EVA closed-cell foam and its effect on transmitted forces - Australian ...

<strong>EVA</strong> <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong> <strong>and</strong> <strong>its</strong> <strong>effect</strong> on transmitted forces in mouthguard material
B. Westerman* 1 , P.M. Stringfellow 2 , J.A. Eccleston 3 & D.J. Harbrow 4
1 Private practitioner, 2 Professional engineer, 3 Department of Mathematics, The University of Queensl<strong>and</strong>, 4 Department
of Dentistry, The University of Queensl<strong>and</strong>
Abstract
Mouthguards are worn to reduce oro-facial injuries in active sports <strong>and</strong> are usually made of ethylene vinyl acetate (<strong>EVA</strong>). The performance or
energy absorption <strong>and</strong> reduction in transmitted forces of these mouthguard materials can be improved, when impacted, by increasing the
thickness or by adding air-inclusions. Increased thickness can result, however, in impaired speech <strong>and</strong> reduced respiratory efficiency. Airinclusions,
on the other h<strong>and</strong>, reduce transmitted forces without increasing thickness. Studies have shown that air-<strong>cell</strong>s with controlled volumes
<strong>and</strong> <strong>cell</strong>-wall thickness reduce transmitted forces when impacted. It seems logical that air-<strong>cell</strong>s present in <strong>foam</strong>s but with indiscriminate gasinclusions
could also improve performance.
Foaming agents were added to ethylene vinyl acetate at different rates to produce samples of <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong> mouthguard material. These
samples contained indiscriminate gas-inclusions which were subsequently impacted with a pendulum impact rig. Transmitted forces through
these <strong>foam</strong> materials were compared with the same thickness of identical <strong>EVA</strong> material without <strong>foam</strong> inclusions.
Foamed <strong>EVA</strong> mouthguard material at 1, 5 <strong>and</strong> 10 percent by weight <strong>foam</strong>ing agent did not significantly improve energy absorption <strong>and</strong> reduce
transmitted forces when compared with non-<strong>foam</strong>ed <strong>EVA</strong> material.
Introduction
Energy absorption is an important characteristic of mouthguards which are worn to reduce injuries to the oro-facial complex in contact sports. 1-
4 Better performance of mouthguards through improved energy absorption <strong>and</strong> reductions in transmitted forces can be observed when
mouthguards are thicker 5-8or when air-inclusions are included in the mouthguard material. 9 However, thicker mouthguards result in impaired
speech <strong>and</strong> reduced respiratory efficiency in the wearer. 10 Air-inclusions have been shown to improve energy absorption, reduce the transmitted
forces <strong>and</strong> eliminate rebound within impacts with no corresponding increase in the thickness of the mouthguard. 11 Mouthguards are manufactured
most commonly from the ethylene vinyl acetate (<strong>EVA</strong>) polymer. It seems logical that <strong>foam</strong>s with gas inclusions in an <strong>EVA</strong> polymer would aid
energy absorption if used in the construction of sporting mouthguards. With a <strong>foam</strong> material, however, gas-<strong>cell</strong>s are formed in an indiscriminate
manner within the polymer.The aim of this study was to compare the transmitted forces through <strong>EVA</strong> mouthguard materials with gas-inclusions
which are formed by the <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong>ing process, with the same <strong>EVA</strong> polymer of the same thickness but without <strong>foam</strong>.
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<strong>EVA</strong> <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong> <strong>and</strong> <strong>its</strong> <strong>effect</strong> on transmitted forces in mouthguard material
B. Westerman* 1 , P.M. Stringfellow 2 , J.A. Eccleston 3 & D.J. Harbrow 4
1 Private practitioner, 2 Professional engineer, 3 Department of Mathematics, The University of Queensl<strong>and</strong>, 4 Department
of Dentistry, The University of Queensl<strong>and</strong>
Materials <strong>and</strong> Method
• Transmitted forces measured through samples of <strong>EVA</strong> (4mm thick), with <strong>and</strong> without <strong>foam</strong>
• <strong>EVA</strong> had Shore A Hardness of 3
• Test impacts all 4.4 joules <strong>and</strong> 3 meters per second velocity
• Constant impacts produced by impact pendulum
• Samples included 0, 1, 5, <strong>and</strong> 10 % <strong>foam</strong>ing agent
• Foaming agent Hydrocerol (citric acid/bicarbonate of soda)
• Flat circular impact head, 12.5 mm in diameter
• 20 test impacts on each sample (different site each time)
• Force sensor measured transmitted forces
• Minitab <strong>and</strong> Excel used for statistical analysis
Results
The cut surface of un<strong>foam</strong>ed <strong>EVA</strong> material showed a homogenous texture with little more than fine score marks from the razor’s edge as it
sectioned through the material. Addition of <strong>foam</strong>ing agent to the <strong>EVA</strong> polymer mixture resulted in the formation of irregular gas inclusions. <strong>EVA</strong>
material containing 1.0 % <strong>foam</strong>ing agent had occasional inclusions of approximately 20 mm diameter. However with increasing concentration
of <strong>foam</strong>ing agent the inclusions became larger <strong>and</strong> more heterogenous in size. <strong>EVA</strong> polymer material containing 10% <strong>foam</strong>ing agent showed
this <strong>effect</strong> the most clearly. The inclusions ranged in size from less than 100 mm diameter <strong>and</strong> regular in shape, to inclusions larger than 1.0mm
diameter <strong>and</strong> irregular in shape. The large inclusions tended to be located in deeper regions of the disc material about 0.5 mm from the surface,
with this region becoming more clearly defined with increasing concentration of the <strong>foam</strong>ing agent.
