Dental Traumatology 2002; 18: 24–27 Copyright C Munksgaard 2002Printed in Denmark . All rights reserved

DENTAL TRAUMATOLOGYISSN 1600-4469

EVA mouthguards: how thick shouldthey be?Westerman B, Stringfellow PM, Eccleston JA. EVA mouthguards: Bill Westerman1,how thick should they be? Dent Traumatol 2002; 18: 24–27. Peter M. Stringfellow2,C Munksgaard, 2002. John A. Eccleston3

1General practitioner and 2Professional engineer,Brisbane; 3Department of Mathematics, TheAbstract – A major consideration in the performance ofUniversity of Queensland, Brisbane, Australiamouthguards is their ability to absorb energy and reduce transmitted

forces when impacted. This is especially important to participantsin contact sports such as hockey or football. The thickness ofmouthguard materials is directly related to energy absorption andinversely related to transmitted forces when impacted. However,wearer comfort is also an important factor in their use. Thickermouthguards are not user-friendly. While thickness of materialover incisal edges and cusps of teeth is critical, just how thick shoulda mouthguard be and especially in these two areas? Transmittedforces through different thicknesses of the most commonly usedmouthguard material, ethylene vinyl acetate (EVA) (Shore AHardness of 80) were compared when impacted with identicalforces which were capable of damaging the oro-facial complex.The constant impact force used in the tests was produced by apendulum and had an energy of 4.4 joules and a velocity of 3 metersper second. Improvements in energy absorption and reductions in

Key words: EVA; mouthguards; thickness;transmitted forces were observed with increasing thickness. How-transmitted forcesever, these improvements lessened when the mouthguard materialBill Westerman, 500 Sandgate Road, Clayfieldthickness was greater than 4 mm. The results show that the opti-4011, Queensland, Australiamal thickness for EVA mouthguard material with a Shore A Hard- Tel: π61 7 3262 2768

ness of 80 is around 4 mm. Increased thickness, while improving Fax: π61 7 3262 2777performance marginally, results in less wearer comfort and accept- e-mail: billwesterman/mgard.com.au

ance. Accepted 1 June 2001

Mouthguards are used to reduce injuries to the oro-facial complex of participants in contact sports.Broken teeth, soft-tissue injuries, bone fractures andbrain concussion are all reduced in wearers ofmouthguards participating in sports which produceimpacts between players and/or sporting implements(1–6). The method of manufacture can be used todefine the two main types of mouthguards currentlyused in contact sports. The mouth-formedmouthguard is an appliance which is manufacturedby the user. The custom-made mouthguard, on theother hand, requires a dental impression, plastermodel of the teeth and specialised manufacturingtechniques for the fomation of an individual-specificmouthguard. There is little doubt that the superior fit

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of the custom-made technique provides a more ac-ceptable mouthguard for active sports. However, costcan influence the wearer’s choice of a mouthguard.Both mouth-formed and custom-made types are gen-erally made with ethylene vinyl acetate (EVA), whichhas been shown to have appropriate physical prop-erties for mouthguards (7).

The performance of mouthguards in terms of en-ergy absorption and transmitted forces has beenshown to improve with thickness (8, 9) or the in-clusion of air-cells (10). Greater thickness detractsfrom wearer comfort while air-inclusions increase en-ergy absorption without increasing thickness. Thickermouthguards reduce the capacity for speech as wellas interfering with respiratory efficiency (11).

How thick should EVA mouthguards be?

The thickness of finished mouthguards can also beinfluenced by their fabrication. While the thicknessof a mouth-formed mouthguard is influenced by thefabrication to a certain degree, the finished thicknessof custom-made mouthguards can be determined ac-curately and modified during fabrication.

