Dégradation de la chaînette élastomérique dans la salive artificielle : étude in vitro

Original articleArticle original

� 2013 CEOPublished by / Edite par Elsevier Masson SAS

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Elastomeric chain force decay in artificialsaliva: An in vitro study

D�egradation de la chaınette �elastom�erique dans lasalive artificielle : �etude in vitro

Abdelali HALIMIa,*, Mohamed-Faouzi AZEROUALa, Anas DOUKKALIb,Khalid EL MABROUKc, Fatima ZAOUIa

aOral biomechanics and biotechnology research unit, University Mohammed V, Souissi (UM5S),College of dental medicine, Ibn Sina Hospital Center, Dentofacial orthopedics department,BP 6212, Rabat, MoroccobAnalytical chemistry laboratory, University Mohammed V, Souissi (UM5S), College ofmedicine and pharmacy, BP 6212, Rabat, MoroccocMASCIR Foundation (Science Marocaine Avanc�ee, Recherche et Innovation), INANOTECH(Institut des nanomat�eriaux et des nanotechnologies), ENSET avenue Royale de l’Arm�ee,Madinat El Irfane, Rabat, Morocco

Available online: 31 January 2013 / Disponible en ligne : 31 janvier 2013

SummaryIntroduction: The main objective of this study was to reexaminethe mechanical properties of elastomeric chains after stretchingin various artificial saliva solutions and in air.

Materials and methods: Five brands of elastomeric chain man-ufactured by different companies were selected. For each brand,four types were tested in different artificial media. A dismoun-table test kit was used to stretch the chains up to various initialforce levels. They were then immersed in pre-prepared solutions,with control samples exposed to air only. Residual force wasmeasured at multiple time points using a hand-helddynamometer.

Results and discussion: The force delivered by the elastomericchains decayed rapidly and differently over time. This decayvaried depending on multiple factors, discussed here.

� 2013 CEO. Published by Elsevier Masson SAS. All rightsreserved

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R�esum�e

Introduction: L’objectif principal de cette �etude est der�e �etudier les propri�et�es m�ecaniques des chaınettes�elastom�eriques apr�es �etirement dans diff�erentes solutionsde salive artificielle et dans l’air ambiant.Mat�eriels et m�ethode: Cinq marques de chaınettes�elastom�eriques fabriqu�ees par des soci�et�es diff�erentes ont�et�e s�electionn�ees pour l’�etude ; pour chaque marque quatretypes ont �et�e test�es dans diff�erents milieux artificiels. Leschaınettes ont �et�e �etir�ees a l’aide d’un kit d�emontable jusqu’aatteindre diff�erents niveaux de force initiale, puis immerg�eesdans les solutions pr�epar�ees tout en gardant un �echantillont�emoin dans l’air. La force r�esiduelle a �et�e mesur�eea diff�erentes reprises avec un dynamom�etre manuel.R�esultats et discussion: La force lib�er�ee par la chaınette�elastom�erique subit une d�egradation rapide et diff�erente dansle temps. Cette variabilit�e de la d�egradation est fonction deplusieurs facteurs qui sont discut�es.� 2013 CEO. Edite par Elsevier Masson SAS. Tous droitsreserves

*Correspondence and reprints / Correspondance et tir�es a part :

Abdelali HALIMI, Lotissement Wifak 1, immeuble 1422, appartement 20, Tamara,Morocco.e-mail address / Adresse e-mail : [email protected]

International Orthodontics 2013 ; 11 : 60-70doi:10.1016/j.ortho.2012.12.007

mailto: [email protected]

http://dx.doi.org/10.1016/j.ortho.2012.12.007

Elastomeric chain force decay in artificial saliva: An in vitro studyD�egradation de la chaınette �elastom�erique dans la salive artificielle : �etude in vitro

Key-words

·Elastomeric chains.
·Biodegradation. ·Biomechanics. ·Tooth movement.
·Orthodontics.
·In vitro study.
Introduction

Elastomeric chains are indispensable tools. They generate apart of the force needed to move teeth during leveling–align-ing–derotating, canine/incisor retraction, space closure, mid-line correction, orthodontic retention, mesial displacement ofthe posterior quadrants, and traction of impacted teeth (fig. 1).The way they behave inside the mouth, however, differs widelydepending on the circumstances.

Elastomeric chains come in different types: open (short/long)and closed. They can be transparent, gray, or other-colored.

Changes in the amount of force they deliver over time lead totherapeutic control problems that can affect their clinicalefficacy and efficiency. It is also sometimes difficult to choosefrom among the many different products available.Several studies (Table I) have reported chains losing 50–75%of their initial force on the first day of use, and then continuingto decay exponentially. This decay is due to intra-oral expo-sure, mastication, oral hygiene, salivary enzymes, and varia-tions in intra-oral temperature, which may accelerate theaging of the chain in vivo.

The main goal of this study was to assess the decay in the forcedelivered by elastomeric chains after stretching and exposureto various media, namely, artificial saliva of different pHlevels and air.We also had three secondary objectives:— to compare force decay in open and closed chains;

[(Fig._1)TD$FIG]

Fig. 1: Some clinical applications of elastomeric chains in orthodontics: aFig. 1 : Applications cliniques de la chaınette �elastom�erique en orthodont

lignes m�edianes incisives.

International Orthodontics 2013 ; 11 : 60-70

Mots-cl�es

·Chaınette �elastom�erique.�
·Biodegradation.� ·Biomecanique.
·D�eplacement dentaire.

·Orthodontie.�
·Etude in vitro.
Introduction

La chaınette est un outil incontournable, elle g�en�ere en partiela force du d�eplacement dentaire des phases d’alignement/nivellement, de la correction des rotations, des r�etractionscanine et incisive, de la fermeture des espaces, de la correc-tion des m�edianes, du maintien des dents entre elles, de lam�esialisation des secteurs post�erieurs et de la traction desdents incluses (fig. 1). Cependant, en milieu buccal, soncomportement diff�ere selon les situations.Les chaınettes �elastom�eriques existent sous diff�erentes for-mes : chaınettes a modules serr�es, chaınettes a modulesrapproch�es et chaınettes a modules espac�es. Elles peuventetre transparentes, grises, ou de diff�erentes couleurs.L’instabilit�e de la force qu’elle lib�ere dans le temps engendredes probl�emes du controle th�erapeutique pour son efficacit�eet son efficience clinique. La diversit�e de l’offre commercialeengendre un probl�eme de choix judicieux de cet outil.Plusieurs �etudes (Tableau I) rapportent que la chaınette pour-rait perdre de 50 a 75 % de sa force initiale pendant le premierjour d’application ; ensuite elle continue a se d�egrader d’unefacon exponentielle. Cette d�egradation s’explique par l’expo-sition intra-orale, l’effet de la mastication, l’hygi�ene orale, lesenzymes salivaires et la variation de la temp�erature buccalequi peut acc�el�erer son vieillissement in vivo.L’objectif principal de ce travail est d’�etudier la d�egradation dela force lib�er�ee par des chaınettes �elastom�eriques apr�es�etirement et exposition dans desmilieux diff�erents : une saliveartificielle avec des PH diff�erents et l’air ambiant.Ce travail a �egalement trois objectifs secondaires :— comparer les d�egradations de la chaınette serr�ee et de lachaınette espac�ee ;

: canine retraction; b: space closure; c: correction of incisor midlines.ie : a : r�etraction canine ; b : fermeture d’espaces ; c : correction des

61

Table IList of studies relevant to force decay over time.

Tableau IListe des �etudes qui s’int�eressent a la d�egradation de la forcelib�er�ee dans le temps.

Force decay over time/D�egradation de la force lib�er�ee dans le tempsAndreasen 1970 AO Unitek C-1 alastik modules and latex elastics/Unitek C-1 modules alastik et

�elastiques en latexHershey 1975 AJO Unitek C-1 alastik modules, Ormco Power Chain, TP Elast-O-Chain/Unitek C-1

modules alastik, Ormco Power Chain, TP Elast-O-ChainWong 1976 AO Unitek C-1 alastik modules, Ormco power chain/Unitek C-1 modules alastik, Ormco

power chainKovatch 1976 JDR Unitek C-1 alastik modules/Unitek C-1 modules alastikAsh 1978 JDR Unitek C-1 alastik modules/Unitek C-1 modules alastikBrantley 1979 AO Unitek C-1 alastik modules, Ormco Power Chain II/Unitek C-1 modules alastik,

