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0099-2399/95/2107-0349503.00/0JOURN AL OF ENDODONTICSCopyr igh t 1995 by The Amer i can Associa t i on o f Endodont i s ts

S C I E N T I F I C A R T I C L E SPr in ted in U S AVOL. 21 No. 7 JULY 1995

P h y s i ca l a n d C h e m i c a l P r o p e r t ie s o f a N e wR o o t E n d F illin g M a t e r i a lM a h m o u d T o r a b i n e j a d , D M D , M S D , P h D , C . U . H o n g , D D S , M S , F . M c D o n a l d , B D S , P h D , a n dT. R . P i t t Ford, BDS, PhD

T h i s s t u d y d e t e r m i n e d t h e c h e m i c a l c o m p o s i t i o n ,p H , a n d r a d i o p a c i t y o f m i n e r a l t r i o x i d e a g g r e g a t eM T A ) , a n d a l s o c o m p a r e d t h e s e t t i n g t i m e , c o m -

pr ess ive s t r ength , and so lub i l i t y o f th is mate r ia lw i t h th o s e o f a m a l g a m , S u p e r - E B A , a n d I n t e r m e -d i a t e R e s t o r a t iv e M a t e r i a l I R M ) . X - r a y e n e r g y d i s -p e r s i v e s p e c t r o m e t e r i n c o n ju n c t io n w i t h t h e 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 w e r e u s e d t o d e t e r m i n et h e c o m p o s i t i o n o f M T A , a n d t h e p H v a l u e o f M T Aw a s a s s e s s e d w i t h a p H m e t e r u s i n g a t e m p e r a -t u r e - c o m p e n s a t e d e l e c t r o d e . T h e r a d i o p a c i t y o fM T A w a s d e t e r m i n e d a c c o r d i n g t o t h e m e t h o d d e -scr ibed by the In te r na t iona l O r gan iz a t ion fo r S tan -d a r d i z a t i o n . T h e s e t t i n g t i m e a n d c o m p r e s s i v es t r e n g th o f t h e s e m a t e r ia l s w e r e d e t e r m i n e d a c -c o r d in g t o m e t h o d s r e c o m m e n d e d b y t h e B r it is hS tandar ds Ins t i tu t ion . The degr ee o f so lub i l i t y o ft h e m a t e r ia l s w a s a s s e s s e d a c c o r d i n g t o m o d i f i e dA m e r i c a n D e n t a l A s s o c i a t i o n s p e c i f i c a t i o n s . T h er e s u lt s s h o w e d t h a t t h e m a i n m o l e c u l e s p r e s e n t i nM T A a r e c a l c i u m a n d p h o s p h o r o u s i o n s . I n a d d i -t ion , MTA has a pH o f 10 .2 in i t i a l l y , wh ich r i ses to1 2 . 5 t h r e e h o u r s a f t e r m i x i n g . M T A i s m o r e r a -d i o p a q u e th a n S u p e r - E B A a n d I R M . A m a l g a m h a dt h e s h o r t e s t s e tt in g t i m e 4 m in ) a n d M T A t h e l o n g -e s t 2 h 4 5 r ain ). A t 2 4 h M T A h a d t h e l o w e s t c o m -p r e s s iv e s tr e n g t h 4 0 M P a ) a m o n g t h e m a t e r i a ls ,bu t i t i nc r eased a f te r 21 days to 67 MP a . F ina l l y ,e x c e p t f o r I R M , n o n e o f t h e m a t e r i a l s t e s t e dshowed any so lub i l i t y under the cond i t ions o f th iss tudy .

W hen nonsu rg ica l roo t cana l the rapy fa i l s o r canno t be pe r fo rmed ,su rg ica l roo t cana l the rapy i s conduc ted . The p rocedure usua l lycons i s t s o f roo t -end exposu re and r e sec t ion , a s we l l a s p repa ra t ion

of a c l a s s I cav i ty and p lacem en t o f a roo t -end f i l l i ng ma te r i a l . Anumber o f subs tances have been sugges ted and used a s roo t -endf i l l i ng m a te r i a l s (1 ) .

Recen t ly , an expe r im en ta l subs tance , mine ra l t r iox ide agg rega te(MT A) , has be en sugges ted a s a po ten t i a l roo t -end f i l l i ng ma te r i a l .In a se r i e s o f in v i t ro s tud ie s , Tora b ine jad e t a l . (2 -5 ) eva lua ted thes e a l in g a b i l i ty o f M TA , c o m p a r e d w i t h c o m m o n l y u s e d r o o t - e n df i l l i ng ma te r i a l s . S ta t i s t i ca l ana lys i s o f the i r da ta showed tha t M TAhad s ign i f i can t ly l e s s dye (2 , 3 ) and bac te r i a l (4 ) l eakage thana m a l g a m , S u p e r - EB A o r I n t e r m e d i a te Re s t o r a t iv e M a t e r i a l ( IRM ) .I n a d d i t i o n, wh e n m a r g i n a l a d a p t a t io n o f M T A r o o t - e n d f il l in g swa s c o m p a r e d w i t h t ho s e o f am a l g a m , S u p e r - EBA, a n d I RM u n d e rscann ing e l ec t ron mic roscope , they r epo r t ed no no t i ceab le gapbe tween MTA and i t s su r round ing den t ina l wa l l s (5 ) .

