PubMed Health⌕ Search

Biomedical subjects

C J Burstone

Publications and source records attributed to C J Burstone.

At least 19 recordsLinked to original sources
PubMed1992

The use of continuous fiber reinforcement in dentistry.

Fiber-reinforced composite (FRC) formulations were developed to serve as structural components for various dental appliances such as prosthodontic frameworks, retainers and splints. Poly(ethylene terephthalate glycol) and poly(1,4-cyclohexylene dimethylene terephthalate glycol) reinforced with continuous S-2 glass fibers were pultruded into continuous lengths with small rectangular cross sections. The microstructure was evaluated with SEM and optical microscopy. Fiber content and flexure properties were measured and compared to previous results by other authors. The present FRC contained 43-45 volume % fiber, which compared favorably with the 5-15 volume % fiber reported by all earlier investigators of dental FRC. The present materials achieved 65% of the theoretically expected modulus, in contrast to the typical value of 40% calculated in the earlier reports. The flexural strength and modulus of the experimental FRC were approximately 565 MPa and 20 GPa, respectively. The present FRC can be formed into individualized devices, and free fibers need not be manipulated by the operator. The improved properties and handling justify further study of these FRC as structural dental materials.

Carbon↗
PubMed1991

Centers of rotation with transverse forces: an experimental study.

A new noninvasive method for simultaneously applying a known force system and measuring tooth movement was developed and tested. The instruments proved to be highly accurate and reliable. Using a model of an upper canine with a simulated periodontal ligament, we located the center of rotation and the center of resistance and found that the product of two distances--a, from the center of resistance to the line of application of force (F) and, b, from the center of resistance to the center of rotation (Co)--yields a constant that represents the parallel transverse forces in the same plane. Knowing this constant enables the clinician to determine the appropriate force position for a given center of rotation. We also found that the occlusoapical position of the center of resistance varies somewhat, depending on the transverse direction of loading around the long axis. Differences in values of the constant were found also to depend on the direction of loading in a given plane. Thus a transverse force exerted in a mesiodistal direction at the level of an orthodontic bracket through the long axis produces different effects from those produced when an identical force is applied in a labiolingual direction.

Computer Simulation↗
PubMed1991

Patterns of initial tooth displacements associated with various root lengths and alveolar bone heights.

The present study was designed to investigate the nature of initial tooth displacements associated with varying root lengths and alveolar bone heights. A three-dimensional model of the upper central incisor was developed for the finite element analysis. Tooth displacements were determined at various levels of the tooth and the apicogingival levels of the center of resistance and centers of rotation were calculated. The results showed that moment-to-force values at the bracket level for translation of a tooth decreased with shorter root length and increased with lower alveolar bone height. In addition, apicogingival levels of the center of resistance shifted more gingivally to the cervix, or the alveolar crest with a shorter root. Alveolar bone loss also shifted the center of resistance toward the alveolar crest, whereas its position was more apical relative to the alveolar bone heights exhibited very slight changes in both cases. The centers of rotation from a single force varied substantially with a short root and alveolar bone loss. However, the relative distances of the centers of rotation from the alveolar crest in comparison with the alveolar bone heights were constant at 0.4 mm, with variations in the root length and alveolar bone height. Because this study showed that root length and alveolar bone height affect the patterns of initial tooth displacements both in the center of resistance and the centers of rotation and also in the amount of displacement, forces applied during orthodontic treatment should take into consideration the anatomic variations in the root length and alveolar bone height so as to produce optimal and desired tooth movement.

Alveolar Process↗
PubMed1989

Force system developed by V bends in an elastic orthodontic wire.

The force system generated by a simple V bend in a straight wire was studied by means of the principles for small deflection of a beam and a model developed for the description of the forces and moments. The relationship between the size of the bend and the interbracket position on the force system developed is analyzed and discussed in relation to clinical problems. The parallel between positioning of a V bend and the "geometries" developed between a straight wire and angulated brackets is drawn. Four principally different force systems could be developed by the V bend and a method for the predetermination of the force systems is provided. The general principles are exemplified for wires with different moduli of elasticity, varying materials, and cross-sectional dimensions. Stainless steel and beta titanium (TMA) wires in dimensions of 0.16 inch and 0.017 x 0.025 inch are given as examples.

Dental Stress Analysis↗
PubMed1989

Effects of a fixed magnetic appliance on the dentofacial complex.

