j dent res 1975 leidal 152 9

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DOI: 10.1177/00220345750540011001

1975 54: 152J DENT RESTorger Ingar Leidal and Leif Tronstad

InstrumentsScanning Electron Microscopy of Cavity Margins Finished with Ultra-Speed

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S c a n n i n g E l e c t r o n M i c r o s c o p y o f C a v i t y M a r g i n s F i n i s h e dW i t h U l t r a - S p e e d I n s t r u m e n t sTORGER INGAR LEIDAL a n d LEIF TRONSTADD e n t a l I n s t i t u t e o f E x p e r i m e n t a l R e s e a r c h ,B l i n d e r n , O s l o 3 , Norway

T h e q u a l i t y o f t h e m a r g i n s o f t h e b o x p o r -t i o n s o f C l a s s I I c a v i t i e s f i n i s h e d w i t h r o t a -t i n g i n s t r u m e n t s a t u l t r a s p e e d w a s a s s e s s e d .I n a c l o s e d r o w o f t e e t h , a n a d e q u a t e f i n i s hw a s o b t a i n e d a t t h e e m b r a s u r e m a r g i n w h e r et h e b u r s r o t a t e d t o w a r d t h e t o o t h s u r f a c ea n d i n t o t h e c a v i t y . T h e f i n i s h o f t h e o p p o -s i t e e m b r a s u r e m a r g i n a n d o f t h e g i n g i v a lm a r g i n w a s i m p e r f e c t , r e g a r d l e s s o f t h e i n -s t r u m e n t u s e d .Th e s u c c e s s o f a r e s t o r a t i o n d e p e n d s t o ag r e a t e x t e n t on p r e c i s e c u t t i n g m e t h o d s a n da d e q u a t e f i n i s h i n g o f c a v i t y m a r g i n s . A f a u l t -l e s s a d a p t a t i o n o f t h e f i l l i n g s i s e s p e c i a l l yi m p o r t a n t i n p r o x i m a l r e g i o n s , w h e r e s e c o n -d a r y a t t a c k s o f c a r i e s o c c u r f r e q u e n t l y . 1 I na p r e v i o u s r e p o r t , t h e q u a l i t y o f t h e m a r g i n so f t h e b o x p o r t i o n s o f C l a s s I I c a v i t i e s f i n -i s h e d w i t h c h i s e l s o r r o t a t i n g i n s t r u m e n t s a tl o w s p e e d w a s s t u d i e d . 2 Of t h e i n s t r u m e n t st e s t e d , e n a m e l h a t c h e t s a n d s l o w r o t a t i n gb u r s c a u s e d c h i p s a t t h e e n a m e l e d g e . Th en e a t e s t m a r g i n a l f i n i s h w a s o b t a i n e d w i t h t h ec o m b i n e d u s e o f a b r a s i v e p a p e r d i s k s a n dg i n g i v a l m a r g i n t r i m m e r s . The p u r p o s e o ft h e p r e s e n t s t u d y w a s t o a s s e s s , b y means o fs c a n n i n g e l e c t r o n m i c r o s c o p y , t h e q u a l i t y o fc a v i t y m a r g i n s f i n i s h e d w i t h h i g h - s p e e d o ru l t r a s p e e d i n s t r u m e n t s u n d e r r e p r o d u c i b l e ,s i m u l a t e d c l i n i c a l c o n d i t i o n s .

M a t e r i a l s a n d MethodsTh e e x p e r i m e n t a l m a t e r i a l c o n s i s t e d o f1 3 6 c l i n i c a l l y i n t a c t p r e m o l a r s e x t r a c t e d f r o mc h i l d r e n f o r o r t h o d o n t i c r e a s o n s . The t e e t h

h a d b e e n f i x e d i n 10% n e u t r a l b u f f e r e dR e c e i v e d f o r p u b l i c a t i o n O c t o b e r 2 6 , 1 9 7 3 .A c c e p t e d f o r p u b l i c a t i o n J u n e 5 , 1 9 7 4 .

