Impact response of different materials for sports mouthguards

M. Mo ei a e alii, F a u a ed In eg i à S u u ale, 57 (2021) 63-69; DOI: 10.3221/IGF-ESIS.57.06 63 Impac esponse o di e en ma e ials o spo s mou hgua ds Ma ia Mo ei a, João Ca los Ramos FMUC, Dep. o Den al Medicine, Uni e si y o Coimb a, Coimb a, Po ugal [email p o ec ed]om; [email p o ec ed], h ps://o cid.o g/0000-0003-1965-1092 Ana Messias, Ma ia Augus a Ne o, Ana Ama o, P.N.B. Reis Uni e si y o Coimb a, CEMMPRE, Dep. o Mechanical Enginee ing, Coimb a, Po ugal [email p o ec ed], h ps://o cid.o g/0000-0003-4019-9379 [email p o ec ed], h ps://o cid.o g/0000-0003-3030-0146 [email p o ec ed], h ps://o cid.o g/0000-0001-5237-0773 [email p o ec ed], h p://o cid.o g/0000-0001-5203-3670 A BSTRACT . Up o his momen , he e is no guideline ega ding he ma e ials o p oduce mou hgua ds. The mos used is E hylene-Vinyl Ace a e (EVA). S udies indica e ha lamina ing EVA shee s wi h igid componen s could inc ease he p o ec ion capaci ies o he mou hgua ds. On he o he hand, o he s udies sugges ha only eplacemen o he ma e ial wi hin i s s uc u e can inc ease ene gy abso p ion. The e o e, his wo k aims o e alua e he impac esponse o ou di e en oils when compa ed o a 4 mm hickness EVA shee . Fi e di e en ma e ials we e subjec ed o impac es s wi h ene gies o 1.72 J, 2.85 J and 4.40 J. In his con ex was conside ed he ollowing ma e ials: EVA oils (G1), EVA oils wi h an EVA oam co e (G2), EVA oils wi h an ace a e co e (G3), Foils o E koloc-p o (G4) and Foils o O ho IBT esin (G5). Compa isons be ween he ma e ials we e made by quali a i e analysis o he a e age ene gy- ime and load-displacemen cu es, as well as by compa ison o he peak load, maximum displacemen , con ac ime and abso bed ene gy using he K uskal-Wallis es . I was possible o conclude ha s a is ically signi ican di e ences we e ound in he ene gy abso bed (p=0.001). Lamina ed oils wi h a so co e (G2) a e a good op ion o p oduce mou hgua ds, while EVA oils wi h an ace a e co e (G3) and oils o O ho IBT esin (G5) we e decla ed unsui able. K EYWORDS . Mou hgua d; Impac esponse; The mo o ming oil; Mechanical es ing. Ci a ion: Mo ei a, M., Ramos, J.C., Messias, A., Ne o, M. A., Ama o, A., Reis, P.N.B., Impac esponse o di e en ma e ials o spo s mou hgua ds, F a u a ed In eg i à S u u ale, 57 (2021) 63-69. Recei ed: 29.04.2021 Accep ed: 13.05.2021 Published: 01.07.2021 Copy igh : © 2021 This is an open access a icle unde he e ms o he CC-BY 4.0, which pe mi s un es ic ed use, dis ibu ion, and ep oduc ion in any medium, p o ided he o iginal au ho and sou ce a e c edi ed. M. Mo ei a e alii, F a u a ed In eg i à S u u ale, 57 (2021) 63-69; DOI: 10.3221/IGF-ESIS.57.06 64 INTRODUCTION is known ha collision o con ac spo s and some ec ea ional ac i i ies can expose p ac i ione s o ha m ul impac s in he o o acial egion, wi h he associa ed isk o inju y. Despi e he cu en call o p e en ion in he heal h a ea, s udies de eloped by G een [1] and Knapik e al. [2] e eal ha he incidence and p e alence o o o acial lesions end o inc ease. Bou guignon and Sigu dsson [3] es ima ed, o example, ha 14% o 25% o child en, adolescen s and young adul s can be he a ge o a leas one auma ic episode in hei li e ime. The e o e, in pa icula , a hle es who p ac ice collision o con