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Management of overbite by controllingincisor and molar movements
Management of Overbite by Controlling Incisor and Molar Movements Cyril Sadowsky and Terry SeUke A controversial subject in the history of orthodontic therapy has been overbite correction. Some authorities insist that overbite correction should occur only via incisor depression, while others insist that the ability to depress incisors is a myth. Traditionally orthodontists have resorted to "leveling and aligning" on full arch wires, achieving overbite correction by a combination of incisor prociination, posterior eruption, holding against growth, and minimally, true incisor depression. Many authorities, recognizing the pitfalls of traditional leveling techniques, have advocated a segmented approach to overbite correction in an attempt to better control the movement of specific teeth during treatment. Adding to the controversy has been the improved understanding of the role of forces in not only accomplishing selective tooth movement, but in avoiding root resorption and other harmful sequellae of orthodontic therapy. The advent of new diagnostic tools to guide our treatment decisions has only added to our need to better understand the mechanics of overbite correction. If a stable result, the most ideal smile, and the least damage to supporting structures are important treatment considerations, then adherence to treatment objectives based on a more sophisticated diagnosis becomes even more important. In this article, we explore the variety of methods currently used to correct overbite and discuss the efficacy of each in achieving ideal individualized treatment objectives. (Semin Orthod 2000;6:43-49.) Copyright © 2000 by W.B. Saunders Company
eep overbite is a c o m m o n feature of m a n y malocclusions. O n e of the objectives of orthodontic t r e a t m e n t is to establish a n o r m a l overbite, and in cases with a severe overbite, to overcorrect the overbite in anticipation of posttreatment relapse. In defining t r e a t m e n t objectives, it is i m p o r t a n t to specifically identify whether the maxillary and m a n d i b u l a r incisors must be i n t r u d e d or whether the posterior teeth must be extruded, or any combination of the above. In the Bioprogressive philosophy, overbite is corrected by intruding the offending incisors to the "functional occlusal plane" estab-
D
From the Department of Orthodontics, University of Illinois at Chicago, Chicago, IL. Address correspondence to Cyril Sadowsk); BD& MS, Department of Orthodontics, University of Illinois at Chicago, 801 S Paulina Street, Chicago, IL 60612. Copyright © 2000 by !~B. Saunders Compasy 1073-8746/00/0601-0005510. 00/0
lished by the posterior teeth. 1 Many o r t h o d o n tists use the smile line to d e t e r m i n e which incisors to intrude. Others believe that that ability to intrude incisors is a myth and that overbite correction must occur by selective eruption of posterior teeth, or the prevention of incisor eruption with ongoing growth. Although overbite correction is a controversial subject, diagnostic systems are available to aid in developing patient-specific treatment objectives. T h e p u r p o s e of this article is to describe the various t r e a t m e n t modalities currently being used by the profession for overbite correction and their effectiveness in p r o d u c i n g the desired outcome. Full-Arch
Mechanics
Most orthodontists follow a historical a p p r o a c h to treatment. They begin by placing bands a n d brackets on all of the teeth in both arches.
Seminars in Orthodontics, Vol 6, No 1 (March), 2000: pp 43-49
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Leveling the mandibular curve of Spee and establishing a compensating curve in the maxillary arch leads to overbite correction as part of the process. Leveling begins with stainless-steel or nickel-titanium arch wires of small crosssection or larger-diameter rectangular arch wires of nickel-titanium or t i t a n i u m - m o l y b d e n u m (TMA) alloys. The purpose of these initial wires is to increase the range of action and p r o d u c e relatively gentle forces and moments. Over time, the clinician works toward progressively heavier (stiffer) wires to achieve control of the teeth in all dimensions. A potential adverse effect of such continuous arch wire mechanics is to procline the incisors leading to the leveling of the incisor tip relative to the occlusal plane (relative intrusion). Mitchell and Stewart 2 reported on six patients who were studied with metallic implants in whom the curve of Spee was leveled with continuous arch wires. The incisors were proclined with relative intrusion, the premolars were extruded, and the terminal molars were slightly extruded. With leveling mechanics, an opening rotation of the mandible may also occur. The cumulative effect is that the overbite decreases. It is generally assumed that in leveling the curve of Spee, arch depth will increase as a result of the need for space to level the curve. However, it has been suggested that additional arch circumference is not n e e d e d to level the curve of Spee. 3,4 Incisor proclination that occurs with traditional leveling is explained by the fact that the forces are labial to the center of resistance of the incisors, resulting in a labial crown-tipping moment. As a result, some advocate the use of initial (resilient) rectangular arch wires in an attempt to control the latter. However, in a recent, prospective, randomized, clinical trial, 5 no difference was f o u n d in the degree of incisor proclination when comparing two samples of patients in whom the curve of Spee was levelled using either r o u n d or rectangular arch wires. If the above effects are desired in a given case, then continuous arch wire mechanics may be appropriate. However, if actual incisor intrusion without proclination is desired, then continuous arch mechanics as described above should be avoided.
Utility Arches Circumventing the premolar and canine teeth with an arch wire to intrude incisors creates an opportunity for light intrusive forces. The Bioprogressive technique incorporates the classic utility arch 1 to apply 60 g of force to intrude lower incisors and 100 g for the u p p e r incisors (Fig 1). Mulligan 6 advocated using a similarly shaped r o u n d arch wire to intrude incisors. There is, however, the potential for incisor proclination that results from the line of force of the arch wire being labial to the center of resistance of the four incisors. Otto et al 7 described the treatment effects of a lower utility arch wire according to the Bioprogressive technique in 24 adults and 31 children having deep overbite. An average of 2.5 m m of actual lower incisor intrusion was f o u n d in the adult group and 2 m m in the child group. There was some proclination of incisors in both groups. Some holding of the incisors against vertical growth (relative intrusion) contributed to overbite correction in the child group. The degree of intrusion was not correlated with age, nor was it influenced by facial type. Dake and Sinclair s c o m p a r e d 30 deep-bite low-angle nonextraction cases treated by Ricketts, to a similar group treated by Schudy in which Class III elastics were added to continuous arch wires while leveling the curve of Spee in the traditional way. The objective in the Shudy group was leveling the curve of Spee without advancing or intruding lower incisors (Tweed technique). The Ricketts group showed more proclination of the lower incisors than the Schudy group (>5 ° of proclination in 64% of the Ricketts cases compared with 40% of Shudy cases). The Ricketts group also demonstrated more posttreatment
Figure 1. Example of a classic lower utility arch wire (Ricketts) extending from the molars and engaging the incisors. The upper arch wire is an example of an advancement utility wire that can also incorporate activation for incisor intrusion.
