Tetsuya Kamegai

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.

Reduction of masseter muscle activity in bottle-fed babies.

Our previous studies suggested that there are significant differences in the growth of the jaw and in muscle activity between breast- and bottle-fed infants. To confirm these differences quantitatively, myoelectric activities of the masseter muscles of bottle-fed babies were studied. Twelve bottle-fed babies, as well as 12 breast-fed babies as a control group, were examined electromyographically during bottle or breast feeds. The duration time of sucking bursts, interval time, cycle time, 0-to-peak amplitude, integrated amplitude of bursts, and integrated amplitude/duration time were measured and the number of bursts over 30 microV was counted. All differences of means were significant by t-test. The masseter muscle activity in bottle-fed babies is significantly reduced. Our results are contrary to previous papers in which almost the same sucking actions in both breast and bottle feeding were reported. The reason why previous researchers thought that the sucking patterns in breast- and bottle-fed babies are essentially the same is considered, and the implications of the differences for dental health are discussed.

Masseter muscle activity in bottle feeding with the chewing type bottle teat: evidence from electromyographs

It was reported that the activity of the masticatory muscles is reduced in bottle fed babies. The effects of chewing type bottle teats distributed in Japan on masticatory muscle activity were evaluated. Myoelectric activities of the masseter muscles of 12 babies bottle fed with chewing type bottle teats were recorded and analyzed by the same method as in the previous study. The electromyographic records of 12 breast fed babies and 12 babies bottle fed with regular sucking type bottle teats, which were reported in a previous study, were used as controls. The results show that the masseter muscle activity of babies bottle fed with chewing type bottle teats was similar to that of breast fed babies qualitatively as well as quantitatively. However, activity was visibly different from that of babies bottle fed with sucking type bottle teats, showing significant difference by ANOVA. These data suggest that babies who are ingesting milk from chewing type bottle teats do so with a chewing action similar to that of breast feeding, but very different from that of bottle feeding with sucking type bottle teats. The conclusion was that the chewing type bottle teat is useful for establishing masseter muscle activity.

Influence of tooth-to-denture-base discrepancy on space closure following premature loss of deciduous teeth

Influence of tooth-to-denture-base discrepancy on so-called physiologic migration of the first molar was studied on serial dental casts of 116 boys and girls, obtained through a dental health program for school children in an area in which there was no dentist. The alteration of spaces following premature loss of deciduous molars was examined comparing the anterior to posterior discrepancies between tooth and denture base. Modes of space alteration showed positive correlation with the size of the discrepancy, especially in the mandibular dental arches. The space deficiency in the posterior region seemed to have a positive effect on the mesial migration of the first molar. Mesial migration of the first molar seems to be pathologic rather than physiologic and is strongly affected by tooth-to-denture-base discrepancies. Space maintenance does not seem to be useful, because it is not necessary in minimum discrepancy cases and is not effective in severe discrepancy cases.

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.