentional step bends related to teeth
angulations or bracket angulations

15. A step bend will always be
associated with vertical
forces
Action of a step bend

16.  “The effects of a step bend are quite different from a ‘V’
bend, because the former creates in the two brackets
moments that are unidirectional and also because
relatively large vertical forces always develops”

17.  A combination of central V bend and two step bends
between the central and lateral on either side given
during the finishing stage . These bends makes the
root of the four incisors slightly divergent , thereby
improving their appearance hence they are named as
‘Artistic bends’

19.  The first row shows the two moments on central
incisor from the action of the center V bend . The
second row shows the moment and force arising from
the two step bends on all four incisors the last row
shows the result of adding effect from all three bends
the overall result is strong moment on central incisor
compared to laterals and extrusion force on centrals
while lateral subjected to intrusion force

20.  Burstone and Koenig, in a classic article titled “Force
system from an ideal arch” published in 1974 in the
American Journal of Orthodontics, described 6
geometric relations that are choosen in all possibilities
of archwire-bracket relations in the vertical plane
using a continuous archwire .These are chosen based
on ratios of the angle that the bracket slot makes to
inter-bracket axis (O1 &O2)

21. Class I to class III geometries

22. Class IV to class VI geometries

23.  The ratio of angle O1 to O2 are 1, 0.5, 0, -0.5, -0.75 and -1
 The ratio of moments produced by a straight wire engaged
in two malaligned brackets depends on the ratio of the
angulations of the brackets to the interbracket axis.
 The vertical force gradually reduced from class I to class V
and become nil in the VI th class.

24. BIOMECHANICAL
CONSIDERATIONS OF
ANCHORAGE

25. Anchorage
 Graber has defined anchorage in orthodontics as “the
nature and degree of resistance to displacement offered by
an anatomic unit for the purpose of effective tooth
movement”.
 White and Gardiner defined anchorage is the site of
delivery from which a force is exerted

26.  It is like a Tug of war between the moving units and
resisting units

27.  If anterior teeth are to be retracted to a significant extent
when the anchor teeth do get displaced to an extent it is
known as loss of Anchorage
 Anchorage could be provided intra orally , extra orally or
both
 Intra oral anchorage could be obtained from teeth in the
same arch (intra-arch anchorage) or from the teeth in the
opposite arch ( inter-arch or inter maxillary anchorage)

28. Various method to save and augment
anchorage
 These can be classified as
A . Making use of natural resistance
1. Balancing the root surface area of moving units v/s the
anchor units : increasing the root surface of the anchorage
units in relation to that of moving units is a logical method
of providing anchorage

30.  If the root surface area of the moving unit and the
resistance unit is equal , both will move equally in opposite
directions
 For total resistance from anchorage the ideal root surface
area of anchor unit to be that of the moving unit be 4:1
 Including second molars early in the treatment increase
posterior anchorage

31. 2.Two stage retraction : Involving separate cuspid distal
movement followed by incisor retraction. After the
cuspids are fully retracted , they along with premolars
and molars teeth form the anchor unit, which has
greater root surface area than that of the incisors

32.  When posterior teeth are used as anchorage unit . A person
with low mandibular plane angle indicating horizontal
growth pattern has a strong masseter-pterygoid sling that
resist the mesial or vertical displacement of posterior teeth
more effectively
 A low mandibular plane angle cases require less anchorage
augmentation than a high angle case for retraction or
intruding anterior teeth

33. Cortical anchorage
 Ricketts introduce the concept of cortical anchorage. In his ‘Bio-progressive
technique ‘ the root of posterior teeth are torqued buccally to the extent that
they start pressing against the buccal cortical plate. The mesial drag on these
teeth during anterior retraction is resisted by their contact against the
cortical plate
Ricketts RM . The logic and key to bioprogressive philosophy and treatment mechanics .
American Institute for Bioprogressive education . Scootsdale , Arizona. 1995. pg 39.

34. Muscular anchorage
 Lib bumpers which transfer the lip pressure in a distal direction on the molars
can be used in patient need for reinforcement of saggital anchorage is mild
 A constant tongue pressure in a vertical direction on a TPA which is kept
slightly away from the palate, would resist the extrusion of upper molars
thereby augmenting vertical anchorage

35. Components of reinforced anchorage
1.Palatal and lingual arches
 Palatal and lingual arches which connect the upper and lower
molars on both sides can provide a reasonable degree of
resistance in which the
a. rigid connection across the molars maintain the inter-molar
width thus making it difficult for them to move into premolar
area due to narrow inter-premolar width
b. connecting the molars on both sides also prevent their
rotation when they are experiencing a forward moving force.
Resistance to rotation offer resistance to forward movement

37.  Nance palatal arch with an acrylic button against anterior
part of palate offer more anchorage than trans-palatal arch
 Trans-palatal arch can serve as a vertical molar anchorage .
The TPA is kept slightly away from the palate . It experience
an intrusive force from the tongue that keeps on pressing
against it , thus resisting extrusion of molar

