Uprighting impacted mandibular permanent second molars with the tip-back cantilever technique-cases report

Transcription

1 Uprighting impacted mandibular permanent second molars with the tip-back cantilever technique-cases report PO-SUNG FU 1 CHERN-HSIUNG LAI 2 YI-MIN WU 1 CHING-FANG TSAI 3 TA-KO HUANG 4 JIN-HUANG ZENG 5 WEN-CHENG CHEN 4 CHUN-CHENG HUNG 3 1 Department of Family Dentistry, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung, Taiwan, ROC. 2 Research Center for Anaerobic and Oral Microbiology, Kaohsiung Medical University, Kaohsiung, Taiwan, ROC. 3 Department of Prosthodontics, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung, Taiwan, ROC. 4 Faculty of Dentistry, Kaohsiung Medical University, Kaohsiung, Taiwan, ROC. 5 Private practice, Kaohsiung, Taiwan, ROC. Very severe inclination of the mandibular second molar is a difficult challenge for dentists. Severe impaction of the mandibular second molars often leads to their extraction to avoid potential damage to the root of the first molars and provide space for the eruption of the third molars. An ideal treatment is orthodontic uprighting with or without surgical uncovering, and one of the effective appliances for molar uprighting is the tip-back cantilever technique. This paper presents the successful tip-back sectional archwire orthodontic treatment of impacted mandibular second molars. (J Dent Sci, 3(3): , 2008) Key words: molar impaction, molar uprighting, tip-back cantilever, pole arm. Impaction of the second permanent molars is not common, and usually occurs in the mandibular arch with a incidence of about 0.3% 1-3. The etiology of impaction may be related to an insufficient arch length, excessive tooth size, or excessive axial inclination 1,4,5. In the normal growth and development process, the second permanent molar tooth buds are distal to the first permanent molar and have a mesial inclination. This inclination is usually self-correcting as the resorption of the anterior border of the mandibular ramus occurs and the first permanent molar migrates into the leeway space for angular adjustment and eruption. However, this correction does not always happen, and the second molar can become impacted. Received: June 7, 2008 Accepted: August 19, 2008 Reprint requests to: Dr. Chun-Cheng Hung, Department of Prosthodontics, Kaohsiung Medical University Hospital, No.100, Tzyou 1st Road, Kaohsiung, Taiwan 80756, ROC. Extraction of impacted second molars has been suggested to make room for unerupted third molars. Unfortunately, there is no guarantee that the third molar will erupt in an upright position 6,7. Severe impaction of lower second/third molars often leads to difficulty in cleaning and necessitates extraction in order to avoid potential damage to the roots of first/second molars. The management of impacted molars used to be a complicated problem. Separating wires and threaded pins have been advocated Other clinicians have soldered helical loop springs to the distal end of a lingual arch or constructed loop springs from the distal end of labial arch wires Surgical approaches for impacted second molars include surgical extraction to allow eruption of the third molars, surgical uprighting of the impacted second molars, surgical uncovering with orthodontically assisted eruption and transplantation of the third molars to the second molar sockets However, orthodontic uprighting might be a better alternative 174

2 Molar uprighting with a tip-back cantilever with a lower risk to the teeth. With the recent development of miniscrews, its clinical application has became various and predictable While it is recognized that any of the uprighting techniques previously mentioned can possibly be applied in a given situation, the technique should be determined by factors such as the severity of the molar impaction, the accessibility of the coronal surface of the impacted molar, the desired type of movement, the undesirable side effects, as well as the simplicity and convenience of the uprighting mechanics 4-6. The proper time to treat impacted second molars is when the patient is 11~14 years old, while second molar root formation is still incomplete and before the third molars complete their development in close proximity to the second molars 4,5. In this study, cases of successfully uprighting impacted molars using a x inch titanium molybdenum alloy (TMA) tip-back sectional archwire, which we termed the pole arm, are presented. MATERIALS AND METHODS Biomechanical considerations The pole arm cantilever produces effects on the tooth in 3 dimensions, principally in the mesiodistal (distal crown tipping) and vertical directions (molar extrusion). The force acting on the impacted molar is of the same magnitude as, but of opposite direction to, the force acting on the main wire. Therefore, the intrusive force is on the anterior segment and the extrusive force on the impacted molar, and the couple distally tips the impacted molar (Figure 1). Figure 1. Force delivered to the pole arm and force as well as moment acting on the impacted molar. Fa, active force acting on the pole arm; Fr, reciprocal force acting on the impacted molar; Frv, vertical (extrusive) component of Fr; Frh, horizontal (distal) component of Fr; M, moment acting on the impacted molar. 175

