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Characterization of enamel surfaces prepared with commercial and experimental etchants
Polished en a m el surfaces w ere etch ed with various com m ercial a nd experim ental etching solutions and evaluated fo r changes in su rface p rofile and topography. E nam el surfaces that w ere exp o sed to solutions of phosphoric acid in a concentration betw een 3 7 % and 50% fo r a m inute gave the most suitable su rfaces fo r retention o f the polym er. E nam el surfaces that w ere ro u gh en ed with a diam ond stone w ere not etch ed uniformly. Enam el that was exp o sed to acid etching solutions »vos better protected by a polycarboxylate cem ent than by either calcium hydroxide or zinc phosphate.
Characterization of enamel surfaces prepared with commercial and experimental etchants J. B. Dennison, D D S , M S R. G. Craig, P h D , A n n A rb o r, M ic h
X he acid etching of enamel is advocated as a mechanism to enhance the retention of resin restora tive materials. The objectives of acid etching are to chemically clean the enamel, to improve wettability and capillary attraction, to increase the surface area available to contact the polymer, and to create m ic ropores into which polymer tags can form. Many acid solutions have been proposed for this purpose1'5 and have been shown to enhance the bonding strength of a restorative polymer to enamel. This study attempts to characterize further6,7 the topography and surface structure of enamel treated with available etching solutions; specific operating methods were used.
Methods and materials Each specimen was prepared by embedding ex tracted incisors into a mold of casting plastic with the flattest portion of the labial surface parallel to the base of the mold. This surface was further flat tened to obtain accurate tracings of the surface profile and then polished with successive grits of metallurgical finishing paper; the final polish was
o b ta in e d w ith 1 5 /¿m a lu m in a o n a fe lt w h e e l. T o th e a re a o f p o lis h e d e n a m e l th a t r e m a in e d e x p o se d th r o u g h th e p la s tic s u r fa c e , a s e le c te d a c id s o lu tio n w a s a p p lie d w ith a fin e s a b le b r u s h fo r 6 0 s e c o n d s , r in s e d fo r at le a s t 1 5 s e c o n d s , a n d d rie d in a s tre a m o f c o m p r e s s e d a ir . T h e e ffe c t o f a c id tr e a tm e n t w a s s tu d ie d b y c o m p a r in g p o lis h e d e n a m e l w ith s im ila r s u r fa c e s c o n d itio n e d w ith a 1 .3 % s o lu tio n o f c itr ic a c id , 5 0 % p h o s p h o r ic a c id , z in c p h o s p h a te c e m e n t liq u id , a n d w ith fiv e c o m m e r c ia lly a v a ila b le a c id e tc h in g m a te r ia ls (B o x ). T h e d e g re e o f e tc h in g o b ta in e d in p r o x im ity to a z in c p h o s p h a te c e m e n t b a s e , a c a lc iu m h y d ro x id e in te r m e d ia r y b a se , a n d a z in c p o ly c a r b o x y la te c e m e n t b a s e w a s a lso s tu d ie d . E a c h c e m e n t w a s m ix e d a c c o r d in g to th e m a n u fa c tu r e r s ’ d ir e c tio n s ; z in c p h o s p h a te a n d z in c p o ly c a r b o x y la te w e re m ix e d to a lu tin g c o n s is te n c y to im p ro v e a d a p ta tio n . S e p a r a te c e m e n t m ix e s w e re p re p a re d fo r e a c h s p e c im e n tre a te d . A th in la y e r (le s s th a n a m illim e t e r th ic k ) o f a s e le c te d b a se m a te ria l w a s a p p lie d to a s m a ll a re a o f th e e x p o s e d p o lis h e d e n a m e l s u r fa c e a n d a llo w e d to se t a t 3 7 C fo r 15 m in u te s . T h e r e m a in in g e n a m e l a d ja c e n t to th e c e m e n t b a se w a s th e n m o is te n e d fo r JADA, Vol. 97, November 1978 ■ 799
M aterials selected for study. M aterial A cid etch an ts C itric acid (1.3% )
B rand nam e
M an ufacturer
R eagen t
J. T. B a k er C h em ica l Co. P h illip sb u rg , NJ L ee P h a rm a ceu tica ls
C itric acid (50% )
9 0 6 0 C av ity C lean ser
P h o sp h o ric acid (0.5% )
3M C aries P rev en tiv e S ea la n t
3 M C o., M in n e a p o lis, M in n
P h o sp h o ric acid (38% )
T e n a c in Z in c P h o sp h ate
L. D. C aulk Co., M ilfo rd , Del
S o u th El M o n te, C a lif
C em en t L iq u id P h o sp h o ric acid (37% ) P h o sp h o ric acid (50% ) Phosphoric acid (50% ) P h o sp h o ric acid (50% ) w ith zinc oxid e (7% ) C em en t bases Z in c ph osph ate C alciu m h ydroxide Z in c p o lyacry late (polycarboxylate)
C o n cise E n am elb on d R eag en t En a m el ite
3 M C o., M in n e a p o lis, M in n M e rck & Co., R ah w ay, NJ L ee P h a rm a ceu tica ls
N u v a-Seal
S ou th El M o n te, C a lif L. D. C au lk C o., M ilford , Del
T e n a c in
L. D. C aulk C o., M ilford , Del
D ycal D urelon
L. D. C aulk Co., M ilfo rd , Del P rem ier D en tal P ro d u cts Co. P h ila d e lp h ia
6 0 s e c o n d s w ith a c id e tc h a n t fro m N u v a -S e a l S e a l a n t (B o x ). E a c h s p e c im e n w a s tre a te d s e p a r a te ly , r in s e d th o r o u g h ly , a n d d rie d c o m p le te ly . T h e c e m e n t b a s e w a s re m o v e d w ith a s h a rp in s tr u m e n t, a n d a c le a n a r e a a c r o s s th e in te r fa c e b e tw e e n e tc h e d e n a m e l a n d e n a m e l p ro te c te d b y c e m e n t w a s e v a lu a te d fo r s u r fa c e to p o g ra p h y . T h e s u r fa c e c h a r a c t e r is tic s th a t r e s u lte d fro m e a c h a c id tr e a tm e n t w e re e v a lu a te d a n d c o m p a re d u s in g tw o m e th o d s . T h e g e n e r a l te x tu r e o f th e s u r fa c e a n d th e q u a lita tiv e in c r e a s e in s u r fa c e a re a w e re e x a m in e d b y g e n e r a tin g m a g n ifie d tr a c in g s o f th e s u r fa c e p r o file o n a B ru s h In s tr u m e n t S u r fa n a ly z e r 1 5 0 S y s te m .* T r a c in g s w e re m a d e th r o u g h e le c tr o n ic r e c o r d in g s p ro d u c e d in r e s p o n s e to th e d is p la c e m e n t o f a tr a v e r s in g d ia m o n d s ty lu s w ith a tip r a d iu s o f 2 5 ¡xm . T h e s u rfa c e w a s fu r th e r c h a r a c te r iz e d b y o b ta in in g s c a n n in g e le c tr o n p h o to m ic ro g ra p h s o f th e s tru c tu r e o f e a c h tre a te d s u r fa c e .
s lig h t w a v in e s s p a tte rn w ith v e ry litt le s u p e r im p o se d r o u g h n e s s , a n d th e p h o to m ic r o g r a p h s h o w s a n e g lig ib le a m o u n t o f ro u g h n e s s . T h e e tc h a n t u s e d w ith th e 3 M C a r ie s P re v e n tiv e S y s te m a n d S e a la n t (B o x ) is a d ilu te p h o s p h o r ic a c id s o lu tio n (0 .5 % ). It is a p p lie d e s s e n tia lly fo r s u r fa c e c le a n in g to e n h a n c e th e u p ta k e o f flu o r id e . T h e p r o file tr a c in g (F ig 2) d e p ic ts a m o d e ra te in c r e a s e in e x p o s e d s u r fa c e a re a a n d a n in c r e a s e d ro u g h n e s s c o m p a re d w ith p o lis h e d e n a m e l (F ig 1 ), w ith s o m e ir r e g u la r itie s e x te n d in g 1 0 to 1 2 m ic r o in c h e s (0 .2 5 to 0 .3 0 ¿u,m) in to th e s u r fa c e a n d o n ly a s lig h t w a v i n e s s p a tte rn . T h e p h o to m ic r o g r a p h s h o w s a s lig h t c h a n g e in to p o g ra p h y ; th e re is a g ra n u la r te x tu r e to th e s u r fa c e a n d a p a rtia l o u tlin in g o f th e e n d s o f e n a m e l ro d s. A d ilu te s o lu tio n o f c it r ic a c id (1 .3 % o f 0 .2 N ) w as u s e d in p re v io u s b o n d in g s tu d ie s 8 a s a c o n d itio n in g
T h r e e s p e c im e n s w e re p re p a re d a n d e v a lu a te d fo r e a c h e tc h in g c o n d itio n ; th e a n a ly s e s o f th e s u r fa c e s s h o w n in th e illu s tr a tio n s a re ty p ic a l o f th e r e s u lts o b ta in e d .
