Browsing by Subject "Minor Tooth Movement"

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    Force Values and Rate of Distal Movement of the Mandibular First Permanent Molar
    (1959-11-01) Kuhn, Robert J.
    A method is described for the distal replacement of mesially tipped mandibular first permanent molars in children nine to thirteen years of age. The study was designed to determine the rate of movement and pain response of this tooth when relatively light specified forces were applied for distal movement. This study was undertaken in the light of recent evidence which suggests that forces many times lighter than those currently employed may enhance rate of movement, diminish the amount of root and periodontal damage, and practically eliminate pain usually associated with tooth movement. The sample was composed of children who had prematively lost deciduous mandibular second molars with resultant mesial tipping of the first permanent molar. There were eighteen cases in the sample of fifteen children, three of the children exhibiting bilateral loss. The method of movement employed a sine loop helical torsion spring attached to a soldered lingual appliance to effect distal molar movement. This appliance was so fabricated to utilize all of the teeth anterior to the primary second molar space as anchorage. Extensive records were taken before treatment began, during active treatment, and at the time of retention. These included models, lateral headplates, periapical radiographs, oriented occlusal radiographs, and direct divider measurement in the mouth. The children were routinely examined every four to ten days and appropriate records and measurements taken at these appointments. It was found in those cases in which under 80 grams had been applied to the teeth there was one pattern of movement while in those above 100 grams another general type was observed. In the below 80 gram group there was a relatively large (0.69 mm.) initial increment of space opening in the first week followed by a one – two week latent period of non-movement. Movement then continued at an average of 0.22 mm/week. The 100 gram group exhibited a very small initial movement (0.27 mm) followed by a two-three week latent period. Movement then continued at a rather rapid rate, (0.39 mm/week). Flaring of the anchorage united was noted in all but one case. The amount ranged between 1 and 2 mm. in four to six weeks. The cases above 100 grams appeared to show the largest amount of flaring. Pain usually associated with tooth movement was non-existent in the patients where below 70 grams of force was applied. The intensity of the pain response in the cases above 70 grams (70 – 194) appeared generally to coincide with the magnitude of force application. The many difficulties and variables associated with distal mandibular molar movement are discussed in detail. These include tooth inclination, occlusion and interlocking, relationship of the second permanent molar, and root configuration. Based on the results of this study, it is suggested that threshold forces for tooth movement may be non-existent and that any force if allowed to remain on a given tooth for a sufficient length of time will elicit tooth movement. The evidence shown both in this study and by other investigators point to the possibility of an optimal range of force for tooth movement.
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    Histologic Tissue Rearrangement Following a Circumferential Supracrestal Fiberotomy on Orthodontically Rotated Teeth in Dogs
    (1987) Powell, Mark L. M.; Garner, LaForrest D.; Sondhi, Anoop; Kafrawy, Abdel; Standish, S. Miles; Shanks, James
    The purpose of this study was to determine whether a circumferential supracrestal fiberotomy has a biologic basis in the management of rotational relapse. The maxillary second incisors of seven beagle dogs, approximately two years of age, were rotated orthodontically from nine to 52 degrees. The incisors were retained. A circumferential supracrestal fiberotomy was performed twice unilaterally on the maxillary left second incisor of six dogs by incising through the gingival crevice parallel to the long axis of the tooth. The seventh dog was sacrificed and used for comparison of the tissue rearrangement after rotation but before fiberotomy and/or retention. The remaining dogs were paired for retention periods of one, three, and six months. Ten days before sacrifice all seven dogs were injected intraperitoneally with procion brilliant red H-8BS to determine appositional activity. At the end of the respective retention periods, the dogs were sacrificed and the specimens were fixed, decalcified, and serially sectioned horizontally, perpendicular to the long axis of the teeth. Sections were stained with H and E for histologic examination using light microscopy. Some sections were left unstained for evaluation of procion labelling using fluorescent light microscopy. The rearrangement of the subcrestal periodontal ligament fibers was determined by whether they produced a force capable of causing an increased alveolar and/or cemental apposition and not by their angulation to the root surface. The results failed to support a biologic basis for performing circumferential supracrestal fiberotomies on orthodontically rotated teeth. The supracrestal fiberotomy combined with retention had no additional effect on increasing the rearrangement of the supracrestal tissues compared to retention alone. Six months of retention, with and without a supracrestal circumferential fiberotomy, was sufficient for the supracrestal tissues to rearrange. Some of the subcrestal periodontal fibers in the tension and pressure areas at six months in retention may play a role in relapse. Undermining root resorption was evident in some pressure areas. Neither the angulation of the subcrestal and supracrestal periodontal fibers to the tooth surface nor the angulation of the epithelium was an accurate measure of the amount of tissue rearrangement. The circumferential supracrestal fiberotomy caused a cemental hyperplasia adjacent to areas nicked by the scalpel blade.
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    The Relation between Force Magnitude and the Center of Rotation in the Maxillary Incisor
    (1962) Kulis, LeRoy Howard
    When a tooth is tipped, it moves about a center of rotation, but the exact location of this center has been the subject of much discussion and confusion. This study was designed to locate the centers of rotation of upper central incisors by application of known forces to the teeth of fourteen patients. Records were taken to ascertain the rate of movement and pain threshold, and the axis of rotation was located by superposing accurate periapical films. The results show that there is no significant difference in the centers of rotation when forces of 51 and 121 gms. were used. The teeth tipped about points located apically at 1.2 and 1.2 mm. from the centroid of the root for groups studied. The teeth moved most rapidly immediately following the first application of force, and then a lag period followed with no tooth movement. This was followed by a steady small incremental rate until the space closed. The pain threshold dropped greatly during the first day of tooth movement. The direction and type of tooth movement were able to be observed on the films. Both the rate of movement and the pain response recorded concurred with observations made daily in the clinic. This study was designed to test the validity of the Moment/ Force Ratio used to locate the centers of rotation. The results obtained were very close to those found using this ratio, and therefore gave clinical support to this theory. The conclusion reached by this study indicates that the procedure was able to accurately locate the center of rotation, found to be just apical by 1.2 to 1.3 mm. from the centroid of the root.