Evaluat ion of t he for ce generat ed by gradual
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m et allic, est het ic, and self- ligat ing bracket s
Manoela Fávaro FRANCISCONI, Guilherme JANSON, José Fernando Castanha HENRIQUES, Karina Maria Salvatore de FREITAS
Universidade de São Paulo, Faculdade de Odontologia de Bauru, Departamento de Odontopediatria, Ortodontia e Saúde Coletiva, Bauru, SP, Brasil.
Corresponding address: Manoela Fávaro Francisconi - Departamento de Odontopediatria, Ortodontia e Saúde Coletiva
Faculdade de Odontologia de Bauru - Universidade de São Paulo - Alameda Octávio Pinheiro Brisolla, 9-75 - Bauru - SP - 17012-901 - Brazil - Phone/Fax: 3235-8000/3235-8217 - e-mail: manuff@usp.br
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ABSTRACT
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EMHFWLYH7KHSXUSRVHRIWKLVVWXG\ZDVWRHYDOXDWHWKHGHÀHFWLRQIRUFHVRI1LWLQROort hodont ic wires placed in different t ypes of bracket s: m et allic, reinforced polycarbonat e w it h m et allic slot s, sapphire, passive and act ive self- ligat ing, by assessing st rengt h valuesYDULDWLRQDFFRUGLQJWRJUDGXDOLQFUHDVHLQZLUHGLDPHWHUDQGGHÀHFWLRQDQGFRPSDULQJ GLIIHUHQWFRPELQDWLRQVLQWKHGLIIHUHQWGHÀHFWLRQV0DWHULDODQG0HWKRGV6SHFLPHQVZHUH
set in a clinical sim ulat ion m odel and evaluat ed in a Universal Test ing Machine ( I NSTRON 3342) , using t he I SO 15841 prot ocol. Dat a were subj ect ed t o One- way ANOVA, followed by Tukey t est s ( p< 0.05) . Result s: Self- ligat ing bracket s present ed t he m ost sim ilar behavior t o each ot her. For convent ional bracket s t here was no consist ent behavior for any of t he
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predict able result s while convent ional bracket s, as est het ic bracket s, showed very different
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com pared w it h t he ot hers, in 0.020- inch w ires.
Ke yw or ds: Ort hodont ic w ires. Mechanical phenom ena. Elast icit y. Com parat ive st udy.
I N TROD UCTI ON
No w a d ay s, h av i n g a n a t u r a l a n d p l ea sa n t sm ile even dur ing or t hodont ic t r eat m ent is one of pat ien t s’ m ain con cer n s. Dev ices com bin in g a cce p t a b l e e st h e t i c a n d a d e q u a t e t e ch n i ca l perform ance, sat isfying bot h t he pat ient and t he clin ician ex p ect at ion s, h av e b een d ev elop ed2.
Nevert heless, est het ic bracket s show higher frict ion
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t he desired m ovem ent35.
Self- ligat ing bracket s, int r oduced as Russel’s accessor ies in t he m id- 1930s, ar e sy st em s t hat present a m echanical device designed t o close t he edgew ise slot33. Their use has becom e com m on
i n r e ce n t y e a r s. Ma n u f a ct u r e s cl a i m se v e r a l advant ages in using t hese accessor ies, and t he low frict ion seem s t o be t he m ost st udied am ong t h em1 1 , 1 5 , 1 8. So m e st u d i es co n f i r m t h a t t h er e
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in a shor t er t r eat m ent t im e15,19. How ever, som e
st udies showed t hat t his reduced frict ion depends on t he t ype and caliper of t he wire and t he degree of crowding30. Furt her st udies and clinical evaluat ions
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T h e r e f o r e , e f f e c t i v e n e s s o f o r t h o d o n t i c m ovem ent result s not only from different bracket syst em s, but also from a series of ot her fact ors, relat ed t o bot h t he pat ient ( t eet h and support ing st r uct ur es) and t he t y pe of m echanics applied. Teet h m ovem ent also depends on t he act ion of ort hodont ic wires, which varies according t o t heir st ruct ural and m echanical propert ies3.