Control of Overbite by Dental Movements
uprighting and overbite relapse (note that the overbite was intentionally overcorrected in the Ricketts group). The Ricketts group also demonstrated an average of 1.2 m m of actual intrusion of the lower incisors in addition to holding against growth, which was relatively stable an average of 4 years posttreatment. Both groups p r o d u c e d similar amounts of distal tipping of the mandibular molars as well as e x t r u s i o n / e r u p tion, the latter being relatively stable posttreatment. It is also argued that the utility arch produces forces and m o m e n t s that are indeterminate, making prediction of tooth movements uncertain. 9 If square or rectangular wires are used in an attempt to control incisor proclination by incorporating labial root torque, additional moments are created that simultaneously increase the intrusion force. The significant rotational m o m e n t on the molars that occurs in response to the depressive force on the incisor teeth can provide adverse effects contrary to the treatment needs of the patient. To counteract these, a sectional wire from the molar to one or more teeth anterior to the molar is used to control molar position. This approach, described by Burstone in 1977, l° allows the clinician to maintain posterior occlusal relations and angulations while the incisors are depressed to the level dictated by the treatment objectives. With segmentation of the arches to achieve overbite correction, the forces and m o m e n t s on the incisors and molars in all dimensions can be understood and controlled.
Segmental Arch Mechanics A statically determinate technique as originally advocated by Burstone ~° is available to control the forces and moments for incisor intrusion, v This involves a segmented arch wire engaging the four incisors as a unit, with the intrusive force generated by a base arch wire as a pure force (Fig 2), whose line of action can be adjusted to pass through the center of resistance of the fourtooth segment if so desired. Therefore, the m o m e n t of the intrusive force can be controlled to avoid incisor proclination as well as mesiodistal angular changes (second-order moments) particularly involving the lateral incisors. A transpalatal arch can also be added for additional
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Figure 2. An example of the Burstone segmental technique for incisor intrusion. Note the segmental buccal wires and segmental anterior wire. The intrusion base arch is tied to the anterior segment. (Reprinted with permission from Burstone CJ, van Steenbergen E, Hanley KJ. Modern Edgewire Mechanics and the Segmented Arch Technique. Department of Orthodontics, University of Connecticut Health Center, Farmington, CT. Ormco Corporation, Monrovia, CA, 1995, pp 40-41.) molar control. It has been shown that approximately 60 g of force is n e e d e d to intrude the lower incisors and 100 g to intrude the u p p e r incisors. The distal crown mesial root m o m e n t on the molars is approximately 1,800 g-mm for the lower molars and 3,000 g-mm for the u p p e r molars, based on an average distance of 30 m m from molars to incisors. The molar rotational m o m e n t can be further controlled by placing posterior segmental arch wires as described previously. The distal crown tipping of the molar as seen with a 2 × 4 (incisors to molar) set-up may be used to advantage in some cases for Class II correction 6 or to establish maximum anchorage J2; it can also be controlled by adding posterior segments. The extrusive forces to the molars or posterior segments are usually counteracted by forces of occlusion in all but the most "weakmuscled" pattern. Segmentation is the key elem e n t to achieving the specific objectives of the case with a reasonable expectation for the desired response.
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Forces and Intrusion Any discussion of overbite correction must include the forces applied. It has b e e n well established that tooth m o v e m e n t is a histological p h e n o m e n o n that involves osteblasts (lay down bone) and osteoclasts (remove bone). T h e stimulation of cellular activity necessary for depression as well as adverse and pathological sequellae can be attributed to some degree to the forces p r o d u c e d by the mechanotherapy. DiVincenzo and Winn a3 r e p o r t e d on a sample of 25 growing females who received an arch wire extending f r o m the maxillary molars to the four incisors for the purpose of incisor intrusion. T h e molar anchorage was reinforced with a transpalatal wire and anterior and posterior acrylic pads that were able to prevent m o l a r tipping and extrusion. An intrusive force of approximately 60 g (_+15 g) was delivered for approximately 6 months using a 0.016 × 0.022 arch wire engaging the four incisors with passive torque and cinched distal to the m o l a r tubes. C o m p a r e d with the m a t c h e d control group, a m e a n of 2 m m o f actual maxillary incisor intrusion and 15 ° of palatal root torque was reported. Based on initial trials, it was f o u n d that the m o l a r palatal anchorage appliance could s u p p o r t approximately 65 g of intrusive force before adverse m o v e m e n t of the a n c h o r unit was observed. This suggests that the usual r e c o m m e n d a t i o n of 100 g of intrusive force for the four incisors, which may p r o d u c e m o r e effective intrusion, must be closely monitored with regard to the reaction of the anchorage units. Melsen et aP 4 r e p o r t e d on 30 adult patients with marginal b o n e loss and deep overbite for w h o m maxillary incisor intrusion was p e r f o r m e d using the Burstone technique. T h e i r base arch applied between 10 to 20 g of intrusion force per tooth in 22 patients. A m u c h smaller sample received either 0.016 × 0.016 Ricketts utility arches (4 patients),J-hook h e a d g e a r (1 patient), or 0.017 X 0.025 l o o p e d continuous arch (3 patients). True intrusion (measured at the center of resistance) of between 0 and 3 m m was achieved. Intrusion was best p e r f o r m e d when forces were low (5-15 grams per tooth) and applied t h r o u g h the center of resistance. Weiland et a115 c o m p a r e d the t r e a t m e n t effects of continuous arch wire mechanics (CAW) with that of the s e g m e n t e d technique (Burst-
one) for correcting malocclusions exhibiting d e e p overbite and low m a n d i b u l a r plane angle in a sample of 50 adults. T h e overbite correction in the CAW g r o u p was achieved by m o l a r extrusion with posterior rotation of the mandible, while the Burstone g r o u p d e m o n s t r a t e d true incisor intrusion (measured at the center of resistance) without significant molar extrusion. On average, the Burstone g r o u p demonstrated 1.5 m m (SD 1.28 m m ) of u p p e r incisor intrusion and 1.7 m m (SD 1.90 m m ) of lower incisor intrusion. An average of 1 m m (SD 1.55 m m ) of intrusion and proclination ( m e a n 5.7 °, SD 8.9 °) of the lower incisor accounted for some of the overbite correction in the CAW group. Although the t r e a t m e n t groups were not randomized, these findings have i m p o r t a n t implications regarding treatment effects, vis-a-vis treatment objectives.
