U sing visual observations, s c a n n in g electro n m icroscopy, a n d an im a g e-a n a ly z in g co m puter, qualitative a n d quantitative co m p a riso n s w e re m a d e o f s e v e ra l d ip -a p p lied corrosion in h ibito rs fo r protection o f ca rb o n s te e l d en ta l in stru m en ts d u rin g a u to cla v e sterilization. A lthough n o n e o f the in hibitors w e r e totally e ffectiv e, s e v e ra l p ro v id e d sign ifica n t inhibition o f corrosion. So d iu m nitrite, 2 % a n d o n e co m m erc ia l p ro p rieta ry in h ibitor w e r e a p p ro xim a tely eq u a lly e ffe c tiv e a n d s u p erio r to the o th er inhibitors that w e re in v estigated.
Inhibition of corrosion during autoclave sterilization of carbon steel dental instruments Raym ond L. Bertolotti, P h D , D D S Valerie Hurst, P h D , S a n F r a n c is c o
.Ü e c e n t e v id e n c e s u g g e s ts th a t ty p e B v ira l h e p a titis (s e ru m h e p a titis ) m a y b e tr a n s m itte d fro m p a tie n t to p a tie n t v ia d e n ta l in s tr u m e n t s .1"13 B e c a u s e th e ty p e B h e p a titis v iru s is r e s is ta n t to m a n y c h e m ic a l a g e n ts , p u b lic h e a lth , d e n ta l, a n d m e d ic a l a u th o r itie s b e lie v e th a t d e n ta l in s tr u m e n ts s h o u ld b e s te r iliz e d b y h e a t or e th y le n e o x id e g a s r a th e r th a n d is in fe c te d (c o ld s te r iliz e d ) w ith c h e m ic a l s o lu tio n s , s u c h as th e q u a te rn a ry a m m o n iu m c h lo r id e c o m p o u n d s , p h e n o ls , a lc o h o l, a n d th e l i k e .1' 9 A u to c la v in g (s te r iliz a tio n i n s a tu ra te d s te a m u n d e r p r e s s u r e ) is p e rh a p s th e m o st p r a c t ic a l m e th o d fo r h e a t s te r iliz a tio n o f in s tr u m e n ts in th e d e n ta l o ffic e . It is a m o re ra p id p r o c e s s th a n d ry -h e a t s te r iliz a tio n a c h ie v e d in a h o t-a ir o v e n . A lth o u g h c o r r o s io n p ro b le m s are s e ld o m e n c o u n te r e d in th e a u to c la v in g o f s ta in le s s s te e l in s tr u m e n ts , th e h o t, m o is t a tm o s p h e r e is e s p e c ia lly c o n d u c iv e to c o r r o s io n o f c a r b o n s te e l c u ttin g in s tr u m e n ts (s u c h as b u rs a n d s u r g ic a l in s tr u m e n ts ). C o r r o s io n is th e d e s tr u c tiv e a tta c k o f a m e ta l b y e le c tr o c h e m ic a l r e a c tio n w ith its e n v ir o n m e n t. D u r 628 ■ JADA, Vol. 97, October 1978
in g a u to c la v in g o f c a r b o n s te e l in th e p r e s e n c e o f o x y g e n a n d w a te r, th e fo llo w in g r e a c tio n o f ir o n o ccu rs: F e + H 2O + V2 O 2—> Fe(O H )2 T h e F e (O H )2 , a lth o u g h w h ite in its p u re fo rm , is n o r m a lly g r e e n to b la c k is h -g r e e n b e c a u s e o f i n c i p ie n t o x id a tio n b y a ir. T h e in itia l s ta g e s o f th is r e a c tio n p r o d u c e p r o d u c ts o n th e s u r fa c e c o m m o n ly te rm e d “ t a r n is h .” F o r th e p u rp o s e o f th is p a p e r, ta r n is h a n d c o r r o s io n a re c o n s id e r e d s y n o n y m o u s . In o r d in a r y a u to c la v in g in w h ic h w a te r o f n e a r ly n e u tr a l p H is u s e d , d is s o lv e d o x y g e n is n e c e s s a r y fo r a p p r e c ia b le c o r r o s io n o f iro n to o c c u r. T h e ra te o f c o r r o s io n in c r e a s e s w ith in c r e a s in g o x y g e n c o n c e n tra tio n u p to a c r it ic a l le v e l; in c o n c e n tr a tio n s g re a te r th a n th is le v e l, c o r r o s io n d e c r e a s e s a g a in .14 C o r r o s io n -in h ib itin g p a s s iv a to rs m a k e u s e o f th is d e c r e a s e in th e ra te o f c o r r o s io n w ith in c r e a s in g o x y g e n a c tiv ity . C a rb o n s te e ls c a n b e m a d e p a s s iv e (e le c tr o c h e m ic a lly a c tiv e , b u t c o r r o d in g a t a v e ry lo w ra te ) b y u s e o f v a r io u s c h e m ic a l p a s s iv a to rs th a t e ffe c tiv e ly p ro v id e m o re o x y g e n to th e m e ta l s u r fa c e
th a n c a n b e r e d u c e d b y th e c o r r o s io n r e a c tio n . T h e e x c e s s is a v a ila b le to fo rm a p a s s iv e , p r o te c tiv e film , th u s r e d u c in g th e e le c tr o c h e m ic a l p o te n tia l o f th e c o r r o s io n r e a c t i o n .15 O n th e b a s is o f th e c o r r o s io n b e h a v io r o f ir o n a llo y s , s e v e r a l a p p r o a c h e s m a y b e ta k e n to in h ib it ta r n is h a n d c o r r o s io n in th e a u to c la v e . T h e s im p le s t a p p r o a c h t h e o r e tic a lly , b u t d if fic u lt p r a c t ic a lly , is to b lo c k th e c o r r o s io n r e a c tio n b y e lim in a tin g o x y g e n fro m th e a u to c la v e a tm o s p h e r e . A s e c o n d , a n d p e r h a p s m o r e p r a c t ic a l, a p p r o a c h is to p r o v id e a p a s s iv e s u r fa c e la y e r o n th e a llo y to r e d u c e th e e le c t r o c h e m ic a l p o te n tia l o f th e r e a c tio n . C o m m o n ly u s e d p a s s iv a to r s fo r s te e l a re in o r g a n ic o x id iz in g s u b s ta n c e s th a t h a v e a n o x id iz in g c a p a c ity th e r m o d y n a m ic a lly a n d a re r e a d ily r e d u c e d . T h e s e in o r g a n ic o x id iz in g s u b s ta n c e s a re th o u g h t to p r o d u c e a p a s s iv e s u r fa c e b y fo rm in g a th in o x id e la y e r th a t s e p a r a te s th e m e ta l fro m its e n v ir o n m e n t. A th ir d a p p r o a c h is to p ro v id e a p o la r, o r g a n ic c o m p o u n d th a t w ill a d s o rb o n th e m e ta l s u r fa c e in a c lo s e ly p a c k e d , o r ie n te d la y e r. L a n o lin is s u c h a s u b s ta n c e a n d h a s b e e n u s e d fo r a lo n g tim e to p r o t e c t m a c h in e p a rts. A fo u rth a p p r o a c h is to u s e v a p o r -p h a s e i n h ib ito r s . T h e s e a re s u b s ta n c e s w ith lo w b u t s ig n if ic a n t v a p o r p re s s u r e ; th e v a p o r h a s c o r r o s io n - in h ib itin g p r o p e r tie s . T h e b e s t k n o w n o f th e s e v a p o rp h a s e in h ib it o r s a re c y c l ic a m in e s . T h e u s e o f v a p o r -p h a s e in h ib it o r s h a s b e e n s u c c e s s fu l in p re v io u s in v e s t ig a t io n s 16,17; h o w e v e r, th e s e c o m p o u n d s are t o x i c .18,19 I n th is s tu d y , th e e ffe c tiv e n e s s o f s e v e r a l c l in i c a ll y c o n v e n ie n t c o r r o s io n in h ib ito r s w a s c o m p a r e d fo r u s e in p r o te c tin g c a rb o n s te e l d e n ta l in s tr u m e n ts d u rin g a u to c la v in g . S e v e r a l in h ib it o r s o f th e p a s s iv a to r ty p e , o n e o r g a n ic c o m p o u n d , a n d tw o c o m m e r c ia l p ro p rie ta r y in h ib it o r s o f u n k n o w n c o m p o s i t io n w e re in v e s tig a te d . E a c h w a s a p p lie d c o n v e n ie n t ly b y a s im p le d ip in to a w a te r s o lu tio n o f th e i n h ib it o r b e fo re a u to c la v in g . V a p o r -p h a s e c y c l ic a m in e s , s im ila r to th o s e r e p o r te d ly e ffe c tiv e fo r p r o t e c tin g d e n ta l in s tr u m e n t s ,16,17 w e re n o t in v e s ti g a te d b e c a u s e w e c o n s id e r e d th e ir t o x ic p r o p e r t i e s 18,19 to b e a n u n a c c e p ta b le h a z a rd to p e r s o n n e l.
