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Apical terminus location of root canal treatment proceduresMin-Kai W u, MD , M SD, PhD, a Paul R. Wessel ink, DD S, PhD, b and Richard E. Walton, DM D,MS, c Amsterdam , Th e Netherlands, and Iow a City, IowaACADEMIC CENTRE FOR DENTISTRYAMSTERDAM (ACTA)AND UNIVERSITYOF IOWA, COLLEGEOF DENTISTRY

The apical terminat ion of root canal treatment is considered an important factor in treatment success. The exactimpact of termination is somewhat uncertain; most publications on outcomes are based on retrospective findings. After vital

pulpectomy, the best success rate has been reported when the procedures terminated 2 to 3 mm short of the radiographicapex. With pulpal necrosis, bacteria and their byproducts, as wel l as infected dentinal debris may remain in the most apicalportion of the canal; these irritants may jeopardize apical healing. In these cases, better success was achieved when the proce-dures terminated at or wit hin 2 mm of the radiographic apex (O to 2 mm). When the therapeutic procedures were shorter than2 mm from or past the radiographic apex, the success rate for infected canals was approximately 20 % lower than that whenthe procedures terminated at 0 to 2 mm. Clinical determination of apical canal anatomy is difficult. An apical constriction isoften absent. Based on biologic and clinica l principles, instrumentation and obturation should not extend beyond the apicalforamen. (Oral Surg Oral Med O ral Pathol Oral R adiol Endod 2000;89:99-103)

Canal ins t rumenta t ion inc ludes bo th c lean ing and

shaping. Cleanin g is the significant reduction of tissue aswell as micro-organisms and their by-products from thepulp system. With a vi tal pulp, micro-organisms wouldnot be pres ent in the apical part o f the canal. In infectedcases, bacterial contamination m ay reach the m ost apicalpart o f the can al 1-3 and occasionally the periapex .4-8

The purpose of shaping during instrumentat ion is tocrea te a canal configura t ion su i tab le for ob tura t ion .Ideally, instrumentat ion should terminate at a sui tablelocation, which is not necessari ly the same for bothvital and infected cases. If the termination is too shortor too long, the outco me is negatively influenced.

Obturation and restoration prevent the reinfection ofthe pulp space by m icro-organisms from the oral cavity,to seal all portals of exit and to serve as a wou nd d ressingagainst which healthy t issue can oppose. Sealers aretoxic, and their irritative effects increase as the mate-rial/tissue co ntact surface area increases. 9 Because obtu-rating materials (particularly sealers) may elicit sensi-t ivity and imm une responses when in contact with vi taltissues, 10 they should r ema in in the canal to m inim izecontact surface and irritative effects. 11-14 Furthe rmore,theoretically, a small contact surface may reduce the riskof leakage as a result o f less material/canal wall interface.

aLecturer.bprofessor and Chairman, Department of Cariolog y EndodontologyPedodontology, Academic Centre for DentistryAmsterdam ACTA),Amsterdam, The Netherlands.cprofessor, Department of Endodontics, Universityof Iowa, Collegeof Dentistry, Iowa City, Iowa.Received for publication Feb 2, 1999; returned for revision Mar 16and June 15, 1999; acceptedfor publication July 10, 1999.Copyright 2000 by Mosby, Inc.1079-2104/2000/$12.00 + 0 7/151101618

On the oth er hand, the extension of the root filling should

not be too short . If the apical canal is not completelyobturated, residual bacteria may survive and multiply1;tissue fluids percolating into the canal may pro vide nutri-tive substrate. The apical 3 mm of the root canal systemhas been considered to be a critical zone in the treatmentof infected ro ot canal. 15

PROGNOSIS STUDIES

In 1994, Stabholz e t a116 sum marize d the fac torsinfluencing the success and fai lure based on a series ofmainly retrospective studies. No influence was foundfor most therapeutic factors, such as number of t reat-

ment sess ions , type of in terappoi n tment in t racanalmedicament, type of fi l l ing material , obturat ion tech-nique, etc. All studies agreed, without exception, thatthe extension of the fi l l ing material indeed influencedthe treatm ent o utcome. 16 However, the analyses werebased solely on radiographic findings, which may notcoinc ide with histo logic healing. 17-19 In additio n, noadequate stat ist ical tests were applied to invest igate thesimultaneous influence of several potential factors ontreatment outcome. 2 However, these studies togetherform a very large sample; the influence o f other factorsmay be similar in the subgroups of over-, under-, and

flush-ex tended roo t f i l l ings . Therefore , the sameconclusion reached in a l l these s tud ies i s l ike ly acorrect observation: prognosis is decreased with over-fill and with significant underfill.

