magnets in prosthetic dentistry

Magnets have generated great interest withindentistry, and their applications are numerous. The 2main areas of their use are orthodontics1,2 and remov-able prosthodontics. The reason for their popularity isrelated to their small size and strong attractive forces;these attributes allow them to be placed within pros-theses without being obtrusive in the mouth. Despitetheir many advantages, which include ease of cleaning,ease of placement for both dentist and patient, auto-matic reseating, and constant retention with numberof cycles, magnets have poor corrosive resistance with-in oral fluids and therefore require encapsulationwithin a relatively inert alloy such as stainless steel ortitanium. When such casings are breached, contactwith saliva rapidly brings about corrosion and loss ofmagnetism.

This review chronicles the development of magnetsin dentistry and critically reviews their current status inremovable prosthodontics.

MAGNETIC MATERIALS

Over the last century, significant advances have beenmade in the development of magnetic materials; theseadvances have been quickly transferred into dental appli-cations. The main magnetic material used is the rareearth material neodymium iron boron (Nd-Fe-B),3,4

which is the most powerful commercially available mag-net material. Other materials used include the RE alloysamarium cobalt (Sm-Co).5,6 Before the developmentof rare earth magnets, Alnicos—alloys based on alu-minum, cobalt, and nickel—were the main materials inuse, although cobalt platinum (Co-Pt) magnets alsoexisted.7

Samarium iron nitride is a promising new candidatefor permanent magnet applications because of its high

resistance to demagnetization, high magnetization,and better resistance than Nd-Fe-B-type magnets totemperature and corrosion.7 This material is still underdevelopment, but it is expected to become availablefor medical and dental applications in the near future.Additional information on magnetic materials andtheir applications may be found in articles by Harris8

and Harris and Williams.9

TYPES OF MAGNETISM

Magnetic materials may be termed either “soft”(easy to magnetize or demagnetize) or “hard” (able toretain magnetic properties and be made into perma-nent magnets). Whether a material is hard or softdepends on whether it retains its magnetic propertiesafter the removal of an applied magnetic field.

Every atom is a magnet because electrons orbit itsnucleus and, as moving charges, produce a magneticfield. However, most electrons are paired, and theequal and opposite fields cancel out. In some atomssuch as Fe, Ni, and Co, there are unpaired electronsthat create a tiny magnetic field. In a magnetic mater-ial, a large portion of these atoms align in small regionscalled “domains.” In an unmagnetized state, the ori-entation of these domains is random and no overallmagnetization is experienced.

On the application of a magnetic field (H), thedomains align and thereby produce an overall magne-tization in the specimen, which will reach a saturationpoint (Ms). Magnetically soft materials require onlysmall fields to reach saturation, whereas magneticallyhard materials require large fields to reach saturation.When the applied field is removed, a permanent mag-net or hard material retains much of the magnetizationor remanence (Br). This magnetization in the speci-men is reduced to zero by the application of an equalbut opposite field to the magnetization in the speci-men. The value of H at this point is the intrinsiccoercivity (iHc). If the applied field is reversedbetween the same positive and negative limits, a sym-metrical loop called a hysteresis loop is traced out.

Magnets in prosthetic dentistry

Melissa Alessandra Riley, BMedSc, PhD,a Anthony Damien Walmsley, BDS, MSc, PhD,b and Ivor RexHarris, BSc, PhD, DScc

The University of Birmingham and St. Chad’s Queensway, Birmingham, United Kingdom

Magnetic retention is a popular method of attaching removable prostheses to either retained rootsor osseointegrated implants. This review chronicles the development of magnets in dentistry andsummarizes future research in their use. The literature was researched by using the ScienceCitation Index and Compendex Web from 1981 to 2000. Articles published before 1981 werehand researched from citations in other publications. Articles that discussed the use of magnets inrelation to prosthetic dentistry were selected. (J Prosthet Dent 2001;86:137-42.)

aRecent PhD graduate, School of Metallurgy and Materials, TheUniversity of Birmingham.

bProfessor, School of Dentistry, St. Chad’s Queensway.cProfessor, School of Metallurgy and Materials, The University of

Birmingham.

