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Bleaching of the discolored pulpless tooth
64 • T H E J O U RN A L O F T H E A M E R I C A N DEN T A L A SSO C I A T I O N
h a v e re ally o c c u rre d w o u ld b e difficu lt to d e te rm in e fro m ro e n tg e n o g ra m s ta k e n in a h a p h a z a r d w ay. T e c h n ic s t h a t m ak e possible th e ta k in g o f c o m p a ra b le ro e n t g en o g ram s a t d iffe re n t tim es a re n ec es sary. I t is c o n c lu d e d , o n th e basis o f th e in v estigations re p o rte d in th is p a p e r, th a t th e m e th o d o f c o m p a ra b le ro e n tg e n o g r a p h y discussed gives a g o o d ro e n tg e n o g ra p h ic p ic tu re o f th e a n a to m ic fe a tu re s
a n d a fa irly g o o d re p re s e n ta tio n o f th e re la tio n o f th e c o n d y le a n d th e fossa. I t sh o u ld b e em p h a siz e d t h a t ro e n tg e n o g ra m s ta k e n a c c o rd in g to several d iffe re n t tech n ic s a re necessary to th e d e te c tio n of disorders o f th e te m p o ro m a n d ib u la r jo in t a n d a re effective in this re g a rd . T h e m e th o d p re s e n te d w ill b e fo u n d u sefu l in p ro v id in g n e w d a t a a n d fa c ilita tin g th e d iffe re n tia l diag n o sis o f d iso rd ers of th e te m p o ro m a n d ib u la r jo in t.
B le a c h in g o f th e d is c o lo r e d p u lp le s s to o th
H y m a n H . P e a r s o n , D .D .S ., M o n tr e a l, Q u e b e c , C a n a d a
B y u tiliz in g p re s e n t d a y co n c ep ts o f b io lo gical a n d h isto lo g ica l fa c to rs, th e d e n tist c a n av o id th e n e e d fo r d e stro y in g a n d artific ia lly re p la c in g to o th tissu e as a m e a n s o f c o rre c tin g esthetics. T h e dis c o lo red pulp less to o th m a y b e re sto re d to n o rm a l fu n c tio n a n d esth etics b y e n d o d o n tic tre a tm e n t to re m o v e th e cause o f d isc o lo ra tio n a n d by b le a c h in g to re m o v e th e a b e rra n t p ig m en ts. V a rio u s tech n ics h a v e b e e n e m p lo y ed o v er th e years fo r b le a c h in g th e d isco lo red p u lp less to o th , b u t, b ec au se o f th e la c k o f p e rm a n e n c e o f th e re sto re d color, b le a c h in g w as d is c a rd e d as a n a c c e p ta b le p ro c e d u re . T h e fa u lt lay n o t w ith th e ag e n ts b u t w ith th e m a n n e r o f th e ir a p p lic a tio n . D e n ta l lite ra tu re re c o rd s m a n y te c h nics, som e u se d as f a r b a c k as th e last ce n tu ry . I n 1895, G a rre ts o n 1 re p o rte d th e u se o f ch lo rid e as a b le a c h in g a g e n t b e cau se h e says, “ I t is a d ec o m p o se r o f o rg a n ic su b stan ces . . . t h a t c o n ta in th e d isco lo red elem e n ts.” B uck ley ,2 B u rc h a rd 3 a n d Jo h n s to n 4 in 1912 a n d H e rm a n P rin z 5 in 1917 re p o rte d v ario u s tech n ic s
fo r th e b le a c h in g o f th e d isco lo red to o th . H a ro ld M a x m e n 6 o f D e tr o it g av e a m o st c o m p le te re p o rt in 1949 o n to o th d is c o lo ra tio n , th e v a rio u s causes a n d th e chem istry . “ N a tu r a l T o o th C o lo r, I ts P ro d u c tio n , G e ria tric and T r a u m a tic C h a n g e s” w o u ld b e a m o st in te re stin g su b je c t fo r in v estig atio n a n d stu d y a n d fo r a c o m p le te trea tise . B ecau se o f th e to p ic ’s m a n y ra m ificatio n s, th e s u b je c t o f th e p re se n t p a p e r w ill be lim ite d to a discussion o f th e
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PEA RSO N . . . V O L U M E 56, J A N U A RY 1958 • 65
b le a c h in g o f th e to o th , w ith p u lp in v o lv e m e n t, t h a t h a s b e c o m e discolored. S in ce th e e a rly 1920’s, I h a v e b een e n c o u ra g e d by m y p a tie n ts a n d s tim u la te d by a d esire to re sto re esth etics w ith th e least a m o u n t o f tissue d e s tru c tio n to ex p e rim e n t w ith som e of th ese technics. M o st o f th e d isco lo red te e th so tre a te d w e re b ro u g h t b a c k to n o rm a l success fully, b u t, a f te r a tim e , a sec o n d a ry d is c o lo ra tio n to o k p la c e t h a t c a n c e le d th e o rig in a l c o rre c tio n . I t th e n b e c a m e m y p ra c tic e to b le a c h o n ly th o se disco lo red te e th t h a t w e re to b e co v e re d e v e n tu a lly w ith p o rc e la in ja c k e t crow ns. T h is w as c o n sid e re d ad v isa b le in o r d e r to c o n tro l th e co lo r o f th e fin ish ed re s to ra tio n , p a r tic u la rly in th e re g io n o f th e g in g iv al th ir d w h e re th e p o rc e la in is th e th in n e s t a n d m o st tra n s lu c e n t. I n 1941, o n e p a tie n t w h o h a d b e e n so tre a te d r e tu r n e d fo r th e re p la c e m e n t o f a f r a c tu r e d ja c k e t cro w n . A stu d y o f th e p a tie n t’s re c o rd s disclosed t h a t th is to o th h a d b e e n b le a c h e d b e fo re th e re sto ra tio n w as m a d e , a n d , o n e x a m in a tio n , it w as fo u n d t h a t th e to o th h a d re ta in e d its re sto re d co lo r a f te r b e in g co v ered f o r a p e rio d o f e ig h t years. I w as c o n v in c e d t h a t th e so u rce o f th e d isc o lo ra tio n h a d b e e n e lim in a te d b y e n d o d o n tic tre a tm e n t, t h a t th e a b e rra n t p ig m en ts h a d b e e n re m o v e d b y b le a c h in g a n d t h a t th e p o rta ls o f e n try in to th e d e n tin h a d b e e n h e rm e tic a lly sealed. I t w as c o n c lu d e d t h a t th e e n a m e l m u s t be p e rm e a b le to th e o ra l fluids a n d t h a t th e a p p e a ra n c e o f a se c o n d a ry d isco lo ratio n w as th e re s u lt o f p ig m e n tin g su bstances c o n ta in e d in th is fluid. O n in v e stig a tin g f u r th e r, it w as d is co v ered t h a t th is se c o n d a ry d isc o lo ra tio n to o k p la c e a n y tim e b e tw e e n 3 a n d 12 m o n th s a f te r b le a c h in g , d e p e n d in g o n th e ag e o f th e p a tie n t a n d th e c o n d itio n of th e e n a m e l. I t w as also d isco v ered th a t, irre sp ectiv e o f w h e th e r th e p rim a ry a b e r r a n t p ig m e n ta tio n w as p u rp le , o ra n g e , b ro w n , yellow , b lu e, g ra y o r g re e n o r an y c o m b in a tio n o f th ese, th e se c o n d a ry d is
