CASE REPORT
Use of Forsus fatigue-resistant device in a patient with Class I malocclusion and mandibular incisor agenesis Ruofang Zhang,a Yuxing Bai,b and Song Lic Beijing, China
Orthodontic treatment in patients with congenitally missing teeth can be challenging. In this case report, we describe the treatment of a 15-year-old girl with mild dental crowding and 2 congenitally missing mandibular incisors. The Forsus fatigue-resistant device was used to move the mandible and the mandibular teeth forward. A new balanced and stable occlusion was achieved after treatment. When the treatment plan includes moving the mandibular teeth forward in a patient with mandibular incisor agenesis, the profile and the skeletal and dental features should be carefully scrutinized to ensure that balanced and esthetic results are achieved. (Am J Orthod Dentofacial Orthop 2014;145:817-27)
H
ypodontia is the congenital absence of at least 1 tooth.1 Orthodontic treatment in patients with congenitally missing teeth can be challenging. The prevalence of hypodontia varies among different ethnicities. The most commonly missing teeth for white populations are the maxillary lateral incisors and the second premolars (third molars excluded).1,2 However, in Chinese, Korean, and Japanese populations, agenesis of the mandibular incisors is more frequently observed.3-5 Mandibular incisor agenesis might be caused by heredity, anomalies of the mandibular symphysis, dentition reduction of an evolutionary trend, or localized inflammation.2 Patients with congenitally missing mandibular incisors usually show retroclination of the mandibular incisors and reduction of the mandibular alveolar bone area.6 Three treatment modalities are common for patients with agenesis of the mandibular incisors. One involves creating space for a fixed denture or an implant restoration, which could help achieve a satisfactory
From the Department of Orthodontics, School of Stomatology, Capital Medical University, Beijing, China. a Associate professor. b Professor and dean. c Professor and vice dean. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Address correspondence to: Song Li, Department of Orthodontics, School of Stomatology, Capital Medical University, Beijing 100050, China; e-mail, [email protected]. Submitted, June 2012; revised and accepted, August 2013. 0889-5406/$36.00 Copyright Ó 2014 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2013.08.021
occlusion. Another choice is extraction of the maxillary incisors or premolars to reduce the severe deep overjet by retracting the anterior teeth. The third option is to create a new balanced occlusion by closing the spaces and moving the mandibular canines and the posterior teeth forward. The Forsus fatigue-resistant device (FRD; 3M Unitek, Monrovia, Calif) is a semirigid fixed functional appliance. It is used most frequently for treating Class II patients. As claimed by the manufacturer, the Forsus FRD can exert consistent forces and is resistant to fracture. It consists of superelastic nickel-titanium coil springs that can be assembled at chairside. Recent studies have reported that the Forsus FRD can restrain sagittal growth of the maxilla, stimulate mandibular growth, and induce mesial movement of the mandibular teeth and distal movement of the maxillary molars.7 We present the treatment of a patient with a Class I malocclusion with 2 congenitally missing mandibular incisors. The treatment plan involved forward movement of the mandible and the mandibular teeth to reduce the deep overjet using the Forsus FRD appliance.
DIAGNOSIS AND ETIOLOGY
The patient was a 15-year-old girl with a chief complaint of dental crowding. She was in good health with no significant systemic medical history. No oral habits and no temporomandibular joint (TMJ) symptoms were noted. The pretreatment facial frontal photographs showed a well-balanced and symmetric face (Fig 1). Her profile 817
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Fig 1. Pretreatment facial and intraoral photographs.
was straight with competent lips, a good chin-throat soft-tissue line, a proper nasolabial angle, and normal vertical proportions. The molar relationships were Class I on both sides. The anterior overbite was deep, with the maxillary incisors overlapping the mandibular incisors by 50%. Anterior overjet was 3 mm. Her maxillary midline was coincident with the facial midline, and the mandibular midline was shifted 1 mm to the left. Both arch forms were U-shaped. There was 5.5 mm of crowding in the maxillary arch. The mandibular central incisors were congenitally missing (Fig 2). The panoramic radiograph confirmed the absence of the 2 mandibular incisors. Four third molars were present, with the mandibular right third molar inclined forward (Fig 3). The cephalometric analysis showed a Class II skeletal base with a low mandibular plane angle. The maxillary incisors were tipped lingually, and the mandibular incisors were labially proclined (Table). No obvious asymmetries were seen in the anteroposterior radiograph (Fig 3).
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TREATMENT OBJECTIVES
Our objectives for this patient were to (1) eliminate dental crowding, and level and align the teeth, considering her main complaint; (2) obtain ideal overbite and overjet; (3) create a stable functional occlusion; (4) improve the mandibular midline shift; and (5) maintain a satisfactory soft-tissue profile. TREATMENT ALTERNATIVES
The main issue for this patient was the congenital absence of the 2 mandibular incisors. Based on the literature review, the following 3 options were proposed to the patient. 1.
Space expansion followed by restoration of the mandibular incisors with fixed dentures or implants. With this plan, an ideal Class I molar relationship and harmonized functional occlusion could be achieved. The disadvantages of this plan were the loss of healthy mandibular anterior teeth for fixed
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Fig 2. Pretreatment study models.
Fig 3. Pretreatment lateral, frontal, and panoramic radiographs.
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Table. Cephalometric data SNA ( ) SNB ( ) ANB ( ) Wits (mm) MP-SN ( ) PP-MP ( ) L1-NB (mm) L1-NB ( ) IMPA ( ) U1-NA (mm) U1-NA ( ) U1-SN ( ) OP-SN ( ) U1-L1 ( ) Nasolabial angle ( ) Lower lip to E-plane (mm)
2.
3.
