I. Introduction

Metal plate dentures using magnetic attachments are difficult to remake the root cap in accordance with the denture when the root cap and keeper separate after preparing the denture. However, because of the recent widespread use of keeper trays, it has become possible to fix the keeper on the root cap in accordance with the magnetic assembly.I would like to report two cases.
In one, I adjusted the keeper for the magnetic assembly within the oral cavity to remake the root cap. In the other, good results were achieved by using the keeper tray for the existing inner cap to improve it to Magnotelescope against the decrease of retentive force of Konuskronen Teleskop.

II. Case 1

The patient was a ninety-year-old woman, who came to our hospital with the chief complaint of an ill-fitting denture. Magnetic attachments were prepared for Nos. 12, 13 and 22. A new metal plate overdenture was made and used as the abutment piece. She has been satisfied with the treatment to date. However, she returned once because the root cap and keeper of No. 13 separated.

Fig.1 shows the separated root cap. No abnormal conditions were observed in the abutment tooth, the residual tooth or the periodontal tissues (except No. 13). The denture fit well. The patient was elderly and did not want to have the denture remade. Thus, I tried to salvage the No. 13 root cap with keeper. The separated root cap was ill-fitting, and softened dentin was observed. Also there was not enough root canal filling. Therefore, I tried to remove the softened dentin, and then performed root canal treatment. Next, I recast a root canal filling. Fig. 2 shows a dental X-ray at the time of the initial visit and after refilling of root canal.
As shown in Fig. 3, I prepared the root surface based on general procedure. I made a temporary crown, which does not affect fitting of the denture for the abutment tooth until the placement of the new root cap. They were temporarily cemented. (Fig. 4)

To take an impression of the abutment tooth, I made an individual tray for the root surface impression using self-curing acrylic resin. SURFLEX F, a polysulfide rubber impression material made by GC (Fig. 5), was used.
To determine the suction surface of the magnet and the formation of the root cap attached to the denture, I made a secondary model of the root cap using EXABITE, a vinyl polysiloxane bite registration cream made by GC (Fig. 6). Taper is fitting the form of denture in accordance with the magnet suction surface, and it is in the ideal form of root cap (Fig. 7).

I made a gingival model and set a secondary model of occlusal sampling material at the abutment part of the root cap, and then welded putty-type EXAFINE, a hydrophilic vinyl polysiloxane impression material made by GC, with pressure from the upper side and gained two pieces of core (Fig. 8, 9). In this case, the core was printed with form of suction surface of magnet and root cap.
As shown in Fig.10, I fixed a keeper tray with wax in accordance with the suction surface of the magnet. I poured wax in the root, and after softening, I welded the core with pressure to position it in the initial place (Fig. 11, 12).

I cut the core in the buccolingual and mesiodistal directions respectively and performed wax up referring to taper. As shown in the slide, the forms of suction surface and root cap are almost matching (Fig. 13). Casting and polishing were done following general procedure to show the place of trial in the oval cavity (Fig. 14).

After confirming placement of the denture, I attached the root cap to the abutment tooth using FUJI LUTE, a glass ionomer group resin cement made by GC. I used direct bonding method with keeper tray to attach the keeper. I performed sandblast processing for the keeper and inside the keeper tray with alumina in 50 micro meters of particle size, then applied METAL PRIMER $B-6(B made by GC and dried it. After that, I attached the keeper to the root cap from above using BISTITE II, a dual-cure type adhesive resin cement made by Tokuyama Dental, and then removed the excess cement with pledget. Next, I returned the denture to the former position, and waited for the initial hardening of the cement. After that, I performed crepuscular-ray radiation (Fig. 15). Since the keeper was induced by the magnet attached, it floated higher than the surface of the root cap. However, as shown in Fig. 16, the form of the root cap and the horizontal position of the magnet suction surface were fine, and the denture was stabilized in the former position. One year has passed since the root cap was installed. She has had no problems with using the denture to date.

III. Case 2

The patient was a fifty-one-year-old woman. I made a metal plate denture with Konuskronen Teleskop for abutment teeth Nos. 44 and No. 45 to replace the losses of Nos. 46 and No. 47 one year earlier.
After several adjustments, the Konuskronen Teleskop could not produce adequate retentivity. No. 45 was the devitalized tooth, but I thought it too dangerous to remove the inner cap and the post to make a root cap with keeper. Therefore, I cut only the upper part of the konus inner cap to set the keeper, and tried to improve it to Magnotelescope by setting a magnet assembly to the outer cap within the denture.
As shown in the Fig.17, I formed the konus inner crown by adjusting the width for receiving the keeper and the height for receiving the keeper and the magnet. I used GIGAUS D600 made by GC to make the length of the tooth crown short for magnet (Fig. 18).

Following standard procedure, I performed wax-up with keeper tray after making a working model. As shown in the chart at the bottom left of the slide, I made the taper bigger than the conus angle, and lowered the position of the keeper tray to be parallel with the upper surface of No. 44.
After casting and polishing, I attached the keeper on the model with BISTITE II, a dual-cure adhesive resin cement made by Tokuyama Dental, using the direct bonding method (Fig. 19).

I would like to show the Magnotelescope completed after attached to the abutment tooth with the same cement (Fig. 20). After the trial test of the denture, I attached a magnet to the outer crown using adhesive cement C&B SUPER BOND C&B made by SUN MEDICAL. While absorbing the magnet to the keeper, I confirmed the required amount of cement by filling the outer crown with conformity test material, FIT CHECKER, made by GC.
Taking the amount as an indication, I set the denture with super bond that was applied by brush-on technique, and removed the residual cement when the cement was hardened (Fig. 21). I applied Konuskronen Teleskop for No. 44 and Magnotelescope for No. 45, so different systems were used. However, they had good retentivity again, and the patient is still using the metal plate denture.

IV. Consideration

Casting method of the root cap with keeper has been generally used from origin of development for the magnetic attachment. However, the problem of casting method came to be indicated now, and direct bonding method that used the keeper tray was designed as a new fixed method of the keeper.
This time, I reported two cases that used keeper trays for repair of the retainer for metal plate dentures with magnets. As a result, it became possible that repaired without reproducing existing metal plate dentures.
Keeper trays have many other uses, and they applicable for cases that used to be difficult to treat. these data will help to further facilitate the use of magnet attachment systems.

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Toshiki Fujimoto
E-Mail:fujimoto-t@dent.nihon-u.ac.jp

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