Taira et al.

Asian Pac J Dent 2018; 18: 15-20

Implant-supported mandibular overdenture retained withmagnetic attachments
Yohsuke Taira, DDS, PhD (1), Michino Sakihara, DDS (2), Kohji Kamada, DDS, PhD(3), and Takashi Sawase, DDS, PhD (2)(1) Division of Cariology and Restorative Dentistry, Department of Prosthetic Dentistry, (2) Departmentof Applied Prosthodontics, Graduate School of Biomedical Sciences, Nagasaki University, and (3)Department of General Dentistry, Nagasaki University Hospital, Nagasaki, Japan
The present report consists of the long-term clinical course of an implant-supported overdenture retained withmagnetic attachments in the edentulous mandible of a patient with a smoking history. A 60-year-old man wasreferred to our hospital with a chief complaint of a mobile mandibular denture. The patient was completelyedentulous and exhibited resorbed alveolar ridges. Four osseointegrated implants were placed in the anterior
mandible between the mental foramina. Following implant surgery, magnetic attachments were placed on each
implant and a temporary denture was applied immediately. However, two of the four implants did not achieveosseointegration; these were removed and replaced after complete healing. The final superstructure was designed
to include four magnetic attachments supported by four implants for retention of the overdenture. Eight years
after placement, no adverse changes were observed in the implant bodies, superstructures, or peri-implant tissues.
This was attributed to the cessation of smoking by the patient; adequate maintenance, including plaque control;and durability of the magnetic attachments. This case also suggests that immediate loading of isolated implants
should be avoided in the presence of risk factors such as smoking.
(Asian Pac J Dent 2018; 18: 15-20.)
Key Words: implant overdenture, magnetic attachment, smoking

Introduction
In edentulous patients with a compromised residual ridge anatomy, it is occasionally difficult to achieve
comfortable function with conventional complete dentures. In such cases, implant-supported overdentures
retained with attachment systems can be used for improving oral functions, including mastication, speech, andswallowing, as well as for improving esthetics [1-3].
A variety of attachments, such as a ball, bar, locator (Nobel Biocare, Göteborg, Sweden) and magnetic
attachments, are applicable to the fabrication of an implant-supported overdenture [4,5]. The retention of an
overdenture depends on the type of attachment and the number, location, and inclination of implants [6,7]. The
cumulative survival rates for implant overdentures placed for an average of 95 months in the maxilla andmandible have been reported to be 91.9% and 98.6%, respectively [8]. Overdentures supported by three or fourimplants have been shown to exhibit higher survival rates compared with those supported by two implants [8]. In
addition, smokers reportedly exhibit higher implant failure rates than non-smokers [8,9].
The successful use of magnet-retained implant-supported overdentures has been reported [10]. In fact,
immediate loading of implants using a magnet attachment-retained overdenture has been used as a treatment
option for edentulous patients [11,12]. However, limited information regarding the long-term outcomes of oral
rehabilitation using such overdentures is available. The present report describes the 8-year follow-up course foran overdenture retained with magnetic attachments in a patient who was a smoker.

Clinical Report
A 60-year-old healthy man presented with a chief complaint of a mobile mandibular denture. The patient wascompletely edentulous and exhibited resorbed alveolar ridges (Figs. 1 and 2). He requested treatment for therestoration of oral function, including mastication, using implants. A current smoking history of approximately

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60 cigarettes a day was reported. We conducted an interview with the patient, obtained radiographs, andprepared a treatment plan.

Fig. 1 Intraoral view before implant treatment of (a) the maxilla and (b) the mandible

Fig. 2 Findings on a panoramic radiograph obtained before implant treatment

After obtaining informed consent and confirming that the patient had no parafunction and had discontinued
smoking, four implant bodies (Brånemark system MkIII Regular platform, Nobel Biocare, Göteborg, Sweden)
were placed in the interforaminal region of the mandible using single-stage implant surgery. The implants, fromright to left, were 11.5, 13.0, 13.0, and 13.0 mm, respectively, in length. A magnetic-attachment keeper (MagfitIP-B Flat type, Aichi Steel Co., Tokai, Japan) was connected to each implant body, and four magnets (diameter,4.9 mm, and thickness, 1.3 mm; Magfit IP-B Flat type) were bonded to a temporary denture. The surfaces ofboth the magnets and the attachment keepers were coated with titanium nitride (TiN). A phosphate primer (AlloyPrimer, Kuraray Noritake Dental Inc., Tokyo, Japan) and a self-curing adhesive (Super-Bond C&B, Sun MedicalCo., Ltd., Moriyama, Japan) were subsequently applied to the magnet surface, and then a self-curing resin(Unifast III, GC Corp., Tokyo, Japan) was used for luting between the magnets and the denture base resin.
However, the two implants on the right side did not achieve osseointegration. Therefore, 5 months after
implant placement, the two implant bodies were removed to allow bone healing. Four months later, two new
implant bodies (Brånemark system MkIII Regular platform) measuring 13 mm in length were placed using
two-stage surgery. After 6 months, an overdenture was fabricated using four magnetic attachments, resin
composite artificial teeth (Endura, Shofu Inc., Kyoto, Japan), and a cobalt-chromium alloy (Biosil, DeguDentGmbH, Hanau-Wolfgang, Germany). Thus, the final superstructure comprised an overdenture supported by four16

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magnetic attachments connected to four implants (Fig. 3). A conventional full denture was also fabricated for themaxilla to achieve full-balanced occlusion. The patient was recalled every 3-6 months for follow-up
examinations.

