Elasticke moduly v ortodoncii Elastic modules in orthodontics

Transcription

1 ORTODONCIE rocïnõâk23 Elasticke moduly v ortodoncii Elastic modules in orthodontics MUDr. Alena Forma nkovaâ, MUDr. Magdalena Kot'ovaÂ, Ph. D. OddeÏ lenõâ ortodoncie arozsïteï povyâch vad Stomatologicke kliniky 3. LF UK FNKV Praha Department of Orthodontics and Cleft Defects, Clinic of Stomatology, 3rd Medical Faculty of Charles University, University Hospital Kra lovskeâ Vinohrady, Prague Souhrn JednõÂm ze zaâ kladnõâch prïedpokladuê uâ speï sïneâ ortodontickeâ leâ cï by je kontrolovaneâ puê sobenõâ ortodontickyâ ch sil. CõÂlem praâ ce je analyâ za silovyâ ch charakteristik beï zï neï pouzï õâvanyâ ch ortodontickyâ ch elastickyâ ch rïetõâzkuê. Byl zkoumaâ n vliv ruê znyâ ch parametruê (tvar rïetõâzku, vyâ robce, prestretching) na produkci sil v zaâ vislosti na cï ase. Byl vytvorïen soubor 18 typuê beï zïneï pouzï õâvanyâ ch elastickyâ ch rïetõâzkuê od 7 ruê znyâ ch vyâ robcuê.rï etõâzky byly rozdeïleny do 3 skupin, podle deâ lky mezicïlaâ nku. Na sledneï byly protazïeny o 50 % a 100 % jejich puê vodnõâ deâ lky a byl meïrïen pokles sõâly v cï ase ve zvolenyâchcï asovyâ ch intervalech ve standardizovanyâ ch podmõânkaâ ch. Studie prokaâ zala, zï e sõâly produkovaneâ elastickyâ mi rïetõâzky jsou velkeâ a znacï neï se lisï õâ dle vyâ robce. BeÏ hem prvnõâch 24 hodin dochaâ zõâ k vyâ razneâ mu poklesu sil, poteâ sõâly klesajõâ uzï jen velmi pomalu. Vliv prestretchingu na snõâzï enõâ vyâchozõâch sil byl patrnyâ pouze u naâ sledneâ ho protazïenõâ rïetõâzku o 50 %, prïi 100 % protazïenõâ tento vliv prokaâzaâ n nebyl (Ortodoncie, 23, cï. 2, s ). Abstract Controlled delivery of orthodontic forces is one of the preconditions for successful orthodontic treatment. The work aims to give the analysis of common orthodontic elastic chains force characteristics. The study focuses on the effect of individual parameters (chain shape, manufacturer, prestretching) on time-related delivery of forces. Our sample included 18 types of common elastic chains produced by 7 manufacturers. The chains were subdivided into 3 groups according to the length of their connecting link. Subsequently, the chains were elongated by 50% and 100% of their original length, and the decrease of force over a period of time was measured at given intervals under standardized conditions. The study proves that forces delivered by elastic chains are big, and that products of individual manufacturers are different. Within the first 24 hours forces decrease significantly, afterwards they lessen very slowly. The effect of prestretching on the decrease of initial forces was evident only in subsequent stretching of a chain by 50%. In case of 100% stretching the effect was not proved (Ortodoncie, 23, No. 2, p ). KlõÂcÏ ovaâ slova: elastickyâ rïetõâzek, pokles sõâly, mezicïlaâ nek, prestretching Key Words: elastic chain, force degeneration, connecting link, prestretching U vod Elasticke rïetõâzky se staly neodmyslitelnou, trvalou abeï zï neï pouzï õâvanou soucï aâ stõâ nasï ich ortodontickyâch praxõâ. Elasticke rïetõâzky aligatury jsou vyrobeny z polyurethanuê. Je pro neï charakteristickeâ,zï e vykazujõâ elasticitu kaucï uku. To znamenaâ,zï e v jednom ze svyâchprïechodo- Introduction Elastic chains have become an inherent and integral part of orthodontic practices. Elastic chains and ligatures are made of polyurethane. They are as elastic as natural rubber; after substantial deformation with a relatively light force they rapidly return to their original di- redakce@orthodont-cz.cz 97

2 rocïnõâk23 ORTODONCIE vyâch stavuê - stavu kaucï ukoviteâ m, je lze pomeï rneï malou silou vratneï deformovat azï o stovky procent. Nesmõ se ale prïekrocï it mez elasticity, to by jizï vratnaâ deformace elastickeâhorïetõâzku nebylamozïnaâ [1, 2]. Chova nõâ elastickyâch rïetõâzkuê azejmeâ napokles sil, kteryâ nastane po jejich natazï enõâ, je oblastõâ, na kterou bylazameï rïenapozornost v mnohastudiõâch. Byly zaznamenaâ ny signifikantnõâ rozdõâly v poklesu sil mezi rïetõâzky jednotlivyâch znacï ek. DuÊ vody, procï by tomu tak mohlo byâ t, spocï õâvajõâ ve variabiliteï prïidanyâ ch aditiv, kteraâ se inkorporujõâ do vyâ sledneâ struktury elastomeru, atakeâ v morfologickeâ variabiliteï rïetõâzku. Mnoho studiõâ poklesu sil produkovanyâch rïetõâzky bylo provaâdeï no in vitro. DuÊ voduê, procï studie degradace sil probõâhajõâ veïtsï inou in vitro ane in vivo, je võâce alze je shrnout do konstatovaâ nõâ, zï e standardizace podmõânek pro experiment v dutineï uâ stnõâ je velmi obtõâzïnaâ, ne-li nemozïnaâ. SÏ õârïe testovacõâch podmõânek prïi experimentech in vitro bylavelikaâ (vlhkost, ph, protazï enõâ vzorkuê...). I prïes vsï echnatato rozdõâlnaâ kriterialze rïõâci, zï e dosï lo k vyâ razneâ shodeï zaâ veï ruê ruê znyâ ch studiõâ v tom, zï e beï hem prvnõâch 24 hodin dojde k strmeâ mu poklesu sil v rozsahu o % vyâchozõâ hodnoty sõâly. Na slednyâ pokles beï hem dalsï õâch dvou azï trïõâ tyâ dnuê je jizï vyâ razneï pomalejsï õâ [3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]. JednõÂm z faktoruê, kteryâ ovlivnï uje produkci sil rïetõâzkuê, je fenomeâ n ªsta rnutõ⪠rïetõâzkuê in vivo. Hlavnõ faktor odlisï ujõâcõâ prostrïedõâ dutiny uâ stnõâ je prïõâtomnost oraâ lnõâ floâ ry ajejõâch vedlejsï õâch produktuê arovneï zï akumulace zubnõâho plaku. V studiõâch in vitro se v soucï asneâ dobeï nedajõâ tyto podmõânky simulovat. Je oveï rïeno, zï e vystavenõâ ruê znyâch materiaâluê podmõânkaâ m dutiny uâ stnõâmuêzï e vyvolat podstatneâ zmeï ny v jejich strukturïe apovrchovyâch vlastnostech. CõÂlem teâ to praâ ce, provedeneâ in vitro, je analyâ zasilovyâ ch charakteristik beï zï neï pouzï õâvanyâ ch ortodontickyâ ch elastickyâch rïetõâzkuê. Chceme odpoveï deï t naotaâ z- ky, zdajsou vyâ chozõâ hodnoty sil produkovanyâ ch rïetõâzky stejneâ, nebo sõâly klesajõâ ruê znou rychlostõâ, zda ovlivnõâ prïõâtomnost adeâ lkamezicï laâ nku sõâly produkovaneâ rïetõâzky azdabude mõât provedenõâ prestretchingu (¹prÏednatazÏ enõâª) vliv nauâ rovenï vyâ chozõâch sil ajejich pokles ve srovnaâ nõâ s rïetõâzky, u kteryâ ch prestretching proveden nebyl. MateriaÂl Nejprve byl analyzovaân ameï rïen uâ bytek sõâly v cï a se po natazï enõâ u 18 typuê ortodontickyâch rïetõâzkuê od 7 ruê z- nyâch vyârobcuê : Dentaurum, Ispringen, Germany; American Orthodontics, Sheboygan, WIS, USA; G&H Wire Company, Franklin, IN, USA; Ormco, Glendora, CA, USA; Highland Metals Inc., San Jose, CA, USA; Ortho-Care /UK/ Ltd, Saltaire, UK; 3M/Unitek, Monrovia, CA, USA. mensions, i.e. the deformation is reversible. However, the elastic limit must not be exceeded [1, 2]. Elastic chains behaviour, especially decrease of forces occurring after they are stretched, has been the focus of many