biomechanics of incisor intrusion and retraction

biomechanics

1. BIOMECHANICS OF INCISOR INTRUSION AND RETRACTION SAMYUKTHA S 2 ND YEAR PG

2. INTRUSION: Intrusion refers to the apical movement of the geometric center of the root (centroid) in respect to the occlusal plane or plane based on the long axis of the tooth.[Burstone 1977]

3. DENTO ALVEOLAR DEEP BITE: The dental alveolar deep overbite is of two types : 1. True deep bite- caused by infra-occlusion of the molars. 2. Pseudo deep bite - caused by supra eruption of the incisors

4. True intrusion is achieved by moving the root apices of the anteriors closer to the bony base. Relative intrusion is achieved by keeping them where they are, while the mandible grows and the posterior teeth erupt. Apparent intrusion is achieved by extrusion of the posterior teeth William R.Proffit contemporary orthodontics 6 th edition

5. PRINCIPLES OF BURSTONE:  Controlling force magnitude Anterior single point contacts Point of force application Selective intrusion Control of reactive units Avoid extrusive mechanics Deep overbite correction by intrusion Charles R burstone AJO 1977

6. Controlling force magnitude: The lowest magnitude of force capable of intruding must be used. If the magnitude of force are too great , rate of intrusion will not increase Rate of resorption will increase reciprocal effect on post anchorage Deep overbite correction by intrusion Charles R burstone AJO 1977

7. Anterior single point contacts The intrusion arch is not placed directly into the brackets of the teeth to be intruded. It is tied to the anterior segment usually forming two point contact. If placed in bracket it may introduce torque. If labial torque is placed then there will be increase in intrusive force thereby increase side-effect on anchorage. If lingual root torque is present there is decrease in intrusive force but may actually extrude the teeth Deep overbite correction by intrusion Charles R burstone AJO 1977

8. Point of force application: • Intrusive force through the center of resistance of any tooth will intrude the tooth without producing any labial or lingual rotation of the tooth being intruded. • If intrusive force is labial to CORe a greater moment is created which will flare the tooth. To overcome this 1) if tooth is forwardly placed, retrude and then intrude. 2) and to apply the vertical force lingual to the center of resistance. Deep overbite correction by intrusion Charles R burstone AJO 1977

9. Selective intrusion  Leveling with a continuous arch or with a sectional wire can produce undesirable side effects. Many times the overbite is corrected not because of intrusion but by extrusion Deep overbite correction by intrusion Charles R burstone AJO 1977

10. Control of reactive units The largest effect upon the anchorage unit will be a result of the moment produced by the intrusive force which is large because of the long moment arm. • So add more teeth for anchorage. • Keep intrusion forces as low as possible. Do as  much retraction as possible to decrease the length of moment arm. Also, moment on the molar will tip molar crown lingually and root buccally, which can be prevented by lingual arch or TPA. Deep overbite correction by intrusion Charles R burstone AJO 1977

11. Avoid extrusive mechanics Extrusive mechanics such as employing class II or class III elastics should be avoided in patient who need genuine intrusion. One of the classic situation for inadvertently erupting incisors which have been intruded or are going to be intruded is placement of continuous arch wire. Deep overbite correction by intrusion Charles R burstone AJO 1977

12. Dr Charles J burstone., modern edgewise mechanics and the segmented arch technique

13. RICKKET’S UTILITY ARCH: Developed according to the biomechanical principles as described by Burstone in 1977 and refined by Ricketts for Bioprogressive therapy – It was first developed for leveling deep curve of spee in the mandibular arch but now it has many other modifications and uses. Material And Dimension   of Wire – Wire 0.016 x 0.016 or 0.016 x 0.022 in an 0.022 slot . They are available in three different metals: stainless steel, Nitanium Super Elastic, and Bio- Kinetix Thermal NiTi .

14. DESIGN All utility arches   have a common design The molar segment The posterior vertical segment The vestibular segment. The anterior vertical segment Incisal segment.