AUGUST 2001 THE JOURNAL OF PROSTHETIC DENTISTRY 137

For a permanent magnet, it is the maximum energyproduct, (BH)max, that gives an indication of its power.The larger this value, the greater the flux produced by amagnet of a given volume. The development of variousmagnetic materials and improvements in energy prod-uct ([BH]max) over the last century are shown inFigure 1. Additional information on magnetism may befound in the text by Jiles.7

REMOVABLE PROSTHODONTICS

Various devices such as springs, suction cups, clips,and studs all have been used to retain complete andremovable partial dentures within the mouth.10

Magnets also have been used for this purpose becausethey are easy to incorporate into a denture and cansimplify both clinical and technical procedures.However, there are limitations to their use; these lim-itations are related mainly to their low corrosionresistance within the mouth.11,12

The first attempts at using magnets to retain den-tures involved implanting them within the jaw13,14;problems ensued because of the large size of the mag-nets and the inadequate forces that they provided. Asmaterial technology improved, smaller magnets weremade that could be incorporated into retained rootswith similar units built into the denture. Later devel-opments included the replacement of the root magnetwith a soft magnetic material that is magnetized whilethe denture is in place but returns to a demagnetizedstate on removal of the denture.

In the last 20 years, the design of magnetic attach-ments has changed to reduce the external magnetic

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138 VOLUME 86 NUMBER 2

fields present while the denture is in place. The meth-ods of corrosion protection have also improved.15

Improvements in magnetic materials have allowedsmaller and more powerful magnetic attachments tobe produced from Sm-Co and Nd-Fe-B alloys.

IMPLANTATION OF MAGNETSMagnet repulsion

The first recorded use of magnets in prosthetic den-tistry involved using the repulsion of like poles ofmagnets to maintain and improve the seating of com-plete dentures.16 The magnetic material used was anAlnico type that has been discontinued in dental appli-cations because of the large bulk necessary for magnetstrength. The magnets were embedded in molarregions in the bases of complete dentures so that thelike poles were orientated toward each other. As thepatient closed his or her jaws together, mutual repul-sion of the like poles of the magnets seated the dentureagainst the alveolar ridges.17 However, the constantrepelling force promoted resorption of bone in thealveolar ridge, and the seating effect fell dramaticallywhen the jaws were apart and the need for the seatingeffect was at its greatest.

Magnet attraction

The use of the attractive force between 2 magnetsfor denture retention was reported in the early1960s.13,14 These first attempts were made withAlnico V and both rectangular and cylindrical PMMA-coated magnets, which were surgically implanted inthe mandible of an edentulous patient. This trial

Fig. 1. Improvements in (BH)max with time (from Harris and Williams4).

showed that, because of the distance between the 2magnets, they provided inadequate force to aid den-ture retention. The introduction of smaller, strongerCo-Pt magnets allowed continuation of clinical tri-als.14 Unfortunately, several disadvantages wereassociated with Co-Pt magnets, including their highcost, limited availability, and difficult fabrication. Itwas also found that the implanted magnet migratedthrough the bone and tissues until it became exposedin the oral cavity.18 The procedure was eventuallyabandoned because of the high costs involved andpoor success rates.

With the introduction of the powerful magnet mate-rial Sm-Co, the use of implanted magnets to aid dentureretention was investigated again.19 These magnets couldbe produced in dimensions approximately one fifth ofthe Co-Pt magnets and still provide the same force.Because of the susceptibility of the magnets to corro-sion, a proplast coating (polytetrafluoroethylene[PTFE] and pyrolytic graphite) was used. Experimentswere carried out on dogs to establish whether proplastcould be used as an effective coating for Sm-Co mag-nets in the in vivo environment. The study concludedthat the coating provided corrosion protection if therewere no faults or damage to the coating during surgicalplacement. Proplast is no longer used as a coating mate-rial, but PTFE is used as the binder in polymer-bondedmagnets.7 However, these are unsuitable for long-termuse within the body because diffusion of moisturethrough the polymer results in inadequate corrosionprotection of the magnet material.

Section summary

Early attempts at using magnets for denture reten-tion were unsuccessful, mainly because of the large sizeof magnets at that time and the inadequate forces thatthey provided. However, since the introduction of rareearth magnets such as Sm-Co5,6 and Nd-Fe-B,3,4 it hasbecome possible to produce magnets with smallenough dimensions to be used in dental applicationsand still provide the necessary force. This negates theneed to implant the materials; consequently, interest inusing magnets for denture retention has once againincreased, as is demonstrated by the number of clinicalreports on this subject.

