3 Piece Intrusion Arch- Bhavana Shroff

Segmented approach to simultaneous intrusion and space closure: Biomechanics of the three-piece base arch applianceBhavna Shroff, DDS, M Dent Sc, a Steven J. Lindauer, DMD, M Dent Sc, b Charles J. Burstone, DDS, MS, c and Jeffrey B. Leiss, DDS a Baltimore, Md., Richmond, Va., and Farmington, Conn. Deep overbite correction and space closure in patients with flared incisors are mechanically difficult to achieve with conventional orthodontic treatment, The purpose of this article is to present an appliance design that allows simultaneous intrusion and retraction of anterior teeth as well as correction of their axial inclinations. A three-piece base arch was used to achieve simultaneous intrusion and space closure, Various clinical situations are discussed and analyzed from a biomechanical standpoint. Sequences of treatment, appliance design, and management of side effects are described in detail. The segmented approach to simultaneous intrusion and space closure is useful for achieving precise control of tooth movements in the anteroposterior and vertical dimensions. (AM J ORTHOD DENTOFACORTHOP 1995;107:136-43,) D u r i n g orthodontic therapy, correction of deep overbite in patients with flared incisors is a difficult biomechanical challenge, since uprighting of incisors often lengthens the crowns vertically and increases the overbite. Deep overbite may be accompanied by intraarch spacing associated with flared incisors, or intraarch crowding requiring premolar extractions. In extraction cases, alignment of the anterior teeth does not correct their axial inclinations or the deep overbite. In either extraction or nonextraction therapy, the deep overbite must be corrected to ensure that full space closure is possible when the canine relationship is Class I; therefore simultaneous intrusion and retraction of the anterior teeth may be desirable to achieve optimum treatment results. During intrusion of the anterior teeth, control of their labiolingual axiaI inclinations during retraction is critical for successful completion of treatment. This article describes a technique to intrude flared incisors, control their axial inclinations, and retract them simultaneously with good anchorage control, by using frictionless mechanics. The orthodontic correction of deep overbite can be achieved with several mechanisms that will result in true intrusion of anterior teeth, extrusion of posterior teeth, or a combination of both. For aDepartment of Orthodontics, University of Maryland School of Dentistry. bDepartment of Orthodontics, Medical College of Virginia, Virginia Commonwealth University. CDepartment of Orthodontics, University of Connecticut. Copyright © 1995 by the American Association of Orthodontists. 0889-5406/95/$3.00 + 0 8/1/47903 example, leveling of a mandibular curve of Spee can be achieved by extrusion of molars and premolars. Extrusion of posterior teeth will result in increased lower facial height, steepening of the occlusal plane, and downward and backward rotation of the mandible with a worsening of the Class II skeletal relationship. The long-term stability of such a correction is questionable unless suitable growth occurs. Deep overbite correction by intrusion of anterior teeth affords a number of advantages including simplifying control of the vertical dimension and allowing forward rotation of the mandible to aid in Class II correction. 1 Intrusion of anterior teeth to correct deep overbite may be indicated in patients with unesthetic excessive maxillary incisor showing at rest and a deep mandibular curve of Spee associated with a long lower facial height. By using segmented arch mechanics, genuine intrusion of the anterior teeth may be obtained. 2-4 During intrusion of anterior teeth, optimal magnitudes of force may be delivered constantly using low load deflection springs. Low forces are used during intrusion to minimize root resorption and decrease side effects on the reactive unit. It has been documented that the use of heavier forces will not increase the rate of intrusion. 5'6 The use of a point contact of force application is critical for obtaining true intrusion because the force may then be applied directly through the center of resistance of the anterior segment. This can be achieved by using an intrusion arch tied to the anterior segment to give a statically determinate force system? Alternative mechanisms such as a utility arch or a 136 To achieve deep overbite correction and close extraction spaces simultaneously. The intrusive force is applied with a 0.017 x 0. When no further retraction is possible because of the presence of a deep bite and the reduction of the overjet. the center of resistance of the anterior segment lies further lingual to the incisors crowns. 