studies. There were reported significant differences in force decrease between chains by individual producers. The reasons may be seen in various additives incorporated into the resulting structure of elastomer, and in morphological variability of chains. The majority of studies focusing on force degradation have been conducted in vitro. There are several reasons for the research to be done mostly in vitro, not in vivo, the primary one being that to achieve standard conditions for the experiment in oral cavity is very demanding, if not impossible. There is a number of parameters examined during experiments in vitro (humidity, ph, stretching of samples, etc.). Most studies agree in that within the first 24 hours there is significant amount of force degradation %. Subsequent force degradation, i.e. during the following two or three weeks, is significantly slower [3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]. One of the factors affecting delivery of chain force is the ¹ageingª of chains in vivo. Differences in the mouth cavity conditions are mainly due to oral flora and its side effects, as well as plaque accumulation. This artificial environment can not be exactly duplicated in studies in vitro. It has been proved that the exposure of different materials to mouth cavity environment can provoke significant changes in their structure and surface characteristics. The aim of the presented study, performed in vitro, is the analysis of force characteristics of common orthodontic chains. We strive to answer the following questions: Are the initial forces delivered by chains identical or do they decrease at different rate? Do the presence and length of the connecting link affect forces induced by chains? Does prestretching affect the level of the initial force and its degradation in comparison with chains without prestretching? Material First we analyzed and measured force decrease over aperiod of time after stretching in 18 types of orthodontic chains by 7 manufacturers: Dentaurum, Inspringen, Germany; American Orthodontics, Sheboygan, WIS, USA; G&H Wire Company, Franklin, IN, USA; Ormco, Glendora, CA, USA; Highland Metals Inc., San Jose, CA, USA; Ortho-Care /UK/ Ltd., Saltaire, UK; 3M/Unitek, Monrovia, CA, USA. The sample of 18 chains was subdivided according to whether a chain has a connecting link or not, and according to the connecting link length. As the length of connecting links and description given by individual manufacturers are different and do not correspond to redakce@orthodont-cz.cz

3 ORTODONCIE rocïnõâk23 Soubor 18 rïetõâzkuê byl rozdeï len podle toho, zdarïetõâzek meïlcï i nemeï l mezicïlaâ nek adaâ le podle deâ lky mezicï laâ nku. ProtozÏe deâ lkamezicï laâ nkuê aslovnõâ oznacï enõâ rïetõâzkuê jednotlivyâ ch vyâ robcuê se lisï õâ avzaâ jemneï si neodpovõâdaâ, byla stanovena hranice 0,9 mm, kterou se rïõâdilo zarïazenõâ rïetõâzku bud'do skupiny rïetõâzkuê s kraâ tkyâm nebo s dlouhyâm mezicïlaâ nkem. Sedm rïetõâzkuê bylo zarïazeno do skupiny rïetõâzkuê bez mezicï laâ nku: Dyna-Link Continuous (G&H), Plastic Chain Closed (AO), Memory Chain Closed (AO), Dura Chain Close Link (Ortho-Care), Power Chain Closed Space (Ormco), Alastik Chain CK Blue Met (3M/Unitek), Elasto Force Closed (Dentaurum). CÏ tyrïi rïetõâzky byly zarïazeny do skupiny rïetõâzkuê s kraâtkyâ m mezicï laâ nkem: Dyna-Link Short (G&H) - deâ lka mezicï laâ nku 0,2 mm, Chain Elastic Short (Highland Metals) - deâ lkamezicïlaâ nku 0,2 mm, Plastic Chain Short (AO) - deâ lkamezicïlaâ nku 0,3 mm, Power Chain Open Space (Ormco) - deâ lkamezicïlaâ nku 0,5 mm. Sedm rïetõâzkuê bylo zarïazeno do skupiny rïetõâzkuê s dlouhyâm mezicïlaâ nkem: Dyna-Link Long (G&H) - deâ lkamezicïlaâ nku 0,9 mm, Plastic Chain Long (AO) - deâ lkamezicï laâ nku 0,9 mm, Elasto Force Connector (Dentaurum) - deâ lkamezicï laâ nku 1 mm, DuraChain Medium Link (Ortho-Care) - deâ lkamezicï laâ nku 1,2 mm, Power Chain Wide Space (Ormco) - deâ lkamezicïlaâ nku 1,7 mm, Memory Chain Long (AO) - deâ lkamezicïlaâ nku 1,8 mm, DuraChain Wide Link (Ortho-Care) - deâ lkamezicïlaâ nku 1,8 mm. Da le byla provedena analyâzatvaru ocïekuvsï ech rïetõâzkuê zahrnutyâ ch do experimentu, protozï e jednotliveâ rïetõâzky se mohou lisï it i tvarem ocï ek. Bylo zjisïteï no, zïe vsï echnaocï ka u vsï ech rïetõâzkuê majõâ kruhovyâ tvar. Take byl porovnaâ n tvar pruê rïezu rïetõâzku. VsÏ echny zkoumaneâ rïetõâzky majõâ obdeâ lnõâkovyâ tvar pruê rïezu. DalsÏ õâm uâ kolem bylo zhodnotit vliv prestretchingu elastickeâ ho rïetõâzku nahodnotu vyâ chozõâ sõâly ajejõâ naâslednyâ pokles v cï ase. V tomto experimentu byly pouzï ity trïi rïetõâzky od jednoho vyâ robce: Power Chain Closed Space, Power Chain Open Space a Power Chain Wide Space, vsï echny od firmy Ormco. Metodika K prvnõâmu experimentu bylo od kazïdeâho rïetõâzku zhotoveno 20 vzorkuê vdeâ lce 11 apuêlocï ek. Vzorky byly oddeï leny bez natazï enõâ pomocõâ skalpelu. Na jedneâ straneï vzorku bylaponechaâ napolovinaocï ka, aby prïi oddeï lovaâ nõâ skalpelem nedosï lo k posï kozenõâ krajnõâho ocï ka, ktereâ se v experimentu navleâ kalo na ocelovyâ trn urcï enyâ k natazï enõâ rïetõâzku. Nadruhe straneï vzorku bylo ponechaâno ocï ko celeâ. To pak slouzï ilo k meïrïenõâ ado neï j byl zasouvaâ n hrot silomeï ru. Vzorky byly rozdeïleny do dvou skupin po 10 kusech v kazïdeâ skupineï. Bylo rozhodnuto, zï e v prvnõâ skupineï budou vzorky jednoraâ zoveï natazïeny o 50 % jejich puê vodnõâ deâ lky ave each other, we set out the limit of 0.9 mm according to which a chain was classified as the one with short or long connecting link. Seven chains were in the group of chains without connecting link: Dyna-Link Continuous (G&H), Plastic Chain Closed (AO), Memory Chain Closed (AO), Dura Chain Close Link (Ortho-Care), Power Chain Closed Space (Ormco), Alastik Chain CK Blue Met (3M/Unitek), Elasto Force Closed (Dentaurum). Four chains were in the group of chains with a short connecting link: Dyna-Link Short (G&H) - the connecting link length 0.2 mm; Chain Elastic Short (Highland Metals) - the connecting link length 0.2 mm; Plastic Chain Short (AO) - the connecting link length 0.3 mm; Power Chain Open Space (Ormco) - the connecting link length 0.5 mm. Seven chains were in the group of chains with a long connecting link: Dyna-Link Long (G&H) - the connecting link length 0.9 mm; Plastic Chain Long (AO) - the connecting link length 0.9 mm; Elasto Force Connector (Dentaurum) - the connecting link length 1 mm; Dura Chain Medium Link (Ortho-Care) - the connecting link length 1.2 mm; Power Chain Wide Space (Ormco) - the connecting link length 1.7 mm; Memory Chain Long (AO) - the connecting link length 1.8 mm; Dura Chain Wide Link (Ortho-Care) - the connecting link length 1.8 mm. Individual chains may differ in a unit shape; therefore the shapes of units of all the chains included in the experiment were analyzed. In all chains the units were circular, and the crossection oblong. Further effects of prestretching on the amount of the initial force and its subsequent decrease over a period of time were evaluated. For this experiment three chains by the same manufacturer were used: Power Chain Closed Space, Power Chain Open Space, and Power Chain Wide Space by Ormco. Methods For the first experiment there were 20 samples of each chain, of 11.5 units. Samples were cut with a lancet. On one end of the sample a half of a unit was left in order that a lancet would not damage an outside unit that was attached to the steel pin for stretching. On the other side a whole unit was left, that was used for measurements - a dynamometer was inserted into it. Samples were divided into two groups of 10. The samples in the first group were stretched by 50% of their initial length, in the second group by 100%. First, in each chain we measured the length of ten units before elongation. The length of each chain after stretching by 50%, and 100% was calculated. To stretch all samples, measurement plastic (PHS) plates were produced width of 3 mm. At the calculated distances corresponding to agiven stretching, holes were pred- redakce@orthodont-cz.cz 99

4 rocïnõâk23 ORTODONCIE druheâ skupineï o 100 % puê vodnõâ deâ lky. Nejprve byla u ka zïdeâho rïetõâzku zmeï rïenadeâ lkadeseti ocï ek v klidu prïed natazï enõâm. BylaspocÏ õâtaâ na deâ lkakazïdeâ ho rïetõâzku prïi protazïenõâ o 50 % jejich puê vodnõâ deâ lky aprïi protazï enõâ o 100 % puê vodnõâ deâ lky. Pro standardnõâ natazïenõâ vsï ech vzorkuê byly vyrobeny meïrïõâcõâ plastoveâ desticï ky (materiaâ l PSH) tlousït'ky 3 mm. Ve vypocï tenyâch vzdaâ lenostech odpovõâdajõâcõâch zvoleneâ mu natazï enõâ byly prïedvrtaâ ny otvory ado nich byly zafixovaâ ny oceloveâ trny o pruêmeï ru 1,1 mm pro uchycenõâ vzorkuê. Prvnõ ocïkorïetõâzku bylo navlecï eno najeden ocelovyâ trn, pomocõâ peaâ nu byl rïetõâzek jednoraâ zoveï protazïen do nastaveneâ vzdaâ lenosti adesaâ teâ ocï ko rïetõâzku bylo navlecï eno na druhyâ ocelovyâ trn. MeÏ rïenõâ u vsï ech rïetõâzkuê probeï hlo ve zvolenyâch cï asovyâch intervalech: 0, 2, 8, 24 hodin, 7 dnuê a21 dnuê. CelkoveÏ probeï hlo 2160 meïrïenõâ. Cely experiment probõâhal in vitro za prïesneï specifikovanyâ ch podmõânek. RÏ etõâzky, po natazï enõâ nameï rïõâcõâch desticï kaâ ch, byly vlozï eny do polyfunkcï nõâho inkubaâ toru CulturaM, vyâ robce ALMEDICA AG, Guglera1, 1735 Giffers, Switzerland. Po celou dobu experimentu byla zajisï teï nakonstantnõâ teplota37 C, teplotnõâ prïesnost teplomeïru je ± 1 C. Cely experiment probõâhal za vlhka. Vlhkost prostrïedõâ zajisï t'oval pruh gaâ zy vlhcï enyâ ka zïdyâch 12 hodin 20 ml vody pokojoveâ teploty. K meï rïenõâ sõâly, kterou produkovaly natazï eneâ rïetõâzky v jednotlivyâch cï asovyâ ch intervalech, byl pouzï it rucï nõâ analogovyâ silomeï r SHITO DGD-8 s meï rïõâcõâm rozsahem gramuê s prïesnostõâ 2 %, vyâ robce Huatest Electronic Co, Ltd, Shenzhen, China. MeÏ rïenõâ bylo provedeno tak, zï e hrot silomeï ru byl zasunut do poslednõâho jedenaâ cteâ ho ocï ka rïetõâzku. HodnotasõÂly bylaodecï tena v okamzï iku, kdy se desaâ teâ ocï ko rïetõâzku nedotyâ kalo oceloveâ ho trnu atrn byl v okamzïiku meïrïenõâ uprostrïed ocï ka(obr. 1). Pro druhyâ experiment bylo zhotoveno 20 vzorkuê vdeâ lce 11 apuêlocï kaze vsï ech trïõâ rïetõâzkuê abyly rozdeïleny do dvou skupin po 10 kusech v kazïdeâ skupineï. RÏ etõâzky byly opeï t natazï eny nameï rïõâcõâ desticï ku navzdaâlenost odpovõâdajõâcõâ protazïenõâ o 50 ao 100 % puê vodnõâ deâ lky. PrÏed tõâmto natazï enõâm bylo nejprve provedeno ªprÏednatazÏenõª rïetõâzkuê na180 % puê vodnõâ deâ lky 5x po sobeï. NameÏ rïõâcõâ desticï ku bylazakreslenalinie odpovõâdajõâcõâ 180 % vyâ chozõâ deâ lky deseti ocï ek rïetõâzku. Krajnõ ocï ko bylo navlecï eno naocelovyâ trn. Pea nem byl zachycen konec rïetõâzku (jedenaâ cteâ ocï ko) a5x po sobeï byl rïetõâzek natazïen k vyznacï eneâ linii. Toto 5x opakovaneâ ªprÏednatazÏ enõ⪠trvalo celkem 5 vterïin. Pote byly rïetõâzky definitivneï umõâsteï ny do pozic avzdaâ lenostõâ odpovõâdajõâcõâch stanovenyâ m podmõânkaâ m experimentu. MeÏ rïenõâ probõâhalo podle stejneâ ho protokolu jako u prvnõâho experimentu. V druheâ m experimentu bylo provedeno 360 meïrïenõâ. rilled into which steel pins, the diameter of 1.1 mm, were inserted (they served for a sample attachment). The first unit of a chain was attached to one steel pin, the chain was stretched to the set distance with the help of a clamp, and the tenth unit of the chain was attached to the other steel pin. Measurements were performed at the given time intervals: 0, 2, 8, 24 hours, 7 days, and 21 days. There were 2160 measurements performed. The experiment was carried out in vitro under specific conditions. After stretching on measurement plates, the chains were put into polyfunctional incubator CulturaM, fy ALMEDICA AG, Guglera1, 1735 Giffers, Switzerland. During the experiment there was the constant temperature 37 C, the accuracy of a thermometer ± 1 C. The experiment was performed in a humid environment. The humidity was ensured with a band of gauze that was moistened every 12 hours with 20 ml of water of room temperature. To measure forces induced by stretched chains at individual intervals a manual analogue force gauge SHITO DGD-8 was used, the range of measurement g, the accuracy of 2%, fy Huatest Electronic Co., Ltd., Shenzhen, China. The point of the force gauge was inserted into the last (eleventh) chain unit. The force was read at the moment when the tenth unit did not touch the steel pin, and the pin was in the middle of the unit (Fig. 1). For the second experiment 20 samples were prepared, the length of 11.5 units, of all the three chains, and they were divided into two groups of 10 samples each. Again, the chains were stretched on the measuring plate - elongated by 50% and by 100% of the initial length. Prior to that, ¹prestretchª to 180% of the initial length was carried out 5 times in a row. On the measure plate the line representing 180% of the original length of ten units was drawn. An outside unit was attached to the steel pin. The end of the chain (the eleventh unit) was held with a clamp, and the chain was 5 times stretched according to the line drawn. This prestretching Obr. 1. Uka zkameïrïenõâ sõâly silomeï rem SHITO DGD-8 Fig. 1. Force measurement with SHITO DGD-8 force gauge redakce@orthodont-cz.cz

