Adhesive Force of Magnetic Assembly to Denture Base with Self-Curing Resin

H. Mizutani, S. Ishikawa, T. Ando, H. Sasaki, A. Nishiyama, M. Hideshima and Y. Igarashi

Section of Removable Prosthodontics
Graduate School, Tokyo Medical and Dental University Tokyo, Japan

Introduction

As the magnetic attachment (MA) is one of the most useful retainers to stabilize the natural root- and/or implant- supported overdenture, it is essential to fix magnetic assemblies into denture base and keepers into abutments firmly. Newly developed MAs are stronger in force and smaller in size compared with the old ones ¹⁾: that is to say new MAs are easily to be detached from the denture base or abutments. Therefore, it is very important to evaluate the adhesive force of magnetic assembly to denture base whether or not the assembly has a retentive groove, preliminary treatment of sand blast or adhesive resin coating.

Objective

Aim of this study is to examine the adhesive force of magnetic assembly to denture base.

Materials and Methods

1. Samples

Totally 40 samples, SUS four four seven J1 (SUS447J1) made, simulated magnetic attachment assemblies were used in this study. They were divided into five groups according to their form of retentive groove. Group A, which is a control group, has no groove; that is 0 degree and 0 mm deep retentive groove. Then Group B has a 60 degree and 0.15 mm deep groove, followed by Group C, D, E. Their groove sizes are shown in Fig.1.

After having been cleaned up by alcohol cotton rolls, these samples were set into an acrylic cylindrical tube which is filled with self curing resin, so that they were equally covered with this self-curing having a thickness of 0.8mms. As shown in Fig.2, a rod for testing machine was also set into this cylindrical tube immediately after self-curing resin was poured.

2. Measurement of adhesive force

After all resin capped samples were immersed into 37centigrade water for 24hours, they were set on a table of universal testing machine AGS-H (Shimazu Co. Ltd, Japan),shown in Fig.3, adhesive force when resin cap was detached from the SUS model was measured.

After measurements, all samples were cleaned up again and were covered with self curing resin with the same way as before. They were immersed into 37 centigrade water for 35 days and then maximum adhesive force was measured followed by the same method as mentioned before.

3. 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 had been evaluated by Tukey's HSD (honestly significant difference) test comparisons (p < 0.05).

Results

Fig.4 shows the adhesive force between resin and metal models after 24hours immersion. The maximum adhesive force was observed in Group C and the minimum was in Group A. Compared with Group A (no groove), the differences were all significant in every group. These significant differences clarify that the existence of retentive groove is very important to keep the magnetic assembly into the denture base.

On the other hand, Fig.5 shows the adhesive force after 35days immersion. The maximum adhesive force was in Group C and the minimum was in Group A, and the differences between Group A and other groups were all significant. Same results have been observed in 24hours immersion.

Fig.6 shows adhesive force difference between 24hours and 35days. A definite tendency has not been observed. In Group A, B and C, adhesive force after 24hours immersion was larger than that after 35days immersion, but In Group D and E, 24hours was smaller than 35days. However, the changes between them were not so large and there were no significant differences in all groups.

Discussions

Our in Vitro study of adhesive force of magnetic assembly to denture base with self-curing resin was reported. It was found that the existence of retentive groove is very important to keep the magnetic assembly into the denture base. So, the question is whether or not magnetic attractive force gets decreased if this groove is attached to the magnetic assembly.

Therefore we have evaluated attractive force of “with retentive groove” and “without retentive groove” using with Finite Element Method²⁾. The results we have got were that: the attractive force of the magnetic assembly with retentive groove exactly got down, but the down ratio was within 5%. Therefore we have concluded that the retentive groove should be attached.

Regarding the ISO standardization, it is very difficult to standardize the adhesive force between magnet and denture, because adhesion very much depends on humidity and cleanliness and our daily clinics are always exposed to those stuffs³⁾⁴⁾. However, it might be concluded that at least more than 50 N forces are required in Vitro experiment taking into consideration of magnetic attractive force.

Fig.7 shows one of the Japanese magnetic attachments named Hicorex. A is the first-generational attachment and its attractive force is about 4 N. While B is the third-generational referred to our data. B attachment has retentive groove and its attractive force is about 7.2N.

Conclusions

1. Retentive groove or wing on magnetic assembly should be needed to retain magnetic assembly into denture base.

2. At least 50N experimental adhesive force is required to retain magnetic assembly into denture base with consideration of magnetic attractive force.

References

1. Nakamura K, Mizutani H, Ai M, Ishikawa S, A Newly Developed Magnetic Attachment “Hicorex Slim”. Its characteristics and clinical cases. J J Mag Dent 7(1):84-84, 1998.

2. Ishikawa S, Mizutani H, Ai M, Takahashi T, Yoshino T, Nakamura K, Influences of the Side Slot Form of Magnetic Attachments on the Combining Force to Resin and the Attractive Force. J J Mag Dent 3(1):23-29, 1994.

3. 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.

4. Mizutani H, Destine D, Rutkunas V, et al. Comparison of Retentive Force of Different Overdenture Stud Attachments in Various dislodgements. In Vitro Study Part 2 Changes after Fatigue Test J J Mag Dent 15(2):5-9, 2006.

Discussion Board