Report of a hands-on seminar on magnetic attachment skills
D. Kurihara, Y. Suzuki, J. Takeyama, H. Shimpo, C. Ohkubo
Department of Removable Prosthodontics, Tsurumi University School of Dental Medicine

Introduction
Unlike conventional mechanical force-application mechanisms, magnetic attachments use magnetic
force and have many advantages, such as their small size, simple shape, and their use of a less harmful
lateral force. For clinical success with magnetic attachments, accurate positioning of the magnetic
assembly on the keeper and its connection are very important, as inadequate attachment causes a gap
between the contact surface and a significant reduction in retentive force. In order to acquire theneeded skills, a hands-on seminar titled “Learning Magnetic Attachments—Laboratory and Clinical
Procedures” was held at the 131st Annual Meeting of the Japanese Society of Prosthetic Dentistry incooperation with the Japan Society of Magnetic Applications in Dentistry. In this paper, we will reporton this seminar.

Objective
In the seminar, a 40-minute lecture on the characteristics of magnetic attachments and how toproceed with treatment, their application, design, treatment procedures, and possible problems wasgiven. After the lecture, 50 minutes was provided to practice using a simulation model and overdenture
and to train in the clinical procedure of fixing the magnetic assembly to the denture base using
autopolymerized resin.
Lecture1. Explanation of points to note when placing magnetic attachments(1) Causes of significant decrease in retention
Failures in the attachment procedures include misalignment of the magnetic assembly, namely, airgaps due to the intrusion of the resin onto the keeper surface or polymerization shrinkage.
As for the misalignment of the magnetic assembly and the keeper, it has been reported that theattractive force decreased by about 1/3 when an air gap of 0.1 mm was vertically created and by about
2/3 when the magnetic assembly was horizontally displaced by 0.5 mm (Figs. 1, 2)1) .

Fig. 1 Effect of vertical gaps
between the magnetic assembly
and the keeper on attraction force1)

Fig. 2 Effect of horizontal deisplacementof the magnetic assembly on the keeper
on the attractive force1)(2) Polymerization shrinkage of autopolymerized resins(i) As the amount of autopolymerized resin used when fixing the magnetic assembly was increased,shrinkage of the autopolymerized resins also increased, and the air gap grew.

(ii) The brush-on technique showed lower polymerization shrinkage and better dimensional accuracy
as compared to the mixing technique (Fig. 3)2).
(iii) The brush-on technique can control the amount of resin on the inner surface of the denture baseby the placement of a spillway. The results include the prevention of misfitting dentures and denturesthat are difficult to remove due to resin that has penetrated into the undercut around the keeper coping(Fig. 4).
(iv) Holding the denture until the resin is polymerized and the timing of denture removal are also
important.

Fig. 3 Polymerization shrinkage of
autopolymerized resin using thebrush-on and mixing techniques2)

Fig. 4 Spillway provided to thedenture base(3) Placement of the magnetic assmbly
The magnetic assmbly should be placed after the denture is settled, considering the minimum
shrinkage of the autopolymerized resin.
2. Movie explaining the clinical procedure of magnetic attachments (Fig. 5)

Fig. 5 Clinical procedure for applying a magnetic attachment

Practice
Placement of magnetic attachments (magnetic assembly) (Figs. 6-9)

Fig. 6 Jaw model of a partially edentulous mandible with left and right remaining canines,
overdenture, and magnetic attachments (Physio Magnet, Kedika Corporation) used in theseminar.

Fig. 7 A space for magnetic attachments was created on the denture. The denture was placedon the jaw model, and a spillway was provided.

Fig. 8 After applying vaseline to the keeper coping and the residual ridge, the magnetic
assembly was placed on the keeper. Using the brush-on technique, the magnetic assembly
was fixed with autopolymerized resin using light pressure.

Fig. 9 After the resin was polymerized, thedenture was removed and polished.

Results
The seminar was held twice, with a total of 40 participants (23 males and 17 females) divided into twogroups of 20. There were 33 university and 7 non-university participants. Difficulties such as thedetachment of the magnetic assembly and lack of retentive force were observed during the fixingprocedures.
The results of the post-seminar questionnaire are shown in Figs. 10-12.

Fig. 11 Work place of participants

Fig. 10 Work years of participants

Fig. 12 Evaluation of the seminar

Discussion
Not using metal primers and the premature removal of the denture from the simulation model during
the polymerization of the resin were considered to be reasons for the detachment. Insufficient retentive
force may be due to misalignment of the magnetic assembly, namely, an air gap caused by the intrusionof the resin onto the keeper surface.

Conclusion
From a post-seminar questionnaire, most of participants learned well the clinical and laboratory
procedures for magnetic attachments and were satisfied with the seminar.

References
1) Ai M, Shiau YY. New magnetic applications in clinical dentistry. Quintessence Publishing Company,Tokyo, 2004, 28–50.
2) Hanatani S, Shibuya N, Muraishi E, et al. Dimensional accuracy of autopolymerized resin applied
using the brush-on technique. Int Chin J Dent. 2009; 9 (1): 9–13.

Acknowledgments
We would like to thank the Morita Corporation, the Kedika Corporation, and the Kikutani
Corporation for their support of this seminar, as well as the teacing staff in our department for theircooperation in organizing the seminar.