ac spo s a e ad ised o use sa e y de ices, such as mou hgua ds, o minimize he isk o auma ic inju ies. Se e al au ho s e en claim ha p ope ly adjus ed mou hgua d educes he incidence o o o acial inju ies in spo s [4-6]. Fo his pu pose, he e a e h ee ypes o mou hgua ds: Ready-Made o S ock Mou h gua d; he Mou h-Fo med “Boil-And- Bi e” and he Cus om-Fi ed Mou h gua d, which is conside ed he bes p o ec ion o ee h, lips and jaw, because i is done by a den is o den al echnician and can be adap ed o he a hle e’s mou h [7]. Acco ding o Bas ian e al. [8] he boil and- bi e mou hgua ds we e he mos ecommended by o hodon is s. Howe e , mos pa ien s who used hese mou hgua ds epo ed o ge ulness as he mos equen eason o no always using hem due o he discom o c ea ed. On he o he hand, some a hle es do no use mou hgua ds because hey conside ha i a ec s pe o mance and p omo es some discom o [9], bu Fe ei a e al. [10] cla i y ha mou hgua ds do no impai he a hle e’s pe o mance. Acco ding o Ame ican Den is y Associa ion Council (see h ps://www.ada.o g/en/membe -cen e /o al-heal h- opics/mou hgua ds), a mou hgua d should no only p o ec ee h and su ounding s uc u es bu also p e en inges ion o inhala ion in case o loss o ac u ed ee h. Also, i mus be made o esilien ma e ials able o dissipa e he o ces applied du ing an impac and o educe he de lec ion ansmi ed o he unde lying s uc u es. The open li e a u e [1, 3, 11, 12] also epo s ha such de ices should be psychologically and physically com o able o he pa ien . Howe e , up o his momen , he e is no guideline ega ding he ma e ials o p oduce mou hgua ds, bu G een [1] and Fukasawa e al. [13] indica e ha E hylene-Vinyl Ace a e (EVA), a he moplas ic co-polyme , is he mos used ma e ial in hese componen s. Ne e heless, he highe inyl ace a e con en p omo es g ea e lexibili y o EVA oils, which is e lec ed in lowe s i ness and ha dness. On he o he hand, highe damping capaci y and, consequen ly, be e ene gy abso p ion. In his con ex , Knapik e al. [2] epo ha , al hough la ex ubbe was a ma e ial widely used in he i s mou hgua ds, i has less shock abso p ion, less ha dness and less ea and ensile s eng h han EVA o polyu e hane. Kado a e al. [14] use mou hgua ds wi h 3 mm o EVA o p o ec weak pe iodon al issue o child en, in which he hickness o he shee is conside ed a de e mining ac o o he educ ion o he ex e nal o ce o ee h. Howe e , o Wes e man e al. [15] his minimum hickness mus be be ween 3 and 4 mm o abso b ene gy and educe he o ces ansmi ed when impac ed. These au ho s also men ion ha he e is an in e se p opo ion be ween he shock abso p ion capaci ies and he hickness o he mou hgua d. Ne e heless, acco ding o Aus alian Den al Associa ion, a minimum hickness o 4 mm is equi ed o he labial lange o a mou hgua d. Mo ei a e al. [16] de eloped s udies using a cus om-made mou hgua d p oduced by he E ko o m 3D Mo ion wi h he Occlu o m-3 accesso y conside ing wo plaques o e hyl inyl ace a e 4 mm and 2 mm hick and ound ha he e we e no s a ically signi ican di e ences conce ning he e en ion pa ame e s. On he o he hand, Takeda e al. [17] and Lun e al. [18] epo ha highe alues o hickness o mou hgua ds imp o e he p o ec ion because hey inc ease he abso bed ene gy, bu excessi e hicknesses impai he a hle es’ com o and pe o mance. Consequen