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m ake t he best choice am ong t he various bracket s and ort hodont ic w ires available, it is essent ial t o know t he m agnit ude of forces released by t hese w ir es and t heir behav ior r egar ding t he gradual
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o f r o u n d Ni t i n o l o r t h o d o n t i c w i r es, p l aced i n convent ional m et allic, r einfor ced polycar bonat e, sapph ir e ( Or m co, Glen da, CA, USA) , an d self-ligat ing bracket s by using a clinical sim ulat ion m odel and follow ing I SO 15841 as prot ocol.
M ATERI AL AN D M ETH OD S
M a t e r ia l - e x pe r im e n t a l gr ou ps
Th e sam ple u sed in t h is st u dy con sist ed of 4 0 0 r ou n d - sect ion Nit in ol w ir es ( St an d ar d or Medium , GAC®, Bohem ia, NY, USA) w it h 0.014,
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dif f er en t br ack et t y pes: con v en t ion al m et allic, r ei n f o r ced p o l y car b o n at e w i t h m et al l i c sl o t s, sapphire, passive and act ive self- ligat ing bracket s ( Fi g u r e 1 ) . Wi r es t h at sh ow ed v er y d i f f er en t behav ior fr om t he ot her s w er e excluded21: t hey
st at ist ically represent out liers t hat would negat ively int erfere wit h t he result s. I n convent ional bracket s, t he wires were t ied wit h “ O” shaped elast om eric ligat ures ( GAC®; Bohem ia, NY, USA) . I n t he
self-Wires (GAC) Section Batch Bracket types Manufacturer
Nitinol 0.014-inch 088637 Conventional metallic (Mini Diamond) Ormco GAC
0.016-inch 088649/ 091986 Conventional reinforced polycarbonate with metallic slots (Spirit)
0.018-inch 089071 Conventional sapphire (Inspire ICE)
0.020-inch 088679 Passive self-ligating (Damon Q)
Active self-ligating (In-Ovation R)
* All groups were tested at a controlled temperature of 36±1°C
Figure 1- Sample used and test conditions
ligat ing bracket s t he w ir es w er e t ied by closing t he passive ( Dam on Q) or act ive ( I n- Ovat ion R) syst em s.
M e t h ods - clin ica l sim u la t ion de vice
I n order t o int ernat ionally st andardize t he t est s as adequat ely as possible, t he m et hods used in t his st udy follow ed t he I SO 15841 St andard: Dent ist ry – Wires for use in ort hodont ics16.
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in a clinical sim ulat ion device represent ing all 10 t eet h of t he m axillary arch11. Figure 2 show s t he
clinical sim ulat ion device t hat was used in t his st udy. This device consist s of a parabola shaped acrylic
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t he m axillary t eet h ( Figure 2) . The parabola shape was det erm ined by t he w ires, reducing t he risk of
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in an unexpect ed way. Bracket s w ere bonded w it h cyanoacrylat e est er gel ( Super Bonder, Loct it e, São Paulo, SP, Brazil) , posit ioned in t he long axis of t he acrylic devices parallel t o t he ground and at t he sam e height . The w ires had t he sam e lengt h12. The
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screw in t he bot t om of t he acrylic resin plat e. Th e t est s w er e per f or m ed on t h e st r u ct u r e corresponding t o t he right m axillary cent ral incisor ( Figure 3) . Unlike t he ot hers, t his st ruct ure was not screw ed, enabling it s labio- lingual m ovem ent . I t had a perforat ion, in w hich a m et al cylinder was placed t o act ivat e it . The t ip of t he act ivat ion head, at t ached t o t he t est ing m achine, had a rounded
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was perform ed wit hout changing t he int er bracket
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depends, am ong ot her t hings, on t his dist ance. The
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Recor d s of t h e f or ce r eleased b y t h e w ir e
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clinically corresponds t o t he beginning of t reat m ent , when t he t eet h are poorly posit ioned and t he wire is forced int o t he accessories slot s. Depending on t he degree of crow ding, t eet h experience m ore or less force t o align t he t eet h.
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Universal Test ing Machine ( I nst ron 3342) , w it h a load cell of 10 N10 ( Figure 3) . This load cell has an
accuracy of 0.5% of t he r eading value w it h t he t em perat ure of 25° C. I n t his st udy, t he load cell was m aint ained at t his t em perat ure. Also according t o t he I SO st andard, t he t est s were always perform ed at t he sam e t est ing t em perat ure of 36± 1° C for all t est groups26. To obt ain t his, an acrylic cont ainer
wit h wat er at a t em perat ure of 36± 1° C, m aint ained w it h t he aid of subm ersible heat er w it h int egral t herm ost at ( Elect ronic At m an Heat er, China) and checked by a decim al precision t herm om et er, wit h a lim it of error of ± 0.2° C ( I ncot erm , reference 5097, São Paulo, SP, Brazil) , was adapt ed t o t he t est ing m achine24 ( Figure 3) .
St a t ist ica l a n a lyse s
The sam ple size, according t o t he I SO 15841 st andards, is of six specim ens in each group16. To
m inim ize t he chances of any t echnical error and incr ease r eliabilit y of t he r esult s, 20 specim ens were chosen for each group. Out liers were excluded t hr ough a st at ist ical pr ogram t hat pr ov ides t he values t o be delet ed22. Nor m al dist r ibut ion w as
evaluat ed wit h Kolm ogorov- Sm irnov t est s. Because all variables showed a norm al dist ribut ion, one- way
ANOVA and Tukey t est s w ere used.
All st at ist ical an aly ses w er e per for m ed w it h St at i st i ca so f t w ar e ( St at i st i ca f o r Wi n d o w s – Release 7.0 - Copyright St at soft I nc., Tulsa, OK, USA) . Resu l t s w er e co n si d er ed si g n i f i can t at p< 0.05.
RESULTS
T h e d e a c t i v a t i o n f o r c e s w e r e g e n e r a l l y
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self- ligat ing bracket s, w it h 0.014 and 0.016- inch
nickel- t it anium w ir es, except w it h t he act ivat ion of 2 m m , in w hich t he opposit e occurred ( Tables 1 and 2) . Overall, I nspire I CE show ed t he highest deact ivat ion forces w hile I n- Ovat ion R show ed t he lowest .
T h e d e a c t i v a t i o n f o r c e s w e r e g e n e r a l l y
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ligat ing bracket s, wit h 0.018- inch nickel- t it anium wires ( Table 3) . Overall, I nspire I CE showed t he h igh est deact iv at ion f or ces w h ile I n - Ov at ion R show ed t he low est .
Th e r e w a s a n i n v e r s i o n o f t h e p r e v i o u s
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(mm)
Mini Diamond (N=15)
Spirit (N=20)
Inspire ICE (N=17)
Damon Q (N=16)
In-Ovation R (N=16)
P
Mean (SD)
Mean (SD)
Mean (SD)
Mean (SD)
Mean (SD)
0.5 123.78 (22.70)A 60.13 (32.77)B 97.23 (41.87)A 61.08 (5.61)B 39.15 (9.46)B <0.001
1.0 143.27 (10.56)AD 118.32 (8.74)B 149.73 (16.70)A 135.10 (5.96)D 100.27 (10.21)C <0.001
2.0 76.57 (10.36)A 92.63 (15.15)B 91.74 (20.94)B 156.59 (9.45)C 153.56 (10.02)C <0.001
3.0 391.28 (18.28)A 341.65 (15.03)B 498.63 (32.73)C 204.24 (9.52)D 190.19 (9.38)D <0.001
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Table 1- Deactivation forces (cN) comparisons of the bracket types with 0.014-inch nickel-titanium wire, in progressive
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(mm)
Mini Diamond (N=19)
Spirit (N=17)
Inspire ICE (N=17)
Damon Q (N=18)
In-Ovation R (N=20)
P
Mean (SD)
Mean (SD)
Mean (SD)
Mean (SD)
Mean (SD)
0.5 112.97 (65.22)A 59.69 (43.36)B 130.14 (53.65)A 86.58 (4.80)B 70.72 (16.22)B <0.001
1.0 231.49 (26.93)AD 184.01 (20.76)B 248.30 (24.89)A 226.47 (12.22)D 162.65 (19.95)C <0.001
2.0 218.93 (32.20)A 224.54 (25.33)A 232.22 (21.29)A 281.85 (15.04)B 273.24 (15.80)B <0.001
3.0 479.55 (31.76)A 459.29 (18.29)A 569.15 (38.27)B 372.87 (12.22)C 353.17 (21.67)C <0.001
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Table 2- Deactivation forces (cN) comparisons of the bracket types with 0.016-inch nickel-titanium wire, in progressive
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(mm)
Mini Diamond (N=16)
Spirit (N=19)
Inspire ICE (N=14)
Damon Q (N=18)
In-Ovation R (N=19)
P
Mean (SD)
Mean (SD)
Mean (SD)
Mean (SD)
Mean (SD)
0.5 158.85 (21.14)A 101.08 (53.22)B 141.52 (43.53)AC 108.70 (9.86)BC 96.85 (16.57)B <0.001
1.0 289.29 (17.81)AD 236.63 (26.26)B 269.06 (17.09)A 304.09 (12.66)D 209.14 (21.53)C <0.001
2.0 400.40 (31.08)A 351.94 (18.07)B 397.88 (37.32)A 392.24 (15.60)C 354.15 (22.05)B <0.001
3.0 626.94 (27.36)A 588.17 (32.19)B 674.28 (31.55)C 538.04 (17.69)E 486.04 (38.02)D <0.001
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Table 3- Deactivation forces (cN) comparisons of the bracket types with 0.018-inch nickel-titanium wire, in progressive
t endency w it h 0.020- inch nickel- t it anium w ir es.
