Welding of TMA wire. Clinical applications.
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Dental Alloys↗
Biomedical subjects
C J Burstone
Publications and source records attributed to C J Burstone.
Soft-tissue profile--fallacies of hard-tissue standards in treatment planning.
The study was designed to test the efficacy of using a cephalometric dentoskeletal standard as a clinical tool to produce predictable and desirable facial esthetics. Thirty adolescent patients were randomly selected who, at the completion of treatment, had lower incisors positioned approximately 1.5 mm anterior to the A-pogonion plane. A normal sample of excellent faces (Indiana sample) was used for comparison. Both profile measurements of hard and soft tissues were made. The most striking observation was the large variation in the facial profiles even in cases successfully treated to a cephalometric dentoskeletal standard. The variation (2 standard deviations) of lip protrusion from the subnasale pogonion plane was 5 mm or a total of 10 mm. Similar variations were found in other soft-tissue measurements. The results suggest that any given dentoskeletal standard has questionable validity in producing either desirable esthetics or reproducible profiles following treatment.
Adolescent↗
The center of resistance of anterior teeth during intrusion using the laser reflection technique and holographic interferometry.
The aim of this investigation was to define the location of the center of resistance of various consolidated units of the maxillary anterior dentition using a dry human skull when subject to intrusive forces. The laser reflection technique and the holographic interferometric technique were employed to measure the displacement of the dentition to the applied forces. The units studied consisted of two central incisors, four incisors, and six anterior teeth. The incorporation of the lateral incisors into the upper incisor segment resulted in a small distal shift of the center of resistance (+/- 2 mm). However, when the canines were included into this unit, the center of resistance shifted distally by a significantly larger amount (+/- 7 mm). Increasing the magnitude of intrusive forces applied to the various units appeared to have no effect on the location of the center of resistance.
Cuspid↗
[Biomechanical basis of tooth movement].
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Biomechanical Phenomena↗
Chinese NiTi wire--a new orthodontic alloy.
Chinese NiTi wire was studied by means of a bending test to determine wire stiffness, springback, and maximum bending moments. Chinese NiTi wire has an unusual deactivation curve (unlike steel and nitinol wires) in which relatively constant forces are produced over a long range of action. The characteristic flexural stiffness of NiTi wire is determined by the amount of activation. At large activations NiTi wires has a stiffness of only 7% that of a comparable stainless steel wire, and at small activations 28% of steel wire. For the same activation at large deflections, the forces produced are 36% that of a comparable nitinol wire. Chinese NiTi wire demonstrates phenomenal springback. It can be deflected 1.6 times as far as nitinol wire or 4.4 times as far as stainless steel wire without appreciable permanent deformation. NiTi wire is highly useful in clinical situations that require a low-stiffness wire with an extremely large springback.
Alloys↗
Diagnosis and treatment planning of skeletal asymmetry with the submental-vertical radiograph.
The purpose of this study was to assess the reproducibility of landmarks visible in the submental-vertical radiographic projection. Ten subjects with at least a 2 mm apical base discrepancy as diagnosed by means of a posteroanterior headfilm were selected. Mean tracing and measurement error was found to be less than 1 mm for all landmarks. A system of patient orientation and radiographic technique is presented. The radiographs were made at 90 kVp, 15 mA, 1 second exposure, using Kodak Lanex X-D film with a speed of 600. A system of cephalometric analysis is presented for the assessment of skeletal asymmetry in the horizontal plane. This system of analysis uses landmarks within the cranial base, maxilla, and mandible to construct reference lines with which to assess asymmetry. These reference systems allow the assessment of asymmetry within each component part of the craniofacial complex as well as the relative relationship of these parts to one another. Examples are presented to demonstrate the use of this system in assessing skeletal asymmetry. These examples show how this system of analysis can be incorporated into the data base for a particular patient and how it can be useful in making treatment decisions for patients with skeletal asymmetries. This method lends itself to future incorporation into a three-dimensional computerized cephalometric analysis.
Adult↗
Mechanics of tooth movement.
Orthodontic forces can be treated mathematically as vectors. When more than one force is applied to a tooth, the forces can be combined to determine a single overall resultant. Forces can also be divided into components in order to determine effects parallel and perpendicular to the occlusal plane, Frankfort horizontal, or the long axis of the tooth. Forces produce either translation (bodily movement), rotation, or a combination of translation and rotation, depending upon the relationship of the line of action of the force to the center of resistance of the tooth. The tendency to rotate is due to the moment of the force, which is equal to force magnitude multiplied by the perpendicular distance of the line of action to the center of resistance. The only force system that can produce pure rotation (a moment with no net force) is a couple, which is two equal and opposite, noncolinear but parallel forces. The movement of a tooth (or a set of teeth) can be described through the use of a center of rotation. The ratio between the net moment and net force on a tooth (M/F ratio) with reference to the center of resistance determines the center of rotation. Since most forces are applied at the bracket, it is necessary to compute equivalent force systems at the center of resistance in order to predict tooth movement. A graph of the M/F ratio plotted against the center of rotation illustrates the precision required for controlled tooth movement.
Biomechanical Phenomena↗
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↗
Maximum forces and deflections from orthodontic appliances.
