Use of the Multi-Tooth Intruder for Maxillary Posterior Intrusion and Torque Control by Alexander Waldman, DMD

The past decade in orthodontics has been marked by major advancements in mechanics using skeletal anchorage. One specific area that has been significantly affected is vertical control of the dentition.

Multiple clinical and research papers have demonstrated the efficacy of temporary orthodontic implants—often called TADs, mini-implants or miniscrews—to intrude maxillary posterior teeth. In certain cases, it is clinically advantageous to control the crown torque of individual maxillary posterior teeth, or to intrude smaller or unilateral groups of teeth. In this article, I will introduce an appliance called the multi-tooth intruder (MTI) and demonstrate its use in both fixed appliance and clear aligner cases.

Maxillary posterior intrusion
Multiple techniques have been proposed for orthodontic intrusion of maxillary posterior teeth. One of the most common techniques is the use of palatal TADs and a transpalatal arch, with elastic or coil-spring traction from the TADs to the transpalatal arch. Another well-accepted technique is the fabrication of an occlusal splint that allows for en masse intrusion and transverse stabilization using palatal TADs, buccal TADs or both.

Common to the above techniques is the en masse nature of the movements. In other words, there is a single point of application of the intrusive force to the dentition. This can be a very successful strategy in the treatment of many forms of vertical malocclusion, including anterior open bite. However, some cases require more specific control over the torque of individual teeth, or vertical movements of smaller or unilateral groups of teeth. The MTI appliance was developed to address this need in both fixed appliance and clear aligner cases.

The MTI is a generic soldered appliance that can be used with any skeletal anchorage system. Two palatal TADs are placed in the anterior palate. After 1–2 weeks, stability of the TADs is confirmed and a pickup impression is taken to create a working model. The MTI is soldered in the lab per the specific needs of the case, and can be fabricated in a bilateral or unilateral fashion. The main features of the appliance are cantilevered shepherd's hooks, which allow for attachment of an elastic force to multiple posterior teeth. For additional stability, the appliance can have a transverse crossbar, and could also be bonded to the canines or first bicuspids.

Clinically, the MTI is bonded to the TADs using flowable composite. Bonded buttons are placed on the palatal surfaces of the posterior teeth needing intrusion, and elastic chain is activated from the shepherd's hook to the bonded buttons. If necessary, buccal TADs can be added to help control the transverse constriction effects of the palatal intrusion mechanics.

The activation of intrusion forces on specific teeth can be changed throughout the case, making the MTI an extremely flexible appliance. Furthermore, the proximity of the shepherd's hooks to the palatal wall promotes vertical forces along the long axis of the tooth, allowing for excellent torque control of the palatal roots and minimal transverse constriction. The case reports that follow will demonstrate the clinical use of the MTI with fixed appliances and with clear aligners.

Conclusion
The MTI appliance is an effective adjunct to comprehensive orthodontic treatment with fixed appliances or clear aligners. It is useful in cases that benefit from specific torque control of maxillary posterior teeth or in cases that benefit from unilateral or partial maxillary posterior intrusion.

Alexander Waldman, DMD, owns a private practice in Beverly Hills, California. He is a diplomate of the American Board of Orthodontics. He received his undergraduate and dental degrees from the University of Pennsylvania, where he graduated with honors and was inducted into the national dental honor society Omicron Kappa Upsilon, and received the National Board Achievement Award.Waldman completed his fellowship in orthodontics at Harvard University and received the Joseph L. Henry Award for Excellence in Clinical and Research Training.