Ormco Power Chain IIDe Genova 1985 AJO Ormco Power Chain II, Rocky mountain Energy chain, TP Elast-O-ChainRock 1985 BJO 13 different types of chain/13 types de chaınettes diff�erentesKilliany 1985 JCO Rocky Mountain Energy Chain/Kuster 1986 EJO Unitek C-1 alastik modules, Ormco Power Chain II/Unitek C-1 modules alastik,

Ormco Power Chain IIBaty 1992 IP Unitek C-1 alastik modules, Ormco Power Chain II and Masel colored chains/

Unitek C-1 modules alastik, Ormco Power Chain II et chaınettes color�ees MaselEliades 2003 HOR Open and closed chain types (ORMCO)/Types de chaınettes �elastom�eriques

ouvertes et serr�ees (ORMCO)Chimenti 2001 PO 6 different types of elastomeric chain, total of 312 chains/6 diff�erents types de

chaınettes �elastom�eriques sur un total de 312 chaınettes �elastom�eriquesEliades 2005 JOR 3 polyurethane elastomeric modules (Generation II, Dentaurum, Alastic)/3 modules

�elastom�eriques en polyur�ethane (Generation II, Dentaurum, Alastic)Eliades 2004 EJO 2 types (open and closed, with and without link) from three brands of elastomeric

module/2 types (chaınettes ouvertes et serr�ees, avec et sans liaisons) de 3 marquesde modules �elastom�eriques

Storie 1994 AO Fluor-I-Chain, standard gray elastomeric chain/Fluor-I-Chain, chaınettes�elastom�eriques grises standards

Stevenson 1993 AJO-DO Transparent and gray elastomeric chains/Chaınettes �elastom�eriques transparenteset grises

Renick 1994 AO 3 polyurethane-based elastomeric chains (Nihon, Pellethane, Texin)/3 chaınettes�elastom�eriques a base de polyur�ethane (Nihon, Pellethane, Texin)

Sang 2004 AJO-DO 3 different-colored chains (gray, red, and purple) from 3 manufacturers (RMO, Ormcoand G&H)/3 diff�erentes chaınettes color�ees (grise, rouge et violet) de 3 fabricants(RMO, Ormco et G&H)

Blahs 2008 SKQYX Chains of different filament types and numbers of loops, specific initial force/Chaınettes de diff�erents types de filament et de nombres de boucles, et dont la forceinitiale est d�efinie

Chau Lu 2011 JO Closed (non-spaced), gray elastomeric chains from 4 companies/Serr�ee (sansespaces), chaınettes �elastom�eriques grises de 4 fournisseurs

AO: angle orthodontist; AJO: American journal of orthodontists; JCO: Journal of clinical orthodontics; EJO: European journal of orthodontics; BJO: British journal of orthodontics; JDR: Journal

dental research; AJO-DO:American journal of orthodontics and dentofacial orthopedics; HOR:Hellenic orthodontic review; PO: Progress in orthodontics; JOR: Journal of oral rehabilitation; JMS:

Journal of materials science: materials in medicine; BOR: Brazilian oral research; OCR: Orthodontics & craniofacial research; SKQYX: Shanghai Kou Qiang Yi Xue; JCDP: The journal of

contemporary dental practice; JCPD: The journal of clinical pediatric dentistry; PNSCRC: Proceedings of the national science council, Republic of China; JO: Journal of orthodontics; OW:

orthodontic waves; PC: personnel communication; IP: in press.

Abdelali HALIMI et al.

— to compare force decay in gray and transparent chains;

— to compare force decay in all five brands of chain.

62

— comparer les d�egradations de la chaınette grise et de lachaınette transparente ;— comparer les d�egradations de la force g�en�er�ee par les cinqmarques de chaınettes.



Materials and methods

We studied five brands of polyurethane chain marketed bydifferent companies (GAC, RMO, Ortho-Organizers Inc.,G&H, G�en�eration II). For each brand, two distinct colors(gray/clear) and two chain types (open/closed) (Table II,fig. 2) were tested in various media: air and artificial salivaat different pH levels (pH 7, pH 4, and pH 2.5). The salivaformula used for this study was Saliveze [1,2], a therapeuticartificial saliva whose properties are close to those of realhuman saliva (Table III).

Each chain segment was stretched to an initial force of roughly200 g as measured using a hand-held dynamometer (fig. 3).The segments were then maintained in their stretched positionbetween two sliding hooks 35 mm apart (standard distance forclassic canine retraction) and immersed for 6 weeks airtightcontainers filled with saliva.

