Development of a Simple Measuring Device of the Attractive Force withMagnetic Attachment － part 2 －○K. Shoji, Y. Nakamura, R. Kanbara, M. Takahasi1，Y. Takada1 and Y. Tanaka.
Department of Removable Prosthodontics School of Dentistry Aichi-Gakuin University
1

Division of Biomaterials, Tohoku University Graduate School of Dentistry

Abstract
The most effective attractive force measuring method of a dental magnetic attachment is considered to bea combination of biaxial jig and high sensitivity tension testing machine. The biaxial jig device wasdeveloped at the Aichi Gakuin School of Dentistry. The high sensitivity testing machine presently serves
as the standard testing device for magnetic attachment ISO measurements. Although this device permits
high accuracy measurements, it has a complex structure and high cost.
The Japanese Society of Magnetic Applications in Dentistry has developed an improved testing jig device
to improve upon the problems of the biaxial jig testing device. This improved jig design was simplified
from a biaxial measurement design to a uniaxial type which has also lowered the overall cost.
As the existing device measuring system utilizes the jig together with a high performance tension testingmachine, high versatility and performance are required for both jig and the tension testing machine.
The use of multiple devices required simplification and design improvements for efficiency ofmeasurements and reduction of cost. A simplified attractive force measuring device was thus developed thatincludes both jig and tension testing machine into a single unit. This paper reviews the measurement
accuracy and testing of the new device. The results demonstrate the utility and efficiency of this new
attractive force measurement device.

Introduction
The character of retentive force of magnetic attachments used in dentistry requires

specialized

methods of evaluation to determine the relative quantitative performance different magneticattachments.

Relative retention is a comparative measurement a magnetic attachment to the metallickeeper. Various studies have been conducted on magnetic attachment attractive force measurement
techniques at the Department of Removable Prosthodontics, School of Dentistry, Aichi-Gakuin University.
An effective dental magnetic attachment attractive force measuring technique has been recently developed.
This new technique utilizes a device that combines the a biaxial jig, previously devised at Aichi-Gakuin,
and an EZ test high-performance tension testing machine, which presently serves as an approved ISO
standard testing device.

Although independently the biaxial jig design itself permits high-accuracy of measurement, its complex
structure and high cost precludes ease of use. An improved jig device (hereafter “uniaxial jig”) has beendeveloped by the group, Japanese Society of Magnetic Applications in Dentistry, to improve upon biaxial
jig design. The improved jig was simplified from a biaxial to uniaxial design which simplified design andcost factors, increasing versatility.
While previous attractive force measuring systems rely on the compatibility and standardization capacityof the high-performance tension testing machine utilized. The inclusion of a standardized tension testingmachine apparatus with a uniaxial jig device was devised to improve upon standardization andcompatibility concerns.

Objective
The purpose of the present study was to develop a simplified attractive force measuring device thatcombines the an axial motion limiting jig device and tension testing machine. The combination device
design permits simplified manufacture while maintaining accurate capacity for attractive force
measurements, specifically useful for the uniform evaluation of different dental magnetic attachments. The
purpose of this study was to evaluate and test the measurement accuracy of such a new attachment
measuring device.

Material and method1.

Simplified attractive force measuring machine

The following shows a simplified attractive force measuring machine including a jig and tension testingmachine developed in the present study.
a. Device dimensions
The simplified attractive force measuring machine weights 5 kg, and is 120 mm in width, 105 mm in depth,
and 370 mm in height. This is less than half the size and weight of a conventional EZ-test tension testingmachine (Fig. 1).

b. Components
The uniaxial jig device was embedded into the measuring machine and fabricated using several
pre-manufactured products (Fig. 2).

The crosshead speed can be set, and a dashpot (KINECHEK, Meiyu) was installed to maintain the speed(Fig. 3). Figure 4 shows the inner structure of a dashpot. When the plunger rod is pushed in, speed ismaintained constant by oil pressure, and the rod is returned to its original position by the return action of astretched spring. The size of the inner oil droplet can be changed by adjusting the bottom scale to change
the speed.