1 5 2

U n i v e r s i t y o f O s l o ,

F o r m a l i n a n d s t o r e d i n 70% e t h y l a l c o h o l .The p r e m o l a r s w e r e m o u n t e d i n p l a s t e r t oi m i t a t e a n a t o m i c c o n t a c t s , a s d e s c r i b e d p r e -v i o u s l y . 2 M e s i o - o c c l u s a l C l a s s I I c a v i t i e s w e r ep r e p a r e d i n t h e t e e t h u n d e r s i m u l a t e d c l i n -i c a l c o n d i t i o n s , a l w a y s f a c i n g a n i n t a c t s u r -f a c e o f a n e i g h b o r i n g t o o t h . Th e g i n g i v a lm a r g i n s w e r e p l a c e d a b o u t 1 mm c o r o n a l l yt o t h e c e m e n t o e n a m e l j u n c t i o n . A l l c a v i t i e sw e r e p r e p a r e d b y t h e s a m e o p e r a t o r ( T . I . L . )w i t h a n o . 1 5 5 7 t u n g s t e n c a r b i d e b u r a i n a na i r t u r b i n e w i t h w a t e r s p r a y . b Th e m a r g i n so f t h e b o x p o r t i o n o f t h e c a v i t i e s t h e n w e r ef i n i s h e d b y v a r i o u s t e c h n i q u e s w i t h t h e u s eo f r o t a t i n g i n s t r u m e n t s . Th e t y p e s o f i n s t r u -m e n t s u s e d a r e d e s c r i b e d i n T a b l e 1 .R O T A T I N G INSTRUMENTS AT ULTRA-SPEED( : 4 0 0 , 0 0 0 rpm).-The i n s t r u m e n t s u s e da n d t h e number o f m a r g i n s i n c l u d e d i n t h i se x p e r i m e n t a l s e r i e s a r e s h o w n i n T a b l e s 2a n d 3 . A l l i n s t r u m e n t s w e r e d r i v e n w i t h a na i r t u r b i n e c t h a t r o t a t e d i n a c l o c k w i s e d i -r e c t i o n . T h u s , a t o n e e m b r a s u r e m a r g i n o ft h e C l a s s I I b o x e s , t h e b u r r o t a t e d i n t o w a r dt h e t o o t h s u r f a c e a n d i n t o t h e c a v i t y . A c -c o r d i n g t o L i n k e , 3 t h i s i s t h e " e n t r y s i d e " o ft h e c a v i t y . A t t h e o p p o s i t e e m b r a s u r e m a r -g i n , t h e b u r r o t a t e d o u t o f t h e c a v i t y t o w a r dt h e t o o t h s u r f a c e , a n d t h i s i s t h e " e x i t s i d e "o f t h e c a v i t y . 3 A l l e m b r a s u r e m a r g i n s w e r ef i n i s h e d w h i l e t h e y f a c e d a n i n t a c t s u r f a c eo f a n e i g h b o r i n g t o o t h . Th e g i n g i v a l m a r -g i n s , h o w e v e r , e i t h e r w e r e f i n i s h e d w h i l e t h e yf a c e d a n i n t a c t s u r f a c e o f a c o n t a c t i n g t o o t h ,o r a f t e r t h e c o n t a c t i n g t o o t h h a d b e e n r e -moved ( F i g 1 , T a b l e 3 ) . I n t h e l a t t e r i n -s t a n c e s , t h e g i n g i v a l m a r g i n s w e r e f i n i s h e dw i t h t h e b u r s h e l d a t a n a n g l e o f a b o u t 2 0 0

a S . S . W h i t e , P h i l a d e l p h i a , P a .b M i d w e s t A m e r i c a n , M e l r o s e P a r k , I l l .e M i d w e s t A m e r i c a n , M e l r o s e P a r k , I l l .

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CAVITY MARGINS FINISHED AT ULTRA SPEED 1 5 3TABLE 1

INSTRUMENTS U S E D I N F I N I S H I N G C A V I T Y M A R G I N SI n s t r u m e n t

T u n g s t e n c a r b i d e i n s t r u m e n t s :F i s s u r e b u r , c r o s s - c u t , d o m e - e n d e d 1 5 5 8 *F i s s u r e b u r , c r o s s - c u t , d o m e - e n d e d 1 5 5 6 tF i s s u r e b u r , p l a i n , s a f e - e n d e d 56LNtF i s s u r e b u r , i n v e r t e d t a p e r , p l a i n ,d o m e - e n d e d 3 3 2 L tT w e l v e - b l a d e b u r , i n v e r t e d t a p e r ,p l a i n , d o m e - e n d e d 7 3 0 3 tF i n i s h i n g b u r , t a p e r e d , p l a i n ,s a f e - e n d e d 7 2 0 4 tDiamond i n s t r u m e n t sD i a m o n d , n o r m a l g r i t , s q u a r e - e n d e d ,e n d - c u t t i n g o n l y 3 4 X +F i n i s h i n g d i a m o n d , e x t r a - f i n e g r i t ,c y l i n d r i c a l Z l O * S . S . W h i t e , D e n t a l P r o d u c t s D i v i s i o n , P h i l a d e l p h i a ,P a .t J e t , B e a v e r s D e n t a l P r o d u c t s , M o r r i s b u r g , C a n .$ H o r i c o , H o p f , R i n g l e b & C o , B e r l i n , G e r . F i s , F i n z l e r , S c h r o c k & K i m m e l , Bad E m s , G e r .

t o t h e l o n g a x i s o f t h e t e e t h t o a c c o m p l i s h as i m i l a r b e v e l i n g o f t h e m a r g i n s as o b t a i n e db y t h e u s e o f g i n g i v a l m a r g i n t r i m m e r s .

ROTATNG INSTRUMENTS AT HIGH SPEED( , z 1 2 0 , 0 0 0 rpm).-In some t e e t h ( T a b l e4 ) t h e e m b r a s u r e m a r g i n s w e r e f i n i s h e dw i t h b u r s d r i v e n b y a c o n v e n t i o n a l e n g i n ee q u i p p e d w i t h a h i g h - s p e e d h a n d p i e c e . dWith t h i s e q u i p m e n t , f r i c t i o n g r i p b u r smay b e r o t a t e d a t a s p e e d o f a b o u t 1 2 0 , 0 0 0rpm i n a c l o c k w i s e , a s w e l l as i n a c o u n t e r -c l o c k w i s e d i r e c t i o n . T h u s , i n t h i s s e r i e s , a l le m b r a s u r e m a r g i n s w e r e f i n i s h e d a s e n t r ym a r g i n s . ,W h e n t h e f i n i s h i n g p r o c e d u r e s were com-p l e t e d , t h e c a v i t i e s were s u b j e c t e d t o a h e a v yw a t e r s p r a y f o r t en s e c o n d s and t h e n to ab l a s t o f a i r f o r f i v e s e c o n d s . Th e t e e t h werer e m o v e d f r o m t h e p l a s t e r , d e h y d r a t e d , anda i r - d r i e d , and t h e r e g i o n s o f i n t e r e s t were

d M icroMega E , P r o d o n t a S A , G e n e v a , S w i t z .

