"Safe zones": a guide for miniscrew positioning in the maxillary and mandibular arch.

The aim of this study was to provide an anatomical map to assist the clinician in miniscrew placement in a safe location between dental roots. Volumetric tomographic images of 25 maxillae and 25 mandibles taken with the NewTom System were examined. For each interradicular space, the mesiodistal and the buccolingual distances were measured at two, five, eight, and 11 mm from the alveolar crest. In this article, measurements distal to the canines are presented. In the maxilla, the greatest amount of mesiodistal bone was on the palatal side between the second premolar and the first molar. The least amount of bone was in the tuberosity. The greatest thickness of bone in the buccopalatal dimension was between the first and second molars, whereas the least was found in the tuberosity. In the mandible, the greatest amount of mesiodistal dimension was between first and second premolar. The least amount of bone was between the first premolar and the canine. In the buccolingual dimension, the greatest thickness was between first and second molars. The least amount of bone was between first premolar and the canine. Clinical indications for a safe application of the miniscrews are provided, as well as the ideal miniscrew features.

Mechanical properties of three different commercially available miniscrews for skeletal anchorage.

BACKGROUND: During the last 5 years, anchorage control with self-tapping miniscrews has become an important part of the clinical management of orthodontic patients. Yet, no studies have been performed for measuring mechanical properties of the currently available systems. OBJECTIVES: The purpose of this study is the evaluation of mechanical properties of three commercially available self-tapping screw systems used in orthodontic treatment. MATERIALS: three systems with a 1.5 mm diameter and 11 mm length screw (Leone, Firenze, Italy; M.A.S. Micerium, Avegno, Italy; Dentos, Korea) were examined. The results compared the resistance to bending, torque, pullout of each screw and the insertion moments needed to screw down each sample. CONCLUSIONS: All three miniscrews have mechanical properties that contribute to their safe use as skeletal anchorage in orthodontics. Although stainless steel has demonstrated to be more resistant to failure than titanium, its overall performance as material for miniscrews could be inferior to titanium. In order to facilitate the insertion, the asymmetric profile of the thread should be preferred to the symmetric cut. The ratio between the diameter of the drill and the diameter of the corresponding miniscrew is pivotal for the successful implantation and resistance of the miniscrews. Looking at the mechanical properties evaluated in this study, a cylindric shape of the screw is better than a conic one. The conic shape could be preferred in case the site of insertion is iterradicular and therefore limited to 2.5-3.5 millimetres.

Clinical applications of the Mini-Screw-Anchorage-System (M.A.S.) in the maxillary alveolar bone.

AIMS: anchorage control with self-tapping screws has become an important part of the clinical management of the orthodontic patients. Mechanical resistance and sites of insertion of miniscrews as orthodontic anchorage are critical to ensure successful outcomes. Aim of this clinical study was threefold: 1) to measure the mechanical resistance of the M.A.S., 2) to evaluate if the alveolar areas usually selected for mini-screws placement are adequate, 3) to illustrate the most frequent clinical application on the maxillary alveolar bone. METHODS: two methods were chosen to test these screws mechanically, representing two potential modes of failure during insertion or removal: torsional strenght and bending strenght. Three-dimension images of fifty maxillas have been retrieved from a group of 200 patients, age range between 20 and 40 years with a new type of tomogram called Newtom System. For each area mesio-distal and labio-lingual measurements from four horizontal cuts made at 2-5-8-11 mm below the bone-crest have been evaluated. RESULTS: the mean value of resistance to breakage in torsion is of 48.7 N.cm (around 5 Kg) for the miniscrew of 1.5 diameter, while the mean value of resistance to breakage in torsion is of 23.4 N.cm (around 2 Kg) for the miniscrew of 1.3 diameter.. The mean value of resistance to breakage in flexion is of 120.4 N (around 12 Kg) for the miniscrew of 1.5 diameter, while the mean value of resistance to the flexion is of 63.7 N (around 6 Kg) for the miniscrew of 1.3 diameter. On the maxillary alveolar bone the highest amount of bone was in mesio-distal dimension between 6 and 5 on the palatal side (minimum 1.9 mm at -11 mm cut; maximum 5.5 mm at -5 mm cut). The smallest amount of bone was in the tuber (minimum 0.2 mm; maximum 1.3 mm). Examination of the labio-palatal dimension demonstrated similar high thickness between 5-6 and 6-7 (minimum 3.7 mm at -11 mm cut; maximum 13.2 mm at -2 mm cut). The smallest amount of bone was recorded on the tuber (minimum 0.6 mm; maximum 4.1 mm). The following clinical applications are described: Closure of the extractions space, Symmetric intrusion of the incisors, Correction of the cant of the plane of occlusion and of the dental midline, Molar intrusion of one or two teeth, Molar distalization with the Distal Jet and miniscrews, Molar mesialization, Intermaxillary anchorage. CONCLUSIONS: the mechanical resistance of the miniscrews M.A.S. is suitable for their use in orthodontics. The best anatomical zones for their implantation are the interradicular spaces mesial to the first maxillary molars. From our experience to date, the miniscrews are a reliable and convenient system for skeletal anchorage when compared with other more invasive osseo-integrated systems.