Root Resorption and Incisor Intrusion At this point, we have discussed the forces and m o m e n t s involved in incisor intrusion and the forces appropriate for their effective and efficient movement. We have discussed the value of segmentation as c o m p a r e d with continuous arch mechanics. It is necessary to address adverse effects of mechanics used to correct deep overbite. Melsen et aP 4 r e p o r t e d root resorption of the u p p e r incisors o f between 1 to 3 m m in their sample of 30 adults who had incisor intrusion as described previously. DiVencenzo and Winn a~ also r e p o r t e d some root resorption in most cases. McFadden et a116 r e p o r t e d an average a m o u n t of root resorption of 1.84 m m for maxillary incisors and 0.61 m m for m a n d i b u l a r incisors in a sample of 38 deep-bite cases treated with utility arches for incisor intrusion according to the Bioprogressive technique. No relationship was f o u n d between the degree of incisor intrusion and the degree of root resorption. D e m a u t and De Munck 17 r e p o r t e d m e a n resorption of 18% (approximately 2.5 ram) of the original root length of the maxillary incisors in a sample of 20 patients (only 3 patients older than 20 years) following intrusion mechanics. Segmental mechanics was used to avoid incisor proclination, for an average of 29 weeks. No relationship was f o u n d between the a m o u n t of intrusion or the duration of intrusion and the degree of resorp-
Control of Ove~t~iteby Dental Movements
tion. It is important to note that the forces used in these studies was not reported. The potential risk of root resorption, and particularly the forces applied, must be considered when incisor intrusion is planned for a particular patient. In addition, it is important to note that root resorption is prevalent following orthodontic treatm e n t in general, ls,m It is therefore possible that root resorption may be more a function of the forces used rather than the m e c h a n o t h e r a p y chosen for overbite correction.
Increasing the Vertical Dimension An opening rotation of the mandible often occurs as a side effect of fixed appliance treatment. If treatment is p e r f o r m e d in growing patients, tile a m o u n t and direction of growth may compensate for the adverse effects of the mechanics, so that treatment o u t c o m e is not significantly compromised. To illustrate the point, cervical extraoral traction with fixed appliances for correction of Class II malocclusions has an extrusive c o m p o n e n t of force. Similarly, mechanotherapy that attempts to m o v e / t i p posterior teeth distally tends to rotate the mandible open,
Figure3.
47
thereby increasing the vertical dimension. Class II and Class III intermaxillary elastics have a vertical as well as horizontal vector of force, which tend to extrude the posterior teeth. In Class II malocclusions, this may be troublesome, because the opening rotation of the mandible makes Class II correction more difficult. In Class III malocclusions, an o p e n i n g rotation of the mandible can be advantageous in p r o d u c i n g a less prognathic mandible; however, many Class III malocclusions exhibit an open bite. The use of many functional appliances to correct Class II malocclusions in growing patients relies on an anterior bite plate to enhance eruption of the posterior teeth. Hans et al 2° c o m p a r e d the cephalometric changes achieved between 45 growing patients who received cervical h e a d g e a r / t a n d e m mechanics (Class III elastics to a lower arch wire) and 50 patients who received a bionator appliance. A group of 95 cases from the Bolton study served as untreated controls. In the fixed-appliance group, the overbite was corrected partly by u p p e r incisor intrusion (as a consequence of using an incisor to molar 2 × 4 intrusion arch wire), and partly by vertical mandibular skeletal change (growth), in
An example of a deep overbite (A) in which a removable anterior bite plate was used (B). The posterior teeth are separated when the bite plate is worn (C). Eruption/extrusion of the posterior teeth following a few months of bite plate wear (D).
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Sadowsky and SeUke
e q u a l p r o p o r t i o n s . T h e o v e r b i t e in t h e b i o n a t o r g r o u p was c o r r e c t e d a l m o s t exclusively by m a n d i b u l a r skeletal b i t e o p e n i n g (which p r e s u m a b l y i n c l u d e d m o l a r e r u p t i o n ) . T h e r e was g r e a t e r i n c r e a s e in t h e m a n d i b u l a r p l a n e a n g l e t h a n in t h e f i x e d - a p p l i a n c e g r o u p . A slight i n h i b i t i o n o f vertical d e v e l o p m e n t o f t h e u p p e r a n d l o w e r incisors was also f o u n d (relative i n t r u s i o n ) . T h e effect o f an a n t e r i o r bite plate, w h i c h allows s p o n t a n e o u s e r u p t i o n o f t h e p o s t e r i o r teeth, is well u n d e r s t o o d . I f t h e t r e a t m e n t objective is to allow (or p r o m o t e ) e r u p t i o n o f t h e p o s t e r i o r teeth, t h e n a n a n t e r i o r bite p l a t e can be used either before placement of fixed applia n c e s o r d u r i n g f i x e d - a p p l i a n c e t r e a t m e n t (Fig 3). Even t h o u g h a r c h wires m a y b e p r e s e n t , t h e p o s t e r i o r t e e t h will e r u p t . E r u p t i o n / e x t r u s i o n o f t h e p o s t e r i o r t e e t h will also i n c r e a s e t h e vertical d i m e n s i o n o f t h e face, w h i c h s h o u l d b e anticip a t e d a n d b e a p a r t o f t h e t r e a t m e n t objectives. This a p p r o a c h to o v e r b i t e c o r r e c t i o n is o f t e n u s e d in g r o w i n g p a t i e n t s especially with brachyfacial ( s t r o n g m u s c l e ) p a t t e r n s . However, D a h l a n d I ~ o g s t a d 2~ d e m o n s t r a t e d a n i n c r e a s e in vertical d i m e n s i o n o f b e t w e e n 1.8 m m a n d 4.7 m m in a s a m p l e o f 20 a d u l t p a t i e n t s with p a t h o l o g i c a l a t t r i t i o n o f t h e a n t e r i o r t e e t h f o l l o w i n g t h e use o f a p a r t i a l f i x e d splint. U s i n g m e t a l l i c i m p l a n t s and cephalometric radiographs, they found that p o s t e r i o r t o o t h e r u p t i o n a c c o u n t e d f o r 1.47 m m ( a p p r o x i m a t e l y 6 0 % ) , a n d 1.05 m m was attribu t e d to a n t e r i o r t o o t h i n t r u s i o n . T h e splints w e r e w o r n full-time f o r 6 to 14 m o n t h s , a l t h o u g h m o s t o f t h e effects h a d t a k e n p l a c e a f t e r 2 m o n t h s . T h e y o u n g e s t subjects t e n d e d to show m o r e p o s t e r i o r t o o t h e x t r u s i o n . I n a 5.5-year follow-up study z2 f o l l o w i n g p l a c e m e n t o f crowns o n t h e t e e t h , t h e y r e p o r t e d t h a t 12 o f 19 subjects h a d p r a c t i c a l l y c o m p l e t e l y stable vertical relations o f 1.9 m m o n average. T h e r e was l a r g e i n d i v i d u a l v a r i a t i o n , b u t n o p a t i e n t r e t u r n e d to t h e o r i g i n a l vertical d i m e n s i o n .