ANATOMY OF THE APICAL CANALThe apical anatom y of the root canal system (Fig 1) is

important in un derstanding the principles of root canaltreatment (RCT). The tradit ional classical concept of

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100 Wu, Wesselink, and Walton ORAL SURGERY ORAL M EDICINE ORAL PATHOLOGYJanuary 2000

root canal

dentin

cementum

_ Apex

Fig 1. Concept of the apex. Distance between the 2 landmarks, the apical constriction (AC) and the apicalforam en (AF), and the true ap ex varies in each roo t considerably. The presence, location, and relationships o fthe AC to the A F is m ore theoretical than actual.

th i s anato my i s f rom Kut t ler. 21 He found that usual lyt he roo t cana l na r rowed t oward t he apex an d expandedt o fo rm t he ap i ca l fo ram en (AF ) . F u r t he r, t h e n a r rowes tpa r t o f t he cana l fo rm ed t he ap i ca l cons t r ic t i on (AC ) ,j u s t s ho r t o f t he AE However, i n ano t he r pub l i ca ti o n , 22t he " t r ad i ti ona l " s i ng le AC w as found i n l e ss t h an ha l fof the t eeth . F requent ly, the very ap ical por t ion of rootcanal was tapered or paral le l . 22 Other au thors lS , 23 hadsugge s ted that of ten no AC i s present , par t i cu lar ly wi thap i ca l pa t hos i s and roo t r e s o rp t i on .15 , 23 The c l a s s i cconcep t (F i g 1 ) i s a l s o t ha t t he AC fo rm s t he m i n o rfo ram en (o r m i no r d i am ete r )24 ; t he m o s t ap i ca l o pen i n go f t he roo t canal i s des i gna ted t he AF o r m a j o r fo ram enor g reater d iameter. 24 In real i ty, in m ore than 6 0% of thecana l s , t he AF i s no t l oca t ed a t t he apex , and t h ed i s t a n c e b e t w e e n t h e A F a n d t h e r ad i o g r a p h i c a p e xvarie s fro m 0 to 3 .0 mm.21,22, 4-27 Th e co nclu sion is thatthe c lass ic ap ical canal an atomy , as show n by Kut t ler, 21i s more conceptual than actual .

T h e A C i s c o m m o n l y a d v o c a t e d a s th e i d e a l te r m i -n a t i o n f o r R C T, b e i n g a n a t u ra l n a r r o w i n g o f t h e r o o tc a n a l a n d a l m o s t a t t h e t e r m i n a t i o n o f t h e p u l p . T h i si s s u p p o s e d l y w h e r e a n a p i c a l s to p i s f o r m e d , a g a i n s tw h i c h t h e o b t u r a t i o n m a t e r i a l s a r e p a c k e d . B e c a u s et h i s cons t r i c t i on i s u s ua l l y no t p res en t , t h e AF m ayb e a m o r e u s e f u l l a n d m a r k . T h e d i s t a n c e b e t w e e n t h eA C ( w h e n p r e s e n t ) a n d t h e A F r a n g e s f r o m 0 . 5 t o 1 . 0m m for t ee th of d i fferen t ages.21 ,22 , 24-27 W hen the A Fi s l oca t ed , t he pos i t i on o f t he AC ( i f i t ex i s ts ) can b ees t i m a t ed ; i f t he AC i s no t p res en t , t h e p repa ra t i ona n d o b t u r a t i o n w i l l u s u a l l y b e w i t h i n t h e c o n f i n e s o ft he roo t .

In fact , i t is d i ff i cu l t to locate e i the r the AC o r the AFcl in ical ly. Usual ly v i s ib le rad iographical ly i s the rootapex . A l t hough 0 .5 t o 1 m m s ho r t o f t he r ad i og raph i capex i s com m on l y u s ed a s t he t e rm i na t i on po in t , t h is i son l y an e s t i m a t e . I t is an a t t em p t t o deb r i d e and o b t u -

r a t e c l o s e t o t h e A F b u t h o p e f u l l y, n o t b e y o n d .Ob v i ous l y, th i s w i l l o f t en n o t b e t he o u t co m e .

