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The construction of a model for the measurement of palatal root torque is described. It was demonstrated that: 1. Halfway between the apex of a tooth and the arch wire the force was double that which was delivered at the apex. 2. The lateral incisors were subjected to appreciably more force than the central incisors. 3. The smaller the number of teeth acted upon, the greater the force they received.
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The postoperative behavior of premolars transplanted before completion of root formation and the long-term prognosis for such teeth have recently been studied. After postoperative observation periods ranging between 3 years 4 months and 13 years 9 months, all of the thirty-four teeth in question were found to still be in place. Root formation had continued, supporting tissues had developed, and the teeth had erupted. In most instances they had functioned normally without giving rise to problems of any kind. Their status during the re-examination implied that most of them would function normally for many years to come, perhaps for a lifetime. Autotransplantation of missing premolars in many cases is the only alternative to prosthetic substitution, and it is our method of preference. However, substitution by autotransplantation cannot be applied unless a suitable transplant is available. Any premolar destined to be extracted for orthodontic reasons is a possible transplant. In young patients it is also a suitable one. In orthodontic extraction cases, therefore, suitable transplants are usually available. In nonextraction cases, none is available unless teeth in other dental arch quadrants are "sacrificed." In the present report six cases are presented as examples of solutions to the problem of missing premolars by autotransplantation. The main combinations of missing teeth and types of malocclusion in which premolars extracted for orthodontic reasons can advantageously be used as substitutes for other premolars are defined. Also, the justification for "sacrificing" a premolar in one quadrant to the advantage of another quadrant is discussed.
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Data from a sample of 198 Class II cases treated with various appliances which deliver distally directed forces to the maxilla were examined to determine the frequency of absolute distal displacement of the upper first molar and of the maxilla. Analysis revealed that such distal displacement is possible and that it is, in fact, a frequent finding following treatment. Long-range stability of distal displacement was not assessed.
The ballista spring system is a simplified orthodontic system for treating impacted teeth. The impacted tooth is retracted by a spring that accumulates a continuous force from being twisted on its long axis. The necessary operation on the impacted tooth is simple and less traumatic. The force exerted on the tooth is vertical, without compressing the impacted tooth toward the adjacent roots. This force is well controlled and easily modified. By the lack of appliance on the front teeth during a great part of the treatment, the esthetic side of the treatment is respected. Complicated impacted teeth in adults can be treated.
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A new tool for measuring tooth movement--laser holography--offers an accurate, noninvasive approach for determining movement in three dimensions. This in vitro study is designed to establish the required force system applied on the crown of a maxillary incisor that would produce different centers of rotation, as in lingual tipping, translation, and root movement. The relationship between moment-to-force ratios and centers of rotation is shown. The experimental data are compared to theoretic approaches. With respect to the location of the center of resistance and centers of rotation, force systems needed to produce different centers of rotation are given for a central incisor of average root length.
An analysis of the mechanics required for distal movement of canine roots is presented and, on the basis of this analysis, a specific clinical approach is outlined. Three different root spring designs were tested for their ability to meet the previously determined requirements. The only spring that approached the established requirements was spring A-2. Spring types B and C did not meet the established requirements. Angular activations in excess of 20 degrees in 0.018 by 0.025 inch stainless steel wire without benefit of a loop resulted in permanent deformation of the appliance.
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.
A case of a patient whose upper first molars suffered severe root resorption as a result of distal tooth movement is presented. Complete destruction of one root was found to have occurred. The initial objective in treatment was to regain arch length and improve the molar relationships with headgear. Subsequently, full-bonded orthodontic therapy was initiated after extraction of all first molars, as loss of root length could be observed radiographically. Examination of the extracted upper first molar roots in a scanning electron microscope revealed extensive areas of superficial root surface resorption which were not detectable on radiographs of these teeth. Care should be taken to avoid impingement of roots on adjacent unerupted teeth, which may result in extensive root damage.
Previous studies reveal that the application of buccal root torque to upper molars by means of a transpalatal arch without appropriate adjustments of the arch width can produce, initially, an adverse buccal tipping of the molar crowns. Clinical observation suggests that the amount of this buccal crown tipping depends on the arch form of the palatal bar. In order to determine the influence of the arch width and height, an in vitro experiment was performed on the forces and moments produced by transpalatal arches of the Golshgarian type when symmetrical buccal root torque was applied. The torque moments and expansive lateral forces developed by nine different arch forms of varying height and width were measured and the corresponding moment-to-force ratios were calculated at three different torque levels. It was found that the moment-to-force ratio acting on the upper molars depended mainly on the amount of torque applied and the arch height. This indicates that when low palatal bars are used, the application of buccal root torque of clinically relevant amounts leads to an initial buccal crown tipping, whereas the same amounts of torque, when applied by means of high arches, bring about an initial buccal root tipping. The clinical implications of these findings are discussed.
The purpose of this article is to describe and discuss a relatively unknown and underestimated technical approach to the orthodontic extrusion of impacted canine teeth. It constitutes a preliminary report of a researcher project conducted in our undergraduate clinics on patients treated for orthodontic extrusion of impacted teeth. Of these patients, twenty-seven had maxillary canine impaction, sixteen unilateral and eleven bilateral, for a total of thirty-eight teeth. Some surgical considerations and various fixation appliances for impactions are discussed, as well as the advantages and disadvantages of exerting an extrusive force by means of a Hawley type of removable appliance.