Single-sheet EVA materials with thicknesses be-tween 3 mm and 5 mm are commonly used in thefabrication of custom-made mouthguards. Thicknesscan be adjusted by removing materials during fin-ishing or limiting thinning during manufacture. Thepressure-laminated manufacturing process allows thethickness of finished mouthguards to be adjusted withextra laminates or by material removal during forma-tion. The manufacturing process can also directly in-fluence the thickness of materials over the incisal edg-es and cusps in custom-made mouthguards either bythinning when heating the material or by stretchingthe mouthguard material on pull-down.

Various authorities have identified what they con-sider to be ideal thicknesses of mouthguards, particu-larly inthe areas of high impact stress, the incisal edg-es and cusps. The question which needs to be asked,however, ‘‘is there an ideal thickness of EVA materialsin these two areas?’’ The aim of this study was tocompare the transmitted forces through various thick-nesses of the most commonly used EVA mouthguardmaterials, when impacted with identical forces cap-able of damaging the oro-facial complex.

Material and methods

The ethylene vinyl acetate mouthguard material usedin this study was DrufosoftA (Dreve-DentamidGMBH, Unna, Germany), which had a Shore AHardness of 80. The various thicknesses tested in-cluded 1, 2, 3, 4, 5 and 6 mm sections. The testsamples of each thickness were impacted eight timesand each impact was on a new surface of the testmaterial. The test impacts were produced by a pen-dulum impact machine similar to an Izod or Charpyimpact pendulum as described in Australian Stan-dards (AS1544, 1989). The strike face on the pendu-lum was flat and circular with a diameter of 12.75mm. Transmitted forces through the EVAmouthguard materials were recorded with a forcesensor (model 2084; PCB, Depew, NY, USA) with asignal amplifier, conditioner (model F484 B06; PCB,Depew) and analyser (model 2200; Diagnostic Instru-ments, Livingston, Scotland).

Data and statistical analysis used Microsoft ExcelA

(Microsoft Corporation, Seattle, WA, USA) and Mini-tabA (Minitab Inc, State College, PA, USA). Statisti-cal tests were conducted at the 0.05 level of confi-dence. The energy of impact was 4.4 joules with avelocity of 3 meters per second. All tests were con-ducted in an air-conditioned room at 24æC.

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Table 1. Mean maximum transmitted forces (kN)

Thickness (mm) Mean maximum transmitted force

1 Not recorded2 15.703 11.404 4.385 4.036 3.91

Results

Table 1 describes the mean maximum transmittedforces through the various thicknesses of mouthguardmaterial. The greatest transmitted force was throughthe 1 mm samples but results were not recorded asthe force exceeded the performance envelope of theforce sensor. The 1 mm section material showed littleenergy absorption and minor reductions in trasmittedforces. The greatest recorded transmitted force wasthrough the 2 mm material, which transmitted a forceof 15.7 kN. The smallest transmitted force wasthrough the 6 mm material, which transmitted a forceof 3.91 kN. Fig. 1 shows the mean maximum trans-mitted forces through the materials when measured

Fig. 1. Mean maximum transmitted forces (kN).

Fig. 2. Mean maximum transmitted forces (kN) and thickness (mm).

Westerman et al.

by the force sensor with time and are shown graphi-cally.

This study shows that 2-mm-thick EVA provideslittle protection in terms of energy absorption, as ittransmitted a force of 15.70 kN, nearly four times theforce through the 4 mm material with the same im-pact force. Similarly, while there was an improvementof 27.4% in the transmitted forces over the 2 mmmaterial, the thicker 3 mm material transmitted morethan twice the force that was passed through the 4mm material when impacted with the same force.

Further increases in mouthguard material thicknessfrom 4 mm to 5 mm and 6 mm showed smaller im-provements in energy absorption and transmittedforces with 8% and 10.7% less force, respectively,than the 4 mm material. This reduction in transmit-ted forces was not statistically significant in the thickermaterials. Fig. 2 compares the transmitted forcesthrough the materials with different thicknesses.