Norm 82.8 6 4.0 80.1 6 3.9 2.7 6 2.0 1.1 6 2.9 32.5 6 5.2 27.6 6 4.6 6.7 6 2.1 30.3 6 5.8 93.9 6 6.2 5.1 6 2.4 22.8 6 5.7 105.7 6 6.3 16.1 6 5.0 124.2 6 8.2 97.1 6 10.7 1.4 6 1.9
Pretreatment 84.1 78.6 5.5 3.6 27.6 17.5 5.0 28.4 102.5 2.5 20.7 103.4 16.8 127.2 102.9 0
restoration or the presumed risks for implantation of mandibular incisors. Extraction of the maxillary second premolars and retraction of the maxillary incisors to obtain a Class II molar relationship. In this method, the maxillary canines would occlude with the mandibular first premolars. The disadvantages were the loss of 2 healthy premolars and the Bolton tooth-ratio problems. Anterior movement of the mandibular teeth to obtain ideal overjet and overbite. The adverse effect of this plan was that the occlusion would be settled in a new position and result in a Class III molar relationship after treatment.
After explaining the pros and cons of each alternative with the patient and her parents, they selected the third option for treatment.
Posttreatment 85.6 80.7 4.9 1 27.5 16.5 8.5 34.2 106.4 5.0 30.3 114.0 14.5 114.5 100.7 1.5
Follow-up at 6 months 84.1 79.5 4.6 2.8 27.8 17.5 8.2 34.5 107.5 5.0 31.0 108.5 14.8 116.4 103.5 1
Follow-up at 42 months 84.5 79.3 5.2 2.6 28.2 17.5 7.5 35.7 110.5 4.5 29.2 112.4 17.5 111.2 99.4 1.5
the mandibular teeth forward. The mandibular teeth were moved forward, and the molars reached Class III relationships on both sides after the Forsus FRD was used for 6 months. At this stage, ideal anterior overbite and overjet were achieved. The midline remained unchanged (Fig 5). The Forsus FRD was removed after an ideal anterior overlap was achieved and occlusion detailing and settling began. The mandibular right third molar was uprighted to occlude with the maxillary second molar. Intermaxillary elastics were applied for better functional occlusion. Active treatment took 26 months. Hawley retainers were used to maintain the positions of the teeth after treatment. TREATMENT RESULTS
TREATMENT PROGRESS
Treatment began with banding the first molars and bonding all other teeth (0.022 3 0.028-in edgewise appliance; Tomy, Tokyo, Japan). Tooth leveling and alignment were completed in 8 months by sequential changing of nickel-titanium wires. At the end of this phase, the anterior overjet was increased, and the molar relationship was still Class I (Fig 4). To prepare the teeth for Forsus FRD treatment, 0.019 3 0.025-in stainless steel wires were continually placed; for convenient use of the appliance, U loops were applied in the wires. Tight ligation from the mandibular left to the mandibular right first molars, rigid tieback of the arches, and cinchback of the wires were used to secure the mandibular arch position and to increase its anchorage. The Forsus FRD (32 mm) was assembled at chairside to push the mandible and
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The teeth were well aligned and leveled after treatment. The first molars were in a Class III relationship, with the mesial buccal tip of the maxillary first molar occluded in the distal buccal groove of the mandibular first molar. Ideal anterior overbite and overjet were established. Occlusal contacts between the maxillary and mandibular teeth were achieved, although the interdigitation was not good. The 1.5-mm midline discrepancy remained unchanged. The patient's harmonized profile and facial esthetics were maintained (Figs 6 and 7). The posttreatment cephalometric analysis and superimposition showed that the skeletal discrepancy between the maxilla and the mandible remained unchanged. The maxillary and mandibular incisors were labially proclined. The mandibular plane angle was not affected by the treatment. Root parallelism
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Fig 4. Progress photographs before placement of the Forsus FRD.
Fig 5. Progress photographs after treatment with the Forsus FRD.
was achieved, and no marked root resorption was detected according to the posttreatment panoramic radiograph (Fig 8). Posttreatment follow-ups were carried out at 6 and 42 months (Figs 9-11; Table). In general, the
teeth were well aligned, and the occlusion remained stable. The positions and inclinations of the maxillary and mandibular incisors were unchanged. The mandibular third molars were in good positions, and the maxillary third molars were buccally
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Fig 6. Posttreatment facial and intraoral photographs.
erupted, so we proposed the extraction of both to the patient. DISCUSSION
Congenitally missing mandibular incisors can be a challenge to orthodontists. Options for treating malocclusions accompanying this problem vary according to patient preference, orthodontist preference, and even the patient's ethnicity. Chinese people will not preferentially choose extraction and restoration options when they are provided with a nonextraction and nonrestoration plan. In our patient, extraction of the 2 maxillary premolars would not have achieved ideal intercuspation, and a tooth size discrepancy would still remain in the occlusion detailing stage. Space expansion for a future bridge or a veneer restoration would jeopardize healthy teeth, and implant restoration would lead to more clinical risks associated with that technique. So, the patient selected the plan of moving the mandibular teeth forward, and it turned out to be a good choice, as shown by the final result.
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The Forsus FRD is usually recommended for treating Class II patients. The Forsus FRD can bring about mandibular growth and favorable changes in dental and soft tissues while correcting the Class II relationship in patients at or just before the peak phase of pubertal growth.8-11 For young adult patients near the end of the pubertal growth period, the Forsus FRD could only lead to dental compensations.12 However, in this report, the patient, who was a 15-year-old girl at cervical vertebral stage 5, showed forward displacement of the mandible as well as dental compensations after treatment.13 When using the Forsus FRD, one should be cautious about increasing mandibular tooth anchorage to prevent unfavorable effects. Techniques such as tight ligation, rigid tiebacks of the arches, cinchbacks of the wires, and anterior minus crown torque added to mandibular incisors were applied to secure the mandibular arch positioning and increase its anchorage. Even with all these anchorage enhancement techniques, the cephalometric analysis showed that the incisors
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Fig 7. Posttreatment study models.
