Application of cast iron-platinum keeper to collapsed denture for a patient with constricted oral opening: A case report

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Chikahiro OHKUBO, DMD, PhD¹, Yoshihiro MAEDA, SDT²,
Ikuya WATANABE, DDS, PhD³, Naoki BABA, DDS, PhD⁴,
Yasuhiro TANAKA, BS, MS⁵, Toshio HOSOI, DDS, PhD⁶

¹Instructor, Department of Removable Prosthodontics, Tsurumi University School of Dental Medicine
²Instructor, The Dental Technician Training Institute, Tsurumi University School of Dental Medicine
³Assistant Professor, Department of Biomaterials Science, Baylor College of Dentistry, Texas A&M University System Health Science Center
⁴Visiting Scientist, Department of Biomaterials Science, Baylor College of Dentistry, Texas A&M University System Health Science Center
⁵Instructor, Department of Biomaterials Science, Nagasaki University Faculty of Dentistry
⁶Dean, Tsurumi University School of Dental Medicine

Chikahiro Ohkubo
Department of Removable Prosthodontics
Tsurumi University School of Dental Medicine
2-1-3 Tsurumi Tsurumi-ku
Yokohama 230-8501, Japan
PH: +81-45-581-1001
Fax: +81-45-573-9599
e-mail: Okubo-c@tsurumi-u.ac.jp

Corresponding author

Introduction

Dental practitioners must occasionally treat patients with constricted oral openings that are caused by temporomandibular joint (TMJ) dysfunction syndrome, rheumatoid arthritis, or damage to the masticatory muscles by craniotomy.¹ As the size of the oral opening decreases, the difficulty of the required treatment increases. In cases when the opening is less than 20 mm, most dental instruments cannot be inserted into the mouth.² Even if the patient can open his/her mouth to 30 mm, it is very difficult to insert or remove a large conventional removable partial denture (RPD) or complete denture (CD). There have been several reports^3-11 regarding prosthodontic treatment for medically compromised patients, including patients with limited intraoral access (microstomia, resected cancer patients, etc.). Sectional dentures and/or collapsed dentures have usually been prescribed for these patients.^3,5,8,11 A hinge is used to connect the segments of such a collapsed denture system.^3,11 Other methods of assembling the two segments of sectional dentures are clasps,^3-5 cast locking recesses,⁵ swing-lock attachments,¹¹ pin attachments,⁸ and a telescope system^.11
Recently an attachment system using magnets has been developed, and several types are commercially available for retention of overdentures or implant-retained prostheses.^12-14 Also it has been found that Fe-Pt alloys have magnetic properties, and the possibility of applying them to dentistry has been investigated. Watanabe et al.¹³ reported that cast Fe-Pt keeps yield great attractive force to dental Fe₁₄Nd₂B magnets (Fig. 1). Additionally, Fe-Pt alloys exhibit excellent corrosion resistance because they contain a large amount of platinum (approximately 70 wt% Pt).¹⁴ The great advantage of this system is that they can be cast using a dental casting machine and any size or shape of keeper can be fabricated. Thin (less than 1 mm) or specially shaped keepers are needed in each particular case.
This clinical report describes the application of a Fe-Pt keeper to a collapsed RPD for a patient with an extremely constricted oral opening.

CLINICAL REPORT

The patient was a 69-year-old partially edentulous woman with missing posterior teeth, namely, two right molars and two premolars, two left molars, and the first premolar, of the mandibular (eight teeth, #17, #21 to #27 remained in the mandibular arch) (Figs. 2a-c). Her oral opening had been gradually constricted by rheumatoid arthritis for approximately 20 years. The oral opening became even more constricted after amputation of her temporal muscle by craniotomy for a subarachnoid hemorrhage in October 1999. The size of the oral opening was less than 15 mm at her first visit to the division of Maxillo-facial Oral Surgery of our dental school hospital in December 1999. In this division, the patient was trained for one year at opening her mouth using an oral expansion device (Figs. 3a, 3b). When she visited the division of Prosthodontics, she was able to open her mouth approximately 25 mm. She had an extremely small RPD that was unserviceable when the denture flanges and clasps were removed.