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<strong>EVA</strong> <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong> <strong>and</strong> <strong>its</strong> <strong>effect</strong> on transmitted forces in mouthguard material
B. Westerman* 1 , P.M. Stringfellow 2 , J.A. Eccleston 3 & D.J. Harbrow 4
1 Private practitioner, 2 Professional engineer, 3 Department of Mathematics, The University of Queensl<strong>and</strong>, 4 Department
of Dentistry, The University of Queensl<strong>and</strong>
The different mean maximum transmitted forces through the various materials are shown in Table 1. The <strong>EVA</strong> material without <strong>foam</strong> transmitted
a force of 4.04 kN. Of the <strong>foam</strong>ed materials, the best energy absorption <strong>and</strong> least transmitted force occurred with the ten percent-by-weight
<strong>foam</strong>ed polymer which transmitted a force of 3.88 kN. Figure 1 illustrates the mean maximum transmitted forces graphically.
A one-way analysis of variance was completed on the test data. The maximum transmitted force for each set of five impacts per sample were
averaged for each test material <strong>and</strong> the control. Analysis was performed on these averages <strong>and</strong> no significant differences were found between
the tested samples. Although there were small differences between the various levels of <strong>foam</strong>ing, these were not statistically significant.
Discussion
The impact results from the indiscriminate addition of gas by <strong>foam</strong>ing in <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong>s can be compared with other air-inclusions in
mouthguard materials. A previous study identified the reduction in transmitted forces through samples made from Stay-guard material (Rudolf
Gunz <strong>and</strong> Co., Sydney). This commercially available <strong>EVA</strong> polymer with a Shore A Hardness of 85 <strong>and</strong> the same thickness of 4mm showed
more than 30 percent reduction in transmitted force when impacted with a similar force. This compares with a reduction of 4.96 percent in the
transmitted force with the present study of <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong>.
The earlier study featured air-inclusions in which the air-<strong>cell</strong>s were all the same dimension throughout the test samples. The volumes of the air<strong>cell</strong>s
were also constant at either 8 cubic millimeters (2x2x2mm) or 18 cubic millimeters (3x3x2 mm). The wall thickness between air-<strong>cell</strong>s was
also controlled at either one or two millimeters. This contrasts with the <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong> where the formation of gas-inclusions provided variable
<strong>cell</strong> volume <strong>and</strong> wall thickness.
There was also a slight difference in the Shore A Hardness of the polymers in the two studies with the different air or gas inclusions. The early
study used an <strong>EVA</strong> polymer with a Shore A Hardness of 85 while the latter showed a Shore A Hardness of 83. It would be expected that the
harder material (85) would transmit more force because of <strong>its</strong> greater hardness <strong>and</strong> reduced elasticity. However, the transmitted forces through
the air-inclusion material with fixed air-<strong>cell</strong> volume <strong>and</strong> wall thickness were reduced by 32 percent when compared with the <strong>EVA</strong> polymer
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<strong>EVA</strong> <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong> <strong>and</strong> <strong>its</strong> <strong>effect</strong> on transmitted forces in mouthguard material
B. Westerman* 1 , P.M. Stringfellow 2 , J.A. Eccleston 3 & D.J. Harbrow 4
1 Private practitioner, 2 Professional engineer, 3 Department of Mathematics, The University of Queensl<strong>and</strong>, 4 Department
of Dentistry, The University of Queensl<strong>and</strong>
without air-<strong>cell</strong>s. In contrast, <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong> <strong>EVA</strong> polymer showed a 4.96 percent reduction in transmitted forces compared with <strong>EVA</strong> without
the gas inclusions. The reduction in transmitted forces under the same conditions (magnitude of test impact force, thickness of test samples
<strong>and</strong> similar air-conditioned environment) <strong>and</strong> with similar <strong>EVA</strong> polymers showed that the improvements in the <strong>foam</strong> <strong>EVA</strong> polymer were only one
sixth of those shown with the more controlled air-inclusions with regular volume <strong>and</strong> wall thickness.
