Biomedical subjects

H A Schumacher

Publications and source records attributed to H A Schumacher.

At least 19 recordsLinked to original sources

PubMed1999

The influence of bracket design on frictional losses in the bracket/arch wire system.

In arch guided tooth movement, the essential role played by bracket configuration with respect to sliding friction has been recognized by the manufacturers, a fact which has had an increasing impact on the design and marketing of new bracket models in recent years. The aim of the present in-vitro study was to investigate the influence of different bracket designs on sliding mechanics. Five differently shaped stainless steel brackets (Discovery: Dentaurum, Damon SL: A-Company, Synergy: Rocky Mountain Orthodontics, Viazis bracket and Omni Arch appliance: GAC) were compared in the 0.022"-slot system. The Orthodontic Measurement and Simulation System (OMSS) was used to quantify the difference between applied force (NiTi coil spring, 1.0 N) and orthodontically effective force and to determine leveling losses occurring during the sliding process in arch guided tooth movement. Simulated canine retraction was performed using continuous arch wires with the dimensions 0.019" x 0.025" (Standard Steel, Unitek) and 0.020" x 0.020" (Ideal Gold, GAC). Comparison of the brackets revealed friction-induced losses ranging from 20 to 70%, with clear-cut advantages resulting from the newly developed bracket types. However, an increased tendency towards leveling losses in terms of distal rotation (maximum 15 degrees) or buccal root torque (maximum 20 degrees) was recorded, especially with those brackets giving the arch wire increased mobility due to their shaping or lack of ligature wire.

Cuspid↗

PubMed1998

Frictional forces when rectangular guiding arches with varying edge bevel are employed.

In orthodontic treatment employing arch guided tooth movement, rectangular wires are usually used to achieve three-dimensional controlled tooth movement. In the intention to optimize sliding mechanics and to improve the comfort of patients, edge beveled rectangular orthodontic wires are offered by different manufacturers. The objective of the study presented was to investigate the influence of differing but defined wire roundings on sliding mechanics of canine retraction. Employing the 0.018" slot system, 0.016" x 0.022" standard steel wires (Remaloy and Remanium, Dentaurum Comp.) were tested. Force loss due to friction during canine retraction was determined using the Orthodontic Measurement and Simulation System (OMSS). In the arch guided distalization of canines, the average loss of force caused by friction was determined to be approximately 50%. Comparing wires with different edge bevel, the rounded wire in contrast to the wire with sharpest edge configuration results in a reduction of friction. Even a moderate wire rounding of the 0.016" x 0.022" steel wire results in about 10% reduction in frictional losses. However, dynamic analysis of tooth movement with the OMSS shows that there is no further improvement of sliding mechanics using wires with edge bevel exceeding the standard rounding of rectangular wires. In contrast, a strong edge bevel may result in a considerable loss of leveling.

Cuspid↗

PubMed1996

Analysis of forces and moments in arch guided molar protraction using Class I and Class II elastics. An in-vitro study.

The use of class I and II elastics in arch guided tooth movement of the lower molars belongs to the proven clinical methods to achieve space closure even though risks are present. The vertical force component of class II elastics tends to interact with the sagittal force and thus the vertical force may change the desired sagittal force and movement direction. The objective of the study presented here was to investigate friction behavior and the movement dynamics of the arch guided protraction of the lower first molar being acted on by differing class I and class II elastic band geometries. The influence of class I and class II elastics at different force levels (1 N and 2 N) were studied. The pattern of the force line varied in the area of angulation from 0 degree to 40 degrees relative to the arch plane. The orthodontic measurement and simulation system (OMSS) was employed to determine force loss due to friction and to analyze side effects. In the arch guided mesialization of the lower first molar, the vertical component of class II elastics induces a minor force loss in comparison with class I elastics. This holds, however, only for the lower 1 N force level. When employing class II bands at a greater force level and with increased angulation, relatively greater force loss and increased side effects, such as extrusion and mesial tipping of the first molar, occur.

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↗

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↗

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

[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 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

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↗

PubMed1988