TrÏenõÂ ortodontickyâchzaâ mkuê Friction in Orthodontic Brackets

Transcription

1 ORTODONCIE rocïnõâk24 TrÏenõ ortodontickyâchzaâ mkuê Friction in Orthodontic Brackets *MUDr. Daniela StrakovaÂ, **Mgr. KaterÏina LangovaÂ, Ph.D., Doc. *MUDr. PavlõÂna CÏ ernochovaâ, Ph.D. *Ortodonticke oddeï lenõâ, Stomatologicka klinika FN u sv. Anny v BrneÏ *Department of Orthodontics, Clinic of Dentistry, St.Anne's University Hospital, Brno **Katedra leâ karïskeâ biofyziky, LF UP Olomouc **Department of Medical Biophysics, Medical Faculty of Palacky University, Olomouc Souhrn CõÂl: CõÂlem teâ to praâ ce bylo zmeï rïit statickeâ a dynamickeâ trïenõâ mezi ruê znyâ mi druhy ortodontickyâch zaâ mkuê in vitro. Zjistit, zda se meï nõâ hodnoty trïenõâ se zmeï nou angulace zaâ mku a porovnat trïenõâ mezi materiaâ lovyâ mi skupinami zaâ mkuê. Materia l a metodika: PromeÏ rïeno bylo celkem 24 druhuê ortodontickyâ ch zaâ mkuê (s draâ zï kou velikosti 0.018). MeÏrÏenõ trïenõâ probõâhalo na prïõâstroji ZWICK Z020 u vsï ech 72 ortodontickyâ ch zaâ mkuê s jednõâm ortodontickyâ m draâ tem z nerezaveï jõâcõâ oceli. VsÏ echna meï rïenõâ byla provedena za standardnõâch podmõânek v laboratorïi, v sucheâ m prostrïedõâ a v angulaci 0, 5 a10. Vy sledky: Zvy sledkuê praâ ce vyplyâvaâ,zïe statickeâ i dynamickeâ trïenõâ se mezi druhy zaâ mkuê lisï õâ, nejvysïsï õâch hodnot dosahujõâ zaâ mky z monokrystalickeâ keramiky. Se zvysï ujõâcõâ se angulacõâ se zvysï ujõâ i hodnoty trïenõâ prïõâmo uâ meï rneï. Mezi ortodontickyâ mi zaâ mky ze stejneâ ho materiaâ lu (kovoveâ, plastoveâ, keramickeâ a s vlozï enou kovovou draâ zï kou) jsme nezjistili statisticky vyâ znamnyâ rozdõâl ve velikosti dynamickeâhotrïenõâ. ZaÂveÏr:I kdyzï situace in vitro prïi zkoumaânõâtrïenõâ materiaâluê ortodontickyâchzaâ mkuê je odlisïnaâ od situace in vivo v dutineï uâ stnõâ, je snaha o snizï ovaâ nõâ trïenõâ u ortodontickyâ ch materiaâ luê ovlivnï ovaâ nõâm mechanickyâ ch faktoruê, mezi ktereâ patrïõâ volba materiaâ lu ortodontickyâchzaâ mkuê, velmi duê lezïitaâ (Ortodoncie 2015, 24, cï. 3, s ). Abstract Aim: The aim of the presented study was to measure static and dynamic friction in different types of orthodontic brackets in vitro; to determine whether the friction values change with modified angulation of the bracket, and to compare friction in groups of brackets made of different materials. Material and method: 24 types of orthodontic brackets (with a slot of 0.018ª) were measured. Measurements were done with the tensile test machine ZWICK Z020 in all 72 orthodontic brackets with one orthodontic wire made of stainless steel. All measurements were performed under standard conditions in a laboratory, in a dry environment and in angulation of 0, 5, and 10. Results: It follows from the results that both static and dynamic friction is different for different types of brackets; the highest values are found in the brackets made of monocrystalline ceramics. Increasing angulation corresponds proportionally to increasing values of friction. Between the orthodontic brackets made of the same material (metal, plastic, ceramic, and with an inserted metal slot) we did not find a statistically significant difference in the value of dynamic friction. Conclusion: Though in vitro condition when examining friction of materials of orthodontic brackets differs from in vivo condition of mouth cavity, the effort to reduce the friction of orthodontic materials by influencing mechanical factors (e.g. material of orthodontic brackets) is very important (Ortodoncie 2015, 24, No. 3, p ). KlõÂcÏ ovaâ slova: statickeâ trïenõâ, dynamickeâ trïenõâ, angulace Key words: static friction, dynamic friction, angulation redakce@orthodont-cz.cz 153

2 rocïnõâk24 ORTODONCIE U vod Ortodoncie vyuzïõâvaâ ortodontickeâ zaâ mky a draâ teï neâ oblouky pro pohyb zubuê a nevyhne se tedy fyzikaâ lnõâm jevuê m, jako je trïenõâ. TrÏenõ je fyzikaâ lnõâ jev, kteryâ vznikaâ prïi posouvaânõâ (smyâkaâ nõâ) jednoho teï lesa po povrchu jineâ ho teï lesa. VeÏ tsï inou je tõâmmõâneï no trïenõâ mezi pevnyâmi teï lesy. Jeho puê vod je prïedevsï õâmv nerovnosti obou stycï nyâ ch ploch, kteryâ m i se teï lesa vzaâ jemneï dotyâ kajõâ. Nerovnosti povrchuê prïi posouvaâ nõâ teï les na sebe vzaâ jemneï naraâ zï ejõâ, deformujõâ se a obrusï ujõâ. Tak vznikaâ trïecõâ sõâla, jejõâzï puê sobisïteï je na stykoveâ plosï e obou teï les a jejõâzï smeïr mõârïõâ vzï dy proti smeï ru pohybu teï lesa. Jakost stycï nyâch ploch urcï uje materiaâl, z neï hozï jsou plochy vyrobeny (kov, plast, keramika, ocel), zatõâmco drsnost urcï uje zpuê sob opracovaâ nõâ ploch (lesï teï nõâ, povrchovaâ uâ prava) [1,2]. TrÏenõ muêzï eme definovat vztahem: Ft = f x Fn [N], kde Ft je trïecõâ sõâla, f je soucï initel trïenõâ a Fn je sõâla puê sobõâcõâ kolmo tlakem mezi teï lesy [3]. TrÏenõ mezi plochami dvou teï les, ktereâ se dotyâ kajõâ, nenõâ-li mezi nimi kapalnaâ nebo plynnaâ mezivrstva, se nazyâvaâ sucheâ trïenõâ. RozlisÏ uje se neï kolik druhuê sucheâhotrïenõâ: a) Staticke trïenõâ (klidoveâ ), ktereâ je definovaâ no nejmensï õâ silou potrïebnou k uvedenõâ teï lesa do pohybu. b) Kineticke (dynamickeâ /smykoveâ /v pohybu), ktereâ je daâ no minimaâ lnõâ silou udrzï ujõâcõâ teï leso v pohybu. PrÏi uvaâdeïnõâteï lesa do pohybu (za jinak stejnyâch podmõânek) je trïenõâ veïtsï õâ nezï uteï lesa pohybujõâcõâho se. TrÏenõ maâ v ortodoncii velkyâ vyâ znam, protozï e jeho vysokeâ hodnoty mohou ovlivnit vybranou mechaniku pohybu, snõâzï it efektivitu pohybu zubu a zatõâzïit kotevnõâ jednotku. Ortodonticke materiaâ ly podleâ hajõâ neustaâ leâ mu technologickeâ m u vyâ voji, cozï znacï neï ovlivnï uje hodnoty trïenõâ, je ale duê lezï iteâ znaâ t biologickeâ principy prïi pohybech zuby k tomu, aby vznikaly noveâ a vylepsï eneâ kombinace materiaâluê a biomechanickeâ principy. V pruêbeïhu poslednõâch dvaceti let jizï vznikly noveâ zaâ mky, draâ ty i ligatury slibujõâcõâ nizïsïõâ trïenõâ [4]. PrÏi klouzaâ nõâ draâtuê draâzï kami zaâmkuê a kanylami, vzïdy dochaâ zõâ k urcï iteâ mu odporu na rozhranõâ zaâmkuê a draâtuê. Tento jev vznikaâ nejen prïi nivelizaci, zavõâraâ nõâ mezer, ale iprïi torznõâmpohybu na konci leâcï by. Takto se ztraâcõâcïaâst sõâly aplikovaneâ na zub, zbytek je prïeveden na zub a jeho periodonciuma zpuê sobuje pohyb zubu. Podle Kojimy a Fukui [5] je azï 60% aplikovaneâ sõâly ztraceno ve statickeâ m trïenõâ. TudõÂzÏ odpoveï d' biologickyâ ch tkaâ nõâ nastaâ vaâ azï prïi sõâle prïekonaâ vajõâcõâ statickeâ trïenõâ. Toto nutõâ ortodontisty pouzï õâvat prïi kluzneâ mechanice vysï sï õâ sõâly a zateïzïovat tak kotevnõâ jednotku. PromeÏ nneâ ovlivnï ujõâcõâ trïenõâ muê zï eme rozdeï lit na biologickeâ a mechanickeâ: Introduction In orthodontics the brackets and wire arches are used for teeth movement, and therefore orthodontics has to deal with physical phenomena, such as friction. Friction is a physical phenomenon arising from moving (dragging) one solid surface on surface of another body. Mostly it is the friction between two solid objects. It arises due to the uneveness of both contact surfaces. During the objects movement, the uneven surfaces collide, deform, and abrade. Thus friction force originates which operates on the contact surface of both objects; its direction goes always against the direction of the object movement. The quality of contact surfaces is given by the material of which the surfaces are made (metal, plastic, ceramics, steel), while the roughness is given by the treatment of the surfaces (polishing, surfacing) [1,2]. Friction is defined as follows: Ft = f x Fn [N], where Ft is friction force, f is friction coefficient, and Fn is force operating with pressure across the objects [3]. Friction between surfaces of two objects that are in contact without a fluid or gaseous inter-layer is called dry friction. Dry friction is subdivided into: a) Static friction (friction of repose) is determined by the least force required to get the object in motion. b) Kinetic friction (dynamic/shear/moving friction) is determined by the minimum force required to maintain the object in motion. When getting the object in movement (under the same conditions), friction is greater than in case of the object which is in movement already. In orthodontics the friction plays an important role as its great values may influence the selected movement mechanics, lower the effectiveness of a tooth movement, and load an anchorage unit. Orthodontic materials have been undergoing technological development, which considerably influences friction values. For the new and upgraded combinations of materials and biochemical principles it is necessary to know biological principles in teeth movement. During the last two decades new brackets, wires and ligatures were developed that may lead to reduced friction [4]. During sliding of wires through brackets slots and tubes, there is always present some resistance on the border between brackets and wires. This occurs not only in nivelization, space closing, but also during torque movement at the end of the treatment. Thus a part of the force applied on a tooth is lost, the rest is transmitted onto the tooth and its periodontium, and results in the tooth movement. Kojima and Fukua [5] report that as much as 60% of the force applied is lost due to static friction. The response of biological tissues thus occurs only when the force overcomes the static friction. Therefore, orthodontists have to ap redakce@orthodont-cz.cz

3 ORTODONCIE rocïnõâk24 a) Biologicke - slina, plak a zbytky potravy, biodegradace materiaâlu puê sobenõâmv dutineï uâ stnõâ, kdy zkoumaâ nõâmkovovyâch zaâ m kuê po ortodontickeâ leâ cï beï se zjistilo, zïe dosï lo ke korozi, uâ naveï materiaâ lu a plastickeâ deformaci. Takte zï se zjistilo, zï e takto posï kozeneâ zaâ m- ky zvysï ujõâ trïenõâ o 20% oproti stejnyâ mnovyâ mkusuê m[6]. b) Mechanicke - mõâsto a smeïr puê sobõâcõâ sõâly, sïõârïka zaâmkuê, mezizaâ mkovaâ vzdaâ lenost, vyâbeï r materiaâ lu, povrch v draâzïce zaâ mku, charakter draâ tu jako materiaâl, pruzï nost, tvrdost, hrubost povrchu, pruê m eï r pruê rïezu, tvar pruêrïezu, kompozice, opotrïebenõâ [7]. Elasticka deformace draâ tu, deformovanyâ draâ t tlacï õâ proti steï neï draâzïkyzaâ mku silou, kteraâ jezaâ vislaâ na pruzïnosti draâ tu. TrÏenõ je pak uâ m eï rneâ teâ to prïõâtlacï neâ sõâle. CÏ õâmje draâ t elasticïteïjsï õâ, tõâmprïõâtlacïnaâ sõâla ubyâvaâ. A ligace, ta hraje zaâsadnõâ roli ve vyâ znamu trïenõâ, prïipevneï nõâ draâ tu do zaâ m ku pomocõâ ligatur muê zï e znacï neï ovlivnit trïecõâ sõâlu, protozïe zaâ visõâ na velikosti utazï enõâ, kterou prïitlacï uje ligatura draâ t do zaâ mku. U kovovyâch ligatur jsme schopni vyvinout sõâlu i 5 N, proto muêzï evykazovat veïtsïõâtrïenõâ nezï elastickaâ ligatura [8]. Ota zka trïenõâ je poneï kud slozï itaâ, existuje mnoho promeï nnyâ ch, ktereâ ovlivnï ujõâ velikost trïecõâ sõâly, obzvlaâ sï teï jejich kombinace zaâ mek/draâ t/ligace. Materia l a metodika K testovaâ nõâ bylo pouzï ito 24 druhuê ortodontickyâch zaâ m kuê (pravyâ hornõâ sï picï aâ k), od kazïdeâ ho druhu byly 3 zaâ mky, celkem 72 zaâ m kuê s velikostõâ draâ zï ky palcuê. Aby bylo mozïno prïipevnit testovaneâ vzorky do pevneâ cï aâ sti prïõâstroje, museli jsme ortodontickeâ zaâ m ky fixovat na vaâ lcoveâ blocï ky z polyamidu 6 (PA6) o pruêmeï ru do 2 cm. PrÏedemjsme si prïipravili stupnici s uâ hly 0, 5, 10, kterou jsme na jednotliveâ blocï ky nalepili. KazÏdy zaâmek byl prïilepen k plastoveâ mu blocï ku lepidlembison Epoxy 2- component adhesive (vyâ robce Bison International corp.) v angulaci 0 (podle prïipraveneâ stupnice). Pode lnaâ osa draâzïky zaâ mku byla vzï dy stejneï orientovanaâ jako prïõâmka pro nulovou angulaci. Torzi 0 jsme zajistili tak, zïe osa draâzïky zaâ mku na bokorysu byla vzï dy kolmaâ na povrch