15. TYPES OF UTILITY ARCH: PASSIVE UTILITY ARCH INTRUSION UTILITY ARCH INTRUSION AND RETRACTION UTILITY ARCH RETRACTION UTILITY ARCH PROTRUSION UTILITY ARCH

16. RETRACTION AND INTRUSION UTILITY ARCH: Retraction and intrusion of the incisors by incorporting loops in arch wire anterior to the anterior vestibular segment. The incorporation of the loop into the design allows for a longer range of activation. The loop is formed so its anterior leg crosses behind the posterior leg. USES: a. Retraction and intrusion of upper incisors in case of flaring b. Closure of interproximal spaces c. Correcting midline discrepancies

17. ACTIVATION: Activation of retrusive force by weingart plier grasp the wire posterior to the band tube Pull it 2-3 mm Bend 90 degrees gingivally An occlusally directed gable bend in the vestibular segment is used to produce intrusion.

18. Burstone’s three piece intrusion arch: In patient’s with proclined incisors, a continuous intrusion arch tied at the midline cannot be used because the force system generated tends to worsen the axial inclination of the anterior teeth So the selection of the point of application of the intrusive force with respect to the center of resistance of the anterior segment is important to precisely define the type of tooth movement that will occur Bhmecavana Shroff, Steven J Lindauer , Charles J Burstone “ Segmented approach to simultaneous intrusion and space closure: biohanics of three piece base arch appliance” Am J Orthod dentofac Orthop 1995:107: 136- 43.

19. In many extraction cases the axial inclination of flared anterior teeth is corrected first by retraction of the incisors during initial space closure. When no further retraction is possible because of the presence of a deep bite and the reduction of the overjet, intrusion is initiated to open the bite and allow subsequent space closure. To achieve deep overbite correction and close extraction spaces simultaneously, An appliance design needs to incorporate a variable point of application of the intrusive force, as well as a mechanism to direct the intrusive force along the long axis of the anterior teeth. This is a segmented approach to simultaneously intrude and retract the flared by using frictionless mechanics Introduced by Bhavna Shroff, Steven J. Lindauer, Charles J. Burstone, Jeffrey B. Leiss in 1995. Bhmecavana Shroff, Steven J Lindauer , Charles J Burstone “ Segmented approach to simultaneous intrusion and space closure: biohanics of three piece base arch appliance” Am J Orthod dentofac Orthop 1995:107: 136- 43.

20. PRINCIPLES OF SEGMENTED ARCH TECHNIQUE: different wire cross-sections in a given arch rather than continuous wires develop a precise and predictable force system between an anterior segment (incisors) and a posterior segment (premolar and molars) enabling pure intrusion of the anterior teeth and control of their axial inclinations Three piece intrusion arch Consists of: Posterior anchorage segment Anterior segment with posterior extension Intrusive cantilevers Sometimes chain elastics Bhmecavana Shroff, Steven J Lindauer , Charles J Burstone “ Segmented approach to simultaneous intrusion and space closure: biohanics of three piece base arch appliance” Am J Orthod dentofac Orthop 1995:107: 136- 43.

21. Anterior segment with POSTERIOR EXTENSION It is bent gingivally distal to the laterals and then bent horizontally creating a step of approximately 3 mm Distal part extends to distal end of canine bracket where it forms a hook 0.021 X 0.025 SS POSTERIOR SEGMENT Aligned posteriors 0.017 X 0.025 SS TPA can be given for more consolidation Bhmecavana Shroff, Steven J Lindauer , Charles J Burstone “ Segmented approach to simultaneous intrusion and space closure: biohanics of three piece base arch appliance” Am J Orthod dentofac Orthop 1995:107: 136- 43.

22. Cantilever or Intrusion spring: Made from 0.017" X 0.025" TMA wire. The wire is first bent gingivally mesial to the molar tube and then a helix is formed. On the mesial end the cantilever, hook is bent through which the intrusion force can be applied to the anterior segment. The cantilever is then activated by the making a bend mesial to the helix at the molar tube, and then cinched back. Bhmecavana Shroff, Steven J Lindauer , Charles J Burstone “ Segmented approach to simultaneous intrusion and space closure: biohanics of three piece base arch appliance” Am J Orthod dentofac Orthop 1995:107: 136- 43.

23. A small distal force can be added by attaching chain elastic from the hook of anterior segment to the molar tube to facilitate simultaneous intrusion and retraction of the anteriors on each side Bhmecavana Shroff, Steven J Lindauer , Charles J Burstone “ Segmented approach to simultaneous intrusion and space closure: biohanics of three piece base arch appliance” Am J Orthod dentofac Orthop 1995:107: 136- 43.

