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 Table of Contents  
REVIEW ARTICLE
Year : 2020  |  Volume : 12  |  Issue : 3  |  Page : 168-171

Magnets – Role in prosthodontic rehabilitation: A review


Department of Prosthodontics Including Crown and Bridge, Maharishi Markandeshwar University, Ambala, Haryana, India

Date of Submission04-Apr-2020
Date of Decision16-May-2020
Date of Acceptance16-May-2020
Date of Web Publication14-Aug-2020

Correspondence Address:
Reena Roy Rassawet
Department of Prosthodontics Including Crown and Bridge, Maharishi Markandeshwar University, Mullana, Ambala, Haryana
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/IJDS.IJDS_52_20

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  Abstract 


The success of prosthesis bases on retention stability and support. Magnets have been used as an aid for denture retention for many years with some success. The reason of the popularity of magnets is their small size and their attraction or repulsion forces, which allow them to be placed within prosthesis without being obtrusive in the mouth. Conventional magnets have been used as retentive devices for removable partial dentures, obturators, and also the maxillofacial prosthesis. The retentive forces and the compactness of the rare earth magnets particularly have resulted in their widespread use for overdentures. This article reviews the type of magnet available, design of magnetic attachment, their application, and new magnetic attachment system, followed by the advantage and disadvantage of magnets.

Keywords: Dental implant, magnets, maxillofacial prosthesis, overdenture, rare earth


How to cite this article:
Rassawet RR, Mittal S, Kalra H. Magnets – Role in prosthodontic rehabilitation: A review. Indian J Dent Sci 2020;12:168-71

How to cite this URL:
Rassawet RR, Mittal S, Kalra H. Magnets – Role in prosthodontic rehabilitation: A review. Indian J Dent Sci [serial online] 2020 [cited 2020 Sep 23];12:168-71. Available from: http://www.ijds.in/text.asp?2020/12/3/168/292277




  Introduction Top


Magnets have generated considerable interest within dentistry. Earlier, magnets were being used in limits due to the unavailability of small-sized magnets, but after that, rare earth magnets introduced, which were available in smaller sizes. They can be positioned within prosthesis without being obtrusive in the mouth.[1] Magnets at first were used in dentistry to improve the retention of mandibular dentures in patients with severely resorbed edentulous mandibles. The reason for the acceptance of magnets is due to their small size and strong, attractive forces. They are being used as a retentive aid for overdenture, removable partial denture, implants, and in orthodontics for the correction of malocclusions and for treating unerupted teeth. Magnetic attachments serve to disperse vertical and lateral forces, preventing them from being transferred to the implants or surrounding bone.


  History Top


In 1953, Freedman initially used a magnet to improve retention and seating of complete denture against the alveolar ridges by using mutual repulsion at the time of closing the jaw.[2] In 1956, Nadeau used magnets in combined extraoral and intraoral prosthesis.[3] In 1960, Behrman used the technique of incorporation of magnets in the jaw to increase the retention of the prosthesis.[4] In 1976, Federick used magnets in a sectional denture.[5] Magnets were also used in the maxillofacial prosthesis in eyelid and lip closure at the time of fabrication of obturators.[6]

Classification of magnets[1]

  1. Based on alloys used:


    • Those which containing cobalt, for example, Aln ico, Alnico V, Co-Pt, and Co5 Sm
    • Those which are not containing cobalt, for examples, Nd-Fe-B, samarium iron nitride.


  2. Based on ability to retain magnetic properties


    • Soft (easy to magnetize or demagnetize)


    • Examples are Pd-Co-Ni alloy, Pd-Co alloy, Pd-Co-Cr alloy, Pd-Co-Pt alloy, magnetic stainless steels, and Cr-Molybdenum alloy.

    • Hard (retain magnetism permanently)


    Examples are: Alnico alloys, Co-Pt, Co5 Sm, and Nd- Fe-B

  3. Based on property of surface coating (materials may be stainless steel, titanium or palladium)


    • Coated
    • Uncoated


  4. Based on the type of magnetism


    • Repulsion
    • Attraction


  5. Based on the type of magnetic field


    • Open field
    • Closed field
    • Rectangular closed-field sandwich design
    • Circular closed-field sandwich design


  6. Based on the number of magnets in the system


    • Single
    • Paired


  7. Based on the arrangement of the poles


    • Reversed poles
    • Nonreversed poles.