plastoveâ ho blocï ku. Takto jsme nachystali 72 blocïkuêse72zaâ mky (24 druhuê po 3 kusech) (Obr. 1). Zajistili jsme, aby dno draâzïky zaâmku bylo vzï dy ve stejneâ vzdaâ lenosti od povrchu plastoveâ ho blocï ku a to tak, zï e jsme vyrobili kovoveâ desticï ky s vyfreâ zovanyâ motvorem, kteryâ odpovõâdal pruê m eï ru teï chto plastovyâ ch blocï kuê, ale byly vysï sï õâ. Na plastoveâ blocï ky se zaâ mky lepily fixovaneâ na draâ t z nerezaveï jõâcõâ oceli, kteryâ byl tvarovaâ n do põâsmena Z se dveï ma pravyâmi uâ hly a lezï el celou svou plochou na kovoveâ desticï ce, kromeï cïaâ sti s otvorem, tam byl umõâsteïnzaâ mek. Volny prostor mezi baâ zõâ zaâ mku a plastovyâ mblocï kemvyplnilo ply more force in sliding mechanics, and thus to load anchorage. Variables influencing friction may be divided into biological and mechanical ones: a) Biological - saliva, plaque and remains of food, biodegrading of the material in mouth cavity - the examination of metal brackets after the orthodontic treatment revealed corrosion, fatigue of material, and plastic deformation. It was always found out that the brackets thus damaged increased friction by 20% in comparison with the same new brackets [6]. b) Mechanical - place and direction of the force, width of brackets, distance between the brackets, material, surface of the bracket slot, characteristics of the wire, e.g. material, elasticity, hardness, surface roughness, diameter of cross section, shape of cross section, composition, wear [7]; elastic deformation of the wire, when the distorted wire pushes against the bracket slot wall with the force that depends on the wire elasticity. Friction then corresponds to this pressure force. The more elastic the wire, the less pressure. Ligation play a key role in friction; adjustment of the wire in the bracket with ligatures may greatly influence friction force, as it depends on the extent of tightening by which ligature pushes the wire into the bracket. In case of metal ligatures the force may be up to 5 N, and therefore this ligature can show greater friction than the elastic one [8]. The problemof friction is rather complicated, there are many variables influencing the amount of friction force, especially when they are combined - bracket/ wire/ligation. Material and method 24 types of orthodontic brackets (maxillary right canine) were tested, 3 brackets of each type, i.e. the total of 72 brackets with the slot of inches. To mount the tested samples onto the firm part of the test machine, the orthodontic brackets had to be fixed onto cylindrical blocks made of polyamide 6 (PA6) with the diameter up to 2 cm. The scale with angles 0, 5, 10 was glued to individual blocks. Each bracket was glued onto the plastic block with Bison Epoxy 2-component adhesive (Bison International Corp.) at the angulation of 0 (according to the scale). Longitudinal axis of the bracket slot was oriented in the same direction as the straight line for the new angulation. 0 torque was secured in such a way that the bracket slot axis on profile plane went perpendicular on the plastic block surface. This way 72 blocks with 72 brackets (24 types, 3 pieces each) were prepared (Fig.1). The bottomof the bracket slot was always at the same distance from the plastic block surface - we manufactured metal plates with a milled out hole corresponding to the blocks diameter. However, the plates were higher. Brackets (fixed on the stain- redakce@orthodont-cz.cz 155

4 rocïnõâk24 ORTODONCIE Obr. 1 lepidlo. Zajistili jsme tak nejen stejnou vzdaâ lenost dna zaâ mku od plastoveâ ho blocï ku, ale i nulovou torzi a spraâ vnou orientaci stupnice na plastoveâ mblocï ku i nulovou angulaci. PrÏipravene blocï ky tõâmto zpuê sobem bylo mozïneâ upnout do meïrïõâcõâho prïõâstroje ZWICK Z020 a pouzïõât pro vsï echna potrïebnaâ meïrïenõâ. MeÏ rïõâcõâ prïõâstroj byl univerzaâ lnõâ zkusï ebnõâ trhacõâ prïõâstroj rïõâzenyâ pocï õâtacï emzwick Z020 (Obr. 2). SõÂla byla meï rïena pomocõâ tenzometrickeâ silomeï rneâ hlavy s maximaâ lnõâ kapacitou 100 N a minimaâ lnõâ rozlisï ovacõâ schopnostõâ 0,03 N. PrÏemõÂsteÏ nõâ bylo snõâmaâ no jako draâha prïõâcïnõâku (pomocõâ inkrementaâ lnõâho snõâmacï e na posuvoveâ m sï roubu). PrÏõÂstroj byl rïõâzen a zkousï ky vyhodnoceny softwaremzwick TestXpert II. RÏ õâdõâcõâ parametr: rychlost prïõâcï nõâku 20 mm/min a podmõânka test-end: prïemõâsteïnõâ20 mm, naâ vrat na nulovou pozici rychlostõâ 100 mm/min. Konec draâ tu, kteryâ byl pomocõâ elastickeâ ligatury prïipevneï nkzaâ mku na plastoveâ mblocï ku, byl upevneï ndo hornõâ samosvorneâ cï elisti zkusï ebnõâho prïõâstroje, do dolnõâ samosvorneâ cï elisti byl umõâsteï n kovovyâ odlitek s vysoustruzï enyâ motvoremve velikosti plastoveâ ho blocï ku, kteryâ doneïho prïesneï zapadl. Pote se inicioval tah, prïi ktereâ mse cï elisti od sebe vzdalovaly rychlostõâ 20 mm za minutu. SõÂlu, prïi ktereâ dosï lo k uvedenõâ draâtu do pohybu a naâ slednou sõâlu prïi pruê chodu draâ tu draâzïkou zaâ mku zaznamenaâ val prïõâstroj v newtonech [N]. V pocï õâtacï oveâ m programu se zaznamenaâ valy hodnoty trïecõâch sil a vykresloval se graf. Kdy na pocïaâ tku dosïlo se zvysï ujõâcõâ se tazïnou silou (osa X) ke vzruê stu sõâly statickeâho trïenõâ (osa Y). Dra t se v zaâ mku nepohyboval. KrÏivka dosaâ hla vrcholu ve chvõâli, kdy se zacï al draât Obr. 2 less steel wire shaped into Z with two right angles and adhering to the metal plate except the part with a hole, in which the bracket was placed) were stuck onto the plastic blocks. The space between the bracket base and the plastic block was filled in with an adhesive. Thus we secured not only the same distance of the bracket bottom from the plastic block, but also a zero torque and the correct orientation of the scale on the plastic block, as well as zero angulation. These blocks could be firmly fixed in the testing machines ZWICK Z020 and used for measurements. The measuring device was a universal testing shredding appliance controlled by a computer - ZWICK Z020 (Fig.2). The force was measured with a tensometric dynamometer prop with the maximum capacity 100 N, and the minimum resolving power 0.03 N. The transfer was scanned as a bind binder path (with the help of incremental scanner on the sliding redakce@orthodont-cz.cz