8 In patients with proclined incisors. To design the appliance optimally to obtain the desired force system. intrusive forces on the upper anterior teeth can be used to tip back the posterior teeth while partially or completely correcting a Class II buccal relationship. Calif.). and the moment to force ratio (M/F) at the centers of resistance easily regulated to produce the desired tooth movements. as well as a mechanism to direct the intrusive force along the long axis of the anterior teeth. The same mechanism with higher forces can be used to tip back buccal segments. In clinical situations where incisors are proclined. This is because the intrusive force is applied anterior to the center of resistance of the incisors and the moment consequently produced tends to further flare the anterior teeth. 137 continuous arch wire with tip back bends located mesial to the first permanent molars may not achieve intrusion because the full engagement of the arch wire in the brackets of the anterior teeth produces an undesirable force system. intrusion is initiated to open the bite and allow subsequent space closure. the following procedures are generally followed. After careful differential diagnosis and planning. The appliance described enables the magnitude of the moments and forces delivered to be well controlled. In these cases. After satisfactory alignment of the premolars and molars. Movement of the posterior segment is also well controlled. True intrusion without axial inclination change is obtained by directing the intrusive force through the center of resistance of the anterior teeth. Sometimes. ~° Segmented arch mechanics uses different wire crosssections in a given arch rather than continuous wires? ~The advantage of using such an approach is that it is possible to 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.025 stainless steel) are placed in the right and the left posterior teeth for stabilization. If only anterior intrusion and retraction is indicated. relative intrusion and flaring of the anterior teeth are achieved. 12 Consequently. A three-piece base arch is used to intrude the anterior segment (Fig. The distal extensions end 2 to 3 mm distal to the center of resistance of the anterior segment. . The anterior segment is aligned with a low stiffness arch wire. ~NTRUSION. A precision stainless steel transpalatal arch (0. Since displacement of the intrusive force away from the center of resistance will result in either flaring or uprighting of the incisors.018 x 0. No. 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.025 TMA tip-back spring (Ormco.032 × 0. resulting in a modification of the axial inclination of the anterior teeth that may or may not be desirable. 7 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. an appliance design needs to incorporate a variable point of application of the intrusive force.017 × 0.American Journal of Orthodontics and Dentofacial Orthopedics Volume 107. constant levels of force can be maintained. The next stage of treatment will involve the simultaneous intrusion and retraction of the incisor segment.RETRACTION MECHANICS The mechanism described here uses the principles of the segmented arch technique. passive segmented wires (0. Glendora. A heavy stainless steel segment (0. 13 Canines may be retracted separately and incorporated into the buccal segments 14'~5 or left at their initial positions. careful evaluation is necessary to monitor the axial inclination of the anterior teeth during intrusion. 2 S h r o f f et al.032) placed passively between the first maxillary molars consolidates the posterior unit now consisting of right and left posterior teeth. One solution to this problem is the use of distal extensions to the anterior segment of wire where segmented intrusion springs can be hooked at a point where the force acts at the estimated center of resistance of the anterior segment. 1).025 or larger) with distal extensions below the center of resistance of the anterior teeth is placed passively in the anterior brackets. treatment is initiated by aligning the teeth included in the right and the left posterior segments. 