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higher w it h self- ligat ing t han w it h conv ent ional bracket s ( Table 4) . Overall, Dam on Q show ed t he highest deact ivat ion forces w hile Spirit show ed t he low est . The forces w it h t he Dam on Q w it h 3 m m of act ivat ion exceeded 1000g.
D I SCUSSI ON
Sa m ple a n d m e t h odology
A cl i n i ca l si m u l a t i o n d e v i ce w a s u se d t o ap p r ox im at e t h e lab or at or y r esu lt s t o clin ical sit uat ions, providing m ore pract ical applicat ions32.
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was used for ort hodont ic w ires laborat ory t est s16.
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it is clinically closest t o t he ort hodont ist s’ int erest s, since t hat is w hat t hey do w hen adapt ing a w ire t o t he pat ient ’s t eet h. Alt hough engineer s w or k w it h param et ers such as elast ic m odulus and yield value, t he ort hodont ist is m ore concerned about know ing t he force released regarding t he am ount
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Re su lt s
I n general, it was observed t hat t he deact ivat ion for ce incr eased w it h t he incr ease in am ount of d ef lect ion ( Tab les 1 t o 4 ) . Th ese f in d in g s ar e consist ent w it h ot her st udies29.
The result s found in different com binat ions of t he bracket s w it h 0.014- inch nickel- t it anium w ires are in agreem ent wit h ot her st udies in t he lit erat ure t hat
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large variat ion in t he difference of force values, and
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devices36 ( Table 1) .
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m m , present ed t he highest forces w hen com pared w it h convent ional bracket s ( Table 1) . This result can be ex plained by assum ing t hat par t of t he force is used t o overcom e t he great er resist ance
t o sliding, generat ed in t est s w it h convent ional bracket syst em s during unloading6,347KHVH¿QGLQJV
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NiTi wires, along wit h self- ligat ing bracket syst em s,
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wit h convent ional bracket s1,9.
Ho w ev er, i n d ef l ect i o n o f 3 m m , t h e sel f-ligat ing bracket s pr esent ed t he sm allest for ces, cont radict ing pr ev ious inv est igat ion27 ( Table 1) .
This occurs because sm aller diam et er wires release sm aller f or ces, sin ce t h ey ar e n ot com p let ely pressed against t he slot s. I n convent ional bracket s, even sm all diam et er wires are pressed int o t he slot s by t he elast ic t ie.
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differences in t he discharge forces bet ween Dam on and I n- Ovat ion self- ligat ing bracket s wit h
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m ay be a consequence of t he m ore uniform w ire m echanical lock ing sy st em t han t he w ir e t y ing process of convent ional bracket s, w it h elast om eric ligat ur es36. Ther e m ay be m or e var iat ion in t he
process of t ying t he elast om eric ligat ures t han when closing t he self- ligat ing bracket s.
