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Biomedical subjects

D Drescher

Publications and source records attributed to D Drescher.

At least 55 records · Page 3Linked to original sources
PubMed1991

[Arch-guided tooth movement--its dynamics, efficacy and side effects].

Canine retraction on a continuous arch wire was simulated using the OMSS. The influence of wire dimension, force generating element (power chain, coil spring, powerhook, uprighting spring), bracket width and the position of the center of resistance on the effectiveness of the distalization of the canine and its side effects such as extrusion, rotation and tipping were examined. Stainless steel, nickel titanium and multi-stranded wires were tested. Employing the 0.018"-slot system, the use of an 0.016" X 0.022"-arch wire gave the best results. Comparing the NiTi coil spring with the elastic chain, the former should be preferred, because, due to its low load deflection it generates a nearly constant force over a wide range of activation. Using powerhooks or uprighting springs, a nearly bodily movement could be achieved. On the other hand, friction may increase if the uprighting is too strong. The rate of tooth movement decreases by increasing length of tooth root represented by the position of the center of resistance. Arch guided tooth movement along multi-stranded wires shows a high effectiveness, nevertheless, these wires should not be used for canine retraction because of the above mentioned side effects.

Computer Simulation↗
PubMed1991

Rare earth magnets and impaction.

Aberration in the eruption process was found to be a prime etiologic factor in inducing impaction. Thus an ideal treatment approach should attempt to mimic the normal eruption modus. However, conventional traction methods have been found to be associated with gingiva inflammation, bone recession, reduced attached gingiva, periodontal pockets, exposed cementoenamel junction, and root resorption of the impacted and adjacent teeth. These side effects are the result of premature exposure of the impacted tooth to the oral cavity through a nonself-cleansing pathway and an uncontrolled force system. The present study introduces a new, magnetic attraction system, with a magnetic bracket bonded to an impacted tooth and an intraoral magnet linked to a Hawley type retainer. Vertical and horizontal magnetic brackets were designed, with the magnetic axis magnetized parallel and perpendicular to the base of the bracket, respectively. The vertical type is used for impacted incisors and canines, and the horizontal magnetic bracket is applied for impacted premolars and molars. A three-dimensional analysis of the magnetic force system, by means of the OMSS apparatus, found the small magnetic bracket combined with a large pole surface area of the intraoral magnet to exhibit the most efficient convergent guidance. For this report the magnetic eruption device was examined on one animal subject and four patients. The Nd2Fe14B magnets were coated with parylene and/or encapsulated in stainless steel housings. In deep impaction, the magnetic bracket was cold-sterilized before surgery, and the surgical mucoperiosteal flap was then sutured over the bonded magnetic bracket. Attraction was initiated 1 to 2 weeks after healing. Thus tooth emergence into the oral cavity replicated normal eruption conditioning. The system operated at an attractive force level of 0.2 to 0.5 N. Adjustment was accomplished by temporarily interposing a magnetic spacer between the two magnetic units. No side effects were observed in this restricted number of treated cases, and treatment time was reduced. The study recommends the application of magnets in the treatment of impaction on the grounds of less invasive surgical procedure, effective attractive forces at short distances, and controlled spatial guidance.

Adolescent↗
PubMed1991

Application of the orthodontic measurement and simulation system (OMSS) in orthodontics.

An orthodontic measurement and simulation system (OMSS) is introduced. The major component of the system consists of two force-moment sensors capable of measuring forces and moments in all three planes of space simultaneously. The two sensors are mounted on motor-driven positioning tables with full three-dimensional mobility. All mechanical components are built in a temperature-controlled chamber. A control programme executed by a personal computer performs various types of measurement which can be classified as absolute measurements (e.g. force-deflection diagrams) and simulations of orthodontic tooth movement. By using the OMSS any orthodontic problem at the level of a two-tooth model can be analysed statically and dynamically. Besides other applications, the study evaluates three mechanical systems available for uprighting molars, namely a straight wire, a conventional uprighting spring, and a modified Burstone uprighting spring. It was found that the force systems produced by the straight wire and by the conventional uprighting spring showed a severe extrusive force component which may lead to occlusal trauma. The uprighting performance of the straight wire was inadequate. The conventional uprighting spring produced a large uprighting moment (17.8 Nmm), but also a strong lingual tipping moment (1.5 Nmm). The modified Burstone loop showed the best static and dynamic performance. It produced a force system with substantial uprighting moments in both the sagittal (11.6 Nmm) and frontal plane (4.2 Nmm). A slight intrusive force (0.09 N) might prevent the development of occlusal trauma during treatment. However, concern should be addressed to the fact that intra-oral adjustment of this uprighting spring is difficult because of its high susceptibility to minor modifications of its geometry.