38. Extra oral anchorage
 Reinforced anhorage from extra oral source has a unique
advantage that it has no reciprocal adverse effect on other
teeth because the reactionary effect is entirely distributed on
extra oral areas
Mini/ micro Implant (TSAD-Temporary Skeletal
Anchorage Device)
 the TSADs have absolute anchorage , since they are capable
of resisting the reciprocal effect of the tooth movement
without undergoing noticeable movement

39. Practical considerations
 Anchorage needs of any case must be planned carefully at
the beginning of treatment
 Anchorage requirements of a case are analyzed considering
the following
1. Distance over which teeth are to be moved : Greater the
distance , greater is the anchorage requirement
2. Type of tooth movements required: Anchorage
requirement will gradually increase from uncontrolled
tipping to controlled tipping , translation and root
movement.

40. 3This would decide the possibility of growth modulation to correct
the jaw relation ( reduction of over jet) ,arch expansion ,molar
distalization etc
4. Patient compliance in using head gear , lip bumper etc .
These factors are considered to decide if non- extraction treatment is
possible or not ,when the anchorage requirement is great , first
premolar are extracted . For lesser requirement other extractions are
c. Growth pattern : A mild anchorage situation in a hypo-divergent
face may become a moderate anchorage situation in a normo-
divergent face and a critical anchorage situation on a hyper-
divergent face.
5. Other anatomic limits imposed by tongue , dense alveolar bone ,
constriction at the site of extraction site , curved root etc.

41.  When approximately 2/3 rd of the extraction space is
to be utilized for anterior teeth correction it is termed
as ‘A’ type of anchorage.
 When about 1/2 of extraction space is to be utilized ,it
is termed as ‘B’ type of anchorage
 And when 1/3 or less space is utilized for anterior
correction ( most of the space is closed by protraction
of posterior teeth) it is called as ‘C’ type of anchorage

43. Anchorage requirements in use of Edgewise/ PAE
appliance
 Anchorage consideration become even more critical both in
sagittal and vertical direction with the introduction of modern
PAE bracket due to
1. Built-in tip and torque are respectively meant for correct root
angulations and inclination , since crown movement occur more
easily than root movement , the in built second and third order
moment tent to move the crown before the root moment takes
place

44. a. Built –in tip in the incisor and cuspid bracket not
only resists posterior movement of anterior teeth ,
their crown actually tend to move mesially as soon as
initial arch wire are placed,
b. Built –in torque in upper incisor bracket further
enhance this tendency when rectangular wire are
engaged . Anchor unit have to bear this additional
burden in sagittal direction.
2 . Built –in tip in cuspid bracket also causes a deflection
of arch wire in an incisal direction resulting in
deepening of bite ,this mean that additional vertical
anchorage needs to be provided for bite opening

45.  MBT technique has made a conscious effect to reduce
the strain on molar anchorage in following ways
1. it has reduced the tip in upper and lower anterior teeth
and upper premolars
2. It reintroduce measures like lace back and bend
backs to be used the initial phased.
3. The labial root torque in lower incisor bracket resist
the forward movement
4. Light continuous force are best suitable for
conservative anchorage.

48.  Resistance to sliding is termed as ‘friction’,
 The efficiency of an appliance is considered to be
greater when a relatively smaller portion of applied
force needs to be utilized for overcoming friction.
 During space closure it is the retraction /protraction
of individual teeth or group of teeth by sliding
mechanics which involve significant amount of
friction.

49.  Kusy divided the resistance to sliding into three
components
a. Classical friction (FR) : is the resistance that
impedes sliding from the point the force is applied
up to that point of tooth movement when the arch
wire starts binding against the mesio-distal bracket
corner or upper and lower bracket walls.
b. Fr consist of (a) the static component, which is the
resistance that tries to prevent the motion before it
has started .(b) the dynamic component , which is
the exist during motion.
Kusy RP, Whitley JQ .Friction between different wire-bracket configurations and
materials. Sem.Orthod1997:3:166-177

50.  Thus ,when bracket tends to slide over the arch
wire on application of a force, the resistance to
this tendency is the static friction and the
resistance to the motion after the sliding starts is
the dynamic friction.
 The actual contact occur only at certain points
called ‘Asperities’ which are the peaks of
microscopic surface irregularity

51.  The inherent properties of arch wire and brackets
such as hardness and surface smoothness can
increase classical friction in 3 ways by
1. plowing: It occur when hardness of the arch wire
material and bracket material are substantially
different and the harder material happens to be a
corner or edge . The harder material removes a
part of the softer material

52. 2. Roughness interlocking : occur due to
engagement of asperities of antagonizing
surfaces. Depending on the yield strength of the
materials from which the bracket and arch wire
are made the asperities may flatten by
undergoing plastic deformation due to applied
lode, following which movement starts