Results P o lis h e d e n a m e l w a s u se d as a b a s is fo r c o m p a r is o n as a ll tr e a tm e n ts w e r e a p p lie d to s im ila r ly p re p a re d s u r fa c e s , a n d th e re s u ltin g in c r e a s e s in s u r fa c e r o u g h n e s s c o u ld b e r e fe r e n c e d to a n e s s e n tia lly fla t p o lis h e d p la n e . T h e p ro file tr a c in g (F ig 1) h a s o n ly a 80 0 ■ JADA, Vol. 97, November 1978
SCA LE:
ja g jjn -
5 0 0 M in/div.
Fig 1 ■ Scanning electron photomicrograph and surface profile tracing of polished enamel (original magnification x 3,000).
9» ■es 3* s o.
5*
SCALE:
3 3 0 Uia
500
m in/div.
Fig 2 ■ Enamel surface treated with dilute solution of phosphoric acid (original magnification x 3,000).
Ol
p a tte rn o f r o u g h n e s s , s im ila r in d e p th to th a t o b ta in e d w ith th e 1 .3 % s o lu tio n . T h e p h o to m ic r o g ra p h s h o w s a re g u la r p a tte r n o f d e te r io r a tio n at th e ro d e n d in g s w ith s ig n ific a n t m ic r o p o r o s ity , a l th o u g h th e p la n e o f o r ie n ta tio n o f th e s a m p le a p p e a rs to b e q u ite d iffe re n t. T h e c i t r i c a c id e tc h a n ts a p p e a r g e n e r a lly to h a v e a m o re s e le c t iv e e ffe c t o n th e c r y s ta llite s in th e c e n te r o f th e ro d s th a n th o s e at th e p e r ip h e r y , a lth o u g h th is p a tte r n m a y v a ry a c c o r d in g to th e a re a o f e n a m e l th a t is tr e a te d .9 T h e c h a r a c t e r is tic s o f e n a m e l e tc h e d w ith th e l iq u id fro m z in c p h o s p h a te c e m e n t (3 8 % p h o s p h o r ic a c id b y w e ig h t) w e re e v a lu a te d to d e te r m in e th e in f lu e n c e th a t b u ffe r in g s a lts m ig h t h a v e o n th e e tc h in g p r o c e s s . T h e p r o file tr a c in g (F ig 5) o f e n a m e l e tc h e d in th is w a y s h o w s a m o re d is t in g u is h a b le p a tte rn o f r o u g h n e s s w ith w id e r s p a c in g b e tw e e n m a jo r ir r e g u la r itie s , b u t w ith n o g re a te r in c r e a s e in s u r fa c e a re a th a n w a s p r o d u c e d w ith th e c it r ic a c id s . T h e p h o to m ic r o g r a p h s h o w s a m o re p r o n o u n c e d d e te r io r a tio n a t th e p e r ip h e r y o f th e
SCALE:
.3 3 0 . ji.ij.
" 5 0 0 M in/div.
Fig 3 ■ Enamel surface treated with dilute solution of citric acid (origi nal magnification x 3,000).
e n a m e l ro d s tr u c tu r e , w ith le s s in v o lv e m e n t in th e c e n te r o f th e ro d a n d le s s fin e d e ta il in th e e n d s o f e x p o s e d e tc h e d e n a m e l s tru c tu r e . A s o lu tio n o f 5 0 % p h o s p h o r ic a c id (re a g e n t g ra d e ) in w a te r is m o re c o n c e n tr a te d th a n th e z in c p h o s p h a te c e m e n t liq u id a n d e tc h e s s h a r p ly a n d m o re u n ifo r m ly . T h e p r o file tr a c in g
SCALE:
,3 1 0
M»"-
(F ig
6) sh ow s a
5 0 0 u in/div.
Fig 4 ■ Enamel surface treated with 50% citric acid solution (original magnification x 3,000). SCALE'
a g e n t. T h e p r o file tr a c in g o f e n a m e l tre a te d w ith c it r ic a c id (F ig 3) is m o re w a v y th a n th e tra c in g p ro d u c e d b y th e e tc h a n t u s e d w ith th e 3 M s e a la n t; ir r e g u la r itie s a p p e a r to b e c lo s e r to g e th e r a n d d e e p e r, a n d m a n y e x te n d 2 0 to 2 5 m ic r o in c h e s (0 .5 to 0 .6 /Am) in to th e s u r fa c e . T h e p h o to m ic r o g r a p h s h o w s m ic r o p o r o s ity , w ith d is tin c t to p o g r a p h ic a l c h a n g e s a n d c o m p le te o u tlin in g o f th e e n d s o f
-3 3 0 (im
5 0 0 |i in/div.
Fig 5 ■ Enamel surface treated with buffered solution of phosphoric acid (zinc phosphate cement liquid) (original magnification x 3,000).
e n a m e l ro d s. A 5 0 % c itr ic a c id s o lu tio n is u s e d in th e L e e 9 0 6 0 C a v ity C le a n s e r (B o x ) a n d a ls o in 9 0 7 0 S e a la n t . It is s ig n ific a n tly s tro n g e r th a n th e 1 .3 % s o lu tio n an d h a s a m o re p r o n o u n c e d e ffe c t o n th e m ic r o p o r o s ity w ith in th e ro d e n d in g s . T h e p r o file tr a c in g (F ig 4) s h o w s a s lig h t in c r e a s e in s u r fa c e a re a a n d a d is tin c t
SCALE;
3 3 0 Min.
5 0 0 p in/div.
Fig 6 ■ Enamel surface treated with 50% phosphoric acid solution (orig inal magnification x 3,000).
D ennison-C raig : ENAMEL SURFACES PREPARED WITH COMMERCIAL, EXPERIMENTAL ETCHANTS ■ 801
ONE MINUTE
SCALE;
330 I) in.
5 0 0 uin/div.
Fig 7 ■ Enamel surface treated with 37% phosphoric acid solution (Concise Enamelbond) (original magnification x 3,000).
TWO MINUTES
SCALE:
. 330 H
500
m in/div.
Fig 10 ■ Enamel surfaces treated with 50% solution of phosphoric acid (Enamelite Etchant) for one minute (top) and for two minutes (bottom) (original magnification x 3,000).
S C ALE:
530 V in-
5 0 0 min/div.
Fig 8 ■ Enamel surface treated with 50% phosphoric acid solution con taining 7% zinc oxide (Nuva System) (original magnification x 3,000). BEVEL ONLY
NUVA SEAL ETCH
SCALE:
Fig 9 ■ Surface profile tracings of labial and occlusal enamel surfaces treated with Nuva System etching solution.
g r e a te r d e g r e e o f w a v in e s s , a w id e r s p a c in g b e tw e e n ir r e g u la r it ie s , a n d a g re a te r p e n e tr a tio n in to th e e n a m e l (as m u c h as 5 0 m ic r o in c h e s [ l . 2 5 / xm ]).T h e p h o to m ic r o g r a p h v e r ifie s th e in c r e a s e in s u r fa c e a re a a n d s h o w s a re g u la r p a tte rn o f e tc h in g th e e x p o s e d e n a m e l ro d s w ith a n in c r e a s e d a m o u n t o f fin e m ic r o p o r o s ity . T h e C o n c is e A c id E tc h S y s te m (F ig 7) u s e s a 3 7 % s o lu tio n o f p h o s p h o r ic a c id , b u t th e in c r e a s e in s u r fa c e a re a a n d th e to p o g ra p h y a re s im ila r to th a t p ro d u c e d w ith a 5 0 % s o lu tio n . M ic r o p o r o s ity m a y b e 802 ■ JADA, Vol. 97, November 1978
2000
m In.