Because these s tud ie s show that M TA l e a k s le s s a n d h a s b e t te radap ta t ion to the roo t -end cav i ty wa l l s than commonly used roo t -end f i l l i ng ma te r i a l s , i t s o the r cha rac te r i s t i c s - - - such a s chem ica lcompos i t ion , phys ica l p rope r t i e s , an t ibac te r i a l e f f ec t s , cy to tox ic -i t y , a n d b i o c o m p a t i b i l i t y - - s h o u l d a l s o b e i n v e s ti g a te d .

The pu rpose o f th i s s tudy was f i r s t t o de te rmine the chemica lc o m p o s i t i o n , p H o f t h e s e t ti n g c e m e n t , a n d r a d i o p a c i t y o f M TA ,and secon d to comp are the se t t ing t ime , com press ive s t r eng th , andso lub i l i ty o f th i s ma te r i a l wi th those o f th ree com mon ly usedr o o t - e n d f il l i n g m a t e r i a l s, a m a l g a m , S u p e r - EBA , a n d I RM .

4 9

M A T E R I A L S A N D M E T H O D S

C h e m i c a l C omp o s i t i o nTo s t u d y t h e c h e m i c a l c o m p o s i t i o n o f M T A, w e u s e d t h e KVEX

De l t a 4 4 6 0 X- r a y En e r g y d i s p e r s i v e s p e c tr o m e t e r , m o d i f i e d w i t hM i c r o EDS s o f t wa r e ( BEM AX UK L t d . ) , i n c o n j u n c t i o n w i t h aHi t a c h i 5 2 0 s c a n n i n g e l e c tr o n m i c r o s c o p e . M T A wa s m i x e d w i t hs t e r i l i zed d i s t i l l ed wa te r and a l lowe d to se t i n a 37C incuba to rwi th 5% ca rbon d iox ide and mois tu re . The ma te r i a l was se t on ag la s s cove r s l ip tha t had been p rev ious ly s t e r i l i zed us ing a l coho land f l aming . F ive se t spec imens wi th d i f f e ren t p ropor t ions o f wa te rand powder were examined . Fo r quan t i t a t ive X- ray ana lys i s , t hespec imens were ca rbon-coa ted to a th i ckness o f 100 nm and aga inm o u n t e d i n t h e 5 2 0 u s i n g t h e q u a n t u m DV EX s y s t e m . Ac c e l e r -

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3 5 0 T o r a b i n e j a d e t a l J o u r n a l o f E n d o d o n t i c sT A BL E 1 M a t e r i a l u s e d f o r e x p e r i m e n t s

Mater ia l ManufacturerSyb raloy am algam Kerr Mfg. Co. Romulus MISuper-EBA Harry J. Bosw orth Co. Skokie ILIRM I .D . Cau lk Co. M i lfo rd DEMTA Lom a Linda University Lom a Linda CA

ating v o l t a g e f o r s t a n d a r d e x a m i n a t i o n w a s 1 5 k V a n d t h a t f o rX - r a y a n a l y s i s w a s 1 0 k V .

pH ValueT h e p H o f M T A a s i t s e t w a s m e a s u r e d w i t h a p H m e t e r ( P y e ,

C a m b r i d g e , U K ) u s i n g a t e m p e r a t u r e - c o m p e n s a t e d e l e c t r o d e .

T h e s e t t in g t i m e s o f t e st m a t e r i a l s w e r e d e t e r m i n e d a c c o r d i n g t ot h e m e t h o d r e c o m m e n d e d b y t h e I S O ( 6 ) . B e f o r e m i x i n g , t h e t e s tm a t e r i a l s , m i x i n g p a d s , s p a t u l a s , a n d f i a t g l a s s p l a te s w e r e p l a c e di n a r o o m w i t h a t e m p e r a t u r e o f 2 3 - + I C f o r 1 h . E a c h m a t e r i a lw a s t h e n m i x e d a n d p l a c e d i n a c i r c u l a r m e t a l m o l d ( 1 5 m md i a m e t e r a n d 5 m m h i g h ) . T h e a s s e m b l y , c o m p r i s i n g m o l d a n d t e s tm a t e r i a l , w a s p l a c e d o n a m e t a l b l o c k i n a c a b i n e t a t 3 7 C a n dr e l a t i v e h u m i d i t y o f 9 5 t o 1 0 0 % , 2 m i n a f t e r t h e s ta r t o f m i x i n g .A f t e r a f u r t h e r 3 0 s t o 1 m i n , t h e i n d e n t o r n e e d l e ( G i l l m o r e ) w a sl o w e r e d v e r t i c a l l y o n t o t h e s u r f a c e o f t h e m a t e r ia l ( 1 . 0 m m / m i n )a n d a l l o w e d t o r e m a i n t h e r e f o r 5 s . T h i s p r o c e s s w a s r e p e a t e de v e r y 3 0 s u n t i l t h e n e e d l e f a i l e d t o m a k e a c o m p l e t e c i r c u l a ri n d e n t a t i o n i n t h e t e s t m a t e r ia l . T h e s e t t in g t i m e w a s t h e d u r a t i o no f t i m e t h a t e l a p s e d f r o m s t a r t o f m i x i n g t o w h e n t h e i n d e n t o rn e e d l e f a i l e d to m a k e a n i n d e n t a t i o n i n t h e m a t e r i a l . T h i s t e s t w a sr e p e a t e d s i x t i m e s f o r e a c h m a t e r i a l .