CONVENTIONAL USE OF MAGNETSOpen-field systems

The first reported use of magnets for the retentionof overdentures took place in the 1960s20 with therehabilitation of a patient with a cleft lip and palate.The magnetic Co-Pt alloy was used to produce crownsfor 3 remaining teeth with cast Co-Pt also built intothe denture. This was soon followed by the techniqueof cementing magnets within retained roots for theretention of overdentures.21 An Sm-Co magnet was

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AUGUST 2001 139

cemented into a prepared cavity in the root surface,and a similar magnet was placed in the denture. Thetechnique was modified to prevent corrosion of themagnets in the oral environment22 with the use of acast gold coping to cover the magnet; whether this wassuccessful is unclear.

Soft magnetic root keepers: Various studies have beencarried out on the effects of magnetic fields and mag-netic materials with conflicting results.18,23-33 Thedetails of this work are beyond the scope of this article,but there is nothing to suggest that adverse clinicaleffects have occurred after 40 years of magnetic applica-tions within medicine and dentistry. However, becauseof fears over the effects of magnetic fields on the soft tis-sues, a soft magnetic material, Pd-Co-Ni alloy, wasdeveloped for use in the root face.34 Three alloys wereinvestigated as replacements for the root element com-ponent: Pd-Co, Pd-Co-Cr, and Pd-Co-Ni. Afterassessment of the magnetic and physical properties andcorrosion resistance, the Pd-Co-Ni alloy was found tobe the most suitable.35 However, it was also shown thatPd-Co-Pt alloys are the most corrosion-resistant.36 Theadvantage of these alloys is that the root element pos-sesses no permanent magnetic properties; thus, nomagnetic fields are experienced within the oral envi-ronment once the dentures are removed. Other softmagnetic materials used for root keepers have includ-ed magnetic stainless steels, Permendur (an alloy ofiron and cobalt37), and chromium-molybdenumalloys.38

Such alloys have been cast to form a root coping orpre-formed into a keeper with or without a screwthread for cementation into the root or attachment toan implant.39 The cast copings have been cementedand, in some situations, cross-pinned into the root toavoid loss of the keeper should breakdown of theadhesive occur.40 Although there have been fears overthe effects of magnetic fields on human tissues, open-field systems are commonly used in both dentureretention and orthodontic applications today.

Closed-field systems

Many commercial systems are now of the closed-field type; these attempt to reduce the magnetic fieldeffects in the oral cavity. The magnetic attachmentsincorporate soft magnetic materials (such as ferritic ormartensitic stainless steel or a Pd-Co-Ni alloy) thatconnect the 2 poles of a magnet so the external field isshunted through the path of less resistance, reducingexternal fields in situ. This is demonstrated in Figure 2,which shows the differences in the external magneticfields experienced with open- and closed-field systems.

Attachment of closed-field magnets is more effi-cient because both the north and south poles can beused for attachment to the keeper (in open-field sys-tems, only one pole is used) and the keepers can

contain the magnetic flux. Although these systemsgenerally provide a higher retentive force than a simi-larly sized open-field system, the retention reducesrapidly with increasing separation.41,42 The firstclosed-field design was the split pole design,43 whichconsisted of 2 magnets arranged with opposite polesadjacent to each other. A soft magnetic keeper wasattached to the top of the magnets, and a similar keep-er was built into the root.

Comparisons of the forces provided by paired mag-nets, single magnets and soft magnetic material, andreversed and nonreversed poles have been performed.Paired magnets provided a greater breakaway forcethan a single magnet with a soft magnet keeper. Areversed split pole system, as designed by Gillings,43

provided a greater force than a nonreversed split poledesign.44

Since then, other commercial systems have comeinto use, and the designs of these systems haveevolved.35 Various designs exist that are based on cir-cular and rectangular assemblies. A magnet sandwichdesign has been shown to work well,45 although theamount of retention provided by this design dependson the thickness of the side plates and the base.46

Finite element analysis (FEA) has been used toimprove the design of these attachments to maximizethe force that they provide.38 FEA is able to showmagnetic flux distributions within a design and alsogive information on contact forces and the force sep-aration characteristics of magnetic systems. Aclosed-field design consisting of a magnet in a cup,which in turn is placed in an outer cup (Fig. 2), pro-vides a higher retention force than a simple open-fieldsystem that incorporates a similarly sized magnet.However, a circular closed-field sandwich-type designprovides a greater amount of retention still. If thekeeper materials are made ellipsoidal, then retentionwill increase further.38