5 0 0 m in/div.
Fig 11 ■ Enamel surface abraded with flame-shaped diamond and then exposed to Nuva System etching solution for 60 seconds (original mag nification X500).
less, but the roughness and waviness patterns are comparable. The Nuva System is supplied with a 5 0 % solution of phosphoric acid that contains 7 % zinc oxide. The tracing of an enamel surface etched with this solu tion (Fig 8) illustrates an even greater increase in surface area with large, widely spaced irregularities; however, the variation among specimens was great with this material. The topography is similar to that obtained with the zinc phosphate cement liquid, but there is evidence of larger openings at the ends of enamel rods, with an increase in porosity along the
e x p o s e d s u r fa c e a re a o f in d iv id u a l ro d s tru c tu r e s . U s e o f th e N u v a -S e a l e tc h a n t o n b o th th e la b ia l 10
s u r fa c e o f in c is o r s a n d th e o c c lu s a l s u r fa c e o f m o la rs r e s u lte d in s im ila r tr a c in g s (F ig 9 ). T h e ir r e g u la r itie s
m in/div.
a re s o m e w h a t d e e p e r a n d m o re w id e ly s p a c e d o n th e tr a c in g fo r th e o c c lu s a l s u r fa c e , b u t th e g e n e r a l p a tte rn s o f r o u g h n e s s a re s im ila r . D o u b lin g th e e x p o s u r e tim e o f th e a c id a p p lie d to e n a m e l fro m o n e m in u te to tw o m in u te s a n d u s in g th e 5 0 % s o lu tio n o f p h o s p h o r ic a c id s u p p lie d w ith E n a m e lite le d to c h a n g e s in b o th th e s tr u c tu r e a n d th e ro u g h n e s s o f th e s u r fa c e (F ig 1 0 ). A fte r a m in u te
SCALE
IQ P fi Uin,
5 0 0 Min/div
Fig 13 ■ Enamel surface, portion of which has been protected by calcium hydroxide cement before exposure to Nuva-Seal etching solution (origi nal magnification x 1,000).
o f e x p o s u r e , th e ty p ic a l ro d s tr u c tu r e s c a n b e id e n tifie d , a n d la rg e a c c u m u la tio n s o f fin e p o r o s itie s a re p r e s e n t. A fte r tw o m in u te s o f e x p o s u r e , th e p r o file tr a c in g s h o w s d e e p e r ir r e g u la r itie s w ith w id e s p a c in g , a n d th e s u r fa c e s tr u c tu r e s h o w s d e e p p e n e tr a tio n w ith a h e a v y tr a b e c u la r p a tte r n a n d a d im in is h in g o f th e fin e p o ro u s a re a s. R e s to r a tiv e p ro c e d u re s h a v e in d ic a te d th e n e e d fo r p la c in g a lo n g b e v e l a t th e c a v o s u r f a c e a n g le s o f fra c tu re d te e th to e n h a n c e s h a d e b le n d in g a n d to p ro v id e a g re a te r w id th o f e n a m e l fo r re te n tio n . W h e n a n e n a m e l s u r fa c e w a s p re p a re d w ith a s u p e r fin e d ia m o n d s t o n e t (F ig 1 1 ), th e N u v a -S e a l e tc h a n t a p p e a re d to e tc h m o re s e le c tiv e ly o n th e p e a k s th a n in th e d ia m o n d fu rro w s . A lth o u g h th e tr a c in g s s h o w lit t le o v e r a ll c h a n g e in th e h e ig h t a n d s p a c in g o f g ro o v e s , th e p e a k s a re m o re ro u n d e d . In th e p h o to m ic r o g r a p h s , d e p th p e r c e p tio n is d if fic u lt , b u t th e e tc h in g is m o re e x te n s iv e a t th e p e a k s a n d a p p e a rs m o re irr e g u la r in s tru c tu r e a n d le s s s e v e r e th a n th a t o b ta in e d o n th e fla t s u r fa c e . T h e fin a l p h a s e in v o lv e d a c o m p a r is o n o f th e e f fe c t o f th e N u v a -S e a l e tc h a n t o n e n a m e l a d ja c e n t to e a c h o f th r e e c e m e n t b a s e m a te r ia ls . T h e s u r fa c e o f a z in c p h o s p h a te c e m e n t b a s e b e c a m e w e a k a n d c h a lk y o n c o n t a c t w ith th e a c id fo r a m in u te , a n d th e a re a u n d e r n e a th th e b a s e w a s n o t w e ll d e fin e d . B o th th e p r o file tr a c in g (F ig 1 2 ) a n d th e p h o to m ic r o g r a p h
SCALE:
1 0 0 0 u in.
5 0 0 (i in/div.
Fig 14 ■ Enamel surface, portion of which has been protected by zinc polycarboxylate cement before exposure to Nuva-Seal etching solution (original magnification x 1,000).
illustrate a gradual transition from the center of the etched area toward the margin of the base material. Either the etchant has leaked under the base or it has reacted less effectively on enamel in immediate proximity to the base. A quick-setting calcium hydroxide intermediary base material had the same characteristics (Fig 1 3 ), possibly resulting from a neutralizing effect of the base on the acid. The material became weak and much of it dissolved completely. Both the tracing and the photomicrograph show gradual transitions from the margin of the base to the center of the fully etched area. Zinc polycarboxylate cement, however, cir cumscribed a well-defined margin (Fig 1 4 ). On one side of the cement-enamel interface, protection was provided by cement from exposure to the acid; on the exposed enamel, complete etching occurred immediately adjacent to the cement base.
Discussion SCALE :
1000 Min
5 0 0 u in/div.
Fig 12 ■ Enamel surface, portion of which has been protected by zinc phosphate cement before exposure to Nuva System etching solution (original magnification x 1,000).