Method and materials
Fig 1 ■ Etched m icrostructure o f carbon steel used for quantitative data.
c o r r o s io n . (P r e lim in a r y s tu d ie s s h o w e d th a t th e c a r b id e tip a n d its w e ld a re n o t a s s u s c e p tib le to a u to c la v e c o r r o s io n a s w a s th e s te e l s h a n k .) C a rb o n s te e l, lo w -s p e e d b u rs w e r e u s e d fo r s u b je c tiv e v is u a l e v a lu a tio n . A lth o u g h th e c o m p o s itio n s o f th e s te e ls u s e d in th e s e b u rs a re p r o p r ie ta r y , m ic r o s c o p y o f e tc h e d s p e c im e n s c o m b in e d w ith a n a ly s is o f X -r a y e m is s io n s h o w e d th a t b o th w e re t y p ic a l to o l s te e ls w ith in c lu s io n s o f c a r b id e s a n d in te r m e ta llic -fo r m in g e le m e n ts . T h e m ic r o s tr u c tu r e o f th e s te e l u s e d fo r q u a n tita tiv e s tu d y is s h o w n in F ig u r e 1. B o th ty p e s o f b u rs w e re s e p a ra te d in to th r e e g ro u p s : n o n a u to c la v e d c o n t r o l, n e it h e r tre a te d n o r a u to c la v e d ; a u to c la v e d c o n t r o l, n o t tr e a te d b u t a u to c la v e d ; a n d e x p e r im e n ta l, b o th tre a te d a n d a u to c la v e d . CO RRO SIO N IN H IB IT O R S. P a s s iv a to r -ty p e
i n h ib i
to rs th a t w e re in v e s tig a te d w e r e s o d iu m n itr ite (N aN O z); s o d iu m o r th o p h o s p h a te (N a 3 P 0 4 ); s o d iu m o r th o p h o s p h a te d i-H (NaHhPO.»); a n d s o d iu m te t ra b o ra te (N a 2 B 4 0 7 ), a ll a p p lie d a s 2 % s o lu tio n s in d is tille d w a te r. O n e o r g a n ic -ty p e i n h ib it o r c o n s i s t in g o f a n e m u ls io n o f 2 % l a n o lin p lu s p o ly s o r b a te 8 0 (T w e e n -8 0 ) in w a te r w a s a ls o u s e d . A v a p o r -p h a s e in h ib ito r c o m m o n ly u s e d in p r o te c tiv e p a p e rs , c o n s is tin g o f 2 % u r e a (H 2N C O N H 2) p lu s 2 % s o d iu m n itr ite , w a s in v e s tig a te d as a d ip -a p p lie d in h ib ito r . F o r c o m p a r a tiv e p u r p o s e s , tw o p ro p rie ta r y i n h ib ito r s ,* s o ld s p e c if ic a lly fo r a u to c la v in g d e n ta l in s tr u m e n ts , w e re e v a lu a te d w h e n u s e d a c c o r d in g
of
to th e m a n u fa c tu r e r ’s d ilu t io n d ir e c tio n s . B o th th e e x p e r im e n ta l a n d th e c o n t r o l b u rs w e re
h ig h -s p e e d , c a r b id e -tip p e d b u rs w e re u s e d fo r th e q u a n tita tiv e c o r r o s io n s p e c im e n s . T h e s e s p e c im e n s w e r e m e ta llu r g ic a lly p o lis h e d w ith s u c c e s s iv e ly fin e r g ra d e s o f d ia m o n d a b ra s iv e d o w n to 1 /txm to p r o v id e a fla t s u r fa c e th a t fa c ilita te d m e a s u r e m e n t o f
u ltr a s o n ic a lly c le a n e d in A lc o n o x , r in s e d in d is t i l le d w a te r, a n d th e n a ir -d r ie d . T h e d ip in h ib it o r s w e re a p p lie d to th e e x p e r im e n ta l b u rs b y im m e r s io n in th e in h ib it o r s o lu tio n fo r tw o m in u te s . P a s s iv a to r a c tio n m a y b e tim e d e p e n d e n t,20 m a k in g it a n e x p e r
ST E E L SPEC IM EN S. T h e
s te e l s h a n k
p o r tio n s
Bertolotti—H u rst: CORROSION INHIBITION DURING AUTOCLAVING ■ 629
Fig 2 ■ Carbon steel round burs be fore (left) and after (right) three cy cles o f autoclaving w ithout any cor rosion inhibitor (original magni fication X230).