9 In many extraction cases the axial inclination of flared anterior teeth is corrected first by retraction of the incisors during initial space closure. This article will emphasize the use of intrusive forces for retraction of anterior teeth when intrusion is needed. the position of the center of resistance of the anterior teeth may be estimated on a lateral cephalometric x-ray film. 1. B. It is possible to change the direction of the net intrusive force by applying a small distal force. The line of . Class I elastics are needed to redirect force parallel to the long axis of the incisor. The anterior segment extends 2 to 3 mm distal to the center of resistance (CR) of the anterior teeth. A. Intrusive force through CR will intrude incisor along line of action of this force. 3). Force acts through center of resistance. 3. An intrusive force perpendicular to the distal extension of the anterior segment and applied through the center of resistance of the anterior teeth will intrude the incisor segment (Fig. 2. This appliance design allows the application of the intrusive force to get true intrusion of the incisors along their long axes. Diagramatic representation of three-piece base arch. The design of this appliance enables lowfriction sliding to occur along the distal extension of the anterior segment during space closure (Fig. BIOMECHANICS Anterior segment and direction of intrusive force A number of different clinical situations may arise and they should be thoroughly analyzed from a biomechanical standpoint to determine the correct force system necessary to achieve the treatment objectives. The application of a light. 2).) The overall force system obtained is an intrusive force anteriorly and an extrusive force posteriorly associated with the tip back moment. Diagram of three-piece base arch and Class I elastic stretched from maxillary first permanent molar to distal extension of anterior segment. distal force delivered by a Class I elastic to the anterior segment is used to alter the direction of the intrusive force on the anterior segment. Fig.138 Shroff et aL American Journal of Orthodontics and Dentofacial Orthopedics February 1995 Fig. (The point of application of the intrusive force on the distal extension of the anterior segment will be discussed later. Fig. An intrusive force perpendicular to the distal extension and through CR will have the same effect as in A. A. Thus the line of action of the resultant force can be made parallel to the long axis of the anterior teeth if an appropriate distal force is combined with a given intrusive force. The farther lingual the force. The correct appliance design is chosen after careful analysis of the clinical situation as discussed above. the force is redirected to be parallel to the long axes of the incisors. the desired force system should be determined with respect to the centers of resis- tance of the anterior and posterior segments. Direction of net intrusive force through CR may be changed by application of a small distal force. B. B. If the intrusive force is placed farther distally and an appropriate small distal force is applied (Fig. 4. 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. 4. The force system generated on a molar is shown in Fig. A) and a combination of intrusion and tip back of the anterior teeth will occur. One advantage of this system is the low magnitude of force applied on the reactive or anchorage unit. 6. The distal force used in this intrusion retraction system is of very low magnitude and is used to redirect the line of action of the intrusive force. 5). To obtain a line of action of the intrusive force through the center of resistance and parallel to the long axis of the incisors. Redirection and movement of the intrusive force distally reduces the moment on the buccal segment of teeth. It is also possible to retract the canines indMdually and to include them in the buccal stabilizing segment of wire before the initiation of intrusion-retraction mechanics.American Journal of Orthodontics and Dentofacial Orthopedics Volume 107. Fig. action of the resultant force will be lingual to the center of resistance (Fig. 5. since a net tip back moment is applied to the posterior segment. The resulting intrusive force has a direction parallel to the long axis of the incisor and is distal to CR. The net force can be directed along the long axis of the incisor by applying the intrusive force more anteriorly. When intrusionretraction mechanics are initiated. . B). It is important to monitor the anterior and posterior segments and alter the force system if indicated. the point of force application must be more anterior and as close to the distal of the lateral incisor bracket as possible (Fig. the anterior teeth will intrude and tip back with progressive space closure between the incisors and the canines. 