The Use of Microimplants in Lingual Orthodontic Treatment Hee-Moon Kyung Irrespective of the appliance used, anchorage control in orthodontics has always been a key requirement for successful orthodontic treatment. Conventionally anchorage is derived from dental, muscular, or skeletal components of the dentofacial complex and is often dependent on a high degree of patient compliance. The recent development of the microscrew implant has provided the clinician with a source of rigid, stationary bony anchorage not dependent on patient compliance. These screws are not osseointegrated and are retained in the bone on a purely mechanical basis. They are inexpensive and easy to place and remove at sites determined by the malocclusion and the quality of bone available at a specific site. This article discusses the use of microimplants as an adjunct to lingual orthodontics. (Semin Orthod 2006;12:186-190.) © 2006 Elsevier Inc. All rights reserved. he development of the edgewise bracket by Dr Edward Angle in the early part of the last century provided the clinician with the ability to achieve accurate tooth movement and high quality orthodontic treatment. For adult and some adolescent patients, the poor esthetics of fixed appliance treatment has been a major inhibiting factor in the acceptance of orthodontic treatment. To counteract this negative feature, Fujita1 and Kurz2 in the 1970s designed lingual brackets and initiated the concept of lingual orthodontics. As with any new technique, in the beginning there were several problems to overcome and the final results were, in many cases, unsatisfactory. Since then, with the development of the indirect bonding technique, bracket positioning has become more accurate3,4 and wire bending simplified using the concepts of the straight wire technique.5 T Department of Orthodontics, Dental School, Kyungpook National University, Daegu, Korea. Address correspondence to Hee-Moon Kyung, DDS, MS, PhD, Department of Orthodontics, Dental School, Kyungpook National University, 188-1, Sam Duk 2 Ga, Jung Gu, Daegu, Korea 700412. Office phone: ⫹ 82-(0)53-420-5947; Cell phone: ⫹82-(0)16504-7996; Fax: ⫹82-(0)53-421-7607; E-mail: hmkyung@ knu.ac.kr © 2006 Elsevier Inc. All rights reserved. 1073-8746/06/1203-0$30.00/0 doi:10.1053/j.sodo.2006.05.006 186 Anchorage control in conventional labial techniques has always been a major concern for orthodontists; this concern is equally applicable to lingual orthodontic techniques. The use of extraoral appliances for anchorage reinforcement is highly compliance dependent and esthetically unacceptable for the majority of patients considering lingual orthodontics.6 The development and incorporation of microimplants in orthodontic treatment7 has provided a means of achieving absolute anchorage for lingual8-11 as well as labial orthodontics.6 This article describes the use of microimplants in lingual orthodontics. Maxillary Microimplants In lingual orthodontic treatment maxillary microimplants can be placed between the roots of teeth in the palatal alveolar bone (Fig 1) or in the midpalatal region (Fig 2). In the young patient, the midpalatal suture is still open and in that situation the microimplant can be placed in the para-midpalatal region (Fig 3). In certain cases, it is possible to place the maxillary microimplant in the buccal region, even when using lingual appliances (Fig 4). When using microimplants at the distal end of the arch for anchorage purposes, it is difficult to control the extrusion of the maxillary anterior Seminars in Orthodontics, Vol 12, No 3 (September), 2006: pp 186-190 Microimplants Figure 1. Maxillary microimplant placed in the palatal alveolar bone. (Color version of figure is available online.) teeth, which can occur during the en masse retraction due to vertical bowing of the archwire. In cases requiring intrusion of anterior teeth, a microimplant can be placed in the labial cortical bone below the anterior nasal spine and an intrusive force applied with a clear elastomeric ligature. The ligature is tied to the two central incisors, bonded together with a clear resin or composite material (Fig 5). Microimplants are available in different lengths; as a general guide, for maxillary microimplants at least 6 mm of the screw portion should be placed into the bone (Fig 6). The mucosal thickness varies with each patient and at different sites in the palate; the thickness can be measured with an anesthetic needle during or following the injection. The following recommendations are given as a general guide Figure 2. Microimplant placed in the midpalatal region. (Color version of figure is available online.) 187 Figure 3. Microimplants placed in the para-midline region. (Color version of figure is available online.) Palatal mucosal thickness of 6 mm, use a 12-mm screw. Midpalatal thinner mucosa, use a 6- to 7-mm screw. Buccal alveolar region, attached gingivae, use 7- to 8-mm screw. Adult patients with thick dense cortical bone, use a 7-mm screw. Young patients, less dense cortical bone, use an 8-mm screw. Labial aspect of maxillary incisors, good quality bone and not subjected to occlusal forces, use a 6-mm screw. The diameter of the screw shanks can range from 1.2 to 2.0 mm. The selection of the screw diameter can be varied depending on the selected site. The following is offered as a guide. Figure 4. Microimplants placed in the buccal region of the maxilla and mandible in a case treated with a lingual appliance. (Color version of figure is available online.) 188 H.