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International Journal for Research in Engineering Application & Management (IJREAM)
ISSN : 2454-9150 Special Issue - AMET-2019
116| AMET201926 @ MIT College of Engineering, Pune. Vol.05, Special Issue AMET-2019 DOI : 10.35291/2454-9150.2020.0121
Studies on Mouthguard Material Thickness for
Minimum Energy transfer to Skull –A Review
S.B.Girase, Assistant Professor, MIT college of Engineering,Pune. shailendra.girase@mitcoe.edu.in
Prof. Dr. B.S.Kothavale, Professor, MITCOE,Pune. basavraj.kothavale@mitcoe.edu.in
S.P.Shisode , Assistant Professor, MITCOE,Pune. shailendra.shisode@mitcoe.edu.in
C.K.Patil, Assistant Professor, MITCOE,Pune. chetan.patil @mitcoe.edu.in
Abstract: Mouthguards (MG) are used to reduce injuries during contact sports. Thickness of MG material is directly
related to amount of energy absorption ability and hence reduction in energy transfer to skull. Many studies had
shown that Ethylene Vinyl Acetate (EVA) is best suited material for MG. Studies had been conducted on EVA material
to find optimum thickness. As thickness of Material increases its Impact absorption ability is also increasing. Beyond 4
mm thickness its rate of energy absorption reduces very much, Also beyond 4 mm it is not comfortable for wearer.
Studies were also conducted on inclusion of air cells in EVA material and showed that its absorption ability increases
significantly. But detailed study using different materials, designs with different combinations were not conducted . So
there is need to conduct studies on it
Keywords: Mouth guard, Mouth Protector, Ethylene Vinyl Acetate, Impact absorption, contact sports
I. INTRODUCTION
Mouth guard is mainly used for absorbing and spreading
Impact energy during sporting activities. In both contact as
well as Non contact sports such as Rugby, Boxing and
Basketball, there are possibilities of orofacial damage such
as injuries to soft tissues and the temporomandibular joint,
tooth fracture, tooth displacement, bone fracture and hence
Injuries to skull. So to minimize possibilities of Injuries to
skull as well as to teeth, It is necessary to wear Mouth
Guard (MG). This will minimize Impact energy transfer to
Skull. The impact absorption ability of a MG is believed to
be proportional to its thickness . Therefore It is necessary to
make MG to be sufficiently thick to prevent an Injury.
There are some conflicts for thickness of MG material. To
date, Minimum thickness is assumed to be equal to 2mm to
4 mm and beyond 4 mm neither there is effectiveness in
terms Absorption capabilities nor it is comfortable for
wearing. Also material suggested was an ethylene vinyl
acetate (EVA) mouth guard with a Shore A hardness of
80.This material is having required properties such as Non-
toxic, high Tear resistance, high shock absorption
capabilities, sufficient molding capabilities By using Air
cells in EVA material its absorption capability is increasing
too much about 32%. But if MG material is reinforced with
Titanium material , there is no significant difference in
terms of shock absorption capacity. MG materials was been
tested for impact energy absorption by using drop-ball
and/or pendulum devices. Though EVA material was
proved best for absorbing Impact energy, still most of
researchers were agreed to improve the impact absorption
ability by improving designs and developing new materials
II. MOUTH GUARD MATERIAL
CHARACTERISTICS
The Clinical and physical requirements of MG materials
are as follows:
1] Non-Toxicity: It should not be Toxic
2] Comfort: It should be comfortable.
3] Taste: No Taste or odor
4] forming or molding: It must have higher forming
capabilities.
5] Elasticity : It must have Good elastic properties.
6] Shock absorption: It must have high shock absorption
capabilities.
7] Tear resistance: It must have high tear resistance
8] Water absorption: It must have low water absorption
properties as it could lead to change in dimension and loss
of retention in teeth.
