September 11, 2018
by Mohammad R. Razavi, DDS, MSD, FRCD(C)
Since the mid-2000s, Temporary Anchorage Devices (TADs) have given orthodontists a helpful tool to move teeth in ways that were previously impossible. One such movement in the vertical dimension is the intrusion of the posterior dental segments to aid in the correction of anterior open bite malocclusion. This is a powerful alternative to orthagnathic surgery. While TADs are most useful for a relatively small number of orthodontic cases, in these cases the advantages are quite significant. TADs provide tangible patient benefits by providing patients with a less invasive treatment option.
The hyperdivergent profile that is typically associated with an anterior open bites is one of the most complex malocclusions facing orthodontists. Often this malocclusion is characterized by excessive development of the maxillary posterior dentoalveolar height and a resultant steep mandibular plane. 1 Until recently, orthognathic surgery was the treatment of choice to correct this type of malocclusion. Posterior impaction of the maxillary posterior segments through a LeFort 1 osteotomy enabled closure of the anterior open bite and reduction of the mandibular plane. 2 TADs now offer an alternative treatment choice for intrusion of the posterior dental segments enabling open bite correction. Many sites have been advocated by various clinicians and academics as the “sites of choice” for placing TADs or Mini-Screw Implants (MSIs). 3 However, only the palate presents with thick, dense cortical bone levels, making it one of the most suitable sites for successful MSI placement. Other than the incisive foramen, the palate provides a site of limited potential for nerve and blood vessel damage from MSI placement. Furthermore, the palate is covered with keratinized tissue of ample thickness, which presents an environment that naturally limits tissue irritation and inflammation. 4 In addition, access for mini-screw placement is simple if proper contra-angled drivers are utilized. However, the clinician should always aim to place the MSI in the paramedian region, near but not directly on the midpalatal suture, as the suture may not be fully ossified, especially in younger patients.
The purpose of this report is to outline a novel technique of palatal skeletal anchorage using the 3M™ TAD system (Fig. 1) in the treatment of an adolescent patient with a Class I malocclusion and an anterior open bite. The use of mini-screw implants allowed for efficient and effective treatment in the closure open bite.
Diagnosis and Treatment Plan
A 14-year-old female presented with the chief complaint of an inability to bite properly. A clinical examination revealed a Class I malocclusion with an anterior open bite and mild maxillary and mandibular tooth-size-arch-length discrepancy. The anterior open bite extended between the right and left first premolar teeth (Fig. 2). A profile analysis revealed an increased lower anterior facial height with an increased mandibular plane angle. Two treatment options were discussed with the patient: Option 1 consisted of surgical orthodontic treatment including orthognathic surgery to impact the posterior maxilla through a Le-fort-1 procedure. Option 2 was a non-surgical orthodontic treatment utilizing palatal anchorage using a palatal TAD. Correction of the anterior open bite was to be achieved via intrusion of the maxillary posterior segments. The patient opted to proceed with the non-surgical treatment option.
Fig. 2 (A, B, C)
Fixed appliances (022×028 SmartClip™ Self-Ligating* brackets) were bonded and dental arch leveling and aligning initiated. At the same time as the bonding, a modified Trans Palatal Arch (TPA) was inserted. This had distal extensions soldered to the TPA such that they extended distally towards the second molars as was first described by Cope (Fig. 1). 5 The TPA was fabricated such that there was space between the bar and palatal tissue: 5mm away from the depth of the palate, and 3 mm away from the palatal walls. Wires were sequenced to 019×025 Beta Titanium wires. A 6 mm 3M™ TAD System* mini-screw implant was placed in the palate and at the level of the first molars, 1 mm lateral to the mid-palatal suture. The mini-screw implant was activated by securing two 3 mm nitinol coils to the head of the implant using a 010 stainless steel ligature, and attaching the other end of the spring to the distal extensions on the TPA (Fig. 1). Molar intrusion was maintained for 19 weeks. Once the open bite correction was achieved, fixed maxillary and mandibular lingual retainers were placed, and the patient was debonded.
The patient was seen for a total of eleven appointments during the 20-month active treatment period. Post-treatment records revealed a Class I molar relationship with ideal overjet and overbite (Fig. 3). Cephalometric superimposition (Fig. 4) indicated an improvement in the antero-posterior projection of mandible due to autorotation of the mandible as a result of the maxillary molar intrusion. Regional superimposition of the maxilla revealed 2 mm intrusion of the maxillary molars, while the extrusion of the mandibular molars was compensated by minimal amount of late mandibular growth.
Fig. 3 (A, B, C)
Discussion and Conclusion
In this case presentation, a palatal MSI allowed for a light, constant force application to the maxillary molars, leading to their intrusion and closure of the anterior open bite. The palatal application of the intrusive force prevented buccal tipping of the maxillary molars, and the resulting hanging palatal cusps of the molars; a problem often observed when the intrusive force is delivered from the buccal aspect. In more severe open bite cases, mini-screw implants placed in the mandibular buccal shelf can be combined with a lower lingual arch to also intrude the mandibular molars.
Of importance is that the use of mini-screw implants eliminated the need for patient cooperation as there are no removable appliances required to achieve the final treatment outcome. The system is readily accepted by the patient as a viable alternative to orthognathic surgery, as all components are intraoral, presenting minimal discomfort to the patient’s daily activities. OH
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* 3M Unitek Co., 2724 South Peck Rd. Monrovia, CA 91016; www.3munitek.com.
About the Author
Dr. Razavi received his dental training at Case Western Reserve University – DDS (‘02), orthodontic certificate (’05), and MSD (’05). Upon completion of his orthodontic training, he was invited to join the department as an assistant clinical professor, where he founded and directed the Skeletal Anchorage Clinic, and has integrated various TAD systems into the training program. Dr. Razavi is a diplomate of the American Board of Orthodontists, a Fellow of the Royal College of Dentists in Canada, and an ad hoc reviewer for the American Journal of Orthodontics, and the Journal of Clinical Orthodontics, Journal of Clinical Orthodontics, and Angle Orthodontist. He has served as an advocate for 3M™ Unitek since 2007, and has presented many lectures in the field of Mini-Screw Implants, Self-Ligating brackets, and non-compliant Class II correctors. He has contributed publication to multiple orthodontic journals and authored textbook chapters. Dr. Razavi’s maintains a private practice in Ottawa, Canada.