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Jou nal o ma e ials science-ma e ials in medicine
(2011
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1
In luence o Su ace Pa e n on he Fluo ide
Co osion o Ni-Ti O hodon ic A chwi es
Camilo Abalos,a An onio Paul,b Asunción Mendoza,c En ique Solano,d and
F ancisco Ja ie Gil.e
aDepa men o Den al Ma e ials, cDepa men o Pedia ic Den is y and
dDepa men o O hodon ics, School o Den is y, Uni e si y o Se illa, Spain.
bDepa men o Mechanical and Ma e ials Enginee ing, School o Enginee ing,
Se ille, Spain.
eDepa men o Ma e ials Science and Me allu gical Enginee ing, Poly echnic
Uni e si y o Ca alonia, Ba celona, Spain.
Abalos,C. Mendoza, A. and Solano, E.: Facul ad de Odon ología, c/ A icena s/n, 41009-Se illa,
Spain. Telephone numbe : +34954481137. Fax numbe : 0034954481157. E-mail add ess:
[email p o ec ed], e[email p o ec ed], [email p o ec ed]
Paul, A.: Escuela Técnica Supe io de Ingenie os, A da. de los Descub imien os s/n, 42092
Se illa, Spain. Telephone numbe : +34954487304. Fax numbe : +34954460475. E-mail add ess:
[email p o ec ed]
Gil, FJ: Depa amen o de Ciencia de Ma e iales e Ingenie ía Me alú gica, Uni e sidad Poli écnica
de Ca aluña, Diagonal 647, 08028 Ba celona, Spain. Telephone numbe : +34934016111. Fax
numbe : +34934016210. E-mail add ess: [email p o ec ed].
2
Abs ac
In oduc ion: Di e en manu ac u ing p ocesses o Ni-Ti a chwi es espond di e en ly o
co osion. The in luence o su ace condi ion is impo an . In his s udy we es ablish se e al
su ace pa e ns and s udy hei in luence in luo ide co osion. Me hods: In a p elimina y s udy
we de e mined ou su ace pa e ns (smoo h, sc a ch, dimple and c ack) acco ding o he main
su ace de ec . We selec ed a chwi es wi h hese pa e ns (n=40). Imme sion es s we e pe o med
in a i icial sali a+ luo a ed p ophylac ic gel (12500 ppm) o 28 days. The su ace was
cha ac e ised by SEM and Lase Con ocal Mic oscopy. Ano a es was ca ied ou (α≤0.05).
Resul s: The e is an inc ease in he su ace de ec s and/o oughness o he c ack and sc a ch
pa e ns. Conclusions: The e is a ela ionship be ween he su ace pa e n and he ex en o luo ide
co osion. Tha ac o should be aken in o accoun in u u e s udies. The inc ease in de ec s is
independen o oughness. Manu ac u ing p ocesses ha p oduces su ace c acks should be
a oided.
Key wo ds: NiTi, O hodon ic a chwi e, Su ace pa e n, Su ace opog aphy, Roughness,
Fluo ide, Co osion esis ance.
Abb e ia ions: NiTi: Nickel-Ti anium alloys; SEM: Scanning Elec on Mic oscope;
EDS: Ene gy Dispe si e Spec ome y; LSCM: Lase Scanning Con ocal Mic oscope Sys em;
PP: polyp opylene; Ra: he a i hme ical mean o he absolu e alues o he scanned su ace p o ile;
Rms: he oo -mean-squa e alue o he scanned su ace p o ile; Rp: he highe alue o he
scanned p o ile; R : he lowe alue o he scanned p o ile.
1 In oduc ion
Nickel-Ti anium alloys (NiTi) nea equia omic composi ion ha e wide
clinical applica ion in o hodon ics due o hei excellen mechanical p ope ies
[1,2]. They ha e good biocompa ibili y in a i icial sali a, Ringe ’s solu ion and
physiological sal solu ion [3]. Ne e heless, he co osion esis ance o NiTi
alloys dec eases in acidic sali a [4-6] and chlo ine [7] o luo ide solu ions [8-12],
which is equen ly used in o hodon ic ea men s o he p e en ion o den al
ca ies.
Fluo ide ions can de e io a e he passi e ilm o he i anium oxide su ace
[9,13-15] by hyd ogen abso p ion [15], dec easing he co osion esis ance o he
alloy and hence i s biocompa ibili y [3,5,6]. Fac o s such as exposu e ime
[15,16], luo ide concen a ion [8,9,17] and a mo e acidic pH [15,17] acili a e he
su ace co osion o Ni-Ti alloys since hese ac o s a e in e ela ed [16]. A pH
dependen c i ical concen a ion has e en been de ined [8,18,19] which can
deg ade he passi e ilm o supe icial oxides. When his happens, he e ec o
3
he co osion is a elease o me allic ions [5,8,14,19,20], mo phological su ace
changes [8,15,16] and inc eases in he oughness [5,8] and ic ion coe icien s
[21] among o he s.
Besides he a o emen ioned ac o ela ed o luo ine ions, he wi e su ace
plays an impo an ole in co osion, al hough he esul s published a e
con o e sial. P e ious s udies [5,20,22,23] poin o su ace de ec s p oduced
du ing wi e manu ac u ing as p e e en ial co osion a eas while in o he s udies
hey do no [4,9]. O he au ho s [13] conside he oughness o he a chwi e o be
an indica o o he endency owa d co osion, al hough o he esea ch [4,5,8,9]
did no ind such a ela ionship when including esidual s esses and he deg ee o
homogenei y as co osion accele a o s [4,9]. This is o say ha di e en a chwi e
su aces ha e a be e o wo se esponse o co osi e luo ide. Thus, he a chwi e
manu ac u e is a a iable i sel [4,8], al hough mo e esea ch is equi ed [8,9].
The wi e su ace, su ace de ec s and oughness a e ela ed o he
manu ac u ing p ocesses [8] ha lead o di e en su ace inishes [24]. The
objec i e o his s udy is o examine he in luence o he su ace (su ace de ec s
and oughness), as a esul o he manu ac u ing p ocess, in he co osion o NiTi
a chwi es exposed o a high luo ide concen a ion bu in a way ne e done
be o e. In p e ious s udies [4,7-9,16,17,19,20] he e a e 1 o 4 a chwi es om
di e en manu ac u e s and he su ace inish is ela ed o a speci ic comme cial
b and. In ou s udy, we analyze 16 b ands om di e en manu ac u e s and
es ablish a su ace pa e n o each wi e depending on he p edominan de ec
(c ack, sc a ch, po e, dimple o smoo h). We g oup he wi es om di e en
manu ac u e s acco ding o he su ace pa e n which co esponds o he di e en
manu ac u ing p ocesses. Then, we s udy he in luence o each pa e n on he
luo ide co osion by means o a su ace s udy (Scanning Elec on Mic oscopy)
and oughness (Lase Con ocal mic oscopy) cha ac e iza ion. The hypo hesis is
ha di e en su ace pa e ns, de i ed om di e en manu ac u ing p ocesses,
espond di e en ly o luo ide co osion.
4
2 Ma e ials And Me hods
2.1 P elimina y S udy
We s udied he su aces o 16 NiTi a chwi es (0.016x0.022 inch.) om 9
comme cial b ands in he as- ecei ed condi ion [25] (Table 1). The su ace
mo phology and composi ion was e alua ed by Scanning Elec on Mic oscope
(SEM) (Philips XL-30 Philips, Eindho en, Ne he lands) and Ene gy Dispe si e
Spec ome y (EDS) (Edax In e na ional, Mahwah, U.S.A.); oughness was
measu ed using a Lase Scanning Con ocal Mic oscope Sys em (LSCM) (Leica
TCS-SP2, We zla , Ge many). We s udied h ee samples om each ba ch o
a chwi es, each sample coming om a di e en a chwi e wi hin he ba ch. The
a chwi es we e classi ied acco ding o hei su ace pa e ns using 18 a iables.
