Int Poster J Dent Oral Med 2008, Vol 10 No 01, Poster 391
Retention performance of magnetic attachments on dental implants
Dr. med. dent. Arne F. Boeckler, Carolin Ehring, Prof. dr. med. dent. habil. Jürgen M. Setz
Poliklinik für Zahnärztliche Prothetik, Martin-Luther-Universität Halle-Wittenberg
Halle / Saale, Germany
March 9-12, 2005
83rd General Session & Exhibition of the IADR
Baltimore, Maryland, USA
Sensodyne-Poster-Studien-Award 2009 für das beste Poster 2008
Implants in the edentulous jaw have become standard treatment. The use of
an implant retained overdenture with magnets offers a simple treatment
approach to the problem of instability of complete denture 1, 2. Advantages
with magnets include a simplified clinical technique and reduced lateral
stresses on the abutments 3. Contemporary three different physical and
technical concepts can be found: dual systems with two unlike magnets and an
open magnetic field (DO) and mono systems consisting of a magnet and a
corresponding keeper from magnetizable alloy with an open (MO) or with a
closed magnetic field (MC) 4. The force produced by any two magnets is
inversely proportional to the square of the distance between them 5.
Separation between magnet and keeper, however caused, will result in a
drastic reduction in the retention. DO's are relatively voluminous and
providing a lower initial retention force which is admittedly remaining when
the magnets are separated for a small distance. So an adequate re-seating
force for the prosthesis is given. MC's have a smaller design and produce
the highest initial retention force. The characteristics of MO's are
positioned between the other two types. The retention provided would be
quite close to that claimed by the manufacturer as long as the magnet and
the abutment remain in contact. This condition may not be possible in the
clinical situation. The retention in function is very sensitive to distance.
The point to be made, therefore, is that the manufacture's claimed retention
may not be what is obtained clinically. Following the manufacturers'
information recently developed or improved products despite their small size
should produce high retention forces.
The aim of this study was to verify and to compare the initial retention
force and the force-distance relation of contemporar magnetic systems for
Material and Methods
12 products of different height and diameter were tested (Tab 1 and Fig
1). All of these retention systems consisted essentially of a magnetic
assembly which is incorporated into the prostheses and a corresponding
magnetic implant abutment. In the magnetic units rear earth magnets from
SmCo or NeFeB are embedded. The magnetic implant abutments consist of a
magnetizable corrosion resistant alloy or a rear earth magnet as well. To
protect the brittle rare earth magnets against corrosion they are
incorporated into a thin non magnetizable alloy casting (Ti or stainless
steel). From each product or combination 5 specimens were tested in an
adjusted and computer navigated pull-testing machine (Z005, Zwick, Ulm,
Germany). A special non magnetizable holder for the implant abutments was
locked onto the base of the testing machine (Fig 2). To avoid tilting of the
moving magnet it was fixed on the tip of a special holder which was
connected with the crosshead by a nonflexible string. The crosshead speed
was set at 20 mm/min (s=40 mm). The breakaway force was the maximum force
during the separation of the magnet and the abutment when the magnet slowly
moved away. The breakaway force measurement was repeated ten times and the
mean for each sample was used. The results were descriptive and statistical
analysed (H-/U-Test, p0.05). The findings were compared with the
|Fig.3 Force-distance-relation of magnetic attachments on implants
|Tab.1 Magnetic attachments for dental implants
||Tab.2 Initial retention force of the tested implant magnetic attachments
The highest initial retention force was 5.8 N. In a recently developed and
distinctly smaller specimen an initial force of 5.1 N were found. The
smallest initial breakaway force was measured with 0.7 N (Fig 3 and Tab 2).
Beside the different initial forces the recorded force-distance relations
according to the respective type of magnetic system were characteristically
for each of the samples. The highest retention forces achieved the MC's
followed by the DO's and MO's. After a separation of 1 mm the remaining
forces were reversed (Fig 3). The DO's produced about one third of their
initial force whereas the MC's showed approx. 5 % of their initial breakaway
forces. The results of the MO's were between. The value of the retention
force is depending on the dimension of the magnet unit. Therefore the
discrepancies of the recorded breakaway forces and the manufacturers'
claimed retention were determinate (Fig 3 and Tab 2). In one product there
was nearly no difference between the experimental and the manufacturers'
values. In another specimen more than 90 % of retention that was claimed by
the respective manufacturer could be found. In 7 samples there were more
than 75 % but in 3 products under 50 % of the indicated breakaway force.
|Fig.1 Tested specimens
||Fig.2 Non magnetizable holder and mounting
Within the limits of this study it could be drawn that there were
significant differences between the clinically important breakaway forces.
In the majority of cases the maximum retention forces were found notable
under the manufacturers' claimed retention. Mono-systems with a closed
magnetic field were the smallest and produced the highest breakaway forces.
Concerning the reseating forces the force-distance relations could indicate
advantages for the more voluminous dual-systems with an open magnetic field.
These results should be taken into consideration when choosing implant
supported magnetic attachments for individual situations.
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- Naert I, Gizani S, Vuylsteke M, van Steenberghe D. A 5-year prospective randomized clinical trial on the influence of splinted and unsplinted oral implants retaining a mandibular overdenture: prosthetic aspects and patient satisfaction. J Oral Rehabil 1992;26:195-202.
- Walmsley A,.Frame J. Implant supported overdentures-the Birmingham experience. J Dent 1997;25 (Suppl 1):543-547.
- Riley M, Walmsley A, Harris I. Magnets in prosthetic dentistry. J Prosth Dent 2001;86:137-142.
- Jackson T. The application of rare earth magnetic retention to osseointegrated implants. Int J Oral Maxillofac Implants 1986;1:81-92.
This Poster was submitted by Dr. med. dent. Arne F. Boeckler.
OA Dr. med. dent. Arne F. Boeckler
Poliklinik für Zahnärztliche Prothetik
Grosse Steinstrasse 19
06108 Halle / Saale