5 ORTODONCIE rocïnõâk23 VsÏ echnameï rïenõâ byla statisticky zhodnocena. Nejprve byly hodnoty popsaâ ny pomocõâ popisneâ statistiky (aritmetickyâ pruê meï r, mediaâ n, minimaâ lnõâ amaximaâ lnõâ hodnoty, smeï rodatnaâ odchylka). Na sledneï byly jednotliveâ soubory nameï rïenyâ ch hodnot testovaâ ny nanormaâ lnõâ rozlozï enõâ. Pokud meï ly hodnoty normaâ lnõâ rozlozï enõâ, byly podrobeny parametrickyâ m testuê m (Studentovy t-testy, paâ roveâ t-testy s Bonferroniho korekcõâ), v opacï neâ m prïõâpadeï byly podrobeny testuê m neparametrickyâ m (FriedmanuÊ v test, Wilcoxonovy testy s Bonferroniho korekcõâ, Mann-Whitney U-testy). Vy sledky byly zpracovaâ ny do tabulek s vyznacï enõâm statisticky vyâ znamnyâ ch hodnot nahladineï statistickeâ vyâ znamnosti 0,05. Vy sledky Vy sledky vsï ech provedenyâch meï rïenõâ sõâly produkovaneâ rïetõâzky ve zvolenyâ ch cï asovyâ ch intervalech v prvnõâm i druheâ m experimentu byly zaznamenaânydo tabulek a grafuê azpracovaâ ny v programu Microsoft Excel. Byly vypocï teny aritmetickeâ pruê meï ry pro kazïdeâ meï rïenõâ sõâly aprocentuaâ lnõâ poklesy sil. PrÏi protazïenõâ rïetõâzkuê o 50 % puê vodnõâ deâ lky se pocïaâtecï nõâ hodnoty sil v cï ase 0 pohybovaly v rozmezõâ od 2,5 N (Dura Chain Wide Link, Ortho-Care) do 5,8 N (Dyna Link Continuous, G&H). Po 21 dnech bylo rozmezõâ sil produkovanyâch rïetõâzky od 1,5 N (DuraChain Wide Link, Ortho-Care) do 2,4 N (Dyna Link Continuous, G&H; Power Chain closed space, Ormco; Plastic chain, AO; Elasto Force with connector, Dentaurum). Procentua lnõâ pokles sil se pohyboval od 24 % do 62 % po 24 hodinaâ ch aod 31 % do 70 % po 21 dnech. NejmensÏ õâ procentuaâ lnõâ pokles sil s ohledem navyâ chozõâ poskytovanou uâ rovenï sõâly meï ly rïetõâzky Memory chain closed, AO; Elasto Force with connector, Dentaurum a Dura Chain close link, Orthocare. took 5 seconds. Then the chains were placed into positions and distances according to the set conditions of the experiment. The measurement followed the same protocol as in the first experiment. There were 360 measurements performed. All measurements were statistically processed. First, the data obtained were described by means of descriptive statistics (arithmetic mean, median, minimum and maximum values, standard deviation). Further the individual sets of measured values were tested for normal distribution. In case the values showed normal distribution, they were subjected to parametric tests (Student's t-tests, pair t-tests with Bonferroni's correction), otherwise they were subject of non-parametric tests (Friedman's test, Wilcoxon tests with Bonferroni's correction, Mann-Whitney U-tests). The results were plotted in tables, statistically significant values on the level of statistical significance of 0.05 were highlighted. Results The results of all measurements of chain induced forces at given intervals in both experiments were plotted in tables and graphs, and processed with Microsoft Excel software. Arithmetic means for each force measurement and percentage of force degeneration were calculated. After stretching of chains by 50% of their initial length, the initial values of forces at time 0 fluctuated between 2.5 N (Dura Chain Wide Link, Ortho-Care) and 5.8 N (Dyna Link Continunous, G&H). After 21 days the range was between 1.5 N (Dura Chain Wide Link, Ortho-Care) and 2.4 N (Dyna Link Continuous, G&H; Power Chain Closed Space, Ormco; Plastic Chain, AO; Elasto Force with connector, Dentaurum). The Tab. 1. PruÊmeÏ rneâ hodnoty sil aprocentuaâ lnõâ poklesy sil pro protazï enõâ o 50 % puê vodnõâ deâ lky ve zvolenyâch cï asovyâch intervalech Tab. 1. Mean values of forces and forces degeneration in per cents after stretching by 50% of the initial length at given time intervals redakce@orthodont-cz.cz 101

6 rocïnõâk23 ORTODONCIE Tab. 2. PruÊmeÏ rneâ hodnoty sil aprocentuaâ lnõâ poklesy sil pro protazï enõâ o 100 % puê vodnõâ deâ lky ve zvolenyâch cï asovyâch intervalech Tab. 2. Mean values of forces and forces degeneration in per cents after stretching by 100% of the initial length at given time intervals Obr. 2. Pokles pruêmeï rnyâch sil v cï ase prïi protazïenõâ o 50 % vyâchozõâ deâ lky rïetõâzku Fig. 2. Mean forces degeneration over a period of time after stretching by 50% of the initial length Naobr. 2 je patrnyâ rozptyl vyâ chozõâch hodnot sil produkovanyâ ch elastickyâ mi rïetõâzky. PruÊ beï h krïivek pro vsï echny rïetõâzky i charakter jejich poklesu je si velmi podobnyâ. NejstrmeÏjsÏ õâpruêbeï h je v prvnõâch 24 hodinaâ ch. PrÏi protazïenõâ o 100 % puê vodnõâ deâ lky se pocïaâ tecïnõâ hodnoty sil produkovanyâch v cï ase 0 pohybovaly v rozmezõâ od 3,2 N (Dura Chain Wide Link, Ortho-Care) do 6 N (DynaLink Continuous, G&H). Po 21 dnech bylo rozmezõâ sil produkovanyâch rïetõâzky od 1,6 N (DuraChain Wide Link, Ortho-Care) do 3,2 N (Dyna Link Continuous, G&H). Procentua lnõâ pokles sil se pohyboval od 28 % do 60 % po 24 hodinaâ ch aod 39 % do 68 % po 21 dnech. NejmensÏ õâ procentuaâ lnõâ ztraâ tu sil oproti vyâ chozõâ sõâle meï ly rïetõâzky Power Chain open space, Ormco; Memory chain closed, AO a Elasto Force with connector, Dentaurum. Naobr. 3 je videï t podobnyâ charakter poklesu sõâly apruêbeïhukrïivek jako prïi protazïenõâ o 50 %, opeï t s nejstrmeï jsï õâm poklesem v prvnõâch 24 hodinaâ ch. KrÏivkapo- Obr. 3. Poklesu pruêmeï rnyâch sil v cï ase prïi protazï enõâ o 100 % vyâchozõâ deâ lky rïetõâzku Fig. 3. Mean forces degeneration over a period of time after stretching by 100% of the initial length percentage of force degeneration oscillated between 24 and 62 per cents after 24 hours and between 31 and 70 per cents after 21 days. The least force degeneration in per cents was recorded for Memory Chain Closed, AO; Elasto Force with connector, Dentaurum; and Dura Chain close link, Orthocare. In Figure 2 we can observe an obvious distribution of initial values of forces induced by elastic chains. Shapes of curves for all chains as well as their decline are very similar. The steepest shape is observed within the first 24 hours. After stretching of chains by 100% of their initial length, the initial values of forces induced by chains at time 0 fluctuated between 3.2 N (Dura Chain Wide Link, Ortho-Care) and 6N (Dyna Link Continuous, G&H). After 21 days the range was between 1.6 N (Dura Chain Wide Link, Ortho-Care) and 3.2 N (Dyna Link Continuous, G&H). The percentage of force degeneration oscillated between 28 and 60 per cents after 24 hours and bet redakce@orthodont-cz.cz

