13. The comparison between Domestic and Foreign Magnetic Attachments

Nakamura Y., Masuda T., Shoji K., Ando A., Kumano H., Miyata T. and Tanaka Y.

The First Department of Prosthodontics , School of Dentistry ,Aichi – Gakuin University

Introduction

　Magnetic attachment of different manufacture, may offer differences in physical property and quality including greater stability and retention, ease of manipulation, superior esthetic applications, and reduction of stress to abutment teeth in the various clinical settings shown through research and development. There are several magnetic attachments available on the foreign market. However, since many of these products are available only through commercial means, development process and proprietary details of design and specifications are not readily available in academic journals, and thus even accurate development time remains unknown.

Objective

　In this preliminary study on seven foreign-made magnetic attachments that were obtained and compared to the GC GIGAUSS. We measured attractive force of magnetic attachments, and investigated the change in surface morphology of keepers after applying cyclic loads to measure the mechanical strength of keepers.

Materials and Methods

Fig. 1 show seven foreign-made magnetic attachments and GC GIGAUSS that we used in the present study.

Fig.1: Foreign-made magnetic attachments

Attractive force was measured by a table-top material tester (EZ Test) using a customized JIG and die device. Measurement conditions were as follows; Crosshead speed: 5mm/min, number of samples: 6 samples of each kind, number of measurement: 10 times (Fig.2 ).

Fig.2:Measuring device and custom made JIG

Fig.3: Repetitive Swats Machine

　Subsequently, cyclic loading testing was performed to measure the mechanical strength of keepers. The susXM27 stainless steel bar was used to apply cyclic loads (Fig. 3).

　　　We conducted surface observation, strain measurement, and attractive force measurement after applying cyclic loads on samples. A stereoscopic microscope was used for the surface observation. The shape of keepers was measured with three-dimensional digitizer for the strain measurement (Fig. 4).

Fig.4: Three-dimensional digitizer

The digital data obtained was modeled using three-dimensional CAD system, and strain was measured on this model. Attractive force measurement followed the same procedure as used in the preliminary study.

Results

(1) Preliminary study before the tapping test

　　Fig. 5 shows a comparison of attractive force between our measurement results and values provided by manufacturers. Our measurement value was lower by 10-20% compared with values provided by manufacturers.

　　Fig. 6 shows a comparison of attractive force per unit adsorption area.

　 Foreign-made magnetic attachments showed attractive force less than half of Japanese GIGAUSS D600.

Fig.5: Attractive force

Fig.6:Attractive force of per unit area.

Fig. 7 shows the attractive force per unit volume.

　The results showed significantly low attractive forces in foreign-made magnetic attachments except MAGNEDISC 800 (US) compared to GIGAUSS D800. This is considered to be due to the differences in the magnetic properties and magnetic circuit.

Fig.7: attractive force per unit volume

(2)After the tapping test

　Fig. 8 shows the surface texture of keepers before and after applying cyclic loads in each magnetic attachment (Left: before loading, Right: after loading). Each of four magnetic attachments showed a loss of surface gloss, scratches overall, and stretched parts in the margins.

　The following four magnetic attachments showed the similar results. However, in the Smart Magnet Kit, marginal region of a keeper was found flat. This is because a beater bar kept pounding the protruded marginal region (Fig. 9).

Fig.8 Surface texture of keepers

Fig.9 Surface texture of keepers

　Fig. 10 shows the results of the strain test.

DYNA demonstrated the smallest strain of 0.007 mm. An outward bulge was observed in MicroPlant.

　Marginal strains were observed in the following four types of magnetic attachments. Outwards bulges were also observed in SmartKit and Maximagnet (Fig. 11).

Fig.10 Results of the strain test

Fig.11 Results of the strain test

Fig. 12 shows the results of attractive force measurement.

　　Little decrease in the attractive force was observed in DYNA, Titanium Magnetix, GIGAUSS D600. Multi-purpose MAGNET SYSTEM, Magnedisc, Maximagnet demonstrated moderate decrease. MicroPlant and Maximagnet demonstrated significant decrease due to their unique figures.

Fig.12 Attractive force

Discussions

In recent years, magnetic attachments have been recognized as a dental tool in Japan, and have been widely used in clinical practice. Magnetic attachments with various shapes and performances are also available on the foreign market.　　However, details of their performance have yet to be revealed.

Most of the seven foreign-made magnetic attachments that we obtained have open magnetic circuit structure or have magnets embedded in keepers as well. These findings suggest that these magnetic attachments designs aim for the epithesis or large-size implants rather than retention and stability of dentures.

Conclusions

Although some of the large size foreign-made magnetic attachments that we used in this study showed the same level of attractive force as domestic magnetic attachments, attractive force per unit area/volume was extremely small, suggesting a lack of high performace of attachments.

Several samples demonstrated fine scratch on the surface and deformation at the margin of a keeper after the tapping test. All seven samples showed a decrease in the attractive force after load application, but no significant decrease in the attractive force was observed in GIGAUSS.

References

1. Gillings, B. R. D.: Magnetic retention for complete and partial overdentures, Part. J. Prosthet. Dent., 45(5): 484-491, 1981.

2. Jackson,T.R.: The applicaiton of rare earth magnetic retention toosseointegrated implants. Int. J. Oral ＆ Maxill. Imp., 1: 81-92, 1986.

3. Tanaka, Y.: Dental Magnetic Attachment, Q＆A, Ishiyaku Publishers, Inc. (Tokyo), 1995.

4. Mizutani, H., Ishihata, N. and Nakamura, K.: Removable partial denture used the magnetic attachment, Quintessence Publishing Co., Ltd. (Tokyo), 1994.

Discussion Board

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