Table IIChains under study.

Code (type) Company/Soci�et�e Color/CouleuI GAC

Gray, transpaII Generation II/G�en�eration IIIII OrmcoIV Ortho-OrganiserV G&H

[(Fig._2)TD$FIG]

Fig. 2: The different types of elastomeric chain under study (a: types I,Fig. 2 : Diff�erents types de chaınettes �elastom�eriques �etudi�ees dans l’�etud

couleurs vari�ees).


Mat�eriel et m�ethodes

Cinq marques de chaınettes en polyur�ethanecommercialis�ees par des soci�et�es diff�erentes (GAC, RMO,Ortho-Organizers Inc, G&H, G�en�eration II) ont �et�e choisiespour l’�etude. Pour chaque marque, deux couleurs diff�erentes(grise/claire) et deux types diff�erents (serr�e/espac�e)(Tableau II, fig. 2) ont �et�e test�es dans diff�erents milieux : l’airambiant et la salive artificielle a diff�erents niveaux de pH : pH7,pH4 et pH2,5. La formule de la salive utilis�ee dans notre �etudecorrespond a la saliveze [1,2] : une salive artificielle th�erapeu-tique qui se rapproche de la salive humaine (Tableau III).Chaque segment subit un �etirement jusqu’a atteindre uneforce initiale d’environ 200 g dos�ee a l’aide d’un dynamom�etremanuel (fig. 3). Ensuite, chaque segment est gard�e �etir�e entredeux crochets coulissants s�epar�es de 35 mm (distance habi-tuelle pendant un recul canin classique) et est immerg�e pen-dant six semaines dans la salive dans des boıtes �etanches.

Tableau IIDiff�erentes chaınettes �evalu�ees dans l’�etude.

r Type

rent/Grise, transparente Open, closed/Espac�ee, serr�ee

II, III, IV, V, and b: long, closed, short in various colors).e (a : types I, II, III, IV, V et b : modules espac�e, serr�e, rapproch�e avec

63

Table IIISaliveze formula, borrowed from Preetha and Banerjee2005 [2].

Tableau IIIFormule de la saliveze : composition emprunt�ee a Preetha etBanerjee, 2005 [2].

Component/Composantes Quantity en g/L/Quantit�e en g/L

Sodium carboxymethylcellulose 10Potassium chloride 0.62Sodium chloride 0.87Magnesium chloride 0.06Calcium chloride 0.17Di-potassium hydrogen orthophosphate 0.80Potassium di-hydrogen orthophosphate 0.30Sodium fluoride 0.0044Sorbitol 29.95Methyl p-hydroxybenzoate 1.00Spirit of lemon 5 mL


Chain force measurements were performed using a manualdynamometer at time point zero (initial force H0), 1 hour(H1), 12 hours (H12), 24 hours (H24), 2 days, 2 days, 4 days,6 days, 2 weeks, 3 weeks, 4 weeks, 5 weeks, and 6 weeks.Measurements were retaken using an Instron 88215 deviceso as to gauge the dynamometer’s validity.

Lastly, representative samples were analyzed under a scan-ning electron microscope (SEM) to compare the chains’ micro-scopic features before and after stretching.

Results

The results of this study showed that the force delivered by thevarious chains decayed rapidly and continuously over time,both in air and in artificial saliva. This decay varied depend-ing on the pH of the test medium: the more acidic the pH, thegreater the force decay (fig. 4).

In artificial saliva with a pH of 7 and a temperature of 37�, theclear chain decayed more rapidly than the gray chain (fig. 5).The closed chain decayed less quickly than the open chain(fig. 6). The different chain types under study decayed differ-ently in saliva, and can easily be ranked in ascending orderaccordingly: type III, type I, type II, type IV, and lastly type V(fig. 7).Microscopic analysis of types V and I in their initial statesshowed a rectilinear structure for type V and a more fibrous,crisscross structure for type I (fig. 8).

