Abstract

Dental implant treatment is an indispensable portion of oral rehabilitation in patients who are to undergo reconstructive surgery following the removal of an oral cancerous lesion. However, ideal dental implant treatment cannot be achieved easily in patients who have undergone mandibular reconstruction with a free vascularized flap, usually because of the limited length, height, and width of the bone graft. Shorter implants ( <10 mm in length) therefore are occasionally used in vascularized fibula graft sites. In such cases, however, shorter implants tend to be overloaded, thereby endangering its longevity. In this article, we discuss how a magnetic abutment system was introduced for such a patient. This was designed to discourage overloading of the mandatory short implants. The outcome was successful without overloading 1.5 years after the placing of the mandibular overdenture.

USE OF MAGNETIC ABUTMENTS FOR SHORTENDOSSEOUS IMPLANTS FOLLOWING A FIBULABONE GRAFT IN AN ORAL CANCER PATIENT: ACASE REPORTCLINICALJunnosuke Ishii, DDS, PhDTatsuya Yoshida, DDSSatoshi Yokoo, DDS, PhDTakahide Komori, DDS, PhDKEY WORDSMagnetic abutmentDental implantsVascularized fibula graftJunnosuke Ishii, DDS, PhD, TatsuyaYoshida, DDS, Satoshi Yokoo, DDS, PhD,and Takahide Komori, DDS, PhD are fromthe Department of Oral and MaxillofacialSurgery, Kobe University Graduate School ofMedicine, Kobe, Japan. Address correspondenceto Dr Junnosuke Ishii, Department of Oral andMaxillofacial Surgery, Kobe UniversityGraduate School of Medicine, 7-5-2, Kusunokicho,Chuo-ku, Kobe 650-0017, Japan(e-mail: ishiijun@med.kobe-u.ac.jp).Dental implant treatment is an indispensable portion of oral rehabilitation inpatients who are to undergo reconstructive surgery following the removal of anoral cancerous lesion. However, ideal dental implant treatment cannot beachieved easily in patients who have undergone mandibular reconstruction witha free vascularized flap, usually because of the limited length, height, and widthof the bone graft. Shorter implants (,10 mm in length) therefore are occasionallyused in vascularized fibula graft sites. In such cases, however, shorter implantstend to be overloaded, thereby endangering its longevity. In this article, wediscuss how a magnetic abutment system was introduced for such a patient. Thiswas designed to discourage overloading of the mandatory short implants. Theoutcome was successful without overloading 1.5 years after the placing of themandibular overdenture.by endangering their longevity. In addition,a decreased number of implantscan be placed, which will necessitatechanging the prosthetic design to anoverdenture. For those patients whosuffer from an encumbered oral environment,the bar attachments used inoverdentures often induce tongue discomfortand speech difficulties. To corhaTve been used for mandibular recon-, e v o m o f r e suff n te ula d 3 dius,larizedaniliac,1fibscapula,4 graf2 ratshostd tobone. Shorrt implantsrloading(,10thmm)erees nsi e dim limited e th f o ca scu- V . v r i y tl greacancer recempntloyedhasabeen thuseese patients may be restrionctedof tbefuired req lants p i e th f o e l d an m re wing l fIhoNTRODUCTIONelofree vascularizedoval of oflapralachievngthed in such pm atients. The numbehorrstruction after mandibular resection asa treatment for progressive cancer ofthe tongue and the floor of the mouth,as well as for aggressive cases of gingivalcarcinoma. Although dental implanttreatment is indispensable to oralrehabilitation in such patients, idealimplant treatment cannot be easilyJournal of Oral Implantology 289MAGNETIC ABUTMENTS FOR SHORT ENDOSSEOUS IMPLANTSFIGURES 1-3. FIGURE 1. Panoramic radiograph immediately postoperative showing reconstruction with the vascularized fibula graft extendingfrom the right to the left mandibular angle region. FIGURE 2. Intraoperative view of placement of short implants. FIGURE 3.Illustration of the magnetic abutment system.rect these problems, magnetic abutmentswere used for dental implantrestoration in a patient who presentedwith a long-span, vascularized fibulagraft.290 Vol. XXIX/No. Six/2003CASE REPORTA 45-year-old Japanese woman was referredto the Department of Oral andMaxillofacial Surgery