The Pea son co ela ion es was pe o med o e alua e he exis ence o linea
co ela ions be ween he a iables and he su ace pa e ns. We ound ha i e o
hese co ela ed wi h he pa e n: dimples, sc a ches, c acks, po es and smoo h/no
de ec . As a esul we classi ied he NiTi a chwi es acco ding o hese i e
pa e ns (Table 1) depending on he p edominan su ace de ec s. The di e en
su ace de ec s a e de e mined in he ollowing way: C ack is a long, deep issu e
wi h i egula edges and a iable wid h (Fig. 1C); Sc a ch is a long issu e wi h
smoo h edges and cons an wid h, in which he bo om is clea ly isible (Fig. 1D);
Po e is a deep, usually ounded de ec ; Mic opo e is a po e wi h diame e smalle
han one mic ome e . Dimple is a small hole, an ellip ical o ounded dep ession
on he su ace simila o he dimples in a gol ball (Fig. 1B).
2.2 Ma e ial and Imme sion Tes
Eigh NiTi wi es wi h nea equia omic composi ions made by di e en
manu ac u e s we e used in his s udy. Each su ace pa e n (dimple, sc a ch,
c ack, po e and smoo h/no de ec ) co esponds o wo di e en comme cial
b ands (Table 1). The po ous su ace pa e n was elimina ed om his s udy
because he e was only one manu ac u e . Fo he es s, we used 5 samples o
di e en a chwi es om he same ba ch (n=40). The samples we e 2 cm segmen s

5
ex ac ed om he s aigh pa o he a ch. P e ious o imme sion es each
specimen was cleaned and deg eased o 5 minu es in ace one.
The samples we e pu in a polyp opylene (PP) ube (15 ml) wi h 2 ml a i icial
sali a o 28 days a 37ºC. Modi ied Fusayama a i icial sali a composi ion: NaCl
(0.4 g/l), KCl (0.4 g/l), CaCl2 .2H2O (0.906 g/l), NaH2PO4 .H2O (0.690 g/l),
Na2S.9H2O (0.005 g/l), KSCN (0.3 g/l) and u ea (1 g/l) was used. [5,6,9,10] The
pH was measu ed by means o a pH-me e (mic opH 2001, C ison Ins umen
S.A., Ba celona, Spain) gi ing a alue o 5.3. Then hey we e placed in a 15 ml
PP ube wi h 2 ml a i icial sali a + luo ide solu ion wi h a pH o 4. Imme sion
ime was 8 minu es, which is equi alen o 4 weeks o oo h b ushing o 2
minu es pe week. The luo ide solu ion was p epa ed by ul asonic agi a ion in
he PP ube o 5 ml a i icial sali a and 5g luo a ed p ophylac ic gel (12500 ppm)
(Elmex gel, GABA GmbH, Lö ach, Ge many); he mix u e was cen i uged o
10 minu es a 2000 pm. The uppe clea liquid wi hou he deposi s in he PP ube
was used as he imme sion es solu ion and kep a 37ºC. [8] Righ a e he
imme sion es he samples we e insed o 5 minu es in dis illed wa e and 5
minu es in me hanol in a s i e main ained a he es ing empe a u e o 37ºC.
2.3 Su ace Cha ac e isa ion
The su ace opog aphy o he NiTi a chwi es was examined be o e and a e
he imme sion es s. SEM mic og aphs a low (400x) and high (1600x)
magni ica ion we e aken o ep esen a i e deg aded a eas o he su ace. We used
he 400x images o measu e he su ace occupied by each de ec (dimples,
sc a ches, c acks and po es) in h ee di e en a eas o 10000 μm2. The h ee
measu emen s we e hen a e aged. When small mic opo es appea ed on he
su ace we used he 1600x images wi h an a ea o 400μm2. So, we ha e 5 samples
pe b and o wi e (n=40) and 3 a eas pe specimen.
