One of major challenges in orthodontics is to inhibit relapse and ensure stability of treatment outcomes. Retention is the phase of orthodontic treatment that attempts to keep teeth in the corrected position after correction with orthodontic braces. Without retention there is a tendency for the teeth to return to their initial position (1). Retention is usually necessary to overcome the elastic recoil of the periodontal supporting fibers and to allow remodeling of the alveolar bone. The bonded orthodontic lingual retainer constructed from composite and orthodontic wires provides an esthetic and efficient system for maintained retention and has been shown to be an effective means of retaining aligned anterior teeth in the post treatment position in the long term. This has been in popular use as a method of retention since the late 1970s (2).
The traditional retainers, which are still in use, are multi-strand stainless steel retainers such as Penta-one® 0.0215 (Masel Orthodontics, Carlsbad, CA, USA). The main problem with multistrand stainless steel retainers is their high rate of failure. Clinical studies indicate that 5% to 37% of mandibular retainers fail during retention in some form, either bond failure or wire breakage (3-5). Reliance Orthodontic Products, Inc. (Itasca, IL, USA) recently introduced a bonded retainer system (Ortho-Flextech™ chain). This retainer's bonding is claimed to be quick and easy by reducing chairside time and eliminating laboratory costs (6). One other recently introduced retainer is Memotain™ (CA-Digital in Mettmann, Germany). Memotain is a CAD/CAM fabricated lingual retainer made of 0.014 X 0.014-inch rectangular nickel-titanium. The wire is highly flexible and custom cut to precisely adapt to the patient's lingual tooth anatomy. According to manufacturer, Memotain offers numerous perceived advantages to traditional multistranded lingual wires, including no need for wire measuring or bending, individually optimized placement, greater accuracy of fit, tighter interproximal adaptation, less tongue irritation, better durability, and resistance to microbial colonization (6). However, randomized clinical trials are necessary to determine whether these advantages are substantiated with scientific data.
A recent review by the Cochrane group concluded that to date there is insufficient evidence to single out any particular retention strategy as the preferred method: it was recommended that future studies should include true randomization, reporting of dropouts, adequate sample size calculation, and a minimum follow-up period of 3 months (8). Thus, the aims of this multicenter, randomised controlled trial are:
* To compare and evaluate the effectiveness and failure rate of Penta-one multistrand, Ortho-Flextech and Memotain retainers with each other
* To compare the possible complications between the three retainers over time
* To establish the cost-effectiveness of the three retainers
* To evaluate the effectiveness of sandblasting in the retention of the wires