Biomechanical Phenomena↗
PubMed1991

[Optimization of arch guided tooth movement by the use of powerhooks].

Arch guided tooth movement is today still the most often used technique to move teeth bodily in mesiodistal direction. One of the most important disadvantage of this method, however, is friction between bracket and arch wire, which impairs tooth movement and may result in dangerous overload of the anchorage units. Powerhooks are used to accomplish a more effective orthodontic tooth movement by reduction of the tipping and rotating moments. This investigation answers the question which mechanical dimensions powerhooks should have in order to minimize friction. If the point of force application lies coronally to the center of resistance (CR) and rotatory moments are eliminated, friction can be reduced by as much as 90%. Concerning length, powerhooks must not be extended beyond. Otherwise, if the point of force application lies apically to CR, friction increases dramatically. In the horizontal direction, a unilateral powerhook should not be extended to more than the half of its length.

Dental Stress Analysis↗
PubMed1990

[The loss of force by friction in arch-guided tooth movement].

Employing arch-guided tooth movement always results in a loss of force by friction. In order to quantify the loss of force, an apparatus was designed featuring a simulated tooth with full three dimensional mobility. Five different wire alloys in five wire dimensions were combined with three brackets of different widths. Under optimal circumstances the ratio of applied force to orthodontically effective force was 2.3. In respect to the wire dimension the generated friction primarily depends on the vertical diameter. Wide brackets generate less friction than narrow ones. There are significant differences between the examined wire alloys. To minimize friction, a low surface roughness is of high importance.

Biomechanical Phenomena↗
PubMed1990

[The effect of the ligature on the friction between bracket and arch].

The combinations of five different wire materials and six ligatures were analysed with the help of a testing apparatus in order to determine the loss in orthodontic force caused by friction between arch wire and ligature. The bracket was fixed at an angulation of zero degrees with respect to the arch wire. The results of our measurements can be summarized as follows: 1. Friction is determined mostly by the sort of ligature and by the way of ligation and not by the dimensions of the different arch wires. 2. Friction caused by alastics is significantly less than friction caused by steel-ligatures. This can be observed especially if standard-steel wires are used. 3. Frictional forces are astonishingly low if multistrand wires are used. Even the 0.016 x 0.022 Force 9 wire shows little friction. 4. Orthodontic force may even be neutralized if a steel ligature is combined with standard steel wires (0.016 and 0.016 x 0.022). 5. This leads to the proposal that a steel ligature should be retwisted for about 90 to 180 degrees next to the bracket, if orthodontic tooth translation is to be achieved. 6. Using the Unitek Quicksticks causes least friction beneath the alastics.

Biomechanical Phenomena↗
PubMed1990

[The materials engineering characteristics of orthodontic nickel-titanium wires].

Since their introduction in 1971 nickel-titanium wires have been widely used in orthodontics. Today, there is a multitude of new NiTi-alloys, whose properties are described. Beside the memory effect, these alloys have particular elastic properties, which can be characterized by a low modulus of elasticity, excellent springback, and pseudoelasticity (superelasticity). These properties are a consequence of the fact that depending on temperature and mechanical stress NiTi-alloys have two crystalline structures: martensite and austenite. The transition between these two phases, called martensitic transformation, is responsible for the memory effect, where a one way and a two way effect can be distinguished. For orthodontic applications pseudoelasticity is regarded as a highly favourable property. Pseudoelastic behavior is caused by stress induced martensite. Analysing the elastic properties of the available wires two categories can be distinguished: "work hardened martensite" and "pseudoelastic alloy". The biocompatibility of NiTi is sufficient, it can be used as an implant material.

Crystallography↗
PubMed1990

[The friction behavior of the ceramic bracket in arch wire-guided tooth movement].

In spite of their wellknown disadvantages ceramic brackets are in great demand by orthodontic patients because of their aesthetic features. The amount of friction produced during tooth movement when a ceramic bracket slides along an arch wire, is still unknown. Using a custom-made friction test device the current study was undertaken to measure friction values of brackets of different manufactures with an 0.018 inch slot sliding along an 0.016 x 0.022 inch stainless steel arch wire. The results of this study showed that stainless steel brackets had slightly lower values than polycrystalline ceramic brackets. The monocrystalline bracket however showed significant greater friction values than both stainless steel and polycrystalline brackets even though its surface, as revealed with the scanning electron microscopy, proved to be quite smooth.