Fig 8. Posttreatment radiographs.
proclined by 4 and were significantly protrusive compared with normal values. However, the results were stable and supported the statement that no cephalometric data are useful for establishing a prognosis regarding relapse.14 Some factors might have contributed to the stability of the mandibular incisors in this patient. One reason might be that there was no significant crowding in the mandibular arch before treatment, because the degree of crowding is a factor related to the amount of relapse.15-17 Another possible explanation for it was that the facial soft tissues were balanced and unstrained after treatment. Muscle force would tend to push the incisors back and cause relapse in the incisor area under strained soft-tissue surroundings.18 All the studies so far have evaluated the effect of the Forsus FRD at the end of treatment. There are no reports in the literature concerning the treatment stability of the Forsus FRD. However, as a kind of fixed functional appliance, its mechanism would have some similarities with the fixed functional appliance (Herbst) in the treatment of Class II Division 1 malocclusions. Bock et al19 evaluated 26 adults with Class II Division 1 treated with the Herbst appliance. They found that the molar relationships in 77.6% of the teeth and the canine relationships in 71.2% were stable. Ruf and Pancherz20 also found fewer cases of relapse in postpeak patients
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Fig 9. Facial and intraoral photographs after 42 months of retention.
than in those at the peak of pubertal growth undergoing treatment for Class II Division 1 malocclusion. These studies imply that adults can have stable treatment results, even if the amounts of skeletal changes contributing to overjet and molar correction are smaller than those in adolescents. The reason for this might be that an adult's permanent dentition allows for finishing treatment with stable interdigitation, which prevents unfavorable occlusal changes. Sood et al21 documented neuromuscular adaptations with the Forsus FRD after 6 months of treatment that remained stable in the following 24-month observation period. The stable neuromuscular condition might also contribute to the occlusal retention. The more than 3-year follow-up results of this patient concurred with previous research, suggesting that the Forsus FRD obtains stable results after treatment in young adult patients. Another concern about the Forsus FRD is its effect on the TMJ. There is a consensus that functional appliances, such as Herbst, Twin-block, and activator,
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do not have adverse effects on the TMJs of patients at various ages from puberty to adulthood.22-24 Condyles and condylar fossae respond well to the functional force through effective remodeling. However, studies regarding the effects of the Forsus FRD on the TMJ are limited. After Forsus FRD treatment, Aras et al25 reported that the articular disc was positioned more anteriorly compared with its pretreatment position in patients at the peak of pubertal group. Arici et al26 stated that the condyle was more posteriorly positioned in the glenoid fossa in the prepubertal group than in the untreated group. They reported that Forsus treatment is not a risk factor for temporomandibular dysfunction in subjects with no signs or clinical symptoms of dysfunction. In this case, no TMJ discomfort appeared during active treatment or the passive retention period. Although further studies are required to verify the effects of the Forsus FRD on the TMJ, it can be safely used as a good fixed functional appliance because it can provide continuous and elastic force to the mandible.27
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Fig 10. Study models after 42 months of retention.
Fig 11. Cephalometric radiographs at A, pretreatment; B, posttreatment; C, 6 months postretention; D, and 42 months postretention; E, superimposition on the sella-nasion plane at sella (left); superimposition of the maxilla on the lingual curvature of the palate and the maxillary bony structures (center); and superimposition of the mandible on the mandibular plane at menton (right).
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There were limitations, however, with this plan. The mandibular teeth were moved forward to reduce the anterior overjet and overbite problems; thus, a Class I molar relationship was replaced by a Class III relationship, and ideal interdigitation was not obtained. Newman and Newman2 reported treatment of a patient with a Class II Division 2 malocclusion and 2 congenitally missing mandibular incisors. They moved the mandibular teeth forward for anterior guidance. Their 2-year out-of-retention results showed that a new and safe occlusion was achieved. For our patient, the 42-month retention results also showed a stable and functional occlusion. The common feature of these patients was that the patient profile, dental crowding, and TMJs allowed forward movement of the mandible and the mandibular teeth. Whether it is worthy of solving anterior problems at the price of ideal posterior occlusion depends on prudent diagnostic analysis and personalized treatment objectives. Other treatment techniques could also achieve a balanced occlusion, esthetics, and stability for malocclusions with agenesis of the mandibular incisors with careful diagnosis. It is natural to be concerned about the Bolton discrepancy in patients with congenitally missing mandibular incisors. In this patient, the mandibular canine width was 7 mm and 1 mm greater than the mandibular incisor, which was 6 mm; the mandibular first premolar is as wide as the mandibular canine. Thus, a width 2 mm greater than ideal appeared with the anterior mandibular teeth. To obtain proper interdigitation at the end of orthodontic treatment, more forward movement of the mandibular arch and then reduction of the mandibular anterior teeth would be recommended. This plan was discarded by the clinician and the patient because it would prolong the treatment time, add more risks to the TMJs, and induce the loss of enamel in stripping even within the safety limit. Although tooth size harmony was important for proper occlusion, it must be prudent and evaluated for each, considering the high frequency of significant tooth size discrepancies.28-30 It is well known that a Class I canine relationship is important for functional occlusion.31,32 In this situation, a canine-protected occlusion became a premolar-protected occlusion during the mandibular lateral or working excursions. For the mandible, the first premolar frequently resembles the canine in every aspect important to substitution: length of crown and root, buccal cusp height, and mesiodistal diameter.33 Moyers34 stated that premolars possess periodontal proprioceptor impulses to the same degree as do the canines. The mandibular first premolar can serve as an appropriate substitute for the canine, both functionally
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and esthetically.33 Moving a canine into the position of a missing lateral incisor has been considered an acceptable compromise in clinical work. Another compromise in this treatment was the midline discrepancy at the end of treatment. A midline discrepancy less than 2 mm appears to have a less noticeable impact on dentofacial esthetics. Sometimes correction of a dental-to-facial midline discrepancy is not straightforward and might increase the complexity and duration of treatment.35-37 For this patient, the mandibular midline deviation was less than 2 mm and remained stable during 3.5 years of retention. The midline discrepancy was not noticeable even when smiling, and it was acceptable to the patient. Our findings were similar to those of Valinoti38 that the absence of a mandibular dental midline does not apparently affect occlusion, esthetics, periodontal health, or stability—the principal requirements of orthodontic therapy. CONCLUSIONS
This case report demonstrates a new use for the Forsus FRD in a patient with 2 congenitally missing mandibular incisors. A new functional and stable occlusion was established after treatment. When moving mandibular teeth forward for patients with mandibular incisor agenesis, facial profile, crowding, and TMJ conditions should be scrutinized to ensure that balanced and esthetic results can be achieved after treatment, which should also contribute to future stability. REFERENCES 1. Barros SE, Janson G, Torres FC, de Freitas MR, de Almeida RR. Class I malocclusion treatment: influence of a missing mandibular incisor on anterior guidance. Am J Orthod Dentofacial Orthop 2010;138:109-17. 2. Newman GV, Newman RA. Report of four familial cases with congenitally missing mandibular incisors. Am J Orthod Dentofacial Orthop 1998;114:195-207. 3. Davis PJ. Hypodontia and hyperodontia of permanent teeth in Hong Kong school children. Community Dent Oral Epidemiol 1987;15:218-20. 4. Endo T, Ozoe R, Kubota M, Akiyama M, Shimooka S. A survey of hypodontia in Japanese orthodontic patients. Am J Orthod Dentofacial Orthop 2006;129:29-35. 5. Chung CJ, Han JH, Kim KH. The pattern and prevalence of hypodontia in Koreans. Oral Dis 2008;14:620-5. 6. Endo T, Ozoe R, Kojima K, Shimooka S. Congenitally missing mandibular incisors and mandibular symphysis morphology. Angle Orthod 2007;77:1079-84. 7. Franchi L, Alvetro L, Giuntini V, Masucci C, Defraia E, Baccetti T. Effectiveness of comprehensive fixed appliance treatment used with the Forsus fatigue resistant device in Class II patients. Angle Orthod 2011;81:678-83.