Radiopaei tyT h e r a d i o p a c i t y o f M T A w a s d e t e r m i n e d a c c o r d i n g t o t h e

m e t h o d d e s c r i b e d b y t h e I n t e r n a t i o n a l O r g a n i z a t i o n f o r S t a n d a r d -i z a t io n ( I S O 6 8 7 6 ) , s e c t i o n 7 . 7 (6 ) . A f t e r m i x i n g , M T A w a s p a c k e di n t o a st a i n l e ss s t e e l r in g m o l d w i t h a n i n t e r n al d i a m e t e r o f 1 0 m ma n d a d e p th o f i m m . T h e m o l d w a s p l a c e d o n a g l a s s s l ab b e f o r einse r t ion of the m a te r ia l . I t wa s c ove re d wi th a g la s s s l ide a nda l lowe d to s e t for 3 h .

R a d i o g r a p h s w e r e t a k e n w i t h a t a r g e t - f i l m d i s t a n c e o f - 3 0 c mu s i n g a c a r d b o a r d e x t e n s i o n t o t h e c o n e o f t h e X - r a y m a c h i n e .

T h e d e n t a l X - r a y u n i t ( H e l i o d e n t M D , S i e m e n s , B e n s h e i m ,G e r m a n y ) w a s s e t a t 7 0 k V , a c u r r e n t o f 7 m A , a n d a n e x p o s u r et i m e o f 0 .2 5 s t o g i v e a r a d i o g r a p h i c d e n s i t y r e a d i n g o f - 2( i n c l u d i n g b a s e a n d f o g ) f o r th e e x p o s e d a n d p r o c e s s e d f i l m u n d e rt h e 1 - m m t h i c k s e c t i o n o f t h e s t e p w e d g e ( P r o t e x T e n - S t e p A l u -m i n u m S t e p w e d g e , E v e r y t h i n g X - R a y L t d ., W a t f o r d , U K ) . T h es p e c i m e n s w e r e p l a c e d d i r e c t ly o n t h e f i l m p a c k e t . A t o t a l o f f i v ef i l m s w e r e t a k e n f o r e a c h s p e c i m e n . T h e f i l m s w e r e p r o c e s s e d i na n a u t o m a t i c d e v e l o p i n g m a c h i n e ( P 1 0 , H o p e I n d u s t r ie s , L e t c h -w o r t h , U K ) .

T h e p h o t o g r a p h ic d e n s i to m e t e r ( M e l i c o / P h o t o l o g , B / W T r a n s-m i s s i o n D e n s i t o m e t e r , M o d e l T D X , M e d i c a l a n d E l e c t r i c a l I n s t ru -m e n t a t i o n L t d . , L o n d o n , U K ) w a s u s e d t o t a k e r e a d i n g s o f th er a d i o g r a p h i c i m a g e o f t h e s p e c i m e n s , e a c h s t e p o f t h e s t e p w e d g e ,a n d t h e u n e x p o s e d p a r t o f t h e f i l m . T h r e e r e a d i n g s w e r e t a k e n f o re a c h f i l m a n d t h e m e a n c a l c u l a t e d . T h e n e t r a d i o g r a p h i c d e n s i t yw a s d e r i v e d f r o m t h e f o l l o w i n g e q u a t i o n :

N e t R a d i o g r a p h i c D e n s i t y= ( G r o s s R a d i o g r a p h i c D e n s i t y ) - ( B a s e an d F o g ) .

G r a p h s w e r e p l o t t e d f o r l o g - n e t r a d i o g r a p h i c d e n s i t y o f t h e a Iu -m i n u m s t e p s v e r s u s t h ic k n e s s o f a l u m i n u m ( m m ) f o r e a ch g r o u p .T h e s e g a v e s t r a ig h t l i n e p l o t s , a n d f r o m t h e s e t h e m e a n n e t r a d io -g r a p h i c d e n s i t y v a l u e s o f t h e m a t e r i a l s w e r e t r a n s f o r m e d i n t or a d i o p a c i t y e x p r e s s e d a s e q u i v a l e n t t h i c k n e s s o f a l u m i n u m .

ompress ive StrengthT h e c o m p r e s s i v e s t r e n g t h s o f t e s t m a t e r i a ls w e r e d e t e r m i n e d