64

Les mesures de la force lib�er�ee par les diff�erentes chaınettesont �et�e r�ealis�ees dans un premier temps a l’aide d’un dyna-mom�etre manuel, a diff�erentes reprises : au d�epart (forceinitiale H0), apr�es une heure (H1), apr�es 12 heures (H12),apr�es 24 heures (H24), apr�es deux jours, apr�es trois jours,apr�es quatre jours, apr�es six jours, apr�es deux semaines,apr�es trois semaines, apr�es quatre semaines, apr�es cinqsemaines et apr�es six semaines. Dans un deuxi�eme temps,les mesures ont refaites a l’aide de l’appareil Instron88215 pour juger de la validit�e du premier outil.Finalement, une analyse au microscope �electronique a balay-age (MEB) d’�echantillons repr�esentatifs a �et�e r�ealis�ee pourcomparer l’�etat microscopique des diff�erentes chaınettesavant et apr�es �etirement.

R�esultats

Les r�esultats de notre �etude montrent que la force lib�er�ee parles diff�erentes chaınettes �etudi�ees se d�egrade rapidementavec le temps et d’une facon continue ; cela aussi bien dansl’air ambiant que dans la salive artificielle. Cette d�egradationvarie en fonction du pH dumilieu d’�etude : plus le pH est acide,plus la d�egradation est importante (fig. 4).Dans la salive artificielle pH 7 a 37�, la chaınette transparentese d�egrade plus rapidement que la chaınette grise (fig. 5). Lachaınette serr�ee se d�egrade moins vite que la chaınetteespac�ee (fig. 6). Les types de chaınettes �etudi�ees sed�egradent diff�eremment dans la salive et on peut tr�es viteles classer dans l’ordre de d�egradation croissant suivant : typeIII, type I, type II, type IV et enfin le type V (fig. 7).L’analyse microscopique des type Vet I, a l’�etat initial, montreune structure de fibres rectilignes pour le type V et une struc-ture plutot fibreuse pour le type I dont les fibres sont orient�eesd’une mani�ere diff�erente (fibres crois�ees) (fig. 8).


[(Fig._3)TD$FIG]

Fig. 3: a–d: adjustable stretch kit with hooks 35 mm apart; initial and subsequent force measurements were made under the same conditions.Fig. 3 : a–d : kit d’�etirement r�eglable, la distance entre crochets est fix�ee a 35 mm ; la force lib�er�ee estmesur�ee initialement et a diff�erents reprises

en respectant les memes conditions de mesures.


After 6 weeks’ stretching in air for type V (the type with themost force decay), SEM revealed faint uniform surface distor-tions located on and between the modular rings. However,after 6 weeks’ stretching in artificial saliva at pH 7, wedetected major surface distortion in the form of a large cracklocated in the inter-modular link area (fig. 9). Acid damagefrom the test medium and stretching effects were less visible intype I (less decay), microscopic analysis of which showed a fewtorn fibers in the inter-modular link area (fig. 10).


Apr�es six semaines d’�etirement dans l’air pour le type V (leplus d�egrad�e), nous constatons au MEB une alt�eration desurface faible et homog�ene localis�ee aussi bien dans lenœud que dans l’internœud ; mais apr�es six semainesd’�etirement dans la salive artificielle a pH7, nous constatonsune forte alt�eration de la surface mat�erialis�ee par une fissureimportante localis�ee au niveau de la zone de l’internœud (fig.9). L’attaque du milieu acide et l’effet d’�etirement sont moinsvisibles sur le type I (moins d�egrad�e) et son analyse micro-scopique montre un d�echirement de quelques fibres dans lazone de l’internœud (fig. 10).

65

[(Fig._6)TD$FIG]

Fig. 6: Compared force decay in closed and open chains in saliva at37�, pH 7.Fig. 6 : Comparaison de la d�egradation des chaınettes serr�ee et

espac�ee dans la salive 37�, pH 7.

[(Fig._4)TD$FIG]

Fig. 4: Compared effects of test medium on chain force decay.Fig. 4 : Comparaison des effets du milieu sur la d�egradation de la

chaınette.

[(Fig._5)TD$FIG]

Fig. 5: Compared force decay in gray and transparent chains in salivaat 37�, pH 7.Fig. 5 :Comparaison de la d�egradation des chaınettes grise et transpar-

ente dans la salive 37�, pH7.

66 International Orthodontics 2013 ; 11 : 60-70


[(Fig._7)TD$FIG]

Fig. 7: Compared force decay in the five chain types in saliva at 37�,pH 7.Fig. 7 : Comparaison de la d�egradation de la force des 5 types de

chaınettes dans la Salive 37�, pH7.

