Apical termination of root canal

REVIEW Open Access
Apical termination of root canal
procedures—ambiguity or disambiguation?
James L. Gutmann
Abstract
The issues of working length determination, its apical extent, and the position of the final root canal filling have been
controversial, as differing points of view have existed between the biologically based and clinically based endodontic
gurus regarding this concept for decades. Coupled with the following issues, it has become somewhat of an empirical
bastion for clinicians, especially those in the limelight or who use social media to augment their clinical prowess:
(1) the variable anatomy of the root apex; (2) where to terminate canal enlarging and shaping apically; (3) status
of the accessory communications apically; (4) size of the apical preparation; (5) ability to debride the apical extent
of the root canal and remove both bacteria and biofilm; (6) response of the periapical tissues, when both vital
and necrotic, to the intracanal filling materials and techniques that may impinge on these tissues; and (7) long-term
outcomes and assessments of the procedures rendered. For purposes of succinctness, the concept of working length,
the apical position of instrument termination, and the position of the final filling will be addressed simultaneously in
this paper.
Beyond the apex—danger lurks
Cravens JE. Immediate root filling. Trans Ill State Dent
Soc—29th Annual Meeting, The Dental Review Co., HD
Justi & Son 1893;45–59.
Introduction
One could consider using a systematic review to try and
answer the controversial challenges cited in the abstract;
however, this approach would not work historically, and
from a contemporary standpoint, so very few, if any,
published studies qualify to fit into the higher levels of
the hierarchy of scientific evidence that the essential is-
sues would not be addressed (Gutmann & Solomon
2009). Therefore, a somewhat unorthodox approach to
this concept has been chosen, one in which historical re-
flection and contemporary assessment will be used to
compare and contrast philosophies that address the is-
sues of concern. The starting point will be the First
International Endodontic Conference that occurred in
Philadelphia, PA, USA, in 1953.
Review
Codification of the principles of root canal procedures
Up until the First World Conference on Endodontics
was convened by Dr. Louis I. Grossman (Fig. 1) during
the week of June 22, 1953 (Grossman 1953), multiple
treatment parameters were being used daily by clinicians
and different philosophies of treatment were being es-
poused in dental education around the world. Primarily,
teeth were being extracted as opposed to addressing the
many challenges of root canal procedures due to the
overwhelming impact of the focal infection theory, along
with the apical anatomical challenges that had been
highlighted in the first part of the 20th century.
While not a recognized specialty of dentistry globally
at that time, endodontics and the provision of root canal
procedures had been advocated routinely in some, very
limited, and visionary areas of dentistry, even with the
name of endodontia being proposed by Dr. H. B. John-
ston and accepted by the community at large, including
the American Association of Endodontists (Gutmann
2008). However, this first world conference established
some significant guidelines for clinical procedures based
on historical documentation and treatment philosophy
up to that point, both clinical and biological. It is here
that this manuscript will begin to explore the issue of
working length in an attempt to clarify all aspects of the
Correspondence: jlgh4570@aol.com
Texas A&M University Baylor College of Dentistry, Dallas, TX, USA
Evidence-Based Endodontics
© 2016 The Author(s). Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made.
Gutmann Evidence-Based Endodontics (2016) 1:4
DOI 10.1186/s41121-016-0004-8

challenges involved in apical biology in relation to a pre-
ferred termination point for root canal procedures.
What were the important outcomes of this first
conference?
While 21 principles of treatment parameters were forth-
coming, two very specific guidelines emanated from the
presentations and deliberations from a multitude of
international experts, in particular Drs. Louis I. Gross-
man, Lester B. Cahn, and Ralph Sommer from the USA,
Dr. Francisco Pucci from Uruguay, Dr. Birger Nygaard
Ostby from Norway, and Dr. George C. Hare from
Canada. These two principles were as follows:
1. Traumatic injury to the surrounding (periapical) soft
tissue should be avoided at all times. To this end,
instrument stops should be used and instruments
should be confined entirely within the root canal
(Grossman 1953).
2. “…the canal filling should seal the apical foramen,
and that if the apical millimeter or so of the canal is
filled with healthy living tissue, the root canal filling
should terminate at this level rather than at the
apical foramen” (Grossman 1953).
What was important at that time was the fact that
dentistry and endodontics were still struggling with the
vestiges of the “focal infection theory” (Grossman 1925)
that had been smoldering through various levels of con-
flagration since 1900 (Hunter 1900) but was brought to
a crescendo by William Hunter’s (Fig. 2) diatribe against
the dental profession during his classic presentation “An
Address on the Role of Sepsis and Antisepsis in Medi-
cine” that was delivered to the Faculty of Medicine of
McGill University in Montreal in 1910 and published in
1911 (Hunter 1911). Advanced further by Billings (Bil-
lings 1916) and Rosenow (Rosenow 1919), and perpetu-
ated by others at that time (Grieves 1914a; Grieves
1914b; Grieves 1920), this concept impacted greatly on
tooth retention. If tooth retention was deemed possible
in the presence of a questionable pulp or a tooth with a
periapical lesion, what treatment parameters may be
considered as both acceptable and successful? Therefore,
the issues addressed and the principles put forth from
this conference had to be carefully analyzed and bio-
logically sound. To that end, some of the following ques-
tions could be asked retrospectively:
Historically, what contributed to the thinking that
helped to solidify these principles?
What was it about the biology of the periapical
tissues and the clinical techniques at that time that
led to this definitive position?
Fig. 1 Dr. Louis Grossman—reproduced from the University of
Pennsylvania 1943. (http://www.aae.org/welcome/0207pulp.html)
Fig. 2 Dr. William Hunter—reproduced from Bremner MDK. The
Story of Dentistry, Dental Items of Interest Publishing Co., New York,
1939. Also found in Dent Cosmos 1934; 76(1):19
Gutmann Evidence-Based Endodontics (2016) 1:4 Page 2 of 22

