Effect of crosshead speed on retentive force measured using a device
specified in ISO 13017:2020
M. Takahashi1, G. Togawa1, M. Kanyi2, H. Yamaguchi1,3 and Y. Takada1
1

Division of Dental Biomaterials, Tohoku University Graduate School of Dentistry
Moi Teaching and Referral Hospital, KENYA
3Division of Advanced Prosthetic Dentistry, Tohoku University Graduate School of Dentistry
2Introduction
Retentive force is one of the most important properties of dental magnetic attachments1). Retentive force
testing applies similar principle to tensile test. Tensile (pulling) forces applied to a dental magnetic
attachment until separation of the attachments occurs are measured2). In a tensile test, the appropriate
crosshead speed is specified based on the type of material used3-5). In 2009, Ogawa et al. evaluated theeffect of crosshead speed on the retentive force of a magnetic attachment, and concluded that there was nostatistically significant difference in retentive forces measured at crosshead speeds of 0.5 – 5.0 mm/min6).
Based on the result of this research; International-Organization-for-Standardization (ISO) 13017 publishedin 2012 specified that the retentive force should be measured at a crosshead speed of 5.0 mm/min or less7).
However, it was still difficult to measure retentive force with acceptable accuracy and repeatability. This
necessitated the development of a device for measuring retentive force with sufficient accuracy andrepeatability. Thereafter, ISO 13017 amendment 1 was published in 2015 with detailed specifications of adevice suitable for measuring the retentive force of dental magnetic attachments8).
An SC2/WG22 meeting under ISO/TC106 technical committee responsible for formulating a standard
that combines ISO 13017 and its amendment 1 started in 20179). In 2018 at the Milan meeting; a concernthat the retentive force measured at a crosshead speed of 5.0 mm/min was too fast emerged. Therecommendation was to maintain a crosshead speed of 2.0 mm/min or less. As a result, ISO 13017
published in 2020 specified that the crosshead speed should be 2.0 mm/min or less2). However, there is no
scientific evidence found that confirms the recommended cross head speed value of 2.0 mm/min. The study
done by Ogawa et al. in 2009 was done before specifications on the measuring device, in accordance withISO, were developed. Furthermore, the study only focused on closed magnetic circuit utilized by most of
the dental attachments. Open magnetic circuit is also utilized in some dental magnetic attachments albeit
rare. There are no other studies found which investigate the effect of crosshead speed on retentive force
values. It is important to investigate the effect of crosshead speed on retentive force of both closed andopen magnetic circuit attachment done on a device that matches the ISO 13017:2020 specifications.

ObjectiveThe aim of this study was to investigate the effect of crosshead speed on retentive force value measured
using a device specified in ISO 13017:2020.

Materials and Methods
Magnets and dental magnetic attachment
Magnets portray an open magnetic circuit. They form part of the components used to make dental
magnetic attachments. Two types of magnets and one type of magnetic attachment were used in this study.
One pair of cylindrical neodymium magnets (Nd-Fe-B: 4 mm in diameter and 2 mm in height, Trusco) andone pair of samarium-cobalt magnets (Sm-Co: 4 mm in diameter and 2 mm in height, Magna) wereprepared. GIGAUSS D600 (GC), a dental magnetic attachment that utilizes closed magnetic circuit, wasused in this study. Each set of magnets of the same type and the magnetic attachment was subjected toretentive force measurement five times.
Test procedure for measuring retentive force
The retentive force measuring device used in this study matches the basic description in ISO 13017:2020.
It was connected to a digital force gauge (ZPS, Imada). Retentive forces were measured and recorded inaccordance with the test procedure stipulated in ISO 13017:2020 and retentive force curves generated.
Crosshead speed was controlled by a universal testing machine (AGS-5kNG, Shimadzu).
Crosshead speed
Measurements were done at 19 different crosshead speeds (mm/min): 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15,20, 50, 100, 200, 300, 400 and 500. The retentive force value attained at the lowest speed of 0.5 mm/min
was used as a reference value. This concept was applied in both scenarios of magnet combinations andmagnetic attachment. The obtained data in comparison to reference value was statistically analyzed using
ANOVA and Tukey’s HSD test (α = 0.05).