Fig. 3Intraoral view at completion of prosthodontic treatment(a) Four magnetic attachments supported by four implants(b) The overdenture on the mandible and the conventional
complete denture on the maxilla(c) Four magnets bonded to the mandibular overdenture

Fig. 4(a) Intraoral view at 8 years after completion ofprosthodontic treatment(b) The mandibular overdenture and the maxillary
conventional complete denture that were used for 8years(c) The mandibular overdenture with magnetic
attachments functioned for 8 years17

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Fig. 5 Findings on a panoramic radiograph obtained 3 years after completion of prosthodontic treatment

Fig. 6 Findings on a panoramic radiograph obtained 8 years after completion of prosthodontic treatment

Over a period of 8 years after denture delivery, there were no episodes of severe soft tissue infection,persistent pain, paresthesia, or discomfort. In addition, relining or replacement of the magnetic attachments was
not required. Although the TiN coating showed abrasion and the underlying stainless steel was partly exposed(Fig. 4), the retention strength of the magnets remained largely unchanged. Radiographic assessments did notshow peri-implant pathologies or radiolucency around the implant bodies, and no significant loss of crestal bone
was observed between 3 and 8 years after completion of the prosthodontic treatment (Figs. 5 and 6).

Discussion
We described the long-term findings for an implant-supported overdenture retained using magnetic attachments
in a 60-year-old edentulous man. The failure of two implant bodies that were initially placed may be associatedwith their initial fixation, in addition to his smoking history [8,9,13]. Following the initial single-stage surgery,undesirable micromovement of the right-side implant bodies may have occurred during mastication, given thatthe patient mainly chewed on the right side using temporary denture. We therefore chose a two-stage surgery toplace the two replacement implants in order to decrease the likelihood of implant movement and peri-implant
infection. The findings from this case suggest that immediate loading of isolated implants should not beattempted in the presence of risk factors, such as smoking.
Compared with other attachment types, such as a bar, ball, and locator, the magnets used in our case were18

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relatively thin (1.3 mm). Although such thin magnetic attachments confer an advantage, in that they can beapplied in many cases in which the interocclusal distance is too short for thicker attachment types, the denturebase around the magnetic attachments should be protected against repeated mechanical stress. Therefore, in thiscase a cast metal framework was used in order to prevent fracture of the denture base resin.
In contrast to a traditional magnet that grips the root element with a retentive force of approximately 2.9 N[14], the manufacturer stressed that the cup-yoke type Nd-Fe-B magnets used for our case generate a retentive
force of 7.4 N each. Although the retentive force may be lower than that generated by ball, bar, or locater
attachments [6,15], magnetic attachments alleviate detrimental lateral stresses on the implant because of theirlow horizontal attractive forces [16].
As mentioned above, both the magnets and keepers had a TiN coating. The TiN coating on stainless steel
results in high resistance to corrosion [17], and improves the wear resistance of the stainless steel surface [18].
Indeed, this benefit is a key reason to include the TiN coating on the magnetic attachments. Based on theprotocol from our previous study [19], a phosphate primer and a self-curing luting agent were used for bonding
between the denture base resin and the magnetic component. The absence of debonding failure indicates a highbonding durability of the adhesive system used.
The overdenture was ultimately both comfortable and functional over 8 years. The present case validates theutility of using an implant-supported mandibular overdenture retained with four magnetic attachments foredentulous patients. The present report consists of the long-term follow-up results in a case of animplant-supported mandibular overdenture retained using magnetic attachments in an elderly man with a historyof smoking. The findings from this case suggest that immediate loading of isolated implants should not be
attempted in the presence of risk factors such as smoking, but that with procedural care and the cessation ofsmoking, success is probable.
Acknowledgements
We have received approval from institutional review board of Nagasaki University Hospital, approval No. 17082159.

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Correspondence to:
Dr. Yohsuke Taira
Division of Cariology and Restorative Dentistry, Department of Prosthetic Dentistry,
Graduate School of Biomedical Sciences, Nagasaki University,
1-7-1 Sakamoto, Nagasaki 852-8588, Japan
Fax: +81-95-819-7689 E-mail: yohsuke@nagasaki-u.ac.jp
Copyright ©2018 by the Asian Pacific Journal of Dentistry.

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Accepted June 7, 2018
Online ISSN 2185-3487, Print ISSN 2185-3479