An analysis of variance showed there were signifi-cant differences between the transmitted forces for thevarious thicknesses. Further, there was a significantdifference between the 2 mm and 3 mm thicknessescompared to the 4 mm, 5 mm and 6 mm thicknesses,while there was not a significant difference betweenthe 4 mm, 5 mm and 6 mm thicknesses.

Discussion

A commonly asked question by fabricators ofmouthguards is ‘‘How thick should I make amouthguard?’’ This question is more than likely a re-sponse to the realisation that energy absorption andthe resulting transmitted forces in mouthguards arelinked to the thickness of the material and that weareracceptance also often dictates the choice of amouthguard.

The EVA material used in this study is the mostcommonly used polymer in the manufacture ofmouth-formed and custom-made mouthguardsworld-wide. With a vinyl acetate composition whichprovides a Shore A Hardness of 80, its non-toxic na-ture, elasticity and ease of manufacture make it emi-nently acceptable as a mouthguard material.

The fabrication of mouthguards is often a compro-mise between thickness and wearer comfort. Thickermouthguards are often met with wearer resistance be-cause of discomfort from lip and cheek displacement,speech interference and also respiratory restrictions.At the same time, very thin mouthguards are wellaccepted by users but are far less efficient in terms ofenergy absorption and transmitted forces.

A number of factors play a part in the final thick-ness of custom-made mouthguards. They include thefabricator’s perception of ideal thickness and theuser’s acceptance of the thickness of the finishedmouthguard. As well, various authorities advocate

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different thicknesses. The Australian Dental Associ-ation (The Practical Guides, 6th edn., ISBN0 909961 34 4, Sydney) suggests a thickness of 2 mmon the occlusal aspect of mouthguards. This recom-mendation is for a thickness of 2 mm over incisal edg-es and cusps with a 4 mm thickness over the labialsurface of the mouthguard. This recommendationseems to reflect a notion that impacts to teeth willcome as direct blows from an external source. Incisaledge and cusp coverage is important because of thedanger not just of a direct blow to these areas butalso from a indirect impact from opposing teeth. Mostmouthguards cover the maxillary teeth only. How-ever, a blow to the mandible can result in involuntaryclosing of the mandible with impacts onto the cuspsand incisal edges of both maxillary and mandibulardentitions with resulting damage.

A laminated-mouthguard manufacturer (Playsafe,Melbourne, Australia) classifies its product rangethrough perceived impacts in various levels of contactsports. Thicker mouthguards are advocated for themore extreme sports and for older participants.

The manufacturing process itself can directly in-fluence the thickness of mouthguard material overcusps and incisal edges in finished mouthguards.When the mouthguard material is used as a dia-phragm which separates suction or pressure and adental model, thinning of the materials takes placeeither by thinning-on-heating, when ‘‘droop’’ indi-cates pull-down readiness, and/or stretching of thematerial in the forming process over the cusps andincisal edges. Either way, this thinning should be con-sidered in the final product in the raised sections onthe dental models. Previous studies have identified thegeneral association between thickness and energy ab-sorption. Thicker mouthguards were observed to bebetter interms of energy absorption but comparisonsof energy absorption and transmitted forces betweendifferent thicknesses of the same material were notexamined in detail.

The practical implication from these data is thatwhen EVA material with a Shore A Hardness of 80is used in mouthguard fabrication, there appears littleadvantage in increasing the thickness of material tomore than 4 mm at any point in the formedmouthguard where transmitted forces are concerned.

While this study has identified cusps and incisaledges as critical areas in terms of energy absorptionand transmitted forces, 4 mm seems to represent anideal thickness that should be used at any point inthe mouthguard which is likely to be impacted. Thisincludes the labial flange of the mouthguard, whichcovers the labial aspects of anterior teeth. It also rep-resents a useful compromise with thickness andwearer comfort.

Acknowledgment – This study was supported by a

How thick should EVA mouthguards be?

grant from the Australian Dental Research Founda-tion Inc.

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