c o lo ra tio n w as alw ays a b lu ish g ra y a n d w as m o st p ro n o u n c e d in th e re g io n o f th e g in g iv al th ird , th e lo c atio n o f th e th in n est e n a m e l.7 D ISC U SSIO N
T h e c o n te n ts o f th e in te rp ris m a tic spaces in e n a m e l a n d th e d e n tin a l tu b u le s is of o rg a n ic c o m p o sitio n a n d ac ts as so m a n y w icks. T h e su b stan c e c o n ta in e d in th e d e n tin a l tu b u le s ca rries p ig m e n tin g fluid fro m th e d ec o m p o sin g p u lp ; w h e reas t h a t c o n ta in e d in th e in te rp ris m a tic spaces o f th e e n a m e l c a rries p ig m e n tin g o ra l fluids. A t th e d e n tin o e n a m e l ju n c tio n , th e d e n tin a l tu b u le s sen d o u t a m ass of b ra n c h e s , fo rm in g a lay er t h a t is alm o st en tire ly o rg a n ic . I t is h e re t h a t th e g re a t est in te n sity o f d isc o lo ra tio n m a y b e o b served. O n re -e x a m in in g th e te c h n ic , it w as d e d u c e d t h a t th e d e n tin lin in g th e p u lp c h a m b e r a n d cavities w as satisfacto rily sealed a n d re m a in e d so b u t t h a t it w as th e e n a m e l t h a t c o n ta in e d th e seco n d ary d isco lo ratio n . T h e re fo re , it w as c o n c lu d e d t h a t n o t on ly is e n a m e l p e rm e a b le b u t th is p e rm e a b ility is a c c e n tu a te d by th e b le a c h in g process. T h e sec o n d ary a b e r r a n t p ig m e n ts c a n co m e fro m n o o th e r so u rce th a n th e o ra l fluids. T h is th e o ry o f th e p e rm e a b ility o f e n a m e l w as c o n firm e d re ce n tly by S o g n n aes,8 w h o sa id : R a d io a c tiv e tr a c e r
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66 • T H E J O U RN A L O F T H E A M E R I C A N DEN T AL A SSO C I A T I O N
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T Y P E O F B L E A C H IN G A G E N T
A successful b le a c h in g a g e n t m u s t be in a so lu tio n t h a t h a s th e ab ility to p e n e tra te th e o rg a n ic m a tte r in th e d e n tin a l tu b u le s a n d th e e n a m e l in te rp ris m a tic spaces w ith o u t d e stro y in g th e m a trix o f th e cro w n . I t m u s t b e o f a self-lim itin g n a tu r e a n d le a v e n o re sid u a l effects. A fte r th e p u lp is d estro y e d , a m o n g th e fu n c tio n s t h a t re m a in fo r th e o rg a n ic m a te ria l in th e h a r d tissues a re its a c tio n as a b in d e r o f th e m a trix a n d its ab ility to tra n s m it lig h t fo r co lo r c o n tro l. T h ese fu n c tio n s o f th e o rg a n ic b o d y a re d e stro y ed by th e c h e m ic a l a c tio n o f th e b le a c h in g pro cess a n d s h o u ld b e re sto red. A m a te ria l m u s t b e su b stitu te d t h a t w o u ld a c t as a b in d e r, re sto re th e tra n slu c e n c y a n d , a t th e sam e tim e , a c t as a se a le r o f th e v o id e d d e n tin a l tu b u le s a n d th e in te rp ris m a tic sp aces o f th e e n am e l. I t m u s t b e a liq u id o f low su rfa c e ten sio n t h a t w o u ld easily p e n e tr a te th e m icroscopic spaces a n d h a v e th e a b ility to b e c o n v e rte d in to a n in e rt, in so lu b le m ass.
T H E B L E A C H IN G T E C H N IC
T h e b le a c h in g o f a p u lp less to o th sh o u ld b e u n d e r ta k e n only a f te r th e h e a lth of th e ro o t a n d p e ria p ic a l tissues h as b een re sto red a n d th e c a n a l h a s b e e n h e rm e ti cally sealed. 1. T h e to o th is th o ro u g h ly scaled a n d polished. 2. A c o a tin g o f p e tro le u m jelly is a p p lie d to th e la b ia l a n d lin g u a l ging iv al tissue in v e stin g th e d isco lo red to o th a n d its tw o a p p ro x im a tin g te e th , u n d e r th e fre e g in g iv al m a rg in s a n d in th e in te rp ro x im a l spaces. 3. T h e r u b b e r d a m is p u n c h e d w ith th e sm allest h o le possible a n d is ap p lie d a n d h e ld in p la c e b y m e a n s o f a d o u b le w in d in g o f d e n ta l floss, d o u b le k n o tte d u n d e r th e g in g iv a, as fa r as it w ill go in to
th e g in g iv al crev ice w ith o u t cau sin g tra u m a . 4. A ll fillin g m a te r ia l a n d d ecay are re m o v e d , as w ell as th e c o n te n ts of th e p u lp c h a m b e r. T h e c a n a l is v o id e d o f its c o n te n ts to a d e p th o f 3 m m . a p ica lly to th e g in g iv al level. 5. A ll th e exp o sed to o th tissue is w a sh ed w ith c h lo rin a te d so d a solution, som e o f w h ich is allo w e d to re m a in in th e cavities fo r a b o u t o n e m in u te a n d th e n w a sh e d a w ay w ith w a rm distilled w a te r, a n d th e to o th is d rie d . C a re sh o u ld be ta k e n to w a sh a w ay a ll vestiges o f th e p e tro le u m jelly fro m th e su rfa ce o f th e to o th . A m ix tu re o f o n e p a r t eth y l a lco h o l, 95 p e r c e n t by v o lu m e , a n d tw o p a rts ch lo ro fo rm , ch e m ic ally p u re , is u sed to d e sicc ate all th e exp o sed e n a m e l a n d d e n tin . T h is is allo w e d to re m a in in th e cav ities fo r tw o m in u te s a n d is a sp ira te d u sin g a “ sea le d to th e to o th ” a s p ira to r tip . 