Clinical usage

Magnetic attachments have most commonly beenused for the retention of mandibular overdentures.Many authors have described procedures for the useof magnets in this application,20,47-49 and patientshave reported a high degree of satisfaction withtheir dentures.50 There has been renewed interest inusing magnetic attachments for the provision ofmandibular overdentures with osseointegratedimplants.15,51 The implant-supported overdentureconsists of an implant-supported keeper and a mag-net that is built into the denture. Two to 4 implantsmay be used, and these are placed in the anteriorregion of the mouth and spaced as widely as possi-ble to provide maximum support and stability. Themagnets may be used as attachments on freestand-ing implants or in combination with a barattachment. A bar attachment spans the implants;the magnets are placed in contact with the barrather than individual keepers on implants.51 Manyclinical reports demonstrate the successful use ofmagnetic attachments with implant-supported over-denture systems.52-60 Magnets have been used inboth mandibular and maxillary implant-supported,full-arch bar, fixed-detachable prostheses.51

CORROSION

The main problem associated with the use ofmagnets as retentive devices is corrosion by oral flu-ids.36,61-63 Both Sm-Co and Nd-Fe-B are extremelybrittle and susceptible to corrosion, especially inchloride-containing environments such as saliva. Thecorrosion products from rare earth magnets alsohave been shown to have cytotoxic effects in in vitrotests.28,64 Therefore, magnetic materials must besecurely separated from the oral fluids before use indental applications.



Fig. 2. For simple, cylindrical, open-field magnet encased in nonmagnetic housing, magnet-ic field is experienced outside magnetic specimen (A). However, when soft magneticmaterials are used for encapsulation (for example, in cup design [B]), magnetic flux is con-tained within encapsulation material and channeled into root keeper component.

BA

Although some current magnet assemblies areencapsulated in stainless steel or titanium,15 somedevices fail after only approximately 18 months in clin-ical use because of corrosion and loss of retentionprovided by the attachment.60,65 The buildup of cor-rosion products may also result in discoloration of thedenture teeth.66 Corrosion of magnetic attachmentsmay occur by 2 different mechanisms11: (1) break-down of the encapsulating material, and (2) diffusionof moisture and ions through the epoxy seal betweencan and magnet.

Both Nd-Fe-B and Sm-Co5 magnets corrode rapidlyin saliva, and the presence of bacteria has been shown toincrease the corrosion of Nd-Fe-B magnets.67,68

Various methods have been used to try to eliminate theproblem of corrosion; these involve encapsulating orcoating the magnets for use intraorally. Titanium andstainless steel are the most common materials used forencapsulation of dental attachments,15 but polymericmaterials also have been used in both prosthodontic andorthodontic applications.19,28 However, continual wearof the encapsulating material leads to exposure of themagnet60; this has been shown to occur clinically.59,60

The wear takes the form of deep scratches and gougeson the surface caused by wear debris and other particlesthat become trapped between the 2 surfaces.11 Theexcessive wear of the magnet may be due to the abrasivenature of the titanium-nitride-coated soft magnetic rootkeeper that is used with some implant systems.

The pitting corrosion of stainless steel occursbecause of the corrosive oral environment; similar cor-rosion has been observed in different systems.11,12 Toovercome the problems associated with the use of den-tal magnets, it appears that different encapsulatingmaterials or surface coatings are required. In industry,other coatings such as titanium and chromium nitrideshave been used to prevent wear. These coatingsrequire investigation before use, although titanium-nitride is used in some orthopedic applications.

An additional problem associated with attachmentssealed by polymeric materials is the diffusion of mois-ture and ions, which attack the magnet component,through the seal. This mechanism applies only to mag-nets sealed by this technique, and the time to failure isdependent on the rate of diffusion and path length ofthe seal.11 To achieve a highly reliable system, othernonpermeable sealing techniques such as laser weldingshould be used. Laser welding currently is in use onsome commercial open-field systems such as the Dyna(Dyna Dental Engineering, Bergen op Zoom, TheNetherlands) and Steco (Steco-system-technik, GmbH& Co, Hamburg, Germany) systems15 and merits fur-ther investigation. In some systems, if breakdown ofthe encapsulation material occurs, then corrosionproducts leak out.11 As bulk magnet material is lostfrom within the can, the stainless steel, no longer sup-

ported, is able to plastically deform inward. Clinically,this is observed as a groove down the center of themagnet face.60

FUTURE IMPROVEMENTS

The lifetime of dental magnetic attachmentsdepends on several factors, but the main problem isthe inadequate protection of the encapsulation materi-als; once they are breached, rapid corrosion of theinternal magnet occurs. Improvements in sealing tech-niques (namely, laser welding) have resulted in moreeffective sealing of magnet encapsulations. However,further work is required to find more corrosion- andwear-resistant encapsulation materials.