Conclusion I n g e n e r a l , full f i x e d - a p p l i a n c e t h e r a p y t e n d s to rotate the mandible open and increases anterior face h e i g h t . I f this is a d e s i r a b l e t r e a t m e n t objective, t h e n t r a d i t i o n a l leveling m e c h a n i c s a n d less p r e c i s e c o n t r o l o f forces a n d m o m e n t s c a n b e used. However, if i n c i s o r i n t r u s i o n is i n d i c a t e d a n d m o l a r e x t r u s i o n is to b e a v o i d e d ,
m o r e p r e c i s e m e c h a n o t h e r a p y is necessary. It is a p p a r e n t t h a t s e g m e n t a t i o n l e n d s the g r e a t e s t p r o g n o s i s f o r success. I m p o r t a n t l y , a n a p p r e c i a t i o n o f t h e forces being applied irrespective of the mechanot h e r a p y c h o s e n is essential for m i n i m i z i n g a n c h o r age loss, r o o t r e s o r p t i o n , a n d o t h e r adverse sequellae. The challenge for the modern ortho d o n t i s t is to i n s t i t u t e m e c h a n o t h e r a p y t h a t w o u l d give t h e b e s t o p p o r t u n i t y f o r a successful t r e a t m e n t o u t c o m e while r e m a i n i n g m i n d f u l o f the biologic mechanisms and the unpredictability o f i n d i v i d u a l p a t i e n t r e s p o n s e .
References 1. Ricketts RM. Bioprogressive therapy as an answer to orthodontic needs. Part I. AmJ Orthod 1969;70:241-268. 2. Mitchell DL, Stewart WL. Documented leveling of the lower arch using metallic implants for reference. Am J Orthod 1973;63:526-532. 3. Braun S, Hnat WP, Johnson BE. The curve of Spee revisited. Am J Orthod Dentofac Orthop 1996;110:206210. 4. Chung TS, Sadowsky PL, Wallace DD, et al. A threedimensional analysis of mandibular arch changes following curve of Spee leveling in nonextraction orthodontic treatment. IntJ Adult Orthod Orthognath Surg 1997;12: 109-121. 5. MQabandi AK, Sadowsky C. Leveling the curve of Spee using round compared with rectangular arch wire. Am J Orthod Dentofac Orthop 1999;116:522-529. 6. Mulligan TE Common Sense Mechanics In Everyday Orthodontics. Mulligan TF (ed). Phoenix, AZ, CSM Publishing, 1998, pp 53-57. 7. Otto RL, AnholmJM, Engel GA. A comparative analysis of intrusion of incisor teeth achieved in adults and children according to facial type. AmJ Orthod Dentofac Orthop 1980;77:437446. 8. Dake ML, Sinclair PM. A comparison of the Ricketts and Tweed-type arch leveling techniques. AmJ Orthod Dentofac Orthop 1989;95:72-78. 9. Davidovitch M, Rebellato J. Two-couple orthodontic appliance systems utility arches: A two-couple intrusion arch. Semin Orthod 1995;1:25-30. 10. Burstone CR. Deep overbite correction by intrusion. Am J Orthod 1977;72:1-22. 11. Schroff B, Yoon WM, Lindauer sJ, et al. Simultaneous intrusion and retraction using a three-piece base arch. Angle Orthod 1997;67:455-462. 12. Rajcich MM, Sadowsky C. Efficacy of intraarach mechanics using differential moments for achieving anchorage control in extraction cases. Am J Orthod Dentofac Orthop 1997;112:441-448. 13. DeVincenzo JE Winn MW. Maxillary incisor intrusion and facial growth. Angle Orthod 1987;57:279-289.
Control of Overbite by Dental Movements
14. Melsen B, Agerbaek M, Markenstam G. Intrusion of incisors in adult patients with marginal bone loss. A m J Orthod Dentofac Orthop 1989;96:232-241. 15. Weiland FJ, Bantleon HP, Droschl H. Evaluation of continuous arch and segmented arch levelling techniques in adult patients--A clinical study. Am J Orthod Dentofac Orthop 1996;110:647-652. 16. McFadden WM, Engstrom C, Engstrom H, et al. A study of the relationship between incisor intrusion and root shortening. Pan J Orthod Dentofac Orthop 1989;96:390396. 17. Dermaut LR, De Munck A. Apical root resorption of upper incisors caused by intrusive tooth movement: A radiographic study. Am J Orthod Dentofac Orthop 1986;90:321-326. 18. Brezniak N, Wasserstein A. Root resorption after orth-
19.
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21.
22.