a c c o r d i n g t o t h e m e t h o d r e c o m m e n d e d b y t h e I S O ( 6 ) . T h e i n s t r u -m e n t s a n d t h e t e s t m a t e r i a l s w e r e c o n d i t i o n e d a t 2 3 --- I C i n t h el a b o r a t o r y f o r 1 h b e f o r e t e s t i n g . E a c h m a t e r i a l w a s m i x e d a n dp l a c e d i n s p l i t s t a i n l e s s s t e e l m o l d s ( 1 2 m m h i g h a n d 6 m m w i d e )w i t h i n 2 m i n b e f o r e s t a rt o f m i x i n g . E a c h m o l d w a s p a c k e d t oe x c e s s a n d w a s p l a c e d o n t h e b o t t o m p l a t e w i t h t h e a p p l i c a t i o n o fs l i g h t p r e s s u r e . A f t e r r e m o v i n g a n y e x t r u d e d m a t e r i a l a n d p l a c i n gt h e t o p p l a t e , t h e m o l d a n d p l a t e s w e r e c l a m p e d t o g e t h e r . T h ew h o l e a s s e m b l y w a s t r a n s f e r r e d t o a n o v e n w i t h a c o n s t a n t t e m -p e r a t u r e o f 3 7 -+ I C f o r 3 h w i t h i n 3 r a i n a f t e r s t ar t o f m i x i n g . T h es p e c i m e n s w e r e r e m o v e d f r o m t h e m o l d s a n d e x a m i n e d f o r v o i d sa n d c h i p p e d e d g e s . D e f e c t i v e s p e c i m e n s w e r e d i s c a r d e d , a n d s i xa c c e p t a b l e s a m p l e s w e r e p r e p a r e d f o r e a c h t e s t m a t e r i a l f o r e a c ht i m e i n t e r v a l . T h e s p e c i m e n s w e r e i m m e r s e d i n d i s t i l l e d w a t e r f o r2 1 h o r 3 w k b e f o r e t h e i r c o m p r e s s i v e s t r e n g t h s w e r e m e a s u r e du s i n g a n I n s t r o n 1 1 8 5 T e s t i n g M a c h i n e ( I n s t r o n L t d . , H i g h W y -c o m b e , U K ) . A f t e r p l a c i n g e a c h s p e c i m e n w i t h i t s f i a t e n d s b e -t w e e n t h e p l a t en s o f t h e a p p a r a t u s a n d e n s u r i n g t h a t t h e l o a d w a sa p p l i e d i n t h e l o n g a x i s o f t h e t e s t s a m p l e , t h e m a x i m u m l o a dr e q u i r e d t o f ra c t u r e e ac h s p e c i m e n w a s n o t e d , a n d t h e c o m p r e s s i v es t r e n g t h ( C ) w a s c a l c u l a t e d i n M e g a p a s c a l s u s i n g t h e f o r m u l a

4 PC - , n. D

w h e r e P i s t h e m a x i m u m a p p l i e d l o a d i n N e w t o n s , a n d D i s t h em e a n d i a m e t e r o f t h e s p e c i m e n i n m i l l i m e t e r s ( 6 ) .

O n e w a y a n a l y s i s o f v a r i a n c e w i t h D u n c a n m u l t i p l e c o m p a r i -s o n s w e r e u s e d t o d e t e r m i n e s t a t i s t i c a l d i f f e r e n c e s b e t w e e n c o m -p r e s s i v e s t r e n g t h s o f t h e v a r i o u s t e s t m a t e r i a l s a t b o t h t i m e i n t e r-va l s .

Solubil itySetting Time

T o d e t e r m i n e a n d c o m p a r e t h e s e t t i n g t i m e a n d c o m p r e s s i v es t re n g th o f M T A w i t h o t h e r c o m m o n l y u s e d r o o t - en d f i l l in g m a -t e r i a l s , a m a l g a m , S u p e r - E B A , I R M , a n d M T A w e r e m i x e d a c c o r d -i n g t o t h e m a n u f a c t u r e r s ' d i r e c ti o n s a n d e v a l u a t e d ( T a b l e 1 ).

T h e d e g r e e o f s o l u b i l i t y o f t e s t m a t e r i a ls w a s d e t e r m i n e d b y am o d i f i e d m e t h o d o f t h e A m e r i c a n D e n t a l A s s o c i a t i o n ( A D A )s p e c i f i c a t i o n 3 0 ( 7 ). T h e m a t e r i a l s w e r e p r e p a r e d i n l in e w i t hm a n u f a c t u r e rs ' r e c o m m e n d a t i o n s . S u p e r - E B A c e m e n t a n d M T Aw e r e h a n d - m i x e d , w h e r e a s a m a l g a m a n d I R M w e r e m i x e d i n am a c h i n e . A f t e r m i x i n g , e a c h s u b s t a n c e w a s m a d e i n t o a s m a l l d i sc

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V o l . 2 1 , N o . 7 , J u l y 1 9 9 5p H

1 3 . 0

1 2 . 0

11 . 0

1 0 . 0

9 . 0

8 . 0 0

1 10 [ ] [ ]

5 o l O O 1 ; o 2 o 0 2 ; 0 3 ; 0 '1300 1350Time mins

FIG 1 . pH va lues o f MT A at var i ous t ime i n terva ls .

(20 mm 1.5 mm) by the use of a metal former and two glassplates.

Mixing and weighing of the samples were performed by a singleoperator at 23 _ 2C and a relative humidity of 50 --- 5 . Six discsof each material were fabricated and tested. After fabrication, theywere placed in 100 humid ity for 21 h and then stored individu-ally in glass bottles containing 50 ml of distilled water at 37C. Thespecimens were removed from the water after 1 day. All discs w rdesiccated for 1 h at 37C. Each disc was then weighed to thenearest microgram. After weighing, each disc was replaced in thesame glass bottle. The water in the bottles was neither changed noradded to during the test periods. The desiccation and weighingprocedure was performed at 1 day, then at 7 and 21 days. Analysisof variance with Duncan multip le comparisons were used to de-termine statistical differences between weights of the test materialsat different time intervals.

RESULTSExaminat ion of the MTA shows specific phases throughout the

material. All MTA was divided into calcium oxide and calciumphosphate. Further analysis demonstrated that the former appearedas discrete crystals and the latter as an amorphous structure with noapparent crystal growth but a granular appearance. The mean valueof the prisms was 87 calc ium and 2.47 silica, the remainderbeing oxygen. In areas of amorphous structure, there seemed to be33 calcium, 49 phosphate, 2 carbon, 3 chloride, and 6silica.