ly, i comp omises he use o mou hgua ds in c i ical si ua ions. Besides ha , Lun e al. [18] concluded ha only he combina ion o di e en ma e ials, EVA wi h igid lamina es sandwiches and/o addi ional ai spacing, is possible o p omo e signi ican imp o emen s in he le el o p o ec ion. EVA polyme ic oams ha e gained inc easing impo ance due o a unique combina ion o p ope ies, such as good damping pe o mance, ligh ness, good ageing, chemical esis ance and ine ness. In his con ex , he open li e a u e epo s signi ican bene i s in e ms o abso bed ene gy when ai cells a e in oduced wi hin he EVA shee hickness o wi h he addi ion o oaming agen s [1, 3, 13, 19]. Howe e , he main disad an age o he cu en s anda d o p oduc ion o cus omized mou hgua ds is he ab ica ion p ocess ha equi es wo appoin men s - one o imp ession- aking and ano he o inse ion and a hle e ins uc ion – and implies was ing he excess o he ma e ial, inc easing he associa ed cos s. 3D p in ing could be he solu ion o o e come his limi a ion. New ma e ials wi h sho e A ha dness simila o ha o EVA oils ha e become a ailable and could be use ul o p oduce mou hgua ds, gua an eeing he equi ed p ecision and p e en ing ma e ial was e [1, 2]. Al hough all op ions ha e been widely used in o he spo s o e en in he de elopmen o passi e sa e y ma s o a hle es, om a scien i ic poin o iew, he e a e s ill ew s udies ega ding he mechanical cha ac e iza ion o hese ma e ials o applica ion in mou hgua ds. The e o e, his s udy in ends o e alua e he esponse o he impac o i e ma e ials o ob ain an a chi ec u e wi h be e pe o mance. In his con ex , i can eplace he con en ional EVA in mou hgua ds. Fo his I M. Mo ei a e alii, F a u a ed In eg i à S u u ale, 57 (2021) 63-69; DOI: 10.3221/IGF-ESIS.57.06 65 pu pose, he ollowing ma e ials will be conside ed: EVA oils, EVA oils wi h an EVA oam co e, EVA oils wi h an ace a e co e, Foils o E koloc-p o and Foils o O ho IBT esin. Impac es s we e ca ied ou wi h ene gies o 1.72 J, 2.85 J and 4.40 J, and he esul s compa ed wi h hose ob ained wi h EVA. E XPERIMENTAL PROCEDURE i e g oups o he mo o ming oils, con enien ly desc ibed in Tab. 1, we e p epa ed o pe o m low eloci y impac es s by d op-weigh . The i s g oup used EVA, conside ed a gene ic oil wi h a inyl ace a e a io <0.3 % and Sho e A 82 ha dness. Fo he EVA_SOFT and EVA_HARD g oups, lamina ed oils we e p oduced using a ho p ess machine and by he moulding echnique. E koloc-p o oils (wi h he ha d side o PETG and he so side o TPU) om E koden ® wi h 3 mm we e used in he ERKOLOC g oup. Finally, in he RESIN_IBT g oup, he oils we e p in ed on he Nex Den ™ 5100 3D p in e . The chosen ma e ial was Nex Den Indi ec Bonding T ay (O ho IBT), a monome based on ac ylic es e s wi h Sho e A ha dness simila o EVA. G oup/Ma e ial Thickness S uc u e EVA EVA 4 mm EVA_SOFT EVA + EVA oam 1.5 mm EVA+2 mm EVA oam+1.5 mm EVA EVA_HARD EVA + Ace a e 2 mm EVA+0.5 mm ace a e+2 mm EVA ERKOLOC PETG co-polyes e + The m. polyu e hane 2 mm PETG+1 mm TPU RESIN_IBT Alipha ic U e hane Ac yla e Oligome 4 mm Table 1: Ma e ials analysed in his s udy. The low eloci y impac es s we e ca ied ou using a d op weigh - es ing machine Ins on-Ceas 9340. A 10 mm diame e impac o wi h a mass o 3.4 kg was used. The es was pe o med on ci cula sec ion samples o 55 mm