5 ORTODONCIE rocïnõâk24 v draâzïce zaâ mku pohybovat, naâ sledneï setrïecõâ sõâla snõâzï ila a ideaâ lneï (prïi absolutneï hladkyâ ch stycï nyâ ch plochaâ ch) byla azï do konce meïrïenõâ stejnaâ, jednalo se o sõâlu dynamickeâ ho (kinetickeâ ho) trïenõâ. Tahove zkousïky na meïrïõâcõâmprïõâstroji ZWICK Z020 provaâ deï la vzï dy stejnaâ osoba za stejnyâ ch laboratornõâch podmõânek. PrÏipravene zaâ mky na plastovyâ ch blocï cõâch a draâ ty z nerezaveï jõâcõâ oceli (Remanium, Dentaurum) jsme ocï istili 70% ethanolema osusï ili. Do zaâ mku uchyceneâ ho na plastoveâ mblocï ku jsme vlozï ili ocï isï teï nyâ, vzï dy novyâ ortodontickyâ draâ t z nerezaveï jõâcõâ oceli ve velikosti x a prïichytili pomocõâ vzï dy noveâ elastickeâ ligatury od firmy GAC (staâ le stejnyâ typ, vyârobce i sï arzï e), teï sneï prïed meï rïõâcõâ zkousï kou, aby nedosï lo k uâ naveï materiaâ lu. Upevnili jsme takto prïipravenyâ plastovyâ blocïek se zaâ mkem a draâ temdo kovoveâ ho odlitku. Do neï j byl vysoustruzï en otvor odpovõâdajõâcõâ velikosti plastoveâ ho blocï ku. PrÏesnost umõâsteï nõâ blocï ku do prïõâstroje a tõâmangulaci zaâ mku jsme kontrolovali pomocõâ stupnice na blocï ku. Rysky s angulacemi 0, 5 nebo 10 se musely prïekryâ vat s ryskami na kovoveâ cïaâ sti prïõâstroje. KazÏdyÂza mek byl meïrïen v angulaci 0, 5, 10, pro kazïdeâmeïrïenõâ byl pouzï ityâ novyâ draâ t a novaâ elastickaâ ligatura. Tento postup se opakoval za stejnyâch podmõânek pro vsï ech 72 zaâmkuê. Nutno uveâ st, zïe vsï echny zaâ mky a jejich draâzïky byly zkoumaâ ny z hlediska prïesnosti rozmeï ruê a jakosti ploch zveï tsï enõâmna stereolupeï. Vy sledky jsou soucï aâ stõâ jineâ ho odborneâ ho sdeï lenõâ. Data byla popsaâ na pomocõâ popisneâ statistiky, kteraâ spocï õâvala ve vyâpocï tu aritmetickeâ ho pruêmeï ru, smeï rodatneâ odchylky. Na sledneï bylo provedeno porovnaânõâ analyâzou rozptylu (ANOVA). Vy sledky MeÏ rïili jsme vsï ech 72 zaâmkuê s jednõâmortodontickyâm draâ temz nerezaveï jõâcõâ oceli v angulaci 0, 5 a 10, na prïõâstroji ZWICK Z020. a) statickeâ a dynamickeâ trïenõâ mezi druhy zaâmkuê Druhy zaâ mkuê se ve statickeâ mi dynamickeâ mtrïenõâ prïi angulaci 0 mezi sebou statisticky vyâ znamneï lisï õâ, p < 0,0001. Na slednyâmi Bonferroniho post hoc testy se ukaâ zaly vyâznamneï vysïsï õâ hodnoty u druhu Radiance (safõâroveâ zaâ mky z monokrystalickeâ keramiky) (Tab. 1). b) dynamickeâ trïenõâ mezi skupinami zaâmkuê ze stejneâ ho materiaâlu Dynamicke trïenõâ u ruê znyâ ch skupin zaâ mkuê ze stejneâ ho materiaâ lu bylo porovnaâ no testemanova. Nebyly prokaâ zaâ ny statisticky vyâ znamneâ rozdõâly mezi ruê z- nyâmi skupinami zaâmkuê, p = 0,056. KdyzÏ se ovsï empodõâvaâ me na pruêmeï ry dynamickeâho trïenõâ u jednotlivyâ ch skupin, zjistõâme, zï e skupina keramickyâchzaâmkuê m aâ teâmeï rï dvakraâtveï tsïõâpruê meï rneâ hodnoty dynamickeâhotrïenõâ nezï ostatnõâ skupiny (Tab. 2). screw). The machine was controlled and the tests evaluated with software Zwick TestXpert II. Controlling parameter: a bind binder speed 20 mm/min, and the testend condition: transfer 20 mm, return to zero position with the speed 100 mm/min. The end of the wire fixed onto the bracket placed on the plastic block with elastic ligature was attached to the upper self-locking jaw of the testing machine; a metal casting with a hole corresponding to the plastic block was placed in the lower self-locking jaw of the device. Then the tension was initiated due to which the jaws move away by 20 mm/min. The force at which the wire was set to motion, and the following force during the passage of the wire through the bracket slot was recorded in Newtons [N]. The software recorded values of friction forces and represent themin a graph. At the beginning the force of static friction increased (axis Y) due to the increasing torque force (axis X). The wire did not move in the bracket. The curve reached its top at the moment when the wire in the bracket slot started to move, then the friction force decreased, and ideally (in case of absolutely smooth contact surfaces) remained the same till the end of measurement. It was the dynamic (kinetic) friction force. Tensile tests on ZWICK Z020 were performed by the same person under the same laboratory conditions. The brackets on plastic blocks and stainless steel wires (Remanium, Dentaurum) were cleaned with 70% ethanol, and dried. Into the bracket on the plastic block we inserted cleaned, always new orthodontic wire of stainless steel, size of x 0.025ª, and attached it with always new elastic ligature by fy GAC (the same type, producer and batch) immediately before the test to avoid fatigue of material. The plastic block with the bracket and wire was adjusted in metal casting. In the metal casting a hole corresponding to the size of the plastic block was milled out. The accuracy of the block placement into the instrument, and the bracket angulation, was controlled with help of the scale placed on the block. Gauge marks with angulations 0, 5, and 10 had to meet gauge marks on the metal part of the instrument. Each bracket was measured in angulation of 0,5, 10 ; for each measurement a new wire and a new elastic ligature were used. The process was repeated under the same conditions for all 72 brackets. It is necessary to say that all brackets and their slots were examined from the viewpoint of dimensions accuracy and quality of surfaces with help of magnification with a stereo magnifying glass. The results are presented in another research report. The data were processed with descriptive statistics (arithmetic mean, standard deviation were calculated). Subsequently the comparison with analysis of variance (ANOVA) was made. redakce@orthodont-cz.cz 157

