Yoshikazu Miyazaki

The mechanical properties of dental thermoplastic materials in a simulated intraoral environment

Abstract The present study assessed the mechanical properties of dental thermoplastic materials in a simulated intraoral environment. Eight dental thermoplastic products – EVA (Bioplast), PE (Copyplast), PETG (Duran), PP (Hardcast), PC (Imprelon“S”), A+ (Essix A+), C+ (Essix C+), and PUR (Invisalign) – were examined using the following tests: (1) 2-week water absorption test, (2) thickness-change tests with thermoforming and water absorption, (3) tensile tests under room temperature (23 °C) and in a simulated intraoral environment (37 °C). The results were as follows: (1) water absorption increased with time and ranking was (from highest to lowest): PUR, PETG, A+, PC, EVA, PP, C+, and PE. (2) The changes in thickness ranged from 74.9 to 92.6% in comparison with the specimens before thermoforming. Linear expansion with water absorption ranged from 100.3 to 119.9%. (3) The elastic moduli of PC, PETG, and A+ in the simulated intraoral environment showed significant increases in original sheets; in contrast PP, C+, PE, and EVA were significantly reduced. No significant changes were observed in PUR. Tensile yield stress of the specimens in the simulated intraoral environment decreased in comparison with original sheets. The present result suggests that the mechanical properties of dental thermoplastic materials varied due to environmental factors. Moreover, behavior change is influenced by molecular structure and orientation. The application of thermoplastic materials for orthodontic tooth movement requires a sufficient understanding of the material characteristics, optimal material selection, and design.

Dental Patient Robot

Presently, the simple head model (hereinafter referred to as phantom for practical training) with dentition models is used for dental therapy training. We suggested the patient robot for dental therapy training (hereinafter referred to as patient robot) as one of the practical applications of the humanoid robot technology, and we actually developed patient robots. One of them is the general model provided with 14 degrees of freedom (DOF) in addition to a tongue and lips that may interfere with treatment, allowing reflection of any change in simple expression. Also, active motions of the neck or hand allow various impediments so as to interfere with the actual potential treatment. The robot allowed trainees to do dental therapy training closer to the actual practice involving avoidance of these risks

Dental Patient Robot as a Mechanical Human Simulator

The aim of this research is the development of a patient robot for use in actual clinical training. Electro pneumatic regulators and electromagnetic valves incorporated in the robot is operated by manipulating air cylinders. It is possible to conduct training assuming several patients enabling trainees to learn a flexible response under a wide range of circumstances. A simple interface was used for ease of operation. Further, a built-in sensor inside the oral cavity responds to the trainees actions leading to a vomiting reflex and pain during drilling teeth. Attaching the pain sensor to the body of test subjects, will also be useful for training social service workers during nursing care examinations.

Efficacy of experimental dual-cure resin cement for orthodontic direct bond system

Abstract Chemical-cure resin cement has been widely used for orthodontics. To improve the clinical handling of chemical-cure resin cement, a dual-cure resin cement system composed of methyl methacrylate (MMA), urethane dimethacrylate (UDMA) and light activator was developed. The purpose of this study was to estimate the efficacy of an experimental dual-cure resin cement. A composite bracket was bonded to the teeth with one of eight resin cements: (1) Unifast II (Uni II); (2) Unifast II containing camphor quinone (Uni II-CQ); (3) Transbond XT (TB); (4) Orthomite Superbond (SB); (5) Unifast LC (Uni-LC); (6–8) experimental dual-cure resin cement—Exp1, Exp2 and Exp3, respectively. Shear bond strength (SBS) of all of the bonded brackets was measured after the cementation. The data were statistically divided, the highest cement (Uni-LC), the next group (Exp1, Exp2, Exp3 and SB) and the lowest group (Uni II, Uni II-CQ and TB). The dual-cure resin cement exhibited a bonding efficacy comparable to that of Superbond.

Application of cone beam CT 3D images to cephalometric analysis

Abstract Orthodontic diagnosis is currently based primarily on two-dimensional (2D) measurements. The development of maxillofacial cone beam X-ray computed tomography (CBCT) has promoted the use of three-dimensional (3D) measurements for orthodontic diagnosis. This technology is also expected to generate new analytic methods aiming at establishing optimal occlusion according to the individuals maxillary shape and function. However, during the transitional stage from 2D to 3D measurements, it is necessary to relate 3D data to existing data analysis methods (e.g., lateral cephalogram) for the assessment of skeletal and dental relationship. Our objectives were to develop a new cephalometric analysis method based on 3D data obtained by CBCT from four aspects: (1) measurement of magnification of cephalogram, (2) assessment of the dimensional accuracy of CBCT images, (3) development of a method of cephalometric analysis using CBCT images and (4) comparison of cephalometric analytical values obtained from CBCT images with those obtained from existing cephalograms. The results demonstrated that our analytical method facilitated cephalometric analysis of CBCT images and therefore allowed direct comparison of CBCT images with existing cephalograms. Cephalometric analysis using CBCT images resulted in a smaller range of inter-operator measurement variability than that using conventional cephalograms.