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Biomedical subjects

D Drescher

Publications and source records attributed to D Drescher.

At least 37 records · Page 2Linked to original sources
PubMed1995

[Cervical headgear with angled outer arms. A biomechanically comprehensible system?].

When applying the angulated face bow, it doesn't seem possible to avoid vertical and transversal forces which occur in addition to the distalization force as moments. By varying the length and angulation of the outer bow, it is possible to influence the force components and the moments in the sagittal plane. In the clinical analysis of the force system it is assumed that the face bow is an ideal rigid system. Only under this presupposition is the assumption valid, that the product of the force and the perpendicular distance to the molar tube is responsible for the size of the moment. Under this assumption, however, all forces and moments created by the deflection of the headgear are not taken into consideration. An experimental analysis of the forces and turning moments which occur indicates that this simplifying geometric point of view does not always correspond to reality. It was evident, e.g., that there is no linear correlation between the force and moment in mesio-distal direction due to the deflection of the outer bow. This effect becomes the more obvious the longer the outer bow of the headgear is.

Biomechanical Phenomena↗
PubMed1995

[A functional orthodontic magnetic appliance (FOMA) after Vardimon. 1. A three-dimensional analysis of the force system of the attractive magnets].

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)

Cobalt↗
PubMed1995

Surface structure and roughness of Nickel-Titanium wires.

Nickel-Titanium wires not only show the well known shape memory effect, but also pseudoelastic behaviour. This means, as the material is bent in a wide range of tension, the stress in the material stays constant. This special behaviour allows the improvement of orthodontic devices. The investigation of wires for this application reveals great differences in the surface roughness of the wires from various suppliers. The roughness causes a loss of spring energy for the orthodontic wire by frictional effects. The investigation of the mechanical behaviour of these materials leeds to differences compared with the ideal behaviour expected for the stress/strain curve. Obviously these differences are caused by surface effects of the wires. To evaluate these questions intensive roughness measurements with profilometry, laser spectroscopy and scanning force microscopy have been performed. Further more defined bending and tensile experiments have been carried out and corresponding roughness and structure analysis with the scanning force microscope has been taken into account. By etching the wires significant surface effects could be found.

Journal Article↗
PubMed1994

[A computer-controlled flexing test for determining the elastic parameters of highly flexible orthodontic wires].

Metals are the most commonly used materials in the construction of orthodontic appliances designed for the correction of malocclusions. Knowledge of the force systems at work is a prerequisite for judging the functionality of these appliances. The elasticity parameters (Young's E-moduli, strain limits) of the alloys employed can be drawn upon to calculate numerically forces and torsional moments. Both tensile tests and bending experiments are used to determine the E-moduli and strain limits of standard steel and highly flexible NiTi wires frequently used in orthodontics. However, parameters obtained by tensile tests are less suited for studying the mechanical properties of orthodontic appliances. Since bending deformation prevails, bending experiments should be preferred method for ascertaining the relevant parameters. This study, therefore, presents a new experimental method for testing the bend ability of highly flexible materials and the determination of the underlying material parameters. A comparison of calculated force systems with direct measurements revealed that bending parameters lead to an appropriate description of forces and moments generated during clinical treatment, whereas calculations based on tensile test parameters differ substantially. The bending test proposed here is, thus, a suitable means for dependably predicting the force systems produced by an orthodontic appliance and the test therefore can contribute to an accurate design of new types of therapeutic devices.

Computer-Aided Design↗
PubMed1994

[Retraction of the upper incisors with pseudoelastic treatment elements. Their computational and biomechanical testing and clinical use].

Based on the favorable results achieved by the application of pseudoelastic T loops in the course of canine retraction, this study investigates their application to the retraction of maxillary incisors. A modified Burstone T loop was made of a pseudoelastic orthodontic nickel titanium wire and then subjected to experimental testing. The results obtained were compared with extensive numerical studies. The results of the tests showed that forces and moments generated by the T loop are suitable for the retraction of upper incisors. The clinical application of the pseudoelastic spring was performed using an individualized retraction arch enclosing the whole front segment. Whereas during canine retraction the experimental and clinical results corresponded very well, such was not observed during the retraction of upper incisors. This result implies that the location of the center of resistance of the upper incisors has not been completely clarified. It is thus recommended that this matter should be given further study.

Biomechanical Phenomena↗
PubMed1994

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.

Compliance↗
PubMed1994

[The long-term fracture resistance of orthodontic nickel-titanium wires].

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.

Dental Alloys↗
PubMed1993

[The lateral and transverse forces with indirect headgear and its modifications].

