The use of microscrews in the maxilla and mandible is effective for closing significant anterior open bites in approximately six to seven months.
Have you had a patient where you plan to use miniscrews or microscrews to help provide anchorage for orthodontic treatment? I have treated several of these patients, and these
miniscrews work very well. But have you ever tried them to correct a significant anterior open bite? Some of these patients with severe open bite are not good surgical candidates.
Sometimes their facial features can be comprised by maxillary surgery, and mandibular closure of an open bite is perhaps subject to instability. By placing screws in both the
maxilla and mandible, these open bites can be closed by intruding both maxillary and mandibular posterior teeth. At least that is the theory. But, does it work and how long does it take? Those questions were addressed in a recent study. The purpose of this study was to investigate the effectiveness of microscrew anchorage in the treatment of skeletal anterior open bite. The sample for the study consisted of 12 patients with an average age of 18 years. All subjects had completed primary facial growth, and all had skeletal anterior open bite with mild Class II skeletal relationships.
All the subjects had declined orthognathic surgery, and all of these subjects had either four premolars or four first molars extracted to help reduce protrusion and eliminate crowding. Then, as a part of the treatment, self-drilling titanium alloy microscrews, which were about 1.6 mm in diameter and 7 mm in length, were inserted into the buccal alveolar bone on each side of the mandible. These were placed between the first and
second molars. In the maxilla, in the palate specifically, a 9 mm long screw was inserted in the posterior midpalatable area corresponding to the upper first molar. In each patient,
a fixed transpalatal arch and a lingual arch were attached to the upper and lower first molars and were located 5 mm from the palatel or lingual tissues. Two weeks after implantation, the intrusion treatment was initiated, Then, nickel titanium coil springs were placed bilaterally in the maxillary arch between the miniscrew or microscrew and the traction hooks on the transpalatal arch. In the mandible, power chains were used o
deliver the force between miniscrew and the main mandibular arch wire. About 150 gof force were applied on each side. In order to document the changes, preintrusion and
postintrusion, cephlametric radiographs were compared.
Authors showed an average over bite increase of 4mm and an average open bite decrease of 2mm.This was significant. The maxillary first molars and mandibular first molars were intruded an average of about 1.6 mm. In addition, the mandibular plane angle decreased in average about 2.5 degrees and the anterior facial height decreased about 2mm. this type of treatment was found to be very effective.
Authors showed some of the treatment results, and the changes are definitely impressive. I liked the fact the patients faces did not change significantly, as we sometimes see in orthgnathic surgery, especially the maxilla. I do have some concerns. Although this treatment works, the authors did not document post-treatment changes. We know from past studies maxillary impaction surgery to correct open bites does relapse. In fact, the
maxillary and mandibular molars erupt after surgery. Now, if the incisors also erupt, then the open bite stays closed. This is essentially a long-term study looking at postintrusion changes that occur up to two years after molar intrusion using microscrews. I hope these authors continue to follow this sample of subjects to document those types of changes and report on them in the near future.
By Vincent G. Kokich, DDS, MSD
Based on: Xun C, Zeng X, Wang X. Microscrew Anchorage in
Skeletal Anterior Open-Bite Treatment. Angle Orhtod 2007; 77
(1): 47-56