6. A n e th e r-p e ro x id e m ix tu re (P y ro zo n e ) is u se d as th e b le a c h in g a g e n t. A p e lle t o f c o tto n is p la c e d in th e p u lp c h a m b e r a n d th e c a v ity a n d is s a tu ra te d w ith th e e th e r-p e ro x id e m ix tu re b y m ean s o f a c u rv e d glass d ro p p e r. T h e solu tio n is th e n fo rce d in to th e d e n tin b y u sin g a p u m p w h ic h is co m p o sed o f a so ft-ru b b er p o lish in g c u p m o u n te d o n a p o rte -p o lisher. T h e c o tto n m a y b e s a tu ra te d several tim es, a n d th e p u m p in g m a y b e re p e a te d w ith th e rim o f th e c u p re stin g o n th e e n a m e l b ey o n d th e ca v ity m arg in s. 7. T h e to o th is co v ered w ith a strip o f m u slin o r c o tto n d e n ta l n a p k in c u t to fit th e e n tire la b ia l a n d lin g u a l surfaces, a n d th e ta il e n d is tu c k e d in to th e ca v ity to m e e t th e c o tto n p e lle t t h a t w as p la c e d in th e p u lp c h a m b e r. T h e m u slin a n d th e c o tto n p e lle t a re s a tu ra te d w ith th e e th e r-p e ro x id e m ix tu re , w ith th e m u slin a c tin g as a w ick. 8. T h e p a tie n t’s fa ce is c o v e red w ith a w e t tow el fo r p ro te c tio n fro m th e rays o f th e b le a c h in g la m p , a no. 2 p h o to flo o d la m p , w h ic h is h e ld a b o u t 20 in ch es fro m th e to o th . T h e c o tto n is re p e a te d ly r e
PEA RSO N . . . V O L U M E 56. J A N U A RY 1958 • 67
p le n ish e d w ith th e e th e r-p e ro x id e m ix tu r e a b o u t ev ery five m in u te s o r as it e v a p o ra te s. T h is pro cess u su ally tak es a b o u t 20 m in u te s. 9. T h e m u slin strip a n d th e re m a in in g p e lle t o f c o tto n a re re m o v e d , a n d th e cav ities a r e d rie d b y a b la st o f w a rm a ir. A d re ssin g o f 30 p e r c e n t h y d ro g e n p e r o x id e in w a te r is p la c e d in th e p u lp c h a m b e r, a n d a ll cav ities a re sealed w ith a w h ite o x y p h o sp h a te o f zin c ce m e n t. T h e oxygen fro m th e d re ssin g w ill a tte m p t to fo rce its w a y th ro u g h th e s e ttin g ce m e n t a n d w ill cause a leak y fillin g unless th e c e m e n t is co v e red im m e d ia te ly w ith a p ie c e o f ru b b e r d a m o r a p la stic s trip h e ld in p la c e b y fin g er p re ssu re u n til th e c e m e n t is set. A fte r th e c e m e n t sets a n d ju s t b e fo re th e rubbfer d a m is re m o v e d , th e to o th is g iv en a fresh c o a t o f p e tr o le u m je lly to seal th e e n a m e l te m p o ra rily . T h e n th e first tr e a tm e n t is c o m p le te d . T h r e e day s sh o u ld elap se b e fo re th e seco n d tre a tm e n t. 10. A t th e second o r su b se q u e n t sit tings, th e ru b b e r d a m is a p p lie d as d e scrib e d previo usly. T h e to o th is c lea n sed o f p e tro le u m jelly a n d o th e r depo sits by u sin g p ro p h y la c tic p o lish in g p a s te ; th e n it is w a sh e d a n d d e sicc a te d w ith th e a lco h o l-c h lo ro fo rm m ix tu re . T h e fillin g m a te r ia l is re m o v e d , a n d th e b le a c h in g process is re p e a te d u n til th e to o th b e com es p e rc e p tib ly lig h te r in co lo r th a n is re q u ire d . A t th e la s t sittin g , th e r u b b e r d a m m u s t n o t b e re m o v ed u n til a ll th e d e n tin a n d e n a m e l su rfaces a r e h e r m e ti cally sea le d , as fo llo w s: 11. A ll th e exposed e n a m e l a n d d e n tin o n th e la b ia l a n d lin g u a l su rfaces a n d th e w alls o f th e cavities a n d p u lp c h a m b e r a re p a in te d w ith a self-c u rin g ac ry lic re sin m o n o m e r; a c a m e P s-h air b ru s h is used fo r th is p u rp o se . S ev eral co ats a re a p p lie d , e a c h a f te r th e la s t h a s b e e n ab so rb ed . T h e to o th is ex posed to th e p h o to flo o d la m p fo r five m in u tes. T h e la m p is tu r n e d off, a n d th e b ru s h te c h n ic is u se d in fillin g th e c a n a l a n d p u lp c h a m b e r w ith a lig h t sh a d e o f self-cu rin g
filling acry lic resin. T h e to o th is ex poséd to th e p h o to flo o d la m p a g a in fo r e ig h t m in u te s to co m p le te p o ly m e riz a tio n o f th e ac ry lic re sin m o n o m e r as w ell as of th e fillin g p ro p e r. 12. R e te n tio n p o in ts a re p re p a re d in all th e cavities, w h ic h th e n a re filled w ith a sy n th etic p o rc e lain . R A T IO N A L E O F T E C H N I C
T h e p e tro le u m jelly is u sed o n th e soft tissue to p re v e n t an y a c tio n o f th e e th e rp e ro x id e m ix tu re , w h ic h m ig h t leak in a d v e rte n tly u n d e r th e ru b b e r d a m . T h is so lu tio n w ill n o t d estro y th e tissue, b u t it w ill leav e a p a in fu l a re a . P e tro le u m jelly is a p p lie d to th e e n a m e l b efo re th e r e m o v a l o f th e r u b b e r d a m a t th e first b le a c h in g s ittin g in o rd e r to seal th e e n a m e l su rfa ce tem p o ra rily . T h is is n e c essary b ecau se o f th e solv en t q u a lity of th e e th e r-p e ro x id e m ix tu re . T h e a lc o h o l-c h lo ro fo rm m ix tu re is a so lv en t a n d desicc ato r. T h e se q u alities a re re q u ire d fo r p rim a ry c lea n sin g a n d d ry in g . T h e s o ft-ru b b e r p o lish in g c u p in th e p o rte -p o lis h e r is u sed as a p u m p in ste a d o f u n v u lc a n iz e d r u b b e r a n d a n o ra n g e w o o d stick in sid e th e cavity, as orig in ally p re sc rib e d in th e e a rlie r technics. T h e l a tte r is a d a n g e ro u s p ro c e d u re a n d m ay re s u lt in fr a c tu rin g o f