4. A. 2 Shroff et aL 139 Fig. In Fig. A tip back moment is created during intrusion of the anterior segment and will have a typical value of 900 gm-mm for an intrusive force of 30 g and an interbracket distance of 30 mm. and thus reduces the tendency for its natural plane of occlusion to steepen. The resulting force system can be modified by changing the magnitudes and points of application of the intrusive and distal forces with respect to the center of resistance of the anterior segment. the larger will be the moment acting to tip the incisors lingually. intrusive force can be directed along long axis of anterior teeth and applied lingual to CR. Distal movement of the canines may occur as the anterior segment contacts the canines. 6. CLINICAL APPLICATIONS OF THE INTRUSION RETRACTION MECHANICS After treatment planning and developing treatment objectives. Headgear is not usually required for anchorage control. Spacing or crowding among the incisors is usually addressed early in treatment.No. CASE REPORT A 10-year. Deep overbite was corrected by upper and lower incisor intrusion. and the overbite was 65%. Division 1 malocclusion in the late mixed dentition (Fig. a three-piece base arch was selected to intrude them and a light distal force was applied to redirect the intrusive force along their long axes. Note reduction of the moment on the molar in B. As intrusion occurred.. Her upper and lower lips were significantly procumbent with respect to the soft tissue line Sn-Pg (subnasale-Pogonion). A deep curve of Spee was present in the mandibular arch. The application of an intrusive force anterior to the center of resistance . She presented with an acute nasolabial angle and a deep labiomental fold.140 Shroff et aL American Journal of Orthodontics and Dentofacial Orthopedics February 1995 gl a o turn . 8). The patient had a Class II skeletal relationship primarily because of a protrusive maxilla. Parallel to the incisor long axis and lingual to CR. Simultaneous intrusion and retraction of the upper incisors was initiated after consolidation of spaces in the maxillary arch between the lateral and central incisors. 9-month-old black female patient presented to the orthodontic clinic of UMAB Dental School for treatment. The upper incisors were labially tipped with respect to Frankfort horizontal. and the lower incisors were in relatively normal position with respect to the mandibular plane. B. The treatment objec- tives included a reduction of the maxillary protrusion both orthopedically and dentally." ~ 1 gr B Fig. Comparison of force system developed on molar with identical 30 gm intrusive forces.. The extraoral examination of the patient showed good facial symmetry and a convex profile.. 7). with palatal impingement. Because of the proclination of the maxillary incisors. correction of the deep overbite. The occlusogram confirmed 11 mm of spacing in the maxillary arch. and achievement of maxillary space closure. the incisors tipped back and space closure was achieved simultaneously (Fig. The anterior overjet was approximately 10 mm. In the maxillary arch. Dentally. High-pull headgear wear was initiated to correct the Class II occlusion and control the vertical dimension.. A. A continuous intrusion arch tied to the central incisors could not have been used in this situation because of the proclined position of the upper incisors. the patient displayed a Class II. rotation of the first molars was achieved initially with a removable stainless steel transpalatal arch. 6. and her interlabial gap was 9 mm at rest. Perpendicular to the occlusal plane. A. The chain elastic is redirecting the intrusive force along the long axes of the maxillary incisors. maxillary occlusal view. Intraoral views of the right and left buccal occlusion showing a deep curve of Spee in the lower arch and a Class II. Intraoral view of occlusion: Frontal aspect. 7. Fig. C and D. Intraoral view of occlusion: Frontal aspect. After preliminary alignment of the molars and premolars and separate retraction of the canines. A. Intraoral views of the occlusion. Intraoral views of the right and left buccal occlusion: The tip back spring is carefully positioned and activated. B and C. Division 1 type of malocclusion in the late mixed dentition. The maxillary anterior teeth are in tabioversion. No. 2 Shroff et aL 141 Fig. a three-piece base arch was used to simultaneously intrude and retract the maxillary incisors. The maxillary arch is symmetric with respect to the median Raphe and the soft tissue of the cheeks and lips. The maxillary arch has 11 mm of spacing confirmed by the occlusogram. .American Journal of Orthodontics and Dentofacial Orthopedics Volume 107. 