Results and Discussion
1. Measured values of retentive force and crosshead speeds
Measured values of retentive force to crosshead speeds are shown in Figs. 1-3. There was no significant
difference (p>0.05) in the measured values obtained at crosshead speed of 0.5 – 50 mm/min in eachcombination. On the other hand, the measured values at 100 mm/min and more were significantly higher(p<0.01) than those obtained at 0.5 mm/min.

6.0

Nd-Fe-Bno significant difference

Retentive force (N)

5.0

4.0
3.0
2.0
1.0500

400

300

200

100502015109876543210.50.0
Crosshead speed (mm/min)Fig. 1 Measured values of retentive force to crosshead speeds in Nd-Fe-B magnets

4.0Sm-Cono significant difference

3.0
2.5

2.0
1.5
1.0

0.5

Crosshead speed (mm/min)Fig. 2 Measured values of retentive force to crosshead speeds in Sm-Co magnets

500

400

300

200

100502015109876543210.00.5Retentive force (N)

3.5

7.0

GIGAUSS

Retentive force (N)6.0

no significant difference

5.0

4.0
3.0

2.0
1.0
500

400

300

200

100502015109876543210.5

0.0
Crosshead speed (mm/min)Fig. 3 Measured values of retentive force to crosshead speeds in GIGAUSS magnetic attachment
Retentive force values of neodymium (Nd-Fe-B) magnet at different crosshead speeds are represented in
the form of a bar chart in Fig 4a whereas Fig 4b is a scatter diagram. Beyond 50 mm/min, the measuredvalues of retentive force increase with increase in crosshead speed. As shown in Fig. 4b; at crosshead speedof 100 mm/min and more, retentive force and crosshead speed show a strong positive correlation (R2 =0.995). Both Sm-Co and GIGAUSS show a strong positive correlation.
In all combinations, the measured retentive force value at crosshead speed of 50 mm/min was higher
than the reference value. The difference was not statistically significant. The crosshead speed above which
the parameter speed has no influence on retentive force values measured, was determined as theintersection between lines 𝑦 = 𝑎𝑥 + 𝑏 (linear approximate equation) and 𝑦 = 𝑐 (𝑐: reference value), asshown in Fig. 4b. The results are shown in Table 1.

5.5
Retentive force (N)

5.0

4.5

y = 0.0018x + 4.2336
R² = 0.995
5.0

4.5
y = 4.298

Crosshead speed (mm/min)

500

300

100

20108642

4.0
0.5

Retentive force (N)5.5

4.00100 200 300 400 500
Crosshead speed (mm/min)a: Bar graphb: Scatter diagram
Fig. 4 Retentive force and crosshead speed in Nd-Fe-B magnetsTable 1 The minimum crosshead speed that influences the retentive force values, derived from theregression analysis.
Nd-Fe-B
Sm-Co
GIGAUSS
Minimum speed (mm/min)
35.8
42.6
46.8

Although retentive forces can be accurately measured at crosshead speed of up to 50 mm/min using adevice as specified in the ISO 13017:2020; it is advisable to limit speed to approximately 35 mm/min basedon the above results. Ogawa et al. reported6) that retentive forces could be accurately measured at crosshead
speed of up to 5.0 mm/min. With the development of a high-performance device such as the one specified
in ISO 13017; retentive forces can be accurately measured at faster speeds of up to 35 mm/min. Crosshead
speed of 2.0 mm/min or less which is specified in ISO 13017:2020 is very slow albeit accurate.
2. Increase in measured values of retentive forces
There was a general increase in retentive forces with increase in crosshead speed. This may be attributed
to the influence of friction by the ball bearing slider and acceleration force required to induce movement of
the movable part of measuring device up to the set crosshead speed.
2.1 Effect of dynamic friction on measured values of retentive force
Two different types of dynamic friction forces exist: sliding friction and rolling friction. The low frictionball bearing slider used in the measuring device undergoes a rolling type of friction force. The coefficientof rolling friction increases with increase in the rolling speed. In spite of the sharp increase in crosshead
speed from 10 to 500 mm/min as shown in the retentive force curves Fig. 5 only the peak force values
showed a spike. The baseline force values measured remained steady. These results reveal that the impactof dynamic friction on measured values of retentive force is negligible.

