[A functional orthodontic magnetic appliance (FOMA) after Vardimon. 1. A three-dimensional analysis of the force system of the attractive magnets]. / Das funktionskieferorthopädische Magnetsystem (FMS) nach Vardimon. Teil 1. Dreidimensionale Analyse des Kraftsystems anziehender Magnete.

The functional magnetic system (FMS) is a removable functional appliance which induces mandibular advance by means of mandibular and maxillary magnets in an attracting configuration. The maxillary and mandibular plates are each equipped with 2 cylindrically shaped cobalt-samarium magnets, 4 mm in diameter and 3 mm in height, which are welded into stainless steel housings. The force system of this magnetic configuration was analyzed using the orthodontic measurement and simulation system (OMSS). OMSS simulated the mandibular jaw movements by separating the installed magnets vertically, corresponding to a mouth opening of X = -10 mm, transversally (right excursion, +/left excursion, -) at Y = +/- 10 mm and sagittally (anterior displacement, +/posterior displacement, -) at Z = +/- 10 mm. The resulting 2D and 3D force/displacement diagrams elucidate the outstanding centripetal-spatial orientation characteristics of the functional magnetic appliance in reference to the full overlap brought about by the attraction of the mandibular magnet by the maxillary magnet. The maximum centripetal forces reached a value of approximately FY, max = 0.65 N for the vertical attracting force at full overlap of the mandibular and maxillary magnets (X = 0.55 mm, Y = Z = 0 mm), a value of FY, max = 0.65 N for the medial shearing force at a partial transversal overlap Z = 0, Y = +/- 2 mm and Y = +/- 6 mm), and for the sagittal shearing force a value of FZ, max = 1.2 N at a partial sagittal overlap of the magnets (Y = 0 mm, Z = +/- 2 mm).(ABSTRACT TRUNCATED AT 250 WORDS)

[The long-term fracture resistance of orthodontic nickel-titanium wires]. / Dauerbruchfestigkeit orthodontischer Nickel-Titan-Drähte.

This study reports on the long-term fracture resistance of orthodontic nickel titanium wires, a material property that has not been investigated thoroughly, yet. A computer-controlled apparatus was designed to perform long-term bending tests. The investigated material comprised 9 nickel titanium wires (dimensions 0.016", round and 0.016" x 0.022", rectangular) as well as a stainless steel and a beta-titanium wire that were included as reference. Compared with the steel wire, the nickel titanium wires exhibited 2- to 5-fold higher yield forces in bending. At a specified deflection angle, the generated bending forces of the nickel titanium wires reached one half to one fourth of the values of steel. The fracture resistance under longterm loading was determined using the Wöhler-method. After 10(5) loadings, 0.016" nickel titanium wires were subject to break failure, if forces exceed values greater than 1.2 to 3.1 N. Steel and TMA wires could be loaded with forces of up to 4.4 and 3.7 N, respectively. The 0.016" x 0.022"-rectangular wires allowed forces of approximately twice this magnitude. Elastic fatigue of the superelastic specimens "Memorywire", "Rematitan Lite", and "Sentalloy medium" showed up as hardening of the wire by up to 70%. Material degradation lead to a severe deformation of the hysteresis loop and to plastic deformation. Work-hardened martensitic NiTi wires did not show these effects to this extent.

3-D force and moment analysis of repulsive magnetic appliances to correct dentofacial vertical excess.

Repulsive magnetic appliances can intrude posterior teeth, but create a lateral shift of the mandible and also decrease in force as the mouth opens. To model their optimal use, the 3-D spatial force/displacement (F/D) and moment/displacement (M/D) diagrams of four magnetic repulsive appliances in diverse overlapping arrangements were characterized and compared. In this orthodontic measurement and simulation system, only the medial eccentric magnetic arrangement, of the four compared, partially met the criteria of an optimal repulsive force system, i.e., keeping a constant intruding force and excluding shearing force. The moment analysis found that eccentric arrangements, however, developed high Z-moment. Thus, a perplexing point was reached where the force analysis favored medial centric arrangement and the moment analysis favored centric arrangement. When the gap between juxtaposed magnets increased over 2 mm, the repulsive force declined and the attractive force was favorably eliminated. At gap distances of 3 to 6 mm, the intrusive force was almost constant. These data suggest that centric arrangement is indicated clinically when the gap is minute and Müller prongs are used to prevent deleterious lateral shearing forces.

The application of computerized tomography (CT) in cases of impacted maxillary canines.

A comparison is made between conventional X-rays and computerized tomography (CT) based on eight patients with thirteen impacted upper permanent canines. The use of CT yields information which is much more detailed than that observed on conventional X-rays, such as: pathological resorption on adjacent teeth caused by aberrant canines; the localization of the injury and the position of the canine in relation to one or both incisors. The amount of radiation per exposure is still rather high for the CT (Köster and Ewen, 1986). Further research is necessary in order to reduce this exposure and to determine the appropriate and most effective use of CT in the dental field.

[The surface roughness of orthodontic wires--a laser optical and profilometric study]. / Die Oberflächenrauheit orthodontischer Drähte--eine laseroptische und profilometrische Untersuchung.

The surface roughness of orthodontic wires is an essential factor that determines the effectiveness of arch guided tooth movement. Using the nondestructive technique of laser specular reflectance, the surface roughness of 11 nickel titanium orthodontic wires and a standard steel as well as a beta-titanium wire was measured. The results were compared with the results from surface profilometry. The smoothest wire, standard steel Hi-T, has an optical roughness of 0.10 microns, while the roughness from profilometry reached a value of 0.06 microns. The titanium molybdenum wire has an optical as well as a profilometric roughness of about 0.20 microns, while the roughness of the NiTi wires ranges from 0.10 microns to 1.30 microns. As the surface roughness not only influences the effectiveness of sliding mechanics, but also the corrosion behaviour and aesthetics, the manufacturers of orthodontic wires are asked to improve the surface quality of their products.

Milestones in the development and practical application of functional appliances.

The current interest in functional appliances in the United States is based on apparent success of one or more modifications of appliances that have been used in Europe for many years. Because a number of authors considered these appliances the universal answer to treatment of malocclusions, many modifications were developed. The history is replete with changes induced by failures as well as successes, resulting in the current approach in Europe to the use of both fixed and removable appliances, separately or in combination, to achieve the best possible result. This historical discourse presents some of the background that is not well known in the United States. It should give the clinician a better understanding of the physiologic bases, as well as the reason for the broad gamut of appliances that have been used at one time or another. The original work of Andresen, Häupl, Petrik, Eschler, Balters, etc. is described, as well as the work of later contributors to the current "state of the art" in functional jaw orthopedics.