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8. Bilgic¸ F, Hamamci O, Bas¸aran G. Comparison of the effects of fixed and removable functional appliances on the skeletal and dentoalveolar structures. Aust Orthod J 2011;27:110-6. 9. Jones G, Buschang PH, Kim KB, Oliver DR. Class II non-extraction patients treated with the Forsus fatigue resistant device versus intermaxillary elastics. Angle Orthod 2008;78:332-8. 10. Karacay S, Akin E, Olmez H, Gurton AU, Sagdic D. Forsus Nitinol flat spring and Jasper jumper corrections of Class II Division 1 malocclusions. Angle Orthod 2006;76:666-72. 11. Mahamad IK, Neela PK, Mascarenhas R, Husain A. A comparision of Twin-block and Forsus (FRD) functional appliance–a cephalometric study. Int J Orthod Milwaukee 2012;23:49-58. 12. Upadhyay M, Yadav S, Nagaraj K, Uribe F, Nanda R. Mini-implants vs fixed functional appliances for treatment of young adult Class II female patients: a prospective clinical trial. Angle Orthod 2012;82: 294-303. 13. Baccetti T, Franchi L, McNamara JA Jr. An improved version of the cervical vertebral maturation (CVM) method for the assessment of mandibular growth. Angle Orthod 2002;72:316-23. 14. Shields TE, Little RM, Chapko MK. Stability and relapse of mandibular anterior alignment: a cephalometric appraisal of first-premolar-extraction cases treated by traditional edgewise orthodontics. Am J Orthod 1985;87:27-38. 15. Freitas KM, de Freitas MR, Henriques JF, Pinzan A, Janson G. Postretention relapse of mandibular anterior crowding in patients treated without mandibular premolar extraction. Am J Orthod Dentofacial Orthop 2004;125:480-7. 16. Kahl-Nieke B, Fischbach H, Schwarze CW. Post-retention crowding and incisor irregularity: the long-term follow-up evaluation of stability and relapse. Br J Orthod 1995;22:249-57. 17. Artun J, Garol JD, Little RM. Long-term stability of mandibular incisors following successful treatment of Class II, Division 1, malocclusions. Angle Orthod 1996;66:229-38. 18. Proffit WR. Equilibrium theory revisited: factors influencing position of the teeth. Angle Orthod 1978;48:175-86. 19. Bock NC, von Bremen J, Ruf S. Occlusal stability of adult Class II Division 1 treatment with the Herbst appliance. Am J Orthod Dentofacial Orthop 2010;138:146-51. 20. Ruf S, Pancherz H. Herbst/multibracket appliance treatment of Class II division 1 malocclusions in early and late adulthood: a prospective cephalometric study of consecutively treated subjects. Eur J Orthod 2006;28:352-60. 21. Sood S, Kharbanda OP, Duggal R, Sood M, Gulati S. Neuromuscular adaptations with flexible fixed functional appliance—a 2-year follow-up study. J Orofac Orthop 2011;72: 434-45. 22. Chintakanon K, Sampson W, Wilkinson T, Townsend G. A prospective study of Twin-block appliance therapy assessed by
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magnetic resonance imaging. Am J Orthod Dentofacial Orthop 2000;118:494-504. Ruf S, Pancherz H. Temporomandibular joint remodeling in adolescents and young adults during Herbst treatment: a prospective longitudinal magnetic resonance imaging and cephalometric radiographic investigation. Am J Orthod Dentofacial Orthop 1999;115:607-18. Ruf S, W€ usten B, Pancherz H. Temporomandibular joint effects of activator treatment: a prospective longitudinal magnetic resonance imaging and clinical study. Angle Orthod 2002;72:527-40. Aras A, Ada E, Saraco glu H, Gezer NS, Aras I. Comparison of treatments with the Forsus fatigue resistant device in relation to skeletal maturity: a cephalometric and magnetic resonance imaging study. Am J Orthod Dentofacial Orthop 2011;140:616-25. Arici S, Akan H, Yakubov K, Arici N. Effects of fixed functional appliance treatment on the temporomandibular joint. Am J Orthod Dentofacial Orthop 2008;133:809-14. El-Sheikh MM, Godfrey K, Manosudprasit M, Viwattanatipa N. Force-deflection characteristics of the fatigue-resistant device spring: an in vitro study. World J Orthod 2007;8:30-6. Johe RS, Steinhart T, Sado N, Greenberg B, Jing S. Intermaxillary tooth-size discrepancies in different sexes, malocclusion groups, and ethnicities. Am J Orthod Dentofacial Orthop 2010;138: 599-607. Othman S, Harradine N. Tooth size discrepancies in an orthodontic population. Angle Orthod 2007;77:668-74. Othman SA, Harradine NW. Tooth-size discrepancy and Bolton's ratios: a literature review. J Orthod 2006;33:45-51. D’Amico A. The canine teeth—normal functional relation of the natural teeth of man. J Calif Dent Assoc 1958;26:6-23. Clark JR, Evans RD. Functional occlusion: I. A review. J Orthod 2001;28:76-81. Simms RA. Management of orthodontic treatment when first premolars are substituted for canines. Angle Orthod 1977;47: 239-48. Moyers RE. Some physiologic considerations of centric and other jaw relations. J Prosthet Dent 1956;6:183-94. Johnston CD, Burden DJ, Stevenson MR. The influence of dental to facial midline discrepancies on dental attractiveness ratings. Eur J Orthod 1999;21:517-22. Cardash HS, Ormanier Z, Laufer BZ. Observable deviation of the facial and anterior tooth midlines. J Prosthet Dent 2003;89:282-5. Janson G, Branco NC, Fernandes TM, Sathler R, Garib D, Lauris JR. Influence of orthodontic treatment, midline position, buccal corridor and smile arc on smile attractiveness. Angle Orthod 2011;81:153-61. Valinoti JR. Mandibular incisor extraction therapy. Am J Orthod Dentofacial Orthop 1994;105:107-16.