th e crow n. A n e x c elle n t p u m p in g a c tio n c a n be d e v e lo p ed w ith th e rim o f th e c u p re stin g o n th e su rfa c e b ey o n d th e m a rg in s o f th e cavity. P y ro zo n e is th e so lu tio n used. I t c o n ta in s 25 p e r c e n t h y d ro g e n p e ro x id e in 75 p e r c e n t e th e r. T h e e th e r dissolves th e o rg a n ic m a tte r t h a t h o ld s th e a b e rra n t p ig m e n ts in th e d e n tin a l tu b u les a n d in th e in te rp ris m a tic spaces in th e en a m el. Besides b e in g a so lvent, th e e th e r p e n e tra te s th e se spaces, c a rry in g w ith i t th e p e ro x id e t h a t bleach es th e p ig m en ts. T h e e th e r ra p id ly ev a p o rate s, le a v in g n o m o is tu re in th e spaces. I t is th e a c tin ic rays o f th e p h o to flo o d lig h t t h a t a c tiv a te th e oxygen to sy n th e
68 • T H E J O U RN A L O F T H E A M E R I C A N DEN T A L A SSO C I A T I O N
size th e p ig m en ts, c h a n g e th e m ch e m ic ally in to colorless su b stan ces a n d ca u se th e m to be destroyed. T h e h e a t ac tiv a te s th e solvent q u alitie s o f th e e th e r. H e a t w ith o u t lig h t is in a d e q u a te . T h e v o id e d d e n tin a l tu b u le s a n d in te rp rism a tic spaces re q u ire re fillin g w ith a n in e rt, tra n s lu c e n t su b sta n ce in o rd e r to re sto re th e o rig in al q u alitie s o f lig h t r e fra c tio n a n d a t th e sam e tim e e lim in a te th e spaces th a t m a y in v ite a sec o n d ary d isco lo ratio n . I n m o st o f th e te ch n ic s p re v io u sly r e p o rte d ,2'6 th e use of a c o n c e n tra te d so lu tio n o f c h lo ra l h y d ra te as a sea ler o f th e d e n tin a l tu b u le s w as suggested . N o m e n tio n h a s b e e n m a d e of th e n e e d f o r a sealer o f e n a m e l. A n 80 p e r c e n t so lu tio n o f ch lo ra l h y d ra te is a h eav y , sy ru p y fluid w ith h ig h su rfa c e tension. I t w ill n o t p e n e tr a te th e tu b u le s, a n d it is of n o v a lu e as a se a le r o f e n a m e l since it is w a te r soluble a n d w o u ld b e re p la c e d by th e o ra l fluids c o n ta in in g p ig m e n tin g su b stances. T h e self-cu rin g ac ry lic re sin m o n o m e r w as fo u n d to be a n id e a l p re p a ra tio n w ith th e n ecessary q u a litie s to fill th e n e e d fo r sea lin g th e en a m e l. I t is colorless a n d tra n s lu c e n t a n d h a s ex tre m ely low s u r
fa ce ten sio n , a n d , w h e n p o ly m erize d , it becom es a n in soluble , in e r t sealer. T h e acry lic resin m o n o m e r s h o u ld b e k e p t a t a te m p e ra tu re b elo w 5 0 ° F . u n til re a d y to use a n d sh o u ld n o t b e a p p lie d w h e n th e p h o to flo o d la m p is lit. SU M M A RY
B leac h in g o f th e d isco lo red p u lp less to o th m ay be successfully p e rfo rm e d . T h e sec o n d ary d isco lo ra tio n w h ic h m a y a p p e a r a f te r a successful p rim a ry b le ac h in g h as b e e n show n to b e c a u se d b y th e p ig m e n tin g su bstances c o n ta in e d in th e o ra l fluids. B ecause e n a m e l is p e rm e a b le a n d this p e rm e a b ility is a c c e n tu a te d by th e b le a c h in g chem icals, it ab sorbs th ese su b stances th u s c h a n g in g th e color. T h e b le a c h in g te c h n ic t h a t h as b een p re s e n te d in th is p a p e r elim in a te s c e rta in causes o f fa ilu re e x p e rie n ce d in th e p ast. T h e n o rm a l color o f th e d isco lo red p u lp less to o th c a n b e re sto re d a n d re ta in e d . T h e seco n d ary d isco lo ra tio n t h a t a p p e a rs a f te r a successful first b le a c h in g is d u e to th e p e rm e a b ility o f th e en a m e l. T h is m ay b e p re v e n te d by h e rm e tic a lly sea lin g th e e n a m e l as w ell as th e d e n tin . 5 0 0 B ir k s B u i l d i n g
R e a d in g E ffic ie n c y
• I n t h e m o d e r n w o r l d t h e e f f i c i e n c y o f a w o r k e r is c o m m o n l y m e a s u r e d b y t h e o u t p u t o f w o r k i n a g i v e n p e r i o d o f t i m e . A s s u m i n g t h a t t h e w o r k is s a t i s f a c t o r y in q u a l i t y , t h is is a s a t i s f a c t o r y d e f i n i t i o n o f e f f i c i e n c y f o r o r d i n a r y e c o n o m i c p u r p o s e s . H o w e v e r , w h e n e a s e o f s e e i n g is i m p o r t a n t , a s i t is i n a l l p r o l o n g e d ta s k s o f c r i t i c a l s e e i n g , t h e o v e r - a l l e ffic ie n c y o f th e w o r k e r h a s b e e n ig n o r e d , o w in g t o a g ro ss la c k o f th o u g h t a n d k n o w le d g e p e r ta in in g t o e a s e o f s e e in g . A p p l y i n g t h e s a m e l o g i c t o t h e t a s k o f r e a d i n g , i t is s e l f - e v i d e n t t h a t t h e r a t e o f r e a d i n g is n o t a p r io r i a m e a s u r e o f th e r e a d e r ’ s e ffic ie n c y . N e v e r th e le s s , it h a s b e e n a s su m e d w it h o u t a d e q u a t e p r o o f , t h a t s p e e d o f r e a d i n g i n w o r d s p e r m i n u t e o r l i n e s p e r h o u r is a s u i t a b l e m e a s u r e o f r e a d a b i l i t y . M u c h e v i d e n c e is a v a i l a b l e t o c o n d e m n t h is v i e w p o i n t a s t o o n a r r o w a n d t h e a s s u m p tio n as u n t e n a b le . S p e e d o f r e a d i n g is n o t a n a c c e p t a b l e c r i t e r i o n o f r e a d a b i l i t y i n t h e a b s e n c e o f a d d i t i o n a l e v i d e n c e , a n d a t b e s t i t is a n i n s e n s i t i v e c r i t e r i o n w h i c h h a s v a r i o u s l i m i t a t i o n s . M a t t h e w
L u c k ie s h a n d F r a n k K . M o s s, R e a d in g as a V is u a l T a s k , 1 9 4 4 .