Impression and wax denture fabrication

Preliminary impressions for both dental arches were made using a sectional stock tray (Figs. 4a-d). This tray was developed from a full arch tray sectioned into right and left halves and could be reconnected using a slide-lock system on the tray handle.¹⁷ A border molding and definitive impression was also made using a sectional custom tray with slide-lock joint (Figs. 5 a-c).² The upper and lower jaw relationship was registered using a sectional occlusion rim with a dowel-pinhole joint (Fig. 6). The master casts were mounted on an average valued articulator (Gysi Simplex OU-II, Onuki-Iki, Tokyo, Japan), and the artificial teeth (Duradent, GC Corp., Japan) were conventionally arranged. The wax denture could be collapsed on the right denture base with a clip hinge (Binder clip 36, Kokuyo, Osaka, Japan) as shown in Fig. 7. The feasibility of placement and removal of the final prosthesis was carefully confirmed using this wax denture.

Denture designs

The right distal extension base of the denture was composed of upper and lower segments, which were collapsed using a hinge (Swing-lock attachment, Idea Development Co., Dallas, TX) at the edge of the lingual flange, allowing for insertion into the mouth (Fig. 8). The metal frameworks of both segments were separately cast with Co-Cr-Ti alloy (Crutanium, Krup Inc., Essen, Germany). The clearance was too small (approximately 4 mm in the thinnest region) between the maxillary natural teeth and mandibular residual ridge to place commercial attachments connecting the two segments. Also the shape of the keeper fitted to the framework and residual ridge was complicated. Therefore, a cast Fe-Pt keeper (Fe-66.3 wt% Pt) and the thinnest commercial magnets available (Hicorex-slim, Hitachi Metals, Japan) were used for this case.

Denture fabrication

The wax pattern for the lower segment including a plastic pattern of the convex hinge was designed to be assembled with the keeper and was fabricated on the refractory cast. The pattern was invested (Crutavest, Krup Inc.,) and cast with Co-Cr-Ti alloy in a centrifugal casting machine (Grove Cast, Krup, Inc.). After it was desprued and polished, the lower framework was replaced on the master cast, and the Fe-Pt keeper pattern was then made. The keeper pattern was invested in a mold with a magnesia-based investment (Selevest CB, Selec Co., Osaka, Japan) and cast from a custom-made Fe-Pt ingot using a high-frequency centrifugal casting machine (Jelenko Eagle, Jelenko, NY). After casting, the Fe-Pt keeper underwent heat treatments in accordance with procedures reported by Watanabe et al.^13,14 The cast Fe-Pt keeper was then welded to the Co-Cr-Ti lower framework using a laser (neolaser L ALC 30, Selec Co.). The pattern for the upper segments of the framework with a concave hinge was fabricated and cast with the same alloy in the same manner as for the lower framework. After the upper framework was polished, the concavo-convex hinge was laser-welded to join the two frameworks (Figs. 9 a-f). Denture-base PMMA resin (Palapress Vario, Heraeus Kulzer Inc, Irvine, Calif.) was polymerized for the upper and lower segments according to the manufacturer's instructions. Three commercial magnets (Hicorex-slim) were embedded under the metal teeth in the upper segment with auto-polymerized resin (Uni-fast 2, GC Corp. ). Figure 10 show the final RPD, which could be collapsed using a lingual flange hinge and magnetic attachments.

Delivery of dentures

The denture was inserted in the mouth by collapsing the right denture base to the lingual side. After being inserted into the mouth, the upper segment was rotated and connected to the lower segment. The denture was fitted after it was restored to its original form in the mouth (Figs. 11a, 11b). Figure 12 shows an occlusal view of the denture after placement.
After an observation period of 1 year and 2 months, the collapsed denture, which was easily inserted into the mouth, continues to deliver adequate function with no problem, and the patient is very satisfied.

