Ultrasonics in Dentistry

Shear Bond Strength and Mode of Failure of Polypropylene Fibers in Orthodontic Flash-Free Adhesive

The purpose of this research is to evaluate the effects of magnetostrictive and piezoelectric scalers on the shear bond strength (SBS), failure mode of the polypropylene fiber adhesive brackets, and the load of both scaler tips. The adhesive precoated (APC) Flash-Free brackets were placed on the buccal surfaces of sixty maxillary first premolars, which were divided into three equal groups of 20 specimens each, following the control group (no scaling), the magnetostrictive group, and the piezoelectric group. All specimens were measured for SBS value by using a universal testing machine at a crosshead speed of 0.75 mm/minute. The mode of failure was examined under a×10 magnification light microscope digital camera and scores for the adhesive remnant index (ARI) were recorded and measured load between the magnetostrictive and piezoelectric groups. For statistical analysis, ANOVA and multiple comparison, as well as unpaired t-test and chi-square tests, at the 0.05 significance level were used. The results showed that the average SBS value of the control group was greater than that of the magnetostrictive group and the piezoelectric group. However, the SBS was not significantly influenced by ultrasonic instruments (p > 0.05). The ARI score and load showed no significant differences among the groups (p > 0.05). In conclusion, the SBS of the APC Flash-Free bracket wasn’t affected by using ultrasonic instrumentation around the base of the bracket.

Dental technology of Taiwan during the Japanese colonial period

Background/purpose

During the Japanese colonial period, the Taipei Hospital had already provided complete dental services with a fixed price per treatment. This study tried to compare the differences in the prices of various dental treatments between the Japanese colonial period and today.

Materials and methods

This study used the “Dental Treatment Fees in the 27th Annual Report of Taipei Hospital (Taisho 12)” as the study materials to compare the differences in the prices of various dental treatments between the Japanese colonial period and today using the monthly salary of a novice elementary school teacher as an income benchmark.

Results

A hundred years ago, the Taipei Hospital had already provided the dental treatments such as scaling and endodontic, operative dentistry, prosthodontic, and orthodontic treatments. Of these treatment items, the prices for prosthodontic and orthodontic treatments were more expensive. After a century of development, the costs of scaling and operative dentistry treatments dropped, while the costs of endodontic, prosthodontic, and orthodontic treatments increased.

Conclusion

During the Japanese colonial period, Taiwan's dental treatment technology had already had the forms of modern dentistry with several dental specialties. At that time, the costs of dental treatments are quite expensive. Today's dental treatment items are more detailed and diverse. The health insurance system provides Taiwanese people with convenient and cheap general dental treatments such as scaling and treatments related to operative dentistry, endodontics, periodontics, and oral surgery. However, the costs of prosthodontic and orthodontic treatments increase and have to be paid by the patients themselves.

Numerical investigation of cavitation generated by an ultrasonic dental scaler tip vibrating in a compressible liquid

Bacterial biofilm accumulation around dental implants is a significant problem leading to peri-implant diseases and implant failure. Cavitation occurring in the cooling water around ultrasonic scaler tips can be used as a novel solution to remove debris without any surface damage. However, current clinically available instruments provide insufficient cavitation around the activated tip surface. To solve this problem a critical understanding of the vibro-acoustic behaviour of the scaler tip and the associated cavitation dynamics is necessary. In this research, we carried out a numerical study for an ultrasound dental scaler with a curved shape tip vibrating in water, using ABAQUS based on the finite element method. We simulated the three-dimensional, nonlinear and transient interaction between the vibration and deformation of the scaler tip, the water flow around the scaler and the cavitation formation and dynamics. The numerical model was well validated with the experiments and there was excellent agreement for displacement at the free end of the scaler. A systematic parametric study has been carried out for the cavitation volume around the scaler tip in terms of the frequency, amplitude and power of the tip vibration. The numerical results indicate that the amount of cavitation around the scaler tip increases with the frequency and amplitude of the vibration. However, if the frequency is far from the natural frequency, the cavitation volume around the free end decreases due to reduced free end vibration amplitude.