SUMMARY

Magnets provide a useful method for attachingdental prostheses to either retained roots or osseoin-tegrated implants. Magnetic technology is constantlyimproving: currently available magnets based on Nd-Fe-B are small (which allows them to be incorpo-rated into dentures) and have attractive forces thatenable them to provide retention. The major researchquestion that has not been solved is the problem ofcorrosion. When in contact with saliva, magnets cor-rode and experience subsequent loss of magnetism.Encapsulating materials such as stainless steel areeffective but susceptible to wear. Magnets thereforehave a relatively short life, although more research isrequired to help the clinician determine their poten-tial lifespan within the mouth. The development ofsamarium-iron-nitride may offer better resistance tocorrosion, and its introduction into prosthodonticswill be viewed with much enthusiasm.

REFERENCES

1. Blechman AM, Smiley H. Magnetic force in orthodontics. Am J Orthod1978;74:435-43.

2. Springate SD, Sandler PJ. Micromagnetic retainers: an attractive solutionto fixed retention. Br J Orthod 1991;18:139-41.

3. Sagawa M, Furimura S, Togowa N, Yamatoto H, Matsuura Y. New mater-ial for permanent magnets on a base of Nd and Fe. J Appl Phys1984;55:2083-7.

4. Croat JJ, Herbst JF, Lee RW, Pinkerton FE. Pr-Fe and Nd-Fe-based materi-als: a new class of high-performance permanent magnets (invited). J ApplPhys 1984;55:2078-82.

5. Strnat KJ. The hard magnetic properties of rare earth-transition metalalloys. IEEE Trans Magn 1972;8:511-6.

6. Tawara Y, Strnat KJ. Rare earth-cobalt permanent magnets near the 2-17composition. IEEE Trans Magn 1976;12:954-8.

7. Jiles D. An introduction to magnetism and magnetic materials. 2nd ed.London: Chapman and Hall; 1988. p. 3-16, 44-48, 89-102, 363-93.

8. Harris IR. Hard magnets. Mater Sci Tech 1990;6:962-6.9. Harris IR, Williams AJ. The attractions of rare earth magnets. Mater World

1999;7:478-81.10. Basker RM, Harrison A, Ralph JP. Overdentures in general practice. Part

5—the use of copings and attachments. Br Dent J 1983;155:9-13.11. Riley MA, Williams AJ, Speight JD, Walmsley AD, Harris IR.

Investigations into the failure of dental magnets. Int J Prosthodont1999;12:249-54.

12. Wirz J, Lopez S, Schmidli F. Magnetverankerungen auf implanten. Teil 2:korrosionsverhalten. Quintessenz 1993;44:737-49.

RILEY, WALMSLEY, AND HARRIS THE JOURNAL OF PROSTHETIC DENTISTRY

AUGUST 2001 141

13. Behrman SJ. The implantation of magnets in the jaw to aid denture reten-tion. J Prosthet Dent 1960;10:807-41.

14. Behrman SJ. Magnets implanted in the mandible: aid to denture reten-tion. J Am Dent Assoc 1964;68:206-15.

15. Wirz J, Lopez S. Magnetverankerungen auf implanten. Teil 1: bestandesauf-nahme. Quintessenz 1993;44:579-88.

16. Freedman H. Magnets to stabilize dentures. J Am Dent Assoc 1953;47:288.17. Winkler S, Pearson MH. The effectiveness of embedded magnets in com-

plete dentures during speech and mastication: a cineradiographic study.Dent Dig 1967;73:118-9 passim.

18. Toto PD, Choukas NC, Abati A. Reaction of bone to a magnetic implant.J Dent Res 1963;42:643-52.

19. Connor RJ, Svare CW. Proplast-coated high-strength magnets as potentialdenture stabilization devices. J Prosthet Dent 1977;37:339-43.