h a v e re ally o c c u rre d w o u ld b e difficu lt to d e te rm in e fro m ro e n tg e n o g ra m s ta k e n in a h a p h a z a r d w ay. T e c h n ic s t h a t m ak e possible th e ta k in g o f c o m p a ra b le ro e n t g en o g ram s a t d iffe re n t tim es a re n ec es sary. I t is c o n c lu d e d , o n th e basis o f th e in v estigations re p o rte d in th is p a p e r, th a t th e m e th o d o f c o m p a ra b le ro e n tg e n o g r a p h y discussed gives a g o o d ro e n tg e n o g ra p h ic p ic tu re o f th e a n a to m ic fe a tu re s
a n d a fa irly g o o d re p re s e n ta tio n o f th e re la tio n o f th e c o n d y le a n d th e fossa. I t sh o u ld b e em p h a siz e d t h a t ro e n tg e n o g ra m s ta k e n a c c o rd in g to several d iffe re n t tech n ic s a re necessary to th e d e te c tio n of disorders o f th e te m p o ro m a n d ib u la r jo in t a n d a re effective in this re g a rd . T h e m e th o d p re s e n te d w ill b e fo u n d u sefu l in p ro v id in g n e w d a t a a n d fa c ilita tin g th e d iffe re n tia l diag n o sis o f d iso rd ers of th e te m p o ro m a n d ib u la r jo in t.
B le a c h in g o f th e d is c o lo r e d p u lp le s s to o th
H y m a n H . P e a r s o n , D .D .S ., M o n tr e a l, Q u e b e c , C a n a d a
B y u tiliz in g p re s e n t d a y co n c ep ts o f b io lo gical a n d h isto lo g ica l fa c to rs, th e d e n tist c a n av o id th e n e e d fo r d e stro y in g a n d artific ia lly re p la c in g to o th tissu e as a m e a n s o f c o rre c tin g esthetics. T h e dis c o lo red pulp less to o th m a y b e re sto re d to n o rm a l fu n c tio n a n d esth etics b y e n d o d o n tic tre a tm e n t to re m o v e th e cause o f d isc o lo ra tio n a n d by b le a c h in g to re m o v e th e a b e rra n t p ig m en ts. V a rio u s tech n ics h a v e b e e n e m p lo y ed o v er th e years fo r b le a c h in g th e d isco lo red p u lp less to o th , b u t, b ec au se o f th e la c k o f p e rm a n e n c e o f th e re sto re d color, b le a c h in g w as d is c a rd e d as a n a c c e p ta b le p ro c e d u re . T h e fa u lt lay n o t w ith th e ag e n ts b u t w ith th e m a n n e r o f th e ir a p p lic a tio n . D e n ta l lite ra tu re re c o rd s m a n y te c h nics, som e u se d as f a r b a c k as th e last ce n tu ry . I n 1895, G a rre ts o n 1 re p o rte d th e u se o f ch lo rid e as a b le a c h in g a g e n t b e cau se h e says, “ I t is a d ec o m p o se r o f o rg a n ic su b stan ces . . . t h a t c o n ta in th e d isco lo red elem e n ts.” B uck ley ,2 B u rc h a rd 3 a n d Jo h n s to n 4 in 1912 a n d H e rm a n P rin z 5 in 1917 re p o rte d v ario u s tech n ic s
fo r th e b le a c h in g o f th e d isco lo red to o th . H a ro ld M a x m e n 6 o f D e tr o it g av e a m o st c o m p le te re p o rt in 1949 o n to o th d is c o lo ra tio n , th e v a rio u s causes a n d th e chem istry . “ N a tu r a l T o o th C o lo r, I ts P ro d u c tio n , G e ria tric and T r a u m a tic C h a n g e s” w o u ld b e a m o st in te re stin g su b je c t fo r in v estig atio n a n d stu d y a n d fo r a c o m p le te trea tise . B ecau se o f th e to p ic ’s m a n y ra m ificatio n s, th e s u b je c t o f th e p re se n t p a p e r w ill be lim ite d to a discussion o f th e
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PEA RSO N . . . V O L U M E 56, J A N U A RY 1958 • 65
b le a c h in g o f th e to o th , w ith p u lp in v o lv e m e n t, t h a t h a s b e c o m e discolored. S in ce th e e a rly 1920’s, I h a v e b een e n c o u ra g e d by m y p a tie n ts a n d s tim u la te d by a d esire to re sto re esth etics w ith th e least a m o u n t o f tissue d e s tru c tio n to ex p e rim e n t w ith som e of th ese technics. M o st o f th e d isco lo red te e th so tre a te d w e re b ro u g h t b a c k to n o rm a l success fully, b u t, a f te r a tim e , a sec o n d a ry d is c o lo ra tio n to o k p la c e t h a t c a n c e le d th e o rig in a l c o rre c tio n . I t th e n b e c a m e m y p ra c tic e to b le a c h o n ly th o se disco lo red te e th t h a t w e re to b e co v e re d e v e n tu a lly w ith p o rc e la in ja c k e t crow ns. T h is w as c o n sid e re d ad v isa b le in o r d e r to c o n tro l th e co lo r o f th e fin ish ed re s to ra tio n , p a r tic u la rly in th e re g io n o f th e g in g iv al th ir d w h e re th e p o rc e la in is th e th in n e s t a n d m o st tra n s lu c e n t. I n 1941, o n e p a tie n t w h o h a d b e e n so tre a te d r e tu r n e d fo r th e re p la c e m e n t o f a f r a c tu r e d ja c k e t cro w n . A stu d y o f th e p a tie n t’s re c o rd s disclosed t h a t th is to o th h a d b e e n b le a c h e d b e fo re th e re sto ra tio n w as m a d e , a n d , o n e x a m in a tio n , it w as fo u n d t h a t th e to o th h a d re ta in e d its re sto re d co lo r a f te r b e in g co v ered f o r a p e rio d o f e ig h t years. I w as c o n v in c e d t h a t th e so u rce o f th e d isc o lo ra tio n h a d b e e n e lim in a te d b y e n d o d o n tic tre a tm e n t, t h a t th e a b e rra n t p ig m en ts h a d b e e n re m o v e d b y b le a c h in g a n d t h a t th e p o rta ls o f e n try in to th e d e n tin h a d b e e n h e rm e tic a lly sealed. I t w as c o n c lu d e d t h a t th e e n a m e l m u s t be p e rm e a b le to th e o ra l fluids a n d t h a t th e a p p e a ra n c e o f a se c o n d a ry d isco lo ratio n w as th e re s u lt o f p ig m e n tin g su bstances c o n ta in e d in th is fluid. O n in v e stig a tin g f u r th e r, it w as d is co v ered t h a t th is se c o n d a ry d isc o lo ra tio n to o k p la c e a n y tim e b e tw e e n 3 a n d 12 m o n th s a f te r b le a c h in g , d e p e n d in g o n th e ag e o f th e p a tie n t a n d th e c o n d itio n of th e e n a m e l. I t w as also d isco v ered th a t, irre sp ectiv e o f w h e th e r th e p rim a ry a b e r r a n t p ig m e n ta tio n w as p u rp le , o ra n g e , b ro w n , yellow , b lu e, g ra y o r g re e n o r an y c o m b in a tio n o f th ese, th e se c o n d a ry d is