6 rocïnõâk24 ORTODONCIE Tab. 1. Staticke a dynamickeâ trïenõâ ortodontickyâch zaâmkuê s angulacõâ 0 Tab. 1. Static and dynamic friction in orthodontic brackets with 0 angulation statickeâ trïenõâ, static friction dynamickeâ trïenõâ, dynamic friction N.B. name material prod. n mean [N] SD mean [N] SD 1 Jewels Keramicky Dentaurum, NeÏ mecko Elegance SL Plastovy Dentaurum, NeÏ mecko Equilibrium2 MBT Kovovy Dentaurum, NeÏ mecko Equilibrium2 Roth Kovovy Dentaurum, NeÏ mecko Aspire Gold Keramicky se zlatou draâzïkou Forestadent, NeÏ mecko Brillant Plastovy Forestadent, NeÏ mecko Aesthetik-Line Bracket Plastovy Forestadent, NeÏ mecko Clarity Metal Reinforced Keramicky s kovovou draâzï kou 3M Unitek, USA Victory Kovovy 3M Unitek, USA Victory Series Gold Br. Zlaty 3M Unitek, USA Envision Plastovy Ortho Organizers, USA Edgewise Plastovy Ortho Organizers, USA Illusion Keramicky s kovovou draâzï kou Ortho Organizers, USA AlexandruÊ v zaâ mek Kovovy jednokrïõâdeâ lkovyâ Ortho Organizers, USA Mystique Keramicky GAC International, USA Sierra Plastovy s kovovou draâzïkou American Orthodontics, USA Virage Keramicky s kovovou draâzï kou American Orthodontics, USA Minimaster Gold Zlaty American Orthodontics, USA Silkon Plus Plastovy American Orthodontics, USA GlamKeramicky Forestadent, NeÏ mecko Omniarch Kovovy GAC International, USA Radiance Keramicky - safõârovyâ American Orthodontics, USA Opti - MimMini Twin Kovovy Ortho Organizers, USA Clarity Advanced Keramicky 3M Unitek, USA p < < N.B. - cï õâslo druhu zaâ mku, number of bracket type, name - naâ zev zaâ mku, material - material zaâ mku, bracket material, prod. - vyârobce, producer, n - pocïetmeïrïenõâ, number of measurements, mean - pruêmeï r ze 3 meïrïenõâ v Newtonech, mean from 3 measurements in Newtons, S.D. - smeï rodatnaâ odchylka, standard deviation. V poslednõâmrïaâ dku je uvedena dosazï enaâ hladina statistickeâ vyâznamnosti (p). The degree of the statistical significance is in the last line (p). Tab. 2. Dynamicke trïenõâ mezi skupinami zaâ mkuê ze stejneâ ho materiaâlu Tab. 2. Dynamic friction in groups of brackets of the same material dynamickeâ trïenõâ, dynamic friction skupina zaâ mkuê, n mean [N] S.D. group of brackets kovovyâ, metal plastovyâ, plastic keramickyâ, ceramic s kovovou draâzï kou, with an inserted metal slot n - pocïetmeïrïenõâ, number of measurements, mean - pruêmeï rnaâ hodnota dynamickeâho trïenõâ v Newtonech, mean value of dynamic friction in Newtons. p Tab. 3. Za vislost trïenõâ na angulaci Tab. 3. Correlation of friction with angulation statickeâ trïenõâ static friction dynamickeâ trïenõâ dynamic friction angulace angulation n mean [N] S.D p < < n - pocï et provedenyâch meï rïenõâ, number of measurements. V poslednõâmsloupci je uvedena dosazï enaâ hladina statistickeâ vyâznamnosti (p). The degree of the statistical significance is in the last column (p) redakce@orthodont-cz.cz

7 ORTODONCIE rocïnõâk24 c) angulace 0, 5 a 10 Porovna nõâmstatickeâ ho a dynamickeâ ho trïenõâ prïi ruê z- nyâ ch angulacõâch bylo provedeno neparametrickyâ m Friedmanovy mtestema naâ slednyâ mi Wilcoxonovy m i testy mnohonaâ sobneâ ho porovnaâ nõâ s Bonferroniho korekcõâ. TeÏ mito testy bylo prokaâzaâ no, zï e se zvysï ujõâcõâ se angulacõâ se zvysï ujõâ hodnoty statickeâ ho i dynamickeâ ho trïenõâ. DosazÏ enaâ hodnota statistickeâ vyâ znamnosti p byla mensï õâ nezï 0,0001 u Friedmanova testu i u vsï ech naâ sledneï provedenyâ ch Wilcoxonovy ch testuê (Tab. 3). Diskuse Je hodneï dostupneâ literatury na teâma trïenõâ u ortodontickyâch zaâmkuê. VeÏ tsï ina studiõâ porovnaâvaâ zaâmky s draâzïkou velikosti a mnoho se zabyâvaâ i samoligujõâcõâmi zaâ mky. CÏ asto byly srovnaâvaânyzaâ mky z nerezaveï jõâcõâ oceli se zaâ mky z polykrystalickeâ keramiky. ReferencÏ nõâmi ortodontickyâ mi draâ ty nebyla jen nerezaveïjõâcõâ ocel, ale i nikltitanoveâ a betatitanoveâ draâ ty. Existuje velkeâ mnozï stvõâ pracõâ, zabyâ vajõâcõâ se tõâmto teâ ma- tem, vyâ sledky jsou cï asto velmi rozdõâlneâ, neï kdy azï protichuê dneâ. DuÊ lezï ityâ mfaktorem, kteryâ vyâ razneï ovlivnï uje trïecõâ sõâlu mezi ortodontickyâmzaâ mkem a draâ temje druh ligace. V nasï õâ studii jsme pouzï ili elastickeâ ligatury od firmy GAC, pouzïõâvali jsme je pro kazïdeâmeïrïenõâ. VzÏdy jsme pouzï ili novou ligaturu teï sneï prïed provedenyâm meï rïenõâma to proto, aby nedochaâ zelo cï asemk uâ naveï materiaâ lu. Zvolili jsme elastickou ligaturu z toho duêvodu, zïe prïi pokusech s kovovou ligaturou se naâ mnikdy nepodarïilo dosaâ hnout stejneâ prïõâtlacï neâ sõâly. MeÏ rïili jsme ji speciaâ lnõâmsï roubovaâ kems nastavitelnyâ mmomentem. Na trhu existujõâ i elastickeâ ligatury se speciaâ lnõâmtvarem(nekonvencï nõâ elastickeâ ligatury), ktereâ zabraânõâ prïitlacï enõâ ortodontickeâ ho oblouku do draâzïkyzaâ mku. ZabyÂvali se jimi Baccetti a kol. [9]. Porovna vali pouzïitõâ konvencï nõâch a nekonvencï nõâch elastickyâ ch ligatur. Sestavili meï rïõâcõâ systeâ m, kde napodobili situaci v uâ stech. Bylo simulovaâ no postavenõâ 5 zubuê (strïednõâ rïezaâ k, lateraâ lnõâ rïezaâk,sï picïaâ k, prvnõâ a druhyâ premolaâ r) a to pro dva druhy zaâ mkuê z nerezaveï jõâcõâ oceli a keramiky. PouzÏ ili 0,014 silnyâ nikltitanovyâ oblouk. Postavenõ sï picï aâ ku bylo 1,5 mm, 3 mm, 4,5 mm a 6 mm od roviny draâ tu. Nalezli signifikantnõâ rozdõâly mezi konvencï nõâmi a nekonvencïnõâmi elastickyâ mi ligaturami mezi vsï emi testovanyâ mi variacemi, kromeï prïi postavenõâ sï picï aâ ku 1,5 mm od roviny draâ tu. UvaÂdõÂ, zïe pouzïityâ typ ligace ovlivnï uje velikost trïenõâ võâce nezï materiaâ l zaâ mku. DalsÏ õâ studie zabyâ vajõâcõâ se nekonvencï nõâmi ligaturami porovnaâ vala zaâ mky z nerezaveï jõâcõâ oceli ligovaneâ teï mito ligaturami a pasivnõâ samoligujõâcõâ zaâ mky. Gandini P. a kol. [10] uvaâdõâ, zï e nekonvencï nõâ typ ligatur a pasivnõâ Results 72 orthodontic brackets with one orthodontic wire of stainless steel were measured at angulation 0, 5, and 10 in the tensile test machine ZWICK Z020. a) Static and dynamic friction in different types of brackets Types of brackets differ significantly in both static and dynamic friction at angulation of 0, p < The following Bonferroni post hoc tests revealed significantly higher values in Radiance type of brackets (sapphire brackets made of monocrystalline ceramics) (Table 1). b) Dynamic friction in groups of brackets made of the same material Dynamic friction in different groups of brackets made of the same material was compared with ANOVA test. No statistically significant differences were proved, p= However, when we consider mean values of dynamic friction in individual groups, we can see that the group of ceramic brackets shows nearly twice as big mean values of dynamic friction as the rest of groups (Table 2). c) Angulation 0, 5, and 10 Comparison of static and dynamic friction at different angulations was done by non-parametric Friedman test and subsequently by Wilcoxon tests of multiple comparison with Bonferroni's correction. The tests proved that the increasing angulation corresponds to increased values of both static and dynamic friction. The value of statistic significance p was less than in Friedman test, as well as in all subsequent Wilcoxon tests (Table 3). Discussion There is a lot of literature dealing with friction in orthodontic brackets. Most studies compare the brackets with the slot of 0.022ª (inches), and many studies discuss self-ligating brackets. Often the brackets made of stainless steel are compared with the brackets made of polycrystalline ceramics. Reference orthodontic wires are not only stainless steel, but also nickel-titaniumand beta-titaniumwires. There is a lot of studies dealing with this topic. The results are frequently different, sometimes contradictory. A very important factor influencing bracket-wire friction is the type of ligation. We used elastic ligatures of fy GAC for each measurement. We always used a new ligature immediately before the measurement to avoid fatigue of material. We decided for an elastic ligature because in experiments with metal ligature we never achieved the same thrust/pressure force. We measured the force with a special screwdriver with adjustable momentum. redakce@orthodont-cz.cz 159

8 rocïnõâk24 ORTODONCIE samoligujõâcõâ zaâ mky meï ly teâ meï rï nulovou trïecõâ sõâlu u draâzïky velikosti 0,022 a draâ tu 0,014 i draâ tu pruêrïezu 0,019 x 0,025. ZatõÂmco prïi pouzï itõâ klasickyâ ch elastickyâch ligatur se trïecõâ sõâla prudce zvysï ovala. Naproti tomu Bednar a spol. [11] ve sveâ studii zjistili, zï e samoligujõâcõâ zaâ mky nemajõâ nizï sï õâ trïenõâ nezï zaâ mky z nerezaveï jõâcõâ oceli zaligovaneâ lehce kovovou ligaturou nebo elastickou ligaturou. MeÏ rïili zaâ mky s draâ zï kou velikosti 0,018 x 0,025. Dra ty, ktereâ pouzï ili, byly velikosti 0,014, 0,016, 0,018, 0,016 x 0,016 a 0,016 x 0,022. Da le jsme se v praktickeâ cïaâ sti zabyâvali otaâ zkou, zda prïi zmeïneï angulace dojde i ke zmeïneïtrïenõâ. K cï emuzï by logicky meï lo dojõât, protozï e draâ t v takoveâmprïõâpadeï neprochaâ zõâdraâzï kou zaâ mku rovneï,nyâbrzï se ohyâbaâ a dojde ke styku ortodontickeâ ho draâ tu s vnitrïnõâ hranou krïõâdla zaâ mku. Dra t se ohne a zacïnepuê sobit faktor bindingu. Pokud se angulace jesï teï zvyâsï õâ a prïekrocï õâ kritickyâ uâ hel mezi draâ zï kou zaâ mku a ortodontickyâ mdraâ tem, objevõâ se i faktor notchingu (zadõâraâ ni, zaryâvaâ nõâ se) do draâtuê. TõÂmpa demje trïenõâ vysï sï õâ nezï prïi 0 angulaci. Tento fakt se naâ mv nasï õâ studii potvrdil, pokud nasïe vyâsledky srovnaâ me s jinyâmivyâzkumy, dojdeme ke shodeï. Hamdan a Rock [12] zjistili, zï e velikost trïecõâ sõâly se se zveïtsï ujõâcõâ angulacõâ zaâ mku a torzõâ zvysï uje. MeÏ rïili angulaci od 0do12 na ruê znyâch kombinacõâch zaâmkuê a draâtuê. Podobna studie jako nasï e, ovsï ems mensï õâmmnozïstvõâmmeïrïenyâch draâtuêazaâmkuê, je studie Nishio a spol. [13]. Zkoumali trïenõâ mezi trïemi druhy zaâmkuê (z nerezaveï jõâcõâ oceli, z keramiky a keramickeâ zaâ mky s kovovou draâ zï kou) a trïemi druhy draâ tuê (z nerezaveï jõâcõâ oceli, nikltitanovyâ, beta-titanovyâ draâ t) prïi angulaci 0 a10. Zjistilo se, zï e nejvysï sï õâ trïenõâ vykazoval keramickyâ zaâ mek se speciaâ lneï povrchoveï upravenou keramickou draâ zï kou (silica-inserted slot), naâ sledoval keramickyâ zaâ mek s kovovou draâzïkou a nejnizïsïõâtrïenõâ vykazoval zaâ mek z nerezaveï jõâcõâ oceli. Shodli ve vyâ sledcõâch s angulacõâ zaâ mkuê. TrÏecõ sõâla rostla prïõâmo uâmeï rneï s rostoucõâ angulacõâ. MeÏrÏenõ provedli na testovacõâmzarïõâzenõâ Emic DL s rychlostõâ posunu draâtuzaâ mkem 0,5 cm/min po dobu 2 minut, ligovacõâ sõâla byla 200 g. Nenalezli jsme statisticky signifikantnõâ rozdõâly mezi skupinami ortodontickyâch zaâmkuê (nerezaveï jõâcõâ ocel, plast, keramika, vlozï enaâ draâ zï ka z nerezaveï jõâcõâ oceli). Stejny vyâ sledek zjistila i studie Downin a kol. [14] MeÏ rïili zaâ mky z nerezaveï jõâcõâ oceli a polykrystalickeâ keramiky (0,022) a ortodontickeâ draâ ty pruêrïezu 0,019 x 0,025 z nerezaveï jõâcõâ oceli, nikltitanu a betatitanu. MeÏrÏicõ prïõâstroj byl Instron Nenalezli signifikantnõâ rozdõâly ve trïenõâ mezi zaâ mky z nerezaveï jõâcõâ oceli a polykrystalickeâ keramiky. Kusy [15] ve sveâ polemice o keramickyâch zaâ mcõâch uvaâdõâ,zï e majõâvysïsï õâkoeficient trïenõânezï zaâ mky z nerezaveï jõâcõâ oceli ne kvuê li sveâ vysokeâ tvrdosti, ale kvuê li sveâ On the market there are also elastic ligatures of special shapes (unconventional elastic ligatures) that prevent pushing of the orthodontic arch into the bracket slot. Bacetti et al. [9] compared the use of conventional and