The 23rd International Conference on Magnetic Applications in Dentistry (Feb. 26 to Mar 15, 2024)
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Progress report on the implant-assisted removable partial denture units(IRPD) using a new method for attaching magnetic assemblies○Hiroaki Yamamoto ，Masayuki Hideshima¹
Tsuda Dental Clinic, Japan Institute for Advanced Dentistry ¹Dental Clinic for Sleep Disorders (Apnea andSnoring), Tokyo Medical & Dental University

Abstract
Since a small air gap in magnetic attachment can cause a significant reduction in attraction, the installationof magnetic assemblies (MAs) must be done with great care. The authors have developed a new method
using a cast frame with metal housings and a permanent cured resin base plate.
Merit: (1) Easy installation of magnets, (2) Accurate positioning of the MA, abutment and keeper. (3) Highly
accurate occlusal grading and trial fitting with detailed checks possible. (4) The retentive force of the magnet
can be checked prior to placement of the final prosthetic device. (5) No exposure of the immediate-curingresin, smooth and easy to clean. (6) The metal surrounds the keeper, making it easy to clean. (7) Less prone
to fracture.
Demerit: (1) Not applicable for mucosa-bearing dentures that require so-called settling. (2) Requires two
separate resin curing proceduresThis technique is considered to be the best solution to the conventional problem of MA fixation in IRPD
using multiple implants and the rigid type IOD.

Introduction
Magnetic attachments require careful installation of magnetic assemblies (MAs), because a small air gap cancause a significant reduction in attractive force. The authors reported a new method for IOD and IRPD usinga cast frame with the metal housings and a permanent cured resin base plate at the 25th and 29th Annual
Meetings of the Japanese Society of Magnetic Dentistry. In this report, we describe the failure events that
occurred for 9 years in IRPD cases using this method.

Summary of a new method for attaching MAs

Fig.1

Fig.2

Fig.3

Fig.4

After intraorally fastening the completed abutment, which will serve as the keeper's receptacle (Fig.1). The
keeper is fixed with Superbond™(Fig.2)．After that, the internal crown of the cornus is placed (Fig.3) anda precise impression is taken to incorporate the internal crown (Fig.4). The keeper is currently attached tothe abutment with cellophane tape to prevent it from falling off.

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The 23rd International Conference on Magnetic Applications in Dentistry (Feb. 26 to Mar 15, 2024)
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Fig.5

Fig.6

Fig.7

Fig.8

An external crown is fabricated as shown in the study model incorporating the inner crown of the cornus,
and the replica of MA is attached to the keeper (Fig.5). The undercut of the abutments with the replica areblocked out (Fig.6) and a refractory model is fabricated. After looking at the current 10-year case, we feelthat metal touch around the abutment is very useful from view point of preventing the induction of periimplantitis. The finished cast frame with metal housing (Fig.7.8). Since the thickness of the resin cannot betaken for #18, a reinforcement bar is given to the upper part of the housing (Fig.7). In addition, the bonding
surface to the resin is blasted with Rocatec ™ sand to reinforce the strength of the cast frame.

Fig.9

Fig.10

Fig.11

Fig.12The housing should have a cutout as shown in the photo (Fig.9). The cast frame is returned to the study modelwith the MA replica removed, and after waxing the external crown of the conus and cast frame (Fig.10), thepermanent foundation base is fabricated with poured-in-place polymerized resin. The photo (Fig.11) shows
the completed permanent base restored to the duplicate model of which undercuts of the alveolar bonemucosa are removed. The permanent base is placed in the oral cavity with a trial fit of the internal crown, theMAs are attached (Fig.12). and they are fixed in the metal housing by immediate-curing resin (Fig.13).

Fig.13

Fig.14

Fig.15

Fig.16

The permanent base is held in place for 10 minutes (Fig.14). And it is removed from the oral cavity. Looking
at the area around the MA from the mucosa surface, there are areas where there is insufficient resin, so add
resin with an ultra-fine brush, wipe off the excess, and re-test. After that, the occlusion is taken using thepermanent base. The model is returned to the duplicate model that will be attached to the articulator, and theartificial teeth are placed. If there are residual teeth in the esthetic area, as in this case, it is necessary to returnto the duplicate model of which undercuts of the alveolar bone mucosa is removed for placing of the artificialteeth. On the other hand, if the remaining teeth are not affected by the removal of the artificial teeth, as in the[Web Presentation] PS2-2-2

The 23rd International Conference on Magnetic Applications in Dentistry (Feb. 26 to Mar 15, 2024)
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case of the IOD and the case shown in the photo (Fig.16), it can be used laboratory silicone when the modelis attached to the articulator. The denture was then trial-fitted, and the remaining wax portion was replacedwith poured polymerized resin to complete the denture

Case Summary
1.

