BIOMECHANICS IN ORTHONTICS , DENTISTRY..

· This document provides an overview of biomechanics and its key concepts. It begins by defining biomechanics as the application of mechanical principles to the study of living things.

1. DR MUHAMMAD FAYYAZ NAFEES ORTHODONTIST

2. CONTENTS Introduction Newton’s laws of motion. Vectors. Parallelogram principle. Centre of mass. Centre of gravity Centre of resistance. Centre of rotation. Moment and moment of force. Couple.

3. 11. Moment to force ratio. 12. Cue ball priciple , row boat efect , diving board effect. 13. Types of tooth movement. 14. One couple , two couple system. 15. Biomechanics of leveling & aligning. 16. Biomechanicss of space closure. Biomechnics of finishing. Conclusion.

4. INTRODUCTION Orthodontists are biological scientists and have not always been comfortable with the physical sciences. These mechanical principles are found within the branch of engineering science called as mechanics. It is the study of mechanics as it affects the biologic systems. It is the application of mechanics to the biology of tooth movement – BIOMECHANICS. Biology + Mechanics = Bio-mechanics. Biomechanics in Orthodontics. Michael R. Marcotte , 1 st Edition

5. Scalar Vecto r : When a physical property has both magnitude and direction its called a vector quantity. (E.g.. A force vector characterized by magnitude, line of action, point of origin and sense)

6. Vectors can also be resolved into components .

7. NEWTON’S 1 st LAWS OF MOTION

8. NEWTON’S 2 ND LAW

9. NEWTON’S 3 RD LAW

10. FORCE Force is the effect that causes an object in space to change its place or its shape/ the state of rest or motion of the body In orthodontics, the force is measured in grams, ounces, or Newtons

11. RESULTANT OF FORCES A b C d

12. CENTER OF MASS: Each body has a point on its mass , which behaves as if the whole mass is concentrated at that single point. We call it the center of mass in a gravity free environment. The same is called center of gravity in an environment where gravity is present.

13. CENTER OF RESISTANCE. Since the tooth is partially restrained as its root is embedded in bone its center of gravity moves apically and this is known as Center of resistance. Center of resistance varies D epending up on the Root length & morphology - Number of roots Level of alveolar bone support.

14. CENTER OF ROTATION It may be defined as a point about which a body appears to have rotated as determined from its initial to final positions. A simple method of determining a center of rotation. Draw the long axis of the tooth in its initial and final positions; we will see that both these lines intersect at a point. This is the point around which the tooth rotates and is called center of rotation.

15. The centre of rotation can be at the centre of resistance,apical to it,at the root apex or at infinity.

16. TYPES OF TOOTH MOVEMENT POSITION OF THE CENTER OF ROTATION Translation Uncontroued tipping Controlled tipping Root movement of torquing Lies at infinity Slightly apical to center of resistance Apex of root Incisal or occlusal edge

17. MOMENT OF THE FORCE The moment of the force is the tendency for a force to produce rotation. It is determined by multiplying the magnitude of the force by the perpendicular distance of the line of action to the center of resistance Unit= Newton. mm

18. The direction of moment of force can be determined by continuing the line of action around the Cres .

19. COUPLE A couple is a system having two parallel forces of equal magnitude acting in opposite directions. The result is a moment with no net force. The object rotates about it’s center of resistance regardless of the point of application of the couple.

20. M/F (moment to force ratio) is the relationship between the force and the counter balancing couple that determines the type of tooth movement The ratio of the counter-balancing moment produced to the net force that is applied to the tooth will determine the type of tooth movement that will occur.

21. Force applied on a tooth Crown moves more than root To maintain the inclination Of the tooth Overcome the moment Created by the force applied to the crown Counter moment

22. M/F 5 : 1 Uncontrolled tipping M/F 8 : 1 Controlled tipping M/F 10 : 1 Translation M/F >10 : 1 Root movement MOMENT TO FORCE RATIO FOR VARIOUS TOOTH MOVEMENTS

23. A force off center causes the cue ball to rotate as well as move forward in a straight line. No left or right rotation is produced when the force is applied through the center of the cue ball. When the line of force acts through the center of resistance, only translation results. CUE BALL CONCEPT Equal and opposite forces (couple) produce pure rotation. Mulligan TF: Common sense mechanics 2 . Forces & moments. JCO 13:676-683,1979

24. Tendency of the anterior teeth to move forward as anterior lingual root torque is provided and vice versa. ROW BOAT EFFECT Mulligan TF: Common sense mechanics 2 . Forces & moments. JCO 13:676-683,1979

25. With a constant tipback angle, the deflection doubles as the wire length doubles, the force is reduced to one fourth When the length of the diving board is doubled, only one-eighth the force is required to produce the same amount of deflection. B. The same force acting at twice the length will produce eight times as much deflection. DIVING BOARD CONCEPT Mulligan TF: Common sense mechanics 2 . Forces & moments. JCO 13:676-683,1979

26. BIOMECHANICAL CLASSIFICATION OF ORTHODONTIC APPLIANCES Equal and opposite force system. One couple appliance system. Two couple appliance system.

27. EQUAL AND OPPOSITE FORCE SYSTEM. Simplest orthodontic appliance ,an elastic band stretched between two points of attachment is the best example . T his produces force of equal magnitude on either end but opposite direction.  

