Changes of Magnetic Attractive Force after Incorporation of Magnetic Assembly into Denture Base with Self-Curing Resin
Section of Removable Prosthodontics
Graduate School, Tokyo Medical and Dental University Tokyo, Japan
Introduction
It is very important to apply reliable technique for incorporation of magnetic assemblies into denture base. Intimate contact between magnetic assembly and keeper in the outset of treatment will aid providing retention and stability to overdenture for long time. Various kinds of techniques for incorporating the magnetic assemblies into the overdenture base are presently used1). However, as distortion of acrylic resin during setting, it is said that direct technique in the oral cavity is more preferable compared with indirect technique2).
Objective
The aim of this study is to compare two different direct techniques of magnetic assembly into denture base with self curing resin.
Materials and methods
1. Magnetic assembly and resin cap
Fifteen magnetic attachments (MAGFIT DX 600 Aichi Steel Corporation, Aichi-ken, Japan) were used in this experiment. They were divided into 3 groups: C group (control group n=5), WOS group (without spillway group n=5), WS group (with spillway group n=5) as shown in Fig.1. Ten resin caps, substituted for overdentures were fabricated by heat curing resin (Acron, GC Corporation, Tokyo, Japan). They were used only for WOS group and WO group and not for C group. As for the resin cap, the dummy former (Aichi Steel Corporation, Aichi-ken, Japan) was used in order to keep same internal space.
A screwed rod for attaching to the jig of universal testing machine (Autograph AGS-H, Shimadzu Co., Kyoto, Japan) was directly fixed to the top of the magnetic assembly by glue (Aron alpha Toagosei Japan) in C group. But in WOS and WS group, the jig was fixed on the top of resin cap by self-curing resin (Unifast Trad, GC Corporation, Tokyo, Japan). After setting the rod, a spill-was was made by round bur (Size ISO-023) on the top of resin cap in WS group.
![[Fig. 1]](image001.jpg)
Fig.1. Magnetic assemblies and resin caps for each group
2. Incorporation of Magnetic Assembly
In WOS and WS groups, magnetic assembly was placed on the prepared Aluminum block where the keeper (MAGFIT DX 600) had been embedded with adhesive resin (Super Bond Sun Medical Co. Japan) as shown in Fig.2. In order to acquire the maximum attractive force, the magnetic assembly was placed so that its and keeker's central axes incorporate as much as possible.
![[Fig. 2]](image002.jpg)
Fig.2. Aluminum block with keeper and resin cap fixed to testing machine
Then, the resin cap was fixed to the jig of the testing machine and the aluminum block with magnetic assembly was set on the table of the universal testing machine. Thirty μgf polymer and 30μl monomer of Self-curing resin (Unifast Trad) for WS group and 15μgf polymer and 15μl monomer for WOS group were filled in each resin cap. The measurements of resin were performed with Pipettor (PipetPal. BM Equipment Co. Ltd., Japan) shown in Fig.3 and Electronic-balance (Sartotius BP310S, Germany) shown in Fig.4. The jig of the testing machine was moved down and incorporation program of magnetic assembly was started. Resin-caps were loaded by 25N for 15 minutes. After 15minutes the load was released and the incorporation program was finished.
![[Fig. 3]](image003.jpg)
Fig.3 Pipettor (PipetPal. BM Equipment Co. Ltd., Japan) for measuring resin monomer
![[]](image004.jpg)
Fig.4 Electronic-balance (Sartotius BP310S, Germany) for measuring resin polymer
3. Attractive Force Measurement
After incorporation, the magnetic assembly itself (C group) or the resin cap (WOS and WS groups) and the Aluminum block with the keeper were fixed to the Universal Testing Machine (AGS-H Shimazu Co. Ltd, Japan) and the maximum attractive force was measured 10 times for each sample with cross head speed 50 mm per minute. Raw data were stored by sampling rate 100Hz with an interface software Trapezium2.24 (Shimadzu Co., Kyoto, Japan) .
4. Statistical analysis
The statistical analysis was made by SPSS for Windows software Ver.11. Comparison was made using the one-way analysis of variance. Significance of differences between each group were evaluated by Tukey's HSD test comparisons (p < 0.05).
Results
Maximum attractive forces of WS and WOS group were converted into percentage from mean attractive force of C group as shown in Table 1. Attractive force is the largest in C group, followed by WOS, WS.
![[Table 1]](image005.gif)
Table 1 Maximum attractive force of each group (%)
Table 2 shows statistical analysis evaluated by Post hoc test. Judging from this Table, statistical difference (p < 0.05) was found between C group and WS group but not between C and WOS.
![[Table 2]](image006.gif)
Table 2 Statistical analysis evaluated by Post hoc test (p<0.05).
Conclusions
Incorporation techniques of magnetic assemblies into denture base were evaluated from the view point of attractive force. And we concluded the following;
1. Attractive force of WOS (without spill way) group was larger than that of WS (with spill way) group.
2. The retentive force reduction was statistically significant different between the control and WS.
3. WOS (without spill way) incorporation technique is more recommendable.
References.
1) Mizutani H, Rutkunas V, Maintenance of Magnetically Retained Overdentures and Troubleshooting. New Magnetic Applications in Clinical Dentistry. edited by Ai M and Shiau Y, Quintessence Publishing Co., Ltd. Tokyo, 97-105, 2004.
2) Mizutani H, Nakao K, Basic Clinical Manual of Magnetic Overdenture. Quintessence Publishing Co., Ltd. Tokyo, 38-40, 2006.
3) Tsuchida F, Suminaga Y, Takishin N, et al. Comparison of the Attractive Forces of Dental Magnetic Attachments Fabricated by Cast- and Direct-Bonding Techniques. Prosthodont Res Pract 6:14-19, 2007.