Was this approach to managing the apical portion of
the root canal and root apex to be the same in teeth
with viable apical tissues or necrotic apical tissues
with or without the obvious presence of an apical
rarefaction?
Was the best evidence available to the individuals in
this conference? What role did apical resorption
play in these guidelines, if any?
What was known about the root apex in 1953 that
was not known in 1911 or before?
What was known about treatment outcomes in 1953
relative to current practices at that time and
previous practices that may have impacted on tooth
retention or successful outcomes?
Historical gleanings
A sense of respect for the apical constriction in the roots
and the periapical tissues during root canal procedures
already appears in the mid-1800s, when Dr. Harwood of
Boston had communicated with Chapin Harris (Fig. 3),
one of the co-founders of the first dental school, the Balti-
more College of Dental Surgery, Baltimore, MD, USA, his
considerations in the operations of cleaning the root canal
of its pulp tissue (Harris 1855).
It should be borne in mind, that at the point where
the vessels and nerves in question enter the root, the
passage is much smaller that it is immediately within.
This strait (constriction) will be easily recognized
when reached, by the touch, the instrument appearing
to be arrested by an obstacle, and not by being
wedged in a narrow passage. Care should be taken, I
think, that the instrument is not allowed to pass
through the strait, either by being too small or by
being revolved there till it cuts its way through. For,
by wounding the parts without the tooth, and forcing
particles of bone (dentin) out upon the parts external
to the roots, the danger of an unfavorable result
would be greatly increased. (Harris 1855)
Subsequently, Edmund Noyes of Chicago noted that:
…the treatment of pulps was not seriously undertaken
by the profession previous to 1865, and that after
1870 the attempts to save teeth with exposed living
pulps, or with dead pulps, became quite common
practice, the method generally employed being the
removal of the contents of the canal and placing of
from one to many treatments of creosote on cotton,
most operators leaving such a treatment as a root
filling. (Noyes 1922)
Little change in this philosophy existed until the late
1800s and the early 1900s, at which time the playing
field was identified as being far more challenging due to
studies on the root apex anatomy and apical root canal
that proliferated at that time (Fischer 1909; Preiswerk
1912; Hess 1917; Grove 1916; Noyes 1921) (Fig. 4). First,
recognizing the fact that there were significant apical
ramifications led dentists to performing many proce-
dures that only resulted in the removal of one half to
two thirds of the dental pulp (partial pulpectomy)
(Davis 1923);
It is our practice at this time to amputate large pulps
somewhere in the apical third of the root. With small
canals, as in the buccal roots of upper molars and the
mesial roots of lower molars, we have been excising at
the floor of the chamber… (Davis 1923);
leaving challenges of the unpredictable apical anatomy
to normal healing processes; or focusing on the use of
substances such as arsenic to “sterilize” the retained ap-
ical pulp tissue and kill bacteria or tannic acid to form
an albuminate of tannin, which was insoluble and pre-
vented tissue disintegration (Mills 1897):
…where we cannot (reach the apical foramen), as in
contracted or tortuous root canals, we force tannic
Fig. 3 Dr. Chapin Harris—reproduced from Prinz H. Dental
Chronology, Lea Febiger, Philadelphia, 1945