7 ORTODONCIE rocïnõâk23 Tab. 3. PruÊ meï rneâ hodnoty sil aprocentuaâ lnõâ poklesy sil pro protazï enõâ o 50 % a100 % puê vodnõâ deâ lky ve zvolenyâch cï asovyâch intervalech u rïetõâzkuê s prestretchingem abez neï ho(rïetõâzky s prestretchingem oznacï eny barevneï av oznacï enõâ rïetõâzku jsou oznacï eny P ( CP, MP, WP) ) Tab. 3. Mean values of forces and forces degeneration in per cents after stretching by 50% and 100% of the initial length at given time intervals for the chains with prestretching, and without prestretching. Chains with prestretching have the letter P in the name/acronym of their type (CP, MP, WP). Obr. 4. RÏ etõâzky s prestretchingem abez neï ho prïi vyâ chozõâm protazï enõâ o 50% vyâchozõâ deâ lky. RÏ etõâzky s prestretchingem jsou oznacï eny prïidaâ nõâm P v typu ( CP, MP, WP). Fig. 4. Chains with and without prestretching at stretching by 50% of the initial length. Chains with prestretching have the letter P in the name/acronym of their type (CP, MP, WP). klesu sõâly jednoho rïetõâzku se ale svyâm pruêbeï hem vymykaâ. PrÏi 100 % protazï enõâ hodnoty sil tohoto rïetõâzku klesajõâ pomalu a i v zaâveï ru experimentu se pohybujõâ nahodnoteï 3,2 N. V experimentu zkoumajõâcõâm vliv prestretchingu byly do tabulky 3 zapsaâ ny pruêmeï rneâ hodnoty sil aprocentuaâ lnõâ poklesy sil prïi protazïenõâ o 50 % a100 % vyâchozõâ deâ lky rïetõâzkuê s prestretchingem ahodnoty pro tyteâzï rïetõâzky, ktereâ prestretchingem neprosï ly. Z pruê beï hukrïivek (obr. 4) lze usuzovat, zï e provedenyâ prestretching, prïinaâ sledneâ m protazïenõâ o 50 % vyâchozõâ deâ lky, ovlivnil produkci sil rïetõâzkuê. Dle pruêbeïhukrïivek (obr. 5) muêzï eme v tomto prïõâpadeï usuzovat, zï e provedenyâ prestretching, prïi naâ sledneâ m protazï enõâ o 100 % vyâ chozõâ deâ lky sõâly produkovaneâ rïetõâzky neovlivnil. Obr. 5. RÏ etõâzky s prestretchingem abez neï ho prïi vyâ chozõâm protazï enõâ o 100% vyâchozõâ deâ lky. RÏ etõâzky s prestretchingem jsou oznacï eny prïidaâ nõâm P v typu ( CP, MP, WP). Fig. 5. Chains with and without prestretching at stretching by 100% of the initial length. Chains with prestretching have the letter P in the name/acronym of their type (CP, MP, WP). ween 39 and 68 per cents after 21 days. The least force decrease in per cents was recorded for Power Chain Open Space, Ormco; Memory Chain Closed, AO; and Elasto Force with connector, Dentaurum). In Figure 3 we can observe similar force degeneration as in stretching by 50%; the steepest shape is observed within the first 24 hours. However, the shape of curve representing force degeneration of one chain is different. After stretching by 100%, forces of this chain decline slowly, and at the end of the experiment they are still at 3.2 N. In the experiment on prestretching, mean forces values and percentage of forces degeneration after stretching by 50 and 100% of the initial length of chains with prestretching were plotted in Table 3; there were plotted also values for the same brands of chains that did not undergo prestretching. redakce@orthodont-cz.cz 103

8 rocïnõâk23 ORTODONCIE Souhrn statistickeâ ho hodnocenõâ Pro obeï vyâchozõâ protazï enõâ (50 i 100 %), bylo signifikantneï prokaâ zaâ no, zï e pruê meï rnaâ sõâla v cï ase klesaâ, stoupaâ hodnotaprocentuaâ lnõâho poklesu sõâly arychlost poklesu sõâly v cï ase klesaâ, prïicï emzï v prvnõâch 24 hodinaâ ch je pokles sõâly nejveïtsïõâ. PrÏi vzaâ jemneâ m porovnaânõâ pruêmeï rnyâch sil prïi protazï enõâ o 50 % se silami prïi protazï enõâ o 100 % bylave vsï ech cï asech statisticky vyâznamneï vysï sï õâ hodnotapruê meï rnyâ ch sil prïi protazï enõâ o 100 % vyâchozõâ deâ lky rïetõâzku. Rychlost poklesu sõâly bylasignifikantneï vysï sï õâ prïi protazï enõâ o 100% pouze vcï asoveâ m intervalu 0-2 hodiny. PrÏi posouzenõâ vlivu deâ lky mezicï laâ nku naprodukci sil elastickyâmi rïetõâzky se nepodarïilo jednoznacï neï prokaâzat, zïe deâ lkamezicï laâ nku tuto produkci ovlivnõâ. Byl pouze zachycen trend, kteryâ naznacï uje, zï e hodnotapruêmeï rnyâ ch sil pro obeï protazï enõâ je statisticky vyâ znamneï nizï sï õâ u rïetõâzkuê s dlouhyâ m mezicï laâ nkem oproti rïetõâzkuê m s kraâ tkyâm mezicïlaâ nkem abez mezicïlaâ nku. PrÏi protazï enõâ o 100 % vyâchozõâ deâ lky rïetõâzku pak byl zachycen i trend vysï sï õâ rychlosti poklesu sõâly u rïetõâzku bez mezicïlaâ nku. PrÏi srovnaâ nõâ sil rïetõâzkuê, u kteryâch byl proveden prestretching s teï mi, u kteryâ ch prestretching proveden nebyl, byl prokaâzaânprïi protazïenõâ o 50 % vyâchozõâ deâ lky rïetõâzku ve vsï ech cï asech statisticky vyâ znamnyâ procentuaâ lnõâ pokles sõâly u rïetõâzkuê, ktereâ prestretching nepodstoupily. HodnotapruÊ meï rnyâ ch sil arychlost poklesu sõâly byly signifikantneï vysïsï õâ pouze v cï ase 0 u rïetõâzkuê bez prestretchingu. PrÏi protazï enõâ o 100 % vyâ chozõâ deâ lky nebyl prokaâzaâ n vliv prestretchingu ani na pruêmeï rnou hodnotu sil ani na procentuaâ lnõâ pokles sil ve vsï ech cï asech. Rychlost poklesu sõâly byla signifikantneï vysï sï õâ pouze v intervalu 2-8 hodin u rïetõâzkuê s prestretchingem. Diskuse PouzÏ itõâ elastickyâch rïetõâzkuê skyâtaâ ortodontistuê m rïadu vyâ hod. Pro jejich pouzï itõâ hovorïõâ jednoznacï neï jejich jednoduchaâ aplikovatelnost, nenõâ nutnaâ spolupraâce pacientaajsou relativneï levneâ. Jejich uzï itõâ maâ i nevyâ hody. Po vlozï enõâ do dutiny uâ stnõâ absorbujõâ vodu a slinu, zbarvujõâ se adochaâ zõâ k posï kozenõâ vnitrïnõâch vazeb vedoucõâ k trvaleâ deformaci aplikovanyâch rïetõâzkuê. NavõÂc na povrchu rïetõâzkuê dochaâ zõâ k precipitaci iontuê atvorbeï proteinoveâ ho filmu. Z toho pak pramenõâ rychlaâ ztraâ tasõâly vedoucõâ k postupneâ mu snizï ovaâ nõâ efektivity [2, 15, 16, 17]. KvuÊ li teâ to ztraâ teï je pro ortodontistu obtõâzïneâ urcï it aktuaâ lnõâ sõâlu prïenaâsï enou nazuby. NavõÂc je sõâlu nutno posuzovat individuaâ lneï dle prostrïedõâ dutiny uâ stnõâ jednotlivyâch pacientuê. Navzdory probõâhajõâcõâm debataâ m, zda lze aplikovat vyâ sledky experimentuê provedenyâ ch in vitro napodmõânky dutiny uâ stnõâ, kde musõâme vzõât v uâ vahu dalsï õâ vlivy Shapes of curves (Fig.4) suggest that prestretching affected forces induced by chains. Shapes of curves (Fig.5) suggest that prestretching did not affect forces produced by chains. Summary of statistical evaluation For both elongations (by 50 and 100 per cents) it was proved that the mean force decreases over a period of time, the value (in per cents) of force degeneration increases, and the rate of force degeneration decreases with time, and that the force degeneration is the greatest within the first 24 hours. Comparison of mean forces stretched by 50% and mean forces stretched by 100% showed that mean forces value was always statistically higher in case of stretching by 100%. In case of 100% stretching the rate of force degeneration was significantly higher only at the interval 0-2 hours. The effect of connecting link length on the delivery of force by elastic chains was not proved. There is only a tendency suggesting that mean force value for both stretchings is significantly lower in chains with a long connecting link (unlike in chains with a short connecting link or chains without a connecting link). In case of stretching by 100% there was