  Types of Magnetism Top


Magnetic materials can be divided into “soft” magnets or “hard” magnets based on their magnetic properties. Soft magnets can easily magnetize or demagnetize. The hard-magnetic materials are difficult to magnetize and demagnetize. The hard-magnetic materials are, therefore, used for permanent magnets in devices such as motors, loudspeakers, and in household and industrial devices. The soft magnetic materials can be magnetized and demagnetized easily. Ferromagnetic nickel and cobalt are naturally occurring permanent magnetic materials. The ferromagnetic metals when combine with metals or with oxides form ferromagnetic substances. Permanent magnets are alnico, platinum-cobalt, chromium-cobalt-iron, cobalt-samarium, and neodymium-iron-boron.

Magnetic systems

Open-field systems: The first device was of an “open -field” type. This was used in the rehabilitation of a patient with a cleft lip and palate. Here, two magnets were used; one in the jaw and the other in the denture. In this configuration, the magnets were unshielded, and hence magnetic fields were experienced in the oral cavity.

Closed field systems: In order to reduce magnetic field effects in the oral cavity, a soft ferromagnetic material can be implanted into the jaw (e.g., ferritic or martensitic stainless steel or a Pd-Co-Ni alloy), which serve as the keeper rather than a magnet. This then connects the two poles of the magnet in the denture. The keeper provides a closed field pathway for the magnetic field. In this arrangement, the magnetic field lines are shunted through the path of minimum energy keeper, and hence, there is no magnetic field experienced in the oral cavity. Numerous commercially available magnetic systems are of this type.[7]


  Clinical Application of Magnets Top


Magnets have their role in various fields of dentistry. They are used in different branches, such as:

  1. Prosthodontics
  2. Orthodontics.


Application of magnets for complete dentures

The use of magnetism in dentistry is not new, although it has not been investigated extensively.[7] Its most common application has been in the field of prosthetic dentistry, where use has been made of both repulsive and attractive properties. Magnetic repulsion has been used to limit the displacement of complete dentures, with bar magnets being incorporated into the posterior segments with like poles in opposition, while attractive forces have been employed by implantation of magnets within the alveolar bone or beneath the mucoperiosteal unlike magnetic poles being included in the denture overlying them.[4] The magnets in complete dentures can be used and retained in mouth with numerous devices such as springs, suction cups, clips, and studs. Patients with microsomia who must wear removable dental prostheses often complain of difficulty in insertion or removal of the prosthesis because of the restrained opening of the oral cavity. The magnet used in these situations as Co-Cr framework that contains clasps which hold sectional complete dentures and the cast Co-Cr hinges and swing-lock attachments are used for removable partial or complete dentures. The literature also contains application of custom cast iron-platinum keeper to collapsible denture and Nd Fe B magnetic attachments, which are incorporated in sectional denture for patients with microstomia. Lingual and palatal midline hinges along with cast Fe-Pt magnetic attachment helps in easier insertion and function of sectional denture in patient's mout.[8],[9]

Use of magnets in overdenture

Numerous problems reported by conventional complete denture wearers can be abolished when implants are used to support fixed prosthesis or removable overdentures. Roots can be used as abutment with magnetic appliances if these have bone support of 3 mm. A more popular method was the magnetic retention unit, which contains a denture retention element and a demountable―keeper element. The denture-retention element has paired, cylindrical, cobalt samarium magnets, axially magnetized and arranged with their opposite poles adjacent.[10]

Use of magnets in maxillofacial prosthesis

Because the Fe Pt magnetic attachment system (magnet and keeper) useful for the retention of the prosthesis can be cast in a dental casting machine, any size or shape of castable magnetic attachment can be fabricated for prostheses. Magnets are used in the orbital prosthesis, auricular prosthesis, large and small maxillary defects, and intraoral-extra oral combination prosthesis.[11],[12]

