7. Influence of Sterilization on Magnetic Attachment
D. Okano, E. Muraishi, F. Tsuchida, N. Takishin and T. Hosoi
Department of Removable Prosthodontics, Tsurumi University School of Dental Medicine
Introduction
Sterilization is important in dental treatment. Although magnetic attachments have been used in clinical dentistry for about ten years, sterilization method has not been frequently studied, and there is no sterilization method established for magnetic attachments. As heating can weaken magnetic assemblies and keepers, and chemicals can corrode metals; sterilization may alter the surface properties of magnetic surfaces or lower attractive force.
Objective
The purpose of this study was to optimize and standardize the sterilization method for magnetic attachments by measuring the surface roughness and attractive force of magnetic attachments after subjecting them to conventional dental sterilization.
Materials and Methods
Table 1 summarizes the sterilization method used in this study. Three kinds of magnetic attachments; PHYSIO MAGNET 35 (Nissin Co. Ltd., Kyoto, Japan), GIGAUSS D600 (GC Co. Ltd, Tokyo, Japan) and MAGFIT DX600 (Aichi Steel Co. Ltd, Aichi, Japan) were examined.
Table 2 summarizes the diameter and the thickness of magnetic assemblies and keepers and the attractive force of magnetic attachments indicated by the manufacturer. Five magnetic assemblies and five keepers were subjected to each sterilization method. As a control, five magnetic assemblies and five keepers that were not sterilized were used in comparison.
After sterilization, the surface roughness (Ra) of magnetic assemblies and keepers was measured using non-contact 3-dimensional measurement equipment (NH-4H, Mitaka Kohki Co., Ltd., Japan) (Fig.1).
Then, attractive force was measured using a digital force gauge (FGC-1, NIDEC-SHIMPO Co., Kyoto, Japan) (Fig.2).
Statistical analysis was performed using one-way layout analysis of variance and Scheffé's test (SPSS ver.12, SPSS Japan Inc., Tokyo, Japan) at significance level of α= 0.05.
Table.1 Sterilization methods
Condition
Name and Manufacturer
High pressure steam sterilization
(Autoclave)
135℃, 2.0kg/cm2,
20minutes
Quick Clave DA-7, Osada Denki, Tokyo, Japan
Ethylene oxide gas sterilization
(EOG)
50℃, 4 hours
AssocieNSEV-M09, Sakura Seiki Co., Ltd, Osaka, Japan
Table.2 The diameter, thickness and attractive force of magnetic attachments
Name
Manufacture
Magnetic assembly
Keeper
Attractive force
Diameter
Thickness
Diameter
Thickness
PHYSIO MAGNET 35
Nissin Co., Ltd, Kyoto, Japan
3.5mm
1.3mm
3.5mm
0.8mm
5.50N
GIGAUSS D600
GC Co., Ltd, Tokyo, Japan
3.6mm
1.3mm
3.6mm
0.7mm
5.88N
MAGFIT DX600
Aichi Steel Co., Ltd, Aichi, Japan
4.0mm
1.2mm
3.6mm
0.7mm
5.88N
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Fig.1 |
Fig.2 |
Fig.1 Non-contact 3-dimensional measurement equipment (NH-4H, Mitaka Kohki Co., Ltd., Tokyo, Japan) Fig.2 Digital force gauge (FGC-1, NIDEC-SHIMPO Co., Kyoto, Japan)
|
Results
Figure 3 shows the surface roughness of magnetic assemblies. Compared to the control, the surface roughness of sterilized magnetic assemblies was increased. There were significant differences between the control and the two sterilization methods. There was no significant difference in the surface roughness of magnetic assemblies between both sterilization methods. Among the three kinds of magnetic attachments, there was a significant difference between PHYSIO MAGNET and MAGFIT in EOG sterilization.
Figure 4 shows the surface roughness of keepers. In all three products, there were significant differences between control and autoclave. In MAGFIT, there was a significant difference between control and EOG sterilization. There was no significant difference among three products. In PHYSIO MAGNET and GIGAUSS, the surface roughness showed no change by EOG sterilization.
Figure 5 shows the results of attractive force. In all three products, there were significant differences between control and autoclave. In GIGAUSS, there was a significant difference between control and EOG sterilization. Among the three kinds of magnetic attachments, there were significant differences in attractive force between GIGAUSS and other two magnetic attachments under all three conditions; control, autoclave, EOG sterilization. By the sterilization, decrease of the attractive force was observed. Therefore it was thought that the range of the change was too small to be a problem in clinically.
Fig.3 Surface roughness of magnetic assemblies
Fig.4 Surface roughness of keepers
Fig.5 Attractive force of magnetic attachments
Discussions
It seems that the surface roughness of keepers was not affected by EOG sterilization because it does not corrode metals. Also, the differences in the surface roughness between magnetic assemblies and keepers were likely due to the stainless steel compositions, in particular Cr contents. The results suggested no correlation between the surface roughness and the attractive force..
Conclusions
1. As for either sterilization method, increase of the surface roughness and decrease of the attractive force were observed.
2. There was no significant difference in surface roughness of the magnetic assemblies between autoclave and EOG sterilization. However, there was a significant difference in surface roughness of the keepers. About the surface roughness, there were fewer changes of the property by EOG sterilization compare to autoclave.
3. In both sterilization methods, decrease of the attractive force
was observed. Therefore it was thought that the range of the change was too
small to be a problem in clinically.
4. EOG sterilization was evaluated as the
sterilization method suitable for the magnetic attachment.
References
1. Nakamura K., Kotake M., Mizutani H. et al; Influences of the Heat Treatment for Magnet Assemblies with or without Keepers on Attractive Force of Magnetic Attachments, J J Mag. Dent 12(1):27-32,2003.(in Japanese)
2. Nakamura Y., Tanaka Y., Ishida T. et al; Experimental Research of Some Clinical Treatments on theAttractive Force of a Magnetic Attachment;MAGFIT. Aichi-Gakuin Dent Sci 36(4):731-735, 1998.(in Japanese)
3. Nakamura K., Mizutani H., Fukazawa N. et al; Influences of Heat Treatments on Attractive Force of Magnetic Attachments, J J Mag. Dent 6(1):63-70,1997. (in Japanese)