The purpose of the study was to design and evaluate the effects of a fixed magnetic appliance that hinged the mandible open and exerted an intrusive force on the teeth. Ten patients between the ages of 8 years and 10 years 6 months, with Class II, Division 1 malocclusion associated with mandibular retrusion and increased lower facial height, were treated with this appliance. The length of treatment was 4 months, after which the appliance was removed and the patients were followed up for 4 months. Ten children with similar age, sex, and dentofacial characteristics acted as controls and did not receive any appliance therapy. Changes in morphology of the dentofacial complex were evaluated by use of lateral cephalograms and study models. In addition temporomandibular joint and muscle functions were assessed. During treatment mandibular length increased 3.2 mm, angle of facial convexity decreased 2.8 degrees, the upper and lower teeth intruded an average of 1.5 mm each, and the mandibular plane angle decreased 1.3 degrees. In the follow-up period, some rebound eruption was noted; however, all other changes were stable.

Cephalometry↗
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

Space closure in adult patients using the segmented arch technique.

Periodontally compromised adult patients may benefit from modified appliance designs for space closure. TMA T-loops of .016" x .022" and .017" x .025" cross sections, with angulations incorporated via concentrated bends and gradual curvature bends are presented. The force systems these appliances produce are measured, and their clinical performances discussed. Templates for these T-loops are presented. By producing lower forces and higher moment to force ratios, this type of T-loop may benefit patients with bony loss.

Adult↗
PubMed1989

Advances in diagnosis and detection of oral diseases.

Medicine, particularly with respect to diagnostic decision-making, has seen remarkable advances in the last ten years. The art of diagnosis has become much more of a science. Basic science advances have moved from the laboratory into the hospital and radically changed the way a medical diagnosis is arrived at or confirmed. Dentistry, especially oral diagnosis, as yet has not been a significant part of this general medical advance. However, several examples demonstrate that this situation is starting to change. Oral conditions are beginning to be evaluated with greater precision and sophistication. This report reviews some recent advances in oral diagnostic research and suggests where they will carry dentistry over the next 25 years.

Diagnosis, Oral↗
PubMed1989

Biomechanical responses of tooth associated with different root lengths and alveolar bone heights: changes of stress distributions in the PDL.

The purpose of the present study was to elucidate the nature of stress distributions in the PDL varied by different root lengths and alveolar bone heights. A three-dimensional model of the upper central incisor was constructed for the finite element method (FEM). The model was modified to produce various root lengths and alveolar bone heights. A lingually directed 100 g horizontal force was applied at a point on the labial crown surface. Stress distributions were determined in the center of the PDL for various apicogingival levels. Stress levels in the PDL gradually decreased with a longer root. Rates of changes in stress levels to those with an original root length were approximately 1.5 at maximum and 0.8 at minimum. Patterns of stress distributions were varied by different alveolar bone heights in both the qualitative and quantitative aspects; i.e., apicogingival level of stress transition shifted more apical, and stress levels also increased following a reduction of the alveolar bone in the apicogingival direction, approaching about eight times with a half alveolar bone height as the original. It is found that the root length and alveolar bone height affect stress distributions in the PDL. Thus, it is shown that an orthodontic force application should be determined on the basis of anatomical variations in root length and alveolar bone height to induce an optimal stress level in the PDL, which is a key to desirable tooth movement.

Alveolar Process↗
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↗
PubMed1987

Three-dimensional finite element analysis for stress in the periodontal tissue by orthodontic forces.

This study was designed to investigate the stress levels induced in the periodontal tissue by orthodontic forces using the three-dimensional finite element method. The three-dimensional finite element model of the lower first premolar was constructed on the basis of average anatomic morphology and consisted of 240 isoparametric elements. Principal stresses were determined at the root, alveolar bone, and periodontal ligament (PDL). In all loading cases for the buccolingually directed forces, three principal stresses in the PDL were very similar. At the surface of the root and the alveolar bone, large bending stresses acting almost in parallel to the root were generally observed. During tipping movement, stresses nonuniformly varied with a large difference from the cervix to the apex of the root. On the other hand, in case of movement approaching translation, the stresses induced were either tensile or compressive at all occlusogingival levels with some difference of the stress from the cervix to the apex. The pattern and magnitude of stresses in the periodontium from a given magnitude of force were markedly different, depending on the center of rotation of the tooth.

Alveolar Process↗
PubMed1987

Location of the centers of resistance for anterior teeth during retraction using the laser reflection technique.

The location of the centers of resistance for various symmetric units of the anterior maxillary dentition for a lingually directed force was studied in two dry human skulls. The units investigated were composed of two incisors, four incisors, and six anterior teeth. In addition, the effect of change in force magnitude on the location of the centers of resistance of these units was investigated. The laser reflection technique was used to study both the direction and magnitude of the initial displacement of the consolidated teeth under loading. The results indicated that the center of resistance shifted apically with the incorporation of a greater number of teeth into an anterior segment. With a unit of six anterior teeth, the apical shift of the center of resistance was the greatest. Increasing force levels had little effect on the location of the center of resistance of a given unit. This phenomenon was observed in both the skulls tested, suggesting that general trends may exist in the displacement characteristics of the dentition when subject to controlled force systems.

Cuspid↗