at Kobe Universityin February 1999 complaining of anulcer of the right mandible. A panoramicradiograph showed an alteration inarchitecture of the body of the mandible.An enhanced magnetic resonanceFIGURES 4-5. FIGURE 4. (a) Intraoral view after placing the keeper on the abutment. (b) The magnetic assembly is connected to theoverdenture. FIGURE 5. (a) Panoramic radiograph after 15 months of the prosthetic load showing an adequate bone-implant interface. (b)Intraoral view after placement of the overdenture.image confirmed the extent of the lesion,showing growth to the contralateralside of the mandible. Biopsy examinationof the specimen revealed thatthe lesion was a squamous cell carcinoma.She underwent a radical resectionextending from the mandibularright to the left angles, bilateral radicalneck dissections, and mandibular reconstructionwith a vascularized fibulagraft inMarch 1999 (Figure 1). One yearlater, she underwent removal of the fattissue of the skin pedicle followed byvestibuloplasty. Subsequently, a mandibulardenture was fabricated for her,but it was not satisfactory because of instability.Therefore, dental-implantbasedtreatment was planned.Plates and screws that fixed thegrafted fibula were removed to creategreater room. This was followed bymeasurements of the depth of thegraft, which was recorded as 8 mm atthe point of the fibula, although 10 mmhad been noted immediately postoperatively.Branemark implants (NobelBiocare, Japan, Tokyo) were placed inthe grafted bone in May 2001. At thefirst planning stage, the use of a barattachment to connect the abutmentswith an overdenture had been suggested.A total of 4 implants (diameter,3.75 mm; length, 7 mm) were used inthe grafted anterior part of the mandible(Figure 2).However, a magnetic abutmentsystem (MAGFIT-IP, Aichi Steal Co,Nagoya, Japan), which is composed ofa dome-shaped keeper (diameter, 4.5mm; height, 1.5 mm), a keeper ring (diameter,4.5 mm; height, 0.9 mm), anda magnetic assembly (diameter, 4.4-4.0mm; height, 1.4 mm; retentive force,600 gf) became commercially availableJunnosuke Ishii et alprior to the second-stage surgery (Figure3). Therefore, the original plan forrehabilitation was altered. Two of the 4cover screws were removed, permittingthe connection of the healing abutments.After wound healing was complete,2 standard abutments of 3 mmin length were connected. Subsequently,a new overdenture was fabricated.The magnetic abutment system wasused to fix the overdenture to the implants.First, the keeper ring and thekeeper were connected to each standardabutment using a screwdriver from theBranemark implant system and thiswas followed by setting the magneticassembly on each keeper. Then, 2 holesof approximately 5 mm in diameterwere made in the anterior labial side ofthe new overdenture, correlated withthe position of each magnetic assembly.This allowed the magnetic assembly toJournal of Oral Implantology 291MAGNETIC ABUTMENTS FOR SHORT ENDOSSEOUS IMPLANTSbe attached to the overdenture usingacrylic resin (Figure 4). Satisfactory stabilizationwas achieved, which permittedthe patient to eat a much broaderspectrum of food. The design of the superstructureand the less-than-rigid relationshipit had with the underlyingsupport mechanism deterred overloading(Figure 5).DISCUSSIONA variety of vascularized bone grafts,including iliac,1 scapula,2 radius,3 andfibula4 have been used for mandibularreconstruction. However, each hasdrawbacks. The iliac crest harvest maylead to complications such as injury tothe femoral cutaneous nerve, abdominalherniation, and prolonged gaitpain,5 although it can provide signifi-cant amounts of bone volume.6 Thescapula has limited width7 and length,although the height is adequate to accommodateimplants. The radius is oflimited length7 and it does not offer adequatebone volume for implant placement.8 Donor-site morbidity is relativelyhigh because fracture of the donorradius may occur.9The fibula is the most appropriatesource for mandibular reconstructionlong-span defects because it can bemade available in lengths of up to 25cm.10 Therefore, it has become popularfor use in mandibular reconstruction. Itis also suitable to encourage implantosseointegration because of its