im e n ta l v a r ia b le ; th e r e fo r e , th e a p p lic a t io n tim e w a s s ta n d a r d iz e d a t tw o m in u te s to a p p r o x im a te p r a c t i c a l u s a g e in a d e n ta l o ffic e . A U TO CLAVIN G. T h e a u to c la v e u s e d in th is s tu d y w a s o f th e d o w n d r a ft-d is p la c e m e n t ty p e o p e ra te d w ith d is tille d w a te r. T h e c y c le u s e d w a s to h e a t to 2 7 0 F , h o ld fo r 2 0 m in u te s , th e n d ry w ith fo r c e d a ir. C O R R O SIO N M EA SU R EM EN TS. Q u a n tita t iv e c o r r o s io n m e a s u r e m e n ts w e re m a d e w ith a p ro g ra m m e d im a g e -a n a ly z in g c o m p u t e r .t A fte r a u to c la v in g , th e s p e c im e n s w e r e p h o to g ra p h e d o n a m e ta llu r g ic a l m ic r o s c o p e a t a p p r o x im a te ly X 1 0 0 ; th e p h o to g ra p h s w e re s c a n n e d b y th e c o m p u te r to m e a s u re th e fr a c tio n o f 5 0 0 ,0 0 0 s e le c te d p ic tu r e p o in ts e ith e r l ig h te r or d a rk e r th a n th e s e le c te d s ta n d a rd . T h is s ta n d a rd v a lu e w a s a r b itr a r ily s e le c te d to b e i n te r m e d ia te b e tw e e n th e h ig h ly r e fle c t iv e u n c o r r o d e d a re a s a n d th e d a r k e r -c o lo r e d a re a s w h e n s u b je c t iv e ly a s s e s s e d b y v is u a l e x a m in a tio n . A r e a s d a rk e r th a n th e s ta n d a rd v a lu e w e re c o u n te d “ c o r r o d e d ” a n d lig h te r a re a s w e r e c o u n te d “ u n c o r r o d e d .” T o c h e c k th e r e p r o d u c ib ility o f th e c o m p u te r r e a d in g in a g iv e n a re a , te n s u c c e s s iv e m e a s u r e m e n ts w e re m a d e o f o n e a re a a n d w e re r e p r o d u c ib le w it h in 1 % o f th e fr a c tio n a l a re a re p o rte d . T h e m e a s u r e m e n t o f c o r r o s io n is c o m p le te d m u c h m o re r a p id ly b y c o m p u te r s c a n n in g th a n b y e s ta b lis h e d c h e m ic a l m e th o d s .16 A lth o u g h th e c o m p u te r m e th o d d o e s n o t m e a s u r e th e d e p th o f c o r r o s io n o r th e a c tu a l m a s s o f c o r r o s io n p ro d u c ts a s d o c h e m ic a l m e th o d s , it d e te r m in e s th e e x te n t to w h ic h th e s u r fa c e o f th e s p e c im e n is a ffe c te d , w h ic h is p e rh a p s m o re s ig n if ic a n t fo r d e n ta l in s tr u m e n ts w h e re th e m a in te n a n c e o f a c u ttin g e d g e o r s u r fa c e fin is h is o f p rim a ry im p o r ta n c e . 630 ■ JADA, Vol. 97, October 1978
Results and discussion T h e a p p e a r a n c e o f a ty p ic a l c a r b o n s te e l b u r b e fo re a n d a fte r th r e e c y c le s o f a u to c la v in g w ith o u t a n y c o r r o s io n in h ib ito r is s h o w n in F ig u r e 2 . A la rg e fr a c tio n o f th e s u r fa c e o f th e a u to c la v e d b u r is c o v e re d w ith p r o d u c ts o f c o r r o s io n . N o q u a lita tiv e d if fe r e n c e w a s n o te d in th e c o r r o s io n b e h a v io r o f th e tw o ty p e s o f s te e l s p e c im e n s e x a m in e d . B e c a u s e o f th is o b s e r v a tio n a n d b e c a u s e th e c o m p o s itio n o f s te e l h a s b e e n r e p o r te d to h a v e n o p r a c t ic a l e ffe c t o n th e ra te o f c o r r o s io n in th e n e a r n e u tr a l ra n g e o f p H ,21 q u a n tita tiv e e v a lu a tio n s w e re r e s tr ic te d to o n e ty p e o f s te e l in o u r stu d y . T h e r e s u lts o f th e q u a n tita tiv e te s ts s h o w n in th e T a b le a re r e p o r te d a s th e a v e ra g e o f n in e m e a s u r e m e n ts (th re e a re a s o n e a c h o f th r e e d if fe r e n t s p e c i m e n s ). A ty p ic a l p h o to g ra p h o f a s p e c im e n u s e d fo r q u a n tita tiv e d a ta is s h o w n in F ig u r e 3 a lo n g w ith a s c a n n in g e le c tr o n m ic r o g r a p h o f th e s a m e s p e c i m en. W h e n th e s p e c im e n s w e re e x a m in e d w ith a n o p ti c a l m ic r o s c o p e im m e d ia te ly a fte r m e ta llu r g ic a l p o lis h in g , it w a s n o te d th a t th e s p e c im e n s b e g a n c o r r o d in g s p o n ta n e o u s ly in lo c a liz e d a re a s u n d e r Table ■ Quantitative results. % o f a rea corroded* In crea se in a re a corrod ed f N onautoclaved control N aN 02 P ro p rieta ry solution A U rea and N a N 0 2 N a3P 0 4 N a 2B 40 , L an o lin plus Tw een-80 N a H 2P 0 4 A utoclaved control P ro p rieta ry solution B
33 (5) 39 (5) 39 (9) 45 (7) 50 (10) 63 (6) 70 (21) 70 (9) 78 (5) 80 (5)
0 6 6 12 17 30 37 37 45 47
* N u m bers in p aren th eses a re stan d ard dev iation s o f nine m ea su rem ents, t G re a te r than nonautoclaved control.
Fig 3 ■ Left, metallurgical microscope photograph and, right, scanning electron micrograph of a typical quantitative corrosion specimen.
ro o m a m b ie n t c o n d itio n s , b u t w ith in m in u te s r e a c h e d a v is u a lly ju d g e d s ta te o f e q u ilib r iu m . T h is c o r r o s io n w a s n o t a p p a r e n t in th e s c a n n in g e le c tr o n m ic r o s c o p e , p ro b a b ly b e c a u s e o f th e m in u te t h i c k n e s s o f th e c o r r o s io n la y e r. H o w e v e r, th e im a g e a n a ly z in g c o m p u te r r e a d ily d e te c te d th e s e c o r ro d e d a re a s a s d iffe r e n t in r e fle c t iv ity a n d c o u n te d a t le a s t s o m e o f th e m as c o r ro d e d ; th is e x p la in s th e la rg e p e r c e n ta g e o f c o r ro d e d a re a fo r th e n o n a u to c la v e d c o n tr o l. T h e in c r e m e n ta l d if fe r e n c e s b e tw e e n th e n o n a u to c la v e d c o n tr o l a n d th e a u to c la v e d s a m p le s a re g iv e n in th e T a b le a n d a re th o u g h t to b e th e m o s t q u a n tita tiv e m e a s u re o f th e e ffe c tiv e n e s s o f th e c o r r o s io n in h ib it o r s th a t w e re in v e s tig a te d . Q u a lita tiv e v is u a l a tte m p ts to p la c e th e s p e c im e n s in o r d e r o f in c r e a s in g c o r r o s io n p ro v e d to b e q u ite
d if fic u lt a n d y ie ld e d n o n r e p r o d u c ib le r e s u lts , e x c e p t th a t th e n o n a u to c la v e d c o n tr o l w a s c le a r ly th e le a s t c o r r o d e d a n d th e a u to c la v e d c o n t r o l w a s c le a r ly th e m o st c o r r o d e d . T h e N a F h P C k -tre a te d s p e c im e n s h a d w h a t a p p e a re d to b e s a lt c r y s ta ls o n th e s u r fa c e , w h ic h m a d e th e ir v is u a l a p p e a r a n c e m u c h w o rs e th a n th e q u a n tita tiv e v a lu e d e r iv e d fro m th e im a g e -a n a ly z in g c o m p u te r . T h e a p p e a r a n c e o f a ty p ic a l c a r b o n s te e l b u r a fte r th r e e c y c l e s o f a u to c la v in g w ith s o d iu m n itr ite in h ib it o r tr e a tm e n t b e fo re e a c h c y c le is s h o w n in F ig u r e 4 . N u m e r o u s s a lt c r y s ta ls a re s e e n o n th e s u r fa c e o f th e b u r, b u t c o r r o s io n a s o b s e rv e d o n th e a u to c la v e d c o n t r o ls is c o n s id e r a b ly re d u c e d .