SUMMARY

This report described a removable collapsed denture connected by hinges and a magnetic retention system consisting of a cast iron-platinum keeper and commercial magnet (Hicorex-slim) for a patient with a severely constricted oral opening. With the use of a cast keeper and flange hinges, the collapsible RPD was successfully and easily installed, and the patient expressed satisfaction regarding her masticatory function.

ACKNOWLEDGMENTS

Editorial assistance by Mrs. Jeanne Santa Cruz is greatly appreciated.

REFERENCES

1) Fricton JR, Kroening RJ, Hathaway KM. TMJ and craniofacial pain: Diagnosis and management. Ishiyaku EuroAmerica, Inc. S. Louis, 1-11, 1988.
2) Ohkubo C, Maeda Y, Sugiyama K, Suzuki Y, Ishikawa Y, Hosoi T. Impression techniques for patients with microstomia or constricted oral opening. Tsurumi Univ Dent J 28: 145-151, 2002.
3) Conroy B, Reitzik M. Prosthetic restoration in microstomia. J. Prosthet. Dent. 26: 324｡ﾁ327, 1971.
4) Hagiwara H, Nakamura H, Matsumura M, Seto K, Abe K, Nomura T. The mouth circumference of normal adults and patients of microstomia. J Jpn Maxillofacial Prosthet 5: 37-43, 1982.
5) Winkler S, Wongthai P, Wazney JT. An improved split-denture technique. J. Prosthet. Dent. 51: 276-279, 1984.
6) Luebke RJ. Sectional impression tray for patients with constricted oral opening. J. Prosthet. Dent. 52: 135｡ﾁ137, 1984.
7) Whitsitt JA, Battle LW. Technique for making flexible impression trays for the microstomic patient. J. Prosthet. Dent. 52: 608｡ﾁ609, 1984.
8) McCord JF, Moody GH, Blinkhorn AS. An overview of dental treatment of patients with microstomia. Quintessence Int. 21: 903｡ﾁ906, 1990.
9) Mirfazaelian A. Use of orthodontic expansion screw in fabricating section custom trays. J. Prosthet. Dent. 83: 474｡ﾁ475, 2000.
10) Baker SP, Brandt RL, Boyajian G. Impression procedure for patients with severely limited mouth opening. J. Prosthet. Dent. 84:241｡ﾁ244, 2000.
11) Suzuki Y, Abe M, Hosoi T et al. Sectional collapsed denture for a partially edentulous patient with microstomia: A clinical report. J Prosthet. Dent. 84: 256｡ﾁ259, 2000.
12) Kurtz KS, Ohkubo C, Watanabe I Shimizu H, Cai Z, Okabe T. Evaluation of magnet system retaining a midfacial maxillofacial prosthesis. J Dent Res 79: 178(Abstr. 277), 2000.
13) Watanabe I, Tanaka Y, Fukunaga H, Hisatsune K, Atsuta M. Attractive force of castable iron-platinum magnetic alloys. Dent Mater 17:197-200, 2001.
14) Watanabe I, Hai K, Tanaka Y, Hisatsune K, Atsuta M. In vitro corrosion behabior of cast iron-platinum magnetic alloys. Dent Mater 17:54-61, 2001.
15) Mastumoto Y, Abe M, Hosoi T, Mizuno Y. Removable prosthesis using hinge in distal-end for path of insertion. J. Jpn. Soc. Magnet. Applicat. Dent. 9:17-22, 2000.
16) Mastumura H, Kawasaki K. Magnetically connected removable sectional denture for a maxillary defect with severe undercut: A clinical report. J. Prosthet. Dent. 84:22-6, 2000.
17) Ohkubo C, Ohkubo C, Hosoi T. Development of sectional stock tray system. The Nippon Dental Review. 61: 103-105, 2001.

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