The change in pH as a function of time for MTA is shown inFig. 1. The pH of MTA after mixing was 10.2, and it rose to 12.5at 3 h; thereafter, it remained constant. The mean radiopacity forMTA was 7.17 mm o f equivalent thickness of aluminum.

The mean setting time and standard deviation for the test ma-terials were as follows: amalgam, 4 min (+30 s); Super-EBA, 9min (+-30 s); IRM, 6 min (+-30 s); and MTA, 2 h 45 min (+-5 min).

The means and standard deviations of compressive strength ofthe test materials after the two time intervals are shown in Table 2.Amalgam had the highest compressive strength among the mate-rials tested. Statistical analysis of the data regarding the remainingthree materials showed that the compressive strength of Super-

R o o t - E n d F i ll in g M a t e r i a l 3 5 1T AB L E 2 . M e a n s a n d s t a n d a r d d e v i a t i o n s i n p a r e n t h e s e s ) o fc o m p r e s s i v e s tr e n g t h M P a ) f o r a m a l g a m , S u p e r - E B A , IR M ,

a n d M T A a f te r t w o t i m e i n t e r v a ls n = 6 )Mater ia l 24 h 21 days

A m a l gam 312 . 5 311 .1(20.1) (23.8)S upe r - E B A 60 . 0 78 .1(5.5) (9.3)I R M 52 . 2 57 . 4(3.4) (5.9)

M T A 4 0 . 0 6 7 . 34 . 4 ) 6 . 6 )

EBA was signif icant ly greater than that of IRM and MTA after 24h (p < 0.05); compressive strength of IRM was signif icant ly morethan MTA (p < 0.05) at the same time interval. The compressivestrength of all cements increased after 3 wk, and the strength ofSuper-EBA was significantly higher than that of IRM (p < 0.05),but there was no signifi cant difference between the strengths ofSuper-EBA and MTA at these time intervals.

The mean weights (g) of specimens and standard deviation forthe test materials at various time in tervals are shown in Table 3.Statistical analysis of the data regarding weight loss changesshowed no significant changes for amalgam, Super-EBA, andMTA when the mean weight of the specimens were compared atdifferent time intervals. However, when the mean weights of IRMspecimens were compared between day 1 and those on days 7 and21, significant differences were noted (p < 0.001). Similar differ-ences were noted when the mean weight of the specimens werecompared at day 7 versus day 21.

DISCUSSIONNumerous investigations have been performed to study the

physical properties of dental filling materials (8-13) . However,information regarding the physical properties of root-end fill ingmaterials is scant. Owadally and Pitt Ford (14) evaluated the effectof adding 10 and 20 hydroxyapatite (HAP) on the physicalproperties of IRM and found that IRM had longer mean workingand mean setting times than IRM + 10 or 20 HAP. IRM alsohad a greater compressive strength than both IRM + 10 HAP orIRM + 20 HAP. In addition, their results indicated that adding10 or 20 HAP to IRM causes disintegrat ion of these materialsin buffered phosphate and in bovine serum after 8 wk. In contrast,IRM and EBA cements showed no noticeable signs of disintegra-tion in the same media after 6 months.

MTA powder consists of fine hydrophilic particles. The princi-ple compounds present in this material are tricalcium silicate,tricalcium aluminate, tricalcium oxide, and silicate oxide. In ad-dition, there are small amounts of a few other mineral oxides thatare responsible for the chemical and physical properties of thisaggregate. Bismuth oxide powder has been added to make theaggregate radiopaque. Electron probe microanalysi s of MTA pow-der showed that calcium and phosphorous are the main ions presentin this material. Because these ions are also the principal compo-nents of dental hard tissues, MTA may prove to be biocompatiblewhen used in contact with cells and tissues. In vitro and i n vivostudies are in progress to test the biocompat ibili ty of this materialin cell culture and tissues. Induct ion of a hard tissue barrier, similarto that obtained in apexification procedures, following root-end

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3 5 2 T o r a b i n e j a d e t a l . J o u r n a l o f E n d o d o n t i c sT AB LE 3 . M e a n w e i g h t g ) o f s p e c i m e n s a n d s t a n d a r d d e v i a t io n f o r t h e f o u r m a t e r i a l s a t v a r io u s t i m e s

T i m e A m a l g a m S u p e r - E B A I R M M T A1 d a y 5 . 3 9 6 1 _+ 0 . 1 5 4 9 1 . 4 4 8 4 _+ 0 . 1 1 4 7 1 . 1 8 8 5 + 0 . 0 3 1 9 1 . 1 7 9 4 _+ 0 . 1 1 0 07 d a y s 5 . 3 9 5 9 + 0 . 1 5 4 7 1 . 4 4 6 6 _+ 0 . 1 1 4 8 1 . 1 8 1 1 _+ 0 . 0 3 1 5 1 . 1 8 1 4 +_ 0 . 1 1 2 22 1 d a ys 5 . 3 9 6 1 _+ 0 . 1 5 4 8 1 . 4 4 6 5 _+ 0 . 1 1 4 4 1 . 1 7 7 4 _+ 0 . 0 3 1 5 1 . 1 7 4 6 _+ 0 . 1 1 3 0

f i l li n g w o u l d m i n i m i z e t h e i n t e r a c ti o n b e t w e e n m a t e r i a l a n d h o s tt i s su e s . B e c a u s e M T A h a s a h i g h p H s i m i l a r t o c a l c i u m h y d r o x i d ec e m e n t , i t i s p o s s i b l e t h a t i n d u c t i o n o f h a r d t i s s u e f o r m a t i o n m a yo c c u r f o l l o w i n g t h e u s e o f t h i s s u b s t a n c e a s a r o o t - e n d f i l l i n gmate r ia l .

