loop mechanics explained

1. LOOP MECHANICS
DR MARYAM GHAZAL

2. LEARNING OBJECTIVES
• Basic principles of space closure
• Concept of moment to force ratio
• Methods of space closure
• Optimization of loops
• Space closure with loop mechanics

3. BASIC PRINCIPLE OF SPACE CLOSURE
• Bring together opposing teeth or segments of teeth by applying a
force between them.
• The force is usually applied on the bracket attached to the crown of
the teeth and is occlusal and buccal to the center of resistance
(CRES).
• This generates moments (moment due to force, or MF).
• MF cause tipping and rotation of the teeth in the direction of the
applied force.

5. • The nature of tooth movement can be controlled by applying a
counteracting moment (MC) to the MF.
• The easiest way to generate this MC is to place a straight wire in the
tipped brackets
• This ratio of moment to force (MC/F ratio) at the orthodontic bracket
can bring about various types of tooth movement.

6. MOMENT TO FORCE (M/F) RATIO:
• Predict the quality of tooth movement.
• M/F ratio of 5 : 1 is required for uncontrolled tipping
• 7 : 1 is required for controlled tipping
• 10 : 1 is required for translation
• 12 : 1 is required for root correction.

8. MOMENT TO FORCE (M/F) RATIO:
• Type of tooth movement can be altered by
• Altering the point of force application.
• Adding a counterbalancing moment.

9. ALTERING THE POINT OF FORCE
APPLICATION.
• Use of power arms
• Side effect of power arms

11. ADDING A COUNTERBALANCING MOMENT
• Traditional way of applying a counterbalancing moment
• Creating a couple in bracket

12. METHODS OF SPACE CLOSURE
• Segmented mechanics
• Sliding mechanics

13. PRINCIPLE OF SEGMENTAL MECHANICS
• Teeth not connected to each other by continuous arch wire.
• Active( teeth to move ) and passive segments ( serve as anchorage ).
• Closure of space with loops

14. SPACE CLOSURE WITH LOOPS
• Loops mechanics depends upon the M/F ratio
• For severe space closure scenarios — high M/F ratio desireable.
• For minor space closure scenarios — loops with low M/F ratio.
• Incisor retraction — M/F ratio increase for posterior teeth ( anchorge
preservtion).

15. LOOPS FOR SPACE CLOSURE
• T. Loop
• Vertical Helical Loop
• Double Key Hole Loop
• Box Loop
• Omega Loop
• Sandusky Loop

16. • Delta Loop
• Opus Loop
• Bull Loop
• Gjessing springs
• L Loop
• Tear Drop Loop

17. OPTIMIZATION OF LOOPS FOR SPACE
CLOSURE
• Loop height:
• Loop height increases — M/F ratio increases.
• Burstone states , if we kept horizontal loop length constant 7 mm ,
• 6mm high loop — M/F ratio 2.
• 10mm high loop — M/F ratio 4.

18. LIMITATIONS OF LOOP HEIGHT:
• Bending difficulties
• Inconvinience to patient when inserted into mouth.
• Due to the depth of the vestibule, the orthodontist is limited to how
high the loop can be made.
• In order to overcome this problem, a wire, such as a T-loop, can be
added horizontally, or there might be addition of helices

19. LOOP SHAPE
• T loop — high M/F ratio, than vertical loops.
• Opus loop — L shape with helix in apical portion of L .
( increase M/F ratio ).
Opus loop with vertical legs tipped 70 degree backward — M/F ratio
8.7 mm
• L loop with similar dimension — highest M/F ratio.

20. LOOP PLACEMENT
• Position of loop — modify M/F ratio.
• Off centre positioning of loop
• Higher moments at bracket closer to loop

21. ACTIVATION BENDS
• Horizontal activation of two legs of loop form an angle with each other.
• Bends in loops — increase M/F ratio.

22. BAUSCHINGER EFFECT
• The Bauschinger effect is normally associated with conditions in which
the strength of a metal decreases when the direction of strain is
changed.
• It is a phenomenon found in most polycrystalline metals.
• if we have two different T-loop designs, when one closure loop is
activated, if all bends are bent in the same direction, it provides more
resistance to permanent deformation than if all bends are bent in the
opposite direction

23. A) Closing loop with bends in the winding-direction. This configuration presents more resistance to
permanent deformation during activation; B) Closing loop with bends in unwinding-direction.