T E R M I N AT IO N P O I N T W I T H A V ITA L P U L P

With an i r revers ib le pulp i t i s (v i ta l pu lp) , bacter ia ( i fpresent ) are usual ly l imi ted to the chamber. Ins t rume nta-t ion ap ical ly i s to remove the noninfected t i s sue and toshape the canal . For these cases , the favorable poin t tot e rm i n a t e i n s t rum en t a t i on an d t o fo rm an ap i ca l s t opappears to be 2 to 3 m m shor t of, ra ther than 0 to 2 m mfrom , the apex. 12,28 This princip le (part ial pulp ecto my )was o r i g i na l l y p rop o s ed b y Dav i s 29 in 1 9 22 . H es ugg es t ed p res e rva t i on o f v i t a l p u l p ap i ca l l y, o f t enreferred to as the ap ical pu lp s tump. F ol lowing th i s pr in-c ip le , a good success ra te was obta ined by Kerekes andTron s t ad28 and by S j rgren e t a l .12 Therefore , for v i ta lcases , the b io logic and c l in ical ev idence indicates i t i sunnecessary to t erminate the procedures c lose to the AF.

W h e n t h e a p i c a l p u l p s t u m p r e m a i n s , e x t ru s i o n o fi r r i t a t ing f i l l ing mater ia l s in to the per i rad icu lar t i s suesm ay b e p reven t ed , t he reb y f av o r i ng ap i ca l h ea l i ng . 14Ap paren t l y, t h e r eac t i o n o f t h e p u l p s t um p t o t h e f i l li n gm at e r i a l s w i l l n o t n eg a t i v e l y i n f l uen ce t he hea l t h o fp e r i ap i ca l t i s s u es . Th e con cep t t h a t t he ap i ca l pe r i -o d o n t i u m s hou l d n o t b e ch a l l enged wi t h t h e ex t ru s i ono f ro o t cana l f i l l i n g m a t e r i a l s b eyo n d t he end o f t hecana l i s s uppo r t ed b y m an y au t ho r s. 30

T E R M I N AT IO N P O I N T F O R I N F E C T ED

C A N A L S

I n f e c t e d c a n a l s l i k e l y d i f f e r f r o m t e e t h w i t h v i t a lpu l p s . In add i t i o n t o r em o va l o f n ec ro t i c t i s s ue andd e b r i s , a n i m p o r t a n t g o a l i s t o r e d u c e o r e l i m i n a t eb a c t e r i a . B e c a u s e i t i s u n k n o w n h o w m a n y b a c t e r i arem a i n i n g i n t he ap i ca l p o r t i o n o f t h e ro o t can a l canb e m a n a g e d b y h o s t d e f e n s e s, i n s t r u m e n t a t io n l e n g t hs hou l d p re s um ab l y n o t be s ho r t e r t han t h e ap i ca l lev e l

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ORAL SURGERY ORAL MED ICINE O RAL PATHOLOGY Wu, Wesselink, an d Walton 10 1Volume 89 , Number 1

A

" -: . " d e n t i n~ ' .{ d e b r i s

I I I

Fig 2. Recapitulation to the working length with a small file. A, Dentin deb ris ma y shorten the working lengthand plug the canal a t and beyon d the working length. B, Recapitulation with a small file will aid in maintaining

the full working length; the canal beyo nd the working length m ay still be plug ged by debris.

o f bac t e r ia . B ac t e r i a m ay r em ai n s ea l ed i n t h e ro o t -f i ll e d c a n a ls o f m a n y r a d i o g r a p h i c a l l y s u c c e s sf u lcas es . 31 As l ong as t he re i s no p a t hw ay o f bac t e r i a o rb a c t e r i a l b y - p r o d u c t s t o t h e p e r i a p e x , a p e r i a p i c a lr e s pon s e wi l l no t deve l op . I f an av enue i s l a t e r e s tab -l i s hed , a nu t r i t i ona l ( s ubs t r a t e ) s upp l y wi l l dev e l op ,b a c t e r i a w i l l p r o l if e r a t e a n d a n i n f l a m m a t o r y r e a c t io nm a y e n s u e.