Conclusion and summary C o m p a r is o n s w e re m a d e o f s e v e r a l d ip - a p p lie d c o r r o s io n in h ib it o r s fo r p r o te c tio n o f c a r b o n s te e l d e n ta l in s tr u m e n ts d u rin g a u to c la v in g . A lth o u g h n o n e w e re to ta lly e ffe c tiv e , s e v e r a l p ro v id e d s ig n if ic a n t c o r r o s io n in h ib it io n . S o d iu m n itr ite a n d o n e p r o p r ie ta r y in h ib it o r w e re a b o u t e q u a lly e ffe c tiv e a n d n o ta b ly s u p e r io r to th e o th e r in h ib it o r s in v e s tig a te d . B e c a u s e s o d iu m n itr ite is a fo o d p r e s e r v a tiv e th a t is r e la t iv e ly h a r m le s s w h e n in g e s te d in s m a ll q u a n t itie s , w h e r e a s c o m m e r c ia l in h ib it o r s a re o f p r o p r ie ta r y c o m p o s itio n a n d u n s p e c ifie d to x ic it y , w e p re fe r to u s e s o d iu m n itr ite fo r c o r r o s io n in h ib it io n d u rin g a u t o c la v in g .22 S o d iu m n itr ite is r e a d ily a v a ila b le fro m c h e m ic a l s u p p lie r s a n d is g e n e r a lly m u c h le s s e x p e n s iv e th a n m o s t c o m m e r c ia l i n
Fig 4 ■ Carbon steel bur after three cycles of autoclaving with sodium nitrite inhibitor treatment before each cycle (original mag nification X 2 3 0 ).
h ib ito r s . A lth o u g h th e a u to c la v e u s e d in th is in v e s tig a tio n is ty p ic a l o f m a n y u s e d in c l in i c a l s it u a tio n s , m in o r v a r ia tio n s in d e s ig n , s te a m im p u r itie s , a n d o th e r Bertolotti—Hurst : CORROSION INHIBITION DURING AUTOCLAVING ■ 631
u n k n o w n fa c to r s m ig h t e ffe c t th e r e s u lts . F u r th e r r e s e a r c h is n e e d e d to d e te r m in e th e c o r r o s iv e e ffe c ts o f im p u r itie s in th e s te a m s u p p ly , r e s id u a l d e te r g e n ts , m e th o d o f p o s ta u to c la v e d ry in g , s te a m s u p p ly d e o x y g e n a tio n , p H , a n d p o s s ib ly th e u s e o f o x y g e n s c a v e n g e r s w ith in th e a u to c la v e .
*T h e authors w ill furnish the names of these products on written re quest. tlm ango Quantimet 720, Image Analysing Computer Ltd. The “field standard” was used as a reference for detection purposes. T his work was supported by grants from the California Dental Associa tion and the Committee on Research, School of Dentistry, and the Commit tee on Research of the Academ ic Senate, University of California, San Francisco. The authors thank Joseph P. Moffa and M alcolm D. Jendresen for techni cal assistance and helpful discussions. 1. Type B (serum) hepatitis and dental practice. Council on Dental Therapeutics. JADA 92:153 Jan 1976. 2. Crawford, J.J. New light on the transm issibility of viral hepatitis in dental practice and its control. JADA 91:8 2 9 Oct 1975. 3. Sterilization or disinfection of dental instruments. Council on Dental Therapeutics. In Accepted Dental Therapeutics, ed 37. Chicago, American Dental Association, 1977, p 54. 4. Am erican A ssociation of Dental Schools Report of Actions of the 1974 House of Delegates, resolution no. 9-74-H. J Dent Educ 38:316 June 1974. 5. Morbidity and m ortality weekly report, Center for Disease Control. Perspectives on the control of viral hepatitis, Type B. 25(suppl):3 May 7, 1976. 6. An oral surgeon-related hepatitis B outbreak. California Morbidity W eekly Report, no. 14, State of California Dept of Health, April 16, 1976. 7. W atkins, B.J. Viral hepatitis B: a special problem in prevention. J Am Soc Prev Dent May-June 1976, p 8. 8. Parker, R.B. Dental office procedures for breaking the chain of infec tion. J Am Soc Prev Dent May-June 1976, p 18. 9. Levin, M .L., and others. Hepatitis B transm ission by dentists. JAMA 2 28:1139 May 27, 1974. 10. Schwim m er, A., and Howitt, N.G. Hepatitis: a review of the disease and its prevention. NY J Dent 43:73 M arch 1973. 11. Sim s, W. Serum hepatitis and the dental surgeon. J Dent 4:151 July 1976. 12. M acFarlane, T.W ., and Mason, D.K. The dentist and the prevention of serum hepatitis. Br Dent J 132:487 June 20, 1972.
632 ■ JADA, Vol. 97, October 1978
BERTOLOTTI
HURST
THE AUTHORS Dr. Bertolotti has a PhD in ceramic engineering and has recently received his DDS from the University of California— San Francisco. Dr. Hurst is associate professor of microbiology, School of Den tistry, University of California— San Francisco, San Francisco, 94143. Address requests for reprints to Dr. Hurst.
13. McLundie, A.C., and others. Sterilisation in general dental practice. Br Dent J 124:214 M arch 5, 1968. 14. Uhlig, H.H., and others. Effect of oxygen, chloride, and calcium ion on corrosion inhibition of iron by polyphosphates. J Electrochem Soc 102:59 Feb 1955. 15. Uhlig, H.H. Corrosion and corrosion control, ed 2. New York, John W iley & Sons Inc., 1971, p 94. 16. Fajers, C-M., and others. On steam corrosion and steam corrosion inhibition. Stockholm , Acta Polytechnica Scandavavica, Chemistry in cluding Metallurgy Series no. 87, 1969. 17. M cCulloch, W.T., and Sm ith, D.C. Vapour-phase inhibition of cor rosion in autoclaving. Br Dent J 116:78 Jan 21, 1964. 18. Perkins, J.J. Principles and methods of sterilization in the health sciences, ed 2. Springfield, 111, Charles C Thom as, 1969, p 103. 19. Sax, N.I. Dangerous properties of industrial m aterials, ed 3. New York, Van Nostrand Reinhold Co., 1968, p 605. 20. Burns, R.M. Electrochem ical techniques in corrosion study. J Appl Phys 8:398 June 1937. 21. Uhlig, H.H. Corrosion and corrosion control, ed 2. New York, John W iley & Sons Inc., 1971, p 118. 22. Hurst, V. Reducing the risk of transm itting viral hepatitis. IADR Program and Abstracts of papers, no. 408, March 1972.