Previous studies10,11 indicated that the characteris tics of an enamel surface demineralized by acid are related to both the concentration of the acid solution
D ennison-C raig : ENAMEL SURFACES PREPARED WITH COMMERCIAL, EXPERIMENTAL ETCHANTS ■ 803
a n d th e le n g th o f tim e th e e n a m e l is e x p o s e d to th e s o lu tio n . R e s u lts o f th is s tu d y h a v e fu r th e r c o n fir m e d th is c o n c lu s io n ; o p tim u m e tc h in g p a tte rn s w e r e o b ta in e d w ith a n e x p o s u r e o f o n e m in u te to e ith e r 3 7 % o r 5 0 % p h o s p h o r ic a c id . A n a d d itio n a l m in u te o f e x p o s u r e to th e e tc h a n t r e s u lte d in a m o re s e v e r e d e s tr u c tio n o f th e e n a m e l ro d s w ith lo s s o f th e n o r m a l a r c h ite c tu r a l p a tte rn s (F ig 1 0 ). C lin i c a lly , th e d e p th o f p e n e tr a tio n o f a p o ly m e r in to an a c id - e tc h e d s u r fa c e o f e n a m e l h a s n o t b e e n fo u n d to b e s ig n if ic a n tly g re a te r a fte r e tc h in g th e s u r fa c e fo r th e a d d itio n a l m i n u t e .12 T h e r e fo r e , th e re is little in d ic a t io n fo r, a n d p o s s ib ly a d e tr im e n ta l e ffe c t in , o v e r e x te n s io n o f th e e tc h in g tim e b e y o n d o n e m in u te , u n le s s s ig n s o f flu o r o s is a re p r e s e n t o r th e fr e s h ly e tc h e d s u r fa c e h a s a n o n u n ifo r m a p p e a r ance. T h e w e a k e r a c id s , s u c h a s c i t r i c a c id , h a v e a le s s p r o n o u n c e d a n d m o re v a r ia b le e ffe c t (F ig 4 ) o n a n y e n a m e l s u r fa c e th a n p h o s p h o r ic a c id (F ig 6 ). In g e n e ra l, th e c it r ic a c id s o lu tio n s a ffe c t th e e n a m e l ro d p e r ip h e r y , w h e re a s th e p h o s p h o r ic a c id s a p p e a r m o re e ffe c tiv e in d is s o lv in g th e c o r e a re a . T h e r e w e re , h o w e v e r, a re a s o f b o th c o r e a n d p e r ip h e r a l ro d d is s o lu t io n in a ll s a m p le s e v a lu a te d . T h e a d d itio n o f b u ffe r in g a g e n ts a n d m o d ifie r s to a n a c id s o lu tio n te n d s to in tr o d u c e s ig n if ic a n t v a r ia tio n in th e to p o g r a p h y o f th e e tc h e d s u r fa c e . B o th th e z in c p h o s p h a te liq u id a n d th e N u v a -S e a l e tc h a n t s h o w e d g re a te r v a r ia tio n in e ffe c tiv e n e s s o f th e e tc h a n t o n e n a m e l fro m o n e s a m p le to a n o th e r , a n d th e m ic r o s tr u c tu r e p a tte rn s w e re e s s e n tia lly s im ila r fo r th e tw o s o lu tio n s . A s o lu tio n o f r e a g e n t g ra d e 5 0 % p h o s p h o r ic a c id p ro d u c e d th e m o s t c o n s is te n t a n d s h a r p ly e tc h e d s u r fa c e s . W h e n a c id e tc h in g is u s e d in c o n ju n c tio n w ith a r e s to r a tiv e p r o c e d u r e , it a p p e a rs th a t a s m o o th ly f in is h e d e n a m e l b e v e l a d ja c e n t to th e m a r g in w ill e tc h m o re u n ifo r m ly th a n a r o u g h e n e d a re a . S e le c tiv e d é c a lc if ic a t io n o c c u r r e d in a re a s in w h ic h a c id
n e u tr a liz e d th e a c id to s o m e e x te n t in a re a s im m e d ia te ly a d ja c e n t to th e b a s e , a n d o n ly w e a k e t c h in g c o u ld b e s e e n . In c o n tr a s t, th e p o ly c a r b o x y la te b a s e (F ig 1 4 ) p e rm itte d m o re e ffe c tiv e e tc h in g to ta k e p la c e a lo n g th e s trip o f e n a m e l a d ja c e n t to th e b ase. D u rin g th e h a n d lin g a n d e v a lu a tio n o f s a m p le s , it b e c a m e e v id e n t th a t a fr e s h ly e tc h e d e n a m e l s u r fa c e is e x tr e m e ly s e n s itiv e a n d fra g ile . T h e s u r fa c e s tr u c tu re c a n b e d e s tr o y e d e a s ily w ith e v e n a s lig h t a b ra s iv e p r o c e s s . E v e ry e ffo rt m u s t b e m a d e to a p p ly p o ly m e r c o a tin g s im m e d ia te ly a fte r th e e tc h in g p r o c e d u r e is c o m p le te d to s e c u r e th e m a x im u m e ffe c t fro m a p r o p e r ly c o n d itio n e d s u r fa c e .
Conclusions C itr ic a c id s o lu tio n s p ro v id e d a le s s e r d e g r e e o f e tc h in g o n p o lis h e d e n a m e l th a n d id p h o s p h o r ic a c id s o lu tio n s . B u ffe r e d e tc h in g s o lu tio n s , s u c h as z in c p h o s p h a te c e m e n t liq u id a n d 5 0 % p h o s p h o r ic a c id w ith 7 % z in c o x id e , p ro d u c e d e n a m e l s u r fa c e s w ith s im ila r m ic r o s c o p ic c h a r a c t e r is tic s , b u t w ith le s s r e lia b le e tc h in g p a tte rn s th a n c o u ld b e o b ta in e d w ith u n b u ffe re d s o lu tio n s . L e n g th e n in g th e tim e o f e x p o s u r e o f th e a c id i n c r e a s e s th e d e p th o f d e m in e r a liz a tio n , a lth o u g h th is is n o t u s u a lly n e c e s s a r y c l in ic a lly . E tc h in g a n e n a m e l s u r fa c e th a t h a s b e e n a b ra d e d w ith a d ia m o n d s to n e p ro d u c e d a m o re e ffe c tiv e e tc h o n th e p e a k s o f a b ra s io n tr a c ts th a n in th e fu r ro w s. A m o r e e ffe c tiv e e tc h w a s p ro d u c e d o n e n a m e l a d ja c e n t to th e in te r fa c e w ith z in c p o ly c a r b o x y la te
lo c a liz e d a lo n g la r g e r s u r fa c e ir r e g u la r itie s in th e a b r a s io n tra c ts . U s e o f c e m e n t b a s e s to p r o te c t e x p o s e d d e n tin as p a rt o f th e c a v ity p r e p a r a tio n is fu n d a m e n ta l w ith th e a p p lic a t io n o f m a te r ia ls c a p a b le o f s tim u la tin g p u lp a l in fla m m a tio n . E x a m in a tio n o f th e s tru c tu r e o f th e e n a m e l u n d e r th e c e m e n t b a s e s h o w e d th a t th e p o ly c a r b o x y la te c e m e n t p ro v id e d a d e q u a te p r o te c tio n a g a in s t th e in g r e s s o f a c id . W ith th e z in c p h o s p h a te c e m e n t, e tc h in g to o k p la c e u n d e r th e c e m e n t b a s e . T h is e tc h in g w a s le s s s e v e r e a n d m a y r e s u lt fro m a c tio n o f th e p h o s p h o r ic a c id fro m th e c e m e n t liq u id , r a th e r th a n le a k a g e o f th e e tc h a n t liq u id u n d e r th e c e m e n t b a s e . C a lc iu m h y d r o x id e c e m e n ts 804 ■ JADA, Vol. 97, November 1978
DENNISON
CRAIG
THE AUTHORS Dr. D en n iso n is professor, d ep artm en ts o f o p era tiv e d en tistry and d en tal m a teria ls, and Dr. Craig is p rofesso r and ch a irm a n , d ep artm en t o f d en tal m a terials, S ch o o l o f D en tistry, U n iv ersity o f M ic h ig a n , A n n A rbor, 4 8 1 0 9 . A d d ress requ ests for re p rin ts to Dr. D en n iso n .
cem ent than w ith either zinc phosphate or calcium hydroxide cem ent bases. Roughness profile tracings can be used to estim ate the exposed surface area of etched enam el and to qualitatively com pare corresponding changes w ith varied treatm ents.
*Brush Instrument Surfanalyzer System, no. 150, Clevite Corp., El Monte, Calif. tDensco Superfine Diamond no. SF1/8A, Teledyne Dental, Densco Div., Denver. The authors wish to extend appreciation to Dr. Anne Rowe, research associate in the department of dental materials, for her assistance with the scanning electron microscopy. 1. Buonocore, M.G.; Matsui, A.; and Gwinnett, A.J. Penetration of resin dental materials into enamel surfaces with reference to bonding. Arch Oral Biol 13:61 Jan 1968. 2. Gwinnett, A.J. Morphology of the interface between adhesive resins and treated human enamel fissures as seen by scanning electron micros copy. Arch Oral Biol 16:237 Feb 1971.
3. Gwinnett, A.J. Histologic changes in human enamel following treat ment with acidic adhesive conditioning agents. Arch Oral Biol 16:731 July 1971. 4. Laswell, H.R.; Welk, D.A.; and Regenos, J.W. Attachment of resin restorations to acid pretreated enamel. JADA 82:558 March 1971. 5. Lee, B.D.; Phillips, R.W.; and Swartz, M.L. The influence of phos phoric acid etching on retention of acrylic resin to bovine enamel. JADA 82:1381 June 1971. 6. Retief, D.H. The use of 50 per cent phosphoric acid as an etching agent in orthodontics: a rational approach. Am J Orthod 68:165 Aug 1975. 7. Eick, J.D., and others. Surface topography: its influence on wetting and adhesion in a dental adhesive system. J Dent Res 51:780 May-June 1972. 8. Eden, G.T.; Craig, R.G.; and Peyton, F.A. Evaluation of a tensile test for direct filling resins. J Dent Res 49:428 March-April 1970. 9. Jorgensen, K.D. Contralateral symmetry of acid etched enamel sur faces. Scand J Dent Res 83:26 Jan 1975. 10. Myers, C.L.; Rossi, F.; and Cartz, L. Adhesive taglike extensions into acid-etched tooth enamel. J Dent Res 53:435 March-April 1974. 11. Silverstone, L.M. Fissure sealants. Laboratory studies. Caries Res 81:2, 1974. 12. Jorgensen, K.D., and Shimokobe, H. Adaptation of resinous restora tive materials to acid etched enamel surfaces. Scand J Dent Res 83:31 Jan 1975.