The use of the various variants of indirect headgear engenders transversal and lateral forces as an inevitable side effect. Direct clinical assessment of these forces, however, is not possible. To deal with this problem the study presented here employed 3D force sensors to measure in vitro the sagittal and transversal forces generated by diverse headgear modification. The results show that the transversal and lateral forces reach magnitudes which have direct clinical relevance. A common symmetrical indirect headgear, for instance, generates an expansive force that amounts to 20% of the distal. Transversal forces generated by expansion and compression headgear rapidly exceed therapeutically desirable magnitudes. All asymmetric headgear included in the study produced lateral forces which may lead to unwanted scissor or cross bites. The study presents a method whereby these inevitable lateral forces engendered by asymmetric headgear can potentially be minimized.

Biomechanical Phenomena↗
PubMed1993

[The computer-aided development of orthodontic treatment elements made from NiTi memory alloys exemplified by a pseudoelastic retraction spring].

Employing the segmented arch technique, specifically designed loops are employed to bring about sufficient force and turning moments to achieve a purely translatory retraction. Most importantly, the moment to force ration (M/F) is determined by the occluso-gingival height, but, as there are intraoral limitations to the spring height, the maximum possible M/F is also limited. Consequently the M/F is no longer constant and activation of the loop to achieve a specific M/F can become critical. This potential problem can be overcome by the use of highly flexible wires, particularly those made of the superelastic alloy nickel titanium. The data presented in this study result from calculations arrived at with the help of a plane numerical model of pseudoelasticity which in turn is based on the finite element method. The calculations are compared with those resulting from experimentations using the orthodontic measurement and simulation system. A variation in the different parameters led to the design of a T-loop with a height and an apical length of 10 mm each. A T-segment made of superelastic NiTi alloy Sentalloy (0.016" x 0.022") was joined to steel horizontal arms. This loop produces a constant M/F ratio of -7 mm and requires no uprighting bends. The range of activation is approximately 15 mm. A superelastic plateau was calculated between an activation of 10.5 mm and 2.5 mm, with a distalizing force from 0.9 N to 0.5 N. The experimental values corresponded to the numerical data. The clinical application of the superelastic T-loop is thus demonstrated.

Biomechanical Phenomena↗
PubMed1993

[Frictional forces and movement dynamics in the mesialization of the second molar after the extraction of the sixth-year molar. An in-vitro study].

In this study the frictional forces and dynamics of arch guided molar mesialization were investigated. The influence of two different slot/arch combinations (.018" slot/.016" x .022" arch and .022" slot/.019" x .025" arch) as well as partial fortification of an .016" x .022" wire and the reduction of interbracket distance were studied. In guiding the arch wire, a convertible bracket was tested in tube and in bracket configurations. The tipping movement could be compensated by adding an uprighting spring. The orthodontic measurement and simulation system (OMSS) was employed to determine frictional loss in forces and to analyze side effects. Results showed that frictional forces were almost independent from the wire stiffness, whereas a reduced cross section resulted in distinct side effects. These effects can be countered either by employing a correctly dimensioned uprighting spring or by increasing the wire stiffness. The .019" x .025" wire in a .022" slot proved to be the optimum combination for molar mesialization.

Biomechanical Phenomena↗
PubMed1993

[The maxillary sixth-year molar and its relation to the maxillary sinus. A comparative study between the panoramic tomogram and the computed tomogram].

Panoramic radiographs (OPGs) and computer tomograms (CTs) of 30 patients, the latter taken on average 2.5 months later, were evaluated for the purpose of comparing the relation of their roots to the bottom of the maxillary sinus. The CT and OPG images yielded significant differences in the topographic relations between the roots and the maxillary sinus. In the OPG 64 out of 129 roots seemed to penetrate the maxillary sinus. In the CT transversal slices, on the other hand, penetration could be observed for only 37 roots. This phenomenon became more apparent when the relations between the mesial, distal, buccal, and oral root surfaces and their relations to the sinus were assessed. Applying a three stage scoring scheme, it was found that in the large majority of cases only the apices were in contact with the mucosa of the sinus. Thus, the possible loss of anchorage in these cases is below five percent.

Adolescent↗
PubMed1992

[The deactivation behavior and effectiveness of different orthodontic leveling arches--a dynamic analysis of the force systems].

Using the orthodontic measuring and simulation system (OMSS), the deactivation behaviour of diverse orthodontic levelling arches was investigated. The vertical forces and uprighting moments, as also the levelling effectiveness for initial malalignments of tooth 21 (1 mm and 2 mm infraocclusion, 20 degrees angulation) were measured, with the influence of various ligatures used in clinical practice being taken into account. The results may be summarized as follows: In the case of a large vertical offset (infraocclusion) the vertical forces can attain values of up to 3.8 N, depending on the type of levelling arch used. On deactivation, we can observe a sharp decrease in force caused by the frictional resistance between bracket and arch wire, which has to be overcome by the wire. The loss of desired force caused by friction may be as much as 50%, and is determined by the arch wire, bracket and mode of ligation. A smaller vertical offset (infraocclusion) (1 mm) is associated with extrusive forces of 0.2 N--0.8 N. Using looped levelling arches made of 0.016" standard steel wire, there is no frictional loss of orthodontic force, so that the highest vertical forces (more than 3.0 N) are observed with these arch wires. With an initial angulation of the tooth of about 20 degrees, uprighting moments of between 3.0 Nmm and 33.0 Nmm are measured, the looped arches again generating the highest moments. To ensure adequate uprighting moments in a combination of vertical offset (infraocclusion) and angulation, very high extrusive forces must be accepted. As a dynamic analysis of the tooth movement with the OMSS shows, the use of a specific arch wire results in a typical levelling defect. There is no general correlation between extrusive force or uprighting moment and the levelling effectiveness of an orthodontic arch. It is not possible to recommend a particular levelling arch.