c o lo ra tio n w as alw ays a b lu ish g ra y a n d w as m o st p ro n o u n c e d in th e re g io n o f th e g in g iv al th ird , th e lo c atio n o f th e th in n est e n a m e l.7 D ISC U SSIO N
T h e c o n te n ts o f th e in te rp ris m a tic spaces in e n a m e l a n d th e d e n tin a l tu b u le s is of o rg a n ic c o m p o sitio n a n d ac ts as so m a n y w icks. T h e su b stan c e c o n ta in e d in th e d e n tin a l tu b u le s ca rries p ig m e n tin g fluid fro m th e d ec o m p o sin g p u lp ; w h e reas t h a t c o n ta in e d in th e in te rp ris m a tic spaces o f th e e n a m e l c a rries p ig m e n tin g o ra l fluids. A t th e d e n tin o e n a m e l ju n c tio n , th e d e n tin a l tu b u le s sen d o u t a m ass of b ra n c h e s , fo rm in g a lay er t h a t is alm o st en tire ly o rg a n ic . I t is h e re t h a t th e g re a t est in te n sity o f d isc o lo ra tio n m a y b e o b served. O n re -e x a m in in g th e te c h n ic , it w as d e d u c e d t h a t th e d e n tin lin in g th e p u lp c h a m b e r a n d cavities w as satisfacto rily sealed a n d re m a in e d so b u t t h a t it w as th e e n a m e l t h a t c o n ta in e d th e seco n d ary d isco lo ratio n . T h e re fo re , it w as c o n c lu d e d t h a t n o t on ly is e n a m e l p e rm e a b le b u t th is p e rm e a b ility is a c c e n tu a te d by th e b le a c h in g process. T h e sec o n d ary a b e r r a n t p ig m e n ts c a n co m e fro m n o o th e r so u rce th a n th e o ra l fluids. T h is th e o ry o f th e p e rm e a b ility o f e n a m e l w as c o n firm e d re ce n tly by S o g n n aes,8 w h o sa id : R a d io a c tiv e tr a c e r
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T Y P E O F B L E A C H IN G A G E N T
A successful b le a c h in g a g e n t m u s t be in a so lu tio n t h a t h a s th e ab ility to p e n e tra te th e o rg a n ic m a tte r in th e d e n tin a l tu b u le s a n d th e e n a m e l in te rp ris m a tic spaces w ith o u t d e stro y in g th e m a trix o f th e cro w n . I t m u s t b e o f a self-lim itin g n a tu r e a n d le a v e n o re sid u a l effects. A fte r th e p u lp is d estro y e d , a m o n g th e fu n c tio n s t h a t re m a in fo r th e o rg a n ic m a te ria l in th e h a r d tissues a re its a c tio n as a b in d e r o f th e m a trix a n d its ab ility to tra n s m it lig h t fo r co lo r c o n tro l. T h ese fu n c tio n s o f th e o rg a n ic b o d y a re d e stro y ed by th e c h e m ic a l a c tio n o f th e b le a c h in g pro cess a n d s h o u ld b e re sto red. A m a te ria l m u s t b e su b stitu te d t h a t w o u ld a c t as a b in d e r, re sto re th e tra n slu c e n c y a n d , a t th e sam e tim e , a c t as a se a le r o f th e v o id e d d e n tin a l tu b u le s a n d th e in te rp ris m a tic sp aces o f th e e n am e l. I t m u s t b e a liq u id o f low su rfa c e ten sio n t h a t w o u ld easily p e n e tr a te th e m icroscopic spaces a n d h a v e th e a b ility to b e c o n v e rte d in to a n in e rt, in so lu b le m ass.
T H E B L E A C H IN G T E C H N IC
T h e b le a c h in g o f a p u lp less to o th sh o u ld b e u n d e r ta k e n only a f te r th e h e a lth of th e ro o t a n d p e ria p ic a l tissues h as b een re sto red a n d th e c a n a l h a s b e e n h e rm e ti cally sealed. 1. T h e to o th is th o ro u g h ly scaled a n d polished. 2. A c o a tin g o f p e tro le u m jelly is a p p lie d to th e la b ia l a n d lin g u a l ging iv al tissue in v e stin g th e d isco lo red to o th a n d its tw o a p p ro x im a tin g te e th , u n d e r th e fre e g in g iv al m a rg in s a n d in th e in te rp ro x im a l spaces. 3. T h e r u b b e r d a m is p u n c h e d w ith th e sm allest h o le possible a n d is ap p lie d a n d h e ld in p la c e b y m e a n s o f a d o u b le w in d in g o f d e n ta l floss, d o u b le k n o tte d u n d e r th e g in g iv a, as fa r as it w ill go in to
th e g in g iv al crev ice w ith o u t cau sin g tra u m a . 4. A ll fillin g m a te r ia l a n d d ecay are re m o v e d , as w ell as th e c o n te n ts of th e p u lp c h a m b e r. T h e c a n a l is v o id e d o f its c o n te n ts to a d e p th o f 3 m m . a p ica lly to th e g in g iv al level. 5. A ll th e exp o sed to o th tissue is w a sh ed w ith c h lo rin a te d so d a solution, som e o f w h ich is allo w e d to re m a in in th e cavities fo r a b o u t o n e m in u te a n d th e n w a sh e d a w ay w ith w a rm distilled w a te r, a n d th e to o th is d rie d . C a re sh o u ld be ta k e n to w a sh a w ay a ll vestiges o f th e p e tro le u m jelly fro m th e su rfa ce o f th e to o th . A m ix tu re o f o n e p a r t eth y l a lco h o l, 95 p e r c e n t by v o lu m e , a n d tw o p a rts ch lo ro fo rm , ch e m ic ally p u re , is u sed to d e sicc ate all th e exp o sed e n a m e l a n d d e n tin . T h is is allo w e d to re m a in in th e cav ities fo r tw o m in u te s a n d is a sp ira te d u sin g a “ sea le d to th e to o th ” a s p ira to r tip . 