53. 3. If the asperities are relatively high and if the yield
strength are more, they have to break before the
movement starts. The resistance felt at the time the
asperities break off is Shearing
 But the movement doesn’t continue in a smooth manner
after the interlocking is overcome by flattening or
shearing of some asperities; because some other
asperities would then get interlocked and another phase
of flattening or shearing will have to take place for next
phase of movement , thus the cycle will repeat which is
termed as ‘slick-slip’ phenomenon

54.  Binding (BI) : Is the resistance that arises when
the archwire starts contacting the diametrically
opposite mesio-distal corners of the bracket due
to mesio-distal tipping of the tooth; or the edges
of a rectangular archwire starts touching the
incisal and gingival walls of the bracket due to
facio-lingual tipping.
 Notching : Refer to the resistance to sliding from
a permanent damage in archwire surface . It
further hinders sliding to an extent that sliding
may become impossible

55.  They are divided into mechanical and biological
variables
 The mechanical variables are
1. Arch wire characteristics: materials, cross sectional
shape and size, surface texture and stiffness
2. Bracket characteristics; materials, slot dimensions
and shape, built in adjustments and manufacturing
process
3. Mode of ligation
4. Appliance features: inter-bracket distance and force
applied
5. The biological variables are salivary action ,plaque,
and corrosion

56.  Slot size and arch wire dimension: Archwire alloy and bracket
material being similar , 0.018” and 0.022” slot exhibit the same
amount of friction in the passive configuration till the binding
occurs.
 The difference b/w the wire slot dimension will determine the
friction in the two brackets ,
 closer the fit of archwire in the slot greater is the friction
 Archwire stiffness: Stiffer wires cause less friction than flexible
wires of same dimension; because increased flexion increase the
wire bracket angulations thus increasing the chances of binding
and latter possible notching
 More the force with which the contacting surfaces of the arch
wire and bracket are pressed together , greater is friction
experienced

57.  This force can come from two sources
a. Tightness of the ligature; that ties down the archwire slot
of the bracket will determine the coefficient of friction
b. The binding resistance force arising when a tooth tips in
the initial part of movement whereby the diagonally
opposite corners of the bracket start pressing against the
archwire will form contact angle ( the angle at which the
bracket corners meet the archwire) . Greater the angle
more is the resistance.
Contact area: There is no direct relation b/w the apparent
area of contact and the amount of friction

58.  Surface roughness: surface roughness play only a minor role
in increasing the coefficient of friction
 Arch alloy composition : when archwire made from
different alloys are engaged in SS bracket , frictional
resistance experienced by beta titanium, Niti Cobalt
chromium and stainless steel wire varies in a reducing
order
 Bracket material: Friction changes in a reducing order in
ceramic, titanium, and SS brackets, among ceramic
brackets monocrystalline brackets have less friction than
polycrycalline ones. Ceramic brackets with metal inserts are
made to reduce the friction within their slot

59.  Apart from the individual materials from which the arch
wire or brackets are made their coupling also play an
important role. The coupling of SS bracket and SS wires
experience the least friction while friction in coupling of SS
bracket with Co-Cr ,Niti and Beta Titanium archwires
change in ascending order
 Role of saliva as a lubricant to reduce the friction :
According to Kusy et al the saliva act as lubricant depends
not on its viscosity but on the material of the archwire
bracket couple. If the archwire firmly presses against the
bracket surface and squeeze out the saliva , it causes a
relatively dry state of contact, which could increase the
coefficient of friction significantly

60. Practical considerations
 SS wide bracket or twin bracket in 0.022 slot are generally
preferred for reducing friction.
 Avoid sliding teeth on Niti or beta titanium archwire
 Avoid contact between dissimilar bracket and archwire
materials because such contact generally causes more
friction
 Bio-efficient bracket which has a triangular design- two
incisal/ occlusal tie wing opposed by a single gingival tie
wing

61.  Method of ligation also play a role in determining frictional
levels . Passive self ligating bracket cause less friction than
the active ones
 Archwire should be sufficently rigid and strong to reduce
binding and notching
 Elastomeric ring cause more friction than SS ligatures,
especially when they swell up after being left in the mouth
for some time, hence SS ligatures are preferred during
sliding mechanics

62. Conclusion
 The scientific basis of orthodontics rests on a knowledge of
anatomy, physiology and growth, and in particular,
biomechanics—the relationship between force systems and
dental or orthopaedic correction.

63. Reference
 Contemporary orthodontics 5th edition : Proffit
 Biomechanics in clinical Orthodontics : Nanda
 Current orthodontic principles & techniques : Graber, Swain
 Essentials of orthodontic biomechanics- Basic and applied : Vijay P
Jayade, Chetan V Jayade
 Mulligan TF. Common sense mechanics part 1 Clin Orthod 1979,Nov
;13(11):676-683
 Burstone CJ , Koening HA. Creative wire bending the force system
from step and V bends ,Am.j Orthod Dentofac Orthop 1988;93:59-67
 Bennett JC, MCLaughlin RP .Anchorage control during levelling and
aligning with preadjusted appliance system . J Clin Orthod
.1991;25:687-696