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Use of Forsus fatigue-resistant device in a patient with Class I malocclusion and mandibular incisor agenesis Ruofang Zhang,a Yuxing Bai,b and Song Lic Beijing, China
Orthodontic treatment in patients with congenitally missing teeth can be challenging. In this case report, we describe the treatment of a 15-year-old girl with mild dental crowding and 2 congenitally missing mandibular incisors. The Forsus fatigue-resistant device was used to move the mandible and the mandibular teeth forward. A new balanced and stable occlusion was achieved after treatment. When the treatment plan includes moving the mandibular teeth forward in a patient with mandibular incisor agenesis, the profile and the skeletal and dental features should be carefully scrutinized to ensure that balanced and esthetic results are achieved. (Am J Orthod Dentofacial Orthop 2014;145:817-27)
H
ypodontia is the congenital absence of at least 1 tooth.1 Orthodontic treatment in patients with congenitally missing teeth can be challenging. The prevalence of hypodontia varies among different ethnicities. The most commonly missing teeth for white populations are the maxillary lateral incisors and the second premolars (third molars excluded).1,2 However, in Chinese, Korean, and Japanese populations, agenesis of the mandibular incisors is more frequently observed.3-5 Mandibular incisor agenesis might be caused by heredity, anomalies of the mandibular symphysis, dentition reduction of an evolutionary trend, or localized inflammation.2 Patients with congenitally missing mandibular incisors usually show retroclination of the mandibular incisors and reduction of the mandibular alveolar bone area.6 Three treatment modalities are common for patients with agenesis of the mandibular incisors. One involves creating space for a fixed denture or an implant restoration, which could help achieve a satisfactory
From the Department of Orthodontics, School of Stomatology, Capital Medical University, Beijing, China. a Associate professor. b Professor and dean. c Professor and vice dean. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Address correspondence to: Song Li, Department of Orthodontics, School of Stomatology, Capital Medical University, Beijing 100050, China; e-mail, [email protected]. Submitted, June 2012; revised and accepted, August 2013. 0889-5406/$36.00 Copyright Ó 2014 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2013.08.021
occlusion. Another choice is extraction of the maxillary incisors or premolars to reduce the severe deep overjet by retracting the anterior teeth. The third option is to create a new balanced occlusion by closing the spaces and moving the mandibular canines and the posterior teeth forward. The Forsus fatigue-resistant device (FRD; 3M Unitek, Monrovia, Calif) is a semirigid fixed functional appliance. It is used most frequently for treating Class II patients. As claimed by the manufacturer, the Forsus FRD can exert consistent forces and is resistant to fracture. It consists of superelastic nickel-titanium coil springs that can be assembled at chairside. Recent studies have reported that the Forsus FRD can restrain sagittal growth of the maxilla, stimulate mandibular growth, and induce mesial movement of the mandibular teeth and distal movement of the maxillary molars.7 We present the treatment of a patient with a Class I malocclusion with 2 congenitally missing mandibular incisors. The treatment plan involved forward movement of the mandible and the mandibular teeth to reduce the deep overjet using the Forsus FRD appliance.
DIAGNOSIS AND ETIOLOGY
The patient was a 15-year-old girl with a chief complaint of dental crowding. She was in good health with no significant systemic medical history. No oral habits and no temporomandibular joint (TMJ) symptoms were noted. The pretreatment facial frontal photographs showed a well-balanced and symmetric face (Fig 1). Her profile 817
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Fig 1. Pretreatment facial and intraoral photographs.
was straight with competent lips, a good chin-throat soft-tissue line, a proper nasolabial angle, and normal vertical proportions. The molar relationships were Class I on both sides. The anterior overbite was deep, with the maxillary incisors overlapping the mandibular incisors by 50%. Anterior overjet was 3 mm. Her maxillary midline was coincident with the facial midline, and the mandibular midline was shifted 1 mm to the left. Both arch forms were U-shaped. There was 5.5 mm of crowding in the maxillary arch. The mandibular central incisors were congenitally missing (Fig 2). The panoramic radiograph confirmed the absence of the 2 mandibular incisors. Four third molars were present, with the mandibular right third molar inclined forward (Fig 3). The cephalometric analysis showed a Class II skeletal base with a low mandibular plane angle. The maxillary incisors were tipped lingually, and the mandibular incisors were labially proclined (Table). No obvious asymmetries were seen in the anteroposterior radiograph (Fig 3).
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TREATMENT OBJECTIVES
Our objectives for this patient were to (1) eliminate dental crowding, and level and align the teeth, considering her main complaint; (2) obtain ideal overbite and overjet; (3) create a stable functional occlusion; (4) improve the mandibular midline shift; and (5) maintain a satisfactory soft-tissue profile. TREATMENT ALTERNATIVES
The main issue for this patient was the congenital absence of the 2 mandibular incisors. Based on the literature review, the following 3 options were proposed to the patient. 1.
