Practical application of self- and light-curing resin for attaching amagnetic assembly into the denture base resin
M. Imamura, S. Nakabayashi, T. Ishii, S. Saito, N. Tsukimura, T. Ohyama, D. Akita,and T. Ishigami
Department of Partial Denture Prosthodontics, Nihon University School of Dentistry

Introduction
Generally, the magnetic assembly was attached into the denture base resin using self-curing resin.
However, an enough retentive force is often suppressed by the air gap between keeper and magnetic
assembly due to the polymerization shrinkage.

ObjectiveIn this study, the retentive force was compared with 3 different height spaces onto the magnetic
assembly which were filled with self-curing resin or light-curing resin with low-shrinking.

Materials and Methods
GIGAUSS D400, D600 magnetic assemblies (GC company®) and each gypsum dummy wereused as a specimen. The diameters of the magnetic assemblies increase in order of D400, D600, but
the height is same (1.3 mm). The diameter of the gypsum dummy is 0.3 mm wider than that ofmagnetic assembly, and the height is 0.3 mm higher than the top surface of the magnetic assembly.
(Fig. 1).
90 magnetic assemblies were placed on the keeper which were fixed by the resin and attachedinto each resin blocks using self- or light-curing resin following three groups: (1) Unifast	  Ⅲ
No.8(GC company®) (n=30), (2) Unifast LC (GC company®) (n=30), and (3) G-FIX (GCcompany®) (n=30). The retentive force between keepers and attached magnetic assemblies wereanalyzed.
0.3mm
0.3mm

D4
Gap by gypsum
dummy

1.3mm

3.0mm

Attachment of
the magnet

0.3mm

D61.3mm

3.6mm

Fig. 1

Diameter and height space of magnetic assemblyand gypsum dummy (various)

Additionally, sheet wax of the same thickness as a spacer (0.6 mm and 1.2mm) added to thegypsum dummy.
1)	  Adjustment of the space
The gypsum dummy without adding sheet wax is control. (referred to as C group) （Fig. 2).

0.3mm
GYPSUM DUMMY

Attachmentof the magnet

Height space ofgap 0.3mm

C groupFig. 2

Amount of gap when sheet wax is not added, and it makes it to spaser

0.6 mm of sheet wax (two sheets) onto the gypsum dummy made the spacer at 0.9 mm which isthree times as long as C group (referred to as 0.9 group) (Fig. 3).

sheet wax

0.6mm
0.3mm

GYPSUM DUMMY

Attachmentof the magnet

Height space ofgap 0.9 mm

0.9 group

Fig. 3 Amount of gap when as much as two sheet wax is added

1.2 mm of sheet wax (four sheets) onto the gypsum dummy made the spacer at 1.5 mm which isfive times as long as C group (referred to as 1.5 group) (Fig. 4).

sheet wax

1.2mm

0.3mm
Attachment  of  the  magnet

GYPSUM DUMMYHeight	  space	  of	  gap1.5mm

1.5 group

Fig. 4

Amount of gap when as much as four sheet wax is added2)	  Preparation of resin block
A resin block (10×10×7 mm) was put on a specimen with 3 different spaces (Fig. 5).
Spillway within the resin block was formed with a round bar No. 6 (φ1.6mm) (Fig. 6).

1.6㎜

7㎜

10㎜

Fig.	  510㎜
SpaserResin	  block	  from	  the	  spacer	  adjusted

Spillway

Fig.	  6Resin	  block	  after	  spillway	  is	  formed3)	  Attachment of the magnetic assembly
Before attachment, alumina sandblast was performed on the surface of the magnetic assemblyand metal primer Z (GC company®) was coated.
At Unifast Ⅲ and Unifast LC , the standard ratio of powder and liquid (2 g/1 ml) for 10 seconds
was mixed and filled the same amount in the spacer, and then the magnetic assembly was attachedwithin 60 seconds from the start of mixing.
On the other hand G-FIX was inserted from spillway using the syringe after resin blocks were
held by hands. The material was poured along the edge carefully (Fig. 7).
During attachment of the magnetic assembly using Unifast Ⅲ, 150g of static loading wasapplied after 150 seconds from the start of mixing at room temperature2).

At Unifast LC and G-FIX, while holding by hands, the light was irradiated toward the uppersurface of the magnetic assembly longitudinally for 20 seconds from the top of spillway (Fig. 8).

