10. Hardening time of Self-curing
resin for Installing Magnets and Removing Denture
S.Endo1, T.Ishigami1, 2,
K.Miyata1, H.Toyoma1, 2, M.Tsuyumu1, and
T.Azuhata1
1Department of
Partial Denture Prosthodontics，Nihon University School of Dentistry, Japan
2Division of
Clinical Research, Dental Research Center, Nihon University School of
Dentistry, Japan
Introduction
The self-curing resin is widely
used for installing a magnet into the denture base. Ideally, after the resin have completely hardened, the denture with the magnet is
taken out the intraoral. The self-curing resin that flow
into undercuts may cause difficulty in removing the denture. On the other hand,
because the polymerized resin have insufficient
hardness, magnets cannot be fixed adequately. In this study, we evaluated the optimal
hardening time of the self-curing resin for installing a magnet and removing
the denture safely.
Materials and methods
1. Production
of resin block
For the production of a resin
block, a gypsum spacer (GC, Tokyo,
Japan) was adhered to the base of a rubber
frame and then the self-curing resin (UNIFAST III LIVE PINK, GC) was filled on
top of the rubber frame. After the self-curing resin have
hardened, the resin block was taken out the rubber frame, and a spillway was
made (Fig. 1).
Fig. 1
2. Installing
the magnets
A retentive force testing
jig was made using a linear ball slide (THK Company, Tokyo, Japan) set on a
universal testing machine (Ez-test, Shimadzu, Kyoto, Japan) (Fig. 2). A keeper
was attached to the acrylic prism of the jig traction compartment and then the magnet
was adsorbed to the keeper. The fabricated resin block was bonded to another acrylic
prism of the jig fixation compartment. Thereafter a self-curing resin was
brushed-on to the resin block and the magnet was then installed. The cross-head speed was 100mm/min to remove the keeper (Fig.3).
Fig. 2
Fig. 3
3.
Experimental conditions
Five samples of each of three
sizes of magnets (GIGAUSS D400,
D600 and D800, GC) were used and each magnet was
measured five times in this study. The magnets were installed for 40, 50 or 60
seconds. Moreover, 9 removal times (90, 100, 110, 120, 130, 140, 150, 160 and
170 seconds) were evaluated. The measurements of installing and removal times
were started after the self-curing resin was brushed-on (Fig. 4).
Fig. 4
4. Feasibility of installing the
magnet and removing the resin block
The three conditions considered to cause failure of
setting a magnet are as follows:
(1) The magnet is left on the keeper at the time of keeper
removal.
(2) Hardening of the self-curing
resin is incomplete.
(3) The magnet is not
installed in a good position.
Measurement of retentive force was performed
at a 5 mm/min of the cross-head speed, except under the
three conditions mentioned above. The retentive force stated by the manufacturer
was considered to be the index of the success or failure of assessing
installing feasibility.
Results and Discussion
Figures 5, 6 and 7 show the number of
success in installing the magnets and its relationship to removal time. The
most successful timing for installing the three types of magnet tested was 50
seconds, and the adequate removal times were 130 seconds for D400, 140 seconds
for D600 and 160 seconds for D800. Resin hardening was incomplete at the time
of magnet installation of 40 seconds. There
was also a case in which resin stiffened at a magnet installation time of 60
seconds.
Fig. 5
Fig. 6
Fig. 7
Conclusions
The optimal time for installing
the magnet was 50 seconds, and the adequate removal times were 130 seconds for
D400, 140 seconds for D600 and 160 seconds for D800. In the case of installing a
magnet with strong attractive force, a tendency for a longer removal time was
noted.
Acknowledgement
This study was supported in part
by Grant from Dental Research Center, Nihon University School of Dentistry.
Reference
1. S. Nakabayashi,
Regarding relations between the amounts of cold-curing resin used for attaching
a magnet structure and suction power, JJ Mag Dent 14(5):14-17,
2005