TABLE 2Q U A L I T Y OF EMBRASURE MARGINS OF C L A S S I I B o x E s F I N I S H E D WITH U L T R A - S P E E D I N S T R U M E N T S( a n s 4 0 0 , 0 0 0 r p m ) A c c O R D I N G T O T H E CMIE n t r y M a r g i n E x i t M a r g i n

S c o r e S c o r eN o . o f N o . o fI n s t r u m e n t M a r g i n s 0 1 2 3 M a r g i n s 0 1 2 31 5 5 8 1 0 2 6 1 1 1 0 ... 5 51 5 5 6 1 0 5 5 ... 1 0 ... 1 5 456LN 1 0 6 4 . . . . . . 1 0 5 53 3 2 L 1 0 8 1 1 1 0 1 .. . 8 17 3 0 3 1 0 9 1 ... ... 1 0 1 8 17 2 0 4 1 0 6 4 .. . 1 0 4 5 1Z 1 o 1 0 9 1 1 0 2 5 3 . . .

TABLE 3QUALITY O F G I N G I V A L M A R G I N S O F C L A S S I I B o x E s F I N I S H E D WITH U L T R A - S P E E D I N S T R U M E N T S( = . s 4 0 0 , 0 0 0 r p m ) A c c O R D I N G TO THE CM IN e i g h b o r i n g Tooth M i s s i n g , B u rI n t a c t , N e i g h b o r i n g Tooth P r e s e n t T i l t e d 2 0

S c o r e S c o r eN o . o f N o . o fI n s t r u m e n t s M a r g i n s 0 1 2 3 M a r g i n s 0 1 2 31 5 5 8 8. . . . ... 8 1 0 7 2 1 ...56LN 1 0 .... . 1 0 1 0 7 33 3 2 L 1 0 1 2 7 1 0 6 2 2 . . .7 3 0 3 1 0 . . . 1 2 7 . .. ... ... . . .Z 1 O 1 0 .. . 1 9 ... . ..34X 3....3 .. .

V o l 5 4 N o . I


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1 5 4 LEIDAL AND TRONSTAD

F I G 1 . - P o s i t i o n o f b u r i n f i n i s h i n g o f g i n g i v a l m a r g i n s . L e f t , i n t a c tn e i g h b o r i n g t o o t h i s p r e s e n t , r e s t r i c t i n g m o v e m e n t o f b u r t o w o r k i n g p o s i -t i o n a p p r o x i m a t e l y p a r a l l e l t o l o n g a x i s o f t e e t h . B e v e l i n g o f m a r g i n cannotb e a c h i e v e d . R i g h t , n e i g h b o r i n g t o o t h i s n ot p r e s e n t , a n d m a r g i n i s f i n i s h e dw i t h b u r i n t i l t e d p o s i t i o n 2 0 0 t o o b t a i n b e v e l i n g o f m a r g i n .

g i v e n an e l e c t r i c a l l y c o n d u c t i n g coat o f c a r -bon a n d g o l d i n a vacuum e v a p o r a t o r . Th em a r g i n s t h e n were examined u n d e r a s c a n-n i n g e l e c t r o n m i c r o s c o p e , u s u a l l y o p e r a t e da t 2 5 k v . e Th e q u a l i t y o f t h e m a r g i n s wass c o r e d a c c o r d i n g t o t h e c r i t e r i a o f t h e C a v i t yM a r g i n Index ( C M I ) s y s t e m 2 : 0 , p e r f e c tm a r g i n ; 1 , a c c e p t a b l e m a r g i n ( f e w , i s o l a t e ds m a l l c h i p s a t t h e e n a m e l e d g e ) ; 2 , i m p e r -f e c t m a r g i n ( c o n t i n u o u s row o f s m a l l c h i p so r some l a r g e r c h i p s a t t h e e n a m e l e d g e o rb o t h ) ; a n d 3 , u n a c c e p t a b l e m a r g i n ( m a n yl a r g e c h i p s o r a c o n t i n u o u s f r a c t u r e o f t h ee n a m e l e d g e ) .Th e s c o r i n g s w e r e p e r f o r m e d a t a m a g n i -f i c a t i o n o f 1 5 0 t i m e s .

R e s u l t sEMBRASURE MARGINS AT ULTRA S P E E D . - T h e

e JSM-50A, Jeol, Toky o, Jap.

q u a l i t y o f t h e e m b r a s u r e m a r g i n s f i n i s h e dw i t h c l o c k w i s e r o t a t i n g b u r s a t u l t r a - s p e e d i sshown i n T a b l e 4 . A c o n s i d e r a b l e d i f f e r e n c ei n q u a l i t y b e t w e e n t h e entry s i d e an d t h ee x i t s i d e o f t h e c a v i t i e s was e v i d e n t ( F i g s 2 ,3 ) . A t t h e entry s i d e , o n l y t h r e e o f 7 0 mar-g i n s were r a t e d as i m p e r f e c t (CMI score 2 )o r u n a c c e p t a b l e (CMI score 3 ) , an d a l l i n -st rume nt s t e s t e d except t h e c r o s s - c u t f i s s u r eb u r s gave m e d i a n CM I s c o r e s 0 . Of t h ec r o s s - c u t f i s s u r e b u r s , t h e one w i t h t h e s m a l l -e s t d i a m e t e r ( 1 5 5 6 ) gave f i v e p e r f e c t m a r g i n s(CMI score 0 ) a n d f i v e m a r g i n s t h a t werer a t e d a c c e p t a b l e (CMI s c o r e 1 ) ( F i g 4 ) .S i m i l a r r e s u l t s were o b t a i n e d w i t h some o ft h e p l a i n b u r s (56LN a n d 7 2 0 4 ) . Th e g r e a t -e s t number o f p e r f e c t m a r g i n s was f o u n d i nt h e g r o u p s f i n i s h e d w i t h t h e p l a i n , d o m e -e n d e d b u r s ( 3 3 2 L and 7 3 0 3 ) o r t h e e x t r a -f i n e - g r i t diamond ( Z I O ) . H o w e v e r , t h e mar-