Fig.	  7 Insertion	  the	  syringe	  from	  spillway

Fig.	  8 Irradiation	  from	  the	  top	  of	  spillway	  with	  light	  curing	  units4)	  Tension test
The retentive force was measured in a universal testing machine (EZ-Test, SHIMADZU, Kyoto,Japan), and D400 and D600 magnetic assembly-keeper composition were tested 5 times for eachspecimen with cross head speed 5 mm per minute. The specimens were pulled and measured thepoint at which the magnetic assembly was detached to the keeper and the mean values werecompared.
5)

Statistical Analysis

Two-way ANOVA and the multi-comparison of Tukey test were used to compare with 3
different height spaces onto the magnetic assembly with self-curing resin or light-curing resin withlow-shrinking. ; < 0.05 was considered statistically significant. (Mean ｇ ±SD)

Results
Table. 1 and 2 show the retentive force was compared with 3 different height spaces onto themagnetic assembly which were filled with self-curing resin or light-curing resin with low-shrinking.

G-FIX

Unifast Ⅲ

Unifast LC

C group334.2(±3.1)

310.1(±1.8)313.9(±5.8)

0.9 group319.7(±4.5)304.9(±16.3)

294(±12.0)

1.5 group

293.4(±6.7)

243.8(±21.2)

251(±5.5)

Table. 1

The average value of the retentive force and the standard
deviation in D400
（Mean g ±SD）

G-FIX

Unifast Ⅲ

Unifast LC

C group509.8(±7.9)487.8(±10.4)

463.1(±13.1)

0.9 group473.4(±14.3)

445.3(±9.3)

418.6(±22.7)

1.5 group406.4(±14.3)

363(±5.4)

349.2(±6.2)

Table. 2

The average value of the retentive force and the standard
deviation in D600
（Mean g ±SD）

At Fig. 9, the retentive force was shown for the difference of 3 materials and the 3 spacers in
D400. The underlined value of a vertical axis was a mean of the retentive force of the magnetic
attachment alone, which was specified as a standard value3).
In the atacched material, the retentive force was smaller C group, 0.9 group, 1.5 grouprespectively. Among the spacer, C group in G-FIX had the greatest retentive force significantly
which was closest to standard value in D400.
D600 figure was shown, as the space onto the magnetic assembly was higher, the retentive force
decreased significantly in G-FIX ,Unifast Ⅲand Unifast LC. At 0.9 group and 1.5 group, theretentive force in G-FIX was greater than other materials significantly which was also closest tostandard value at Fig. 10.
The retentive force in Unifast LC had mostly the same data in Unifast Ⅲat each spacer at Fig.9
and 10.

R etentive	 force

(gf)
600

*

*

*500

**
*

400

*
*345300

**

*

*

200
1000C 0.9 1.5

C 0.9 1.5

C 0.9 1.5

G-FIX

U nifastⅢ

U nifast LCn  ＝ 5(＊:P   ＜ 0.05)

Fig.	  9	  Retentive	  force	  when	  using	  different	  materials	  and	  spacer	  in	  D400***

R etentive	 force

*(gf)

*

600

518500

*

*

*

*

*

*

*

*

*

*

*

400
300
0C 0.9 1.5

C 0.9 1.5

C 0.9 1.5

G-FIX

U nifastⅢ

U nifast LC

n  ＝ 5(＊:P   ＜ 0.05)

Fig.	  10	  Retentive	  force	  when	  using	  different	  materials	  and	  spacer	  in	  D600

Conclusions
In D400 and 600, the retentive force reduced clearly C group, 0.9 group, 1.5 groups respectively
in each material as well as previous Nakabayashi’s report1).
In each spacer, G- FIX had the highest retentive force which was showed closest to a standardvalue.
When attaching a magnetic assembly into the denture base resin, a low-shrinkage material like a
G-FIX was capability to suppress occurrence of the air gap. It is supposed to be a material which candemonstrate the enough retentive force reproducibility without the air gap.

References
1. S. Nakabayashi, H. Takimoto, T. Ishigami, et al.: Regarding relations between the amounts ofcold-curing resin used for attaching a magnet structure and suction power, The 14th Scientific
Meeting of the Japanese Society of Magnetic Applications in Dentistry, Kitakyusyu, 2005.
2. S. Endo, T. Ishigami, K. Miyata, et al.: Hardening time of Self-curing resin for Installing
Magnets and Removing Denture, The 18th Scientific Meeting of the Japanese Society ofMagnetic Applications in Dentistry, Morioka, 2009.
3. K. Suda, Y. Umekawa, M. Hasegawa, et al.: The retentive force measurement of magnetic
attachment in ISO measurement jig using a linear ball slide, The 22th Scientific Meeting of theJapanese Society of Magnetic Applications in Dentistry, Noboribetsu, 2013.