6. A n e th e r-p e ro x id e m ix tu re (P y ro zo n e ) is u se d as th e b le a c h in g a g e n t. A p e lle t o f c o tto n is p la c e d in th e p u lp c h a m b e r a n d th e c a v ity a n d is s a tu ra te d w ith th e e th e r-p e ro x id e m ix tu re b y m ean s o f a c u rv e d glass d ro p p e r. T h e solu tio n is th e n fo rce d in to th e d e n tin b y u sin g a p u m p w h ic h is co m p o sed o f a so ft-ru b b er p o lish in g c u p m o u n te d o n a p o rte -p o lisher. T h e c o tto n m a y b e s a tu ra te d several tim es, a n d th e p u m p in g m a y b e re p e a te d w ith th e rim o f th e c u p re stin g o n th e e n a m e l b ey o n d th e ca v ity m arg in s. 7. T h e to o th is co v ered w ith a strip o f m u slin o r c o tto n d e n ta l n a p k in c u t to fit th e e n tire la b ia l a n d lin g u a l surfaces, a n d th e ta il e n d is tu c k e d in to th e ca v ity to m e e t th e c o tto n p e lle t t h a t w as p la c e d in th e p u lp c h a m b e r. T h e m u slin a n d th e c o tto n p e lle t a re s a tu ra te d w ith th e e th e r-p e ro x id e m ix tu re , w ith th e m u slin a c tin g as a w ick. 8. T h e p a tie n t’s fa ce is c o v e red w ith a w e t tow el fo r p ro te c tio n fro m th e rays o f th e b le a c h in g la m p , a no. 2 p h o to flo o d la m p , w h ic h is h e ld a b o u t 20 in ch es fro m th e to o th . T h e c o tto n is re p e a te d ly r e
PEA RSO N . . . V O L U M E 56. J A N U A RY 1958 • 67
p le n ish e d w ith th e e th e r-p e ro x id e m ix tu r e a b o u t ev ery five m in u te s o r as it e v a p o ra te s. T h is pro cess u su ally tak es a b o u t 20 m in u te s. 9. T h e m u slin strip a n d th e re m a in in g p e lle t o f c o tto n a re re m o v e d , a n d th e cav ities a r e d rie d b y a b la st o f w a rm a ir. A d re ssin g o f 30 p e r c e n t h y d ro g e n p e r o x id e in w a te r is p la c e d in th e p u lp c h a m b e r, a n d a ll cav ities a re sealed w ith a w h ite o x y p h o sp h a te o f zin c ce m e n t. T h e oxygen fro m th e d re ssin g w ill a tte m p t to fo rce its w a y th ro u g h th e s e ttin g ce m e n t a n d w ill cause a leak y fillin g unless th e c e m e n t is co v e red im m e d ia te ly w ith a p ie c e o f ru b b e r d a m o r a p la stic s trip h e ld in p la c e b y fin g er p re ssu re u n til th e c e m e n t is set. A fte r th e c e m e n t sets a n d ju s t b e fo re th e rubbfer d a m is re m o v e d , th e to o th is g iv en a fresh c o a t o f p e tr o le u m je lly to seal th e e n a m e l te m p o ra rily . T h e n th e first tr e a tm e n t is c o m p le te d . T h r e e day s sh o u ld elap se b e fo re th e seco n d tre a tm e n t. 10. A t th e second o r su b se q u e n t sit tings, th e ru b b e r d a m is a p p lie d as d e scrib e d previo usly. T h e to o th is c lea n sed o f p e tro le u m jelly a n d o th e r depo sits by u sin g p ro p h y la c tic p o lish in g p a s te ; th e n it is w a sh e d a n d d e sicc a te d w ith th e a lco h o l-c h lo ro fo rm m ix tu re . T h e fillin g m a te r ia l is re m o v e d , a n d th e b le a c h in g process is re p e a te d u n til th e to o th b e com es p e rc e p tib ly lig h te r in co lo r th a n is re q u ire d . A t th e la s t sittin g , th e r u b b e r d a m m u s t n o t b e re m o v ed u n til a ll th e d e n tin a n d e n a m e l su rfaces a r e h e r m e ti cally sea le d , as fo llo w s: 11. A ll th e exposed e n a m e l a n d d e n tin o n th e la b ia l a n d lin g u a l su rfaces a n d th e w alls o f th e cavities a n d p u lp c h a m b e r a re p a in te d w ith a self-c u rin g ac ry lic re sin m o n o m e r; a c a m e P s-h air b ru s h is used fo r th is p u rp o se . S ev eral co ats a re a p p lie d , e a c h a f te r th e la s t h a s b e e n ab so rb ed . T h e to o th is ex posed to th e p h o to flo o d la m p fo r five m in u tes. T h e la m p is tu r n e d off, a n d th e b ru s h te c h n ic is u se d in fillin g th e c a n a l a n d p u lp c h a m b e r w ith a lig h t sh a d e o f self-cu rin g
filling acry lic resin. T h e to o th is ex poséd to th e p h o to flo o d la m p a g a in fo r e ig h t m in u te s to co m p le te p o ly m e riz a tio n o f th e ac ry lic re sin m o n o m e r as w ell as of th e fillin g p ro p e r. 12. R e te n tio n p o in ts a re p re p a re d in all th e cavities, w h ic h th e n a re filled w ith a sy n th etic p o rc e lain . R A T IO N A L E O F T E C H N I C
T h e p e tro le u m jelly is u sed o n th e soft tissue to p re v e n t an y a c tio n o f th e e th e rp e ro x id e m ix tu re , w h ic h m ig h t leak in a d v e rte n tly u n d e r th e ru b b e r d a m . T h is so lu tio n w ill n o t d estro y th e tissue, b u t it w ill leav e a p a in fu l a re a . P e tro le u m jelly is a p p lie d to th e e n a m e l b efo re th e r e m o v a l o f th e r u b b e r d a m a t th e first b le a c h in g s ittin g in o rd e r to seal th e e n a m e l su rfa ce tem p o ra rily . T h is is n e c essary b ecau se o f th e solv en t q u a lity of th e e th e r-p e ro x id e m ix tu re . T h e a lc o h o l-c h lo ro fo rm m ix tu re is a so lv en t a n d desicc ato r. T h e se q u alities a re re q u ire d fo r p rim a ry c lea n sin g a n d d ry in g . T h e s o ft-ru b b e r p o lish in g c u p in th e p o rte -p o lis h e r is u sed as a p u m p in ste a d o f u n v u lc a n iz e d r u b b e r a n d a n o ra n g e w o o d stick in sid e th e cavity, as orig in ally p re sc rib e d in th e e a rlie r technics. T h e l a tte r is a d a n g e ro u s p ro c e d u re a n d m ay re s u lt in fr a c tu rin g o f th e crow n. A n e x c elle n t p u m p in g a c tio n c a n be d e v e lo p ed w ith th e rim o f th e c u p re stin g o n th e su rfa c e b ey o n d th e m a rg in s o f th e cavity. P y ro zo n e is th e so lu tio n used. I t c o n ta in s 25 p e r c e n t h y d ro g e n p e ro x id e in 75 p e r c e n t e th e r. T h e e th e r dissolves th e o rg a n ic m a tte r t h a t h o ld s th e a b e rra n t p ig m e n ts in th e d e n tin a l tu b u les a n d in th e in te rp ris m a tic spaces in th e en a m el. Besides b e in g a so lvent, th e e th e r p e n e tra te s th e se spaces, c a rry in g w ith i t th e p e ro x id e t h a t bleach es th e p ig m en ts. T h e e th e r ra p id ly ev a p o rate s, le a v in g n o m o is tu re in th e spaces. I t is th e a c tin ic rays o f th e p h o to flo o d lig h t t h a t a c tiv a te th e oxygen to sy n th e