unconventional elastic ligatures. They constructed a measurement system in which they imitated the condition of the oral cavity. Position of 5 teeth was simulated (central incisor, lateral incisor, canine, first and second premolar) for two types of brackets - made of stainless steel and ceramics. They used nickel-titanium arch of 0.014ª. Canine was located 1.5 mm, 3 mm, 4.5 mm, and 6 mm from the wire plane. The authors found significant differences between conventional and unconventional elastic ligatures in all variations tested, except of the canine located 1.5 mm from the wire plane. The authors concluded that the type of ligation had greater impact on the friction size than the material of brackets. Another study dealing with unconventional ligatures compared the brackets made of stainless steel ligated with these ligatures and passive self-ligating brackets. Gandini P. et al. [10] report that the unconventional type of ligatures and passive self-ligating brackets had almost zero friction force in case of the slot of 0.022ª and the wire of 0.014ª, as well as the wire x 0.025ª. On the other hand, when conventional elastic ligatures were used, the friction force increased sharply. On the contrary, Bednar et al. [11] came to the conclusion that self-ligating brackets did not have lower friction than the brackets made of stainless steel and ligated with metal or elastic ligature. They measured brackets with the slot of x 0.025ª; the wires had 0.014, 0.016, 0.018, x 0.016, and x 0.022ª. We also dealt with the question whether the change in angulation leads to the change in friction. In such a case the wire does not pass through the bracket slot straight but it bends, and thus the contact between the orthodontic wire and the inner tie wing of the bracket occurs. The wire bends and the binding factor starts to play its role. If the angulation increases even more and exceeds the critical angle between the bracket slot and the orthodontic wire, the notching factor occurs, too. Therefore, the friction is greater than in 0 angulation. Our study proved the fact, our results correspond to the results given by other authors. Hamdan and Rock [12] concluded that the size of friction force increases with increasing bracket angulation and torque. They measured angulation from 0 to 12 in different combinations of brackets and wires. The work of Nishio et al. [13] is similar to our study, however, the authors worked with fewer wires and brackets. They examined friction between three types of brackets (stainless steel, ceramic, and ceramic brackets with metal slots) and three types of wires redakce@orthodont-cz.cz

9 ORTODONCIE rocïnõâk24 vlastnõâ chemickeâ strukturïe. NenasÏ el rozdõâl v koeficientu trïenõâ u mono- a polykrystalickeâ keramiky. ZajõÂmava je studie Cha J.Y. a kol. [16]. Porovna vali mezi sebou ruê zneâ zaâ mky z keramiky a zaâ mky z nerezaveï jõâcõâ oceli pouzï ili jako kontrolu (0,022). KeramickyÂmi zaâ mky protahovali ortodontickeâ draâ ty z nerezaveï jõâcõâ oceli a betatitanu (0,019 x 0,025). Keramicke zaâmky byly rozdeï leny na skupiny polykrystalickeâ, monokrystalickeâ, s vlozï enou kovovou draâzïkou a se speciaâ lneï upravenou keramickou draâ zï kou (prïidanaâ vrstva oxidu krïemicï iteâ ho na polykrystalickou keramiku). Za veï r uvedl, zï e keramickeâ zaâ mky se speciaâ lneï upravenou keramickou draâ zï kou vykazujõâ podobneï maleâ trïenõâ jako zaâ mky z nerezaveï jõâcõâ oceli. Za rovenï se projevilo vysï sï õâ trïenõâ u betatitanovyâ ch ortodontickyâ ch draâ tuê nezï u draâ tuê z nerezaveï jõâcõâ oceli ve vsï ech meïrïenyâch kombinacõâch. Ve studii Guerrero A.P. a spol. [17] srovnaâ vali trïenõâ mezi cï tyrïmi druhy zaâmkuê (poly- a monokrystalickou keramikou, polykrystalickou keramikou s vlozï enou kovovou draâ zï kou a nerezaveï jõâcõâ ocelõâ 0,022) a dveï ma druhy ortodontickyâ ch draâ tuê z nikltitanu a nerezaveï jõâcõâ oceli (0,019 x 0,025). Zjistili, zïe zaâ mky z monokrystalickeâ keramiky vykazujõâ nejvysï sï õâ trïenõâ, cozï se prokaâ zalo i v nasï õâ studii, a zïe zaâ mky z polykrystalickeâ keramiky s vlozï enou kovovou draâ zï kou nevykazujõâ nizï sï õâ trïenõâ nezï bez teâ to draâ zï ky. AutorÏi Choi S.H. a kol. [18] prezentovali studii, ve ktereâ zjistili, zï e plastoveâ zaâ mky majõâ vysï sï õâ trïenõâ nezï zaâmky s kovovou draâzïkou, at'uzï prïõâmo celokovoveâ z nerezaveï jõâcõâ oceli anebo zaâ mky s vlozïenou kovovou draâzïkou. PrÏõÂcÏ inou zrïejmeï bude vysï sï õâ nepravidelnost a drsnost povrchu. ZaÂveÏr 1. NejvysÏ sï õâ statickeâ i dynamickeâ trïenõâ vykazujõâ vsï echny zaâ mky z trojice Radiance (safõâroveâ zaâ mky z monokrystalickeâ keramiky) ve vsï ech angulacõâch. 2. Mezi skupinami ortodontickyâch zaâmkuê ze stejneâ ho materiaâ lu (kovoveâ, plastoveâ, keramickeâ a s vlozïenou kovovou draâ zï kou) jsme nezjistili statisticky vyâznamnyâ rozdõâl ve velikosti dynamickeâho trïenõâ na hladineï signifikance 0,05. OvsÏ emskupina keramickyâch zaâmkuê m aâ teâmeï rï dvakraât veï tsï õâ pruê m eï rneâ hodnoty dynamickeâho trïenõâ nezï ostatnõâ skupiny. 