and he impac o s okes a he cen e o he samples ob ained by cen ally suppo ing he 120x120 [mm] samples. Impac ene gies o 1.72 J, 2.85 J and 4.40 J we e applied, which co espond o impac eloci ies o 1 ms -1 , 1.29 ms -1 and 1.61 ms -1 , espec i ely. The es s we e ca ied ou a oom empe a u e and, o each g oup/condi ion, i e specimens we e es ed. Finally, compa isons be ween mou hgua d ma e ials we e made by quali a i e analysis o he a e age ene gy- ime and load- displacemen cu es, as well as by compa ison o he peak load (N), maximum displacemen (mm), impac ime (ms) and abso bed ene gy (J) using he K uskal-Wallis es . R ESULTS AND DISCUSSION om he impac es s ca ied ou , Fig. 1 shows he ypical cu es ob ained o all ma e ials es ed o he impac ene gy o 4.4 J. Howe e , he p o ile o hese cu es is ep esen a i e o all o he s ob ained o 1.72 J and 2.85 J. Howe e , i is no ed highe ene gies han 4.4 J o EVA and EVA_So , which a e a consequence o hese ma e ials' mechanical p ope ies. In ac , he pla es p oduced wi h hese ma e ials ha e a e y elas ic beha iou . Consequen ly, he displacemen is supe io , p oducing, in his case, highe ene gy alues. Fig. 1a) shows ypical ene gy- ime cu es, which show ha he impac ene gy was no high enough o p omo e ull pene a ion, because he impac o s icks in o specimens and ebound always. The beginning o he pla eau is coinciden wi h he loss o con ac be ween he s ike and he specimen. Hence, his ene gy coincides wi h he abso bed ene gy by he F F M. Mo ei a e alii, F a u a ed In eg i à S u u ale, 57 (2021) 63-69; DOI: 10.3221/IGF-ESIS.57.06 66 specimen [20, 21]. The e o e, he di e ence be ween his ene gy and he ene gy a peak load is he elas ic ene gy. On he o he hand, Fig. 1b) shows ypical load-displacemen cu es, whe e i is possible o obse e ha he load inc eases up o a maximum alue (P max ) ollowed by a d op a e he peak load. This d op is due o he loss o con ac be ween he s ike and specimen. Du ing unloading i is possible o see he in luence o he di e en oils s uc u e. Based on he esul s ob ained in hese es s, Tab. 2 p esen s he maximum load, maximum displacemen , con ac ime and abso bed ene gy, in e ms o a e age alues and s anda d de ia ion o all ma e ials. A s a is ical analysis was also pe o med eso ing o IBM SPSS ® S a is ics e sion 23. G oup compa isons we e made wi h he K uskal-Wallis es and all pos -hoc compa isons conside ing Bon e oni co ec ion. The signi icance le el was se a 0.05. S a is ically signi ican di e ences we e ound in he ene gy abso bed (p=0.001), ega dless o he impac ene gy. Fig. 2. Impac es wi h 4.40 J (a) a ia ion o ene gy in ime; (b) ela ion be ween load and displacemen . Figu e 1: Fo all ma e ials, ypical: a) ene gy e sus ime cu es; b) load e sus displacemen cu es. G oup/Ma e ial Peak Load [N] Max Displacemen [mm] Con ac ime [ms] Abso bed ene gy [J] EVA 511.8 (±25.6) a 20.1 (±0.6) a 18.8 (±0.5) a 3.5 (±0.3) EVA_SOFT 455.5 (±10.5) b,c 23.2 (±0.8) b 21.4 (±0.5) b,c 3.5 (±0.2) EVA_HARD 858.3 (±32.4) c 11.9 (±0.6) 12.7 (±0.6) b 4.1 (±0.1) a ERKOLOC 1549 (±24.9) a,b 7.2 (±0.1) a,b 6.5 (±0.1) 2.9 (±0.2) a,b RESIN_IBT 796.2 (±51.3) 11.9 (±0.9) 11.7 (±0.9) c 4.4 (±0.1) b p <0.001 * <0.001 * <0.001 * <0.001 * Values ep esen a e age (± ) s anda d de ia ion. Simila supe sc ip le e s indica e g oups ha p esen s