Biocompatibility of magnet

The magnetic intensity of dental attachment is about 0.8 Tesla on the surface of the magnetic assembly. Leakage flux on the magnet assembly is about 0.01–0.03 Tesla in contact with keeper and about 0.005 Tesla beyond the abutment tooth. Thus, the static magnetic field induced by a dental magnetic attachment has little effect on the human body and tissues. When magnetic potential that was produced into the surrounding blood vessel by intraoral magnet (2 × 10–5 V) compared to cell membrane resting potential (60–100 V) it results in negligible effect.[13]

Advantages of magnets

  • Magnets provide adequate retention and stability[14]
  • Magnets allow for 24° of abutment divergence, which provides for an easy noncritical path of prosthesis insertion and removal
  • The roots or implants do not need to be parallel; soft-tissue undercuts may be engaged
  • Potentially pathologic lateral or rotating forces are eliminated, providing maximum abutment protection
  • Enables automatic reseating of the denture if dislodged during chewing
  • If misaligned placement occurs, then the orthodontic movement of the root will result in correct contact being reached
  • Roots with as little as 3 mm of bone support are adequate for use as abutments with magnetic appliances
  • They do not directly induce stress to root abutments.


Disadvantages

Corrosion of magnetic attachments may occur by two different mechanisms.

  1. Corrosion of the magnet due to the breakdown of the encapsulating material
  2. Corrosion of the magnet due to the diffusion of moisture and ions through the epoxy seal.


The major problem associated with these magnets as retentive devices are corrosion by oral fluids, which limits their use. Both Sm-Co and Nd-Fe-B are extremely brittle and susceptible to corrosion, especially in chloride-containing environments such as saliva. Improvements in sealing techniques have ensued in greater effective sealing of magnet encapsulations.

Commercially available magnetic systems

  1. Open field – Dyna Golden
  2. Closed field – Innovadent, Solid state, Magnedent Schinner Gillings, Jacksons (regular and mini)


All these provide satisfactory retention. Apart from corrosion/physical damage, all these systems keep their retentive power indefinitely.[15]

Newer magnetic systems

In Japan, a new generation of strong magnetic attachments without corrosion problems called MAGFIT has been developed. They are divided into magnetic attachments for the following:

Recommended applications

  • Natural tooth root
  • Implant


Principle:

MAGFIT is an innovative dental magnetic attachment system consisting of a powerful yet ultra-compact embedded magnet, which retains a prosthesis onto a magnet attractive keeper set on the abutment tooth [Figure 1].
Figure 1: MAGFIT new generation dental magnetic attachment system

Click here to view


Other magnetic attachments currently available are Hitachi, Dyna, Steco, and others. All these products adopt laser welding to prevent the corrosion problem.

Super-thin magnet attachment

The development of a super-thin-shaped magnet attachment is progressing very quickly.

The advantage over a conventional one

With super-thin magnets, the attractive force is about ten times larger than the current MAGFIT, which would make it a great technological advancement in the field of magnetic attachments. As compared with a MAGFIT, it is thin and can be bent easily.

Applications

The application of these super-thin magnetic attachment is expected to make a denture retainer with the use of vital teeth, beyond its current limitation of root cap attachments in which the crown part of the tooth needs to be cut off. By combining super-thin magnetic attachments with conventional mechanical retainers such as clasps or conical telescopic crowns, it can be possible to develop a simple, hybrid-type retainer in which magnetic retention is used.[16]

Future improvement

Magnetic attachments will bring new possibilities in the field of retention of removable prostheses. New types of magnetic appliances may appear in today's magnetic appliances in the near future.

The lifespan of dental magnetic attachments depends on various factors, but the major problem is the insufficient protection of the encapsulation materials; once they are breached, that causes rapid corrosion of the internal magnet. Laser welding has resulted in improvements in sealing techniques of magnet encapsulations. However, more corrosion and wear-resistant encapsulation materials are required to find out.

The technology and engineering of magnets have advanced dramatically over the last 5 years, and it is now possible to produce much smaller magnets, which offer better seating to the keeper.