Ceramics↗
PubMed1990

[A new procedure for profile prognosis in the surgical displacement of the maxilla and the mandible].

One of the most important goals of combined orthodontic-surgical treatment is the harmonization of the soft tissue profile. For a reliable prognosis of the soft tissue profile after surgical intervention, the soft tissue response to hard tissue displacements should be analysed in regard to horizontal and vertical effects. The material consists of the pre- and postsurgical cephalograms of 40 patients who underwent a Le Fort I osteotomy, 54 patients with displacement of the mandible by means of a sagittal split (Obwegeser/DalPont), and 42 patients with combined upper and lower repositioning. In contrast with recent investigations, the analysis of the soft tissue response was not based on the conventional landmarks. Instead of this, changes of the entire soft tissue profile were analysed in relation with the underlying outline of the hard tissue. The processed material resulted in numerical data which permit the elaboration of a profile prognosis with distinction of horizontal and vertical effects also taking the error assessment into account.

Cephalometry↗
PubMed1990

Optimization of arch guided tooth movement by the use of uprighting springs.

One of the most important drawbacks of arch guided tooth movement is the friction between bracket and arch wire. In order to reduce frictional forces the application of an uprighting spring is proposed. The influence of uprighting and derotating moments on frictional forces has been measured with a friction testing assembly. Applying appropriate uprighting moments results in a reduction of friction by 73-89 per cent. Derotating moments have only a minor effect on friction. For clinical purposes, the uprighting moment should be 50 per cent of the tipping moment.

Biomechanical Phenomena↗
PubMed1989

[Materials technology research on the problem of friction between bracket and arch].

Orthodontic tooth movement along the arch wire is associated with a frictional force between bracket and wire. There is as yet little certainty as to how much force is lost as a result of friction. Therefore a measuring apparatus was used to measure torque in relation to bracket angulation. In all, five types of wire, each of different dimensions were measured in three brackets of differing widths. The results showed significant differences between the types of wire. As the wire dimensions are increased, so likewise are the frictional forces. Bracket with and frictional force bear an inverse relationship to each other. Frictional force increases the greater the surface roughness of the wire.

Dental Alloys↗
PubMed1989

Frictional forces between bracket and arch wire.

Guiding a tooth along an arch wire results in a counteracting frictional force. Clinically, a mesiodistally applied force must exceed the frictional force to produce a tooth movement. A friction-testing assembly simulating three-dimensional tooth rotations was constructed to study factors affecting friction magnitude. Five wire alloys (standard stainless steel, Hi-T stainless steel, Elgiloy blue, nitinol, and TMA) in five wire sizes (0.016, 0.016 x 0.022, 0.017 x 0.025, 0.018, and 0.018 x 0.025 inch) were examined with respect to three bracket widths (2.2, 3.3, and 4.2 mm) at four levels of retarding force (0, 1, 2, and 3 N). The following factors affected friction in decreasing order: retarding force (biologic resistance), surface roughness of wire, wire size (vertical dimension), bracket width, and elastic properties of wire. The study recommends the application of 0.016 x 0.022 inch stainless steel wire combined with a medium (3.3 mm) or wide (4.2 mm) bracket for an arch-guided mechanism with an 0.018 inch slot. The effective force of this arrangement has to increase twofold to overcome the friction. For TMA wire, however, the effective force must increase sixfold, resulting in a hazardous overload of the anchorage units.

Alloys↗
PubMed1989

Stabilization of maxillary segments and dental arch after puberty, in cleft lip and palate cases.

To overcome the high tendency to relapse after orthodontic treatment in patients with cleft lip and palate, efficient stabilisation of the dental arch is essential. In patients with an alveolar defect, extended bridges are most suitable, because there is no need for further retention appliances, the functional and cosmetic results are acceptable and extensive prosthetic reconstruction can be avoided, regardless of the patients age.

Adolescent↗
PubMed1985

[Automatic detection of grouped patterns in EEG].

The detection and classification of grouped (so called paroxysmal) activity and of artefacts of similar appearance is a necessary part of the automated description of clinical EEGs. An algorithm for this task is presented. It is based on short-time spectra and on parameters extracted from them. The rate of agreement with the visual assessment is nearly the same as that between well trained EEGers. This is true for the classification and to nearly the same degree for the detection. Nevertheless these patterns must be grouped and validated if the method is to be used in practice. A modification useful for a fast analysis combined with the quantitative description of the background activity is discussed.

Brain Diseases↗