The maximum bending moment of an orthodontic wire is an important parameter in the design and use of an orthodontic appliance. It is the wire property that determines how much force an appliance can deliver. A bending test which allows direct measurement of the maximum bending moment was developed. Data produced from this test are independent of wire length and configuration. The maximum bending moment, percent recovery, and maximum springback were determined for round and rectangular cross sections of stainless steel, nickel-titanium, and beta-titanium wires. The data suggest the need for more specifically defining maximum moment and maximum springback. Three maximum bending moments are described: Me, My, and Mult. My and Mult are clinically the most significant. Appliances that are required to have no permanent deformation must operate below My. Appliances that exhibit marked permanent deformation may be used in some applications and, if so, higher bending moments can be produced. In order of magnitude, the maximum bending moment at yield is largest in stainless steel, beta-titanium, and nickel-titanium for a given cross section. Nickel-titanium and beta-titanium have significantly larger springback than stainless steel determined at the moment at yield. Nickel-titanium did not follow the theoretical ratio between ultimate bending moment and the bending moment at yield, exhibiting a very large ratio. The study supports the hypothesis that most orthodontic appliances are activated in a range where both plastic and elastic behavior occurs; therefore, the use of yield strengths for calculation of force magnitude can lead to a significant error in predicting the forces delivered.
Dental Alloys↗
The flexure modulus of elasticity of orthodontic wires.
The flexure moduli of elasticity of solid and multi-stranded orthodontic wires were determined. Results for the solid wires approximated their tensile values, but the differences were statistically significant for the stainless steel, chromium-cobalt-nickel, and nickel-titanium alloys. The flexure moduli of the multi-stranded wires ranged from 0.89 to 5.11 X 10(6) psi, and were dependent on the direction of activation.
Chromium Alloys↗
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↗
A segmental approach to mandibular molar uprighting.
Diagnosis and treatment in molar uprighting are discussed. The over-all objective in molar uprighting is ideal positioning of the molar which will eventually become an abutment tooth for a fixed prosthesis. The ideal position will provide an optimal periodontal environment for the molar(s). The specific objectives concerning protection against inflammatory periodontal diseases and occlusal traumatism, which together determine the optimal periodontal environment, are explained. Emphasis is placed on the biomechanics of molar uprighting which will achieve the desired periodontal treatment result. The specific technique recommended for the instances in which the molar is considerably angulated involves a segmental approach which utilizes a modification of the Burstone root spring. Proper application results in the dissociation of the correction of angulation and the extrusion of the molar tooth. When extrusion of the periodontally involved molar is required, then it should follow the correction of molar angulation. Other advantages of this approach involve the precision and ease of symmetrical preactivation, favorable load/deflection considerations, the low level of patient discomfort, and the reduced tendency of normal function distorting or dislodging the spring. This technique is compared by these parameters to other popular molar-uprighting techniques. It is recognized that a multidisciplinary approach to this type of dental therapy is ideal and that since treatment planning in individual cases varies greatly, each malocclusion and associated periodontal involvement should be evaluated on an individual case basis.
Biomechanical Phenomena↗
The segmented arch approach to space closure.
The clinical application of frictionless attraction springs using the segmented arch technique is described. Differential space closure is achieved by varying the force system between the anterior and posterior segments. A specially designed force transducer allowed accurate force and moment determination for each spring design. By duplicating predetermined spring geometries, the orthodontist can reproduce the required force system within narrow ranges. The most important considerations in the clinical use of attraction springs are the amount of distal activation, the angulation differential between the anterior and posterior teeth, and the centricity or eccentricity of the loop. Improvements in design have lead to a more efficient, hygienic, and comfortable mechanism for space closure.
Diastema↗
Holographic measurement of incisor extrusion.
A technique based on pulsed laser hologram interferometry was used to study the dynamics of incisor extrusion. Maxillary central incisors of four subjects were loaded with forces acting along the long axis of the tooth, and the resulting motions were measured noninvasively in three dimensions. The incisor translations and rotations were used to determine centers of rotation. The experimentally determined centers of rotation are shown to depend on tooth root geometry and are found to lie at a vertical level coincident with the centroid of the root.
Adult↗
Status report on beta titanium orthodontic wires. Council on Dental Materials, Instruments, and Equipment.
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Chemical Phenomena↗
Unilateral face-bows: a theoretical and laboratory analysis.
The investigation evaluated and compared the effectiveness of five face-bow types in delivering unilateral distal forces to their inner-bow terminals. The face-bow types evaluated were bilaterally symmetrical, soldered offset, spring attachment, swivel offset, and power arm. A strain-gauge transducer system was used in the laboratory analysis. A theoretical analysis was also conducted, patterned after the method of Haack and Weinstein, and the results were compared to those obtained from the laboratory analysis. The method used for the theoretical evaluation of the sample face-bows was found to be a reliable means of approximating the percentage distribution of distal forces to the inner-bow terminals. The magnitude and direction of the net lateral forces delivered to the inner-bow terminals was also reliably determined. The results of the theoretical and experimental study of the five face-bow types indicate that the power-arm unilateral face-bow and the swivel-offset unilateral face-bow were effective in delivering a clinically significant unilateral distal force. The bilaterally symmetrical face-bow, the soldered-offset unilateral face-bow, and the spring-attachment unilateral face-bow were not effective in delivering clinically significant unilateral distal forces. Every face-bow effective in delivering unilateral distal forces will also deliver a net lateral force to the inner-bow terminals. This net lateral force will have a direction running from the inner-bow terminal receiving the greater distal force toward the terminal receiving the lesser distal force.
Biomechanical Phenomena↗
Variable-modulus orthodontics.
Traditionally, orthodontists have varied the size of the wire in order to produce a range of light to heavy forces. A new approach to force control in presented which allows wire size to remain relatively constant and the material of the wire is selected on the basis of clinical requirements. When the material instead of the cross section is varied, superior orientation should be achieved with fewer wires during tooth alignment, and bracket-wire play becomes independent of the forces needed. Since wire stiffness is determined by wire corss section and material, a simplified numbering system is described which aids clinicians in evaluating any orthodontic wire.
Dental Alloys↗
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↗