The su ace oughness o he NiTi a chwi es was analysed be o e and a e he
imme sion es s by means o LSCM. The mic oscope was p e iously calib a ed
using a Mi u oyo p ecision Re e ence Specimen (Code no. 178-601) wi h
Ra=3.1μm, e o coe icien was below 0.3%. The images we e p ocessed using
he Leica Con ocal so wa e ( Leica Mic osys ems GMBH, We zla , Ge many).
Mic og aphs co esponding o 750 linea mic ons we e aken. We andomly
6
selec ed 5 a eas o 10000 μm2 om each opog aphic image and measu ed he
oughness. Ra, Rms, Rp and R alues ob ained in each a ea we e a e aged. Ra
and Rms ep esen he a i hme ical mean o he absolu e alues and he oo -
mean-squa e alue o he scanned su ace p o ile, espec i ely. Rp and R
ep esen he highe and lowe alues o he scanned p o ile. So, o oughness
s udies we analysed 5 a eas om 5 samples o each a chwi e (n=40).
2.4 S a is ical Analysis
Mean alues and s anda d de ia ion o each o he 8 b ands and he 4
su ace pa e ns we e compu ed om he da a ob ained du ing he su ace
cha ac e isa ion. This was done o he as- ecei ed a chwi es as well as a e he
imme sion es . Since he a chwi es used had di e en ini ial alues, in o de o
ensu e a alid compa ison o s a is ical esul s i was deemed app op ia e o use
he di e ence be ween he as- ecei ed and pos -imme sion es alues ob ained
o each wi e es ed. So, he inal da a e e o he inc eases o dec eases in he
a ea occupied by he su ace de ec s o su ace oughness. Posi i e alues mean
su ace deg ada ion while ze o o nega i e alues indica e he absence o
co osion. S a is ical analysis was ca ied ou wi h an analysis o a iance o
compa ison o mean alues, he s a is ical signi icance being se a α ≤ 0.05. The
da a we e analysed using SPSS 14.0 s a is ical so wa e package (SPSS Inc,
Chicago, Ill., USA).
3 Resul s
Table 2 shows he esul s o he su ace de ec in he as- ecei ed
a chwi es. The quan i ica ion was done wi h he su ace alues o each de ec and
he o al su ace de ec s o each a chwi e. The inc emen al alue also e e ed o
each su ace pa e n included o he a chwi es a e he imme sion es s in
sali a+ luo ide. The e a e signi ican di e ences in he pa e n wi h c acks. Figu e
1 shows ep esen a i e SEM images o he changes in he su ace o he ou
pa e ns a e he co osion es s. In he smoo h pa e n, we obse e pi ing
7
co osion and da k ci cula spo s (Fig. 1A). In he sc a ch pa e n he e a e also
some ci cula spo s (Fig. 1D). In he dimple pa e n he e is no pi ing o
discolo a ion bu we see a smoo hing o he su ace which educes he numbe o
dimples (Fig. 1B). Finally, in he c ack pa e n we obse e a 6% inc ease in he
su ace occupied by he de ec s mainly due o he inc eased su ace o he c acks
(Fig. 1C).
The su ace oughness da a (LSCM) o he a chwi es in he as- ecei ed
and pos -imme sion condi ions a e exp essed in Table 3. The e a e signi ican
di e ences o he c acked and sc a ched pa e ns whe e he e is a 33% inc ease in
he su ace oughness: In he c ack pa e n Ra changes om 0.3 μm in he as-
ecei ed a chwi es o 0.4 μm in he pos imme sion samples. In he sc a ched
pa e n Ra changes om 0.35 o 0.48μm. Figu e 2 shows ep esen a i e LSCM
images o he ou pa e ns s udied.
