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Biomedical subjects

H A Koenig

Publications and source records attributed to H A Koenig.

13 recordsLinked to original sources
PubMed1989

Force systems from an ideal arch--large deflection considerations.

A sophisticated mathematical simulation is presented which allows for the consideration of large activations in orthodontic appliances and their effect upon the resulting force systems which are delivered to teeth. Effects of bracket/wire interaction are studied using this new tool. Previous studies of force systems from an ideal arch were redone with the new analysis in which the wire was either rigidly restrained or free to slide. The restraint of the wire produced large mesio-distal forces and increased the magnitude of the moments on each bracket. If the wire is free to slide, both large deflection and small deflection solutions give similar results. The relative force system M1/M2 fundamentally held true with large deflections and restraint; however, some differences were noted. The significance of allowing wire to slide in the bracket is discussed.

Elasticity↗
PubMed1989

Effect of moment to force ratios on stress patterns and levels in the PDL.

This study was conducted to investigate the effect of moment to force (M/F) ratios on stress distributions in the PDL. Three-dimensional finite element method (FEM) was applied to stress analysis, using a three-dimensional model of the upper central incisor. Five force systems were established to produce different M/F ratios with a constant 100 g lingual force and/or varying labial crown couples, applied at a point on the labial crown surface, 4 mm gingival to the incisal edge. Stresses were determined in the center of the PDL for eight apicogingival levels and at sixteen points around the root. Stress patterns and levels in the PDL changed in response to varying M/F ratios, however, stress values were invariable at the level of the center of resistance. M/F ratio for translation of a tooth produced the most uniform pattern of stress distributions and the minimum stress levels. It is found that the stress level induced in tooth translation is approximately 0.29 times as that in simple tipping of a tooth. Thus, it is shown that the M/F ratio is an important determinant for controlling the stress patterns and levels in the PDL and for achieving optimal tooth movement.

Bite Force↗
PubMed1988

Moment to force ratios and the center of rotation.

The purpose of this study was to investigate the relationship between moment to force (M/F) ratios and the centers of rotation by use of the finite element method (FEM). A three-dimensional FEM model was developed for the upper right central incisor on the basis of average anatomic dimensions. The center of resistance and centers of rotation were determined for varying M/F ratios applied at the midpoint of the crown. The center of resistance was located at 0.24 times the root length measured apical to the level of alveolar crest. The centers of rotation varied with the M/F ratios following a curve of hyperbola. The M/F ratio was -9.53 for root movement (Co at the incisal edge), -8.39 for translation, and -6.52 for tipping around the apex. It was found that even a small difference in the M/F ratios produced clinically significant changes in the centers of rotation.

Biomechanical Phenomena↗
PubMed1988

Creative wire bending--the force system from step and V bends.

The force system produced by wires with steps and V bends was studied analytically by means of a small deflection mathematic analysis. Characteristic force relationships were found in both the step and the V bend. Step bands centrally placed between adjacent brackets produce unidirectional couples that are equal in magnitude. Along with these couples, vertical or horizontal forces are produced depending upon the plane of activation. Mesiodistal placement of step bends is not critical because very little alteration in force system occurs if a step is centered or positioned off center. V bends, on the other hand, are very sensitive to the positioning mesiodistally of the apex of the V. If the apex of the V bend is placed on center, equal and opposite couples are produced. As the V-bend apex is moved off center, predictable combinations of moments and forces are created. A method for determination of the relative force system is described that allows for simple interpretation and prediction of the force system from a V bend. The clinical applications of these data and a rational basis for wire bending are presented based on the producing of a desired force system.

Biomechanical Phenomena↗
PubMed1984

Analysis and design of multiple-beam appliances.