All these properties are there in EVA material with shore
hardness of 80 and with ease of manufacture it is widely
accepted by many researchers. Also EVA copolymers is
capable of giving wide range of properties with Polyvinyl
acetate/polyethylene ratio and filler content.[4]
International Journal for Research in Engineering Application & Management (IJREAM)
ISSN : 2454-9150 Special Issue - AMET-2019
117| AMET201926 @ MIT College of Engineering, Pune. Vol.05, Special Issue AMET-2019 DOI : 10.35291/2454-9150.2020.0121
III. TESTING EQUIPMENT AND METHODS
Frontal-impact designs are much useful because their
findings correlate with the high incidence rates of trauma to
anterior teeth. Therefore most of researchers used Pendulum
type testing equipment as like an Izod or Charpy Impact
pendulum.
As shown in fig.1 Mechanical Parameters Strain, Load
and acceleration were measured by using Strain
Guage,Load cell and Accelerometer respectively.Resulting
values were amplified by strain amplifier converted into
electric voltage. Dynamic energy absorption tests were
performed by allowing steel ball to fall from a
predetermined height and height of Rebound were measured
by means of telescope . The ball was always dropped on
non impacted area . The energy of Absorption was
calculated from the difference in potential energy of the ball
between initial height and Rebound height and calculated by
the formula as
Absorbed Energy= mg(Ho-Hi)
Where M- Mass of Ball
g- Gravitational acceleration
Ho- Initial height
Hi- Rebound height
Fig. 1 Test equipment
Researchers had taken test by taking different thickness
EVA material ranging from 1mm to 6 mm. Some had tested
EVA with different combinations of layers of Sponge , Air
cell, steel arch, Titanium wires and used different materials
such as Bio-plast materials.
IV. RESULTS
As the thickness of material increases potential of material
to absorb shock also increases, but further increase in
thickness after 4 mm did not yield significant result from
shock absorption point of view. Results of shock
absorption of various thicknesses from 1mm to 6 mm were
recorded and observed that beyond 4 mm , there is no much
improvement in shock absorption[1],[2]
Maeda et al.[1] had taken test on steel ball and base ball i.e.
Hard and soft material and observed that Steel ball shows
clear results than base ball , also observed that there is no
significant shock absorption beyond 4mm thick material as
shown in fig.2
Fig.2 Impact forces and absorption abilities for steel ball
Westerman et al.[2] also got near about same results with
pendulum device and using EVA material . They Observed
that no significant decrease in Transmitted force after 4 mm
thick EVA. Table 1 shows values of Transmitted force and
Fig.3 shows its graphical representation.
Thickness (mm)
Mean Maximum Transmitted
force (KN)
2
15.7
3
11.4
4
4.38
5
4.03
6
3.91
Table-1 Mean Maximum Transmitted force (KN)
Fig 3 Mean Maximum Transmitted force (KN) and
thickness (mm)
De wet et.al.[5] they had done experimentation on A
pendulum-type device was used to exert force on the skull.
This device enabled an impulse of the same magnitude to be
exerted on a fixed skull for each type of mouth guard when
the pendulum was released from a Uniform height. The
principle of linear impulse Momentum was used to obtain
the results. The physical principle states that the change in
the linear momentum of a moving object (in this case, the
modal hammer) must be equal to the impulse on the
hammer had taken different combination of Materials and
observed that by including sponge material layer in EVA
International Journal for Research in Engineering Application & Management (IJREAM)
ISSN : 2454-9150 Special Issue - AMET-2019
118| AMET201926 @ MIT College of Engineering, Pune. Vol.05, Special Issue AMET-2019 DOI : 10.35291/2454-9150.2020.0121
layer gave best results of absorption of shock than by taking
only EVA material or with inclusion of steel material.
Kataoka et.al.[3] had taken test on EVA material with
and without Titanium wire mesh and observed that there is
additional layer of Titanium did not result beneficial effect
on shock absorption of Impact energy.
They prepared 20 artificial maxillae from a modified
polyether-based synthetic resin to simulate teeth, jawbone
and gingival. They mixed the polyether-resin with calcium
carbonate and barium to replicate the hard tissue structures
of the teeth, the pulp chamber contained a cellulose-based
filling with additions of aniline and other organic pigments.
For the bone, they used polyether-resin with an initial
particle size of 0.02 mm to get a porous structure in the
internal layers and a Shore hardness close to that of bone.