24. SEQUENCE OF SEGMENTAL MECHANICS
1. Canine retraction
2. Incisor retraction (and intrusion if indicated)
3. Align(and level if indicated)
4. Coordination, detailing and finishing

25. SEGMENTAL CANINE RETRACTION BY
LOOP MECHANICS
• Pre-Activation of loop
• Before insertion of loop in extraction space certain pre-activated bends must be
placed
• loop give V and U shaped bends
• Alpha bend ( anterior curvature )
• Beta bend (posterior curvature )
• The bends are necessary to create Moment ( Mc)

26. • Activation of loop
• Final activation is done only when it is placed in the bracket slot
• The wire is pulled distally through the posterior tube , cinched.
• Amount of distal pull depends upon space closure
• Once the loop has been activated and placed in the desired location tooth
movement is initiated by deactivation of loop

27. .
• Space closure with loop progress by three phases
• Phase 1 (Tipping)
• Initial phases of retraction,spring is fully activated-------high force,high M/F.
• Mc/Mf ratio less than 10 so controlled tipping.
• Differential moments in anterior and posterior segments.
• Crown tipping of canine and root tipping of molar , anchorage preserves in posterior
segment.
• If preactivation bends are not enough,uncontrolled tipping of canine ,duming of
canine in extraction space.

28. • Phase 2 (Translation)
• As canine is distalized , distance between two attachments decreased,
force level drops, reduction in Mf.
• Mc/Mf -1
• Canine and molar both are translating towards each other.
• Anchorage loss is high.

29. • Phase 3(Root movement)
• Force level continues to drop so does the Mf drops , but Mc drop is not that significant.
• Mc/Mf is greater than 10 ,reserving the net moment.
• More root movement than crown movement.
• Root correction of canine as it is tipped in phase 1.
• Canine root tipping ----- molar crown tipping.
• Molar mesial movement so anchorage reinforcement is necessary.

30. • Mc/Mf ratio is responsible for optimizing the quality of canine
movement.
• Force is responsible for actual distal movement of canine.
• Canine undergo all three phases, complete deactivation of loop.

31. INCISOR RETRACTION
• Incisors undergo tipping, minimal translation rare circumstances root
uprightning.
• Mf greater than Mc , minimal root movement more crown movement.
• Loop closer to posterior segment
• Mcp greater than Mca.
• Less demand of anchorage on posterior teeth.

32. ADVANTAGES OF LOOP MECHANICS
• Known force systems
• Precise spring design
• Minimizes adverse tooth movements
• Lack of friction
• Differential moments in active and reactive units
• Anchorage control is predictable

33. DISADVANTAGES OF LOOP MECHANICS
• Patient discomfort (loops)
• Difficulty with hygiene maintenance
• Increased chair-side time
• Difficulty in arch coordination
• Decreased ability to delegate

34. REFERENCES
• Monini AC, Gandini LG, Jr, Santos-Pinto A, Maia LG, Rodrigues WC. Procedures adopted by orthodontists for space
closure and Anchorage control. Dental Press J Orthod. 2013;18(6):86–92.
• Haskell BS, Spencer WA, Day M. Auxiliary springs in continuous arch treatment Part 1. An analytical study employing the
finite-element method. Am J Orthod Dentofacial Orthop. 1990;98(5):387–397.
• Queiroz GV, Rino J, Neto, Paiva JB, Rossi JL, Ballester RY. Comparative study of classic friction among different arch
wire ligation systems. Dental Press J Orthod. 2012;17(3):64–70
• . Thiesen G, Shimizu RH, Valle CVM, Valle-Corotti KM, Pereira JR, Conti PCR. Determination of the force systems
produced by different configurations of tear drop orthodontic loops. Dental Press J Orthod. 2013;18(2):19.e1–19.18.
• Kojima Y, Kawamura J, Fukui H. Finite element analysis of the effect of force directions on tooth movement in extraction
space closure with miniscrew sliding mechanics. Am J Orthod Dentofacial Orthop. 2012;142(4):501–508.

35. THANKYOU