Inhibition of corrosion during autoclave sterilization of carbon steel dental instruments Raym ond L. Bertolotti, P h D , D D S Valerie Hurst, P h D , S a n F r a n c is c o
.Ü e c e n t e v id e n c e s u g g e s ts th a t ty p e B v ira l h e p a titis (s e ru m h e p a titis ) m a y b e tr a n s m itte d fro m p a tie n t to p a tie n t v ia d e n ta l in s tr u m e n t s .1"13 B e c a u s e th e ty p e B h e p a titis v iru s is r e s is ta n t to m a n y c h e m ic a l a g e n ts , p u b lic h e a lth , d e n ta l, a n d m e d ic a l a u th o r itie s b e lie v e th a t d e n ta l in s tr u m e n ts s h o u ld b e s te r iliz e d b y h e a t or e th y le n e o x id e g a s r a th e r th a n d is in fe c te d (c o ld s te r iliz e d ) w ith c h e m ic a l s o lu tio n s , s u c h as th e q u a te rn a ry a m m o n iu m c h lo r id e c o m p o u n d s , p h e n o ls , a lc o h o l, a n d th e l i k e .1' 9 A u to c la v in g (s te r iliz a tio n i n s a tu ra te d s te a m u n d e r p r e s s u r e ) is p e rh a p s th e m o st p r a c t ic a l m e th o d fo r h e a t s te r iliz a tio n o f in s tr u m e n ts in th e d e n ta l o ffic e . It is a m o re ra p id p r o c e s s th a n d ry -h e a t s te r iliz a tio n a c h ie v e d in a h o t-a ir o v e n . A lth o u g h c o r r o s io n p ro b le m s are s e ld o m e n c o u n te r e d in th e a u to c la v in g o f s ta in le s s s te e l in s tr u m e n ts , th e h o t, m o is t a tm o s p h e r e is e s p e c ia lly c o n d u c iv e to c o r r o s io n o f c a r b o n s te e l c u ttin g in s tr u m e n ts (s u c h as b u rs a n d s u r g ic a l in s tr u m e n ts ). C o r r o s io n is th e d e s tr u c tiv e a tta c k o f a m e ta l b y e le c tr o c h e m ic a l r e a c tio n w ith its e n v ir o n m e n t. D u r 628 ■ JADA, Vol. 97, October 1978
in g a u to c la v in g o f c a r b o n s te e l in th e p r e s e n c e o f o x y g e n a n d w a te r, th e fo llo w in g r e a c tio n o f ir o n o ccu rs: F e + H 2O + V2 O 2—> Fe(O H )2 T h e F e (O H )2 , a lth o u g h w h ite in its p u re fo rm , is n o r m a lly g r e e n to b la c k is h -g r e e n b e c a u s e o f i n c i p ie n t o x id a tio n b y a ir. T h e in itia l s ta g e s o f th is r e a c tio n p r o d u c e p r o d u c ts o n th e s u r fa c e c o m m o n ly te rm e d “ t a r n is h .” F o r th e p u rp o s e o f th is p a p e r, ta r n is h a n d c o r r o s io n a re c o n s id e r e d s y n o n y m o u s . In o r d in a r y a u to c la v in g in w h ic h w a te r o f n e a r ly n e u tr a l p H is u s e d , d is s o lv e d o x y g e n is n e c e s s a r y fo r a p p r e c ia b le c o r r o s io n o f iro n to o c c u r. T h e ra te o f c o r r o s io n in c r e a s e s w ith in c r e a s in g o x y g e n c o n c e n tra tio n u p to a c r it ic a l le v e l; in c o n c e n tr a tio n s g re a te r th a n th is le v e l, c o r r o s io n d e c r e a s e s a g a in .14 C o r r o s io n -in h ib itin g p a s s iv a to rs m a k e u s e o f th is d e c r e a s e in th e ra te o f c o r r o s io n w ith in c r e a s in g o x y g e n a c tiv ity . C a rb o n s te e ls c a n b e m a d e p a s s iv e (e le c tr o c h e m ic a lly a c tiv e , b u t c o r r o d in g a t a v e ry lo w ra te ) b y u s e o f v a r io u s c h e m ic a l p a s s iv a to rs th a t e ffe c tiv e ly p ro v id e m o re o x y g e n to th e m e ta l s u r fa c e
th a n c a n b e r e d u c e d b y th e c o r r o s io n r e a c tio n . T h e e x c e s s is a v a ila b le to fo rm a p a s s iv e , p r o te c tiv e film , th u s r e d u c in g th e e le c tr o c h e m ic a l p o te n tia l o f th e c o r r o s io n r e a c t i o n .15 O n th e b a s is o f th e c o r r o s io n b e h a v io r o f ir o n a llo y s , s e v e r a l a p p r o a c h e s m a y b e ta k e n to in h ib it ta r n is h a n d c o r r o s io n in th e a u to c la v e . T h e s im p le s t a p p r o a c h t h e o r e tic a lly , b u t d if fic u lt p r a c t ic a lly , is to b lo c k th e c o r r o s io n r e a c tio n b y e lim in a tin g o x y g e n fro m th e a u to c la v e a tm o s p h e r e . A s e c o n d , a n d p e r h a p s m o r e p r a c t ic a l, a p p r o a c h is to p r o v id e a p a s s iv e s u r fa c e la y e r o n th e a llo y to r e d u c e th e e le c t r o c h e m ic a l p o te n tia l o f th e r e a c tio n . C o m m o n ly u s e d p a s s iv a to r s fo r s te e l a re in o r g a n ic o x id iz in g s u b s ta n c e s th a t h a v e a n o x id iz in g c a p a c ity th e r m o d y n a m ic a lly a n d a re r e a d ily r e d u c e d . T h e s e in o r g a n ic o x id iz in g s u b s ta n c e s a re th o u g h t to p r o d u c e a p a s s iv e s u r fa c e b y fo rm in g a th in o x id e la y e r th a t s e p a r a te s th e m e ta l fro m its e n v ir o n m e n t. A th ir d a p p r o a c h is to p ro v id e a p o la r, o r g a n ic c o m p o u n d th a t w ill a d s o rb o n th e m e ta l s u r fa c e in a c lo s e ly p a c k e d , o r ie n te d la y e r. L a n o lin is s u c h a s u b s ta n c e a n d h a s b e e n u s e d fo r a lo n g tim e to p r o t e c t m a c h in e p a rts. A fo u rth a p p r o a c h is to u s e v a p o r -p h a s e i n h ib ito r s . T h e s e a re s u b s ta n c e s w ith lo w b u t s ig n if ic a n t v a p o r p re s s u r e ; th e v a p o r h a s c o r r o s io n - in h ib itin g p r o p e r tie s . T h e b e s t k n o w n o f th e s e v a p o rp h a s e in h ib it o r s a re c y c l ic a m in e s . T h e u s e o f v a p o r -p h a s e in h ib it o r s h a s b e e n s u c c e s s fu l in p re v io u s in v e s t ig a t io n s 16,17; h o w e v e r, th e s e c o m p o u n d s are t o x i c .18,19 I n th is s tu d y , th e e ffe c tiv e n e s s o f s e v e r a l c l in i c a ll y c o n v e n ie n t c o r r o s io n in h ib ito r s w a s c o m p a r e d fo r u s e in p r o te c tin g c a rb o n s te e l d e n ta l in s tr u m e n ts d u rin g a u to c la v in g . S e v e r a l in h ib it o r s o f th e p a s s iv a to r ty p e , o n e o r g a n ic c o m p o u n d , a n d tw o c o m m e r c ia l p ro p rie ta r y in h ib it o r s o f u n k n o w n c o m p o s i t io n w e re in v e s tig a te d . E a c h w a s a p p lie d c o n v e n ie n t ly b y a s im p le d ip in to a w a te r s o lu tio n o f th e i n h ib it o r b e fo re a u to c la v in g . V a p o r -p h a s e c y c l ic a m in e s , s im ila r to th o s e r e p o r te d ly e ffe c tiv e fo r p r o t e c tin g d e n ta l in s tr u m e n t s ,16,17 w e re n o t in v e s ti g a te d b e c a u s e w e c o n s id e r e d th e ir t o x ic p r o p e r t i e s 18,19 to b e a n u n a c c e p ta b le h a z a rd to p e r s o n n e l.