Conclusions
The addition of <strong>foam</strong>ing agent to the <strong>EVA</strong> ( Shore A Hardness 83) commonly used in mouthguard materials produced <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong>s which
showed small increases in energy absorption, when impacted, compared with the same material without <strong>foam</strong>. Reductions of close to 5 percent
in transmitted forces in these <strong>foam</strong> materials contrasted with the larger air-inclusions with fixed air-<strong>cell</strong> volume <strong>and</strong> wall thickness which
demonstrated a 32 percent reduction in transmitted forces.
Closed-<strong>cell</strong> <strong>foam</strong> <strong>EVA</strong> plastics with up to 10 percent by weight <strong>foam</strong>ing agent <strong>and</strong> with indiscriminate gas-inclusions do not provide statistically
significant improvements in energy absorption <strong>and</strong> reductions in transmitted forces when compared with non-<strong>foam</strong>ed <strong>EVA</strong> polymers.
Acknowledgments
This study was supported by a grant from the Australian Dental Research Foundation Inc.
The authors also thank Frank <strong>and</strong> John Oskam for their assistance in preparing the <strong>foam</strong> materials.
References
Wood AW. Head protection- cranial, facial <strong>and</strong> dental in contact sports. Oral Health 62:23-33, 1972
Wei SH. Prevention of injuries to anterior teeth. Int Dent J 24:30-49, 1974
Garon MW, Merckle A, Wright JT. Mouth protectors <strong>and</strong> oral trauma: a study of adolescent football players. J Am Dent Assoc 12:663-6, 1986
Print
Index
Table of Contents
Quit

<strong>EVA</strong> <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong> <strong>and</strong> <strong>its</strong> <strong>effect</strong> on transmitted forces in mouthguard material
B. Westerman* 1 , P.M. Stringfellow 2 , J.A. Eccleston 3 & D.J. Harbrow 4
1 Private practitioner, 2 Professional engineer, 3 Department of Mathematics, The University of Queensl<strong>and</strong>, 4 Department
of Dentistry, The University of Queensl<strong>and</strong>
Hickey JC, Morris AL, Caelson LD, Seward TE. The relation of mouth protectors to cranial pressure <strong>and</strong> deformation. J Am Dent Assoc 74:735-
40, 1967
De Wijn JR, Vrijhoef MMA, Versteegh PA, Strassen HP, Linn EW. A mechanical investigation to the functioning of mouthguards.
Biomedics:Principles <strong>and</strong> applications. The Hague:Martinus Nijhoff Publishers, 1982.
Park JB, Shaull KL, Overton B, Donly KJ. Improving mouthguards. J Prosthet Dent 72:373-380, 1994
Going RE, Loehman RE, Ming Sam Chan. Mouthguard materials: their physical <strong>and</strong> mechanical properties. J Am Dent Assoc 88:132-8, 1974
Westerman B, Stringfellow PM, Eccleston JA. Forces transmitted through <strong>EVA</strong> mouthguard matterials of different types <strong>and</strong> thickness. Aust
Dent J 40:389-391, 1995
Westerman B, Stringfellow PM, Eccleston JA. An improved mouthguard material. Aust Dent J 42:189-191, 1997
Francis KT, Brasher J. Physical <strong>effect</strong>s of wearing mouthguards. Br J Sports Med 25(4):227-31, 1991
Westerman B, Sringfellow PM, Eccleston JA. The beneficial <strong>effect</strong>s of air-inclusions on mouthguard performance. Submitted for publication
2001.