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odontic treatment: Part 1, literature review. AmJ Orthod Dentofac Orthop 1993;103:62-75. Brezniak N, Wasserstein A. Root resorption after orthodontic treatment: Part 2, literature review. AmJ Orthod Dentofac Orthop 1993;103:138-146. Hans MJ, Kishiyama C, Parker SH, et al. Cephalometric evaluation of two treatment strategies for deep overbite correction. Angle Orthod 1994;64:265-276. Dahl BL, Krogstad O. The effect of a partial bite raising splint on the occlusal face height. Acta Odontol Scand 1982;40:17-24. Dahl BL, Krogstad O. Long-term observations of an increased occlusal face height obtained by a combined orthodontic-prosthetic approach.J Oral Rehabi11985;12: 173-176.
eep overbite is a c o m m o n feature of m a n y malocclusions. O n e of the objectives of orthodontic t r e a t m e n t is to establish a n o r m a l overbite, and in cases with a severe overbite, to overcorrect the overbite in anticipation of posttreatment relapse. In defining t r e a t m e n t objectives, it is i m p o r t a n t to specifically identify whether the maxillary and m a n d i b u l a r incisors must be i n t r u d e d or whether the posterior teeth must be extruded, or any combination of the above. In the Bioprogressive philosophy, overbite is corrected by intruding the offending incisors to the "functional occlusal plane" estab-
D
From the Department of Orthodontics, University of Illinois at Chicago, Chicago, IL. Address correspondence to Cyril Sadowsk); BD& MS, Department of Orthodontics, University of Illinois at Chicago, 801 S Paulina Street, Chicago, IL 60612. Copyright © 2000 by !~B. Saunders Compasy 1073-8746/00/0601-0005510. 00/0
lished by the posterior teeth. 1 Many o r t h o d o n tists use the smile line to d e t e r m i n e which incisors to intrude. Others believe that that ability to intrude incisors is a myth and that overbite correction must occur by selective eruption of posterior teeth, or the prevention of incisor eruption with ongoing growth. Although overbite correction is a controversial subject, diagnostic systems are available to aid in developing patient-specific treatment objectives. T h e p u r p o s e of this article is to describe the various t r e a t m e n t modalities currently being used by the profession for overbite correction and their effectiveness in p r o d u c i n g the desired outcome. Full-Arch
Mechanics
Most orthodontists follow a historical a p p r o a c h to treatment. They begin by placing bands a n d brackets on all of the teeth in both arches.
Seminars in Orthodontics, Vol 6, No 1 (March), 2000: pp 43-49
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Leveling the mandibular curve of Spee and establishing a compensating curve in the maxillary arch leads to overbite correction as part of the process. Leveling begins with stainless-steel or nickel-titanium arch wires of small crosssection or larger-diameter rectangular arch wires of nickel-titanium or t i t a n i u m - m o l y b d e n u m (TMA) alloys. The purpose of these initial wires is to increase the range of action and p r o d u c e relatively gentle forces and moments. Over time, the clinician works toward progressively heavier (stiffer) wires to achieve control of the teeth in all dimensions. A potential adverse effect of such continuous arch wire mechanics is to procline the incisors leading to the leveling of the incisor tip relative to the occlusal plane (relative intrusion). Mitchell and Stewart 2 reported on six patients who were studied with metallic implants in whom the curve of Spee was leveled with continuous arch wires. The incisors were proclined with relative intrusion, the premolars were extruded, and the terminal molars were slightly extruded. With leveling mechanics, an opening rotation of the mandible may also occur. The cumulative effect is that the overbite decreases. It is generally assumed that in leveling the curve of Spee, arch depth will increase as a result of the need for space to level the curve. However, it has been suggested that additional arch circumference is not n e e d e d to level the curve of Spee. 3,4 Incisor proclination that occurs with traditional leveling is explained by the fact that the forces are labial to the center of resistance of the incisors, resulting in a labial crown-tipping moment. As a result, some advocate the use of initial (resilient) rectangular arch wires in an attempt to control the latter. However, in a recent, prospective, randomized, clinical trial, 5 no difference was f o u n d in the degree of incisor proclination when comparing two samples of patients in whom the curve of Spee was levelled using either r o u n d or rectangular arch wires. If the above effects are desired in a given case, then continuous arch wire mechanics may be appropriate. However, if actual incisor intrusion without proclination is desired, then continuous arch mechanics as described above should be avoided.
Utility Arches Circumventing the premolar and canine teeth with an arch wire to intrude incisors creates an opportunity for light intrusive forces. The Bioprogressive technique incorporates the classic utility arch 1 to apply 60 g of force to intrude lower incisors and 100 g for the u p p e r incisors (Fig 1). Mulligan 6 advocated using a similarly shaped r o u n d arch wire to intrude incisors. There is, however, the potential for incisor proclination that results from the line of force of the arch wire being labial to the center of resistance of the four incisors. Otto et al 7 described the treatment effects of a lower utility arch wire according to the Bioprogressive technique in 24 adults and 31 children having deep overbite. An average of 2.5 m m of actual lower incisor intrusion was f o u n d in the adult group and 2 m m in the child group. There was some proclination of incisors in both groups. Some holding of the incisors against vertical growth (relative intrusion) contributed to overbite correction in the child group. The degree of intrusion was not correlated with age, nor was it influenced by facial type. Dake and Sinclair s c o m p a r e d 30 deep-bite low-angle nonextraction cases treated by Ricketts, to a similar group treated by Schudy in which Class III elastics were added to continuous arch wires while leveling the curve of Spee in the traditional way. The objective in the Shudy group was leveling the curve of Spee without advancing or intruding lower incisors (Tweed technique). The Ricketts group showed more proclination of the lower incisors than the Schudy group (>5 ° of proclination in 64% of the Ricketts cases compared with 40% of Shudy cases). The Ricketts group also demonstrated more posttreatment
Figure 1. Example of a classic lower utility arch wire (Ricketts) extending from the molars and engaging the incisors. The upper arch wire is an example of an advancement utility wire that can also incorporate activation for incisor intrusion.
