This document discusses mechanical aspects of anchorage control in orthodontic treatment. It covers topics like friction, binding, surface qualities of wires and brackets, and determinate versus indeterminate force systems. Regarding friction, it explains how factors like surface roughness, reactivity and hardness affect friction. It also discusses how binding between brackets and wires increases resistance to sliding. The document concludes by outlining different methods that can be used to control anchorage, including reinforcement of anchorage units and subdivision of tooth movements.

1. MECHANICAL ASPECTS
OF ANCHORAGE
CONTROL

2. Force, Friction and Play

3. How to Prevent Anchorage Loss?
• Reduce the amount of reactionary force on the anchorage unit

4. Friction
• When one object moves relative to another, friction at their interface
produces resistance to the direction of movement.
• Friction ultimately is derived from electromagnetic forces between
atoms
• Friction is proportional to the force with which the contacting surfaces
are pressed together
• Friction is affected by the nature of the surface at the interface
• rough or smooth
• chemically reactive or passive
• modified by lubricants

7. Friction in Fixed ApplianceTreatment
• Friction is independent of the apparent area of contact
• Real contact occurs only at a limited number of small spots at the peaks
of the surface irregularities, called asperities
• Local pressure at the asperities may cause appreciable plastic
deformation at the asperities
• Shearing of asperities on application of force
• The coefficient of friction then is proportional to the shear strength of
the junctions and is inversely proportional to the yield

8. Friction in Fixed ApplianceTreatment
• Two other factors affect friction:
• the interlocking of surface irregularities
• the extent to which asperities on a harder material plow into the surface
of a softer one
• Total Frictional Resistance:
1. The force necessary to shear all junctions,
2. The resistance caused by the interlocking of roughness
3. The plowing component of the total friction force

9. Surface Qualities ofWires
• Surface Roughness
• Beta-Ti > NiTi > SS
• Surface Reactivity
• Beta-Ti > NiTi > SS > Gold
• Surface Hardness
• SS > Gold > NiTi > Beta-Ti
• ColdWelding
• HighTitanium content  Increased Surface Reactivity Welding of
alloys  Increased resistance to sliding (Friction)

10. Surface Qualities ofWires
• Change Surface Qualities:
• Coating
• Teflon
• Epoxy
• Ion implantation (with nitrogen, carbon, and other materials)

11. Surface Qualities of Brackets
• Stainless Steel Brackets:
• Manufactured by different methods
• Metal Injection Molding
• Welding
• Casting
• Sintering
• Have relatively smooth surfaces like steel wires
• Titanium brackets:
• Eliminate the chance of an allergic response to the nickel in stainless steel
• Rougher surfaces
• Increased Friction

12. Surface Qualities of Brackets
• Ceramic brackets
• Esthetics
• Usually made from monocrystalline and
polycrystalline ceramics
• Surface is very rough and hard
• Penetrate the surface wire
• Ceramic brackets with metal slots

13. Surface Qualities of Brackets
• Composite Plastic Brackets
• tooth colored
• Non-allergenic
• Better surface properties than ceramics
• Expensive and unpredictable

14. Elastic and Inelastic Binding in
Resistance to Sliding
• RESISTANCETO SLIDING
• Resistance to sliding = Friction + Binding + Inelastic Binding
• If a tooth is pulled along an archwire
• The tooth will tip
• The corners of the bracket will come in contact with the wire
• The force with which bracket edges contact (bind) with wire will
increase resistance to sliding
• The greater the angle at which the wire contacts the corners of the
bracket, the greater the force between the wire and bracket

15. Binding – Narrow vsWide Brackets

16. Slot Size
• 22 x 28
• Designed to be used with gold wires
• 18 x 25
• Designed to be used with stainless steel wires

17. Inelastic Binding - Notching
• A nick or notch is formed at the edge of wire
• Mechanical hindrance in sliding
• Common when combination of different materials is used

18. Magnitude of Resistance to Sliding
• Binding also results from the ligation method used
• Using tight steel ligature wire to tie the wire can result in binding and
notching and thus the active tooth unit will not move
• Resulting in movement of anchor unit  anchorage loss

19. Frictionless Mechanics
• Use of loops and springs
• Retraction springs
• Closing loops

20. Frictionless Mechanics
• Benefits of Loops
• Frictionless mechanics
• Tooth movement can be carried out with lighter forces
• Tooth movements are more predictable
• Better control of anchor units, occlusal plane, arch form and midlines
• Disadvantages of Closing loops
• More complex to design
• Less patient friendly (hygiene and esthetics)
• Distortions may cause injury or changed forces system

21. Methods to Control Anchorage
• Reinforcement
• The extent to which anchorage should be reinforced (by adding teeth to
the anchorage unit)
• For significant differential tooth movement:
• The ratio of PDL area in the anchorage unit to PDL area in the tooth
movement unit should be at least 2 to 1 without sliding
• With sliding forces - 4 to 1

22. Subdivision of Desired Movements
• Dividing the arch into equal segments cannot cause differential
movements
• Pit the resistance of a group of teeth against the movement of a single
tooth
• E.g. Retract canine against the mesial movement of whole posterior
segment

23. How to achieve differential retraction of
incisors?
• Closure of a premolar extraction site often is desired in a ratio of 60%
retraction of incisors, 40% forward movement of posterior segment
• Methods:
1. one-step space closure with no sliding (closing loop)
2. two-step space closure with sliding mechanics, retracting the canine
individually, and then retracting the four incisors in a second step (the
classicTweed approach)
3. two-step sliding with distal tipping of the canine and incisors initially,
followed by uprighting of these teeth (the classic Begg approach)

25. DETERMINATEVERSUS
INDETERMINATE
FORCE SYSTEMS

26. Force System
• Consists of:
• Body or multiple bodies/structures (Tooth or group of teeth)
• Forces (in any of the three dimensions – can be additive or subtractive)
• Moments (can be clockwise / anticlockwire – can be additive or
subtractive)

27. Determinate Force System
• A force system in which all moment and forces
can be calculated
• E.g. One couple system
• Cantilever Spring

29. Indeterminate Force System
• A force system in which all moment and forces can not be calculated
• There can be too many forces and moments
• Or forces and moments may change their magnitude and direction
rapidly
• E.g.Two couple system
• Ricket’s Utility Arch

31. One-Couple Systems
• One-couple systems are found when two conditions are met:
• (1) One end of wire is placed into a bracket or tube (making two
contacts) and typically attaches to anchor segment
• (2) the other end of the wire is tied to a tooth or group of teeth with at a
single point of contact

33. Two-Couple Systems
• Two-couple systems are found when two conditions are met:
1. One end of wire is placed into a bracket or tube (making two contacts)
and typically attaches to anchor segment
2. The other end of the wire is also placed in a bracket or tube to a tooth
or group of teeth with two points of contact

36. Segmental Arch Mechanics
• Each segments acts as a giant tooth having its own center of resistance
• Segments are usually connected with loops or frictionless mechanics
• If single point contact is made in one of the segments – One couple
system – Determinate force system
• If two point contacts are made in each segment –Two couple system –
Indeterminate force system

37. Continuous Arch Mechanics
• A single wire is passing through all brackets
• Couples are being generated in each bracket
• The force system is changing with even minor tooth movements
• Example of indeterminate force system

38. QUESTIONS?