Space expansion followed by restoration of the mandibular incisors with fixed dentures or implants. With this plan, an ideal Class I molar relationship and harmonized functional occlusion could be achieved. The disadvantages of this plan were the loss of healthy mandibular anterior teeth for fixed
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Fig 2. Pretreatment study models.
Fig 3. Pretreatment lateral, frontal, and panoramic radiographs.
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Table. Cephalometric data SNA ( ) SNB ( ) ANB ( ) Wits (mm) MP-SN ( ) PP-MP ( ) L1-NB (mm) L1-NB ( ) IMPA ( ) U1-NA (mm) U1-NA ( ) U1-SN ( ) OP-SN ( ) U1-L1 ( ) Nasolabial angle ( ) Lower lip to E-plane (mm)
2.
3.
Norm 82.8 6 4.0 80.1 6 3.9 2.7 6 2.0 1.1 6 2.9 32.5 6 5.2 27.6 6 4.6 6.7 6 2.1 30.3 6 5.8 93.9 6 6.2 5.1 6 2.4 22.8 6 5.7 105.7 6 6.3 16.1 6 5.0 124.2 6 8.2 97.1 6 10.7 1.4 6 1.9
Pretreatment 84.1 78.6 5.5 3.6 27.6 17.5 5.0 28.4 102.5 2.5 20.7 103.4 16.8 127.2 102.9 0
restoration or the presumed risks for implantation of mandibular incisors. Extraction of the maxillary second premolars and retraction of the maxillary incisors to obtain a Class II molar relationship. In this method, the maxillary canines would occlude with the mandibular first premolars. The disadvantages were the loss of 2 healthy premolars and the Bolton tooth-ratio problems. Anterior movement of the mandibular teeth to obtain ideal overjet and overbite. The adverse effect of this plan was that the occlusion would be settled in a new position and result in a Class III molar relationship after treatment.
After explaining the pros and cons of each alternative with the patient and her parents, they selected the third option for treatment.
Posttreatment 85.6 80.7 4.9 1 27.5 16.5 8.5 34.2 106.4 5.0 30.3 114.0 14.5 114.5 100.7 1.5
Follow-up at 6 months 84.1 79.5 4.6 2.8 27.8 17.5 8.2 34.5 107.5 5.0 31.0 108.5 14.8 116.4 103.5 1
Follow-up at 42 months 84.5 79.3 5.2 2.6 28.2 17.5 7.5 35.7 110.5 4.5 29.2 112.4 17.5 111.2 99.4 1.5
the mandibular teeth forward. The mandibular teeth were moved forward, and the molars reached Class III relationships on both sides after the Forsus FRD was used for 6 months. At this stage, ideal anterior overbite and overjet were achieved. The midline remained unchanged (Fig 5). The Forsus FRD was removed after an ideal anterior overlap was achieved and occlusion detailing and settling began. The mandibular right third molar was uprighted to occlude with the maxillary second molar. Intermaxillary elastics were applied for better functional occlusion. Active treatment took 26 months. Hawley retainers were used to maintain the positions of the teeth after treatment. TREATMENT RESULTS
TREATMENT PROGRESS
Treatment began with banding the first molars and bonding all other teeth (0.022 3 0.028-in edgewise appliance; Tomy, Tokyo, Japan). Tooth leveling and alignment were completed in 8 months by sequential changing of nickel-titanium wires. At the end of this phase, the anterior overjet was increased, and the molar relationship was still Class I (Fig 4). To prepare the teeth for Forsus FRD treatment, 0.019 3 0.025-in stainless steel wires were continually placed; for convenient use of the appliance, U loops were applied in the wires. Tight ligation from the mandibular left to the mandibular right first molars, rigid tieback of the arches, and cinchback of the wires were used to secure the mandibular arch position and to increase its anchorage. The Forsus FRD (32 mm) was assembled at chairside to push the mandible and
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The teeth were well aligned and leveled after treatment. The first molars were in a Class III relationship, with the mesial buccal tip of the maxillary first molar occluded in the distal buccal groove of the mandibular first molar. Ideal anterior overbite and overjet were established. Occlusal contacts between the maxillary and mandibular teeth were achieved, although the interdigitation was not good. The 1.5-mm midline discrepancy remained unchanged. The patient's harmonized profile and facial esthetics were maintained (Figs 6 and 7). The posttreatment cephalometric analysis and superimposition showed that the skeletal discrepancy between the maxilla and the mandible remained unchanged. The maxillary and mandibular incisors were labially proclined. The mandibular plane angle was not affected by the treatment. Root parallelism
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Fig 4. Progress photographs before placement of the Forsus FRD.
Fig 5. Progress photographs after treatment with the Forsus FRD.
was achieved, and no marked root resorption was detected according to the posttreatment panoramic radiograph (Fig 8). Posttreatment follow-ups were carried out at 6 and 42 months (Figs 9-11; Table). In general, the
teeth were well aligned, and the occlusion remained stable. The positions and inclinations of the maxillary and mandibular incisors were unchanged. The mandibular third molars were in good positions, and the maxillary third molars were buccally
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Fig 6. Posttreatment facial and intraoral photographs.
erupted, so we proposed the extraction of both to the patient. DISCUSSION
Congenitally missing mandibular incisors can be a challenge to orthodontists. Options for treating malocclusions accompanying this problem vary according to patient preference, orthodontist preference, and even the patient's ethnicity. Chinese people will not preferentially choose extraction and restoration options when they are provided with a nonextraction and nonrestoration plan. In our patient, extraction of the 2 maxillary premolars would not have achieved ideal intercuspation, and a tooth size discrepancy would still remain in the occlusion detailing stage. Space expansion for a future bridge or a veneer restoration would jeopardize healthy teeth, and implant restoration would lead to more clinical risks associated with that technique. So, the patient selected the plan of moving the mandibular teeth forward, and it turned out to be a good choice, as shown by the final result.