24. BIOMECHANICS: To obtain a line of action of the intrusive force through the center of resistance and parallel to the long axis of the incisors, the point of force application must be more anterior and a small distal force should be given Intrusive force through CR will   intrude incisor along line of action of this force.  An intrusive force perpendicular to the distal extension and through CR will have the same effect as in A. Bhmecavana Shroff, Steven J Lindauer , Charles J Burstone “ Segmented approach to simultaneous intrusion and space closure: biohanics of three piece base arch appliance” Am J Orthod dentofac Orthop 1995:107: 136- 43.

25. if the  intrusive force is placed farther distally and an appropriate small distal force is applied, intrusion and simultaneous retraction of the anterior teeth occurs because of the tip back (clockwise) moment created around the center of resistance of the anterior segment consisting of four incisors. Bhmecavana Shroff, Steven J Lindauer , Charles J Burstone “ Segmented approach to simultaneous intrusion and space closure: biohanics of three piece base arch appliance” Am J Orthod dentofac Orthop 1995:107: 136- 43.

26. CONNECTICUT INTRUSION ARCH: The CTA is fabricated from a nickel titanium alloy. It incorporates the characteristics of utility arch as well as those of the conventional intrusion arch Two wire size are available 0.016” x 0.022” and 0.17” x 0.25”. Nanda R, Marzban R, Kulberg , “The Connecticut Intrusion Arch” JCO1998 p 708 – 715

27. The maxillary and mandibular versions have anterior dimensions of 34mm and 28mm , respectively, 1.In most cases,   the wire is not directly ligated into the bracket slots, the anterior wire dimension is adequate to allow for it. 2.The bypass, located distal to the lateral incisors, is available in two different lengths to accommodate for extraction, nonextraction or mixed dentition cases. Nanda R, Marzban R, Kulberg , “The Connecticut Intrusion Arch” JCO1998 p 708 – 715

28. Maxillary CTA Anterior dimension 34MM 28MM Posterior dimension(long) Non extraction 22MM 22MM Posterior dimension(short) (extraction and mixed 15MM 15MM Mandibular CTA Nanda R, Marzban R, Kulberg , “The Connecticut Intrusion Arch” JCO1998 p 708 – 715

29. The CTA basic mechanism for force delivery is a V bend lies just anterior to the molar brackets. When the arch is activated, a simple force system results, consisting of a vertical force in the anterior region and a moment in the posterior region. 3.Incisor intrusion requires 50g of force directed apically along the center of resistance. 4.The moment created at the molar will also vary, according to the amount of force at the incisor multiplied by the distance at the molars. These minor changes can be made to ensure proper force delivery. Nanda R, Marzban R, Kulberg , “The Connecticut Intrusion Arch” JCO1998 p 708 – 715

30. A pure intrusion arch would have a point contact at the incisors. Insertion of the wire into the incisor brackets, however, will tend to flare the incisors, which may or may not be desirable. T he CTA’s point of force application is anterior to the center of resistance, which will flare the incisors. A tight cinch-back—a sharp bend distal to the molar tube, preventing forward slippage of the wire—will prevent incisor flaring during intrusion and produce some retraction of the incisors. Nanda R, Marzban R, Kulberg , “The Connecticut Intrusion Arch” JCO1998 p 708 – 715

31. REFERENCE:   Steven. Lindauer , “Basics of mechanics” semin orthod , 7, 2001: 1-15 Charles J. Burstone “ Biomechanics of deep overbite correction” semin orthod 2001: 7: 26-33 Bhmecavana Shroff, Steven J Lindauer , Charles J Burstone “ Segmented approach to simultaneous intrusion and space closure: biohanics of three piece base arch appliance” Am J Orthod dentofac Orthop 1995:107: 136- 43. Jayade “ Refined beggs ” Richard J. Smith, Charles J. Burstone, “ Mechanics of tooth movement” vol 85, 294-307 Mcnamara A J and Brudon WL, Orthodontic and dentofacial orthopedics . Needham press, 2001. Charles J.  Burstone, Modern edgewise mechanics and the segmented arch technique” ed. Ormco 1995. Marcotte MR: Biomechanics In orthodontics. B.C. Decker Inc., 1990. Nanda: Biomechanics in clinical orthodontics. W.B. Saunders Company 1975. Varun Kalra, “simultaneous intrusion and retraction of the anterior teeth” JCO 1998 p535-540. Nanda R, Marzban R, Kulberg , “The Connecticut Intrusion Arch” JCO1998 p 708 – 715 William R.Proffit contemporary orthodontics 6 th edition

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