recorded a tendency to more rapid force degeneration in chains without aconnecting link. Comparison of forces in chains with or without prestretching proved significant percentage of force degeneration in chains without prestretching (they were stretched by 50% at all intervals). Mean forces values and the rate of force degeneration were significantly higher only at time 0 in chains without prestretching. In case of stretching by 100% there was not proved any impact of prestretching with regard either to mean forces value or percentage of forces decline at all intervals. The rate of force degeneration was significantly higher only at interval 2-8 hours in chains with prestretching. Discussion Elastic chains bring a number of advantages for orthodontists - they are easy to use, the cooperation of a patient is not necessary, and they are relatively cheap. However, their application may also have weak points: after they are inserted into mouth cavity they absorb water and saliva, they change in colour, and their internal bonds may be damaged which results in their permanent deformation. Moreover, on the surface of chains there occurs ion precipitation and protein film is formed. That leads to rapid force degeneration resulting in a gradual decrease of effectiveness [2, 15, 16, 17]. Due to this loss, it is difficult for an orthodontist to determine actual force delivered on teeth. In addition, it is necessary to judge the force individually according to individual patients' mouth cavity conditions. Despite the redakce@orthodont-cz.cz

9 ORTODONCIE rocïnõâk23 jako je mikrobiaâ lnõâ flora, enzymy, vyâzï ivoveâ faktory atd., maâ experiment provedenyâ in vitro mnoho vyâ hod, pokud jde o charakteristiky materiaâ luê dõâky mozï nosti standardizace prostrïedõâ. Studie srovnaâ vajõâcõâ vyâ sledky experimentu provedeneâ ho in vitro navzduchu aprovedeneâ ho in vivo ukaâ zaly pomeï rneï velkeâ rozdõâly [8, 10, 12]; naopak srovnaâ nõâ vyâ sledkuê experimentu provedeneâ ho in vitro ve vlhkeâ m prostrïedõâ aexperimentu provedeneâ ho in vivo ukaâ zalo rozdõâly nepatrneâ [8]. VyÂsledky experimentaâ lnõâ cïaâ sti teâ to praâ ce potvrdily velkou variabilitu uâ rovneï vyâ chozõâ sõâly produkovaneâ elastickyâ mi rïetõâzky danou typem rïetõâzku avyâ robcem. PrÏi natazï enõâ o 50 % vyâchozõâ deâ lky se hodnoty sõâly pohybovaly v rozsahu 2,5 N do 5,8 N a prïi natazï enõâ o 100 % vyâchozõâ deâ lky v rozsahu 3,2 N do 6 N.Toto zjisïteïnõâ je v souladu s vyâ sledky mnohapublikovanyâ ch studiõâ [3, 4, 5, 6, 7, 8, 10, 11, 12, 13]. RovneÏzÏsena m podarïilo prokaâ zat a uprïesnit uâ bytek produkovaneâ sõâly v cï ase, prïicï emzï rychlost poklesu sõâly produkovaneâ rïetõâzky je nejveïtsï õâ v prvnõâch 24 hodinaâchadaâlesevcï ase snizï uje po celou dobu testovacõâho obdobõâ 3 tyâdnuê. Take tento poznatek se shoduje s dostupnou literaturou [3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]. Dle dostupneâ literatury delsï õâ testovacõâ obdobõâ ukaâ zalo jen nepatrnyâ pokles uâ rovneï produkovaneâ sõâly, nejdelsï õâ sledovanaâ testovacõâ periodabyla100 dnuê [14]. Pro nasï õâ klinickou praxi to znamenaâ,zïeuâ rovenï sõâly poskytovaneâ elastickyâmrïetõâzkem prïi kontrole pacienta v intervalu 4-6 tyâdnuê, by meïlabyât pravdeï podobneï velmi podobnaâ sõâle nameï rïeneâ po 3 tyâ dnech. Pokud se zabyâvaâ me posouzenõâm vlivu deâ lky mezicï laâ nku nasõâlu produkovanou elastickyâmi rïetõâzky, zde jizï naâ zory jednotneâ nejsou. NaprÏõÂklad De Genova, Stevenson akusy ve svyâ ch studiõâch potvrdili, zï e rïetõâzky s kraâ tkyâ m mezicï laâ nkem produkujõâ vysï sï õâ uâ rovenï sil nezï rïetõâzky s dlouhyâm mezicïlaâ nkem [9, 14]. V nasïem experimentu se naâ m jednoznacï neï nepodarïilo prokaâ zat ovlivneï nõâ produkce sil deâ lkou mezicï laâ nku. Pouze jsme zachytily trend, kteryâ naznacï il, zï e sõâly produkovaneâ rïetõâzky bez mezicïlaâ nku as kraâ tkyâm mezicïlaâ nkem jsou vysïsï õâ nezï ty, ktereâ produkujõâ rïetõâzky s dlouhyâm mezicïlaânkem. Eliades a kol. tvrdõâ, zïerïetõâzky s kraâ tkyâm mezicïlaânkem abez mezicï laâ nku budou ztraâ cet sõâlu rychleji, protozï e zbytkoveâ napeï tõâ v modulu se po jeho natazï enõâ koncentruje do ocï karïetõâzku, cozï ho oslabuje, a navõâc je zde veïtsï õâ riziko posï kozenõâ ocïkaprïi navleâkaâ nõâ nazaâ mek. To je dalsï õâ rizikovyâ faktor, kteryâ muê zï e ovlivnit produkci sil [2, 16]. Na zory naefekt prestretchingu jakozï to mozï neâ ho zpuê sobu ovlivneï nõâ produkce sil elastickyâmirïetõâzky jsou jesï teï võâce kontroverznõâ. VeÏ tsï inastudiõâ dospeï lake zjisï teï nõâ,zï e prestretching vyâ slednou hodnotu sil produkovanyâ ch elastickyâ mirïetõâzky neovlivnõâ [18, 19, 20]. Pokud neï ktereâ z nich prestretching doporucï ily, nedokaâ zaly current debate on application of results of the experiments carried out in vitro in the conditions of mouth cavity, where we have to consider other impacts, e.g. microbial flora, enzymes, nutrition, etc., the experiment carried out in vitro has many advantages with regard to materials characteristics - this is possible thanks to standardized conditions. The study comparing results of the experiment performed in vitro in the open air and the experiment carried out in vivo showed relatively great differences [8, 10, 12]. On the contrary, comparison of results of the experiment performed in vitro in a damp environment and the experiment done in vivo showed only slight differences [8]. Results of the experimental part of the presented study proved a great variability in the value of the initial force induced by elastic chains - it is due to the type and manufacturer of a given chain. When stretched by 50% of the initial length, the force values were between 2.5 N and 5.8 N; when stretched by 100% of the initial length, the values oscillated between 3.2 N and 6 N. This agrees with the results of many studies published [3, 4, 5, 6, 7, 8, 10, 11, 12, 13]. We also proved and specified the force degeneration over a period of time; the rate of the force degeneration is higher within the first 24 hours, and then it gradually decreases during the whole period of 3 weeks. This conclusion agrees with the literature available [3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]. According to the published works alonger testing period showed only aminute decline in the amount of the force induced by chains; the longest testing period took 100 days [14]. For our clinical practice this means that the force delivered by elastic chain measured at the interval of 4-6 weeks during apatient's check-up should be very close to the value obtained after 3 weeks. The views on the impact of a connecting link length on the force induced by elastic chains are not uniform. E.g. De Genova, Stevenson, and Kusy state that chains with a short connecting link produce bigger force than those with a long connecting link [9, 14]. Our experiment did not prove the relationship between force delivery and the connecting link length. However, there is atendency suggesting that the forces induced by chains without aconnecting link or with ashort connecting link are bigger than those induced by chains with a long connecting link. Eliades et al. conclude that chains with a short connecting link or without a connecting link lose the force more quickly because a residual strain in the module concentrates into a chain unit which makes the module weaker, and additionally, there is also a higher risk of damage to the unit during the process of its attachment to a bracket. This is another risk factor that may affect delivery of forces [2, 16]. The views on the effect of prestretching on the production of forces by elastic chains are even more con- redakce@orthodont-cz.cz 105