Method and materials
Fig 1 ■ Etched m icrostructure o f carbon steel used for quantitative data.
c o r r o s io n . (P r e lim in a r y s tu d ie s s h o w e d th a t th e c a r b id e tip a n d its w e ld a re n o t a s s u s c e p tib le to a u to c la v e c o r r o s io n a s w a s th e s te e l s h a n k .) C a rb o n s te e l, lo w -s p e e d b u rs w e r e u s e d fo r s u b je c tiv e v is u a l e v a lu a tio n . A lth o u g h th e c o m p o s itio n s o f th e s te e ls u s e d in th e s e b u rs a re p r o p r ie ta r y , m ic r o s c o p y o f e tc h e d s p e c im e n s c o m b in e d w ith a n a ly s is o f X -r a y e m is s io n s h o w e d th a t b o th w e re t y p ic a l to o l s te e ls w ith in c lu s io n s o f c a r b id e s a n d in te r m e ta llic -fo r m in g e le m e n ts . T h e m ic r o s tr u c tu r e o f th e s te e l u s e d fo r q u a n tita tiv e s tu d y is s h o w n in F ig u r e 1. B o th ty p e s o f b u rs w e re s e p a ra te d in to th r e e g ro u p s : n o n a u to c la v e d c o n t r o l, n e it h e r tre a te d n o r a u to c la v e d ; a u to c la v e d c o n t r o l, n o t tr e a te d b u t a u to c la v e d ; a n d e x p e r im e n ta l, b o th tre a te d a n d a u to c la v e d . CO RRO SIO N IN H IB IT O R S. P a s s iv a to r -ty p e
i n h ib i
to rs th a t w e re in v e s tig a te d w e r e s o d iu m n itr ite (N aN O z); s o d iu m o r th o p h o s p h a te (N a 3 P 0 4 ); s o d iu m o r th o p h o s p h a te d i-H (NaHhPO.»); a n d s o d iu m te t ra b o ra te (N a 2 B 4 0 7 ), a ll a p p lie d a s 2 % s o lu tio n s in d is tille d w a te r. O n e o r g a n ic -ty p e i n h ib it o r c o n s i s t in g o f a n e m u ls io n o f 2 % l a n o lin p lu s p o ly s o r b a te 8 0 (T w e e n -8 0 ) in w a te r w a s a ls o u s e d . A v a p o r -p h a s e in h ib ito r c o m m o n ly u s e d in p r o te c tiv e p a p e rs , c o n s is tin g o f 2 % u r e a (H 2N C O N H 2) p lu s 2 % s o d iu m n itr ite , w a s in v e s tig a te d as a d ip -a p p lie d in h ib ito r . F o r c o m p a r a tiv e p u r p o s e s , tw o p ro p rie ta r y i n h ib ito r s ,* s o ld s p e c if ic a lly fo r a u to c la v in g d e n ta l in s tr u m e n ts , w e re e v a lu a te d w h e n u s e d a c c o r d in g
of
to th e m a n u fa c tu r e r ’s d ilu t io n d ir e c tio n s . B o th th e e x p e r im e n ta l a n d th e c o n t r o l b u rs w e re
h ig h -s p e e d , c a r b id e -tip p e d b u rs w e re u s e d fo r th e q u a n tita tiv e c o r r o s io n s p e c im e n s . T h e s e s p e c im e n s w e r e m e ta llu r g ic a lly p o lis h e d w ith s u c c e s s iv e ly fin e r g ra d e s o f d ia m o n d a b ra s iv e d o w n to 1 /txm to p r o v id e a fla t s u r fa c e th a t fa c ilita te d m e a s u r e m e n t o f
u ltr a s o n ic a lly c le a n e d in A lc o n o x , r in s e d in d is t i l le d w a te r, a n d th e n a ir -d r ie d . T h e d ip in h ib it o r s w e re a p p lie d to th e e x p e r im e n ta l b u rs b y im m e r s io n in th e in h ib it o r s o lu tio n fo r tw o m in u te s . P a s s iv a to r a c tio n m a y b e tim e d e p e n d e n t,20 m a k in g it a n e x p e r
ST E E L SPEC IM EN S. T h e
s te e l s h a n k
p o r tio n s
Bertolotti—H u rst: CORROSION INHIBITION DURING AUTOCLAVING ■ 629
Fig 2 ■ Carbon steel round burs be fore (left) and after (right) three cy cles o f autoclaving w ithout any cor rosion inhibitor (original magni fication X230).