TABLE 4Q U A L I T Y O F E M B R A S U R E M A R G I N S OF C L A S S I I B O X E S F I N I S H E D WITH H I G H - S P E E DI N S T R U M E N T S ( , , - 1 2 0 , 0 0 0 r p m ) A C C O R D I N G T O THE CM IS c o r eN o . o fI n s t r u m e n t s M a r g i n s 0 1 2 3

1 5 5 6C l o c k w i s e r o t a t i o n 9 5 1 . . . 3C o u n t e r c l o c k w i s e r o t a t i o n 1 0 . . . . . . . . . 1 03 3 2 LC l o c k w i s e r o t a t i o n 1 0 .. . 1 9C o u n t e r c l o c k w i s e r o t a t i o n 1 0 . . . 2 1 7

j Dent R e s J a n u a r y - F e b r u a r y 1 9 7 3


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F I G 2 . - P a r t o f p e r f e c t e n t r y m a r g i n f i n i s h e d F I G 4 . - P a r t o f e n t r y m a r g i n f i n i s h e d w i t hw i t h p l a i n t u n g s t e n c a r b i d e f i s s u r e b u r ( 5 6 L N ) c r o s s - c u t t u n g s t e n c a r b i d e b u r ( 1 5 5 6 ) a t 4 0 0 , -a t 4 0 0 , 0 0 0 r p m (CMI s c o r e 0 ) E S , e n a m e l 0 0 0 r p m . T r a c k s o f b u r a r e ( l i s c e r n i b l e i n c a v i t ys u r f a c e ; CW, c a v i t y w a l l ( o r i g m a g x 1 5 0 ) . w a l l ( C W ) . Enamel e d g e e x h i b i t s a f e w i s o -l a t e d s m a l l c h i p s (CMI s c o r e 1 ) E S , e n a m e ls u r f a c e ( o r i g m a g x 1 5 0 ) .

F I G 3 . - P a r t o f e x i t margin f i n i s h e d w i t hplain tungsten c a r b i d e b u r ( 5 6 L N ) a t 4 0 0 , 0 0 0rpm. C h i p p i n g o f s u r f a c e enamel h a s o c c u r r e da t margin (CMI s c o re 2 ) E S , e n a m e l s u r f a c e ;CW , c a v i t y w a l l ( o r i g mag X 1 5 0 ) .

F I G 5 . - P a r t o f e n t r y m a r g i n f i n i s h e d w i t he x t r a - f i n e - g r i t diamond ( Z I O ) a t 4 0 0 , 0 0 0 r p m .S h a l l o w g r o o v e s c o r r e s p o n d i n g t o c u t t i n g u n i t so f d i a m o n d a r e s e e n i n c a v i t y w a l l ( C W ) .Enamel e d g e i s n o t q u i t e s t r a i g h t , b u t w i t h o u tc h i p s (CMI s c o r e 0 ) . E S , e n a m e l s u r f a c e ( o r i gm a g x 1 5 0 ) .

1 5 5


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1 5 6 LEIDAL AND TRONSTADg i n s f i n i s h e d w i t h t h e d i a m o n d , a l t h o u g hw i t h o u t c h i p s , w e r e n o t a s s t r a i g h t a s t h em a r g i n s f i n i s h e d w i t h c a r b i d e b u r s ; t h e y e x -h i b i t e d a s l i g l i t l y u n d u l a t i n g c o u r s e ( F i g 5 ) .

A t t h e e x i t s i d e , o n l y t h r e e o f 7 0 m a r g i n sw e r e r a t e d a s p e r f e c t (CMI s c o r e 0 ) . M o s tm a r g i n s w e r e f o u n d t o b e i m p e r f e c t (CMIs c o r e 2 ) o r u n a c c e p t a b l e (CMI s c o r e 3 ) , a n dt h e median CM I s c o r e f o r a l l e x i t m a r g i n sw a s 2 . C h a r a c t e r i s t i c f o r t h e s e m a r g i n s w a s ac i h i p p i n g o u t o f t h e s u r f a c e e n a m e l f r o m t h ec a v i t y w a l l t o w a r d t h e t o o t h s u r f a c e ( F i g 3 ) .F e w e r c h i p s w e r e o b s e r v e d a t t h e m a r g i n sf i n i s h e d w i t h t h e e x t r a f i n e - g r i t diamond( m e d i a n CM I s c o r e 1 ) . T h e s e m a r g i n s w e r en o t s t r a i g h t , b u t e x h i b i te d s h a l l o w g r o o v e s .EMBRASURE MARGINS AT HIGH SPEED.-Theq u a l i t y o f t h e e m b r a s u r e m a r g i n s f i n i s h e dw i t l h c l o c k w i s e o r c o u n t e r c l o c k w i s e r o t a t i n gb u r s a t h i g l h s p e e d i s shown i n T a b l e 4 .W i t l h t h i s t e c l i n i q u e , t h e b u r s h a d a s t r o n gt e n d e n c y t o " c r a w l " o u t o f t h e c a v i t y a n dt l l e r e b y damage t h e m a r g i n s and t h e a d j o i n -i n g e n a m e l s u r f a c e ( F i g 6 ) . L a r g e c h i p su s u a l l y w e r e b r o k e n o u t o f t h e e n a m e l e d g ef r o m t h i e t o o t h s u r f a c e t o w a r d t h e c a v i t y w a l l( F i g 7 ) . Of t h e n i n e m a r g i n s f i n i s h e d w i t h