Control of Overbite by Dental Movements
uprighting and overbite relapse (note that the overbite was intentionally overcorrected in the Ricketts group). The Ricketts group also demonstrated an average of 1.2 m m of actual intrusion of the lower incisors in addition to holding against growth, which was relatively stable an average of 4 years posttreatment. Both groups p r o d u c e d similar amounts of distal tipping of the mandibular molars as well as e x t r u s i o n / e r u p tion, the latter being relatively stable posttreatment. It is also argued that the utility arch produces forces and m o m e n t s that are indeterminate, making prediction of tooth movements uncertain. 9 If square or rectangular wires are used in an attempt to control incisor proclination by incorporating labial root torque, additional moments are created that simultaneously increase the intrusion force. The significant rotational m o m e n t on the molars that occurs in response to the depressive force on the incisor teeth can provide adverse effects contrary to the treatment needs of the patient. To counteract these, a sectional wire from the molar to one or more teeth anterior to the molar is used to control molar position. This approach, described by Burstone in 1977, l° allows the clinician to maintain posterior occlusal relations and angulations while the incisors are depressed to the level dictated by the treatment objectives. With segmentation of the arches to achieve overbite correction, the forces and m o m e n t s on the incisors and molars in all dimensions can be understood and controlled.
Segmental Arch Mechanics A statically determinate technique as originally advocated by Burstone ~° is available to control the forces and moments for incisor intrusion, v This involves a segmented arch wire engaging the four incisors as a unit, with the intrusive force generated by a base arch wire as a pure force (Fig 2), whose line of action can be adjusted to pass through the center of resistance of the fourtooth segment if so desired. Therefore, the m o m e n t of the intrusive force can be controlled to avoid incisor proclination as well as mesiodistal angular changes (second-order moments) particularly involving the lateral incisors. A transpalatal arch can also be added for additional
45
Figure 2. An example of the Burstone segmental technique for incisor intrusion. Note the segmental buccal wires and segmental anterior wire. The intrusion base arch is tied to the anterior segment. (Reprinted with permission from Burstone CJ, van Steenbergen E, Hanley KJ. Modern Edgewire Mechanics and the Segmented Arch Technique. Department of Orthodontics, University of Connecticut Health Center, Farmington, CT. Ormco Corporation, Monrovia, CA, 1995, pp 40-41.) molar control. It has been shown that approximately 60 g of force is n e e d e d to intrude the lower incisors and 100 g to intrude the u p p e r incisors. The distal crown mesial root m o m e n t on the molars is approximately 1,800 g-mm for the lower molars and 3,000 g-mm for the u p p e r molars, based on an average distance of 30 m m from molars to incisors. The molar rotational m o m e n t can be further controlled by placing posterior segmental arch wires as described previously. The distal crown tipping of the molar as seen with a 2 × 4 (incisors to molar) set-up may be used to advantage in some cases for Class II correction 6 or to establish maximum anchorage J2; it can also be controlled by adding posterior segments. The extrusive forces to the molars or posterior segments are usually counteracted by forces of occlusion in all but the most "weakmuscled" pattern. Segmentation is the key elem e n t to achieving the specific objectives of the case with a reasonable expectation for the desired response.
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Forces and Intrusion Any discussion of overbite correction must include the forces applied. It has b e e n well established that tooth m o v e m e n t is a histological p h e n o m e n o n that involves osteblasts (lay down bone) and osteoclasts (remove bone). T h e stimulation of cellular activity necessary for depression as well as adverse and pathological sequellae can be attributed to some degree to the forces p r o d u c e d by the mechanotherapy. DiVincenzo and Winn a3 r e p o r t e d on a sample of 25 growing females who received an arch wire extending f r o m the maxillary molars to the four incisors for the purpose of incisor intrusion. T h e molar anchorage was reinforced with a transpalatal wire and anterior and posterior acrylic pads that were able to prevent m o l a r tipping and extrusion. An intrusive force of approximately 60 g (_+15 g) was delivered for approximately 6 months using a 0.016 × 0.022 arch wire engaging the four incisors with passive torque and cinched distal to the m o l a r tubes. C o m p a r e d with the m a t c h e d control group, a m e a n of 2 m m o f actual maxillary incisor intrusion and 15 ° of palatal root torque was reported. Based on initial trials, it was f o u n d that the m o l a r palatal anchorage appliance could s u p p o r t approximately 65 g of intrusive force before adverse m o v e m e n t of the a n c h o r unit was observed. This suggests that the usual r e c o m m e n d a t i o n of 100 g of intrusive force for the four incisors, which may p r o d u c e m o r e effective intrusion, must be closely monitored with regard to the reaction of the anchorage units. Melsen et aP 4 r e p o r t e d on 30 adult patients with marginal b o n e loss and deep overbite for w h o m maxillary incisor intrusion was p e r f o r m e d using the Burstone technique. T h e i r base arch applied between 10 to 20 g of intrusion force per tooth in 22 patients. A m u c h smaller sample received either 0.016 × 0.016 Ricketts utility arches (4 patients),J-hook h e a d g e a r (1 patient), or 0.017 X 0.025 l o o p e d continuous arch (3 patients). True intrusion (measured at the center of resistance) of between 0 and 3 m m was achieved. Intrusion was best p e r f o r m e d when forces were low (5-15 grams per tooth) and applied t h r o u g h the center of resistance. Weiland et a115 c o m p a r e d the t r e a t m e n t effects of continuous arch wire mechanics (CAW) with that of the s e g m e n t e d technique (Burst-
one) for correcting malocclusions exhibiting d e e p overbite and low m a n d i b u l a r plane angle in a sample of 50 adults. T h e overbite correction in the CAW g r o u p was achieved by m o l a r extrusion with posterior rotation of the mandible, while the Burstone g r o u p d e m o n s t r a t e d true incisor intrusion (measured at the center of resistance) without significant molar extrusion. On average, the Burstone g r o u p demonstrated 1.5 m m (SD 1.28 m m ) of u p p e r incisor intrusion and 1.7 m m (SD 1.90 m m ) of lower incisor intrusion. An average of 1 m m (SD 1.55 m m ) of intrusion and proclination ( m e a n 5.7 °, SD 8.9 °) of the lower incisor accounted for some of the overbite correction in the CAW group. Although the t r e a t m e n t groups were not randomized, these findings have i m p o r t a n t implications regarding treatment effects, vis-a-vis treatment objectives.
