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Straight Talk Mohammad R. Razavi, DDS, MSD, FRCD(C)

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Anterior open bite is one of the most difficult malocclusions to treat orthodontically. Successful correction and closure of anterior open bites have plagued orthodontists for nearly as long as our profession has existed. Modifications of outer bow of the headgear have been demonstrated to affect molar intrusion and allow for clockwise rotation of the mandible, leading to closure of the anterior open bite.¹ Oftentimes early treatment of patients via molar intrusion has been advocated as a treatment objective in open bite treatment. Commencement of treatment in the mixed dentition allows orthodontists to take full advantage of growth modification in order to increase the posterior facial height to anterior facial height ratio and to forward autorotation of the mandible.²

Treatment success, however, is highly dependent on patient compliance and cooperation. In older patients with limited growth modification potential, the treatment of choice for many years has been orthognathic surgery to impact the maxillary posterior segment and closure of the anterior open bite by mandibular plane reduction.³ A more invasive treatment option, along with the increased treatment costs due to surgery, makes this treatment less appealing for most patients. The recent increase in popularity of temporary anchorage devices has provided orthodontists with treatment alternatives in correcting anterior open bite malocclusions. Posterior teeth can now be intruded to allow for mandibular autorotation and closure of the anterior open bite. The intent of this article is to give the clinicians an overview of various means to intrude posterior teeth in treatment of anterior open bites and discuss their potential complications.



Titanium surgical plates have been documented in treatment of anterior open bites. In patients with excessive maxillary posterior growth, the posterior teeth can be intruded by loading them with a NiTi coil attached to molar brackets and titanium plates fixed bilaterally to the zygomatic buttress.4 This technique, though effective, requires the expertise of another dental specialist in placement and later removal of the plates. Alternatively, the surgical plates were replaced by mini-screw implants as they provided orthodontists with a far less invasive means to achieve molar intrusion and correction of open bites. Mini-screw implants can be inserted bilaterally into the infra-zygomatic crest (Fig. 1), and loaded using NiTi coil springs attached to the molars (Fig. 2), resulting in molar intrusion.5 Clinically however, limited success was achieved when this method to intrude molars was employed. Even though an increase of 2mm in overbite was observed in only 14 weeks, there was significant tissue irritation, causing a soft-tissue infection. The mini-screw implants had to be prematurely removed and open bite correction was not fully achieved (Fig. 3). The tissue overgrowth and inflammation could be attributed to difficulty in maintaining optimal oral hygiene in the depths of the mucobuccal fold, and the lack of keratinized gingiva in the implant site. Upon removal of the mini-screws the soft-tissue irritation resolved and the alveolar mucosa returned to health within two weeks.

In order to avoid this tissue irritation, mini-screw implants were placed interdentally in the attached gingiva. The implants were activated by attaching an elastic chain module to the molar and premolar brackets (Fig. 4). Though the open bite was expected to be reduced upon activation, in theory, the open bite was increased initially. This can be attributed to the application of an intrusive force away from the center of resistance of the molar, leading to a force couple and labial crown tipping. Subsequently, a palatal mini-screw implant was placed, and a chain module that traversed the occlusal surface of the first molars, and attached to the mini-implants buccally and lingually.6 This technique reduced the labial tipping of the molars, and resulted in improved mechanotherapy in the reduction of the anterior open bite. However, there was significant patient discomfort due to the occlusal irritation caused by the elastic module crossing the occlusal table of the molars.

Further research in attempt to prevent molar labial tipping resulted in the routine use of a transpalatal arch in all molar intrusion cases.7 The key to successful use of TPA is maintaining the bar away from palatal tissue. A 3-5mm distance is desired between the TPA and palatal gingiva to avoid tissue impingement (Fig. 5). Well-designed transpalatal arch, combined with interdental buccally positioned mini-screw implants, leads to successful molar intrusion with minimal complication. A common complication observed in using this technique was the premature loosening and loss of the mini-implants. Limitations of interradicular bone, deviations in placement angle, impingement of the PDL space and potential cementum contact have all been reported as potential complications of mini-screw placement.8 In addition, the posterior maxilla and maxillary tuberosity have reduced bone density, and minimal cortical bone thickness leading to reduced primary stability and success rates for mini-screw implants placed in this site.9,10

Alternatively, the palate is now routinely used as the site of choice for mini-screw implant placement (Fig. 6). The palate provides a site of thick, dense cortical bone that provides significant screw retention. Furthermore, the bone is covered with ample keratinized tissue, making it resistant to tissue irritation and inflammation. Other than the incisive foramen, the palate also provides a site of limited potential for nerve and blood vessel damage from mini-screw placement.11 Future publications will outline the specific treatment mechanics and TPA design commonly utilized to predictably intrude molars and close open bites.

References
  1. Kuhn RJ. Control of anterior vertical dimension and proper selection of extraoral anchorage. Angle Orthod. 1967; 340-9.
  2. English JD. Early treatment of skeletal open bite malocclusion. Am J Orthod Dentofacial Orthop. 2002; 121:563-5.
  3. Worms FW, Speidel MT, Bevis RR, Waite DE. Post-treatment stability and esthetics of orthognathic surgery. Angle Orthod. 1980, 50:251-73.
  4. Erverdi N, Keles A, Nanda R. The use of skeletal anchorage in open bite treatment: A cephalometric evaluation. Angle Orthod. 2004; 74:381-90.
  5. Liou EJW, Chen PH, Wang YC, Lin CY. A computed tomographic image study on the thickness of the infrazygomatic crest of the maxilla and its clinical implication for miniscrew insertion. Am J Ortho Dentofacial Orthop. 2007; 131:352-6.
  6. Kravitz ND, Kusnoto B, Tsay PT, Hohlt WF. Intrusion of overerupted upper first molar using two orthodontic miniscrews. Angle Orthod. 2007; 77:915-22.
  7. Xun C, Zeng X, Wang X. Microscrew anchorage in skeletal anterior open-bite treatment. Angle Orthod. 2007; 77:47-56.
  8. Baumgaertel S, Razavi MR, Hans MG. Mini-implant anchorage for the orthodontic practitioner. Am J Orthod Dentofacial Orthop. 2008; 133:621-7.
  9. Lee K, Joo E, Kim K, Lee L, Park Y, Yu H. Computed tomographic analysis of tooth-bearing alveolar bone for orthodontic miniscrew placement. Am J Orthod Dentofacial Orthop. 2009;135:486-94.
  10. Park H, Lee Y, Jeong S, Kwon T. Density of the alveolar and basal bones of the maxilla and the mandible. Am J Orthod Dentofacial Orthop. 2008;133:30-7.
  11. Kang S, Lee S, Ahn S, Heo M, Kim T. Bone thickness of the palate for orthodontic mini-implant anchorage in adults. Am J Orthod Dentofacial Orthop. 2007;131:S74-80.
Author’s Bio
Dr. Mohammad R. Razavi maintains a private practice in Ottawa, Canada. He received his dental and orthodontic training at Case Western Reserve University, where he currently serves as an assistant clinical professor.

He is a diplomate of the American Board of Orthodontists and a fellow of the Royal College of Dentists in Canada. Since 2007 he has served as an advocate for 3M Unitek and has presented many lectures in the field of mini-screw implants and self-ligating brackets.
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