Dennison-Craig : ENAMEL SURFACES PREPARED WITH COMMERCIAL, EXPERIMENTAL ETCHANTS ■ 805
Characterization of enamel surfaces prepared with commercial and experimental etchants J. B. Dennison, D D S , M S R. G. Craig, P h D , A n n A rb o r, M ic h
X he acid etching of enamel is advocated as a mechanism to enhance the retention of resin restora tive materials. The objectives of acid etching are to chemically clean the enamel, to improve wettability and capillary attraction, to increase the surface area available to contact the polymer, and to create m ic ropores into which polymer tags can form. Many acid solutions have been proposed for this purpose1'5 and have been shown to enhance the bonding strength of a restorative polymer to enamel. This study attempts to characterize further6,7 the topography and surface structure of enamel treated with available etching solutions; specific operating methods were used.
Methods and materials Each specimen was prepared by embedding ex tracted incisors into a mold of casting plastic with the flattest portion of the labial surface parallel to the base of the mold. This surface was further flat tened to obtain accurate tracings of the surface profile and then polished with successive grits of metallurgical finishing paper; the final polish was
o b ta in e d w ith 1 5 /¿m a lu m in a o n a fe lt w h e e l. T o th e a re a o f p o lis h e d e n a m e l th a t r e m a in e d e x p o se d th r o u g h th e p la s tic s u r fa c e , a s e le c te d a c id s o lu tio n w a s a p p lie d w ith a fin e s a b le b r u s h fo r 6 0 s e c o n d s , r in s e d fo r at le a s t 1 5 s e c o n d s , a n d d rie d in a s tre a m o f c o m p r e s s e d a ir . T h e e ffe c t o f a c id tr e a tm e n t w a s s tu d ie d b y c o m p a r in g p o lis h e d e n a m e l w ith s im ila r s u r fa c e s c o n d itio n e d w ith a 1 .3 % s o lu tio n o f c itr ic a c id , 5 0 % p h o s p h o r ic a c id , z in c p h o s p h a te c e m e n t liq u id , a n d w ith fiv e c o m m e r c ia lly a v a ila b le a c id e tc h in g m a te r ia ls (B o x ). T h e d e g re e o f e tc h in g o b ta in e d in p r o x im ity to a z in c p h o s p h a te c e m e n t b a s e , a c a lc iu m h y d ro x id e in te r m e d ia r y b a se , a n d a z in c p o ly c a r b o x y la te c e m e n t b a s e w a s a lso s tu d ie d . E a c h c e m e n t w a s m ix e d a c c o r d in g to th e m a n u fa c tu r e r s ’ d ir e c tio n s ; z in c p h o s p h a te a n d z in c p o ly c a r b o x y la te w e re m ix e d to a lu tin g c o n s is te n c y to im p ro v e a d a p ta tio n . S e p a r a te c e m e n t m ix e s w e re p re p a re d fo r e a c h s p e c im e n tre a te d . A th in la y e r (le s s th a n a m illim e t e r th ic k ) o f a s e le c te d b a se m a te ria l w a s a p p lie d to a s m a ll a re a o f th e e x p o s e d p o lis h e d e n a m e l s u r fa c e a n d a llo w e d to se t a t 3 7 C fo r 15 m in u te s . T h e r e m a in in g e n a m e l a d ja c e n t to th e c e m e n t b a se w a s th e n m o is te n e d fo r JADA, Vol. 97, November 1978 ■ 799
M aterials selected for study. M aterial A cid etch an ts C itric acid (1.3% )
B rand nam e
M an ufacturer
R eagen t
J. T. B a k er C h em ica l Co. P h illip sb u rg , NJ L ee P h a rm a ceu tica ls
C itric acid (50% )
9 0 6 0 C av ity C lean ser
P h o sp h o ric acid (0.5% )
3M C aries P rev en tiv e S ea la n t
3 M C o., M in n e a p o lis, M in n
P h o sp h o ric acid (38% )
T e n a c in Z in c P h o sp h ate
L. D. C aulk Co., M ilfo rd , Del
S o u th El M o n te, C a lif
C em en t L iq u id P h o sp h o ric acid (37% ) P h o sp h o ric acid (50% ) Phosphoric acid (50% ) P h o sp h o ric acid (50% ) w ith zinc oxid e (7% ) C em en t bases Z in c ph osph ate C alciu m h ydroxide Z in c p o lyacry late (polycarboxylate)
C o n cise E n am elb on d R eag en t En a m el ite
3 M C o., M in n e a p o lis, M in n M e rck & Co., R ah w ay, NJ L ee P h a rm a ceu tica ls
N u v a-Seal
S ou th El M o n te, C a lif L. D. C au lk C o., M ilford , Del
T e n a c in
L. D. C aulk C o., M ilford , Del
D ycal D urelon
L. D. C aulk Co., M ilfo rd , Del P rem ier D en tal P ro d u cts Co. P h ila d e lp h ia
6 0 s e c o n d s w ith a c id e tc h a n t fro m N u v a -S e a l S e a l a n t (B o x ). E a c h s p e c im e n w a s tre a te d s e p a r a te ly , r in s e d th o r o u g h ly , a n d d rie d c o m p le te ly . T h e c e m e n t b a s e w a s re m o v e d w ith a s h a rp in s tr u m e n t, a n d a c le a n a r e a a c r o s s th e in te r fa c e b e tw e e n e tc h e d e n a m e l a n d e n a m e l p ro te c te d b y c e m e n t w a s e v a lu a te d fo r s u r fa c e to p o g ra p h y . T h e s u r fa c e c h a r a c t e r is tic s th a t r e s u lte d fro m e a c h a c id tr e a tm e n t w e re e v a lu a te d a n d c o m p a re d u s in g tw o m e th o d s . T h e g e n e r a l te x tu r e o f th e s u r fa c e a n d th e q u a lita tiv e in c r e a s e in s u r fa c e a re a w e re e x a m in e d b y g e n e r a tin g m a g n ifie d tr a c in g s o f th e s u r fa c e p r o file o n a B ru s h In s tr u m e n t S u r fa n a ly z e r 1 5 0 S y s te m .* T r a c in g s w e re m a d e th r o u g h e le c tr o n ic r e c o r d in g s p ro d u c e d in r e s p o n s e to th e d is p la c e m e n t o f a tr a v e r s in g d ia m o n d s ty lu s w ith a tip r a d iu s o f 2 5 ¡xm . T h e s u rfa c e w a s fu r th e r c h a r a c te r iz e d b y o b ta in in g s c a n n in g e le c tr o n p h o to m ic ro g ra p h s o f th e s tru c tu r e o f e a c h tre a te d s u r fa c e .
s lig h t w a v in e s s p a tte rn w ith v e ry litt le s u p e r im p o se d r o u g h n e s s , a n d th e p h o to m ic r o g r a p h s h o w s a n e g lig ib le a m o u n t o f ro u g h n e s s . T h e e tc h a n t u s e d w ith th e 3 M C a r ie s P re v e n tiv e S y s te m a n d S e a la n t (B o x ) is a d ilu te p h o s p h o r ic a c id s o lu tio n (0 .5 % ). It is a p p lie d e s s e n tia lly fo r s u r fa c e c le a n in g to e n h a n c e th e u p ta k e o f flu o r id e . T h e p r o file tr a c in g (F ig 2) d e p ic ts a m o d e ra te in c r e a s e in e x p o s e d s u r fa c e a re a a n d a n in c r e a s e d ro u g h n e s s c o m p a re d w ith p o lis h e d e n a m e l (F ig 1 ), w ith s o m e ir r e g u la r itie s e x te n d in g 1 0 to 1 2 m ic r o in c h e s (0 .2 5 to 0 .3 0 ¿u,m) in to th e s u r fa c e a n d o n ly a s lig h t w a v i n e s s p a tte rn . T h e p h o to m ic r o g r a p h s h o w s a s lig h t c h a n g e in to p o g ra p h y ; th e re is a g ra n u la r te x tu r e to th e s u r fa c e a n d a p a rtia l o u tlin in g o f th e e n d s o f e n a m e l ro d s. A d ilu te s o lu tio n o f c it r ic a c id (1 .3 % o f 0 .2 N ) w as u s e d in p re v io u s b o n d in g s tu d ie s 8 a s a c o n d itio n in g
T h r e e s p e c im e n s w e re p re p a re d a n d e v a lu a te d fo r e a c h e tc h in g c o n d itio n ; th e a n a ly s e s o f th e s u r fa c e s s h o w n in th e illu s tr a tio n s a re ty p ic a l o f th e r e s u lts o b ta in e d .