-M. Kyung Figure 5. Maxillary anterior microimplant placed in a case treated with a lingual appliance. An elastomeric thread is tied from the implant to clear plastic buttons on the central incisors. (Color version of figure is available online.) Maxillary buccal or labial regions, 1.3- to 1.5-mm thickness screw. Palatal interdental regions, 1.4- to 1.6-mm thickness screws. Midpalatal regions, depending on bone density, 1.6- to 2.0-mm thickness screws. Several head shapes including flat heads and post heads are available; once again these are selected depending on the site, access, and projected force applications (Fig 7). If there is a potential for the screw head to cause soft tissue irritation, then it is recommended to use a flat head as opposed to a post type head. Ease of access for the clinician and consideration regarding the placement of ligature wire, coil Figure 6. The microimplant should be inserted at least 6 mm into the maxilla. (Color version of figure is available online.) Figure 7. A selection of Absoanchor micro screws showing different types of heads. spring, elastomeric thread, or elastomeric chains all influence the selection of the screw head. Mandibular Micro Implants Within the confines of the mandibular arch, lingually placed microimplants do tend to irritate the tongue; therefore, it is preferable to select a flat head design rather than a post head design. Placing lingual mandibular micro implants is technically a difficult procedure. In view of these drawbacks, it is recommended that mandibular microimplants should be placed in the buccal or labial regions, even for cases undergoing lingual orthodontic treatment (Fig 4). It is unlikely that lingual cases require additional forces for mandibular incisor intrusion; however, if necessary, microimplants may be placed in the cortical bone below the lower incisors. As a general guide, at least 5 mm of the screw shank should be placed in bone (Fig 8). In patients with good quality cortical bone a 6-mm screw is adequate; in younger patients with less dense cortical bone a 7-to 8-mm screw should be selected. In the retromolar region, the mucosal thickness may vary widely; it is advisable to mea- Microimplants 189 cessfully resist a force of 300 g applied immediately after placing the microimplant. Microimplant Removal Figure 8. The microimplant should be inserted at least 5 mm into the mandible. (Color version of figure is available online.) sure the thickness with an anesthetic needle. The labial cortical bone in the mandibular incisor region is generally quite dense; and furthermore, as this region is not subject to occlusal forces a 5-mm screw should be adequate. The diameter of screw selected for the mandibular buccal regions may range from 1.4 to 1.5 mm; and for the mandibular incisal region a thinner screw, ranging from 1.2 to 1.3 mm, should be selected. As a general rule, whether the microimplant is placed in the maxilla or the mandible, always try to place it so that the head of the screw is situated in attached gingivae and not in unattached mucosa. If the screw head is in unattached mucosa, the soft tissues will grow and embed the screw head. If it is the express intention to place the screw in unattached mucosa, then a ligature wire hook should be attached to the head and allowed to protrude through the unattached mucosa (Fig 9). Although some osseointegration will take place between the titanium microimplant and bone, removal is not difficult. Screws with a diameter of 1.4 mm or less can be easily removed with less than 2 to 3 NCm torque force. Only one failure has been reported when removing a screw of 1.6-mm diameter. For ease of removal, use of smaller diameter screws is suggested and turning the hand or motor driver in the opposite direction to that used when inserting the screw. Local anesthetic is generally not required; occasionally topical anesthesia may be needed. Summary Currently excellent clinical results can and are being achieved with lingual orthodontics. For many patients, due to esthetic considerations, this is their only choice. Certain orthodontists may still feel reluctant or hesitant to attempt this form of therapy; however, several articles7-11 have shown that with the indirect bonding techniques available, by using straight wire principles and making use of microimplants for anchorage, the technique has been greatly simplified and has introduced significant treatment alternatives in 21st century orthodontics. Application of Orthodontic Forces Screws are manufactured from a titanium alloy and a degree of osseointegration between the screw and bone does take place. The success of the micro screw implant is not dependent on osseointegration, however; it is dependent purely on the mechanical retention of the screw in the bone. Research has shown that forces may be applied immediately after placing the microimplant.12 The mechanical retention can suc- Figure 9. Microimplants placed in the unattached alveolar mucosa will become buried in the soft tissue during treatment. It is necessary to extend a ligature wire from the head of the microimplant through the mucosa into the oral cavity. (Color version of figure is available online.) 190 H.-M. Kyung References 1. Fujita K: Orthodontic appliance (multiple lingual orthodontic appliance). Japan patent 55-48814, 1976 2. Kurz C: Fixed lingual orthodontic appliance for the maxillary arch. US patent 256961, 1981 3. Kyung HM: Individual indirect bonding technique (IIBT) using set-up model. J Korea Dent Assoc 27:73-82, 1989 4. Kyung HM, Park HS, Sung JH: The mushroom bracket positioner for lingual orthodontics. J Clin Orthod 36: 320-8, 2002 5. Kyung HM, Park HS, Bae SM, Yoon DY: Severe bialveolar protrusion case treated with lingual plain wire appliance & micro-implant anchorage. Dental Focus 24:1330-1343, 2004 6. Kyung HM, Kim IB: Case reports of Class I malocclusion treated with lingual appliance. Korean J Orthod 21:309324, 1991 7. Kyung HM, Park HS, Bae SM, Sung JH, Kim IB: Development of orthodontic micro-implants for intraoral anchorage. J Clin Orthod 37:321-328, 2003 8. Lee JS, Park HS, Kyung HM: Microimplant anchorage for lingual treatment of a skeletal Class II malocclusion. J Clin Orthod 35:643-647, 2001 9. Kyung HM, Park CS, Sung JH: Miniscrew anchorage in lingual orthodontic treatment for severe lip protrusion. Inf Orthod Kieferorthop 35:259-265, 2003 10. Kyung HM, Park HS, Sung JH, Kim IB: Lingual orthodontic treatment—the development of the mushroom bracket positioner (MBP) and its application. Int Orthod 1:21-47, 2003 11. Kyung HM, Park HS, Bae SM, Sung JH, Kim IB: The lingual plain-wire system with micro-implant anchorage. J Clin Orthod 38:388-395, 2004 12. Melsen B, Costa A: Immediate loading of implants used for orthodontic anchorage. Clin Orthod Res 3:23-28, 2000