20. Thompson IM. Magnetism as an aid to a prosthetic problem. Br J OralSurg 1964;2:44-6.

21. Moghadam BK, Skandrett FR. Magnetic retention for overdentures. JProsthet Dent 1979;41:26-9.

22. Maroso DJ, Tischler P, Schmidt JR. A simplified technique for magneticretention of overdentures. J Prosthet Dent 1984;51:599-601.

23. Cerny R. The reaction of dental tissues to magnetic fields. Aust Dent J1980;25:264-8.

24. Altay OT, Kutkam T, Koseoglu O, Tanyeri S. The biological effects ofimplanted magnetic fields on the bone tissue of dogs. Int J OralMaxillofac Implants 1991;6:345-9.

25. Bondemark L, Kurol J, Wennberg A. Biocompatibility of new, clinicallyused, and recycled orthodontic samarium-cobalt magnets. Am J OrthodDentofacial Orthop 1994;105:568-74.

26. Bondemark L, Kurol J, Larsson A. Human dental pulp and gingival tissueafter static magnetic field exposure. Eur J Orthod 1995;17:85-91.

27. Bondemark L, Kurol J, Larsson A. Long-term effects of orthodontic magnetson human buccal mucosa—a clinical, histological and immunohisto-chemical study. Eur J Orthod 1998;20:211-8.

28. Bondemark L, Kurol J, Wennberg A. Orthodontic rare earth magnets—invitro assessment of cytotoxicity. Br J Orthod 1994;21:335-41.

29. Linder-Aronson S, Lindskog S, Rygh P. Orthodontic magnets: effects on gingi-val epithelium and alveolar bone in monkeys. Eur J Orthod 1992;14:255-63.

30. Linder-Aronson S, Lindskog S. A morphometric study of bone surfacesand skin reactions after stimulation with static magnetic fields in rats. AmJ Orthod Dentofacial Orthop 1991;99:44-8.

31. Camilleri S, McDonald F. Static magnetic field effects on the sagittal suturein Rattus norvegicus. Am J Orthod Dentofacial Orthop 1993;103:240-6.

32. Saygili G, Aydinlik E, Ercan MT, Naldoken S, Ulutuncel N. Investigationof the effect of magnetic retention systems used in prostheses on buccalmucosal blood flow. Int J Prosthodont 1992;5:326-32.

33. Donohue VE, McDonald F, Evans R. In vitro cytotoxicity testing ofneodymium-iron-boron magnets. J Appl Biomater 1995;6:69-74.

34. Sasaki H, Kinouchi Y, Tsutsui H, Yoshida Y, Ushita T. Applications of samar-ium cobalt magnets to dentistry. Proceedings of the 4th InternationalConference on Rare Earth Magnets and their Applications. Hakone, Japan;May 1979.

35. Kinouchi Y, Ushita T, Tsutsui H, Yoshida Y, Sasaki H, Miyazaki T. Pd-Codental casting ferromagnetic alloys. J Dent Res 1981;60:50-8.

36. Vrijhoef MM, Mezger PR, Van der Zell JM, Greener EH. Corrosion of fer-romagnetic alloys used for magnetic retention of overdentures. J DentRes 1987;66:1456-9.

37. Okuno O, Nakano T, Hamanaka H, Kinouchi Y. Encapsulated sandwichtype dental magnetic retainers by NdFeB magnet and permandur yoke.Proceedings of the 10th International Workshop on Rare Earth Magnetsand Applications. Kyoto, Japan; May 1989.

38. Tanaka Y, Hiranuma K, Iwama Y, Honkura Y. Sealed dental magneticattachment developed by three-dimensional magnetic analysis.Proceedings of the 10th International Workshop on Rare Earth Magnetsand Applications. Kyoto, Japan; May 1989.

39. Wang NH, von der Lehr WN. The direct and indirect techniques of mak-ing magnetically retained overdentures. J Prosthet Dent 1991;65:112-7.

40. Smith GA, Laird WR, Grant AA. Magnetic retention units for overden-tures. J Oral Rehabil 1983;10:481-8.

41. Highton R, Caputo AA, Matyas J. Retentive and stress characteristics for amagnetically retained partial overdenture. J Oral Rehabil 1986;13:443-50.