bicorticalstructure despite its limitedheight.11 Recently, distraction osteogenesistechniques were used to enhanceseverely resorbed mandibles,which permitted the use of larger implants.12 Chiapasco et al reported theuse of longer implants in the fibula afterthe use of distraction osteogenesis.13However, some problems may occurwith its use, including (1) difficulty indetermining direction, (2) possibility ofsegmental necrosis, (3) potential fractureof the treated bone, and (4) longerduration of treatment.SUMMARY AND CONCLUSIONSIn this study, a grafted bone 18 cm inlength was needed to reconstruct the292 Vol. XXIX/No. Six/2003mandible. It was considered that fibulargrafting was the most favorable reconstructiontechnique. It has been reportedthat the average height of the fibula isabout 10 mm.6 In the present case, theheight of the fibula at the midline wasless than 10 mm. Success was achieveddespite the use of implants of minimallength. Shorter implants are often usedfor severely resorbed mandibles14 andfor bone-anchored facial prostheses.15However, this quality tends to causeoverloading, which would threaten longevity,especially if the ratio of implantsto superstructures is greater than 1:1.16In this study, the ratio of implants tosuperstructures (1:1.30), is reduced byusing a magnetic abutment systemratherthan a ball or bar attachment becausethe total thickness of the keepers areonly 2.4 mm. If a ball or bar attachmenthad been used to connect the abutments,an unfavorable ratio of implantsto superstructures would have been introduced.In addition, the dome-shapedkeeper contributes to minimizing overloadingbecause its specific structure reducesmasticatory forces. It is suggestedthat the magnetic abutment system isuseful not only for grafted fibulas butalso for severely resorbed jaws.REFERENCES1. David DJ, Tan E, Katsaros J,Sheen R. Mandibular reconstructionwith vascularized iliac crest: a 10-yearexperience. Plast Reconstr Surg. 1988;82:792-803.2. Sullivan MJ, Baker SR, CromptonR, Smith-Wheelock M. Free scapularosteocutaneous flap for mandibularreconstruction. Arch OtolaryngolHead Neck Surg. 1989;115:1334-1340.3. Vaughan ED. The radial forearmfree flap in orofacial reconstruction: personalexperience in 120 consecutive cases.J Craniomaxillofac Surg. 1990;18:2-7.4. Serra JM, Paloma V, Mesa F, BallesterosA. The vascularized fibulagraft in mandibular reconstruction. JOral Maxillofac Surg. 1991;49:244-250.5. Kurz LT, Garfin SR, Booth RE.Harvesting autogenous iliac bonegrafts. A review of complications andtechniques. Spine. 1989;14:1324-1331.6. Frodel JL, Funk GF, Capper DT,et al. Osseointegrated implants: a comparativestudy of bone thickness infour vascularized bone flaps. Plast ReconstrSurg. 1993;92:449-458.7. Hidalgo DA. Aesthetic improvementsin free-flap mandible reconstruction.Plast Reconstr Surg. 1991;88:574-585.8. Hayter JP, Cawood JI. Oral rehabilitationwith endosteal implantsand free flaps. Int J Oral MaxillofacSurg. 1996;25:3-12.9. Vaughan ED. The radial forearmflap in orofacial reconstruction. Int J OralMaxillofac Surg. 1994;23:194-204.10. Wei FC, Seah CS, Tsai YC, LiuSJ, TSAI MS. Fibula osteoseptocutaneousflap for reconstruction of compositemandibular defects. Plast ReconstrSurg. 1994;93:294-304.11. Urken ML. Composite free flapsin oromandinular reconstruction: reviewof the literature. Arch OtolaryngolHead Neck Surg. 1991;117:724-732.12. Urbani G, Lombardo G, SantiE, Consolo U. Distraction osteogenesisto achieve mandibular vertical bone regeneration:a case report. Int J Perio RestDent. 1999;19:321-331.13. Chiapasco M, Brusati R, GaliotoS. Distraction osteogenesis of a fibularrevascularized flap for improvementof oral implant positioning in atumor patient: a case report. J OralMaxillofac Surg. 2000;58:1434-1440.14. Stellingsma C, Meijer HJA,Raghoebar GM. Use of short endosseousimplants and an overdenture inthe extremely resorbed mandible: afive-year retrospective study. J OralMaxillofac Surg. 2000;58:382-387.15. Kovacs AF. A follow-up studyof orbital prostheses supported bydental implants. J Oral Maxillofac Surg.2000;58:19-23.16. Saadoun AP, LeGall ML. Clinicalresults and guidelines on Steri-Ossendosseous implants. Int J PeriodontolRestor Dent. 1992;12:487-499.