F i G 6 . - P a r t o f e m b r a s u r e m a r g i n f i n i s h e dw i t h c l o c k w i s e r o t a t i n g p l a i n t u n g s t e n c a r b i d el ) u r ( 3 3 2 L ) a t 1 2 0 , 0 0 0 r p m . Bu r l a s " c r a w v l e d 'o u t o f c a v i t y a n d d a m a g e d m a r g i n a n d a d -j o i n i n g e n a m e l s u r f a c e ( E S ) . CW, c a v i t y w a l l( o r i g m a g X 5 0 ) .

t h e c r o s s - c u t f i s s u r e b u r ( 1 5 5 6 ) r o t a t i n g i n ac l o c k w i s e d i r e c t i o n , f i v e w e r e p e r f e c t (CMIs c o r e 0 ) . H o w e v e r , t h e s a m e b u r , when r o -t a t e d c o u n t e r c l o c k w i s e ( ba c k w a r d s ) , y i e l d e do n l y u n a c c e p t a b l e m a r g i n s (CMI s c o r e 3 ) .Th e u s e o f a p l a i n b u r ( 3 3 2 L ) r e s u l t e d i nm a i n l y u n a c c e p t a b l e m a r g i n s , r e g a r d l e s s o fd i r e c t i o n o f r o t a t i o n .

G I N G I V A L M A R G I N S A T U L T R A S P E F E D . - T h eq u i a l i t y o f t h e g i n g i v a l m a r g i n s f i n i s h e d w i t hc l o c k w i s e - r o t a t i n g i n s t r u m e n t s a t u l t r a s p e e di s s e e n i n T a b l e 3 . Th e m a r g i n s t h a t w e r ef i n i s h i e d w i t h a n e i g h b o r i n g t o o t h p r e s e n tw e r e c h a r a c t e r i z e d b y a c o n t i n u o u s f r a c t u r eo f t h e e n a m e l e d g e , a n d w i t h a f e w e x c e p -t i o n s , r e c e i v e d C M \ I s c o r e 3 ( u n a c c e p t a b l em a r g i n s ) ( F i g 8 ) . O n l y t w o m a r g i n s f i n i s h e dw i t h d o m e - e n d e d b u r s w e r e r a te d a c c e p t a b l e(CMI s c o r e l ) , a n d no m a r g i n w a s p e r f e c t .

H o w e v e r , when a t i l t i n g o f t h e b u r s o fa b o u t 2 0 w a s m a d e p o s s i b l e b y r e m o v a l o ft h e n e i g h b o r i n g t o o t h , a f a i r l y p e r f e c t f i n i s ho f t h e g i n g i v a l m a r g i n s w a s a c l h i e v e d w i t h i a l li n s t r u m e n t s t e s t e d ( m e d i a n CM I s c o r e 0 )( F i g 9 ) . E q u a l l y g o o d r e s u l t s w e r e o b t a i n e dw i t h d i f f e r e n t d o m e - e n d e d , e n d - c u t t i n g b u r s

F I G 7 . - P a r t o f e m b r a s u r e m a r g i n f i n i s h e dw i t h i c o u n t e r c l o c k w i s e r o t a t i n g p l a i n t u i n g s t e nc a r b i d e b t i r ( 3 3 2 L ) a t 1 2 0 , 0 0 0 Y p m . B u r l I a sc u t i n t o e n a m e l s u i f a c e ( E S ) ( a r r o w s ) a n dc a u s e d f r a c t u y e o f e n a m e l e d g e . CW, c a v i t y w a l l( o r i g mag x 5 0 ) .



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CAVITY MARGINS FINISHED AT ULTRA SPEED 1 5 7( 1 5 5 8 an d 3 3 2 L ) a n d w i t h a c y l i n d r i c a l , s a f e -e n d e d b u r ( 5 6 L N ) .CORNERS BETWSEEN EMBRASURE AND GINGIVAL

M I A R G I N S AT ULIRA SPEED. F a v o r a b l e c o r n e ra n g l e s w e r e a t t a i n e d w i t h d o m e - e n d e d b u r s .T h i s t y p e o f i n s t r u m e n t , e s p e c i a l l y t h e p l a i nd o m e - e n d e d b u r s ( 3 3 2 L a n d 7 3 0 3 ) a l s o g a v en e a t l y f i n i s h e d m a r g i n s w i t h f e w f a u l t s a tt h e e n t r y s i d e c o r n e r ( F i g 1 0 ) . A t t h e e x i ts i d e o f t h e c a v i t y , h o w e v e r , t h e f i n i s h o f t h ec o r n e r m a r g i n s w a s w i t h o u t e x c e p t i o n i m -p e r f e c t o r u n a c c e p t a b l e ( F i g 1 1 ) .