4 Discussion
The p oduc ion p ocess o o hodon ic a chwi es is no disclosed by
manu ac u e s. Ne e heless, i lea es ma ks on he su ace o he wi es. I we
obse e he su ace o a chwi es om di e en manu ac u e s wi h an elec on
mic oscope, we will see di e en su ace de ec s (c acks, dimples, sc a ches
o ien ed in he axis di ec ion o no , po es, e c.) [4,5,8,9,20,25]. We will also ind
discolo a ions, deposi s, inclusions and a ious deg ees o oughness [4,9,25].
This is due o he di e en ea men s used h oughou he p oduc ion p ocess
( he momechanical ea men s, wi ed awing, polishing, e c.) [4,5,8,20]. These
indings show e y di e en su ace inishes on he a chwi es which may no
always be o good quali y [20,24,25].
In ou p elimina y s udies [25], we g ouped he wi es acco ding o hei
p edominan su ace de ec , co esponding di e en a chwi es o he same su ace
pa e n and he e o e o a simila inishing p ocess. Consequen ly, we we e able o
s udy he in luence o hese su ace pa e ns. The e is a gene al ag eemen in he
bibliog aphy ha he a chwi e manu ac u e has a s a is ically signi ican
in luence on he co osion esis ance [4,5,9,20]. Howe e , he e is some
8
con o e sy o conside ing he su ace de ec s [4,5,9,20,22,23] and/o he
oughness [4,5,8,9] as he causes o he co osion. These s udies compa e
a chwi es wi h di e en su ace inishes, bu he au ho s do no speci y hei
p edominan su ace pa e n. We ound de ec s ha clea ly in luence he co osion
in luo ide, as is he case o c acks. Howe e , o he su ace pa e ns did no show
any co osion as is he case o smoo h and dimple pa e ns. The p eexis ing
su ace pa e n could p o ide answe s abou he a iabili y o he co osion
esis ance o di e en NiTi a chwi es wi h nea equia omic composi ion. We
hink ha he su ace pa e n should be aken in o accoun when compa ing
di e en NiTi o hodon ic wi es. Ne e heless, we ag ee wi h o he au ho s [8,9]
ha mo e s udies a e necessa y since o he ac o s such as esidual s esses [4,9],
he amoun o esidues [20,24,24) and he deg ee o homogenei y o
mic os uc u es[20], e c. can also be in ol ed.
In ou s udy, we used an amine luo ide gel solu ion wi h a concen a ion
o 1.25 % (12500 ppm) and pH=4 as he imme sion media. Co osion in HF is
p oduced wi h a c i ical concen a ion o 30 ppm ha will des oy he TiO2-based
passi e ilm on NiTi a chwi es [26]. This concen a ion is eached wi h ≥500 ppm
luo ide and pH=4[26] o wi h 2250 ppm luo ide in neu al solu ion [9]. Thus, he
solu ion used in ou esea ch is jus i ied by i s high concen a ion and acid pH,
ensu ing i s co osi e e ec . Di e en kinds o luo ide solu ions (s annous
luo ide, sodium luo ide, e c) ha e di e en deg ees o co osi eness [18,19],
he e o e he in luence o he luo ide solu ion on he su ace pa e n o
o hodon ic a chwi es could be he subjec o u u e esea ch.
A e imme sion in luo ide solu ion, we ound ha he e was an inc ease
in he su ace de ec s in he a chwi es wi h c ack as su ace pa e n, unlike hose
wi h smoo h, sc a ch o dimple su ace pa e ns. The inc eased numbe o de ec s
is caused by an inc emen in he numbe and size o he c acks. In p e ious s udies
[5,20,22,23] p eexis ing de ec s we e iden i ied as co osion si es. In he same
way, s udies on a chwi es wi h polished su aces ind less co osion [23,27].