A new approach for the analysis of multiple-beam structures, such as headgear bows, is developed for beams which contain arbitrary curvatures, twists, and material properties. The generalized transfer matrix of a single-beam analysis is converted to a stiffness matrix and inserted into a global matrix which describes the entire system. The effect of inner bow wire size (0.044 inch and 0.051 inch) on the force system is demonstrated. The inner bow with the larger cross section shows only a slight (not clinically significant) reduction in rotational moment and buccal force applied because of its greater ability to resist deformation during the loading process. Small amounts of tooth and/or tube rotations ("play") result in a significant reduction of the crown rotational moment. With increasing rotation of the tube to the inner bow, the high lateral forces and large moments found about the long axis of the teeth are found to reduce. Symmetrical headgears are chosen to illustrate the analysis and to indicate the manner in which this approach may be used to study and design similar orthodontic appliances.

Elasticity↗
PubMed1983

Plastic deformation of orthodontic wires.

Theoretical predictions of the bending moments in the region of plastic behavior were accurate for beta titanium and stainless steel, but were consistently low in the far-elastic region for the three alloys studied.

Dental Alloys↗
PubMed1981

Precision adjustment of the transpalatal lingual arch: computer arch form predetermination.

Correction of widths and axial inclinations with a transpalatal lingual arch has the advantage of distributing forces across the arch, thus minimizing undesirable side effects. The proper shape of an arch to deliver the required force systems for both unilateral and bilateral width change was determined by using an analytical approach which enabled the deactivated shape of the arch to be established and drawn by computer. The transpalatal lingual arch is extremely sensitive to shape in producing a force system. The critical nature of this shape requires the clinician to understand the over-all pattern of properly forming the arch for various applications and the clinical procedures for evaluation before final insertion. The deactivated shape and the force systems for representative applications are presented; these differ significantly from the concept of the ideally shaped wire.

Activator Appliances↗
PubMed1980

Force systems from orthodontic appliances: an analytical and experimental comparison.

Experimental data is compared with the simulated displacements from a computer program for the clinical activations of two separate orthodontic appliances undergoing a total of four separate loading conditions. Good agreement is shown over the entire range of activation. Suggestions for future strengthening of both the analytical and the experimental methods are given. An interactive design graphics system is shown to be imminently available to the research orthodontist.

Biomechanical Phenomena↗
PubMed1976

Optimizing anterior and canine retraction.

Vertical loops or modified vertical loops are basically frictionless springs which are used for canine and anterior tooth retraction. The design and selection of a proper loop or retraction spring should be based on a number of scientific criteria. Foremost among these would be a sufficiently high moment-to-force ratio so that root apices are not displaced mesially or anteriorly. A retraction spring with zero angulation of its horizontal-occlusal arms delivers a moment when activated to produce a force. The ratio of this moment and force is constant throughout the elastic range of activation of the spring. The higher the moment-to-force ratio, the greater is the clinician's control over the apices of the anterior teeth. An analysis of design factors demonstrates that the higher the loop occluso-gingivally, the shorter its horizontal length occlusally, and the greater the gingival horizontal length as in a T loop; these are significant factors in increasing the moment-to-force ratio. The placement of helices is a useful design consideration but the main effect is in reducing the load-deflection rate. By keeping these design factors in mind, the clinician can build into his retraction springs, without the placement of any gable bend, the largest possible moment-to-force ratio so as to optimize his tooth movement. Although it may be possible to design retraction springs to deliver an adequate moment-to-force ratio for controlled tipping around the apex of an incisor or a canine, translatory movements are not possible, considering the intraoral limitations on spring height. This can be overcome by the placement of gable bends or angulation in a vertical loop or retraction spring. Unfortunately, with the typically used high-load-deflection-rate vertical loops, activation to achieve the desired moment-to-force ratio is too critical, exacting, and changeable with small displaced movements of the tooth. This can be partly overcome by utilizing designs that have not only the highest possible moment-to-force ratio during pure horizontal activation of their arms but low-load deflection rates as well. Because of the low load-deflection rate, moment-to-force ratios are relatively more constant if a gable bend (angulation) is placed. The science of spring design as applied to the problems of canine and anterior tooth retraction in this article allows the clinician to optimize the design of his retraction springs. More important, with properly designed springs, it allows him to estimate with relative accuracy the force systems produced and to avoid undesirable side effects which might not have been apparent from superficial observation.

Biomechanical Phenomena↗