C ana l s w i t h nec ro t i c pu l p t i s s ue wi t h o r w i t h ou t p e r i -rad icu lar pathos i s are t reated as infected canals . % Ana p p r o a c h i s t o e v a l u a t e t h e c o r r e l a t i o n b e t w e e n t h et e r m i n a t i o n p o i n t a n d t h e s u c c e s s r a t e o f i n f e c t e dcana l s by u s i ng t he da t a f rom on l y t hos e cas es w i t hp re t r ea t m en t r ad i o l ucenc i es . Thes e a re l i ke l y t he cas eswi th in fected canals32; the chan ge in s ize of the l es ionaf ter t reatment i s assessed rad iographical ly. A def in i tec o r r e l a t i o n b e t w e e n t h e r a d i o g r a p h i c a n d h i s t o l o g i cf i nd i ngs has been r epo r t ed fo r t he t ee th w i t h p re t r ea t-me nt ap ical rad io lu cencies only. 33 Imp ortan t ly , a too thwi t h no ap i ca l r ad i o l ucency be fo re t r ea t m en t m a y ac t u -a l l y have an ap i ca l pa t hos i s t ha t i s no t r ad i og raph i ca l l yv i s ib l e . 34 There fo re , i n fo rm a t i on abou t t h e chan ge i nl e s ion s i ze a f t e r t he t r ea t m en t m a y no t be p rov i d e d byt he r ad i og raphs i f t he l e s i on r em ai ns i nv i s i b le . P e rh ap st h i s i s why no de f i n i t e co r re l a t i on be t ween t h e r ad i -og raph i c and h i s t o l og i ca l f i nd i ngs cou l d b e fo und fo rthe teeth wi tho ut pre t re atm ent ap ical rad io lucen cies . 33

The bes t s ucces s fo r t r ea t m en t o f t ee t h w i t h nec ro t i cpu l p s has been r eco rded when R C T was t e rm i n a t ed a to r w i t h in 2 m m o f the r ad i og raph i c apex (0 t o 2 m m ) fo rinfected canals wi th v i s ib le ap ical pathos i s . However,s t a t i s t i ca l l y s i gn i f i can t l y l ower s ucces s was r eco rded

wh en t r ea t m en t te rm i na t ed s h o r t o f 2 m m f rom , o r wasbeyo nd the rad iograph ic apex . 12,28,35 W hen proced ureswere m ore t han 2 m m s h o r t o f t h e apex , a s i g n i f i can treduct ion in success ra te was recorded . 12 ,26 An in ter-preta t ion i s that the ap ical canal may harbor a cr i t i ca lcoun t o f m i c roo rg an i s m s t h a t wou l d m a i n t a i n pe ri r ad i c-u lar inf lammat ion . Thus , ins t rumentat ion i s preferred toa l evel deep enough to remove or a t l eas t s igni f icant ly

redu ce t h es e m i c ro o rgan i s m s .Du r i n g i n s t rum en t a t i on , den t i n a l deb r i s , wh i ch m ayb e i n f e c t e d , i s p r o d u c e d a n d m a y r e m a i n w i t h i n t h eapical can al or in the per iap ical t i s sues . 1 In the canal ,t h i s d e b r i s m a y r e d u c e t h e w o r k i n g l e n g t h a n d m a yhin der repair. 36,37 In a s tudy 37 of perir adicu lar biop sies,e x t r u d e d d e n t i n d e b r i s o r o t h e r m a t e r i a l s o f t e n w a sa s s o c i a t e d w i t h s u r r o u n d i n g i n f l a m m a t i o n . T h e s edeb r i s o r m a t e r i a ls were r e l a t ed t o a h i s to ry o f R C T o ra p i c o e c t 0 m y. W h y d e n t i n c h i p s c a u s e p e r i r a d i c u l a ri n f l a m m a t i o n36,37 shou ld be fu rthe r s tudied. R ecap itu-l a t i o n t o t h e w o r k i n g l e n g t h o n l y m a y m a i n t a i n t h e

wo rk i ng l eng t h b u t no t r em o v e t h e d en ti n a l deb r i s t ha th ave p l u gged t h e cana l b eyo n d t he work i ng l en g t h (F i g2 ) . I t p re s u m ab l y wou l d be p re fe rab l e t o p rev en t p l ug -g ing o f dent inal debr i s in the ap ical por t ion of the canal ,a l though i t i s unknown whether th i s debr i s ( infected oruninfected) cons t i tu tes a s igni f icant i r r i t an t .

Wi t h t he u s e o f i n s t rum en t a t i on , t ech n i q u es t ha tinvolved a ro ta t ional mo t ion , such as the balance d force ,Cana l M as ter U , Lightsp eed and P roFi le t echniques 38,39an d f r equen t i r r i g a t i o n i n s u ff i c i en t l y en l a rg ed ap i ca lcan a l s 4 hav e b een fo u nd t o b e e f f i c i en t i n r educ i n gaccum ulated dent inal debr i s in the ap ical canal .