a is ically signi ican di e ences a he 0.05 le el. Table 2: A e age alues o he peak load, maximum displacemen , and elas ic ecupe a ion a impac s o 4.4 J Pai wise compa isons indica e ha EVA_SOFT is s a is ically supe io o ERKOLOC ega ding maximum displacemen (p=0.006 and p<0.001, espec i ely) and con ac ime (p=0.006 and p<0.001, espec i ely). The EVA_SOFT g oup simul aneously p esen ed he highes con ac ime and he lowes alues o peak impac load. As epo ed by Ve dejo and Mills [22] and Mocian e al. [23], so damping sys ems, like his lamina ed oil, end o inc ease he con ac ime o impac s and, consequen ly, sp ead ene gy o e a la ge a ea, dec easing he damage in a local a ea. ERKOLOC p esen s a mean peak impac o ce, s a is ically supe io o EVA (p=0.017) and EVA_SOFT (p<0.001). EVA_HARD and RESIN_IBT p esen s he highe ene gy abso p ion by he impac o s a is ically supe io o ERKOLOC (p=0.001 and p<0.001, espec i ely). F om Tab. 2, o example, i is possible o ind an inc ease o abou 41.4% in he abso bed ene gy when he EVA_HARD ma e ial is compa ed wi h E koloc, bu in e ms o maximum load he e is a dec ease a ound 44.6%. This e idence can be epo ed in Fig. 2, whe e is shown he impac damage obse ed on all ma e ials wi h 4.4 J impac . A close obse a ion o he con ac a ea o he impac o e eals ba ely no iceable pe manen de o ma ion in EVA (a) and EVA_SOFT (b) oils. EVA_HARD (c) oils we e pe o a ed and showed a wide a ea o delamina ion su ounding he impac . ERKOLOC (d) showed he na owes a ea o con ac associa ed wi h punc u e ype pe manen associa ion. Though no pe manen de o ma ion was isible on he su ace o RESIN_IBT (e) i was clea ha he oil ac u ed. (a) (b) M. Mo ei a e alii, F a u a ed In eg i à S u u ale, 57 (2021) 63-69; DOI: 10.3221/IGF-ESIS.57.06 67 Finally, Tab. 3 p esen s he es o ed ene gy o all ma e ials and he impac ene gies o compa e he impac pe o mance in a wide ange o ene gies. O all he es ed ma e ials, i is possible o e i y ha he ones ha p esen ed he highes es o ed ene gy we e EVA and E kolock. The e o e, when compa ing hem, i appea s ha o he lowes impac ene gy (1.72 J) E koloc p esen s a es o ed ene gy a ound 7.5% lowe han ha ob ained wi h EVA. Howe e , when he impac ene gy inc eases, he es o ed ene gy ob ained wi h he E kolock ma e ial is highe han he alues obse ed wi h EVA. In his case, compa ed o EVA, inc eases o a ound 9.7% and 26.7% we e obse ed o E kolock, espec i ely, o impac ene gies o 2.85 J and 4.4 J. The e o e, o highe ene gies, E koloc shows mo e endency o es o e ene gy a e impac . On he o he hand, i is no iced ha o he impac ene gy o 4.4 J, EVA_SOFT was he second ma e ial ha p esen ed he highes es o ed ene gy, which means ha hese oils ha e a good impac abso p ion capaci y o impac s wi h high ene gy le els. These esul s a e in good ag eemen wi h hose ob ained by Mocian e al. [24]. Figu e 2: Impac damages obse ed o an impac ene gy o 4.4 J and o : (a) EVA; (b) EVA_SOFT; (c) EVA_HARD; (d) ERKOLOC; (e) RESIN_IBT. Impac Ene gy [J] Res o ed ene gy [%] EVA EVA_SOFT EVA_HARD ERKOLOC RESIN_IBT 1.72 53.4 (±6.4) 31.5 (±3.4) 28.0 (±2.0) 48.6 (±3.4) 7.3 (±0.9) 2.85 41.4 (±6.3) 25.6 (±5.1) 23.0 (±3.7) 45.0 (±0.7) 11.3 (±1.1) 4.4 30.2 (±6.5) 31.8 (±3.9) 14.4 (±2.3) 37.8 (±3.3) 7.3 (±0.8) Table 3: Res o ed ene gy ob ained o all ma e ials and