Patient Information (case1)

Fig.17 When placing implantFig.18 At 7 years

Fig.18 At the time of first visit Fig.19 When wearing denture

Fig.20 At 7 years

Fig.21 When wearing denture

Fig.23 At 7 years

Fig.22 At 4 years

This is the condition of this denture after 7 years. The resin and the artificial tooth that cover MA #26 havedetached (Fig.22), and the denture has to be fixed with Superbond™. In addition, the boundary line between
the primary and secondary resin in the median palatal area is becoming prominent, and the reinforcement bar[Web Presentation] PS2-2-3

The 23rd International Conference on Magnetic Applications in Dentistry (Feb. 26 to Mar 15, 2024)
http://jsmad.jp/international/23/of housing #18 is exposed (Fig.23). The condition of the remaining maxillary teeth has improved since theinitial examination (Fig.17,20).
2.

Patient Information (case2)

Fig.24 At the time of first visit

Fig.25 At 7 years

Fig.26 When wearing denture

Fig.28 When wearing denture

Fig.27 At 7 years

Fig.29 At 4 years

Fig.30 At 7 years

The 2-armed hooks of #24 and #25 have been fractured (Fig.30), but they are being used as they are. Although
tooth pulp of #15 and #24/25 have been extracted, the condition of the maxillary periodontal tissues is better
than at the initial visit (fig25,27).

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The 23rd International Conference on Magnetic Applications in Dentistry (Feb. 26 to Mar 15, 2024)
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3.

Patient Information (case3)＃24Tooth fracture site

歯牙破折

Fig.31

Fig.34

Fig.37 When wearing denture

Fig.32

Fig.35

Fig.38When placing implantFig.33

Fig.36

Fig.39 keeper of implant abutments when the magnetic attachments were applied to the proximal surfaces of the teeth with various
anr
Tooth #24, which was used as a keeper, was fractured due to an accident and was replaced with an implant.
In order to create the abutment according to the position of the metal housing and MA of the denture, animpression was taken of the denture inner surface and mucosa surface (Fig.34), the impression material wasreturned to the mucosa surface, initial drilling was done from the MA position indicated by the indicator line(Fig.35). And the implant position was determined after it was confirmed that there was sufficient depth forthe height of abutment, After the second surgery, a temporary abutment was fabricated using immediate
curing resin, an impression of the abutment was taken with a digital scanner, and a CADCAM was used tosmooth the submucosal shape indicated by the indicator line and fabricate a zirconia abutment (Fig.36).
Intraoral photographs at the time of denture placement, implant placement, and replacement of the implantsupported zirconia abutment with a keeper (Fig.37,38,39).

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The 23rd International Conference on Magnetic Applications in Dentistry (Feb. 26 to Mar 15, 2024)
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Discussion

This time, we discuss the failure event in Case 1 as a problem specific to IRPD
shortest
with magnetic attachments. The internal structure of the implant and abutment isheightshown on the right. The abutment can only be shortened up to the screw head
position, and then the thickness of the keeper and MA are added and sealed withdenture resin and an artificial tooth. The surgical solution to secure that resin
thickness is to select an implant with the shortest height of abutment and toconsider a deeper placement.
On the other hand, the prosthetic solution is to use the reinforcement bar used for #18 (Fig.7). However, thesite where the reinforcement bar is used should be blocked out of the undercut up to the height of the MA.
The use of a smaller radius magnet may also be effective.

Conclusion
Five to nine years passed after the dentures were delivered, various problems were observed. We would liketo investigate the causes of these problems and solve them in the future. However, all patients are still wearing
the dentures, and it is more certain that the dentures are useful in view point of preserving periodontal tissues
by reducing the load of occlusal forces on the remaining teeth.

References(1) Y. Maeda, Y Takayama, T.Hosoi et al : Effects of the housing for the magnetic assembly on the attractive
force of the magnetic attachment (in Japanese)., J J Mag Dent, 20(1), 44-48,2011(2) T. Miyata, Y.Nakamura, Y Tanaka et al : Influence of the heating on the attractive force of the magneticattachments (in Japanese)., J J Mag Dent, 18(1), 25-31, 2009(3) M.Yokoe, F Ito, Y Tanaka et al : Basic laboratory procedures for successful magnetic dentures (inJapanese)., J J Mag Dent, 23(1), 17-23, 2014
(4) Y.Maeda , A.Damien Walmsley : Clinical practice of implants using magnets, Quintessence,1(1), 2005.
(5) H. Yamamoto, M. Hideshima : A case report of the new procedure of fixing magnetic assemblies toan implant supported partial denture unit (in Japanese), J J Mag Dent, 29(1), 43, 2020.
(6) H. Yamamoto, M. Hideshima : A case report of the new procedure of fixing magnetic assemblies to animplant overdenture unit (in Japanese), J J Mag Dent, 29(1), 96-97, 2016.

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