3 P.S. Fu, C.H. Lai, Y.M. Wu, et al. Appliance design The pole arm appliance is fabricated at chairside with x inch TMA wire (Figure 2). A periapical or panoramic radiograph should be taken of the impacted molar before and after applying the technique to confirm the severity of the impaction and the position of the uprighting spring of the inserted pole arm. Before insertion of the pole arm appliance, we recommend applying local anesthesia to the buccal and lingual gingiva which are between the impacted molar and adjacent tooth. The buccal arm (D) is inserted from the lingual side, passing beneath the contact area between the adjacent tooth and impacted molar and is pulled out buccally. Activation of the uprighting spring is accomplished by bending the distal contact between the first molar tube and buccal arm (D), when the buccal arm is ligated by wire to the anchor teeth. As the contact works towards restoring its original form, it produces a distal uprighting force against the mesial surface of the impacted molar. Finally, a lingual rest (A) is fixed with glass-ionomer or composite resin on the occlusal surface close to the lingual groove of the first molar to avoid it sliding out of position (Figures 2, 3). Moving the pole arm gingival activates the appliance. The pole arm can be reactivated in the mouth by lifting, gently squeezing the buccal arm occlusally, and ligating the buccal arm again. After the initial adjustment at 3~4 weeks, adjustments every 6 weeks seem to be adequate. Case 1 CASE PRESENTATIONS A 13-year-old male presented with impaction of the mandibular left second molar. The patient had a Class I, bimaxillary protrusive malocclusion. The mandibular left second molar was tipped mesially and was obliquely impacted under the distal surface of the first molar. A panoramic radiograph revealed the presence of all permanent teeth and a severe mesial inclination of the mandibular left second molar and developing third molars (Figure 4). The root formation of the impacted molar was still incomplete. The treatment plan was for extraction of four first premolars and a germectomy of the mandibular left third molar. After initial leveling and alignment, we inserted the x inch TMA pole arm uprighting spring into the impacted mandibular second molar and ligated it mesially to the anchor teeth. Ten weeks following insertion of the pole arm, the impacted mandibular second molar had been uprighted to some degree, and a bracket was bonded to it for further alignment. Posttreatment intraoral photographs and a panoramic radiograph (Figure 5) show the corrected inclination of the impacted mandibular left second molar with proper interdigitation. A Hawley retainer and a lingual fixed retainer were respectively used as retentive devices for the maxilla and mandible. Case 2 Figure 2. Pole arm uprighting spring. A, Lingual rest bending; B, occlusogingival bending with length according to the impaction depth; C, buccolingual bending with length according to the buccolingual width of the impacted molar; D, mesial extension following the buccal curve of the anchor teeth. An 18-year-old female presented with Class I, mild crowding and bilateral impactions of the mandibular second molars. A panoramic radiograph revealed that both mandibular second molars were obliquely impacted under the distal contour of the first molars. The root formation of the impacted second molars was complete. The mandibular third molar buds were located on top of the second molar distal roots (Figure 6). The treatment plan was a germectomy of the mandibular third molars. After initial leveling and alignment, the pole arm uprighting springs were placed into both impacted mandibular second molars. 176

4 Molar uprighting with a tip-back cantilever Figure 3. Intraoral photographs and periapical radiograph at insertion of pole arm. Figure 4. Pretreatment photograph and panoramic radiograph showing impacted mandibular left second molar. Figure 5. Posttreatment photographs and panoramic radiograph showing corrected inclination of the mandibular left second molar. 177

5 P.S. Fu, C.H. Lai, Y.M. Wu, et al. Figure 6. Pretreatment photograph and panoramic radiograph showing bilaterally impacted mandibular second molars. At 8 (for the right side) and 10 weeks (for the left side) following insertion of the pole arms, the impacted mandibular second molars had been uprighted to some degree, and brackets were bonded to them for further alignment. Posttreatment intraoral photographs and a panoramic radiograph (Figure 7) show the corrected inclination of the impacted lower molars with proper interdigitation and root parallelism. A Hawley retainer and a lingual fixed retainer were respectively used as retentive devices for the maxilla and mandible. DISCUSSION The impaction of molars is difficult to prevent and detect early due to its multifactorial etiologies. Apart from the well-known etiologies, probably iatrogenic factors of second molar impaction are incorrectly fitted bands cemented onto the first molars, prevention of mesial drift of the first molar caused by a lip bumper or lingual arch therapy, and excessive tip-back of the first molar during previous orthodontic treatment 4, Figure 7. Posttreatment photographs and panoramic radiograph showing corrected inclination of the mandibular left second molar. 178