D i s c u s s i o nThe i m p o r t a n t o b s e r v a t i o n b y L i n k e 3 t h a t

a c o n s i s t e n t d i f f e r e n c e i n q u a l i t y e x i s t s b e -t w e e n t h e e m b r a s u r e m a r g i n s o f t h e e n t r ys i d e a n d t h e e x i t s i d e o f c a v i t i e s f i n i s h e d w i t ha n a i r t u r b i n e w a s f u l l y c o n f i r m e d a n d f u r -t h e r e l u L c i d a t e d i n t h e p r e s e n t s t u d y . A t t h ee n t r y s i d e , a p e r f e c t o r a c c e p t a b l e f i n i s h t o ft l h e m a r g i n s s e e m s t o b e a c c o m p l i s h e d w i t l ht l h i s t e c l h n i q u e a l m o s t r e g a r d l e s s o f b u r t y p eu L s e d . T h l u t s , t h e f i n i s h i a c h i e v e d w i t h t h e 1 5 5 8c r o s s - c u t b u r w a s a m a z i n g l y n e a t , a n d o n l ys l i g l h t l y i n f e r i o r t o t h a t o b t a i n e d w i t h b u r se s p e c i a l l y d e s i g n e d f o r f i n i s l h i n g p u r p o s e s .C o n v e r s e l y , a t t h e e x i t s i d e o f t h e c a v i t i e s ,an a c c e p t a b l e f i n i s h o f t h e m a r g i n s was n o ta c c o m p l i s h e d w i t h a n y t y p e o f b u r t e s t e d .B e c a u s e m a n y d i f f e r e n t l y d e s i g n e d b u r s w e r e

F I c 8 . - P a r t o f g i n g i v a l m a r g i n f i n i s h e d w i t he x t r a - f i n e - g r i t d i a m o n d ( . 1 0 ) a t 4 0 0 , 0 0 0 r p m .B u i r w a s h e l d p a r a l l e l t o l o n g a x i s o f t o o t h .C o n t i n u o u s f d a c t u r e o f enamel e d g e h a s o c -c u r r e d ( C M I s c o r e 3 ) . G F , g i n g i v a l f l o o r ; E S ,enamel s u r f a c e ( o r i g m a g X 1 5 0 ) .

u s e d , i t s e e m s t o b e g e n e r a l l y v a l i d t h a t e x i tm a r g i n s c a n n o t b e f i n i s h e d a d e q u a t e l y w i t hr o t a t i n g i n s t r u m e n t s a t u l t r a s p e e d . D i -amonds h a v e b e e n s h o w n t o c a u s e l e s s c h i p -p i n g a t t h e e x i t m a r g i n s t h a n c a r b i d e b u r s ,b u t d i a m o n d s p r o d u c e r a t h e r d e e p g r o o v e si n t h e m a r g i n s . 4 I n t h e p r e s e n t s t u d y , a d i -a m o n d w i t h e x t r a - f i n e g r i t , o r i g i n a l l y madef o r f i n i s h i n g o f r e s i n f i l l i n g s , w a s u s e d t oo v e r c o m e t h i s u n d e s i r a b l e e f f e c t o f t h e i n -s t r u m e n t . To a c e r t a i n e x t e n t , t h i s w a s a c -c o m p l i s h e d , b u t t h e e x i t m a r g i n s w e r e n o tc o n s i s t e n t l y g o o d e n o u g h f o r t h e method t ob e r e c o m m e n d e d ( T a b l e 2 ) .An o b v i o u s s o l u t i o n t o t h e p r o b l e m w o u l db e t o r u n t h e b u r s c o u n t e r c l o c k w i s e a t t h o s em a r g i n s w h e r e c l o c k w i s e r o t a t i n g b u r s h a v ep r o v e d u n s u i t a b l e . A t p r e s e n t , t h i s i s n o tp o s s i b l e w i t h l o w - t o r q u e , u l t r a - s p e e d e q u i p -m e n t . I n t h e p r e s e n t s t u d y , t h e r e f o r e , t h eg o a l w a s p u r s u e d b y m e a n s o f h i g h - t o r q u e ,h i g h - s p e e d i n s t r u m e n t s r o t a t i n g i n b o t h d i -r e c t i o n s . E v e n a t t h e r e l a t i v e l y h i g h s p e e do f 1 2 0 , 0 0 0 r p m , t h e h i g h t o r q u e o f t h e e q u i p -ment made t h i s t e c h n i q u e u n s u i t a b l e f o rf i n i s h i n g p u r p o s e s . Th e m a r g i n s a n d t h ea d j o i n i n g e n a m e l s u r f a c e u s u a l l y w e r e s e -v e r e l y d a m a g e d , a n d u n f o r t u n a t e l y , t h i s w a se s p e c i a l l y s o a f t e r c o u n t e r c l o c k w i s e r o t a t i o no f t h e b u r s . I t i s c o n c e i v a b l e t h a t e f f e c t i v eb u r s d e s i g n e d f o r c o u n t e r c l o c k w i s e r o t a t i o n

F I G 9 . - P a r t o f g i n g i v a l m a r g i n f i n i s h e d w i t hc r o s s - c u t , d o m e - e n d e d t u n g s t e n c a r b i d e b u r( 1 5 5 8 ) a t 4 0 0 , 0 0 0 r p m . No c o n t a c t i n g t o o t hw v a s p r e s e n t a n d b u r w a s t i l t e d a b o u t 2 0 0 . B e v -e l i n g ( B ) o f m a r g i n w a s a c c o m p l i s h e d , r e s u l t i n gi n p e r f e c t c o n d i t i o n s (CMI s c o r e 0 ) . G F , g i n -g i v a l f l o o r ; E S , e n a m e l s u r f a c e ( o r i g m ag x 1 5 0 ) .

