BIOMECHANICS.pptx Salzmann’s defined, the interdependence of form and function of teeth, jaws relationship, temporomandibular articulation, craniofacial conformation and dental occlusion.

Salzmann’s defined, the interdependence of form and function of teeth, jaws relationship, temporomandibular articulation, craniofacial conformation and dental occlusion.

1. BIOMECHANICS Dr. DHANVI DESAI

2. CONTENTS Static Equilibrium The Diving Board concept Determinate system vs Indeterminate system One couple system Cantilever Spring Auxiliary intrusion and extrusion arches Two couple systems Utility arches for intrusion Symmetric and asymmetric bends

3. Forces and couples created by interbracket bends Two couple archwires to change incisor inclination Posterior crossbite correction Lingual arches Various archwire bracket relation geometries

4. STATIC EQUILIBRIUM An application of Newton’s laws of motion to the analysis of the force system delivered by an orthodontic appliance. The physical laws of statics are governed by Newton’s third law of motion, which states that “ for every action, there is always an equal and opposite reaction ”.

5. Static equilibrium implies that, at any point within a body, the sum of the forces and moments acting on a body is zero; i.e., if no net forces or moments are acting on the body, the body remains at rest (static). Statics is the field of mechanics that examines the action of forces acting on bodies at rest. The orthodontic application is that for every appliance, but not necessarily for every tooth to which it is attached, the sum of the forces and the sum of the moments must be equal to zero.

6. Equilibrium Vertical forces = 0

7. Horizontal forces = 0

8. Sum of moments acting around any point must equal zero

9. Reverse curve of spee Third requirement for static equilibrium

10. Bite opening Example: Posterior end –tip Creating force couple Moment- tip crown distally and root mesially Sum of forces = 0 Equilibrium during bite opening : The moment on the molar is balanced by the equilibrium moment from the couple of intrusive and extrusive forces.

11. Toe-In and Toe-Out bends

12. The Diving Board Concept Stiffness- or load/deflection rate is inversely proportional to the cube of the length Doubling the length stiffness is reduced to one-eighth

13. Determinate vs Indeterminate Force Systems Force systems can be defined as statically determinate, meaning that the moments and forces can readily be discerned, measured, and evaluated, or as indeterminate. Statically indeterminate systems are too complex for precisely calculating all forces and moments involved in the equilibrium. Typically, only the direction of net moments and approximate net force levels can be determined.

14. Determinate systems  in orthodontics are those in which a couple is created at one end of an attachment, with only a force (no couple) at the other (i.e., a one-couple system). There are two sites of attachment: - One in which the appliance is inserted into a bracket or tube where both a couple and force is generated, And one at which the appliance is tied as a point contact where only a force is produced.

15. This type of system are Segmented springs, Auxiliary intrusion and extrusion arches

16. Cantilever Spring Passive state- inserted into the molar auxiliary tube and its anterior end is occlusal to the canine to be extruded. (B) Activating the spring by tying it to the canine generates a couple to tip the molar in a crown- mesial/root-distal direction, an intrusive force to the molar, and an extrusive force to the canine.

17. Used it to avoid the unwanted side effects from extruding high facial canines in a patient with an anterior open bite tendency (Reduced over bite). The tendency for the molars to tip forward and intrude is minimized by joining them together with a transpalatal arch Eruption of palatally impacted canine or to move a palatal canine facially

18. Auxiliary Intrusion Arches A ctivated by pulling the anterior portion incisally and tying it at the level of the incisor brackets, a second- order couple is produced at the molar to tip it crown- distal/root-mesial, intrusive force at incisors and extrusive one at molars S eparate, stabilizing arch wire 

19. Intrusive force - Anterior to the center of resistance of the incisor segment- moment can be created tending to torque the incisor in a crown- facial/ root-lingual direction More posteriorly- this tendency can be decreased substantially or even eliminated Another method  for reducing the tendency of the anterior segment to flare during intrusion is to cinch or tie back the arch to prevent the incisor crowns from moving forward.

20. TWO – COUPLE SYSTEMS Utility arches for intrusion Symmetric and Asymmetric bends Forces and couples created by interbracket bends Two couple archwires to change incisor inclination Posterior crossbite correction Lingual arches

21. At the incisors MF- moment to tip the crowns facially is created by distance of the brackets forward from the center of resistance. MC - an additional moment in the same direction is created by the couple within the bracket as the inclination of the wire is changed when it is brought to the brackets At the molar Extrusion & distal tip of crown UTILITY ARCHES

22. Placing a torque bend in the utility arch creates a moment to bring the crown lingually, controlling the tendency for the teeth to tip facially as they intrude, it also increases the magnitude of the intrusive force on the incisor segment and the extrusive force and couple on the molar