The gingiva also was prepared of polyether-resin in a
higher-viscosity mixture (15.000 centipoise) than that used
to replicate bone and with a Shore hardness of A-10 on the
Shore A Hardness Scale, a gauge of a material’s hardness,
human skin is 10 . They took silicone impressions from the
individual 20 maxillae by using impression material and
then cast stone models from the impressions. They
produced custom-made mouth guards from the individual
stone models.
V. DISCUSSION
An improvement in the absorption energy was initially
observed with an increase in the thickness. However, a
further increase in the thickness from 4 mm did yield a
smaller improvement in the energy absorption, This shows
that from the viewpoint of the energy absorption ability
only, the necessary thickness is 4 mm. Moreover, it
becomes necessary to improve impact absorption by
developing new materials. EVA materials are the most
commonly used in the manufacture of both mouth-formed
and custom-made MG. It is nontoxic and easy to use, it has
become widely accepted as a MG material. However, it
appears to be scope for further improvement. Materials
believed to improve energy absorption by using polyolefin
and polystyrene and by foaming of EVA can be used
.Although these new materials are believed to result in
improvement in energy absorption a detailed study remains
to be performed [1]
Thicker MG were often met with wearer resistance
because of discomfort from lip and cheek displacement,
speech interference and respiratory restrictions. At the
same time, very thin MG had well acceptance by users but
were very less efficient in terms of energy absorption and
transmitted forces. A number of factors play a part in the
final thickness of custom-made MG. They include the
fabricator’s perception of correct thickness and the user’s
acceptance of the thickness of the manufactured MG. Also,
various authorities suggests different thickness. Australian
dental association suggest a thickness of 2 mm for MG[2].
This suggests that it is necessary to improve the impact
absorption ability through improvements in the design of
the MG. Many studies had investigated the improvement
inthe impact absorption ability resulting from the use of
intermediate layers or an improvement in the MG material
itself. All these studies had stressed that the impact
absorption ability of the MG was improved by these
methods. These methods included the use of a modified 4
mm-thick EVA MG by inserting air cells, which reduced the
transmission of forces by 32% as compared with the
traditional EVA MG of the same thickness. A bilaminated
MG with a piece of sponge as an intermediate layer, which
showed the highest shock absorption as49% [1]
So there is a need for further experimentation. Many
more types and designs of MG should be tested and a
variety of thicknesses of materials (4-mm sheets) should be
used for the manufacturing of MG. Also direction of the
force of impact should be varied to assess the shock
absorption potential of the various MG when the force is
directed from the labial direction of the tooth instead of
from the frontal direction. The exact force at the point of
impact (on the labial tooth surface) should also be
measured.[5]
VI. CONCLUSION
The study suggests that
1] EVA is best suited material for Mouth guard , also
addition of layers of different material such as sponge
increases its shock absorption ability
2] From the energy absorption ability point of view, the
minimum thickness required to obtain sufficient energy
absorption is around 4 mm, which is generally too thick
from the point of view of player comfort. This finding
indicates the necessity of improving the impact absorption
ability of mouth guards by considering new design, different
combination of materials and developing new materials.
REFERENCES
[1] M.Maeda,M.Shibhusawa,K.Takayama “In search of Necessary
mouthguard thickness. Part 1: From viewpoint of shock absorption
ability”, J Jpn Prosthodont Soc 52: 211-219,2008 .
[2] Westerman B, Stringfellow PM, Eccleston JA, “EVA mouthguards:
how thick should they be?”,Dent Traumatol 2002; 18:24-27.
[3] Simony H.H.Kataoka, Frank C.Setzer,Eudes Gondim, Jr.and Celso
l.Calderia, “ Impact absorption and force dissipation of protective
mouthguards with or without titanium reinforcement”, JADA 2014;
145(9): 956-959
[4] B.M.Bishop,E.H.Devies, J.A.von Fraunhofer , “Materials for Mouth
Protector” MSc. Thesis ,Institute of Dental surgery, University of
London,England.
[5] Francois A.de Wet M Dent, Michiel Heyns,Johannes Pretorius, “
Shock absorption potential of different mouth guard materials” ,
Journal of Prosthetic Dentistry, Vol.82 no.3 pp 301-306.
