American journal of orthodontics最新文献

To evaluate the clinical crown length relative to fixed-appliance orthodontic treatment of excessive overjet and deep overbite and to correlate such changes to the vertical dental height, the following measurements were undertaken for 12 females and 8 males, between the ages of 16 and 20 years, on three separate occasions-2 days before banding, 2 days after debanding, and 12 months after debanding: (1) overjet, overbite and dental height measured from right lateral cephalometric x-ray films; (2) clinical crown length, measured from study models, of 400 teeth divided into four groups-maxillary incisors and canines (120 teeth), maxillary second premolars and first molars (80 teeth), mandibular incisors and canines (120 teeth) and mandibular second premolars and first molars (80 teeth); and (3) gingival condition by means of the gingival index of Löe and Silness. Fixed edgewise orthodontic appliances were used and the four first premolars were extracted. From the results of the investigation, the following conclusions were evident: (1) after a 12-month follow-up observation period, the achieved reduction in overjet, overbite, and dental height showed relapses of 9%, 11 %, and 29%, successively; (2) only 7% of the 400 teeth examined showed reductions in clinical crown length. This change was probably the result of gingival hyperplasia. The gingival condition greatly improved by approximately 64% after 12 months of debanding, accompanied by 25% to 50% relapse in the amount of change in clinical crown length (noted 2 days after debanding); and (3) the intrusive tooth movement during orthodontic correction of deep overbite was the result of vertical movement of the tooth, with its investing tissues and soft-tissue attachment, into the jaws. The clinical crown length and vertical dental height remained practically constant.

Stainless steel, cobalt-chromium-nickel (Elgiloy), nitinol, and beta titanium wires with diameters from 0.010 to 0.040 inch and in rectangular sizes from 0.017 × 0.025 to 0.019 × 0.025 inch were evaluated with the American Dental Association specification no. 32 bending test and the conventional tension test. The modulus of elasticity (E) and yield strength (YS) obtained with the two mechanical testing procedures are reported for as-received wires and after heat treatment at 900° F for the stainless steel and selected Elgiloy wires. Measured values of E and YS in bending were almost invariably higher than the corresponding values obtained in tension. The only general agreement between the modulus of elasticity in bending and tension was for the 0.040-inch diameter stainless steel wires. Anomalously high values of E in bending were also found for most of the heat-treated stainless steel and Elgiloy groups. Difficulties with the bending test are attributed to loading effects at both ends of the test span and deviation of the bent specimen from a circular arc. Improved procedures are described for performing the tension test on the relatively small cross-section orthodontic wires.

To test the effectiveness of bonding orthodontic attachments to porcelain, edgewise brackets were bonded to 160 lower incisor, porcelain denture teeth by means of two different resin systems and three different porcelain bonding agents. Bonding to porcelain was found to be not only effective, but the use of a porcelain primer before bonding resulted in shear strengths comparable to those achieved with conventional acid-etch enamel bonding when the same resin was used. Roughening the porcelain surface and bonding with a heavily filled resin without a porcelain primer provided shear strengths (30.6 Ibs) comparable to conventional acid-etch enamel bonding with a lightly filled resin (28.8 Ibs). Roughening the porcelain surface before bonding, adding porcelain primers, and using highly filled resins all added significantly to bond strength, but caused a progressively greater risk of porcelain fracture during debonding. One of three methods to polish porcelain completely restored a roughened porcelain surface to its former appearance. The porcelain bonding primers failed to provide a significant increase in bond strength when bonding to gold. However, a roughened gold surface bonded with a heavily filled resin provided shear strengths (27.3 Ibs) comparable to conventional acid-etch enamel bonding by means of a lightly filled resin (28.8 Ibs). The use of a highly filled resin on an intact, glazed porcelain surface without using a porcelain primer may provide sufficient bond strength clinically. If more bond strength is needed, the use of Reliance porcelain primer on an intact glaze is preferable to Ormco porcelain primer or Fusion. Still greater bond strength can be developed by roughening the porcelain surface before application of a primer and use of a highly filled resin. The potential for porcelain fracture in debonding, however, is much increased and it is questionable whether bond strengths of this magnitude are required clinically.

Over the past 2 years an increasing concern has developed about the possible iatrogenic effects of phosphoric acid-etch bonding techniques on the enamel surface. There is an evident heed to develop a mechanical or chemical retention system that would not alter (or would minimally alter) the outer enamel surface. An alternative to the conventional phosphoric acid etch technique has been developed. A preliminary clinical trial showed promising performance under normal clinical conditions. These results were achieved with a minimal loss of surface enamel as evidenced by scanning electron microscopy. Debonding and cleanup were greatly facilitated. Creating a micromechanical retentive surface by the formation of a crystalline interface is a potential alternative to phosphoric acid etching.

Twelve different systems of intrusion, based on the principle of the “segmented arch,” were evaluated on a macerated human skull. The number of teeth involved in the anterior unit and the location of the application points of intrusive force were considered to be variables. Initial displacements of the anterior teeth after loading were registered by means of the laser reflection technique and double exposure holographic recordings. An attempt was made to define “this” intrusive system, achieving the most genuine intrusion (for definition, see text) without flaring of the teeth. When two central incisors were incorporated in the sectional wire, strong torque forces appeared, especially when the intrusive forces seized more distally. When four or six anterior teeth were pinned in the sectional wire, tooth movement seemed to be under better control. When the six front teeth were incorporated in the sectional wire, the center of resistance (for definition, see text) was located more to the distal side of the canines. It seemed more difficult, however, to define the center of resistance of the four incisors; it was situated approximately distal to the lateral incisors. In some of the intrusive systems, the teeth underwent independent mesial or distal rotations. This was easily observed with the laser measuring techniques used.

This study was designed to assess the gingival tissue resistance to remodeling in determining the rate of orthodontic tooth movement. Closed coil spring orthodontic appliances were stretched bilaterally between the first molars and incisors in the maxillary arches of 18 adult rats. The resistance of gingival tissues was eliminated around the randomly chosen first molars by a circumferential fiberotomy procedure. Movements of teeth were measured on submental vertex radiographs against the metallic implants that were placed in zygomatic processes. The data were analyzed by randomized block design analysis of variance. During the 30-day experimental period, the teeth that underwent the fiberotomy procedure moved faster (0.63 mm versus 0.51 mm, P < 0.05), indicating that the resistance of gingival tissues may be a rate-limiting factor in orthodontic tooth movement.

Erupted and impacted teeth from young (12 to 24 years of age) and older persons (over 50 years of age) were bonded by a standard technique using etching times of 0, 15, 30, and 60 seconds. Two subgroups of teeth were soaked for 7 days and compared with those in the remainder of the group. Test specimens were loaded in shear to bond failure by means of a testing machine with a 200-kg load cell and a crosshead speed of 5 mm/minute. Results indicated insignificant bond-strength differences between young-impacted and young-erupted teeth for any given etching time. Very small bond-strength differences were found for various etching times (15, 30, and 60 seconds). A significant difference was found between 24-hour soak and 7-day soak for the etching times of 30 and 60 seconds only.