Root Resorption and Incisor Intrusion At this point, we have discussed the forces and m o m e n t s involved in incisor intrusion and the forces appropriate for their effective and efficient movement. We have discussed the value of segmentation as c o m p a r e d with continuous arch mechanics. It is necessary to address adverse effects of mechanics used to correct deep overbite. Melsen et aP 4 r e p o r t e d root resorption of the u p p e r incisors o f between 1 to 3 m m in their sample of 30 adults who had incisor intrusion as described previously. DiVencenzo and Winn a~ also r e p o r t e d some root resorption in most cases. McFadden et a116 r e p o r t e d an average a m o u n t of root resorption of 1.84 m m for maxillary incisors and 0.61 m m for m a n d i b u l a r incisors in a sample of 38 deep-bite cases treated with utility arches for incisor intrusion according to the Bioprogressive technique. No relationship was f o u n d between the degree of incisor intrusion and the degree of root resorption. D e m a u t and De Munck 17 r e p o r t e d m e a n resorption of 18% (approximately 2.5 ram) of the original root length of the maxillary incisors in a sample of 20 patients (only 3 patients older than 20 years) following intrusion mechanics. Segmental mechanics was used to avoid incisor proclination, for an average of 29 weeks. No relationship was f o u n d between the a m o u n t of intrusion or the duration of intrusion and the degree of resorp-
Control of Ove~t~iteby Dental Movements
tion. It is important to note that the forces used in these studies was not reported. The potential risk of root resorption, and particularly the forces applied, must be considered when incisor intrusion is planned for a particular patient. In addition, it is important to note that root resorption is prevalent following orthodontic treatm e n t in general, ls,m It is therefore possible that root resorption may be more a function of the forces used rather than the m e c h a n o t h e r a p y chosen for overbite correction.
Increasing the Vertical Dimension An opening rotation of the mandible often occurs as a side effect of fixed appliance treatment. If treatment is p e r f o r m e d in growing patients, tile a m o u n t and direction of growth may compensate for the adverse effects of the mechanics, so that treatment o u t c o m e is not significantly compromised. To illustrate the point, cervical extraoral traction with fixed appliances for correction of Class II malocclusions has an extrusive c o m p o n e n t of force. Similarly, mechanotherapy that attempts to m o v e / t i p posterior teeth distally tends to rotate the mandible open,
Figure3.
47
thereby increasing the vertical dimension. Class II and Class III intermaxillary elastics have a vertical as well as horizontal vector of force, which tend to extrude the posterior teeth. In Class II malocclusions, this may be troublesome, because the opening rotation of the mandible makes Class II correction more difficult. In Class III malocclusions, an o p e n i n g rotation of the mandible can be advantageous in p r o d u c i n g a less prognathic mandible; however, many Class III malocclusions exhibit an open bite. The use of many functional appliances to correct Class II malocclusions in growing patients relies on an anterior bite plate to enhance eruption of the posterior teeth. Hans et al 2° c o m p a r e d the cephalometric changes achieved between 45 growing patients who received cervical h e a d g e a r / t a n d e m mechanics (Class III elastics to a lower arch wire) and 50 patients who received a bionator appliance. A group of 95 cases from the Bolton study served as untreated controls. In the fixed-appliance group, the overbite was corrected partly by u p p e r incisor intrusion (as a consequence of using an incisor to molar 2 × 4 intrusion arch wire), and partly by vertical mandibular skeletal change (growth), in
An example of a deep overbite (A) in which a removable anterior bite plate was used (B). The posterior teeth are separated when the bite plate is worn (C). Eruption/extrusion of the posterior teeth following a few months of bite plate wear (D).
48
Sadowsky and SeUke
e q u a l p r o p o r t i o n s . T h e o v e r b i t e in t h e b i o n a t o r g r o u p was c o r r e c t e d a l m o s t exclusively by m a n d i b u l a r skeletal b i t e o p e n i n g (which p r e s u m a b l y i n c l u d e d m o l a r e r u p t i o n ) . T h e r e was g r e a t e r i n c r e a s e in t h e m a n d i b u l a r p l a n e a n g l e t h a n in t h e f i x e d - a p p l i a n c e g r o u p . A slight i n h i b i t i o n o f vertical d e v e l o p m e n t o f t h e u p p e r a n d l o w e r incisors was also f o u n d (relative i n t r u s i o n ) . T h e effect o f an a n t e r i o r bite plate, w h i c h allows s p o n t a n e o u s e r u p t i o n o f t h e p o s t e r i o r teeth, is well u n d e r s t o o d . I f t h e t r e a t m e n t objective is to allow (or p r o m o t e ) e r u p t i o n o f t h e p o s t e r i o r teeth, t h e n a n a n t e r i o r bite p l a t e can be used either before placement of fixed applia n c e s o r d u r i n g f i x e d - a p p l i a n c e t r e a t m e n t (Fig 3). Even t h o u g h a r c h wires m a y b e p r e s e n t , t h e p o s t e r i o r t e e t h will e r u p t . E r u p t i o n / e x t r u s i o n o f t h e p o s t e r i o r t e e t h will also i n c r e a s e t h e vertical d i m e n s i o n o f t h e face, w h i c h s h o u l d b e anticip a t e d a n d b e a p a r t o f t h e t r e a t m e n t objectives. This a p p r o a c h to o v e r b i t e c o r r e c t i o n is o f t e n u s e d in g r o w i n g p a t i e n t s especially with brachyfacial ( s t r o n g m u s c l e ) p a t t e r n s . However, D a h l a n d I ~ o g s t a d 2~ d e m o n s t r a t e d a n i n c r e a s e in vertical d i m e n s i o n o f b e t w e e n 1.8 m m a n d 4.7 m m in a s a m p l e o f 20 a d u l t p a t i e n t s with p a t h o l o g i c a l a t t r i t i o n o f t h e a n t e r i o r t e e t h f o l l o w i n g t h e use o f a p a r t i a l f i x e d splint. U s i n g m e t a l l i c i m p l a n t s and cephalometric radiographs, they found that p o s t e r i o r t o o t h e r u p t i o n a c c o u n t e d f o r 1.47 m m ( a p p r o x i m a t e l y 6 0 % ) , a n d 1.05 m m was attribu t e d to a n t e r i o r t o o t h i n t r u s i o n . T h e splints w e r e w o r n full-time f o r 6 to 14 m o n t h s , a l t h o u g h m o s t o f t h e effects h a d t a k e n p l a c e a f t e r 2 m o n t h s . T h e y o u n g e s t subjects t e n d e d to show m o r e p o s t e r i o r t o o t h e x t r u s i o n . I n a 5.5-year follow-up study z2 f o l l o w i n g p l a c e m e n t o f crowns o n t h e t e e t h , t h e y r e p o r t e d t h a t 12 o f 19 subjects h a d p r a c t i c a l l y c o m p l e t e l y stable vertical relations o f 1.9 m m o n average. T h e r e was l a r g e i n d i v i d u a l v a r i a t i o n , b u t n o p a t i e n t r e t u r n e d to t h e o r i g i n a l vertical d i m e n s i o n .