[(Fig._8)TD$FIG]

Fig. 8: Microscopic analysis of type V, and type I in initial state.Fig. 8 : Analyse microscopique du type V, et du type I a l’�etat initial.


Discussion

The force delivered by the elastomeric chains decayed rapidlyand to a greater extent in artificial saliva versus air.

Nattrass et al. [3] have reported greater force decay in elasto-meric chains in cola and curcuma than in water. Kuster et al.[4] have demonstrated that force decay is greater in vivo thanin air. Ash and Nicolai [5] have reported greater force decay invivo than in vitro.

Conversely, Eliades et al. [6,7] found no significant differencein tensile strength between chains stretched in air and intra-orally.Force decay differed depending on the chain, varying onaverage from 56% to 91% after 4 weeks. The open chains


Discussion

La force lib�er�ee par la chaınette �elastom�erique subit uned�egradation rapide, plus importante dans la salive artificielleque dans l’air ambiant.Nattrass et al. [3] ont constat�e une d�eperdition de la force deschaınettes �elastom�eriques plus importante dans le cola et lecurcuma que dans l’eau. Kuster et al. [4] ont montr�e que cetted�egradation de la force est plus importante in vivo que dansl’air ambiant. Ash et Nicolai [5] ont reconnu que ce ph�enom�enede d�egradation de la force est plus important in vivo qu’in vitro.A l’inverse, Eliades et al. [6,7] ont montr�e qu’il n’y a pas dediff�erence significative en ce qui concerne la r�esistance a latraction entre des chaınettes �etir�ees a l’air et en bouche.La d�egradation est diff�erente en fonction de la chaınette ; ellevarie en moyenne de 56 a 91 % apr�es quatre semaines. La

67

[(Fig._10)TD$FIG]

Fig. 10:Microscopic analysis of type I in its initial state and after 6 weeks’ stretching in air andartificial saliva.Fig. 10 : Analysemicroscopique du type I a l’�etat initial et apr�es 6 semaines d’�etirement dans l’air

et dans la salive artificielle.

[(Fig._9)TD$FIG]

Fig. 9:Microscopic analysis of type V in its initial state and after 6 weeks’ stretching in air andartificial saliva.Fig. 9 : Analyse microscopique du type V a l’�etat initial et apr�es 6 semaines d’�etirement dans l’air

et dans la salive artificielle.

68 International Orthodontics 2013 ; 11 : 60-70



decayed more rapidly than closed ones, transparent chainsless rapidly than gray ones.Ash and Nicolai [5] have joined others [8–27] in reporting anaverage loss of 50–85% of initial force after 4 weeks, depend-ing on the chain and the study.

Eliades et al. [6,23,25] found that open chains exhibitedgreater residual extension than closed ones, allegedly becauseof major extension in the inter-modular link areas.

Conclusion

The force delivered by elastomeric chains decayed rapidlyover time. This decay was greater in saliva than in air, anddepended on the chain.

The results presented in this paper reflect the first stage of ourstudy. The second stage will investigate a larger sample andmeasure variables using an Instron 88512 device.

Disclosure of interest

The authors declare that they have no conflicts of interestconcerning this article.

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chaınette espac�ee se d�egrade plus rapidement que lachaınette serr�ee et la transparente moins vite que la grise.Ash [5] s’accorde avec d’autres auteurs [8–27] pour dire que lachaınette perd en moyenne de 50 a 85 % de sa force initialeau bout de quatre semaines en fonction des diff�erenteschaınettes et des diff�erentes �etudes.Eliades et al. [6,23,25] ont trouv�eque les chaınettes amodulesespac�es pr�esentent des �elongations r�esiduelles plus impor-tantes que celles avec modules serr�es ; cela serait du a une�elongation importante au niveau des r�egions intermodulaires.

Conclusion

La force lib�er�ee par la chaınette �elastom�erique subit uned�egradation rapide dans le temps ; cette d�egradation est plusimportante dans la salive que dans l’air ambiant ; elle estdiff�erente en fonction de la chaınette.Les r�esultats expos�es dans cette pr�esentation constituent unepremi�ere �etape de l’�etude. La deuxi�eme �etape sera consacr�eea l’�etude d’un �echantillon plus large et a la mesure des diff�er-ents variables par l’Instron 88512.

D�eclaration d’int�erets

Les auteurs d�eclarent ne pas avoir de conflits d’int�erets enrelation avec cet article.

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