impac ene gies. Possible mechanical imp o emen s in ha d laye s o hei inse s in mou hgua ds ma e ials ha e also been s udied. In his case, when he impac ene gy inc eases, he shee is pe o a ed, which means ha he ene gy is highe han he ma e ial can abso b. In ac , only e y small amoun s o ene gy a e abso bed in hese cases. Al hough ace a e p esen s adequa e ene gy abso p ion unde low impac ene gies, delamina ion o he oil was obse ed expe imen ally, which makes his ma e ial unsa e because, in hese condi ions, he peak load is ansmi ed o he o al s uc u es. G een [1], Takeda e al. [25] and Wes e man e al. [26] also showed ha sandwiching ha d laye s wi h so e EVA did no imp o e shock abso p ion abili y. In he p esen s udy, his phenomenon occu ed wi h an impac ene gy o 4.4 J in EVA_HARD ma e ial. 10mm a b c e d M. Mo ei a e alii, F a u a ed In eg i à S u u ale, 57 (2021) 63-69; DOI: 10.3221/IGF-ESIS.57.06 68 Rega ding he E koloc-p o oils, hey con ain polyes e and he moplas ic polyu e hane (TPU). These oils ha e high s abili y, biocompa ibili y, good elas ome ic p ope ies, good esis ance o a igue loads and low wa e abso p ion. Fo his s udy, 3 mm oils we e chosen. Ma e ials ha had highe impac loads (as seen on Fig. 1), like ERKOLOC, co espond o mo e b i le ma e ials. The load, in hese cases, d ops suddenly because o he damage and he ma e ial is se e ely punc u ed. Lowe impac load alues indica e less impac shock and, he e o e, impac a enua ion, as epo ed by Mocian e al. [23], Wes e man e al. [26] and Alexand a e al. [27]. Al hough delamina ion didn’ happen, he lowe pa o he skin was damaged wi h impac s o 4.4 J. These indings a e co obo a ed by he le el o pene a ion seen in Fig. 2. 3D p in ing is becoming popula among clinicians. Mcglumphy e al. [28] and Liang e al. [29], o example, ag ee ha he possibili y o educing ma e ial was e, cos s and imp o e accu acy make his echnology a ac i e. The ma e ial used in his s udy, O ho Resin IBT, is a monome based on ac ylic es e s, and i s selec ion was based on a ha dness sho e simila o EVA (A 85). The e o e, om Tabs. 2 and 3, i is possible o conclude ha RESIN_IBT is he ma e ial wi h he highes abso bed ene gy and, consequen ly, he ma e ial wi h he lowes es o ed ene gy (elas ic ene gy). Simila o he s udy de eloped by Mocian e al. [24], hese esul s indica e ha his ma e ial has a weak damping capaci y. Al hough no delamina ion is obse ed, i is no iced a cohesi e ac u e o he oil. Acco ding o he au ho s' bes knowledge, he e a e no da a a ailable in he li e a u e o compa ison. CONCLUSIONS was ound ha he inse ion o an in e media e laye wi h less s i ness han EVA (EVA_SOFT) is a good op ion o p oduce cus omized mou hgua ds, aking in o accoun i s high alues o displacemen . Rigid and hinne ma e ials (ERKOLOC) we e ound o be unsui able due o he damage associa ed, e en hough hey exhibi high le els o elas ic ene gy. I was also ound ha he mo o med oils made wi h semi- igid co e using ace a e su e delamina ion and, as he h ee-dimensionally p in ed ma e ials used in his s udy, a e no sui able o he p oduc ion o mou hgua ds. I is impo an o conside ha o he ma e ials migh sui as semi- igid co e and may no su e delamina ion, which would make hem sui able o his pu pose. 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