3. Velikost statickeâ ho i dynamickeâ ho trïenõâ se se zvysï ujõâcõâ angulacõâ zvysï uje. AutorÏi nemajõâ komercï nõâ, vlastnickeâ nebo financï nõâ zaâ jmy na produktech nebo spolecï nostech popsanyâ ch v tomto cïlaâ nku. (stainless steel, nickel-titanium, beta-titanium) at angulations of 0 and 10. The greatest friction was found in ceramic bracket with a specially finished silica-inserted slot, followed by ceramic bracket with metal slot, and the least friction was measured in the bracket made of stainless steel. The friction force increased proportionally with the increasing angulation. The measurements were performed on the testing machine Emic DL 10000, the wire shift 0.5 cm/min for 2 minutes, ligation force was 200 g. We did not found statistically significant differences between the groups of orthodontic brackets (stainless steel, plastic, ceramic, stainless steel-inserted slot). The same results are reported by Downin et al. [14]. The authors measured brackets made of stainless steel and polycrystalline ceramics (0.022ª) and orthodontic wires of x 0.025ª made of stainless steel, nickel-titanium, and beta-titanium. The measurements were performed with Instron They did not find statistically significant differences in friction between the brackets made of stainless steel and those made of polycrystalline ceramics. In his report on ceramic brackets, Kusy [15] says that ceramic brackets show higher friction coefficient than those made of stainless steel, not due to their hardness but due to their chemical structure. He did not find the difference in friction coefficient in monoand poly-crystalline ceramics. The interesting study by Cha J.Y. et al. [16] compared different brackets made of ceramic materials; brackets of stainless steel were used as a control set (0.022ª). They pulled through the brackets orthodontic wires made of stainless steel and beta-titanium (0.019 x 0.025ª). Ceramic brackets were subdivided into polycrystalline, monocrystalline, with metal-inserted slot, and with specially finished ceramic slot (with added layer of silicon dioxide on polycrystalline ceramics). They concluded that ceramic brackets with a specially finished ceramic slot show similar low friction as those made of stainless steel. In all combinations measured, greater friction was found in beta-titaniumwires in comparison with the wires made of stainless steel. Guerrero A.P. et al [17] compared friction in three types of brackets (polycrystalline, monocrystalline, polycrystalline with stainless steel-inserted slot ª) and two types of orthodontic wires (nickel-titaniumand stainless steel, x 0.025ª). They found the greatest friction in the brackets made of monocrystalline ceramics (that was proved also in our study), and concluded that brackets made of polycrystalline ceramics with metal-inserted slot do not show lower friction than the polycrystalline brackets without metal-inserted slot. redakce@orthodont-cz.cz 161

10 rocïnõâk24 ORTODONCIE Literatura/References 1. [cit ]. Dostupne na: -treni [online] [cit ]. Dostupne na: 3. Otta J.: Alternativnõ techniky k standardnõâmaparaâtuêm edgewise. Odborna atestacï nõâ praâ ce, Olomouc, Pachero, M.R., Jansen, W.C., Oliveira, D.D.: The role of friction in orthodontics. Dental press J. Orthodont. 2012, 17, cï. 3-4, s Kojima, Y., Fukui, H.: Numerical simulation of canine retraction by sliding mechanics. Amer. J. Orthodont. Dentofacial Orthop. 2005, 127, cï. 5, s Regis, S. Jr., Soares, P., Camargo, E.S., Guariza, Filho O., Tanaka, O., Maruo, H.: Biodegradation of orthodontic metallic brackets and associated implications for friction. Amer. J. Orthodont. Dentofacial Orthop. 2011, 114, cï. 4, s Omana, H.M., Moore, R.N., Bagby, M.D.: Frictional properties of metal and ceramic brackets. J. Clin. Orthodont. 1992, 26, cï. 7, s Hain, M., Dhopatkar, A., Rock, P.: The effect of ligation method on friction in sliding mechanics. Amer. J. Orthodont. Dentofacial Orthop. 2003, 123, cï. 4, s Baccetti, T., Franchi, L., Camporesi, M.: Forces in the Presence of Ceramic Versus Stainless Steel Brackets with Unconventional vs. Conventional Ligatures. Angle Orthodont., 2008, 78, cï. 1, s Gandini, P., Orsi, L., Bertoncini, Ch., Massironi, S., Franchi, L.: In vitro frictional forces generated by three different ligation methods. Angle Orthodont 2008, 78, cï. 5, s Bednar, J.R., Gruendeman, G.W., Sandrik, J.L.: A comparative study of frictional forces between orthodontic brackets and arch wires. Amer. J. Orthodont. Dentofacial Orthop. 1991, 100, cï. 6, s Hamdan, A., Rock, P.: The effect of different combinations of tip and torque on archwire/bracket friction. Europ. J. Orthodont. 2008, cï. 30, s Nishio, C., Motta, A.F.J., Elias, C.N., Mucha, J.N.: In vitro evaluation of frictional forces between archwires and ceramic brackets. Amer. J. Orthodont. Dentofacial Orthop. 2004, 125, cï. 1, s Downing, A., McCabe, J., Gordon, P.: A study of frictional forces between orthodontic brackets and archwires. Brit. J. Orthodont. 1994, cï. 21, s Kusy, R.: Commentary: Ceramic brackets, Angle Orthodont, 1991, 61, cï. 4, s Cha, J.Y., Kim, K. S., Hwang, Ch. J.: Friction of conventional and silica- insert ceramic brackets in various bracket-wire combinations. Angle Orthodont. 2007, 1, cï. 77, s Guerrero, A. P., Filho, O., G., Tanaka, O., Camargo, E., S., Vieira, S.: Evaluation of frictional forces between ceramic brackets and archwires of different alloys compared with metal brackets. Braz. Oral Res. 2010, 24, cï.1, s Choi, S.H., Kang, D.Y., Hwang, Ch.J.: Surface roughness of three types of modern plastic bracket slot floors and frictional resistence. Angle Orthodont. 2014, 84, cï.1, s In their study, Choi S.H. et al. [18] concluded that plastic brackets show greater friction than those with metal slot, made either of stainless steel or with metal-inserted slot. The reason might be uneven and rough surface. Conclusion 1) The greatest static and dynamic friction is found in all brackets Radiance (sapphire brackets made of monocrystalline ceramics), in all angulations. 2) There was not found statistically significant difference in the values of dynamic friction at the level of significance 0.05 between the groups of orthodontic brackets made of the same material (metal, plastic, ceramic, with metal-inserted slot). However, in the group of ceramic brackets the mean values of dynamic friction are nearly twice as big as in other groups. 3) The values of static and dynamic friction increase with increasing angulation. The authors have no commercial, ownership or financial interests in the products or companies mentioned in the article. MUDr. Daniela Strakova Stomatologicka klinika FN u sv. Anny PekarÏska 53, Brno redakce@orthodont-cz.cz