23. At the molar, a force to bring the molar mesially is created, along with a moment to tip the molar mesially . Cinching back  the utility arch Creates a force to bring the incisors lingually, and a moment of this force opposes the moment of the intrusion force

24. V bend and Step bend Two couple system Anchor bend- vertical V bend mesial to molar Gable bend- similar bend distal to cuspid Bayonet bend- step bend in horizontal plane Step up and Step down- step bend in vertical plane Tip-back and Tip-forward- step bend for adjusting angulation of posterior teeth

25. Symmetric V-bend

26. As the bend moves closer to one of two equal units, the moment increases on the closer unit and decreases on the distant one, while equilibrium forces increase . Asymmetric V-bend

27. CENTERED V BEND

28. OFF CENTERED A- greater moment Residual moment generated

29. WHY MOMENT AT BRACKET B BECOMES ZERO?

30. MOMENTS SAME DIRECTION

31. STEP BENDS- moments unidirectional, large vertical forces

32. A step bend Will always be associated with vertical forces

33. Brackets- parallel, non parallel

34. Artistic bends- finishing

35. Two couple archwire to change incisor inclination B-If the archwire is cinched behind the molar so that it cannot slide, the effect is lingual root torque and extrusion for the incisors and a mesial force on the molars Asymmetric V-bend between unequal units (molar and incisor, closer to the incisor): A-incisors Moment to rotate the incisors faciolingually , and an extrusive force Molars intrusive force but no moment

36. Torquing arch by BURSTONE For torque of very upright maxillary central incisors (as in Class II division 2 malocclusion), a one-couple torquing arch designed by Burstone can be very effective. resists facial tipping and extrusion of the central incisors, the result is lingual root torque

37. Posterior Crossbite Correction: Transverse Movement of Posterior Teeth ( A) An outward bend a few mm behind the canine bracket results primarily in expansion of the molar, with little or no rotation (B) An outward bend behind the canine combined with a toe-in bend at the molar results in expansion and mesial-out rotation of the molar

38. Lingual Arches as Two-Couple Systems Bilateral toe-in bends at the first molars create equal and opposite couples, so the mesiodistal forces cancel and the teeth are rotated to bring the mesiobuccal cusp facially

39. Bilateral expansion by TPA Moment to torque the roots facially moment of the couple > moment of the force Twist to create stationary anchorage to tip the opposite molar facially

40. ARCHWIRE BRACKET RELATION GEOMETRIES

41. Burstone and Koenig, "Force system from an ideal arch" 1974 AJODO described all possibilities of archwire -bracket relations in the vertical plane using a continuous archwire based on the ratios of the angles that the two bracket slots make to the inter-bracket axis Angles - equal and pointing in the same directions because the brackets are parallel to each other. Moment- same direction Sum total = twice moment High vertical forces ꝋ 2 remains the same and ꝋ I is reduced by 50%, still pointing in the same direction Intermediate - step and V bend Moment – same direction, unequal Vertical forces reduce

42. ꝋ 2 remains the same and ꝋ I is reduced to zero. ꝋ 2 remains the same, ꝋ 1 is pointing in the opposite direction to that of ꝋ 2 and is 50% of the latter. V bend at 1/3 Moment – one bracket

43. ꝋ 2 remains the same, ꝋ 1 is pointing in the opposite direction to that of ꝋ 2 and is increased further to 75% of ꝋ 2. Off centered V bend – ½ and 1/3 position Moment –opposite direction One moment smaller ꝋ 1 is equal in degree but opposite in direction with respect to ꝋ 2. Brackets are symmetrically divergent. Centered V bend Moments – equal and opposite; cancel No vertical forces

44. Equivalent force system at the center of resistance is composed of : 1,. A force equal in magnitude to the original 2. Sum total of : A moment identical to the moment generated at the bracket b. The second moment ( Mf ) equal to F x D (force x its perpendicular distance from the C. Res). How does this translate into tooth movement?

45. REFERENCES Essentials of Orthodontic Biomechanics- Dr. Vijay P. Jayade , Dr. Chetan Jayade Contemporary Orthodontics- William Proffit , Henry W. Fields, David M. Sarver; Sixth edition Mulligan Thomas F. Common sense mechanics - 1,2,3,4,5,6,7,8 Biomechanics in Orthodontics: Principles and Practice; Ram S. Nanda Biomechanics in Clinical Orthodontics. Ravindra Nanda.

46. Biomechanics in Orthodontics. Michael Marcotte Burstone CJ, Koenig HA. Force systems from an ideal arch. Am J Orthod 1974;65:270-289. Burstone CJ, Koenig HA. Creative wire bending-The force system from step and V bends. Am J Orthod Dentofacial Orthop 1988;93:59-67

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