V o l 5 4 N o . I


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1 5 8 LEIDAL AND TRONSTADwould t o some e x t e n t i m p r o v e t h e r e s u l t s o ft h i s m e t h o d . 5 H o w e v e r , i f i t i s d e s i r a b l e t h a ta p e r f e c t f i n i s h o f b o t h e m b r a s u r e m a r g i n so f G l a s s I I b o x e s s h o u l d b e o b t a i n a b l e w i t hr o t a t i n g i n s t r u m e n t s , t h e m a n u f a c t u r i n g o fa n a i r t u r b i n e t h a t r o t a t e s i n a c o u n t e r c l o c k -w i s e d i r e c t i o n i s n e c e s s a r y . S u c h an i n s t r u -ment w o u l d b e u s e f u l f o r f i n i s h i n g p u r p o s e sand c o u l d c o n c e i v a b l y b e u s e d f o r c a v i t y a n dcrown p r e p a r a t i o n .F o r g i n g i v a l m a r g i n s , i t h a s b e e n c l a i m e dt h a t t h e f i n i s h o b t a i n e d w i t h c a r b i d e b u r s a tu l t r a s p e e d i s a t l e a s t a s s a t i s f a c t o r y a s t h a to b t a i n e d w i t h a n y o t h e r method o f i n s t r u -m e n t a t i o n . 6 The r e s u l t s o f t h e p r e s e n t e x -p e r i m e n t s , h o w e v e r , i n d i c a t e t h a t t h i s i s n o tv a l i d u n d e r a l l c l i n i c a l c o n d i t i o n s , b l u t o n l ywhen a c e r t a i n b e v e l i n g o f t h e m a r g i n s h a sb e e n a c h i e v e d .

S i n c e r e p o r t s b y B l a c k 7 i t h a s b e e n g e n -e r a l l y a c c e p t e d t h a t t h e g i n g i v a l m a r g i n ss h o u l d b e f i n i s h e d w i t h i n s t r u m e n t s w o r k -i n g p a r a l l e l t o t h e d i r e c ti o n o f t h e e n a m e lp r i s m s . B l a c k 7 f o u n d t h a t t h e p r i s m s i n t h ec e r v i c a l e n a m e l w e r e a p i c a l l y i n c l i n e d , a n dd e s i g n e d h i s g i n g i v a l m a r g i n t r i m m e r a c -c o r d i n g l y , t o o b t a i n a b e v e l i n g o f t h e mar-g i n s . More r e c e n t s t u d i e s h a v e i n d i c a t e d ,h o w e v e r , t h a t t h e e n a m e l p r i s m s i n t h i s r e -g i o n a r e a s a r u l e h o r i z o n t a l l y d i r e c t e d . 8A f t e r t a k i n g t h e s e f i n d i n g s i n t o c o n s i d e r -

F I C , 1 0 . - C o r n e r b e t w e e n e m b r a s u r e w a l l (EW)a n d g i n g i v a l f l o o r ( G F ) a t e n t i y s i d e o f c a v i t y ,f i n i s h e d w i t h d o m e - e n d e d tu ngsten c a r b i d e bur( 3 3 2 L ) a t 4 0 0 , 0 0 0 r p m . Corner a n g l e i s f a v o r -a b l e and f i n i s h a c c e p t a b l e . E S , enamel s u r f a c e( o r i g mag x 8 0 ) .

a t i o n , R o d d a 9 h a s s t a t e d t h a t a b e v e l i n g o ft h e g i n g i v a l m a r g i n w o u l d b e a m i s t a k e a n ds h o u l d n o t b e c a r r i e d o u t . Th e f i n d i n g s o ft h e p r e s e n t s t u d y a s w e l l a s t h o s e o f a p r e -v i o u s r e p o r t 2 c o n t r a d i c t t h i s v i e w . R a t h e ri t s e e m s t h a t a n i n s t r u m e n t t h a t w o r k sp a r a l l e l t o t h e d i r e c t i o n o f t h e c e r v i c a le n a m e l p r i s m s w i l l c a u s e a f r a c t u r e o f t h ee n a m e l e d g e . H o w e v e r , i f a n i n s t r u m e n tw o r k s a t a n a n g l e t o t h e p r i s m d i r e c t i o n , t h es u r f a c e e n a m e l i s n o t f r a c t u r e d , b u t c u t , a n da n e a t f i n i s h o f t h e g i n g i v a l m a r g i n i s o b -t a i n e d . T h i s o b s e r v a t i o n s e e m s t o h a v e g e n -e r a l v a l i d i t y b e c a u s e e q u a l l y p e r f e c t m a r g i n sw e r e o b t a i n e d w i t h g i n g i v a l m a r g i n t r i m -m e r s 2 a n d w i t h d o m e - e n d e d o r s q u a r e - e n d e db u r s a t u l t r a s p e e d . I t s h o u l d b e n o t e d , h o w -e v e r , t h a t i n a c l o s e d r o w o f t e e t h , a c o r r e c tb e v e l i n g a n d t h e r e b y a n a c c e p t a b l e f i n i s h o ft h e g i n g i v a l m a r g i n s o f C l a s s I I c a v i t i e s s e e mt o b e a t t a i n a b l e o n l y w i t h g i n g i v a l m a r g i nt r i m m e r s .

C o n c l u s i o n sTh e q u a l i t y o f t h e m a r g i n s o f t h e box p o r -t i o n o f C l a s s I I c a v i t i e s f i n i s h e d w i t h c l o c k -

w i s e r o t a t i n g i n s t r u m e n t s a t u l t r a s p e e d( 4 0 0 , 0 0 0 r p m ) w a s a s s e s s e d and s c o r e d a c -c o r d i n g t o t h e c r i t e r i a o f t h e C a v i t y MarginI n d e x ( C M I ) s y s t e m . B u r s o f d i f f e r e n t d e -

F I G 1 1 . - C o r n e r b e t w e e n e m b r a s u r e w a l l (EW)a n d g i n g i v a l f l o o r ( G F ) a t e x i t s i d e o f c a v i t y ,f i n i s h e d w i t h a d o m e - e n d e d t u n g s t e n c a r b i d eb u r ( 3 3 2 L ) a t 4 0 0 , 0 0 0 r p m . F r a c t u r i n g o fe n a m e l e d g e h a s o c c u r r e d , a n d q u a l i t y o fm a r g i n s i s u n a c c e p t a b l e . E S , e n a m e l s u r f a c e( o r i g mag x 8 0 ) .