A m o n g o t h e r c h a r a c t e r is t i c s , a n i d e a l r o o t - e n d f i l l i n g m a t e r i a ls h o u l d b e m o r e r a d i o p a q u e t h a n i t s s u r r o u n d i n g s t r u c t u r e s w h e np l a c e d i n a r o o t - e n d c a v i t y p r e p a r a t i o n . S h a h e t a l . ( 1 5 ) d e t e r m i n e dt h e r a d i o p a c i t y o f p o t e n t i a l r o o t - e n d f i l l i n g m a t e r i a l s u s i n g t h es a m e m e t h o d u t i l i z e d i n o u r s t u d y a n d f o u n d t h a t a m a l g a m w a s t h em o s t r a d i o p a q u e m a t e r i a l t e st e d ( > 1 0 m m e q u i v a l e n t t h i c k n e s s o fa l u m i n u m ) . T h e r a d i o p a c i t y o f o t h e r r e l e v a n t t e s t m a t e r i a l s i n t h e i re x p e r i m e n t w a s a s f o l l o w s : K a l z i n o l ( 7 . 9 7 ) , g u t t a - p e r c h a ( 6 . 1 4 ) ,I R M ( 5 . 3 0 ) , S u p e r - E B A ( 5 . 1 6 ) , a n d d e n t i n ( 0 . 7 0 ) . A c o m p a r i s o nb e t w e e n t h e r a d i o p a c i t y o f M T A a n d t h o s e o f o t h e r p o t e n t i a lr o o t - e n d f i l l i n g m a t e r i a l s i n S h a h e t a l . ' s ( 1 5 ) s t u d y s h o w s t h a tM T A i s s l i g h t l y l e s s r a d i o p a q u e t h a n K a l z i n o l ( r e i n f o r c e d z i n co x i d e - e u g e n o l - b a s e d c e m e n t ) a n d m o r e r a d i o p a q u e th a n I R M a n dS u p e r -E B A . B e c a u s e M T A i s m o r e r a d i o p a q u e t h a n c o n v e n t io n a lg u t t a - p e r c h a a n d d e n t i n , it s h o u l d b e e a s i l y d i s t i n g u i s h a b l e o nr a d i o g r a p h s w h e n u s e d a s a r o o t - e n d f i l l i n g m a t e r i a l.

H y d r a t i o n o f M T A p o w d e r r e s u l t s i n a c o l l o i d a l g e l t h a t s o l i d -i f ie s to a ha rd s t ruc tu re in le ss than 3 h . The charac te r i s t ic s o f thea g g r e g a t e d e p e n d o n t h e s i z e o f t h e p a r t i c l e s , p o w d e r - t o - w a t e rr a t io , t e m p e r a t u r e , p r e s e n c e o f w a t e r , a n d e n t r a p p e d a i r ( 2) . I n t h i ss t u d y , t h e I S O m e t h o d o f d e t e r m i n i n g s e t t i n g t i m e w a s u s e d ( 6 ) .T h e r e s u l t s s h o w e d t h a t a m a l g a m h a d t h e s h o r t e s t s e tt i n g t i m e a n dM T A t h e l o n g e s t . T h e s e t t in g t i m e f o r I R M i n t h is s t u d y w a s v e r ys i m i l a r t o t h a t f o u n d b y O w a d a l l y a n d P i t t F o r d ( 1 4 ) . I t h a sg e n e r a l l y b e e n c o n s i d e r e d t h a t a p o t e n t i a l r o o t - e n d f i l l i n g m a t e r i a ls h o u l d s e t a s s o o n a s i t i s p l a c e d i n t h e r o o t - e n d c a v i t y w i t h o u ts i g n i f i c a n t s h r i n k a g e . T h i s c o n d i t i o n w o u l d a l l o w d i m e n s i o n a ls t a b i l it y o f t h e m a t e r i a l a f t e r p l a c e m e n t a n d l e s s t i m e f o r a n u n s e tm a t e r i a l t o b e i n c o n t a c t w i t h v i t a l t i s s u e s . H o w e v e r , i n g e n e r a lt e r m s , t h e q u i c k e r a m a t e r i a l s e t s t h e m o r e i t s h r i n k s . T h i s p h e -n o m e n o n m a y e x p l a i n w h y M T A i n p r e v io u s e x p e r im e n t s h a ds i g n i f i c a n t l y l e s s d y e ( 2 , 3 ) a n d b a c t e r i a l ( 4 ) l e a k a g e t h a n o t h e rm a t e r i a l s t e s t e d a s r o o t - e n d f i l l i n g m a t e r i a l s .