6 Molar uprighting with a tip-back cantilever Before uprighting the impacted second molar, the need for third molar extraction must be well evaluated. Usually, the third molar can hinder the distal movement of the impacted second molar, implying the need for extraction. Nevertheless, if the root formation of the impacted second molar is incomplete and the degree of impaction is mild, extraction of the third molar is not so urgent until otherwise deemed necessary 4,31,32. The biomechanics of the pole arm are similar to those of the pole vault. The fulcrum is on the distal contact of the first molar tube and the pole arm, while the activation force is on the canine and first/second premolar wire fixation and is opposed by the mesial surface of the impacted molar. As the tooth is being uprighted, a space develops between the uprighting molar and the tooth anterior to it. Crowns of the impacted molar and its front molar are properly ligated together with a figure 8 steel ligature or elastometric chain. Roots of the impacted molar are brought mesially without further reciprocal distal movement of the crowns. In additions, the impacted molar is usually infraoccluded and requires an eruptive force to bring the teeth into occlusion with their antagonist. The tooth should be banded/ bracketed to accomplish space closure, buccolingual correction, and occlusion detailing. There may be slight occlusal interference between the impacted molar and its antagonist or the wire during the uprighting process, but this problem rapidly resolves itself. The pole arm uprighting spring elevates the mesial marginal ridge of the impacted molar to the functional occlusal plane. However, if vertical development of the impacted molar is impeded by its antagonist, then the overerupted antagonist must be intruded. Since treatment planning in individual cases varies greatly, each malocclusion and associated periodontal involvement should be evaluated on an individual case basis. The selection of an appliance should be based on a correct evaluation of the impacted molars and their adjacent teeth as well as their antagonists. The innovation of the pole arm uprighting spring eliminates the need for early bonding or a banding apparatus on the impacted molars, which is difficult and may cause occlusal interference. Furthermore, no demand for surgical exposure of adequate crown surfaces for bonding or banding has increased patient acceptance. This article presents an uprighting technique on impacted second molars that can be used equally effectively on impacted first or third molars. It has the following advantages: (1) simple to construct, (2) inexpensive, (3) requires no considerable patient cooperation, (4) is easily activated, (5) provides rapid treatment, and (6) does not rotate molars (as often occurs with finger springs). REFERENCES 1. Varpio M, Wellfelt B. Disturbed eruption of the lower second molar: clinical appearance, prevalence, and etiology. J Dent Child, 55: , Vedtofte H, Andreasen JO, Kjaer I. Arrested eruption of the permanent lower second molar. Eur J Orthod, 21: 31-40, Johnson DC. Prevalence of delayed emergence of permanent teeth as a result of local factors. J Am Dent Assoc, 94: , Shapira Y, Borell G, Nahlieli O, Kuftinec M, Stom D. Uprighting mesially impacted mandibular permanent second molars. Angle Orthod, 68: , Sawicka M, Racka-Pilszak B, Rosnowska-Mazurkiewicz A. Uprighting partially impacted permanent second molars. Angle Orthod, 77: , Lang R. Uprighting partially impacted molars. J Clin Orthod, 19: , Freeman RS. Mandibular second molar problems. Am J Orthod Dentofac Orthop, 94: 19-25, Levitas TC. A simple technique for correcting an ectopically erupting first permanent molar. J Dent Child, 31: 16-18, Sim JM. Minor tooth movement in children. In Orthodontics Current Principles and Techniques 2nd ed, Graber TM ed, CV Mosby Co, St. Louis, pp , Moro N, Murakami T, Tanaka T, Ohto C. Uprighting of impacted third molars using brass ligature wire. Aust Orthod J, 18: 35-38, Gottlieb EL. Uprighting lower 5's and 7's. J Clin Orthod, 5: 12-19, Canut JA. Clinical management of the mandibular molars. Am J Orthod Dentofac Orthop, 68: , Kogod M, Kogod HS. Molar uprighting with the piggyback buccal sectional arch wire technique. Am J Orthod Dentofac Orthop, 99: , Weiland FJ, Bantleon HP, Droschl H. Molar uprighting with crossed tipback springs. J Clin Orthod, 26: , Majourau A, Norton LA. Uprighting impacted second molars with segmented springs. Am J Orthod Dentofac Orthop, 107: , Zachrisson BU, Bantleon HP. Optimal mechanics for mandibular molar uprighting. World J Orthod, 6: 80-87, Johnson JV, Quirk GD. Surgical repositioning of impacted second molar teeth. Am J Orthod Dentofac Orthop, 91: , Ferrazzini G. Uprighting of a deeply impacted mandibular 179

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