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I0 2 Wu, Wesselink, and Walton O R A L S U R G ERY O R A L M E D I C IN E O R A L PAT H O L O G YJan u ary 2 0 0 0

A n o t h e r t e c h n i q u e t o e n l a r g e a n d c l e a n t h e a p i c a lc a n a l i s " a p i c a l c l e a r i n g ? ' P a r r i s e t al ,4 1 a f t e r s t e p - b a c kf i li n g , u s e d s u c c e s s i v e l y l a r g e r fi l e s a f e w s i z e s l a r g e rt h a n t h e m a s t e r a p i c a l f i l e w i t h a r e a m i n g m o t i o n ; t h i st e c h n i q u e d i d i n d e e d e n l a r g e a n d f u r t h e r d e b r i d e t h ea p i c a l c a n a l w i t h l e s s d e b r i s a c c u m u l a t i o n .

O n e s u g g e s t e d a p p r o a c h t o s o l v e th e p r o b l e m i s th e" a p i c a l p a t e n c y " c o n c e p t . T h i s i s u s i n g a v e r y s m a l l s i z ef i l e ( 1 0 o r 1 5 ) t o 1 m m l o n g e r t h a n t h e f i n a l w o r k i n gl e n g t h i n a n a t t e m p t t o r e m o v e t h e d e n t i n a l d e b r i s f r o mt h e v e r y a p i c a l p o r t i o n o f t h e c a n a l . T h i s c o n c e p t i st a u g h t i n 5 0 % o f t h e U n i t e d S t a t e s d e n t a l s c h o o l s . 4 2

H o w e v e r , t h e e f f i c a c y o f u s i n g a s m a l l f i l e t o r e m o v e t h ed e b r i s r e m a i n s t o b e e v a l u a t e d . C o n s i d e r i n g t h e a p i c a lc a n a l a n a t o m y, t h i s a p p r o a c h s e e m s u n r e a s o n a b l e . I f th ep a t e n c y f i l e e x t e n d s t o t h e r a d i o g r a p h i c a p e x , 43 u s u a l l yt h e i n s tr u m e n t w i l l g o b e y o n d t h e A F b e c a u s e t h e A F i su s u a l l y l o c a t e d s h o r t o f t h e a p e x . 2 1,2 2,25 -2 7 T h e f u r t h e r

t h e d e v i a t i o n o f t h e A F f r o m t h e a p e x , t h e f u r t h e r t h ei n s tr u m e n t w i l l p e n e t r a te a n d d a m a g e a p i c a l p e r i o d o n -t i u m . I n a d d i t i o n , t h e s m a l l f i le w i l l l i k e l y n o t r e m o v es i g n i f i c a n t a m o u n t s o f d e b r i s . A g a i n , t h i s a p i c a l p a t e n c yc o n c e p t r e m a i n s u n t e s t ed .

T E R M I N A T I O N P O I N T F O R R E TR E ATM E N T

W h e n p r e s e nt , t h e A C i s t h e n a r r o w e s t d i a m e t e r o ft h e b l o o d s u p p l y. A p i c a l l y , t h e c a n a l w i d e n s a n d m a yh a v e a r i c h e r b l o o d s u p p l y t h a t m a y a l l ow b e t t e ri m m u n e a c t i v i t i e s t h a n i n th e p u l p c a n a l . H o w e v e r ,b a c t e r i a m a y s o m e t i m e s p e r s i s t i n t h e c a n a l 44 a n ds u r v i v e b e y o n d t h e A C ; a s p e c u l a t i o n i s t h a t t h e s eb a c t e r i a a r e r e l a t e d t o R C T f a i l u r e s . 1 I t s e e m s t h a t i tw o u l d b e p r e f e r a b l e t o c l e a n th e c a n a l t o t h e A F i nr e t r e a t m e n t ; t h e d o w n s i d e i s t h e p o s s i b i l i t y o f o v e r i n -s t r u m e n ta t i o n, w h i c h w o u l d f o r c e m a t e r i a ls a n d d e b r i si n t o p e r i r a d i c u l a r t i s su e s .