C o m p r e s s i v e s t r e n g t h i s a n i m p o r t a n t f a c t o r t o c o n s i d e r w h e n af i l l in g m a t e r i a l i s p l a c e d i n a c a v i t y t h a t b e a r s o c c l u s a l p r e s s ur e .B e c a u s e r o o t - e n d f i l l i n g m a t e r i a l s d o n o t b e a r d i r e c t p r e s s u r e , t h ec o m p r e s s i v e s t r e n g t h o f t h e s e m a t e r i a l s is n o t a s i m p o r t a n t a s t h o sem a t e r i a l s u s e d t o r e p a i r d e f e c t s i n o c c l u s a l s u r f a c e s . I n t h e p r e s e n ts t u d y , M T A i n i t i a l l y h a d t h e l o w e s t c o m p r e s s i v e s t r e n g t h a m o n gm a t e r i a l s t e s t e d , b u t i t s v a l u e i n c r e a s e d w i t h t i m e . I n a p r e v i o u sr e p o r t, t h e c o m p r e s s i v e s t r e n g t h o f M T A w a s r e p o r t e d b y m i s t a k ea s b e i n g e q u a l t o a m a l g a m ( 2 ) . T h e i n c r e a s e i n c o m p r e s s i v es t r e n g t h o f M T A r e q u i r e d t h e p r e s e n c e o f m o i s t u r e . L o n g e r t e r ms t u d i es m i g h t p r o v i d e f u r t h e r i n f o r m a t i o n o n c o m p r e s s i v e s t r e n g t ho f M T A i n t h e p r e s e n c e o f m o i s t u r e . H o w e v e r , t h e c o m p r e s s i v es t r e n g t h v a l u e o b t a i n e d f o r M T A i s s i m i l a r t o t h o s e o b t a i n e d f o rS u p e r - E B A , I R M , a n d z i n c p h o s p h a t e ( 6 9 - 1 1 7 ) , ( 1 6 ) .

S o l u b i l i t y i s a n o t h e r f a c t o r i n a s s e s s i n g t h e s u i t a b i l i t y o f p o t e n -t i a l s u b s t a n c e s t o b e u s e d a s r e s t o r a t i v e m a t e r i a l s i n d e n t i s t r y

( 8 - 1 3 ) . L a c k o f s o l u b i l i t y h a s a l s o b e e n s t a t e d a s a n i d e a l c h a r-a c t e r i s t i c f o r r o o t - e n d f i l l i n g m a t e r i a l s ( 1 ) . D e s p i t e s o m e a d v a n -t a g e s o f c o n t r o l l e d l o n g - t e r m c l i n i c a l s t u d i e s , v a r i a t i o n s i n t h e o r a le n v i r o n m e n t a m o n g p a r t i c i p a ti n g p a ti e n ts a r e a m a j o r d r a w b a c k o fs u c h i n v e s t i g a t i o n s . B e c a u s e o f t h e l o n g s e t t i n g t i m e o f M T A , t h er e c o m m e n d e d m e t h o d s b y I S O ( 6 ) o r A D A s p e c i f i c a t i o n 3 0 ( 7 ) t ot e s t t h e s o l u b i l i t y o f M T A h a d t o b e m o d i f i e d .

F r o m o u r r es u l ts , i t se e m s t h a t a m a l g a m , S u p e r - E B A , a n d M T As h o w e d n o s i g n s o f s o l u b i l i t y i n w a t e r ; d e s p i t e s t a t i s ti c a l d i f fe r -e n c e s b e t w e e n t h e m e a n w e i g h ts o f I R M s p e c i m e n s a t th r e e t i m ei n t e r v a l s , t h e c l i n i c a l s i g n i f i c a n c e o f t h e m e a n d i f f e r e n c e s - -0 . 0 0 7 4 g ( d a y 1 v e r s u s d a y 7 ) a n d 0 . 0 0 3 7 g ( d a y 7 v e r s u s d a y2 1 ) - - i s q u e s t i o n a b l e . O w a d a l l y a n d P i t t F o r d ( 1 4 ) e v a l u a t e d t h er a t e o f d i s i n t e g r a t i o n o f s o m e z i n c o x i d e - e u g e n o l c e m e n t s u t i l i z i n ga r e p l i c a m e t h o d i n c o n j u n c t i o n w i t h 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 , a n d f o u n d th a t I R M a n d S u p e r - E B A s h o w e d n o n o t i c e a b l es i g n s o f d i s i n t e g r a t i o n af t e r 6 m o n t h s i n b u f f e r e d p h o s p h a t e s o l u -t ion .

E r o s i o n o f r e s t o ra t i v e f i l l i n g m a t e r i a l s c a n o c c u r e i t h e r b y a c i d sg e n e r a t e d b y b a c t e r ia , a c i d s p r e s e n t i n f o o d s o r b e v e r a g e s ( 1 7 ) , o rb y m e c h a n i c a l w e a r . T h e r o o t - e n d f i l li n g m a t e r i a l s a r e n o r m a l l y i nc o n t a c t w i t h p e r i r a d i c u l a r t is s u e f l u i d u n t i l t h e y a r e c o v e r e d e i t h e rw i t h f i b r o u s c o n n e c t i v e t i s s u e o r c e m e n t u m . C l i n i c a l l y , b i o c o m -p a t i b l e r o o t - e n d f i l l i n g m a t e r i a l s w i t h g o o d s e a l i n g a b i l i t y s h o u l dg e n e r a t e l i t t l e o r n o i n f l a m m a t o r y r e s p o n s e i n p e r i r a d i c u l a r t i s s u e s ,a n d e n c o u r a g e f o r m a t i o n o f f i b r o u s c o n n e c t i v e t i s s u e a n d / o r c e -m e n t u m c o v e r i n g th e e n t i r e r o o t - e n d . M e c h a n i c a l w e a r , a n i m p o r -t a n t f a c t o r i n c o r o n a l r e s t o r a t i o n , i s n o t a s i g n i f i c a n t f a c t o r i ne r o s i o n o f r o o t - e n d f i l l i n g m a t e r i a l s .