im e n ta l v a r ia b le ; th e r e fo r e , th e a p p lic a t io n tim e w a s s ta n d a r d iz e d a t tw o m in u te s to a p p r o x im a te p r a c t i c a l u s a g e in a d e n ta l o ffic e . A U TO CLAVIN G. T h e a u to c la v e u s e d in th is s tu d y w a s o f th e d o w n d r a ft-d is p la c e m e n t ty p e o p e ra te d w ith d is tille d w a te r. T h e c y c le u s e d w a s to h e a t to 2 7 0 F , h o ld fo r 2 0 m in u te s , th e n d ry w ith fo r c e d a ir. C O R R O SIO N M EA SU R EM EN TS. Q u a n tita t iv e c o r r o s io n m e a s u r e m e n ts w e re m a d e w ith a p ro g ra m m e d im a g e -a n a ly z in g c o m p u t e r .t A fte r a u to c la v in g , th e s p e c im e n s w e r e p h o to g ra p h e d o n a m e ta llu r g ic a l m ic r o s c o p e a t a p p r o x im a te ly X 1 0 0 ; th e p h o to g ra p h s w e re s c a n n e d b y th e c o m p u te r to m e a s u re th e fr a c tio n o f 5 0 0 ,0 0 0 s e le c te d p ic tu r e p o in ts e ith e r l ig h te r or d a rk e r th a n th e s e le c te d s ta n d a rd . T h is s ta n d a rd v a lu e w a s a r b itr a r ily s e le c te d to b e i n te r m e d ia te b e tw e e n th e h ig h ly r e fle c t iv e u n c o r r o d e d a re a s a n d th e d a r k e r -c o lo r e d a re a s w h e n s u b je c t iv e ly a s s e s s e d b y v is u a l e x a m in a tio n . A r e a s d a rk e r th a n th e s ta n d a rd v a lu e w e re c o u n te d “ c o r r o d e d ” a n d lig h te r a re a s w e r e c o u n te d “ u n c o r r o d e d .” T o c h e c k th e r e p r o d u c ib ility o f th e c o m p u te r r e a d in g in a g iv e n a re a , te n s u c c e s s iv e m e a s u r e m e n ts w e re m a d e o f o n e a re a a n d w e re r e p r o d u c ib le w it h in 1 % o f th e fr a c tio n a l a re a re p o rte d . T h e m e a s u r e m e n t o f c o r r o s io n is c o m p le te d m u c h m o re r a p id ly b y c o m p u te r s c a n n in g th a n b y e s ta b lis h e d c h e m ic a l m e th o d s .16 A lth o u g h th e c o m p u te r m e th o d d o e s n o t m e a s u r e th e d e p th o f c o r r o s io n o r th e a c tu a l m a s s o f c o r r o s io n p ro d u c ts a s d o c h e m ic a l m e th o d s , it d e te r m in e s th e e x te n t to w h ic h th e s u r fa c e o f th e s p e c im e n is a ffe c te d , w h ic h is p e rh a p s m o re s ig n if ic a n t fo r d e n ta l in s tr u m e n ts w h e re th e m a in te n a n c e o f a c u ttin g e d g e o r s u r fa c e fin is h is o f p rim a ry im p o r ta n c e . 630 ■ JADA, Vol. 97, October 1978
Results and discussion T h e a p p e a r a n c e o f a ty p ic a l c a r b o n s te e l b u r b e fo re a n d a fte r th r e e c y c le s o f a u to c la v in g w ith o u t a n y c o r r o s io n in h ib ito r is s h o w n in F ig u r e 2 . A la rg e fr a c tio n o f th e s u r fa c e o f th e a u to c la v e d b u r is c o v e re d w ith p r o d u c ts o f c o r r o s io n . N o q u a lita tiv e d if fe r e n c e w a s n o te d in th e c o r r o s io n b e h a v io r o f th e tw o ty p e s o f s te e l s p e c im e n s e x a m in e d . B e c a u s e o f th is o b s e r v a tio n a n d b e c a u s e th e c o m p o s itio n o f s te e l h a s b e e n r e p o r te d to h a v e n o p r a c t ic a l e ffe c t o n th e ra te o f c o r r o s io n in th e n e a r n e u tr a l ra n g e o f p H ,21 q u a n tita tiv e e v a lu a tio n s w e re r e s tr ic te d to o n e ty p e o f s te e l in o u r stu d y . T h e r e s u lts o f th e q u a n tita tiv e te s ts s h o w n in th e T a b le a re r e p o r te d a s th e a v e ra g e o f n in e m e a s u r e m e n ts (th re e a re a s o n e a c h o f th r e e d if fe r e n t s p e c i m e n s ). A ty p ic a l p h o to g ra p h o f a s p e c im e n u s e d fo r q u a n tita tiv e d a ta is s h o w n in F ig u r e 3 a lo n g w ith a s c a n n in g e le c tr o n m ic r o g r a p h o f th e s a m e s p e c i m en. W h e n th e s p e c im e n s w e re e x a m in e d w ith a n o p ti c a l m ic r o s c o p e im m e d ia te ly a fte r m e ta llu r g ic a l p o lis h in g , it w a s n o te d th a t th e s p e c im e n s b e g a n c o r r o d in g s p o n ta n e o u s ly in lo c a liz e d a re a s u n d e r Table ■ Quantitative results. % o f a rea corroded* In crea se in a re a corrod ed f N onautoclaved control N aN 02 P ro p rieta ry solution A U rea and N a N 0 2 N a3P 0 4 N a 2B 40 , L an o lin plus Tw een-80 N a H 2P 0 4 A utoclaved control P ro p rieta ry solution B
33 (5) 39 (5) 39 (9) 45 (7) 50 (10) 63 (6) 70 (21) 70 (9) 78 (5) 80 (5)
0 6 6 12 17 30 37 37 45 47
* N u m bers in p aren th eses a re stan d ard dev iation s o f nine m ea su rem ents, t G re a te r than nonautoclaved control.
Fig 3 ■ Left, metallurgical microscope photograph and, right, scanning electron micrograph of a typical quantitative corrosion specimen.
ro o m a m b ie n t c o n d itio n s , b u t w ith in m in u te s r e a c h e d a v is u a lly ju d g e d s ta te o f e q u ilib r iu m . T h is c o r r o s io n w a s n o t a p p a r e n t in th e s c a n n in g e le c tr o n m ic r o s c o p e , p ro b a b ly b e c a u s e o f th e m in u te t h i c k n e s s o f th e c o r r o s io n la y e r. H o w e v e r, th e im a g e a n a ly z in g c o m p u te r r e a d ily d e te c te d th e s e c o r ro d e d a re a s a s d iffe r e n t in r e fle c t iv ity a n d c o u n te d a t le a s t s o m e o f th e m as c o r ro d e d ; th is e x p la in s th e la rg e p e r c e n ta g e o f c o r ro d e d a re a fo r th e n o n a u to c la v e d c o n tr o l. T h e in c r e m e n ta l d if fe r e n c e s b e tw e e n th e n o n a u to c la v e d c o n tr o l a n d th e a u to c la v e d s a m p le s a re g iv e n in th e T a b le a n d a re th o u g h t to b e th e m o s t q u a n tita tiv e m e a s u re o f th e e ffe c tiv e n e s s o f th e c o r r o s io n in h ib it o r s th a t w e re in v e s tig a te d . Q u a lita tiv e v is u a l a tte m p ts to p la c e th e s p e c im e n s in o r d e r o f in c r e a s in g c o r r o s io n p ro v e d to b e q u ite
d if fic u lt a n d y ie ld e d n o n r e p r o d u c ib le r e s u lts , e x c e p t th a t th e n o n a u to c la v e d c o n tr o l w a s c le a r ly th e le a s t c o r r o d e d a n d th e a u to c la v e d c o n t r o l w a s c le a r ly th e m o st c o r r o d e d . T h e N a F h P C k -tre a te d s p e c im e n s h a d w h a t a p p e a re d to b e s a lt c r y s ta ls o n th e s u r fa c e , w h ic h m a d e th e ir v is u a l a p p e a r a n c e m u c h w o rs e th a n th e q u a n tita tiv e v a lu e d e r iv e d fro m th e im a g e -a n a ly z in g c o m p u te r . T h e a p p e a r a n c e o f a ty p ic a l c a r b o n s te e l b u r a fte r th r e e c y c l e s o f a u to c la v in g w ith s o d iu m n itr ite in h ib it o r tr e a tm e n t b e fo re e a c h c y c le is s h o w n in F ig u r e 4 . N u m e r o u s s a lt c r y s ta ls a re s e e n o n th e s u r fa c e o f th e b u r, b u t c o r r o s io n a s o b s e rv e d o n th e a u to c la v e d c o n t r o ls is c o n s id e r a b ly re d u c e d .