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CAVITY MARGINS FINISHED AT ULTRA SPEED 1 5 9s i g n g a v e s i m i l a r r e s u l t s . A t t h e e m b r a s u r es i d e w h e r e t h e b u r s r o t a t e d t o w a r d t h et o o t h s u r f a c e a n d i n t o t h e c a v i t y ( e n t r ys i d e ) , t h e q u a l i t y o f t h e m a r g i n s w a s p e r f e c to r a c c e p t a b l e ( m e d i a n CM I s c o r e 0 ) . Theq u a l i t y o f t h e o p p o s i t e e m b r a s u r e m a r g i n( e x i t m a r g i n ) w a s i m p e r f e c t ( m e d i a n CM Is c o r e 2 ) . An a t t e m p t t o i m p r o v e t h e q u a l i t yo f t h e e x i t m a r g i n s b y u s e o f h i g h - t o r q u e ,h i g h - s p e e d i n s t r u m e n t s ( 1 2 0 , 0 0 0 r p m ) r o -t a t i n g i n a c o u n t e r c l o c k w i s e d i r e c t i o n w a sn o t s u c c e s s f u l . A c o u n t e r c l o c k w i s e r o t a t i n ga i r t u r b i n e s e e m s t o b e n e c e s s a r y t o a c h i e v et h i s g o a l .Th e f i n i s h o f t h e g i n g i v a l m a r g i n s was u n -a c c e p t a b l e ( m e d i a n CM I s c o r e 3 ) , e x c e p twhen t h e c o n d i t i o n s a l l o w e d a t i l t i n g o f t h eb u r o f a b o u t 2 0 0 , w h i c h r e s u l t e d i n a b e v e l -i n g o f t h e m a r g i n s . I n t h e s e i n s t a n c e s , a n e a tf i n i s h w a s o b t a i n e d ( m e d i a n CM I s c o r e 0 ) .

R e f e r e n c e s1 . S E L L M A N , S . : S t u d i e r o v e r S e k u n d a r k a r i e s -

f r e k v e n s e n p a T a n d l a k a r i n s t i t u t e t e s K l i e n t e l ,O d o n t T 5 2 : 2 4 1 - 2 7 3 , 1 9 4 4 .2 . T R O N S T A D , L . , and L E I D A L , T . I . : S c a n n i n gE l e c t r o n M i c r o s c o p y o f C a v i t y M a r g i n s F i n -

i s h e d w i t h C h i s e l s o r R o t a t i n g I n s t r u m e n t s a tLo w S p e e d , J Dent R e s 5 3 : 1 1 6 7 - 1 1 7 4 , 1 9 7 4 .3 . L I N K E , S . : U n t e r s u c h u n g e n v o n K a v i t i t e n r i i n -

d e r n , d i e m i t S c h l e i f k o r p e r n i n v e r s c h i e d e n e nD r e h z a h l b e r e i c h e n b e a r b e i t e t w u r d e n , i nE I C H N E R , K . ( e d ) : N o r m a l - , h o c h - . . u n dh d c h s t t o u r i g e s B o h r e n u n d S c h l e i f e n v o nZ a h n h a r t s u b s t a n z e n , M u n i c h : H a n s e r V e r l a g ,1 9 6 6 , pp 5 8 - 6 4 .

4 . B O Y D E , A . , an d K N I G H T , P . J . : Th e U s e o fS c a n n i n g E l e c t r o n M i c r o s c o p y i n C l i n i c a lD e n t a l R e s e a r c h , Br Dent J 1 2 7 : 3 1 3 - 3 2 2 ,1 9 6 9 .

5 . B O Y D E , A . : F i n i s h i n g T e c h n i q u e s f o r t h e E x i tM a r g i n o f t h e A p p r o x i m a l P o r t i o n o f C l a s sI I C a v i t i e s , B r Den t J 1 3 4 : 3 1 9 - 3 2 8 , 1 9 7 3 .6 . B O Y D E , A . ; K N I G H T , P . J . ; a n d J O N E S , S . J . :

F u r t h e r S c a n n i n g E l e c t r o n M i c r o s c o p e S t u d -i e s o f t h e P r e p a r a t i o n o f C l a s s I I C a v i t i e s ,Br Dent J 1 3 2 : 4 4 7 - 4 5 7 , 1 9 7 2 .7 . B L A C K , G . V . : A W o r k o n O p e r a t i v e D e n t i s -t r y , V o l I I , C h i c a g o : M e d i c o - D e n t a l P u b -l i s h i n g C o . , 1 9 0 8 , p p 9 3 - 1 1 7 .8 . O S B O R N , J . W . : D i r e c t i o n s a n d I n t e r r e l a t i o n -s h i p o f P r i s m s i n C u s p a l a n d C e r v i c a l Enamel

o f H u m a n T e e t h , J Dent R e s 4 7 : 3 9 5 - 4 0 2 ,1 9 6 8 .9 . R O D D A , J . C . : Modern C l a s s I I Amalgam C a v i t y

P r e p a r a t i o n s , NZ Dent J 6 8 : 1 3 2 - 1 3 8 , 1 9 7 2 .

V o l 5 4 N o . I


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