B a s e d o n t h e r e s u l t s o f t h i s s t u d y , i t s e e m s t h a t M T A h a sa d e q u a t e p h y s i c a l p r o p e r ti e s f o r u s e a s a r o o t - e n d f i l l i n g m a t e r i a l .

We thank Mr. PMM Shah fo r de termin ing the rad iopaci ty o f MTA and Dr .M. Sherri f f for determining the pH of MT A.Dr . Torab ine jad i s P ro fessor o f Endodont i cs and D i recto r o f GraduateProgram in the Depar tment o f Endodont i cs, S choo l o f Dent is t ry , Loma L indaUnivers ity , Loma L inda, CA. Dr . Hong i s Associa te Pro fessor i n DankookUniversi ty, School of Dent istry, Seoul , South Korea. Drs. McDonald and Pi t tFord a re sen io r l ectu rers i n the Depar tme nts o f Ora l B io logy and Co nserva t i veDental Surgery, Uni ted M edical and D ental Schools of Guy s and St. Tho-ma s s Hospi tals, U niversity o f Lond on, London, U K.

References1. Owadal ly ID, Chong BS, Pi t t Ford TR, Watson TF. The seal ing abi l i ty ofIRM wi th the add i t ion o f hydro xyapat i te as a re t rograde roo t f i ll ing . EndodDen t Traumato11993;9:211-5.2. Torabinejad M, Watson TF, Pitt Ford TR. The sealing abil i ty of a mineraltrioxide aggregate as a retrograde root fi l l ing material. J Endodon 1993;19:591-5.3. Torabinejad M, Higa RK, McKendry D J, Pi t t Ford TR. Effects of bloodcontamina t ion o f dye leakage o f roo t -end f il li ng materia ls . J Endodon 1994;2 0 : 1 5 9 -6 3 .4. Torabinejad M, Falah Rasteg ar A, Kettering JD, Pi t t Ford TR. Bacterialleakag e of mineral t r ioxide agg regate as a root end f il ling m aterial . J E ndod on1995;21 :109-112.5. Torabinejad M, Wi lder Smith P, Pi t t Ford TR. Com para t ive investigat iono f marg ina l adapta t ion o f m inera l t r i ox ide aggregate and o ther commonly

used root end f i l l ing materials. J Endodon 1995;6:295-299.

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V o l . 2 1 N o . 7 J u l y 1 9 9 56. International Org anization for Standardization. Specification for dental roo tcanal sealing materials. ISO 6876. London: British Standards Institution, 1986.7 . AN SI /ADA. Revised Amer i can Nat iona l S tandard /Am er i can Denta l As-socia t ion Speci ficat ion No. 30 for dental zinc oxide eugenol cem ents and zincoxid e noneugenol ceme nt 7.5, 1991.8. Eichner K, Lauten Schlager EP, Von R adnoth M. Invest igation concerningthe solubi l ity of dental cements. J Dent Res 1968;47:280-5.9. Wi lson AD. Speci f icat ion test for the solubi li ty and disintegra t ion ofdental cements: a cri t ical evaluat ion of i ts meaning. J Dent Res 1976;55:721-9 .10 . Osborne JW , Sw artz ML, Goo dacre C J, Ph i ll ips RW, G a le EN. Ame thod for assessing the cl in ical so lubi l i ty and disintegrat ion of luting ce -ments. J P rosthe t Den t 1978;40:413-7 .11 . Beech DR, Bandy opadhya y S . A new labora to ry method fo r eva luat ing

R o o t - E n d F i ll in g M a t e r i a l 3 5 3the relat ive solubi l i ty and erosion of dental cements. J Oral Rehabi11983;10:5 7 -6 3 .12. Kuhn AT, Wi lson AD. The dissolut ion mechanisms of si l icate andg lass- ionomer denta l cements. B iomater ia l s 1985;6 :378-82 .13 . Ono K , Matsun oto K . The physica l p roper t i es o f a new seal ing cement .In t Endod J 1992;25 :130-3 .14 . O wada l l y ID , P i t t Ford TR. E f fect o f add i t i on o f hydroxy apat i te on thephysical propert ies of IRM. Int Endod J 1994;27:227-32.15 . Shah PMM , Chong BS, S idhu SK, P i t t Ford TR. Rad iopaci ty o f po ten-t ia l root end f i ll ing materials. O ral Surg in press).16. Craig RG. In: Restorat ive den tal materials. 7th ed. St. Louis: CVMosby, 1985:170.17. Pluim LJ, Arends J. The relationship betw een sal ivary prop ert ies andin vivo solubi l i ty of dental cements. Dent Mater 1987;3:13-8.

A W o r d f o r t h e W i s e

A r e c e n t a r t ic le , wr i t t e n b y a pe r s on no t in the l e ga l pr ofe s s ion but wh o h a d on c e be e n, w a s a t t r ibute d to ar e c ov e r ing l a wy e r .I li ke t h a t; w i ll t h e y f o r m a B a r r is t e rs A n o n y m o u s o r g a n i z a t io n ?

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