28. ONE COUPLE APPLIANCE SYSTEMS. Statically determinate system

29. TWO COUPLE APPLIANCE SYSTEM. The both the ends of the appliance are engaged into attachments{brackets or tubes}.A couple may be generated by the wire at either or both attachment sites . T he force systems produced by two couple appliances cannot be measured clinically and so they are referred as statically indeterminate.

30. FORCE SYSTEM Variety of combinations of two- bracket systems and their force systems

31. PHASES OF ORTHODONTIC TREATMENT. Stage 1: L evelling and aligning. Stage 2 : B ite correction and space closure. Stage 3: Finishing and detailing.

32. LEVELLING AND ALIGNING We put thinner wires at the beginning of alignment ,less applied couple - less M:F - no root moment only crown moment (tipping)

33. The 2 central incisors are rotated mesial in creating a symmetric V geometry. The desired corrective force system involves 2 equal and opposite moments as illustrated Semin Orthod 2001;7:16-25.

34. The force system developed by inserting a straight wire into the brackets of the 4 anterior teeth will create counterclockwise moments on the 2 central incisors as well as lingual movement of the left central incisor and labial movement of the right central incisor. The initial geometry is not favorable for alignment . Semin Orthod 2001;7:16-25.

35. During extrusion of a high canine unilaterally. Figure A shows the force system generated by the placement of a straight wire through a high maxillary right canine. The canine will extrude as desired, but the lateral incisor and first premolar on that side will intrude and tip toward the canine space. An open bite may result on that side of the arch, and the anterior occlusal plane will be canted up on the right side. Semin Orthod 2001;7:16-25.

36. Force vectors in Cl -III elastics Favorable in low angle deep bite cases Force Vectors in Cl -II elastics Favorable in low angle cases

37. SPACE CLOSURE ANCHORAGE CLASSIFICATION. Group A anchorage. This category describes the critical maintenance of the posterior tooth position. Seventy-five percent or more of the extraction space is needed for anterior retraction.

38. Group B anchorage. This category describes relatively symmetric space closure with equal movement of the posterior and anterior teeth to close the space. This is often the least difficult space closure problem .

39. Group C anchorage. This category describes " noncritical"anchorage . Seventy-five percent or more of the space I closed by movement of the posterior teeth.

40. FINISHING The major factors involved in achieving this proper anterosuperior incisor inclination are the bracket and wire coupling . A specific archwire with a medium-to-low load deflection rate (such as a 0.017 x 0.025) can be selected .

41. After the third-order objectives are met, second-order movements are addressed. Adjustments in this plane also take a significant amount of time because they also involve root correction. To achieve second-order objectives, either the same 0.016 x 0.022 beta-titanium or steel round archwire can be used, providing all the third order objectives have been met.

42. The final step in finishing is the correction of first-order problems . Usually these problems are obvious clinically and can be corrected quickly. Tn many instances, only small correction bends in the archwire are needed. Correction can also be achieved with auxiliary plastic rotation wedges on the brackets, or by making small bends in either the 0.016 x 0.022 beta-titanium or 0.016 steel archwire .

43. CONCLUSION The choice of appliances and techniques used by practitioners varies radically among individuals but the fundamental forces and moments they produce are universal. Appliance will always act according to the LAWS OF PHYSICS. Understanding the basic biomechanical principles involved in effective controlled tooth movement makes the final outcome more predictable and consistent.

44. REFFERENCES Smith RJ, Burstone CJ: Mechanics of tooth movement. AJO 85:294-307,1984. Burstone CJ, Koenig HA: Creative wire bending- The force system from step & V bends. AJO DO 93(1):59-67,1988. Burstone CJ, Koenig HA: Force system from the ideal arch. AJO 65(3):270-289,1974. Demange C: Equilibrium situations in bend force system. AJO DO98(4):333-339,1990. Issacson RJ, Lindauer SJ, Rubenstein LK: Moments with edgewise appliance e: Incisor torque control. AJO DO 103(5):428-438,1993. Koing HA, Vanderby R, Solonche DJ, Burstone CJ: Force system for orthodontic appliances: An analytical & experimental comparison. J Biomechanical Eng102(4):294-300,1980. Kusy RP, Tulloch JFC: Analysis of moment/force ratio in the mechanics of tooth movement. AJO DO 90; 127-131,1986. Nanda R, Goldin B: Biomechanical approaches to the study of alteration of facial morphology. AJO 78(2):213-226,1980.

45. 9. Vanden Bulcke MM, Burstone CJ, Sachdeva RC , Dermaut LR: Location of center of resistance for anterior teeth during retraction using the laser reflection technique. AJO DO 91(5):375-384,1987. 10. Vanden Bulcke MM, Dermaut LR, Sachdeva RC, Burstone CJ: The center of resistance of anterior teeth during intrusion using the laser reflection technique & holographic interferometry. AJO DO 90(3): 211-220,1986. 11. Mulligan TF: Common sense mechanics 2 . Forces & moments. JCO 13:676-683,1979. 12. Siatkowski RE: force system analysis of V-bend sliding mechanics. JCO 28(9):539-546,1994. 13. Tanne K, et al: Moment to force ratios & the center of rotation. AJO 94:426-431,1989 14. The basics of orthodontic mechanics. Semin Orthod 2001;7:2-15 15. Leveling & aligning: Challenges & Solutions Semin Orthod 2001;7:16-25. 16. Biomechanics in clinical Orthodontics. Ravindra Nanda, 1 st Edition 17. Biomechanics in Orthodontics. Michael R. Marcotte , 1 st Edition