Conclusion I n g e n e r a l , full f i x e d - a p p l i a n c e t h e r a p y t e n d s to rotate the mandible open and increases anterior face h e i g h t . I f this is a d e s i r a b l e t r e a t m e n t objective, t h e n t r a d i t i o n a l leveling m e c h a n i c s a n d less p r e c i s e c o n t r o l o f forces a n d m o m e n t s c a n b e used. However, if i n c i s o r i n t r u s i o n is i n d i c a t e d a n d m o l a r e x t r u s i o n is to b e a v o i d e d ,
m o r e p r e c i s e m e c h a n o t h e r a p y is necessary. It is a p p a r e n t t h a t s e g m e n t a t i o n l e n d s the g r e a t e s t p r o g n o s i s f o r success. I m p o r t a n t l y , a n a p p r e c i a t i o n o f t h e forces being applied irrespective of the mechanot h e r a p y c h o s e n is essential for m i n i m i z i n g a n c h o r age loss, r o o t r e s o r p t i o n , a n d o t h e r adverse sequellae. The challenge for the modern ortho d o n t i s t is to i n s t i t u t e m e c h a n o t h e r a p y t h a t w o u l d give t h e b e s t o p p o r t u n i t y f o r a successful t r e a t m e n t o u t c o m e while r e m a i n i n g m i n d f u l o f the biologic mechanisms and the unpredictability o f i n d i v i d u a l p a t i e n t r e s p o n s e .
References 1. Ricketts RM. Bioprogressive therapy as an answer to orthodontic needs. Part I. AmJ Orthod 1969;70:241-268. 2. Mitchell DL, Stewart WL. Documented leveling of the lower arch using metallic implants for reference. Am J Orthod 1973;63:526-532. 3. Braun S, Hnat WP, Johnson BE. The curve of Spee revisited. Am J Orthod Dentofac Orthop 1996;110:206210. 4. Chung TS, Sadowsky PL, Wallace DD, et al. A threedimensional analysis of mandibular arch changes following curve of Spee leveling in nonextraction orthodontic treatment. IntJ Adult Orthod Orthognath Surg 1997;12: 109-121. 5. MQabandi AK, Sadowsky C. Leveling the curve of Spee using round compared with rectangular arch wire. Am J Orthod Dentofac Orthop 1999;116:522-529. 6. Mulligan TE Common Sense Mechanics In Everyday Orthodontics. Mulligan TF (ed). Phoenix, AZ, CSM Publishing, 1998, pp 53-57. 7. Otto RL, AnholmJM, Engel GA. A comparative analysis of intrusion of incisor teeth achieved in adults and children according to facial type. AmJ Orthod Dentofac Orthop 1980;77:437446. 8. Dake ML, Sinclair PM. A comparison of the Ricketts and Tweed-type arch leveling techniques. AmJ Orthod Dentofac Orthop 1989;95:72-78. 9. Davidovitch M, Rebellato J. Two-couple orthodontic appliance systems utility arches: A two-couple intrusion arch. Semin Orthod 1995;1:25-30. 10. Burstone CR. Deep overbite correction by intrusion. Am J Orthod 1977;72:1-22. 11. Schroff B, Yoon WM, Lindauer sJ, et al. Simultaneous intrusion and retraction using a three-piece base arch. Angle Orthod 1997;67:455-462. 12. Rajcich MM, Sadowsky C. Efficacy of intraarach mechanics using differential moments for achieving anchorage control in extraction cases. Am J Orthod Dentofac Orthop 1997;112:441-448. 13. DeVincenzo JE Winn MW. Maxillary incisor intrusion and facial growth. Angle Orthod 1987;57:279-289.
Control of Overbite by Dental Movements
14. Melsen B, Agerbaek M, Markenstam G. Intrusion of incisors in adult patients with marginal bone loss. A m J Orthod Dentofac Orthop 1989;96:232-241. 15. Weiland FJ, Bantleon HP, Droschl H. Evaluation of continuous arch and segmented arch levelling techniques in adult patients--A clinical study. Am J Orthod Dentofac Orthop 1996;110:647-652. 16. McFadden WM, Engstrom C, Engstrom H, et al. A study of the relationship between incisor intrusion and root shortening. Pan J Orthod Dentofac Orthop 1989;96:390396. 17. Dermaut LR, De Munck A. Apical root resorption of upper incisors caused by intrusive tooth movement: A radiographic study. Am J Orthod Dentofac Orthop 1986;90:321-326. 18. Brezniak N, Wasserstein A. Root resorption after orth-
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odontic treatment: Part 1, literature review. AmJ Orthod Dentofac Orthop 1993;103:62-75. Brezniak N, Wasserstein A. Root resorption after orthodontic treatment: Part 2, literature review. AmJ Orthod Dentofac Orthop 1993;103:138-146. Hans MJ, Kishiyama C, Parker SH, et al. Cephalometric evaluation of two treatment strategies for deep overbite correction. Angle Orthod 1994;64:265-276. Dahl BL, Krogstad O. The effect of a partial bite raising splint on the occlusal face height. Acta Odontol Scand 1982;40:17-24. Dahl BL, Krogstad O. Long-term observations of an increased occlusal face height obtained by a combined orthodontic-prosthetic approach.J Oral Rehabi11985;12: 173-176.