8.0

8.0

6.0

Tensile force (N)Tensile force (N)peak increase

4.0
2.0

6.0
4.0
2.0

baseline is equal

0.0

0.0

0.0

2.0
4.0
6.0
Distance (mm)

8.0

0.0

2.0
4.0
6.0
Distance (mm)8.0

a: 10 mm/min
b: 500 mm/min
Fig. 5 Retentive force curves of Nd-Fe-B
2.2 Effect of acceleration motion force on measured values of retentive force
Fig. 6 shows the different forces acting on the movable part of the measuring device during retentive
force testing. At the start of the testing shown in Fig. 6a, the movable part of the measuring device requires
energy to change from the static state into motion at the set crosshead speed. The force that sets themovable part of device into motion can be derived on the basis of Newton's law of motion equation
𝐹 = 𝑚𝑎. The “𝑚” in the equation is equal to the mass of the movable part of device and apparent masscaused by the magnets under attractive force. When the set crosshead speed is attained, the set-up changes
from accelerated motion to uniform motion as shown in Fig. 6b. In the absence of force for acceleration,
the baseline force values do not change as they are not dependent on crosshead speeds Fig 5. Therefore, theforce required to accelerate the movable part is the main contributor towards the pattern of increased
measured values of retentive force with increase in crosshead speed.

Force for accelerating
the movable part
Weight of movable part

Friction force

Magnetic attractive force

a: Accelerated motion
b: Uniform motion
Fig. 6 Forces acting on movable part of measuring device
To measure the forces acting to the movable part of measuring device; retentive force measurements
were done with no magnet or keeper on the lower table. The resultant curves are shown in Fig. 7. At low
crosshead speed of 10 mm/min (Fig. 7a), the measured force values showed an initial steep rise thensmoothly stagnated after generation of a force sufficient to counter weight of the movable part and friction
force. Contrastingly, at high crosshead speeds of 500 mm/min (Fig. 7b), a peak representative of increased
force of acceleration exists before stagnation of values measured. Baseline force values for both high andlow crosshead speeds were equal. These results further demonstrated that the force of acceleration affected
the retentive force values measured. Therefore; crosshead speed has an effect on the retentive force values
measured.

3.0

3.0

Tensile force (N)Tensile force (N)peak appear

2.0

1.0

2.0
baseline is equal

1.0

0.0

0.0

0.0

2.0
Distance (mm)

4.0

0.0

2.0
Distance (mm)4.0

a: 10 mm/min
b: 500 mm/min
Fig. 7 Curves of net force on movable part of measuring device at low and high cross head speeds

Conclusion
Using the retentive force measuring device specified in ISO 13017:2020, it is possible to measureretentive forces of magnets and magnetic attachments accurately at crosshead speed of 35 mm/min.

Crosshead speeds higher than 50 mm/min, lead to higher measured values than the actual retentive force
due to an increase in force necessary to accelerate movable part of device to the set speed.

Acknowledgments
The authors gratefully acknowledge contributions from the following individuals of Tohoku University
School of Dentistry: Ms. Yuna OSAKA, Mr. Takumi ANDO and Mr. Kei ITO.

References
1. Y. Tanaka, New dental magnetic attachment, pp 2-90, Ishiyaku Publishers, Inc, Tokyo, 2016.
2. ISO 13017:2020. Dentistry — Magnetic attachments.
3. ISO 22674:2016. Dentistry — Metallic materials for fixed and removable restorations and appliances.
4. ISO 527-1:2012. Plastics — Determination of tensile properties — Part 1: General principles.
5. ISO 37:2017. Rubber, vulcanized or thermoplastic — Determination of tensile stress-strain properties.
6. Y. Ogawa, Y. Umekawa, T. Ishigami, Y. Takeuchi, N. Tsukimura, K. Ohtani and S. Ohno: Effect ofcrosshead speed on magnetic retentive force, J J Mag Dent, 18(2), 39–41, 2009.
7. ISO 13017:2012. Dentistry — Magnetic attachments.
8. ISO 13017:2012/Amd.1:2015 Dentistry — Magnetic attachments.
9. Y. Takada: The commission report of the ISO corresponding committee working toward theinternational standardization of dental magnetic attachments -ISO/TC106 meeting in Osaka-, J J MagDent, 29(1), 20–26, 2018.