3-D experimental identification of force systems from orthodontic loops activated for first order corrections.

Intra-arch irregularities can be corrected using wire of low stiffness, wires of increasing stiffnesses, or by the activation of loops built into the appliance. While the orthodontist controls only the magnitude of force when leveling with continuous arches, the configuration and positioning of loops offer the possibility of controlling the type and direction of force. In the present study, force systems developed by the L-loop, the T-loop, and the rectangular (R-) loop were analyzed with respect to the force systems acting for first order irregularities, buccolingual movement, and rotation along the long axis of the tooth. An interbracket distance of 21 mm was chosen, and the loops were analyzed in a testing machine that made it possible to register forces and moments simultaneously in three planes of space. The activations included a symmetrical translation of 1 mm made in steps of .2 mm, corresponding to a buccolingual movement, and 10-degree rotations clockwise and counterclockwise in steps of one degree. Force systems were recorded during activation and deactivation. Loops made of TMA wire delivered 40% of the force delivered by the same loops made of stainless steel wire. The T-loop generated a force system that deviated qualitatively only slightly from that delivered by a straight wire. The L-loop generated a force system that was dependent on orientation; constancy was better corresponding to the anterior part of the loop. It was evident that the rectangular loop was capable of generating any desired moment-to-force ratio, and the R-loop demonstrated a high degree of constancy of the force system. Rectangular loops should, therefore, be preferred for making first order corrections.

Combined intrusion and retraction generated by cantilevers with helical coils.

Combined retraction and intrusion of the anterior teeth is often needed as part of orthodontic treatment. The use of a statically determinate force system has many advantages over statically indeterminate systems. In the case of the cantilevers the orthodontist can evaluate the line of action of the delivered force directly in the clinical situation. In the present paper the force system delivered by stainless steel and beta titanium cantilevers with an eccentrically placed helix was evaluated. The cantilever consisted of a straight piece of wire bent to form a helix with an external diameter of 3 mm. The wire was fixed into a bracket of sensor 1, touching sensor 2 of a test bench with a 1-point contact to. Activation was induced by rotating sensor 1 into which the wire was tightly fixed. This was done in 2 different modes, one in the direction in which the helix was bent and one in the opposite direction. With an interval of 5 degrees the force system generated with respect to sensor 1 and the direction of the force delivered to sensor 2 (the other bracket) were registered. The results were expressed graphically and the influence of material and activation mode were evaluated statistically by comparing the coefficient of regression. As expected, the influence of the material reflected the relative stiffness of the 2 alloys. As TMA is monocrystalline (i.e. consists of homogeneous crystals) the mode of activation did not reflect any significant Bauschinger effect as seen in the case of stainless steel. Analysis of the force direction confirmed that the suggested wire configuration is useful for delivery of a predetermined combination of horizontal and vertical force. This was confirmed by a finite element analysis.

Measurements of magnetism-related forces and torque moments affecting medical instruments, implants, and foreign objects during magnetic resonance imaging at all degrees of freedom.

We designed a novel force/torque moment transducer with six degrees of freedom. This new sensor is used for measuring the forces and torque moments exerted by static magnetic resonance imaging (MRI) fields on various medical implants, instruments, and ballistic shell fragments. To determine the location of strongest effect the inhomogeneity of the magnetic field between the entrance of the MRI-tube (portal), and the imaging section was measured. Force and torque moments of a sample of 45 objects were measured at two positions, at the portal, and in the center of the imaging section. We classified the objects regarding to the magnetism-related forces measured in the homogeneous part of the MRI tube. About one-third of the objects was non- or weakly magnetic, one-third moderately, and the last third was strongly magnetic. Forces within the inhomogeneous area of the magnetic field at the entrance part of the tube were up to half a magnitude larger than forces inside the homogeneous imaging section. Here the greatest potential risks to patients might occur.

A miniaturised force-torque sensor with six degrees of freedom for dental measurements.

Force-torque sensor systems capable of simultaneously measuring all six spatial degrees of freedom on solid bodies are not very widespread in the medical field, particularly because of the hitherto unacceptably large external dimensions. A sensor based on the strain gauge technique has been developed with a diameter of only 32.5 mm and height of 29 mm. The miniaturised supporting framework for the strain gauges has been cast in a single piece from a wax-plastic model by the one-way mould principle. A sensitivity of 10 mN with an upper limit of 50 N is attained.

[An in-vitro study of the use of palatal arches in controlling the position of the upper molars]. / In-vitro-Studie zur Anwendung von Palatinalbögen bei der Kontrolle der Position oberer Molaren.

An in-vitro study was performed analysing the forces and moments produced by the transpalatal arches of the Goshgarian type (0.036" x 0.032" stainless steel and and of the "Precision Lingual Arch System" advocated by Burstone (0.032" x 0.032" stainless steel and 0.032" x 0.032" TMA) using an electronic force-moment gauge recently developed by Planert. The palatal bars were adapted passively, and in addition, molar expansion, symmetrical molar rotation, and buccal root torque were applied. It was found that under clinical conditions it was impossible to fabricate an absolutely passive arch wire with any of the arch types under investigation. The highest precision in applying forces and moments together with the least side-effects was possible using the low stiffness TMA version of the Burstone system.

Mobile connection of veneer crowns after orthodontic closure of a wide diastema in the maxillae. A clinical report.

A new, mobile splint for artificial crowns is suggested after orthodontic closure of a wide diastema mediale. A smooth mandibular movement in all excursions in considered essential. This approach sustains a physiologic load on the periodontium and prevents a recurrence of the diastema. The restorations in Fig. 6 have been stable and comfortable for 2 1/2 years with independent mobility of each tooth. Similar splinted prosthodontic devices inserted have also been successful.