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Distal Movement of Lower Molars with Miniplate Anchorage CASSIO EDVARD SVERZUT, DDS, PhD ALEXANDRE ELIAS TRIVELLATO, DDS, PhD ALEXANDER TADEU SVERZUT, DDS, PhD RAFAEL TAJRA EVANGELISTA ARAÚJO, DDS EDUARDO SANTANA JACOB, DDS
T
he permanent teeth most likely to become impacted are the upper and lower third molars and the upper canines, followed by the lower premolars.1 Impaction of lower first permanent molars is rare, with an estimated prevalence of .01%.2 Treatment options include extraction, with or without osseointegrated implant placement, dental luxation, or orthodontic loading; orthodontic treatment with intra- or extraoral devices; and orthodontic extrusion with screws or plates as temporary skeletal anchorage.3 Because normal eruption of the lower first and second molars is essential for development and coordination of the dental arches and the facial skeleton,4 a conservative treatment plan aimed at proper positioning of these teeth in the mandibular arch should be considered whenever possible. After the first use of a miniplate for temporary anchorage was reported in 1985,5 numerous strategies for using such devices have been proposed. This article describes how a new plate can be applied to distalize and upright lower first and second molars. Case Report The University of São Paulo’s ethical review board supported this study after the patient’s parents provided written informed consent. The patient was a 9-year-old male who was referred by his orthodontist for removal of the lower right first molar. Panoramic radiographs revealed impaction and severe root dilaceration of this tooth, along with significant bone loss at the distal root surface
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Fig. 1 9-year-old male patient with impacted lower right first molar and loss of bone height distal to adjacent second premolar before treatment.
of the adjacent second premolar (Fig. 1). As an alternative to extraction of the first molar, we recommended removal of the soft and hard tissues covering the lower right first and second molars, followed by observation of their eruption over the subsequent 12 months. We had expected that once the eruption pathway was unblocked, mandibular growth would result in improved positioning of both molars. After the 12-month observation period, the second molar had erupted completely, but only a small portion of the first molar crown was seen (Fig. 2A). Cone-beam computed tomography (CBCT) indicated that 6mm of anteroposterior space would be required for adequate repositioning of the first and second molars. Rather than removing the lower right first molar, we proposed the use of a 1.6mm Sverzut anchor-plate system* for temporary
© 2015 JCO, Inc.
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Dr. Cassio Sverzut
Dr. Trivellato
Dr. Alexander Sverzut
Dr. Araújo
Dr. Jacob
Drs. Cassio Sverzut and Trivellato are Associate Professors, Department of Oral and Maxillofacial Surgery and Periodontology, School of Dentistry of Ribeirão Preto, University of São Paulo, Av. do Café, s/n-Campus USP, 14040-904 Ribeirão Preto, São Paulo, Brazil. Dr. Alexander Sverzut is an Associate Professor, Department of Oral Diagnosis, Oral and Maxillofacial Division, School of Dentistry of Piracicaba, University of Campinas, São Paulo. Drs. Araújo and Jacob are residents, Department of Oral and Maxillofacial Surgery and Periodontology, School of Dentistry of Ribeirão Preto, University of São Paulo. Dr. Cassio Sverzut is the developer of the miniplate system described in this article; e-mail him at
[email protected].
skeletal anchorage. This system consists of two double-faced, non-countersunk “T” plates, fixed with 1.6mm-diameter, 5mm-long screws. Under local infiltrative anesthesia, two small incisions were made from the distal surface of the lower right second molar: one toward the retromandibular triangle, and the other deep into the vestibular sulcus. After soft-tissue detachment, the longer Sverzut plate was cut into an “L” shape, bent in a “step” fashion, and passively adapted and affixed to the bone surface (Fig. 2B). We attempted to use three screws, but only two could be engaged properly. During closure with absorbable Vicryl** 4-0 sutures, care was taken to cover the part of the plate that was fixed to the bone and to leave open the “arm” of the plate, which contains slots for orthodontic purposes. The prescribed medication consisted of oral doses of amoxicillin (500mg) every eight hours for seven days, diclofenac potassium (50mg) every eight hours for three days, and dipyrone (500mg) every six hours as needed for pain. The postoperative period was uneventful. After one week, an orthodontic appliance was bonded to the buccal surface of the second molar, and a 120g load was applied. After 14 months, when no significant clinical or radiographic improvements were observed in the molar areas (Fig. 2C), the strategy was modified: the
*Anton Hipp, Fridingen, Germany; www.anton-hipp.de/. **Trademark of Ethicon, Johnson & Johnson Group, HamburgNorderstedt, Germany; de.ethicon.com.