Measurement value is displayed on the Digital Force Gauge (Imada) at the maximum load of 50 N and±0.2% FS measurement accuracy (Fig. 5).

c. Measuring mechanism
The measuring mechanism of a simplified attractive force measuring machine is shown in Figure 6. The
bottom right screw is a switch, and the lower jig assembly begins movement downward with its own
weight when the stopper is first unlocked. Speed is then controlled by a dashpot preventing acceleration,and measurement is therefore performed at constant speed. A certain minimum weight is required andapplied for appropriate descent movement.

d. Crosshead speed setting
The crosshead speed of the machine was set. Based on the previous studies, the crosshead speed isspecified at under 5 mm/min in ISO 13017. The time required for the jig to descend 5 mm was measured,and the crosshead speed was calculated. The crosshead speed was 4.4 mm/min at 18 on the scale, and,
therefore, the scale was set at 18 in the present study.

2. Attractive force measurementa. Measurement samples: A magnetic attachment (GIGAUSS C 600, GC) was used as a sample (Fig.
7).

b. Measurement conditions
Measurement was performed 10 times, and the average was taken as the final measurement. One sample
was used to avoid inter-product errors. The crosshead speed was 4.4 mm/min.
c. Measurement result verification of a simplified attractive force measuring machine
3. TestingThe results between the conventional system using biaxial jig and tension testing machine and the newsystem using uniaxial jig and tension testing machine were compared to evaluate the measurement
accuracy (Fig. 8).

Statistical Analysis was performed. Measurement results were evaluated using one-way analysis ofvariance and Scheffe Multiple Comparison Method.

Results
Table 1 shows the measurement results. The results were 5.81 N in the measuring method using a biaxial
jig, 5.71 N in the method using a uniaxial jig, and 5.79 N in the method using a newly-developed simplified
attractive force measuring machine. Statistical analysis demonstrated no significant difference between
the three groups.

Discussions
Prior to the development of the new testing device evaluated, a separate measurement jig andhigh-performance tension testing machine were necessary for the measurement magnetic attachment
attractive forces. The uniform testing of devices in a global environment requires improved standardizationand of both measuring devices and measuring frame. A measurement jig was previously accepted for a
global standards was developed by the Japanese Society of Magnetic Applications in Dentistry.
The use of the accepted measurement jig was found to be dependent upon testing machine
standardizations. A designed inclusion of the tension testing machine components within the measurement
jig was designed and developed at the Aichi-Gakuin School of Dentistry. The new attractive force
measuring machine that includes both jig and tension testing machine has been shown to provide highaccuracy and versatility combined with easy of manufacture and low cost. This measuring design has
been determined to be a suitable replacement for the previous conventional measuring system.
The newly-developed measurement machine was produced by combining pre-manufactured components.
The prior conventional method utilized a vertical direction pull using a separate high-performance tension
testing machine. The newly developed device drops the lower portion components along the guide frame toexert the separation power of a magnet (approximately 1.5 kg) and measures attractive force. The

conventional tension-testing machine requires complicated and precise mechanism to pull the machine inan elevated vertical direction using constant speed. The new machine utilizes normal gravity to permit
lowering of the machine which is resisted by the attachment device to be measured.
Both measurement techniques use vertical upward and downward movements. The new device manages
strong magnetic attachments by adding weight to the top part of the bearing for to increase separation force.
The simplified attractive force measuring machine developed in the present study is thus considered tomeet all conditions necessary for the magnetic attachment attractive force measurement. The new machineis reduced in size and overall costs compared to conventional tension testing machines. Virtually identicalattractive force measurement values can be more easily obtained under any worldwide environment, andthus facilitates inter-laboratory testing.

Conclusion
A simplified attractive force measuring machine including both jig and tension testing machine have beendeveloped. Comparative testing has demonstrated measurement accuracy and reproducibility, suggesting
acceptability and consideration as a uniform method and device for attractive force measurement.
The uniformity of access, small size, and availability of components, the new testing device presented as asimplified attractive force measuring device appears to facilitate and enable inter-laboratory testing ofattractive force measurements world wide.

References
1.

Yukyo Takada, ISO Management Committee, ISO Management Committee Journal Report, To
achieve international standardization of a dental magnetic attachment (Discussion) , Journal of The
Japanese Society of Magnetic Applications in Dentistry 20 (1): 81-85, 20112.

ISO13017 Dentistry-Magnetic attachments, International Organization for Standardization, 20123.

Yoshinori Nakamura, Mechanical Analysis of Overdenture and Magnetic Attachment using Finite
Element Method, Journal of Prosthodontics, 42: 234-245, 1998