10 rocïnõâk23 ORTODONCIE stanovit mõâru prestretchingu [6]. Dle nasï eho experimentu se zdaâ,zï e prestretching ovlivnõâ vyâslednou produkci sõâly rïetõâzkuê, pokud vzdaâ lenost, nakterou rïetõâzek nataâ hneme, bude vyâ razneï mensï õâ nezï vzdaâ lenost, na kterou jsme provedli prestretching. Za rovenï tõâm muêzï eme ovlivnit pocï aâ tecï nõâ neprïõâjemneâ pocity vnõâmaneâ pacientem. PodobneÏ se k teâ to problematice ve sveâ studii stavõâ Stevenson a Kusy [14]. S ohledem navyâ sledky experimentu je pomeï rneï zajõâmaveâ zhodnotit problematiku prïenosu sil rïetõâzku na zub jako prostrïedku produkujõâcõâho sõâly kontinuaâ lnõâ nebo, jak tvrdõâ Proffit, sõâly prïerusï ovaneâ [21]. Uka zalo se, zïeprïi protazï enõâ o 100 % vyâchozõâ deâ lky se produkce sil neï kteryâch rïetõâzkuê pohybuje v hodnotaâchprïesahujõâcõâch ªbezpecÏ neâ ª uzï itõâ rïetõâzkuê. PrÏi tomto protazï enõâ by mohly prïevaâ zï it nechteï neâ anezï aâ doucõâ uâ cï inky elastickeâ horïetõâzku. Dle teï chto vyâ sledkuê bychom tyto sõâly produkovaneâ elastickyâmi rïetõâzky zarïadili do kategorie sil nevhodnyâ ch. ZaÂveÏr 1. PodarÏilo se prokaâ zat, zï e sõâly produkovaneâ rïetõâzky protazï enyâmi o 50 a100 % jejich vyâchozõâ deâ lky nejsou stejneâ apodleâ hajõâ sï irokeâ variabiliteï dle typu rïetõâzku avyârobce. Pohybujõ se v rozmezõâ 2,5 N - 5,8 N pro protazï enõâ o 50 % av rozmezõâ 3,2 N - 6 N pro protazïenõâ o 100 % vyâchozõâ deâ lky rïetõâzkuê. 2. Bylo potvrzeno, zïe beï hem prvnõâch 24 hodin dochaâ zõâ k nejveï tsï õâm ztraâ taâ m sõâly produkovaneâ rïetõâzky arychlost poklesu sil v cï ase se daâ le snizï uje. Srovna me-li rychlosti uâ bytku sõâly prïi protazï enõâ o 50 % aprïi protazï enõâ o 100 %, statisticky vyâznamneï vysïsï õâ rychlost poklesu najdeme pouze v intervalu 0-2 hodiny. Velikost pruêmeï rneï puê sobõâcõâch sil vyvinutyâchrïetõâzky je ve vsï ech cï a- sovyâch intervalech vysïsïõâprïi protazï enõâ o 100 % vyâchozõâ deâ lky. 3. PrÏi protazï enõâ rïetõâzkuê o 50 i 100 % jejich vyâchozõâ deâ lky se nepodarïilo jednoznacï neï prokaâ zat vliv deâ lky mezicï laâ nku nauâ rovenï produkovaneâ sõâly ani na rychlost jejõâho naâ sledneâ ho poklesu. 4. PrÏi testovaâ nõâ vlivu prestretchingu nauâ rovenï vyâchozõâ sõâly ajejõâ naâ slednyâ pokles v cï ase se podarïilo jednoznacï neï prokaâ zat, zï e vyâ chozõâ sõâlaprïi prestretchingu anaâ sledneâ m protazï enõâ o 50 % jejich vyâchozõâ deâ lky je nizï sï õâ nezï vyâ chozõâ sõâlau rïetõâzkuê, ktereâ prestretching nepodstoupily. Na slednyâ procentuaâ lnõâ pokles sõâly v cï ase je pak rovneï zï nizïsï õâ u rïetõâzkuê, ktereâ prosï ly prestretchingem ve srovnaâ nõâ srïetõâzky, u kteryâ ch jsme prestretching neprovedly. 5. U rïetõâzkuê, kde prestretching nebyl proveden anaâsledneï byly protazïeny o 100 % jejich vyâchozõâdeâ lky, nebyly vyârazneâ rozdõâly ani ve vyâchozõâ uâ rovni sõâly ani v naâsledneâ m procentuaâ lnõâm poklesu sõâly v cï ase. troversial. The majority of studies conclude that prestretching does not influence the resulting amount of force induced by elastic chains [18, 19, 20]. The works recommending prestretching did not give the extent of elongation [6]. Our experiment suggests that prestretching can influence resulting force delivery by chains only in case that the distance to which the chain is stretched is significantly shorter than the length of prestretching. At the same time, we can also alleviate the initial discomfort of a patient. Stevenson and Kusy maintain the same position [14]. With respect to the results of our experiment, it is interesting to assess the problem of chain induced forces transfer on a tooth as the means producing continual forces or, as Proffit states, interrupted forces [21]. It turned out that after stretching by 100% of the initial length, the force delivery by some chains reached values exceeding ªsafeªchains application. In such cases the unwanted and undesirable effects of elastic chain might prevail. According to these results we would classify such forces induced by elastic chains as unsuitable. Conclusion 1. The study proved that forces induced by chains stretched by 50 and 100% of their initial length are not identical; they differ considerably according to the chain type and brand. The values oscillate between 2.5 N and 5.8 N after 50% stretch and between 3.2 N and 6 N after 100% stretch. 2. The study proved that within the first 24 hours the forces induced by chains degenerate rapidly, and the rate of force degeneration slows down over a period of time. Comparison of the force degeneration after 50% stretching and 100% stretching showed significantly more rapid decline only at the interval 0-2 hours. The mean value of forces induced by chains is higher at all intervals after stretching by 100% of the initial length. 3. In chains stretched by 50 and 100% we could not prove the effect of aconnecting link length on the amount of the force induced or on the rate of its subsequent decline. 4. Testing of prestretching effects on the amount of initial force and its subsequent decline over a period of time proved that the initial force in prestretching and subsequent stretching by 50% is lower than the initial force in chains that did not undergo prestretching. The following decline of force in time (given in per cents) is also lower in chains that underwent prestretching. 5. In chains without prestretching that were stretched by 100% of their initial length, there were found no significant differences in the initial amount of force or in force decline (given in per cents) over aperiod of time. The above given findings may be reflected in the following clinical recommendations: redakce@orthodont-cz.cz