8. There is a 65% overbite with palatal impinge* ment and an anterior overjet of 10 mm. B. a removable lingual arch was placed. CONCLUSION D e e p overbite correction and space closure can be simultaneously achieved with the three-piece .. AFTER Fig. Maxillary and mandibular Hawley retainers were delivered to the patient subsequent to debonding (Fig. A superimposition of maxillary cephalometric tracings before and after treatment shows the movement of the maxillary incisors and molars during treatment (Fig. D and E.017 × 0. The intrusive force applied on the maxillary incisors was redirected along their long axis and simultaneous intrusion and space closure was successfully achieved... The upper arch was finished with a continuous arch wire (0. In the mandibular arch. 10. of the anterior segment would have flared the incisors farther. The three-piece base arch allowed precise control of the delivered force system in the maxillary arch. 9). Right and left buccal aspects.025 TMA) was used for finishing. Maxillary occlusaq aspect. 10). since it was possible to direct the intrusive force along the long axes of the incisors and place it lingual to the center of resistance. American Journal of Orthodontics and Dentofacial Orthopedics February 1995 Fig. and intrusion of the incisors was achieved with a continuous intrusion arch. B.142 Shroff et al.. Intraoral views of finished occlusion: A. a continuous arch wire (0. C.022 TMA). Superimposition of maxillary cephalometric tracings before and after treatment showing movement of maxillary incisors and molars during treatment. 9. BEFORE .016 x 0. Frontal aspect. Mandibular occlusal aspect. After the leveling of the curve of Spee.. We extend our thanks to Mrs. AM J ORTHOD 1967. Burstone CJ. Deep overbite correction by intrusion.American Journal of Orthodontics and Dentofacial Orthopedics Folume 107. Tip-back mechanics. 5. Angle Orthod 1961. 7. 2. No. The application of continuous force to orthodontics. May 3 to 7. Baldwin J J. 11. 1985. Precision lingual archespassive applications. Dallas Convention Center San Diego. ed.82(5):361-78. Smith RJ. statically determinate force system in which only minimal chairside adjustments are required. May 11 to 15. Reitan K.80(1):1-16. MD 21201 AAO MEETING CALENDAR 1995 -- San Francisco.. Space closure in adult patients using the segmented arch technique. Moscone Convention Center (International Orthodontic Congress) 1996 1997 1998 1999 2000 Denver. Baltimore. AM J ORTHOD 1981. Burstone CJ. Manhartsberger C. Lawless DT. 9. May 15 to 19. Philadelphia: WB Saunders: 1977:203-14. Burstone CJ. AM J ORTHOD 1982. Angle Orthod 1989. 4. The design of this appliance allows the clinician to deliver a well-controlled. Colorado Convention Center Philadelphia. 2rid ed. May 12 to 17. REFERENCES 6. 13.. Burstone CJ. Begg orthodontic theory and technique. Colo. Pa.. Bhavna Shroff Department of Orthodontics University of Maryland Dental School 666 West Baltimore St. Calif. The low load deflection rate of this appliance delivers a constant intrusive force. 12. 1. Dellinger EL. Initial tissue behavior during apical root resorption. 8. Burstone CA. Jo-Ann Walker for preparing the manuscript. Romeo DA. Burstone CJ. II1. Burstone CJ. and the levels of force can be kept low. Angle Orthod 1966. 10.36(2):99-120. Koenig HA. The rationale of the segmented arch. AM J ORTHOD 1976. Bnrstone CJ. Burstone CA. !5. AM J ORTHOD 1984. A histologic and cephalometric investigation of premolar intrusion in the Macaca speciosa monkey. Burstone CJ. J Clin Orthod 1988.31:114. Variable modulus orthodontics. Current orthodontic concepts and techniques. 3. April 29 to May 3..72(4):414-21. Morton J. Philadelphia Convention Center Dallas. Bnrstone CJ.70:1-20. The segmented arch approach to space closure.22(7):444-51. Mechanics of tooth movement. Philadelphia: WB Saunders. Calif.85(4):294-307. The force system delivered on the anterior segment depends on the point of application of the intrusive force and its direction. Reprint requests to: Dr. Manhartsberger C. In: Graber TM. Applications of bioengineering to clinical orthodontics. AM J ORTHOD 1977. !4.. AM J ORTHOD 1962. San Diego Convention Center Chicago. 2 Shroff et aL 143 base arch intrusion mechanism in patients with flared incisors. McCormick Place Convention Center . May 16 to 20.44(1):68-82. I.48(11):805-21. Begg PR.53:325-55. Optimizing anterior and canine retraction.72(1):1-22. Angle Orthod 1974. Texas. Burstone CJ.59:205-10. AM J ORTHOD 1977. Kesling PC. This segmented approach to intrusion and retraction is clinically advantageous because it allows simultaneous control of tooth movement in the vertical and anteroposterior planes. Mechanics of the segmental arch technique.