Vibration analysis of maxillary removable partial denture frameworks.

The purpose of this study was to investigate the vibratory characteristics of three designs of the Class I Kennedy maxillary removable partial denture frameworks as the basic study. Their major connectors comprised a U-shaped palatal connector (UPC), single palatal bar (SPB), and anterior-posterior palatal bars (APB). Frequency response functions were measured when the framework was impacted. The modal shape was observed and the decay rate was calculated using modal analysis software. The results showed that the vibratory properties of each framework differed from each other. Within the range of frequencies from 10 to 2000 Hz, the UPC type had seven natural frequencies, while the SPB and the APB types had six. The UPC type had a greater number of natural modes accompanied by elastic deformation, including fluttering and twisting, than the other type, and the UPC type was considered to be unfavourable. The decay rate of the APB type was significantly higher than those of the UPC and the SPB types (P < 0.01).

The vibration analysis of obturator framework designs.

The purpose of this study was to analyze the vibration of obturator framework designs and investigate the vibration effects of connecting parts of the components. Four designs of maxillary obturator framework were used in this study: a partial palatal plate with continuous bar (A), with a part of continuous bar (B), without continuous bar (C) and without continuous bar and indirect retainer (D). In order to investigate the vibration of each framework (total) and some component parts, the measurement points of the retentive parts were divided into 3 groups; anterior, middle and posterior. The framework was activated by a vibration generator. The vibration of each measurement point was detected with a laser doppler vibrometer. The frequency response signals were conducted by an FFT Analyzer between 220-2000 Hz. The maximum displacement (MDP) and the decay rate (DR) of the vibration were analyzed statistically by ANOVA and Fisher's PLSD (p<0.05). The result showed that in the posterior group, MDP of D was higher than those of A, B and C. Regarding the anterior, middle and total group, the DR of D were lower than A, B and C. It was suggested that D might be clinically unfavorable.

The vibratory properties of an obturator prosthesis with a soft lining material.

This study used modal analysis to evaluate the vibratory properties of cast obturator prostheses fitted with soft lining material. Three types of buccal flange bulbs were prepared: a resin (R) type; a 2 mm-thickness relined (RM) type; and a type fully relined with MOLTENO, (M) type. A vibration generator excited the obturator, while a Laser-Doppler Vibrometer detected the vibrations at specified measurement points. Both the excitation and response signals were sent to an FFT analyzer, which calculated the frequency response functions. Then, using DAMPCAL simulation software, the decay rates and the maximum amplitudes of rest and clasp parts were calculated. Statistical analysis was performed by means of one-way ANOVA with Fisher's PLSD test. The results indicated that for impacts simulated on both the defective and non-defective sides, the R type showed a significantly higher decay rate than did the other samples (p<0.0001). When impacts were directed at the non-defective side, the R and M types showed significantly smaller maximum amplitude values than did the RM type (p<0.0001). Only the M type, however, showed significantly smaller values when impacts were directed at the defective side (p<0.0001).

Hollow obturator with removable lid.

Hollowing the obturator reduces the weight of the prosthesis. Closed and open hollow obturator prosthesis each have their particular benefits. However, the obturator with a removable lid has its benefits also, and the advantages have been described.

Depth of penetration of in vitro root surface lesions.

An acidified gel system was used to produce artificial caries lesions in root surfaces and in enamel. The teeth were exposed to the gel system for two weeks and four weeks, after which the lesions were examined by polarized light microscopy and photographed by standardized techniques. The depths of penetration of the lesions were measured from these standardized photomicrographs. The lesions in root surfaces were deeper than those in enamel for all teeth. After two but not four weeks of exposure in the gel system, the lesions in the root surfaces of anterior teeth were deeper than those in pre-molars.

Histopathology of the initial lesion of the root surface: an in vitro study.

An acidified gel system was used to produce artificial caries lesions in root surfaces. Radiopaque surface layers were found with 47% of the lesions. Demineralized bodies of the lesion and mineralized zones of banding were seen in all lesions when examined by microradiography. Cementum and dentin seemed to respond to the acid attack in a similar manner. Although artificial root lesions did not simulate natural root caries entirely, the acidified gel system resulted in a reproducible method that might give insight into initial lesion formation on root surfaces. This technique may be used for studying the physico-chemical process involved in the demineralization of root surfaces and for testing the effects of various agents in the prevention of root caries.