Hirokazu Nakano

Mechanical properties of several nickel-titanium alloy wires in three-point bending tests

The purpose of this study was to clarify the mechanical properties of 42 brands of nickel-titanium alloy orthodontic wires from 9 manufacturers by conducting three-point bending tests under uniform testing conditions. Manufacturers included A-Company, Hoya Medical, Lancer, Ormco, Rocky Mountain, Sankin, Tomy (GAC), TP, and 3M/Unitek. Cobalt-chrome, and titanium-molybdenum alloy wires were also tested as a reference for comparison of force levels. All reported data were recorded during the unloading process to simulate the force that a wire exerts on a tooth as it is moved into the dental arch from a position of malocclusion. The following results were obtained for the nickel-titanium wires tested. (1) Among the 0.016 inch round wires tested under a maximum deflection of 1.5 mm, the difference between the smallest (Copper nickel-titanium 35) and the largest (Aline) load values was 136 g. For the 0.016 x 0.022 inch rectangular wires tested, the difference between the smallest (Copper nickel-titanium 40) and the largest (Aline) load values was 337 g. (2) The change in load between 1.5 and 0.5 mm of deflection was examined to clarify the superelastic properties of the wires tested. For the 0.016 inch wires, 17 wire brands produced a load difference of less than 100 g, and two brands produced a difference of at least 100 g (Aline and Titanal = 100 g). For the 0.016 x 0.022 inch wires, 15 brands produced a load difference of less than 100 g, and eight brands produced a difference of over 100 g. The smallest and largest load differences were 3 g (Copper nickel-titanium 35) and 200 g (Aline). (3) The majority of the samples with a smaller load difference between deflections of 1.5 mm and 0.5 mm in the unloading process were found among super-elastic wires, while samples with a larger load difference were predominantly found among work-hardened wires. Compared with cobalt-chrome and TMA wires, nickel-titanium alloy wires exert significantly less force. However, the amount of force varies greatly from brand to brand. Consequently, when using nickel-titanium alloy wires, brands must be selected carefully by taking into consideration the severity of the malocclusion and the stage of orthodontic treatment in each case. It is the intent of this study to offer clinicians an unbiased guide for the selection of appropriate nickel-titanium alloy wires.

Clinical application of dental implant with root of coated bioglass: Short-term results

During the last 4 years 73 dental implants with root-coated bioglass to replace one to three teeth in the premolar and molar sites of the mandible were inserted. The bonding ratio between implant and bone was observed clinically 1 year after implantation and installation of the superior structure. This ratio measured 52.4% to 63.3%. An acoustoelectric tester was developed that advanced our skills. The emphasis was placed on a tight fit between implant and surrounding bone.

Investigation of Postoperative Stability of Mandibular Asymmetry Cases

The purpose of the present study was to investigate postoperative stability of asymmetric mandible. We performed a cephalometric radiographic evaluation of postoperative stability on 11 patients who had undergone sagittal splitting ramus osteotomy of asymmetric jaw deformities at our clinic from 1989 to 1991.The results were as follows:1. Measurements of areas of right and left mandible by cephalometric radiograms, particulary those in the lower portion, were very useful to evaluate the postoperative change of mandibular asymmetry. The ratio of left area/right area in the lower portion of the mandible was turned to nearly 50/50 at one year after operation in 7 patients.2. Four of 7 patients, who had a difference of over 7mm in setback between right and left of the mandible and had a horizontal movement of over 6mm at the center of both lower central incisors, exhibited less postoperative horizontal stability.3. Only two of 9 patients, who were given preoperative orthodontic therapy, showed postoperative instability of the mandible.4. The correlation between postoperative horizontal instability and posteroanterior instability of the mandible was not definitely confirmed.