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attachment was removed from the second molar, and another appliance was bonded to the occlusal surface of the first molar. A 150g load was applied with an elastomeric chain and wire. After four months, significant improvement was observed in the first-molar angulation (Fig. 2D); nine months later, the first and second molars were in appropriate positions within the mandibular arch (Fig. 2E). As the first molar was uprighted and distalized, the second molar began to contact the arm of the plate, which required periodic trimming. Although the miniplate treatment lasted 27 months, this time could have been reduced substantially if the orthodontic appliance had been bonded to the first molar from the beginning. The lower right third molar was not removed initially to preserve it as an option in case of failure of the plate-anchorage treatment. Following successful repositioning, the plate and the lower right third molar were removed in a single procedure, using the same approach as for the plate placement. After a flap was raised, a thin layer of neoformed bone could be seen partially covering the plate (Fig. 3A). A superficial ostectomy was performed, and a No. 701 surgical-length crosscut-fissure bur mounted in a high-speed handpiece was applied to remove the bone layer (Fig. 3B). The screws were easily removed with a screwdriver, but a Molt periosteal elevator had to be wedged under the plate to dislodge it from the surrounding bone. The third molar was removed, and the flap was repositioned and sutured. Except for the antibiotic, the same medications were prescribed as for the first procedure.
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Distal Movement of Lower Molars with Miniplate Anchorage
Two years after removal of the plate, optimal intercuspation was observed, with the lower first and second molars in normal positions (Fig. 4). The panoramic radiograph confirmed maintenance of the first-molar roots and the bone height distal to the adjacent second premolar. Although
A
clinical evaluation and the postoperative radiograph indicated that the required 6mm of space was gained, it would be impossible to determine the precise amount of tooth movement achieved, considering the mandibular growth that occurred during treatment.
B
C
D
E
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Fig. 2 A. 12 months after removal of soft and hard tissues covering lower right first and second molars. B. Longer miniplate cut into “L” shape, bent, and fixed passively to bone surface with two screws. C. After 14 months of attempted second-molar distalization. D. Four months after bonding of orthodontic appliance to first molar. E. Nine months later, showing lower right first and second molars in appropriate positions.
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Sverzut, Trivellato, Sverzut, Araújo, and Jacob
A
B Fig. 3 A. Thin layer of neoformed bone partially covering plate and screws. B. Plate and screws exposed with superficial ostectomy.
Discussion Temporary skeletal anchorage for lowermolar distalization can be provided by either miniimplants or miniplates. A mini-implant is typically placed in the retromandibular region in a “closed” fashion, with a wire attached to the screw protruding into the buccal cavity for load application.6 The main disadvantages of mini-implants compared to miniplates are the reduced load that can be supported and the tendency of the implant to migrate toward the tooth being moved. Placement of a mini-implant in the posterior area of the mandible also carries the risk of damage to the inferior alveolar nerve, which lies an average 5mm from the buccal cortical plate.7 Shorter screws, typically only 5mm in length, are required to en-
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sure monocortical engagement of a miniplate. In cases where three screws cannot be properly engaged without affecting the position of the plate, as in the patient shown here, two screws may be sufficient. Because the Sverzut plates are not countersunk, they can be used on both sides of the upper and lower jaws. The 1.6mm diameter of these screws is smaller than the more common 2mm, providing more options for placement. The screwheads remain partially untapped on the surface of the plate, and new bone is unlikely to form over the heads, making it easier to remove them. Umemori and colleagues reported successful lower-molar intrusion with anchorage from 2mm surgical plates in two severe open-bite cases.8 Sugawara and colleagues proposed the use of a similar plate for lower-molar distalization in nongrowing patients.9 Ohura and colleagues applied a single plate for intrusion of an upper right first molar and subsequent uprighting of a lower right first molar.3 In contrast to our configuration, these authors fixed the plate to the zygomaticomaxillary buttress and applied interarch elastics to upright the lower first molar. The use of intra-arch elastics, as applied in our case, has two main advantages: improved control of the applied loads and reduced discomfort to the patient, since there is no interference with mandibular movements. Alterations in the direction and intensity of load can have important effects on the length and success of treatment. Sugawara and colleagues reported needing 19-39 months to distalize lower molars with miniplate anchorage in their adult patients.9 On the other hand, Miyahira and colleagues required only three months to distalize and de-impact the lower right second molar with anchorage from a 2mm “T” surgical plate.10 In our patient, CBCT indicated that 6mm of anteroposterior space had to be gained to allow proper positioning of the lower right first and second molars. Sugawara and colleagues found an average distalization of 3.5 ± 1.4mm at the crown level and 1.8 ± 1.4mm at the root level after lowermolar distalization with miniplate anchorage.9 In a report by Kim and colleagues, the available posterior space was less at the root level than at the
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Fig. 4 Optimal intercuspation two years after plate removal, with lower right first and second molars in proper positions. Note maintenance of first-molar roots and bone height distal to adjacent second premolar.