Results P o lis h e d e n a m e l w a s u se d as a b a s is fo r c o m p a r is o n as a ll tr e a tm e n ts w e r e a p p lie d to s im ila r ly p re p a re d s u r fa c e s , a n d th e re s u ltin g in c r e a s e s in s u r fa c e r o u g h n e s s c o u ld b e r e fe r e n c e d to a n e s s e n tia lly fla t p o lis h e d p la n e . T h e p ro file tr a c in g (F ig 1) h a s o n ly a 80 0 ■ JADA, Vol. 97, November 1978
SCA LE:
ja g jjn -
5 0 0 M in/div.
Fig 1 ■ Scanning electron photomicrograph and surface profile tracing of polished enamel (original magnification x 3,000).
9» ■es 3* s o.
5*
SCALE:
3 3 0 Uia
500
m in/div.
Fig 2 ■ Enamel surface treated with dilute solution of phosphoric acid (original magnification x 3,000).
Ol
p a tte rn o f r o u g h n e s s , s im ila r in d e p th to th a t o b ta in e d w ith th e 1 .3 % s o lu tio n . T h e p h o to m ic r o g ra p h s h o w s a re g u la r p a tte r n o f d e te r io r a tio n at th e ro d e n d in g s w ith s ig n ific a n t m ic r o p o r o s ity , a l th o u g h th e p la n e o f o r ie n ta tio n o f th e s a m p le a p p e a rs to b e q u ite d iffe re n t. T h e c i t r i c a c id e tc h a n ts a p p e a r g e n e r a lly to h a v e a m o re s e le c t iv e e ffe c t o n th e c r y s ta llite s in th e c e n te r o f th e ro d s th a n th o s e at th e p e r ip h e r y , a lth o u g h th is p a tte r n m a y v a ry a c c o r d in g to th e a re a o f e n a m e l th a t is tr e a te d .9 T h e c h a r a c t e r is tic s o f e n a m e l e tc h e d w ith th e l iq u id fro m z in c p h o s p h a te c e m e n t (3 8 % p h o s p h o r ic a c id b y w e ig h t) w e re e v a lu a te d to d e te r m in e th e in f lu e n c e th a t b u ffe r in g s a lts m ig h t h a v e o n th e e tc h in g p r o c e s s . T h e p r o file tr a c in g (F ig 5) o f e n a m e l e tc h e d in th is w a y s h o w s a m o re d is t in g u is h a b le p a tte rn o f r o u g h n e s s w ith w id e r s p a c in g b e tw e e n m a jo r ir r e g u la r itie s , b u t w ith n o g re a te r in c r e a s e in s u r fa c e a re a th a n w a s p r o d u c e d w ith th e c it r ic a c id s . T h e p h o to m ic r o g r a p h s h o w s a m o re p r o n o u n c e d d e te r io r a tio n a t th e p e r ip h e r y o f th e
SCALE:
.3 3 0 . ji.ij.
" 5 0 0 M in/div.
Fig 3 ■ Enamel surface treated with dilute solution of citric acid (origi nal magnification x 3,000).
e n a m e l ro d s tr u c tu r e , w ith le s s in v o lv e m e n t in th e c e n te r o f th e ro d a n d le s s fin e d e ta il in th e e n d s o f e x p o s e d e tc h e d e n a m e l s tru c tu r e . A s o lu tio n o f 5 0 % p h o s p h o r ic a c id (re a g e n t g ra d e ) in w a te r is m o re c o n c e n tr a te d th a n th e z in c p h o s p h a te c e m e n t liq u id a n d e tc h e s s h a r p ly a n d m o re u n ifo r m ly . T h e p r o file tr a c in g
SCALE:
,3 1 0
M»"-
(F ig
6) sh ow s a
5 0 0 u in/div.
Fig 4 ■ Enamel surface treated with 50% citric acid solution (original magnification x 3,000). SCALE'
a g e n t. T h e p r o file tr a c in g o f e n a m e l tre a te d w ith c it r ic a c id (F ig 3) is m o re w a v y th a n th e tra c in g p ro d u c e d b y th e e tc h a n t u s e d w ith th e 3 M s e a la n t; ir r e g u la r itie s a p p e a r to b e c lo s e r to g e th e r a n d d e e p e r, a n d m a n y e x te n d 2 0 to 2 5 m ic r o in c h e s (0 .5 to 0 .6 /Am) in to th e s u r fa c e . T h e p h o to m ic r o g r a p h s h o w s m ic r o p o r o s ity , w ith d is tin c t to p o g r a p h ic a l c h a n g e s a n d c o m p le te o u tlin in g o f th e e n d s o f
-3 3 0 (im
5 0 0 |i in/div.
Fig 5 ■ Enamel surface treated with buffered solution of phosphoric acid (zinc phosphate cement liquid) (original magnification x 3,000).
e n a m e l ro d s. A 5 0 % c itr ic a c id s o lu tio n is u s e d in th e L e e 9 0 6 0 C a v ity C le a n s e r (B o x ) a n d a ls o in 9 0 7 0 S e a la n t . It is s ig n ific a n tly s tro n g e r th a n th e 1 .3 % s o lu tio n an d h a s a m o re p r o n o u n c e d e ffe c t o n th e m ic r o p o r o s ity w ith in th e ro d e n d in g s . T h e p r o file tr a c in g (F ig 4) s h o w s a s lig h t in c r e a s e in s u r fa c e a re a a n d a d is tin c t
SCALE;
3 3 0 Min.
5 0 0 p in/div.
Fig 6 ■ Enamel surface treated with 50% phosphoric acid solution (orig inal magnification x 3,000).
D ennison-C raig : ENAMEL SURFACES PREPARED WITH COMMERCIAL, EXPERIMENTAL ETCHANTS ■ 801
ONE MINUTE
SCALE;
330 I) in.
5 0 0 uin/div.
Fig 7 ■ Enamel surface treated with 37% phosphoric acid solution (Concise Enamelbond) (original magnification x 3,000).
TWO MINUTES
SCALE:
. 330 H
500
m in/div.
Fig 10 ■ Enamel surfaces treated with 50% solution of phosphoric acid (Enamelite Etchant) for one minute (top) and for two minutes (bottom) (original magnification x 3,000).
S C ALE:
530 V in-
5 0 0 min/div.
Fig 8 ■ Enamel surface treated with 50% phosphoric acid solution con taining 7% zinc oxide (Nuva System) (original magnification x 3,000). BEVEL ONLY
NUVA SEAL ETCH
SCALE:
Fig 9 ■ Surface profile tracings of labial and occlusal enamel surfaces treated with Nuva System etching solution.
g r e a te r d e g r e e o f w a v in e s s , a w id e r s p a c in g b e tw e e n ir r e g u la r it ie s , a n d a g re a te r p e n e tr a tio n in to th e e n a m e l (as m u c h as 5 0 m ic r o in c h e s [ l . 2 5 / xm ]).T h e p h o to m ic r o g r a p h v e r ifie s th e in c r e a s e in s u r fa c e a re a a n d s h o w s a re g u la r p a tte rn o f e tc h in g th e e x p o s e d e n a m e l ro d s w ith a n in c r e a s e d a m o u n t o f fin e m ic r o p o r o s ity . T h e C o n c is e A c id E tc h S y s te m (F ig 7) u s e s a 3 7 % s o lu tio n o f p h o s p h o r ic a c id , b u t th e in c r e a s e in s u r fa c e a re a a n d th e to p o g ra p h y a re s im ila r to th a t p ro d u c e d w ith a 5 0 % s o lu tio n . M ic r o p o r o s ity m a y b e 802 ■ JADA, Vol. 97, November 1978
2000
m In.
5 0 0 m in/div.