68 • T H E J O U RN A L O F T H E A M E R I C A N DEN T A L A SSO C I A T I O N
size th e p ig m en ts, c h a n g e th e m ch e m ic ally in to colorless su b stan ces a n d ca u se th e m to be destroyed. T h e h e a t ac tiv a te s th e solvent q u alitie s o f th e e th e r. H e a t w ith o u t lig h t is in a d e q u a te . T h e v o id e d d e n tin a l tu b u le s a n d in te rp rism a tic spaces re q u ire re fillin g w ith a n in e rt, tra n s lu c e n t su b sta n ce in o rd e r to re sto re th e o rig in al q u alitie s o f lig h t r e fra c tio n a n d a t th e sam e tim e e lim in a te th e spaces th a t m a y in v ite a sec o n d ary d isco lo ratio n . I n m o st o f th e te ch n ic s p re v io u sly r e p o rte d ,2'6 th e use of a c o n c e n tra te d so lu tio n o f c h lo ra l h y d ra te as a sea ler o f th e d e n tin a l tu b u le s w as suggested . N o m e n tio n h a s b e e n m a d e of th e n e e d f o r a sealer o f e n a m e l. A n 80 p e r c e n t so lu tio n o f ch lo ra l h y d ra te is a h eav y , sy ru p y fluid w ith h ig h su rfa c e tension. I t w ill n o t p e n e tr a te th e tu b u le s, a n d it is of n o v a lu e as a se a le r o f e n a m e l since it is w a te r soluble a n d w o u ld b e re p la c e d by th e o ra l fluids c o n ta in in g p ig m e n tin g su b stances. T h e self-cu rin g ac ry lic re sin m o n o m e r w as fo u n d to be a n id e a l p re p a ra tio n w ith th e n ecessary q u a litie s to fill th e n e e d fo r sea lin g th e en a m e l. I t is colorless a n d tra n s lu c e n t a n d h a s ex tre m ely low s u r
fa ce ten sio n , a n d , w h e n p o ly m erize d , it becom es a n in soluble , in e r t sealer. T h e acry lic resin m o n o m e r s h o u ld b e k e p t a t a te m p e ra tu re b elo w 5 0 ° F . u n til re a d y to use a n d sh o u ld n o t b e a p p lie d w h e n th e p h o to flo o d la m p is lit. SU M M A RY
B leac h in g o f th e d isco lo red p u lp less to o th m ay be successfully p e rfo rm e d . T h e sec o n d ary d isco lo ra tio n w h ic h m a y a p p e a r a f te r a successful p rim a ry b le ac h in g h as b e e n show n to b e c a u se d b y th e p ig m e n tin g su bstances c o n ta in e d in th e o ra l fluids. B ecause e n a m e l is p e rm e a b le a n d this p e rm e a b ility is a c c e n tu a te d by th e b le a c h in g chem icals, it ab sorbs th ese su b stances th u s c h a n g in g th e color. T h e b le a c h in g te c h n ic t h a t h as b een p re s e n te d in th is p a p e r elim in a te s c e rta in causes o f fa ilu re e x p e rie n ce d in th e p ast. T h e n o rm a l color o f th e d isco lo red p u lp less to o th c a n b e re sto re d a n d re ta in e d . T h e seco n d ary d isco lo ra tio n t h a t a p p e a rs a f te r a successful first b le a c h in g is d u e to th e p e rm e a b ility o f th e en a m e l. T h is m ay b e p re v e n te d by h e rm e tic a lly sea lin g th e e n a m e l as w ell as th e d e n tin . 5 0 0 B ir k s B u i l d i n g
R e a d in g E ffic ie n c y
• I n t h e m o d e r n w o r l d t h e e f f i c i e n c y o f a w o r k e r is c o m m o n l y m e a s u r e d b y t h e o u t p u t o f w o r k i n a g i v e n p e r i o d o f t i m e . A s s u m i n g t h a t t h e w o r k is s a t i s f a c t o r y in q u a l i t y , t h is is a s a t i s f a c t o r y d e f i n i t i o n o f e f f i c i e n c y f o r o r d i n a r y e c o n o m i c p u r p o s e s . H o w e v e r , w h e n e a s e o f s e e i n g is i m p o r t a n t , a s i t is i n a l l p r o l o n g e d ta s k s o f c r i t i c a l s e e i n g , t h e o v e r - a l l e ffic ie n c y o f th e w o r k e r h a s b e e n ig n o r e d , o w in g t o a g ro ss la c k o f th o u g h t a n d k n o w le d g e p e r ta in in g t o e a s e o f s e e in g . A p p l y i n g t h e s a m e l o g i c t o t h e t a s k o f r e a d i n g , i t is s e l f - e v i d e n t t h a t t h e r a t e o f r e a d i n g is n o t a p r io r i a m e a s u r e o f th e r e a d e r ’ s e ffic ie n c y . N e v e r th e le s s , it h a s b e e n a s su m e d w it h o u t a d e q u a t e p r o o f , t h a t s p e e d o f r e a d i n g i n w o r d s p e r m i n u t e o r l i n e s p e r h o u r is a s u i t a b l e m e a s u r e o f r e a d a b i l i t y . M u c h e v i d e n c e is a v a i l a b l e t o c o n d e m n t h is v i e w p o i n t a s t o o n a r r o w a n d t h e a s s u m p tio n as u n t e n a b le . S p e e d o f r e a d i n g is n o t a n a c c e p t a b l e c r i t e r i o n o f r e a d a b i l i t y i n t h e a b s e n c e o f a d d i t i o n a l e v i d e n c e , a n d a t b e s t i t is a n i n s e n s i t i v e c r i t e r i o n w h i c h h a s v a r i o u s l i m i t a t i o n s . M a t t h e w
L u c k ie s h a n d F r a n k K . M o s s, R e a d in g as a V is u a l T a s k , 1 9 4 4 .