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The Forsus FRD is usually recommended for treating Class II patients. The Forsus FRD can bring about mandibular growth and favorable changes in dental and soft tissues while correcting the Class II relationship in patients at or just before the peak phase of pubertal growth.8-11 For young adult patients near the end of the pubertal growth period, the Forsus FRD could only lead to dental compensations.12 However, in this report, the patient, who was a 15-year-old girl at cervical vertebral stage 5, showed forward displacement of the mandible as well as dental compensations after treatment.13 When using the Forsus FRD, one should be cautious about increasing mandibular tooth anchorage to prevent unfavorable effects. Techniques such as tight ligation, rigid tiebacks of the arches, cinchbacks of the wires, and anterior minus crown torque added to mandibular incisors were applied to secure the mandibular arch positioning and increase its anchorage. Even with all these anchorage enhancement techniques, the cephalometric analysis showed that the incisors
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Fig 7. Posttreatment study models.
Fig 8. Posttreatment radiographs.
proclined by 4 and were significantly protrusive compared with normal values. However, the results were stable and supported the statement that no cephalometric data are useful for establishing a prognosis regarding relapse.14 Some factors might have contributed to the stability of the mandibular incisors in this patient. One reason might be that there was no significant crowding in the mandibular arch before treatment, because the degree of crowding is a factor related to the amount of relapse.15-17 Another possible explanation for it was that the facial soft tissues were balanced and unstrained after treatment. Muscle force would tend to push the incisors back and cause relapse in the incisor area under strained soft-tissue surroundings.18 All the studies so far have evaluated the effect of the Forsus FRD at the end of treatment. There are no reports in the literature concerning the treatment stability of the Forsus FRD. However, as a kind of fixed functional appliance, its mechanism would have some similarities with the fixed functional appliance (Herbst) in the treatment of Class II Division 1 malocclusions. Bock et al19 evaluated 26 adults with Class II Division 1 treated with the Herbst appliance. They found that the molar relationships in 77.6% of the teeth and the canine relationships in 71.2% were stable. Ruf and Pancherz20 also found fewer cases of relapse in postpeak patients
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Fig 9. Facial and intraoral photographs after 42 months of retention.
than in those at the peak of pubertal growth undergoing treatment for Class II Division 1 malocclusion. These studies imply that adults can have stable treatment results, even if the amounts of skeletal changes contributing to overjet and molar correction are smaller than those in adolescents. The reason for this might be that an adult's permanent dentition allows for finishing treatment with stable interdigitation, which prevents unfavorable occlusal changes. Sood et al21 documented neuromuscular adaptations with the Forsus FRD after 6 months of treatment that remained stable in the following 24-month observation period. The stable neuromuscular condition might also contribute to the occlusal retention. The more than 3-year follow-up results of this patient concurred with previous research, suggesting that the Forsus FRD obtains stable results after treatment in young adult patients. Another concern about the Forsus FRD is its effect on the TMJ. There is a consensus that functional appliances, such as Herbst, Twin-block, and activator,
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do not have adverse effects on the TMJs of patients at various ages from puberty to adulthood.22-24 Condyles and condylar fossae respond well to the functional force through effective remodeling. However, studies regarding the effects of the Forsus FRD on the TMJ are limited. After Forsus FRD treatment, Aras et al25 reported that the articular disc was positioned more anteriorly compared with its pretreatment position in patients at the peak of pubertal group. Arici et al26 stated that the condyle was more posteriorly positioned in the glenoid fossa in the prepubertal group than in the untreated group. They reported that Forsus treatment is not a risk factor for temporomandibular dysfunction in subjects with no signs or clinical symptoms of dysfunction. In this case, no TMJ discomfort appeared during active treatment or the passive retention period. Although further studies are required to verify the effects of the Forsus FRD on the TMJ, it can be safely used as a good fixed functional appliance because it can provide continuous and elastic force to the mandible.27
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Fig 10. Study models after 42 months of retention.
Fig 11. Cephalometric radiographs at A, pretreatment; B, posttreatment; C, 6 months postretention; D, and 42 months postretention; E, superimposition on the sella-nasion plane at sella (left); superimposition of the maxilla on the lingual curvature of the palate and the maxillary bony structures (center); and superimposition of the mandible on the mandibular plane at menton (right).