crown level, indicating that the anatomical posterior limit is not the anterior border of the ramus, but rather the lingual cortex of the mandibular body.11 These authors recommended the use of CBCT to assess the chances of successful distalization whenever cephalometric radiographs indicate less than 3.9mm of available space between the lower second molar and the anterior border of the ramus. Conclusion The potential to safely and effectively distalize and upright lower molars in growing patients opens new possibilities for orthodontic treatment with miniplate anchorage. This innovative technique requires further study to establish its risks and benefits. ACKNOWLEDGMENT: The authors would like to acknowledge Dr. Karina Lima Peixoto Albuquerque for the orthodontic treatment. REFERENCES 1. Sawicka, M.; Racka-Pilszak, B.; and Rosnowska-Mazurkiewicz, A.: Uprighting partially impacted permanent second
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molars, Angle Orthod. 77:148-154, 2007. 2. Bereket, C.; Çakir-Özkan, N.; Şener, I.; Kara, I.; Aktan, A.M.; and Arici, N.: Retrospective analysis of impacted first and second permanent molars in the Turkish population: A multicenter study, Med. Oral Patol. Oral Cir. Bucal. 16:874878, 2011. 3. Ohura, R.; Kuroda, S.; Takahashi, T.; Tomita, Y.; and Tanaka, E.: Efficient usage of implant anchorage to treat overerupted maxillary first molar and mesially inclined mandibular molars, Am. J. Orthod. 139:113-122, 2011. 4. Raghoebar, G.M.; Boering, G.; Vissink, A.; and Stegenga, B.: Eruption disturbances of permanent molars: A review, J. Oral Pathol. Med. 20:159-166, 1991. 5. Jenner, J.D. and Fitzpatrick, B.N.: Skeletal anchorage utilising bone plates, Aust. Orthod. J. 9:231-233, 1985. 6. Park, H.S.: The Use of Micro-Implant as Orthodontic Anchorage, Nare Publishing Co., Seoul, Korea, 2001. 7. Levine, M.H.; Goddard, A.L.; and Dodson, T.B.: Inferior alveolar nerve canal position: A clinical and radiographic study, J. Oral Maxillofac. Surg. 65:470-474, 2007. 8. Umemori, M.; Sugawara, J.; Mitani, H.; Nagasaka, H.; and Kawamura, H.: Skeletal anchorage system for open-bite correction, Am. J. Orthod. 115:166-174, 1999. 9. Sugawara, J.; Daimaruya, T.; Umemori, M.; Nagasaka, H.; Takahashi, I.; Kawamura, H.; and Mitani, H.: Distal movement of mandibular molars in adult patients with the skeletal anchorage system, Am. J. Orthod. 125:130-138, 2004. 10. Miyahira, Y.I.; Maltagliati, L.A.; Siqueira, D.F.; and Romano, R.: Miniplates as skeletal anchorage for treating mandibular second molar impactions, Am. J. Orthod. 134:145-148, 2008. 11. Kim, S.J.; Choi, T.H.; Baik, H.S.; Park, Y.C.; and Lee, K.J.: Mandibular posterior anatomic limit for molar distalization, Am. J. Orthod. 146:190-197, 2014.
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