Print
Index
Table of Contents
Quit

<strong>EVA</strong> <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong> <strong>and</strong> <strong>its</strong> <strong>effect</strong> on transmitted forces in mouthguard material
B. Westerman* 1 , P.M. Stringfellow 2 , J.A. Eccleston 3 & D.J. Harbrow 4
1 Private practitioner, 2 Professional engineer, 3 Department of Mathematics, The University of Queensl<strong>and</strong>, 4 Department
of Dentistry, The University of Queensl<strong>and</strong>
Table 1. Mean maximum transmitted forces through <strong>foam</strong>ed <strong>and</strong> non-<strong>foam</strong>ed <strong>EVA</strong> mouthguard material (kN)
transmitted force (kN)
Foaming agent transmitted forces st<strong>and</strong>ard deviation
(% weight) (kN)
0.0 (control) 4.04 0.21
1.0 4.12 0.08
5.0 4.08 0.10
10.0 3.88 0.16
Figure 1. Mean maximum transmitted forces (kN) in <strong>foam</strong>ed <strong>and</strong> non-<strong>foam</strong> <strong>EVA</strong> mouthguard material - percentage <strong>foam</strong>ing agent
5.00E+00
4.00E+00
3.00E+00
2.00E+00
1.00E+00
0.00E+00
-1.00E+00
1
153
305
457
609
761
913
time (0.001seconds)
Print
0% <strong>foam</strong>
1% <strong>foam</strong>
5% <strong>foam</strong>
10% <strong>foam</strong>
Index
Table of Contents
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<strong>EVA</strong> <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong> <strong>and</strong> <strong>its</strong> <strong>effect</strong> on transmitted forces in mouthguard
material
B. Westerman* 1, P.M. Stringfellow 2, J.A. Eccleston 3 & D.J. Harbrow 4
1Private practitioner
2Professional engineer
3Department of Mathematics, The University of Queensl<strong>and</strong>
4Department of Dentistry, The University of Queensl<strong>and</strong>
ABSTRACT: Mouthguards are worn to reduce oro-facial injuries in active sports <strong>and</strong> are usually made of
ethylene vinyl acetate (<strong>EVA</strong>). The performance or energy absorption <strong>and</strong> reduction in transmitted forces of these
mouthguard materials can be improved, when impacted, by increasing the thickness or by adding air-inclusions.
Increased thickness can result, however, in impaired speech <strong>and</strong> reduced respiratory efficiency. Air-inclusions, on
the other h<strong>and</strong>, reduce transmitted forces without increasing thickness. Studies have shown that air-<strong>cell</strong>s with
controlled volumes <strong>and</strong> <strong>cell</strong>-wall thickness reduce transmitted forces when impacted. It seems logical that air-<strong>cell</strong>s
present in <strong>foam</strong>s but with indiscriminate gas-inclusions could also improve performance.
Foaming agents were added to ethylene vinyl acetate at different rates to produce samples of <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong>
mouthguard material. These samples contained indiscriminate gas-inclusions which were subsequently impacted
with a pendulum impact rig. Transmitted forces through these <strong>foam</strong> materials were compared with the same
thickness of identical <strong>EVA</strong> material without <strong>foam</strong> inclusions.
Foamed <strong>EVA</strong> mouthguard material at 1, 5 <strong>and</strong> 10 percent by weight <strong>foam</strong>ing agent did not significantly
improve energy absorption <strong>and</strong> reduce transmitted forces when compared with non-<strong>foam</strong>ed <strong>EVA</strong> material.
INTRODUCTION: Energy absorption is an important characteristic of mouthguards which are worn to reduce
injuries to the oro-facial complex in contact sports. 1-4 Better performance of mouthguards through improved energy
absorption <strong>and</strong> reductions in transmitted forces can be observed when mouthguards are thicker 5-8or when airinclusions
are included in the mouthguard material. 9 However, thicker mouthguards result in impaired speech <strong>and</strong>
reduced respiratory efficiency in the wearer. 10 Air-inclusions have been shown to improve energy absorption,
reduce the transmitted forces <strong>and</strong> eliminate rebound within impacts with no corresponding increase in the
thickness of the mouthguard. 11 Mouthguards are manufactured most commonly from the ethylene vinyl acetate
(<strong>EVA</strong>) polymer. It seems logical that <strong>foam</strong>s with gas inclusions in an <strong>EVA</strong> polymer would aid energy absorption if
used in the construction of sporting mouthguards. With a <strong>foam</strong> material, however, gas-<strong>cell</strong>s are formed in an
indiscriminate manner within the polymer.The aim of this study was to compare the transmitted forces through
<strong>EVA</strong> mouthguard materials with gas-inclusions which are formed by the <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong>ing process, with the
same <strong>EVA</strong> polymer of the same thickness but without <strong>foam</strong>.