Co osion is due o highe esidual s ess and/o non-uni o m passi e ilm on he
su ace de ec s [5]. Repassi a ion can also be di e en due o di e en su ace
condi ions [28]. These p eexis ing su ace de ec s a e ela ed o he p oduc ion
p ocess [5]. Fu he mo e, o he esea che s ha e no ound any ela ionship
be ween he su ace de ec s and he deg ee o co osion [4,9]. So, he di e ence
15
Rama i an Li e
Den au um
60648
54.5 / 45.5
Sc a ch
G4
G&H
142669
53.3 / 46.7
Sc a ch
M5
G&H
126755
53.3 / 46.6
Sc a ch
The momemo ia
Leone
08022001
53.9 / 46.1
Sc a ch
The maloy
RMO
A07304
53.4 / 46.6
Sc a ch
Re lex Hea -Ac i a ed
TPO
1297060
53.2 / 46.7
Sc a ch
Neo Sen alloy
GAC
H326
53.1 / 46.8
Po ous
(*) %Ni / %Ti (w %)
(†) A chwi es used in he expe imen al s udy
(‡) %Ni / %Ti / %Cu (w %)

16
Table 2 Su ace a ea o de ec s and a ia ion (Δ De , ob ained by sub ac ing a e age To al de ec s) be o e and a e imme sion es . C ack pa e n shows s a is ically signi ican
a ia ion.
Ni-Ti
A chwi es
MANUFACTURING DEFECTS (In 10.000 μm2)
PATTERN
Δ De -SALIVA+F
C acks
Po es
μPo es
Sc a ches*
Dimples
To al
Mean
SD
Re lex SE
0
0
0.8
2.9
0
3.7
Smoo h
39.8
24.6
Ni inol Classic
0
174
1.9
0
25
200.1
O honol
0
228
1.5
0
6215
6444.5
Dimple
-144
48.0
Align XF
73.7
258
3,3
0
1302
1637
Memo ia
577.5
5.1
1.7
12.8
176
773.1
C ack
631.3†
68.0
Ti anol SE
264.5
35.6
1.3
0
0
301.4
Tensic
70
0
0
6.8
0.28
77.1
Sc a ch
51.7
31.6
Ni inol HA
57.9
58.8
7.7
13
138
275.4
(*) μm pe 100 μm in linea sc a ches.
(†) Mean signi ican di e ence (p < 0.05)
17
Table 3 Su ace oughness da a and a ia ion be o e and a e imme sion es . Sc a ch and c ack pa e ns show s a is ically signi ican a ia ions.
Ni-Ti
A chwi es
SURFACE ROUGHNESS AS-RECIEVED (10.000 μm2)
SALIVA+FLUORIDE
Ra
Rms
R
Rp
PATTERN
Ra
Rms
ΔRa
ΔRms
Re lex SE
0.22
0.31
2.31
1.20
Smoo h
0.32 (0.13)*
0.45 (0.18)
0.03 (0.01)
0.03 (0.01)
Ni inol Classic
0.46
0.61
3.46
2.76
O honol
1.32
1.71
8.45
4.53
Dimple
1.01 (0.35)
1.35 (0.47)
-0.06 (0.02)
-0.08 (0.02)
Align XF
0.70
0.95
7.60
4.09
Memo ia
0.44
0.60
4.30
2.23
C ack
0,35 (0.13)
0.48 (0.17)
0.13† (0.04)
0.19† (0.06)
Ti anol SE
0.25
0.37
3.33
1.18
Tensic
0.34
0.47
3.87
1.87
Sc a ch
0.30 (0.09)
0.40 (0.13)
0.10† (0.03)
0.14† (0.04)
Ni inol HA
0.26
0.36
3.14
1.81
* S anda d de ia ions a e gi en in pa en heses.
† Mean signi ican di e ence (p < 0.05)