Fig 11 ■ Enamel surface abraded with flame-shaped diamond and then exposed to Nuva System etching solution for 60 seconds (original mag nification X500).
less, but the roughness and waviness patterns are comparable. The Nuva System is supplied with a 5 0 % solution of phosphoric acid that contains 7 % zinc oxide. The tracing of an enamel surface etched with this solu tion (Fig 8) illustrates an even greater increase in surface area with large, widely spaced irregularities; however, the variation among specimens was great with this material. The topography is similar to that obtained with the zinc phosphate cement liquid, but there is evidence of larger openings at the ends of enamel rods, with an increase in porosity along the
e x p o s e d s u r fa c e a re a o f in d iv id u a l ro d s tru c tu r e s . U s e o f th e N u v a -S e a l e tc h a n t o n b o th th e la b ia l 10
s u r fa c e o f in c is o r s a n d th e o c c lu s a l s u r fa c e o f m o la rs r e s u lte d in s im ila r tr a c in g s (F ig 9 ). T h e ir r e g u la r itie s
m in/div.
a re s o m e w h a t d e e p e r a n d m o re w id e ly s p a c e d o n th e tr a c in g fo r th e o c c lu s a l s u r fa c e , b u t th e g e n e r a l p a tte rn s o f r o u g h n e s s a re s im ila r . D o u b lin g th e e x p o s u r e tim e o f th e a c id a p p lie d to e n a m e l fro m o n e m in u te to tw o m in u te s a n d u s in g th e 5 0 % s o lu tio n o f p h o s p h o r ic a c id s u p p lie d w ith E n a m e lite le d to c h a n g e s in b o th th e s tr u c tu r e a n d th e ro u g h n e s s o f th e s u r fa c e (F ig 1 0 ). A fte r a m in u te
SCALE
IQ P fi Uin,
5 0 0 Min/div
Fig 13 ■ Enamel surface, portion of which has been protected by calcium hydroxide cement before exposure to Nuva-Seal etching solution (origi nal magnification x 1,000).
o f e x p o s u r e , th e ty p ic a l ro d s tr u c tu r e s c a n b e id e n tifie d , a n d la rg e a c c u m u la tio n s o f fin e p o r o s itie s a re p r e s e n t. A fte r tw o m in u te s o f e x p o s u r e , th e p r o file tr a c in g s h o w s d e e p e r ir r e g u la r itie s w ith w id e s p a c in g , a n d th e s u r fa c e s tr u c tu r e s h o w s d e e p p e n e tr a tio n w ith a h e a v y tr a b e c u la r p a tte r n a n d a d im in is h in g o f th e fin e p o ro u s a re a s. R e s to r a tiv e p ro c e d u re s h a v e in d ic a te d th e n e e d fo r p la c in g a lo n g b e v e l a t th e c a v o s u r f a c e a n g le s o f fra c tu re d te e th to e n h a n c e s h a d e b le n d in g a n d to p ro v id e a g re a te r w id th o f e n a m e l fo r re te n tio n . W h e n a n e n a m e l s u r fa c e w a s p re p a re d w ith a s u p e r fin e d ia m o n d s t o n e t (F ig 1 1 ), th e N u v a -S e a l e tc h a n t a p p e a re d to e tc h m o re s e le c tiv e ly o n th e p e a k s th a n in th e d ia m o n d fu rro w s . A lth o u g h th e tr a c in g s s h o w lit t le o v e r a ll c h a n g e in th e h e ig h t a n d s p a c in g o f g ro o v e s , th e p e a k s a re m o re ro u n d e d . In th e p h o to m ic r o g r a p h s , d e p th p e r c e p tio n is d if fic u lt , b u t th e e tc h in g is m o re e x te n s iv e a t th e p e a k s a n d a p p e a rs m o re irr e g u la r in s tru c tu r e a n d le s s s e v e r e th a n th a t o b ta in e d o n th e fla t s u r fa c e . T h e fin a l p h a s e in v o lv e d a c o m p a r is o n o f th e e f fe c t o f th e N u v a -S e a l e tc h a n t o n e n a m e l a d ja c e n t to e a c h o f th r e e c e m e n t b a s e m a te r ia ls . T h e s u r fa c e o f a z in c p h o s p h a te c e m e n t b a s e b e c a m e w e a k a n d c h a lk y o n c o n t a c t w ith th e a c id fo r a m in u te , a n d th e a re a u n d e r n e a th th e b a s e w a s n o t w e ll d e fin e d . B o th th e p r o file tr a c in g (F ig 1 2 ) a n d th e p h o to m ic r o g r a p h
SCALE:
1 0 0 0 u in.
5 0 0 (i in/div.
Fig 14 ■ Enamel surface, portion of which has been protected by zinc polycarboxylate cement before exposure to Nuva-Seal etching solution (original magnification x 1,000).
illustrate a gradual transition from the center of the etched area toward the margin of the base material. Either the etchant has leaked under the base or it has reacted less effectively on enamel in immediate proximity to the base. A quick-setting calcium hydroxide intermediary base material had the same characteristics (Fig 1 3 ), possibly resulting from a neutralizing effect of the base on the acid. The material became weak and much of it dissolved completely. Both the tracing and the photomicrograph show gradual transitions from the margin of the base to the center of the fully etched area. Zinc polycarboxylate cement, however, cir cumscribed a well-defined margin (Fig 1 4 ). On one side of the cement-enamel interface, protection was provided by cement from exposure to the acid; on the exposed enamel, complete etching occurred immediately adjacent to the cement base.
Discussion SCALE :
1000 Min
5 0 0 u in/div.
Fig 12 ■ Enamel surface, portion of which has been protected by zinc phosphate cement before exposure to Nuva System etching solution (original magnification x 1,000).
Previous studies10,11 indicated that the characteris tics of an enamel surface demineralized by acid are related to both the concentration of the acid solution
D ennison-C raig : ENAMEL SURFACES PREPARED WITH COMMERCIAL, EXPERIMENTAL ETCHANTS ■ 803
a n d th e le n g th o f tim e th e e n a m e l is e x p o s e d to th e s o lu tio n . R e s u lts o f th is s tu d y h a v e fu r th e r c o n fir m e d th is c o n c lu s io n ; o p tim u m e tc h in g p a tte rn s w e r e o b ta in e d w ith a n e x p o s u r e o f o n e m in u te to e ith e r 3 7 % o r 5 0 % p h o s p h o r ic a c id . A n a d d itio n a l m in u te o f e x p o s u r e to th e e tc h a n t r e s u lte d in a m o re s e v e r e d e s tr u c tio n o f th e e n a m e l ro d s w ith lo s s o f th e n o r m a l a r c h ite c tu r a l p a tte rn s (F ig 1 0 ). C lin i c a lly , th e d e p th o f p e n e tr a tio n o f a p o ly m e r in to an a c id - e tc h e d s u r fa c e o f e n a m e l h a s n o t b e e n fo u n d to b e s ig n if ic a n tly g re a te r a fte r e tc h in g th e s u r fa c e fo r th e a d d itio n a l m i n u t e .12 T h e r e fo r e , th e re is little in d ic a t io n fo r, a n d p o s s ib ly a d e tr im e n ta l e ffe c t in , o v e r e x te n s io n o f th e e tc h in g tim e b e y o n d o n e m in u te , u n le s s s ig n s o f flu o r o s is a re p r e s e n t o r th e fr e s h ly e tc h e d s u r fa c e h a s a n o n u n ifo r m a p p e a r ance. T h e w e a k e r a c id s , s u c h a s c i t r i c a c id , h a v e a le s s p r o n o u n c e d a n d m o re v a r ia b le e ffe c t (F ig 4 ) o n a n y e n a m e l s u r fa c e th a n p h o s p h o r ic a c id (F ig 6 ). In g e n e ra l, th e c it r ic a c id s o lu tio n s a ffe c t th e e n a m e l ro d p e r ip h e r y , w h e re a s th e p h o s p h o r ic a c id s a p p e a r m o re e ffe c tiv e in d is s o lv in g th e c o r e a re a . T h