42. Akaltan F, Can G. Retentive characteristics of different dental magneticsystems. J Prosthet Dent 1995;74:422-7.

43. Gillings BR. Magnetic retention for complete and partial overdentures.Part I. J Prosthet Dent 1981;45:484-91.

44. Laird WR, Grant AA, Smith GA. The use of magnetic forces in prostheticdentistry. J Dent 1981;9:328-35.

45. Jackson TR, Healey KW. Rare earth magnetic attachments: the state of theart in removable prosthodontics. Quintessence Int 1987;18:41-51.

46. Riley MA. The use of magnets in biomedical applications [PhD thesis].Birmingham: The University of Birmingham; 2000.

47. Gillings BR. Magnetic retention for overdentures. Part II. J Prosthet Dent1983;49:607-18.

48. Gillings BR. Magnetic denture retention systems: inexpensive and effi-cient. Int Dent J 1984;34:184-97.

49. Kroone HB, Bates JF. Overdentures with magnetic retainers. Br Dent J1982;152:310-3.

50. Jonkman RE, Van Waas MA, Kalk W. Satisfaction with complete inter-mediate dentures and complete intermediate overdentures. A 1-yearstudy. J Oral Rehabil 1995;22:791-6.

51. Jackson TR. The application of rare earth magnetic retention to osseoin-tegrated implants. Int J Oral Maxillofac Implants 1986;1:81-92.

52. Carlyle LW, Duncan JM, Richardson JT, Garcia L. Magnetically retainedimplant denture. J Prosthet Dent 1986;56:583-6.

53. Walmsley AD, Brady CL, Smith PL, Frame JW. Magnet-retained overden-tures using the Astra dental implant system. Br Dent J 1993;174:399-404.

54. Burns DR, Unger JW, Elswick RK, Beck DA. Prospective clinical evalua-tion of mandibular implant overdentures: part I. Retention, stability, andtissue response. J Prosthet Dent 1995;73:354-63.

55. Burns DR, Unger JW, Elswick RK, Gigilo JA. Prospective clinical evalua-tion of mandibular implant overdentures. Part II. Patient satisfaction andpreference. J Prosthet Dent 1995;73:364-9.

56. Chan MF, Johnston C, Howel RA, Cawood JI. Prosthetic management ofthe atrophic mandible using endosseous implants and overdentures: asix-year review. Br Dent J 1995;179:329-37.

57. van Waas MAJ, Kalk W, van Zetten BL, van Os JH. Treatment results withimmediate overdentures: an evaluation of 4.5 years. J Prosthet Dent1996;76:153-7.

58. Naert I, Gizani S, Vuylsteke M, van Steenberghe D. A 5-year prospectiverandomized clinical trial on the influence of splinted and unsplinted oralimplants retaining a mandibular overdenture: prosthetic aspects andpatient satisfaction. J Oral Rehabil 1999;26:195-202.

59. Davis DM. Implant supported overdentures—the King’s experience. JDent 1997;25(Suppl 1):S33-7.

60. Walmsley AD, Frame JW. Implant supported overdentures—theBirmingham experience. J Dent 1997;25(Suppl 1):543-7.

61. Angelini E, Pezzoli M, Zucchi F. Corrosion under static and dynamicconditions of alloys used for magnetic retention in dentistry. J ProsthetDent 1991;65:848-53.

62. Drago CJ. Tarnish and corrosion with the use of intraoral magnets. JProsthet Dent 1991;66:536-40.

63. Kitsugi A, Okuno O, Nakano T, Hamanaka H, Kuroda T. The corrosionbehavior of Nd2Fe4B and SmCo5 magnets. Dent Mater J 1992;11:119-29.

64. Gendusa NJ. Magnetically retained overlay dentures. Quintessence Int1988;19:265-71.

65. Davis DM, Packer ME. Mandibular overdentures stabilized by Astra Techimplants with either ball attachments or magnets: 5-year results. Int JProsthodont 1999;12:222-9.

66. Boice GW, Kraut RA. Maxillary denture retention using rare earth mag-nets and endosteal implants. Int J Oral Implantol 1991;7:23-7.

67. Wilson M, Patel H, Kpendema H, Noar JH, Hunt NP, Mordan NJ.Corrosion of intra-oral magnets by multi-species biofilms in the presenceand absence of sucrose. Biomaterials 1997;18:53-7.

68. Wilson M, Kpendema H, Noar JH, Hunt N, Mordan NJ. Corrosion of intrao-ral magnets in the presence and absence of biofilms of Streptococcus sanguis.Biomaterials 1995;16:721-5.

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