Biomechanical Phenomena↗
PubMed1992

[A pseudoelastic NiTi uprighting spring for the molars--its design, biomechanical testing and clinical use].

Uprighting inclined molars is one of the most common problems encountered in pre-restorative orthodontics. To prevent occlusal trauma, an intrusive force has to be applied to the molar in addition to the uprighting moment. Owing to their construction, current mechanical devices for uprighting either to not meet this requirement, or are difficult to adjust when in place. For this reason, an improved uprighting spring is described which utilizes the properties specific to super-elastic (pseudo-elastic) NiTi alloys. The most important property of super-elastic wires is the fact that they produce constant forces or moments within a specific deformation range. In order to utilize this useful property, certain design criteria have to be met. Recent measurements have shown that a super-elastic wire (Sentalloy, 0.016'' x 0.022'') having a length of 10 mm generates a constant moment of 7 to 8 Nmm within a bending angle of 50 degrees to 180 degrees. On the basis of these results, a table that permits the determination of the proper wire length needed to provide a constant moment within a given range of bending angles is proposed. The superelastic uprighting spring described here comprises an NiTi wire segment having a length of 7 mm and a mesial and distal steel wire segment. In the active state, the spring generates an uprighting moment of 8 Nmm and an intrusive force of 0.6 N. Numerical analysis using the finite element program, SOLF/MESY, and biomechanical testing with the orthodontic measuring and simulation system (OMSS) have shown that this force system remains stable throughout the entire uprighting process. The clinical application of the spring is demonstrated in a specific case.

Adolescent↗
PubMed1992

An experimental apparatus for the simulation of three-dimensional movements in orthodontics.

An apparatus for the study of three-dimensional force systems and the resulting movements during orthodontic treatment is presented. The instrument consists of two force-torque transducers which are capable of recording both forces and torques simultaneously, in all spatial directions. Each sensor has a measuring range of 15N (450 Nmm) and a resolution of 0.02 N (0.5 Nmm) and is mounted on a set of three translational and three rotational stages driven by stepping motors. Positioning accuracy is in the range of 1 micron and 0.01 degrees respectively. The apparatus is computer controlled and supported by comprehensive software.

Biomechanical Phenomena↗
PubMed1992

[Numerical analysis of orthodontic treatment elements of pseudo-elastic NiTi alloys].

In orthodontic treatment malpositions of teeth are often corrected by fixed appliances, consisting, in part, of loops made by the orthodontist. The most important alloys in use are steel, cobalt-chromium, or titanium-molybdenium alloys. The static force systems of fixed appliances made of these materials are well known from experimental and numerical studies, but as they may change during tooth movement, we are often confronted with problems in therapy. The introduction of pseudoelastic nickel titanium alloys (NiTi) into orthodontic treatment, offers the chance of improving the effectiveness and reliability of orthodontic devices. In the present paper a plane finite element (FE) for the analysis of orthodontic loops is presented. It enables the determination of the nonlinear behaviour of pseudoelastic NiTi-alloys and is capable of simulating large structural displacements and rotations accompanied by moderate strains. A comparative numerical and experimental study shows the efficiency of this element. The associated results reflect pseudoelastic effects on certain loop designs, and reveal the benefits for the orthodontist and his patients.

Computer Simulation↗
PubMed1992

[The surface roughness of orthodontic wires--a laser optical and profilometric study].

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.

Corrosion↗
PubMed1991

[Orthodontic measuring and simulating systems (OMSS) for the static and dynamic analysis of tooth movement].

An orthodontic measurement and simulation system (OMSS) is presented. The major components of this system are two measuring tables each comprising a force/torque sensor and a motor driven, fully three-dimensionally adjustable positioning stage. The force/torque sensors are capable of measuring simultaneously all forces and torques acting on a tooth. Using the computer program "OMSS" which runs on a personal computer, several different measurements can be conducted. On the one hand, the system supports absolute measurements such as the registration of a force/deflection diagram. Furthermore, even multidimensional force/deflection- or torque/distance curves can be measured. On the other hand, simulations of orthodontic tooth movement can be conducted. In such simulations, the force system acting on a tooth is measured and the resulting tooth movements are calculated. By using this "computer typodont", not only the static but the dynamic behaviour of orthodontic appliances can be studied. The application of this system is demonstrated by the analysis of several orthodontic problems.

Computer Simulation↗