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There were limitations, however, with this plan. The mandibular teeth were moved forward to reduce the anterior overjet and overbite problems; thus, a Class I molar relationship was replaced by a Class III relationship, and ideal interdigitation was not obtained. Newman and Newman2 reported treatment of a patient with a Class II Division 2 malocclusion and 2 congenitally missing mandibular incisors. They moved the mandibular teeth forward for anterior guidance. Their 2-year out-of-retention results showed that a new and safe occlusion was achieved. For our patient, the 42-month retention results also showed a stable and functional occlusion. The common feature of these patients was that the patient profile, dental crowding, and TMJs allowed forward movement of the mandible and the mandibular teeth. Whether it is worthy of solving anterior problems at the price of ideal posterior occlusion depends on prudent diagnostic analysis and personalized treatment objectives. Other treatment techniques could also achieve a balanced occlusion, esthetics, and stability for malocclusions with agenesis of the mandibular incisors with careful diagnosis. It is natural to be concerned about the Bolton discrepancy in patients with congenitally missing mandibular incisors. In this patient, the mandibular canine width was 7 mm and 1 mm greater than the mandibular incisor, which was 6 mm; the mandibular first premolar is as wide as the mandibular canine. Thus, a width 2 mm greater than ideal appeared with the anterior mandibular teeth. To obtain proper interdigitation at the end of orthodontic treatment, more forward movement of the mandibular arch and then reduction of the mandibular anterior teeth would be recommended. This plan was discarded by the clinician and the patient because it would prolong the treatment time, add more risks to the TMJs, and induce the loss of enamel in stripping even within the safety limit. Although tooth size harmony was important for proper occlusion, it must be prudent and evaluated for each, considering the high frequency of significant tooth size discrepancies.28-30 It is well known that a Class I canine relationship is important for functional occlusion.31,32 In this situation, a canine-protected occlusion became a premolar-protected occlusion during the mandibular lateral or working excursions. For the mandible, the first premolar frequently resembles the canine in every aspect important to substitution: length of crown and root, buccal cusp height, and mesiodistal diameter.33 Moyers34 stated that premolars possess periodontal proprioceptor impulses to the same degree as do the canines. The mandibular first premolar can serve as an appropriate substitute for the canine, both functionally
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and esthetically.33 Moving a canine into the position of a missing lateral incisor has been considered an acceptable compromise in clinical work. Another compromise in this treatment was the midline discrepancy at the end of treatment. A midline discrepancy less than 2 mm appears to have a less noticeable impact on dentofacial esthetics. Sometimes correction of a dental-to-facial midline discrepancy is not straightforward and might increase the complexity and duration of treatment.35-37 For this patient, the mandibular midline deviation was less than 2 mm and remained stable during 3.5 years of retention. The midline discrepancy was not noticeable even when smiling, and it was acceptable to the patient. Our findings were similar to those of Valinoti38 that the absence of a mandibular dental midline does not apparently affect occlusion, esthetics, periodontal health, or stability—the principal requirements of orthodontic therapy. CONCLUSIONS
This case report demonstrates a new use for the Forsus FRD in a patient with 2 congenitally missing mandibular incisors. A new functional and stable occlusion was established after treatment. When moving mandibular teeth forward for patients with mandibular incisor agenesis, facial profile, crowding, and TMJ conditions should be scrutinized to ensure that balanced and esthetic results can be achieved after treatment, which should also contribute to future stability. REFERENCES 1. Barros SE, Janson G, Torres FC, de Freitas MR, de Almeida RR. Class I malocclusion treatment: influence of a missing mandibular incisor on anterior guidance. Am J Orthod Dentofacial Orthop 2010;138:109-17. 2. Newman GV, Newman RA. Report of four familial cases with congenitally missing mandibular incisors. Am J Orthod Dentofacial Orthop 1998;114:195-207. 3. Davis PJ. Hypodontia and hyperodontia of permanent teeth in Hong Kong school children. Community Dent Oral Epidemiol 1987;15:218-20. 4. Endo T, Ozoe R, Kubota M, Akiyama M, Shimooka S. A survey of hypodontia in Japanese orthodontic patients. Am J Orthod Dentofacial Orthop 2006;129:29-35. 5. Chung CJ, Han JH, Kim KH. The pattern and prevalence of hypodontia in Koreans. Oral Dis 2008;14:620-5. 6. Endo T, Ozoe R, Kojima K, Shimooka S. Congenitally missing mandibular incisors and mandibular symphysis morphology. Angle Orthod 2007;77:1079-84. 7. Franchi L, Alvetro L, Giuntini V, Masucci C, Defraia E, Baccetti T. Effectiveness of comprehensive fixed appliance treatment used with the Forsus fatigue resistant device in Class II patients. Angle Orthod 2011;81:678-83.
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8. Bilgic¸ F, Hamamci O, Bas¸aran G. Comparison of the effects of fixed and removable functional appliances on the skeletal and dentoalveolar structures. Aust Orthod J 2011;27:110-6. 9. Jones G, Buschang PH, Kim KB, Oliver DR. Class II non-extraction patients treated with the Forsus fatigue resistant device versus intermaxillary elastics. Angle Orthod 2008;78:332-8. 10. Karacay S, Akin E, Olmez H, Gurton AU, Sagdic D. Forsus Nitinol flat spring and Jasper jumper corrections of Class II Division 1 malocclusions. Angle Orthod 2006;76:666-72. 11. Mahamad IK, Neela PK, Mascarenhas R, Husain A. A comparision of Twin-block and Forsus (FRD) functional appliance–a cephalometric study. Int J Orthod Milwaukee 2012;23:49-58. 12. Upadhyay M, Yadav S, Nagaraj K, Uribe F, Nanda R. Mini-implants vs fixed functional appliances for treatment of young adult Class II female patients: a prospective clinical trial. Angle Orthod 2012;82: 294-303. 13. Baccetti T, Franchi L, McNamara JA Jr. An improved version of the cervical vertebral maturation (CVM) method for the assessment of mandibular growth. Angle Orthod 2002;72:316-23. 14. Shields TE, Little RM, Chapko MK. Stability and relapse of mandibular anterior alignment: a cephalometric appraisal of first-premolar-extraction cases treated by traditional edgewise orthodontics. Am J Orthod 1985;87:27-38. 15. Freitas KM, de Freitas MR, Henriques JF, Pinzan A, Janson G. Postretention relapse of mandibular anterior crowding in patients treated without mandibular premolar extraction. Am J Orthod Dentofacial Orthop 2004;125:480-7. 16. Kahl-Nieke B, Fischbach H, Schwarze CW. Post-retention crowding and incisor irregularity: the long-term follow-up evaluation of stability and relapse. Br J Orthod 1995;22:249-57. 17. Artun J, Garol JD, Little RM. Long-term stability of mandibular incisors following successful treatment of Class II, Division 1, malocclusions. Angle Orthod 1996;66:229-38. 18. Proffit WR. Equilibrium theory revisited: factors influencing position of the teeth. Angle Orthod 1978;48:175-86. 19. Bock NC, von Bremen J, Ruf S. Occlusal stability of adult Class II Division 1 treatment with the Herbst appliance. Am J Orthod Dentofacial Orthop 2010;138:146-51. 20. Ruf S, Pancherz H. Herbst/multibracket appliance treatment of Class II division 1 malocclusions in early and late adulthood: a prospective cephalometric study of consecutively treated subjects. Eur J Orthod 2006;28:352-60. 21. Sood S, Kharbanda OP, Duggal R, Sood M, Gulati S. Neuromuscular adaptations with flexible fixed functional appliance—a 2-year follow-up study. J Orofac Orthop 2011;72: 434-45. 22. Chintakanon K, Sampson W, Wilkinson T, Townsend G. A prospective study of Twin-block appliance therapy assessed by
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