MATERIALS AND METHOD:
• Transmitted forces measured through samples of <strong>EVA</strong> (4mm thick), with <strong>and</strong> without <strong>foam</strong>
• <strong>EVA</strong> had Shore A Hardness of 3
• Test impacts all 4.4 joules <strong>and</strong> 3 meters per second velocity
• Constant impacts produced by impact pendulum
• Samples included 0, 1, 5, <strong>and</strong> 10 % <strong>foam</strong>ing agent
• Foaming agent Hydrocerol (citric acid/bicarbonate of soda)
• Flat circular impact head, 12.5 mm in diameter
• 20 test impacts on each sample (different site each time)
• Force sensor measured transmitted forces
• Minitab <strong>and</strong> Excel used for statistical analysis
RESULTS: The cut surface of un<strong>foam</strong>ed <strong>EVA</strong> material showed a homogenous texture with little more than fine
score marks from the razor’s edge as it sectioned through the material. Addition of <strong>foam</strong>ing agent to the <strong>EVA</strong>
polymer mixture resulted in the formation of irregular gas inclusions. <strong>EVA</strong> material containing 1.0 % <strong>foam</strong>ing agent
had occasional inclusions of approximately 20 μm diameter. However with increasing concentration of <strong>foam</strong>ing
agent the inclusions became larger <strong>and</strong> more heterogenous in size. <strong>EVA</strong> polymer material containing 10%
<strong>foam</strong>ing agent showed this <strong>effect</strong> the most clearly. The inclusions ranged in size from less than 100 μm diameter
<strong>and</strong> regular in shape, to inclusions larger than 1.0mm diameter <strong>and</strong> irregular in shape. The large inclusions tended
to be located in deeper regions of the disc material about 0.5 mm from the surface, with this region becoming
more clearly defined with increasing concentration of the <strong>foam</strong>ing agent.
The different mean maximum transmitted forces through the various materials are shown in Table 1. The <strong>EVA</strong>
material without <strong>foam</strong> transmitted a force of 4.04 kN. Of the <strong>foam</strong>ed materials, the best energy absorption <strong>and</strong>
least transmitted force occurred with the ten percent-by-weight <strong>foam</strong>ed polymer which transmitted a force of 3.88
kN. Figure 1 illustrates the mean maximum transmitted forces graphically.

A one-way analysis of variance was completed on the test data. The maximum transmitted force for each set
of five impacts per sample were averaged for each test material <strong>and</strong> the control. Analysis was performed on these
averages <strong>and</strong> no significant differences were found between the tested samples. Although there were small
differences between the various levels of <strong>foam</strong>ing, these were not statistically significant.
DISCUSSION: The impact results from the indiscriminate addition of gas by <strong>foam</strong>ing in <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong>s can
be compared with other air-inclusions in mouthguard materials. A previous study identified the reduction in
transmitted forces through samples made from Stay-guard material (Rudolf Gunz <strong>and</strong> Co., Sydney). This
commercially available <strong>EVA</strong> polymer with a Shore A Hardness of 85 <strong>and</strong> the same thickness of 4mm showed
more than 30 percent reduction in transmitted force when impacted with a similar force. This compares with a
reduction of 4.96 percent in the transmitted force with the present study of <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong>.
The earlier study featured air-inclusions in which the air-<strong>cell</strong>s were all the same dimension throughout the test
samples. The volumes of the air-<strong>cell</strong>s were also constant at either 8 cubic millimeters (2x2x2mm) or 18 cubic
millimeters (3x3x2 mm). The wall thickness between air-<strong>cell</strong>s was also controlled at either one or two millimeters.
This contrasts with the <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong> where the formation of gas-inclusions provided variable <strong>cell</strong> volume <strong>and</strong>
wall thickness.
There was also a slight difference in the Shore A Hardness of the polymers in the two studies with the different
air or gas inclusions. The early study used an <strong>EVA</strong> polymer with a Shore A Hardness of 85 while the latter showed
a Shore A Hardness of 83. It would be expected that the harder material (85) would transmit more force because
of <strong>its</strong> greater hardness <strong>and</strong> reduced elasticity. However, the transmitted forces through the air-inclusion material
with fixed air-<strong>cell</strong> volume <strong>and</strong> wall thickness were reduced by 32 percent when compared with the <strong>EVA</strong> polymer
without air-<strong>cell</strong>s. In contrast, <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong> <strong>EVA</strong> polymer showed a 4.96 percent reduction in transmitted forces
compared with <strong>EVA</strong> without the gas inclusions. The reduction in transmitted forces under the same conditions
(magnitude of test impact force, thickness of test samples <strong>and</strong> similar air-conditioned environment) <strong>and</strong> with
similar <strong>EVA</strong> polymers showed that the improvements in the <strong>foam</strong> <strong>EVA</strong> polymer were only one sixth of those shown
with the more controlled air-inclusions with regular volume <strong>and</strong> wall thickness.