I n o r d e r t o r e d u c e t h e i n t r o d u c t i o n o f i rr i t a n t s i n t o t h ep e r i a p e x , a s u g g e s t i o n i s t o c l e a n t h e c o r o n a l p a r t o f t h er o o t c a n a l f ir s t w i t h a s t e p - d o w n o r c r o w n - d o w ns e q u e n c e 4 5 w i t h c o p i o u s i r r i g a t i o n . H o w e v e r , i n s t r u m e n -t a t i o n e x t e n d e d b e y o n d t h e r a d i o g r a p h i c a p e x , w h i c hc e r t a i n ly w o u l d h a v e i t s a p i c a l te r m i n u s b e y o n d t h e A F,h a s b e e n f o u n d t o h i n d e r a p i c a l h e a l i n g s i g n if i ca n t ly.4648

A l t h o u g h i n s t r u m e n t a t i o n t o t h e A F i s s u g g e s t e d f o rs o m e f a i l u re c a s e s, u s u a l l y t h e a p i c a l s t o p s h o u l d b ec r e a t e d a t 1 to 2 m m s h o r t o f t h e A F t o c o n f i n e t h e i n s tr u -m e n t s , i r r i g a n t s , a n d o b t u r a n t s t o t h e c a n a l s p a c e .

S Y S T E M I C C O N S I D E R AT I O N S

C o n c e r n s h a v e r e c e n t l y b e e n r a i s e d r e l a t i v e t o t h ei m p a c t o f o r a l c o n d i t i o n s o n s y s t e m i c h e a l t h . 49 T h ei m p a c t m a y b e b y b a c t e r i a l o r i m m u n o g e n i c s e e d i n g o fd i s t a n t o r g a n s o r t i s s u e s v i a t h e v a s c u l a r ( b l o o d o rl y m p h a t i c ) s y s t em . I t h as b e e n d e m o n s t r a t e d t h a t a

b a c t e r e m i a o f t e n i s t h e r e s u l t o f o v e r i n s t ru m e n t a t i o n o ft e e t h w i t h n e c r o t i c , b a c t e r i a l l y c o l o n i z e d p u l ps p a c e s . 5 A l t h o u g h t h e r e i s n o d e f i n i t i v e e v i d e n c e t h a ti n t r o d u c i n g b a c t e r i a o r a n t i g e n s f r o m i n f e c t e d c a n a l si n to t h e b l o o d s t r e a m c a u s e s s y s t e m i c d i s e a se s , i t w o u l ds e e m p r u d e n t t o a v o i d t h is s i t u a t io n w h e n p o s s i b l e .

S U M M A R Y

B e c a u s e m o s t p u b l i c a t i o n s o n o u t c o m e s a r e r e t r o -s p e c t i v e , d e fi n i t iv e c o n c l u s i o n s a r e n o t p o s s i b l e . B a s e do n c u r r e n t i n f o r m a t i o n , t h e a p i c a l t e r m i n a t i o n p o i n t o fr o o t c a n a l tr e a t m e n t p r o c e d u r e s s e e m s t o b e a n i m p o r -t a n t in f l u e n c e o n t r e a t m e n t o u t c o m e s . F o r t e e t h w i t hv i t a l p u l p s , l e a v i n g a n a p i c a l p u l p s t u m p o f u p t o 3 m mi s r e c o m m e n d e d . F o r t h e in f e c t e d c a n a l s , th e l e n g t h o fr o o t c a n a l i n s t r u m e n t a t i o n s h o u l d i d e a l l y n o t b e s h o r t o ft h e l e v e l t o w h i c h b a c t e r i a h a v e c o n t a m i n a t e d ; l o c a t i n gt h e A F i s o f m o r e i m p o r t a n c e , b u t i t i s d i f fi c u l t t o

a c c o m p l i s h . T h e f i n a l l e n g t h f o r a f e w c a s e s i n w h i c hr o o t c a n a l t h e r a p y h a s f a i l e d a n d t h e f a i lu r e m a y b er e l a t e d t o i n f e c t i o n i n t h e v e r y a p i c a l p a r t o f t h e c a n a l ,i s t o t h e A F ; a d m i t t e d l y, th e e x a c t l e v e l o f t h e A F c a n n o tb e d e t e r m i n e d w i t h c e r t a i n t y.

I n c o n c l u s i o n , b a s e d o n b i o l o g i c a l p r i n c i p l e s a n de x p e r i m e n t a l e v i d e n c e , i n s t r u m e n t a t i o n o r o b t u r a t i o ns h o u l d n o t e x t e n d b e y o n d t h e a p i c a l f o r a m e n . T h e s er e c o m m e n d a t i o n s m a y c h a n g e a s a d d i t i o n a l w e l l -c o n t r o ll e d , o u t c o m e - a s s e s s m e n t s t u d ie s a r e p u b l i s h e d .

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