e r e w e re , h o w e v e r, a re a s o f b o th c o r e a n d p e r ip h e r a l ro d d is s o lu t io n in a ll s a m p le s e v a lu a te d . T h e a d d itio n o f b u ffe r in g a g e n ts a n d m o d ifie r s to a n a c id s o lu tio n te n d s to in tr o d u c e s ig n if ic a n t v a r ia tio n in th e to p o g r a p h y o f th e e tc h e d s u r fa c e . B o th th e z in c p h o s p h a te liq u id a n d th e N u v a -S e a l e tc h a n t s h o w e d g re a te r v a r ia tio n in e ffe c tiv e n e s s o f th e e tc h a n t o n e n a m e l fro m o n e s a m p le to a n o th e r , a n d th e m ic r o s tr u c tu r e p a tte rn s w e re e s s e n tia lly s im ila r fo r th e tw o s o lu tio n s . A s o lu tio n o f r e a g e n t g ra d e 5 0 % p h o s p h o r ic a c id p ro d u c e d th e m o s t c o n s is te n t a n d s h a r p ly e tc h e d s u r fa c e s . W h e n a c id e tc h in g is u s e d in c o n ju n c tio n w ith a r e s to r a tiv e p r o c e d u r e , it a p p e a rs th a t a s m o o th ly f in is h e d e n a m e l b e v e l a d ja c e n t to th e m a r g in w ill e tc h m o re u n ifo r m ly th a n a r o u g h e n e d a re a . S e le c tiv e d é c a lc if ic a t io n o c c u r r e d in a re a s in w h ic h a c id
n e u tr a liz e d th e a c id to s o m e e x te n t in a re a s im m e d ia te ly a d ja c e n t to th e b a s e , a n d o n ly w e a k e t c h in g c o u ld b e s e e n . In c o n tr a s t, th e p o ly c a r b o x y la te b a s e (F ig 1 4 ) p e rm itte d m o re e ffe c tiv e e tc h in g to ta k e p la c e a lo n g th e s trip o f e n a m e l a d ja c e n t to th e b ase. D u rin g th e h a n d lin g a n d e v a lu a tio n o f s a m p le s , it b e c a m e e v id e n t th a t a fr e s h ly e tc h e d e n a m e l s u r fa c e is e x tr e m e ly s e n s itiv e a n d fra g ile . T h e s u r fa c e s tr u c tu re c a n b e d e s tr o y e d e a s ily w ith e v e n a s lig h t a b ra s iv e p r o c e s s . E v e ry e ffo rt m u s t b e m a d e to a p p ly p o ly m e r c o a tin g s im m e d ia te ly a fte r th e e tc h in g p r o c e d u r e is c o m p le te d to s e c u r e th e m a x im u m e ffe c t fro m a p r o p e r ly c o n d itio n e d s u r fa c e .
Conclusions C itr ic a c id s o lu tio n s p ro v id e d a le s s e r d e g r e e o f e tc h in g o n p o lis h e d e n a m e l th a n d id p h o s p h o r ic a c id s o lu tio n s . B u ffe r e d e tc h in g s o lu tio n s , s u c h as z in c p h o s p h a te c e m e n t liq u id a n d 5 0 % p h o s p h o r ic a c id w ith 7 % z in c o x id e , p ro d u c e d e n a m e l s u r fa c e s w ith s im ila r m ic r o s c o p ic c h a r a c t e r is tic s , b u t w ith le s s r e lia b le e tc h in g p a tte rn s th a n c o u ld b e o b ta in e d w ith u n b u ffe re d s o lu tio n s . L e n g th e n in g th e tim e o f e x p o s u r e o f th e a c id i n c r e a s e s th e d e p th o f d e m in e r a liz a tio n , a lth o u g h th is is n o t u s u a lly n e c e s s a r y c l in ic a lly . E tc h in g a n e n a m e l s u r fa c e th a t h a s b e e n a b ra d e d w ith a d ia m o n d s to n e p ro d u c e d a m o re e ffe c tiv e e tc h o n th e p e a k s o f a b ra s io n tr a c ts th a n in th e fu r ro w s. A m o r e e ffe c tiv e e tc h w a s p ro d u c e d o n e n a m e l a d ja c e n t to th e in te r fa c e w ith z in c p o ly c a r b o x y la te
lo c a liz e d a lo n g la r g e r s u r fa c e ir r e g u la r itie s in th e a b r a s io n tra c ts . U s e o f c e m e n t b a s e s to p r o te c t e x p o s e d d e n tin as p a rt o f th e c a v ity p r e p a r a tio n is fu n d a m e n ta l w ith th e a p p lic a t io n o f m a te r ia ls c a p a b le o f s tim u la tin g p u lp a l in fla m m a tio n . E x a m in a tio n o f th e s tru c tu r e o f th e e n a m e l u n d e r th e c e m e n t b a s e s h o w e d th a t th e p o ly c a r b o x y la te c e m e n t p ro v id e d a d e q u a te p r o te c tio n a g a in s t th e in g r e s s o f a c id . W ith th e z in c p h o s p h a te c e m e n t, e tc h in g to o k p la c e u n d e r th e c e m e n t b a s e . T h is e tc h in g w a s le s s s e v e r e a n d m a y r e s u lt fro m a c tio n o f th e p h o s p h o r ic a c id fro m th e c e m e n t liq u id , r a th e r th a n le a k a g e o f th e e tc h a n t liq u id u n d e r th e c e m e n t b a s e . C a lc iu m h y d r o x id e c e m e n ts 804 ■ JADA, Vol. 97, November 1978
DENNISON
CRAIG
THE AUTHORS Dr. D en n iso n is professor, d ep artm en ts o f o p era tiv e d en tistry and d en tal m a teria ls, and Dr. Craig is p rofesso r and ch a irm a n , d ep artm en t o f d en tal m a terials, S ch o o l o f D en tistry, U n iv ersity o f M ic h ig a n , A n n A rbor, 4 8 1 0 9 . A d d ress requ ests for re p rin ts to Dr. D en n iso n .
cem ent than w ith either zinc phosphate or calcium hydroxide cem ent bases. Roughness profile tracings can be used to estim ate the exposed surface area of etched enam el and to qualitatively com pare corresponding changes w ith varied treatm ents.
*Brush Instrument Surfanalyzer System, no. 150, Clevite Corp., El Monte, Calif. tDensco Superfine Diamond no. SF1/8A, Teledyne Dental, Densco Div., Denver. The authors wish to extend appreciation to Dr. Anne Rowe, research associate in the department of dental materials, for her assistance with the scanning electron microscopy. 1. Buonocore, M.G.; Matsui, A.; and Gwinnett, A.J. Penetration of resin dental materials into enamel surfaces with reference to bonding. Arch Oral Biol 13:61 Jan 1968. 2. Gwinnett, A.J. Morphology of the interface between adhesive resins and treated human enamel fissures as seen by scanning electron micros copy. Arch Oral Biol 16:237 Feb 1971.
3. Gwinnett, A.J. Histologic changes in human enamel following treat ment with acidic adhesive conditioning agents. Arch Oral Biol 16:731 July 1971. 4. Laswell, H.R.; Welk, D.A.; and Regenos, J.W. Attachment of resin restorations to acid pretreated enamel. JADA 82:558 March 1971. 5. Lee, B.D.; Phillips, R.W.; and Swartz, M.L. The influence of phos phoric acid etching on retention of acrylic resin to bovine enamel. JADA 82:1381 June 1971. 6. Retief, D.H. The use of 50 per cent phosphoric acid as an etching agent in orthodontics: a rational approach. Am J Orthod 68:165 Aug 1975. 7. Eick, J.D., and others. Surface topography: its influence on wetting and adhesion in a dental adhesive system. J Dent Res 51:780 May-June 1972. 8. Eden, G.T.; Craig, R.G.; and Peyton, F.A. Evaluation of a tensile test for direct filling resins. J Dent Res 49:428 March-April 1970. 9. Jorgensen, K.D. Contralateral symmetry of acid etched enamel sur faces. Scand J Dent Res 83:26 Jan 1975. 10. Myers, C.L.; Rossi, F.; and Cartz, L. Adhesive taglike extensions into acid-etched tooth enamel. J Dent Res 53:435 March-April 1974. 11. Silverstone, L.M. Fissure sealants. Laboratory studies. Caries Res 81:2, 1974. 12. Jorgensen, K.D., and Shimokobe, H. Adaptation of resinous restora tive materials to acid etched enamel surfaces. Scand J Dent Res 83:31 Jan 1975.
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