11 ORTODONCIE rocïnõâk23 Uvedena zjisïteï nõâ mohou veâstkteï mto klinickyâm doporucï enõâm: 1. Vzhledem k rozdõâlnosti uâ rovneï iniciaâ lnõâ sõâly produkovaneâ rïetõâzky ruê znyâ ch vyâ robcuê zvaâ zï it vyâbeï r odpovõâdajõâcõâho rïetõâzku podle pozï adovaneâ ho uâ cï inku. Nejde totizï pouze o prïõâpadneâ prïetõâzï enõâ zubuê, u nichzï ocï ekaâvaâ me, zïe puê sobenõâm rïetõâzku zmeï nõâ sveâ postavenõâ, ale takeâ o prïõâpadneâ negativnõâ ovlivneï nõâ kotevnõâ jednotky. NasÏ õâm cõâlem je dosaâ hnout pohybu zubu co nejmensïõâ, avsïak uâcï innou aplikovanou silou, abychom eliminovali v nejvysïsï õâ mozïneâmõârïe riziko nechteïnyâch anezïaâ doucõâch uâcï inkuê spojenyâch s pouzï itõâm elastickyâch rïetõâzkuê. 2. Uka zalo se, zïeneï ktereâ rïetõâzky prïi nadmeï rneâ m natazï enõâ budou produkovat sõâly, ktereâ toto riziko vyâ razneï zvysï ujõâ. Proto je namõâsteï urcï itaâ obezrïetnost prïi leâcï beï nasï ich pacientuê iprïi pouzï itõâ tak beïzïneâ pomuê cky jako je elastickyâ rïetõâzek. 3. Pokud budeme chtõât leâ pe kontrolovat sõâly produkovaneâ elastickyâ mi rïetõâzky, je namõâsteï vyâ chozõâ kontrolasõâly nasilomeï ru adle tohoto uâ daje naplaâ novat dalsï õâ kontroly pacienta v ordinaci. 4. PouzÏ itõâm prestretchingu muê zï eme pozitivneï ovlivnit vyâ chozõâ hodnotu aplikovaneâ sõâly, tõâm zmõârnõâme neprïõâjemneâ subjektivnõâ pocity nasï ich pacientuê a naâ slednyâ pokles sõâly v cï ase bude meâneïvyâraznyâ. PodeÏ kovaâ nõâ: Autorky deï kujõâ Mgr. KaterÏineÏ LangoveÂ, Ph. D. za pomoc prïi zpracovaâ nõâ statistickyâ ch vyâ sledkuê. Autorky nemajõâ komercï nõâ, vlastnickeâ nebo financï nõâ zaâ jmy na produktech nebo spolecï nostech popsanyâ ch v tomto cïlaâ nku. Literatura/ References 1. Mleziva, J.: Polymery-vy roba, struktura, vlastnosti a pouzïitõâ, Praha: Sobota les, Brantley, W. A.; Eliades, T.: Orthodontics Materials, Scientific and Clinical Aspects, 1st ed. New York: Thieme Stuttgart, Baty, D. L.; Storie, D. J.; von Fraunhofner, J. A.: Synthetic elastomeric chains: a literature review. Amer. J. Orthodont. dentofacial Orthop. 1994, 105, s Bishara, S. E.; Andreasen, G. F.: A comparison of timerelated forces between plastic alastics and latex elastics. Angle Orthodont. 1970, 40, s Hershey, G.; Reynolds, W.: The plastic module as an orthodontic tooth moving mechanism. Amer. J. Orthodont. 1975, 67, s Wong, A. K.: Orthodontic elastic materials. Angle Orthodont. 1976, 46, s Kovatch, J.; Lautenschlager, D.; Keller, J.: Load extension-time behavior of orthodontic alastiks. J. dent. Res. 1976, 55, s Ash, J.; Nikolai, R.: Relaxation of orthodontic elastic chains and modules in vitro and in vivo. J. dent. Res. 1978, 57, s De Genova, D. C.; McInnes-Ledoux, P.; Weinberg, R.; Shaye, R.: Force degradation of orthodontic elastomeric 1. With regard to different amounts of the initial force induced by chains of different brands, the appropriate chain should be chosen according to the effect required. The problem is not only an eventual overload of teeth that should alter their positions due to chain force delivery, but also the potential negative effect on the anchorage. Our aim is to move a tooth with as light force applied as possible, in order to eliminate potential risks of unwanted and undesirable effects arising from the use of elastic chains. 2. It turned out that during excessive stretching some chains would produce forces that raise the risk significantly. Therefore, we should always be very cautious when treating our patients even if we use as common a tool as an elastic chain. 3. In case we want to better control forces induced by elastic chains, we should set the initial amount of force with a force gauge, and then - depending on the data obtained - plan further check-ups of a patient. 4. Prestretching may positively affect the initial amount of the force applied, and thus can alleviate subjective discomfort of our patients, and the subsequent force decline over aperiod of time will be less noticeable. Acknowledgment: The authors want to express their gratitude to Mgr.KaterÏina LangovaÂ, Ph.D., for her help in statistical processing of the data. The authors have no commercial, proprietary or financial interest in products or companies mentioned in the article. chains-a product comparison study. Amer. J. Orthodont. 1985, 87, s Rock, W.; Wilson, H.; Fisher, S.: A laboratory investigation of orthodontic elastomeric chain. Brit. J. Orthodont. 1985, 12, s Killiany, D.; Duplessis, J.: Relaxation of elastomeric chains. J. clin. Orthodont. 1985, 19, s Kuster, R.; Ingervall, B.; Burgin, W.: Laboratory and intraoral test of the degradation of elastic chains. Eur. J. Orthodont. 1986, 8, s Buchmann, N.; Senn, Ch.; Ball, J.; Brauchli, L.: Influence of initial strain on the force decay of currently available elastic chains over time. Angle Orthodont. 2012, 82, s Stevenson, J. S.; Kusy, R. P.: Force application and decay characteristics of untreated and treated polyurethane elastomeric chains. Angle Orthodont. 1994, 64, s Huget, E. F.; Patrick, K. S.; Nunez, L. J.: Observations on the elastic behavior of a synthetic orthodontic elastomer. J. dent. Res. 1990, 69, s Eliades, T.; Eliades, G.; Watts, D. S.: Structural conformation of in vitro and in vivo aged orthodontic elastomeric modules. Eur. J. Orthodont. 1999, 21, s redakce@orthodont-cz.cz 107

12 rocïnõâk23 ORTODONCIE 17. Ferriter, J.; Meyers, C.; Lorton, L.: The effect of hydrogen ion concentration on the force degradation rate of orthodontic polyurethane chain elastics. Amer. J. Orthodont. dentofacial Orthop. 1990, 98, s Hershey, H.; Brooks, D.: Effect of heat and time on stretched plastic orthodontic modules. J. Dent. Res. 1976, 55B, s [Cit. in: Baty, D. L.; Storie, D. J.; von Fraunhofner, J. A.: Synthetic elastomeric chains: a literature review. Amer. J. Orthodont. dentofacial Orthop. 1994, 105, s ] 19. Young, J.; Sandrik, J. L.: The influence of preloading on stress relaxation of orthodontic elastic polymers. Angle Orthodont. 1979, 49, s von Fraunhofner, J. A.; Coffelt, M.-T. P.; Orbell, G. M.: The effects of artificial saliva and topical fluoride treatments on the degradation of the elastic properties of orthodontic chains. Angle Orthodont. 1992, 62, s Proffit, W. R.; Fields, H. W.: Contemporary orthodontics. 5th ed., St. Louis: Mosby, MUDr. Alena Forma nkovaâ Stomatologicka klinika FNKV Praha SÏ robaâ rova 50, , Praha 1 Stomatologicka klinika a Klinika plastickeâ chirurgie 3. LF UK FNKV Praha porïaâ dajõâ dne od 9 do 17 hodin v posluchaâ rneï Kliniky plastickeâ chirurgie (pavilon N) mezioborovyâ seminaârï RozsÏteÏ py Dopolednõ blok : urcïenprïedevsï õâm pro postgraduaâ lnõâ studenty. Odpolednõ blok : zveme vsï echny zaâ jemce o problematiku rozsïteïpuêzrïad odborneâ verïejnosti. Vstup volnyâ. BlizÏsÏ õâ info , p. BrÏezinova SeminaÂrÏ se konaâ pod zaâsï titou CÏ eskeâ ortodontickeâ spolecï nosti redakce@orthodont-cz.cz