Th e r esu lt s w er e n ot st an dar dized bet w een differ en t br ack et com bin at ion s w it h 0 . 0 1 6 - in ch Nit in ol w ir es, sh ow in g t h at t h e d esig n of t h e experim ent al t est ing qualit at ively and quant it at ively affect s t he dischar ge for ces dur ing leveling and alignm ent w it h super elast ic NiTi w ir es28,36 ( Table
2) . Sim ilar ly, w hen t hese for ces w er e evaluat ed in an experim ent al m odel w it h em bedded bracket syst em s, t he wires t ended t o lose t heir superelast ic pr oper t ies, show ing var iat ions of for ce27. Ot her
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The self- ligat ing bracket s cont inued delivering
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reasons previously provided ( Table 2) .
The result s of com binat ions of different bracket t ypes wit h 0.018- inch Nit inol wires dem onst rat ed
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w hen com pared w it h I n- Ovat ion R ( Table 3) . Ot her
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(mm)
Mini Diamond (N=16)
Spirit (N=18)
Inspire ICE (N=19)
Damon Q (N=18)
In-Ovation R (N=20)
P
Mean (SD)
Mean (SD)
Mean (SD)
Mean (SD)
Mean (SD)
0.5 130.12 (34.33)A 58.56 (46.10)B 127.83 (66.48)A 159.03 (17.74)A 145.61 (26.12)A <0.001
1.0 249.64 (34.96)A 210.17 (26.03)B 259.66 (30.11)A 423.59 (36.33)D 344.09 (25.04)C <0.001
2.0 560.60 (20.07)A 410.95 (41.75)B 550.04 (39.91)A 774.27 (77.22)D 620.34 (52.04)C <0.001
3.0 804.86 (29.18)A 753.09 (24.42)B 815.67 (21.90)A --- 858.98 (84.34)A ** <0.001
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** n=5 because the other wires exceeded the force of 1000g
Table 4- Deactivation forces (cN) comparisons of the bracket types with 0.020-inch nickel-titanium wire, in progressive
st udies4,21 also not iced higher forces w hen passive
( Sm art Clip) were com pared wit h act ive self- ligat ing bracket s ( Tim e3) .
Fin ally, d if f er en t b r ack et com b in at ion s w it h 0.020- inch Nit inol w ires show ed again t hat Dam on Q gen er at ed gr eat er f or ces t h an I n - Ov at ion R
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bracket s show ed great er forces t han t he ot hers. This result is consist ent wit h anot her st udy in which frict ion was responsible for reducing t he am ount of released force36.This part ially explains t he fact
t hat t he highest average was generat ed by t he sim ulat ion device w it h self- ligat ing bracket s14,17.
Clinically, t his explanat ion m akes sense because frict ion increases t he released force during loading, but decreases it during unloading23. Therefore, t he
dev ice w it h higher fr ict ion generat ed less for ce, because frict ion hinders t he ret urn of t he wire t o it s init ial posit ion during t he discharge36. The presence
of t he bracket s, t he dist ance bet w een t hem , t he bands, and t he cr ow ding it self ar e fact or s t hat increase frict ion in t he clinical set t ing. Thus, t his large frict ion would be able t o decrease t he released force by t he wire. Ot her st udies also found higher frict ional resist ance of convent ional bracket s w hen com pared wit h self- ligat ing ones5,13.
Con v en t ion al an d est h et ic b r ack et s sh ow ed ver y differ ent pat t er ns of for ces due t o bracket com posit ion. Thus, t his result should be considered w hen choosing t he t y pe of bracket s t o be used according t o t he t ype of m echanics necessary in ort hodont ic t reat m ent of each case.
An im por t ant aspect t o be consider ed is t he d if f icu lt y in ex t r ap olat in g lab or at or ial f in d in g s regarding frictional forces to the clinical environm ent. Many different fact ors, such as occlusal forces and t ight ening or loosening t he archwire in t he bracket s du r in g t r eat m en t , m ay pr odu ce dif f er en t f or ce
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CON CLUSI ON S
Con v en t ion al an d est h et ic b r ack et s sh ow ed ver y differ ent pat t er ns of for ces due t o bracket com posit ion;
Self- ligat ing bracket s present ed sim ilar behavior t o each ot her and show ed higher st rengt h in all
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0.020- inch w ires.
REFEREN CES
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2- Birnie D. Ceram ic bracket s. Br J Ort hod. 1990; 17: 71- 4. 3- Bur st one CJ. Var iable- m odulus or t hodont ics. Am J Or t hod. 1981; 80: 1- 16.
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