Conclusion and summary C o m p a r is o n s w e re m a d e o f s e v e r a l d ip - a p p lie d c o r r o s io n in h ib it o r s fo r p r o te c tio n o f c a r b o n s te e l d e n ta l in s tr u m e n ts d u rin g a u to c la v in g . A lth o u g h n o n e w e re to ta lly e ffe c tiv e , s e v e r a l p ro v id e d s ig n if ic a n t c o r r o s io n in h ib it io n . S o d iu m n itr ite a n d o n e p r o p r ie ta r y in h ib it o r w e re a b o u t e q u a lly e ffe c tiv e a n d n o ta b ly s u p e r io r to th e o th e r in h ib it o r s in v e s tig a te d . B e c a u s e s o d iu m n itr ite is a fo o d p r e s e r v a tiv e th a t is r e la t iv e ly h a r m le s s w h e n in g e s te d in s m a ll q u a n t itie s , w h e r e a s c o m m e r c ia l in h ib it o r s a re o f p r o p r ie ta r y c o m p o s itio n a n d u n s p e c ifie d to x ic it y , w e p re fe r to u s e s o d iu m n itr ite fo r c o r r o s io n in h ib it io n d u rin g a u t o c la v in g .22 S o d iu m n itr ite is r e a d ily a v a ila b le fro m c h e m ic a l s u p p lie r s a n d is g e n e r a lly m u c h le s s e x p e n s iv e th a n m o s t c o m m e r c ia l i n
Fig 4 ■ Carbon steel bur after three cycles of autoclaving with sodium nitrite inhibitor treatment before each cycle (original mag nification X 2 3 0 ).
h ib ito r s . A lth o u g h th e a u to c la v e u s e d in th is in v e s tig a tio n is ty p ic a l o f m a n y u s e d in c l in i c a l s it u a tio n s , m in o r v a r ia tio n s in d e s ig n , s te a m im p u r itie s , a n d o th e r Bertolotti—Hurst : CORROSION INHIBITION DURING AUTOCLAVING ■ 631
u n k n o w n fa c to r s m ig h t e ffe c t th e r e s u lts . F u r th e r r e s e a r c h is n e e d e d to d e te r m in e th e c o r r o s iv e e ffe c ts o f im p u r itie s in th e s te a m s u p p ly , r e s id u a l d e te r g e n ts , m e th o d o f p o s ta u to c la v e d ry in g , s te a m s u p p ly d e o x y g e n a tio n , p H , a n d p o s s ib ly th e u s e o f o x y g e n s c a v e n g e r s w ith in th e a u to c la v e .
*T h e authors w ill furnish the names of these products on written re quest. tlm ango Quantimet 720, Image Analysing Computer Ltd. The “field standard” was used as a reference for detection purposes. T his work was supported by grants from the California Dental Associa tion and the Committee on Research, School of Dentistry, and the Commit tee on Research of the Academ ic Senate, University of California, San Francisco. The authors thank Joseph P. Moffa and M alcolm D. Jendresen for techni cal assistance and helpful discussions. 1. Type B (serum) hepatitis and dental practice. Council on Dental Therapeutics. JADA 92:153 Jan 1976. 2. Crawford, J.J. New light on the transm issibility of viral hepatitis in dental practice and its control. JADA 91:8 2 9 Oct 1975. 3. Sterilization or disinfection of dental instruments. Council on Dental Therapeutics. In Accepted Dental Therapeutics, ed 37. Chicago, American Dental Association, 1977, p 54. 4. Am erican A ssociation of Dental Schools Report of Actions of the 1974 House of Delegates, resolution no. 9-74-H. J Dent Educ 38:316 June 1974. 5. Morbidity and m ortality weekly report, Center for Disease Control. Perspectives on the control of viral hepatitis, Type B. 25(suppl):3 May 7, 1976. 6. An oral surgeon-related hepatitis B outbreak. California Morbidity W eekly Report, no. 14, State of California Dept of Health, April 16, 1976. 7. W atkins, B.J. Viral hepatitis B: a special problem in prevention. J Am Soc Prev Dent May-June 1976, p 8. 8. Parker, R.B. Dental office procedures for breaking the chain of infec tion. J Am Soc Prev Dent May-June 1976, p 18. 9. Levin, M .L., and others. Hepatitis B transm ission by dentists. JAMA 2 28:1139 May 27, 1974. 10. Schwim m er, A., and Howitt, N.G. Hepatitis: a review of the disease and its prevention. NY J Dent 43:73 M arch 1973. 11. Sim s, W. Serum hepatitis and the dental surgeon. J Dent 4:151 July 1976. 12. M acFarlane, T.W ., and Mason, D.K. The dentist and the prevention of serum hepatitis. Br Dent J 132:487 June 20, 1972.
632 ■ JADA, Vol. 97, October 1978
BERTOLOTTI
HURST
THE AUTHORS Dr. Bertolotti has a PhD in ceramic engineering and has recently received his DDS from the University of California— San Francisco. Dr. Hurst is associate professor of microbiology, School of Den tistry, University of California— San Francisco, San Francisco, 94143. Address requests for reprints to Dr. Hurst.
13. McLundie, A.C., and others. Sterilisation in general dental practice. Br Dent J 124:214 M arch 5, 1968. 14. Uhlig, H.H., and others. Effect of oxygen, chloride, and calcium ion on corrosion inhibition of iron by polyphosphates. J Electrochem Soc 102:59 Feb 1955. 15. Uhlig, H.H. Corrosion and corrosion control, ed 2. New York, John W iley & Sons Inc., 1971, p 94. 16. Fajers, C-M., and others. On steam corrosion and steam corrosion inhibition. Stockholm , Acta Polytechnica Scandavavica, Chemistry in cluding Metallurgy Series no. 87, 1969. 17. M cCulloch, W.T., and Sm ith, D.C. Vapour-phase inhibition of cor rosion in autoclaving. Br Dent J 116:78 Jan 21, 1964. 18. Perkins, J.J. Principles and methods of sterilization in the health sciences, ed 2. Springfield, 111, Charles C Thom as, 1969, p 103. 19. Sax, N.I. Dangerous properties of industrial m aterials, ed 3. New York, Van Nostrand Reinhold Co., 1968, p 605. 20. Burns, R.M. Electrochem ical techniques in corrosion study. J Appl Phys 8:398 June 1937. 21. Uhlig, H.H. Corrosion and corrosion control, ed 2. New York, John W iley & Sons Inc., 1971, p 118. 22. Hurst, V. Reducing the risk of transm itting viral hepatitis. IADR Program and Abstracts of papers, no. 408, March 1972.