CONCLUSIONS: The addition of <strong>foam</strong>ing agent to the <strong>EVA</strong> ( Shore A Hardness 83) commonly used in
mouthguard materials produced <strong>closed</strong>-<strong>cell</strong> <strong>foam</strong>s which showed small increases in energy absorption, when
impacted, compared with the same material without <strong>foam</strong>. Reductions of close to 5 percent in transmitted forces in
these <strong>foam</strong> materials contrasted with the larger air-inclusions with fixed air-<strong>cell</strong> volume <strong>and</strong> wall thickness which
demonstrated a 32 percent reduction in transmitted forces.
Closed-<strong>cell</strong> <strong>foam</strong> <strong>EVA</strong> plastics with up to 10 percent by weight <strong>foam</strong>ing agent <strong>and</strong> with indiscriminate gasinclusions
do not provide statistically significant improvements in energy absorption <strong>and</strong> reductions in transmitted
forces when compared with non-<strong>foam</strong>ed <strong>EVA</strong> polymers.
ACKNOWLEDGEMENTS: This study was supported by a grant from the Australian Dental Research
Foundation Inc.
The authors also thank Frank <strong>and</strong> John Oskam for their assistance in preparing the <strong>foam</strong> materials.
REFERENCES:
1. Wood AW. Head protection- cranial, facial <strong>and</strong> dental in contact sports. Oral Health 62:23-33, 1972
2. Wei SH. Prevention of injuries to anterior teeth. Int Dent J 24:30-49, 1974
3. Garon MW, Merckle A, Wright JT. Mouth protectors <strong>and</strong> oral trauma: a study of adolescent football
players. J Am Dent Assoc 12:663-6, 1986
4. Hickey JC, Morris AL, Caelson LD, Seward TE. The relation of mouth protectors to cranial pressure <strong>and</strong>
deformation. J Am Dent Assoc 74:735-40, 1967
5. De Wijn JR, Vrijhoef MMA, Versteegh PA, Strassen HP, Linn EW. A mechanical investigation to the
functioning of mouthguards. Biomedics:Principles <strong>and</strong> applications. The Hague:Martinus Nijhoff
Publishers, 1982.
6. Park JB, Shaull KL, Overton B, Donly KJ. Improving mouthguards. J Prosthet Dent 72:373-380, 1994
7. Going RE, Loehman RE, Ming Sam Chan. Mouthguard materials: their physical <strong>and</strong> mechanical
properties. J Am Dent Assoc 88:132-8, 1974
8. Westerman B, Stringfellow PM, Eccleston JA. Forces transmitted through <strong>EVA</strong> mouthguard matterials of
different types <strong>and</strong> thickness. Aust Dent J 40:389-391, 1995
9. Westerman B, Stringfellow PM, Eccleston JA. An improved mouthguard material. Aust Dent J 42:189-
191, 1997
10. Francis KT, Brasher J. Physical <strong>effect</strong>s of wearing mouthguards. Br J Sports Med 25(4):227-31, 1991
11. Westerman B, Sringfellow PM, Eccleston JA. The beneficial <strong>effect</strong>s of air-inclusions on mouthguard
performance. Submitted for publication 2001.

Table 1. Mean maximum transmitted forces through <strong>foam</strong>ed <strong>and</strong> non-<strong>foam</strong>ed <strong>EVA</strong> mouthguard material (kN)
Foaming agent transmitted forces st<strong>and</strong>ard deviation
(% weight) (kN)
0.0 (control) 4.04 0.21
1.0
4.12 0.08
5.0 4.08 0.10
10.0
3.88 0.16
Figure 1. Mean maximum transmitted forces (kN) in <strong>foam</strong>ed <strong>and</strong> non-<strong>foam</strong> <strong>EVA</strong> mouthguard material -
percentage <strong>foam</strong>ing agent
transmitted force (kN)
5.00E+00
4.00E+00
3.00E+00
2.00E+00
1.00E+00
0.00E+00
-1.00E+00
1
153
305
457
609
761
913
time (0.001seconds)
0% <strong>foam</strong>
1% <strong>foam</strong>
5% <strong>foam</strong>
10% <strong>foam</strong>