Improved engineering techniques now make it possible to offer different keeper, and magnet shapes. All of these improvements still require long-term clinical trials to assess the durability of the new generation of magnets under clinical function. However, there is no doubt that, if magnets are selected for a particular clinical case, then they serve as a good introduction to the use of attachments and, in many cases, can prove highly successful. Techniques now make it possible to offer different keeper and magnet shape.


  Conclusion Top


Magnets were used only occasionally for dental purposes several decades ago. Since the advent of rare earth magnet alloys, the intraoral magnets are shaping the course of esthetic and retention for both complete and removable partial dentures. Their benefits include simplicity, low cost, self-adjustment, innate stress breaking, comparative freedom of lateral movement, and the minimum potential for trauma to the retained root, also eliminating the need for adjustment in service. Clinical fabrication procedures do not require special skills. Various manufactures offer a variety of options to the dentist to select the appropriate treatment plan. As a result of latest research and development in the field of permanent magnetic alloys, there has been rekindled interest lately in the use of magnets in medicine and dentistry as attachment systems.[15]

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Bhat VS, Shenoy KK, Premkumar P. Magnets in dentistry. Arch Med Health Sci 2013;1:73-8.  Back to cited text no. 1
  [Full text]  
2.
Moghadam BK, Scandrett FR. Magnetic retention for overdentures. J Prosthet Dent 1979;41:26-9.  Back to cited text no. 2
    
3.
Nadeau J. Maxillofacial prosthesis with magnetic stabilizers. J Prosthet Dent 1956;6:114-9.  Back to cited text no. 3
    
4.
Behrman SJ. The implantation of magnets in the jaw to aid denture retention. J Prosthet Dent 1960;10:807-41.  Back to cited text no. 4
    
5.
Federick DR. A magnetically retained interim maxillary obturator. J Prosthet Dent 1976;36:671-5.  Back to cited text no. 5
    
6.
Robinson JE. Magnets for the retention of a sectional intraoral prosthesis: A case history 13. J Prosthet Dent 1963;13:1167-71.  Back to cited text no. 6
    
7.
Riley MA, Walmsley AD, Harris IR. Magnets in pros-thetic dentistry. J Prosthet Dent 2001;86:137-42.  Back to cited text no. 7
    
8.
Watanabe I, Tanaka Y, Ohkubo C, Miller AW. Application of cast magnetic attachments to sectional complete dentures for a patient with microstomia: A clinical report. J Prosthet Dent 2002;88:573-7.  Back to cited text no. 8
    
9.
Shah RJ, Solanki, DJ, Diwan, SJ. Fabrication of sectional denture in a patient with microstomia-a clinical report. IOSR Journal of Dental and Medical Sciences S 2016;15:61-4.  Back to cited text no. 9
    
10.
Gillings BR. Magnetic retention for overdentures. Part 11. J Prosthet Dent 1983;49:607-18.  Back to cited text no. 10
    
11.
Bhat V. A close-up on obturators using magnets: Part I-Magnets in dentistry. J Indian Prosthodont Soc 2005;5:114-8.  Back to cited text no. 11
  [Full text]  
12.
Bhat V. A close-up on obturators using magnets: Part II. J Indian Prosthodont Soc 2006;6:148-53.  Back to cited text no. 12
  [Full text]  
13.
Brewer AA, Robert M. Overdentures. 2nd ed. St., Louis: The CV Mosby Company; 1980. p. 376-97.  Back to cited text no. 13
    
14.
Javid N. The use of magnets in a maxillofacial prosthesis. J Prosthet Dent 1971;25:334-41.  Back to cited text no. 14
    
15.
Raghavan R, Ramzi M, Kumar PR, Shajahan PA, Usman J, Balakrishnan S. Magnets in complete dentures. Int J Oral Health Dent 2015;1:133-7.  Back to cited text no. 15
    
16.
Honkura Y. The new generation of dental magnetic attachment. New Magnetic Applications in Clinical Dentistry. Tokyo: Quintessence International; 2004. p. 51-6.  Back to cited text no. 16
    


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Introduction
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Types of Magnetism
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