Evaluation of Labial Versus Lingual Biocreative Therapy for en Masse Retraction of Maxillary Anterior Teeth: A Randomized Clinical Trial

1. Background:

Maximum anchorage is commonly required in patients with severe protrusion. Conventional retraction by sliding mechanics in extraction cases have been associated with variable degrees of anchorage loss. Use of miniscrew for reinforcement of orthodontic anchorage has become increasingly popular in recent years. Miniscrews are convenient, save time, and do not require patient cooperation. However, sliding mechanics with direct anchorage from mini-screw can have several biomechanical drawbacks. The force used during retraction is not reciprocal, posteriorly it is negated by the miniscrew, not by teeth. As a result, either the entire arch or the anterior segment rotates around the center of resistance. These mechanics produce posterior open bite and anterior deep overbite. To avoid this problem, Chung et al, introduced the technique that minimizes side effects by replacing the posterior appliance segments with the partially osteointegrated C-implant. This system was called "biocreative therapy".

With the bio-creative approach, true intrusion vectors on the anterior teeth can be applied without unwanted reactive forces affecting the posterior teeth, the posterior teeth are left intact.

In Labial biocreative therapy type I, a 0.016 × 0.022-in stainless steel utility archwire is placed from the anterior segment into the implant tube, and gable bends are used to generate an anterior torque moment on the anterior segment of the teeth to provide bodily movement during en-masse retraction. On the other hand, in biocreative therapy type II, en masse anterior retraction is accomplished by applying retraction force via NiTi coil springs between an anterior retraction hook placed between the lateral incisor and the canine and the skeletal anchorage. An overlay intrusion arch wire is used to generate torque on the anterior segment of teeth; thereby various patterns of tooth movement can be obtained through the combination of intrusion force, retraction force, and length of the retraction hook. Location and management of the center of resistance (Cres) with respect to retraction force vectors is critical. The clinician should select the length of a power arm according to the desired type of tooth movement; controlled lingual crown tipping, root tipping, or bodily movement.

Adult orthodontics is an increasing part of the orthodontic practice. However, adult patients are often annoyed by the appearance of labial brackets and tend to delay or avoid starting orthodontic treatment. Lingual orthodontics is a viable option for these patients as being "invisible orthodontic treatment". The disadvantages of lingual orthodontics include the excessive chair time, complicated bio-mechanics, patient discomfort, expensive lab procedures, and high material prices. However, several innovations have improved the use of lingual orthodontics, such as customized lingual brackets and two-dimensional lingual brackets that can be bonded directly. Nonetheless, the efficient control of anterior torque and intrusion during retraction continues to be a limiting challenge.