Multicentric Clinical Study Protocol on Primary Stability of STORM® Miniscrew

Orthodontic miniscrews are intraoral anchorage devices designed to support biomechanics during orthodontic tooth movement. Also known as miniscrews, mini-implants, microscrews, or temporary anchorage devices, they are made of a head, a neck, and a threaded shank. The head may show different designs (bracket-like, rounded with slot, etc.) the threaded shank is generally cylindrical, tapered or a combination of the two, and may be self-tapping (i.e. requiring a pre-drilled pilot hole) and/or self-drilling (not requiring a pilot hole). Because of their small diameter, they may be implanted in a wide variety of anatomic sites, such as the alveolar interradicular spaces or the palatal cortical bone, in order to attend to treatment anchorage needs. The loading protocol for miniscrews loading can be as immediate as delayed; in the beginning in literature was indicated a non-specific period of healing and osseointegration before a screw inserted in the mandible could be loaded; the importance of a healing period was derived by several studies on Branemark protocol on implants. Further experimental studies on orthodontic load were not able to demonstrate loaded implant loosening, even when loads were applied immediately, so that an immediate loading protocol for orthodontic miniscrews appeared as reasonable. Costa and Melsen studied the tissue reaction around the immediately loaded screws in an animal model and suggested the use of immediately loaded screws as an intra-oral extra-dental anchorage. Histomorphometric analyses have shown that the immediate loading of miniscrew implants may help to activate bone remodeling and increase the mineral contents at the loaded region. Compared to traditional endosseous implants, orthodontic miniscrews have relatively high failure rates, varying from 16.4% to 39% ; according to recent reviews, the average failure rate is believed to be less than 20%. Many factors have been proposed to be associated to success rate; among these age, gender, jaw (maxilla or mandible), placement site, tissue mobility (firm or movable tissue), inflammation, distance to the root, insertion torque, loading time, type, length, and diameter of the miniscrew. Recently, an experimental study on primary stability found that bone properties are more important than the screw geometry in establishing primary mechanical retention. Thus the aim of this study is to deeply analyze the bone role related to the success of miniscrews analyzing both insertion/removal torque values, both bone characteristics by the mean of x-rays.