acid solution into the inaccessible pulp tissues…we
used the tannic acid solution because when brought
into contact with any remaining pulp tissues in the
root canal, it forms an albuminate of tannin; a
compound which is insoluble in any of the fluids of
the surrounding tissues, and consequently no
disintegration can take place to cause any after
trouble. (Mills 1897)
The challenging nature of the apical root anatomy was
presented most vividly by Guido Fischer in 1907 (Fig. 5)
when he started his large-scale research, with a new
method in looking at human and animal root canals,
paying special attention to their thin ramifications and
apical terminations (Fischer 2010) (Fig. 6a–c). Fisher di-
vided the different morphologic variations of the pulpal
cavity into:
Simple ramifications or branches and lateral canals
within the radicular dentin
Intercommunicating canal system
Islands of hard tissue within the canal
These differentiations were named as bifurcations and
ramifications, which created a complex system of apical
morphology. With his method, Fisher established the
accurate morphologic variations of a developing tooth,
either in physiological or pathological conditions. He de-
scribed very accurately the neoformation of dentin and
pulpstones within the root canals. Furthermore, by associ-
ating macroscopic and microscopic observations, he
showed how the root canal morphology is very complex
Fig. 4 a Tooth anatomy depicted by dye penetration. From the work of Oskar Keller, Anatomie der Wurzelkanäle des menschlichen Gebisses
nach dem Aufhellungsverfahren. Zürich, Buchdruckerei, Berichthaus. 1928. Keller was a protégé of b Dr. Walter Hess—reproduced by permission
of Nicola Perrini owner of the collection from Fondazione Castagnola that are found in Storia anatomica del sistema dei canali radicolari. Società
Italiana di Endodonzia, 2010
Fig. 5 Dr. Guido Fischer—reproduced by permission of Nicola
Perrini owner of the collection from Fondazione Castagnola that are
found in Storia anatomica del sistema dei canali radicolari. Società
Italiana di Endotonzia, 2010

due to the ramifications present, calling them lateral ca-
nals (Seitenkanal), and also apical ramifications called
regio ramificatoria, which is referred to presently as an ap-
ical delta. The complexity and inability to predict the
canal morphology brought him to name the whole system
as the radicular canal system (Kanalsystem).
Subsequently, there began a true appreciation for the
nature of the tissue at the end of the root, as histological
studies were able to demonstrate that the pulp tissue
ended at the dentinal-cemental junction and that there
were few if any incidences of pulp tissue going all the
way to the end of the root or to the extent of the major
foraminal opening (Grove 1916; Noyes 1921). The issue
now was the clinical management of these tissues.
According to C.J. Grove, “It should be remembered
that the apical foramen of fully developed teeth is
formed by the cementum. If the pulp tissue were present
in this portion of the canal, dentin should be formed by
the odontoblasts in the pulp tissue. I believe the fact that
this does not occur clearly indicates the erroneous char-
acter of the theory that the pulp extends through the
foramen.” (Grove 1916). It is here that this author asks
one of the most crucial questions that the present manu-
script is attempting to address: “The question now con-
fronts us, What shall be done with these tissues when
the pulp is devitalized?” (Grove 1916) (Fig. 7).
Key investigators, such as Noyes (Noyes 1922; Noyes
1921), Grieves (Grieves 1915; Grieves 1919), Blayney
(Blayney 1927; Blayney 1922; Blayney 1926; Blayney 1940;
Blayney 1932; Blayney 1936; Blayney 1929a; Blayney
1929b), Skillen (Skillen 1922), Hatton (Hatton 1922), Coo-
lidge (Coolidge 1921; Coolidge 1922), Groves (Grove
1921; Grove 1931), and Davis (Davis 1922a; Davis 1922b),
recognized these anatomical challenges, including that of
Fig. 6 Apical ramifications as described by G. Fischer: a second premolar, b first maxillary molar, c second maxillary molar. Bau und Entwicklung
der Mundhöhle des Menschen unter Berücksichtigung der vergleichenden Anatomie des Gebisses und mit Einschluβ der speziellen mikroskopischen
Technik. Leipzig; Verlag von Dr. Werner Klinhardt, 1909

cemental permeability, especially in light of the focal infec-
tion theory and still approached teeth with compromised
or necrotic pulps with the same focus, “Shall we, or shall
we not, attempt to retain the pulpless tooth? In the pres-
ence of the irrefutable dictum that the natural organ is
better than any substitute, the answer is ‘We shall.’ Noyes
said it succinctly; ‘…let us rather make it a practice to ex-
tract only such teeth as diligent, conscientious and persist-
ent effort have proven conclusively to be beyond our
present ability to put in wholesome, safe condition.’”
(Noyes 1921).
In 1929, Blayney published his results on 10 years of
making histological analyses of root ends from extract
teeth that had been root treated. He had several thou-
sand teeth in his history profile but chose to examine
histologically 250 of these teeth, some of which were ex-
tracted shortly after treatment due to a diagnosed
failure, while others had been in the mouth for a num-
ber of years (Blayney 1929b). Very early on in his study,
he realized that “it was unusual to find a root-end with
but a single apical foramen.” His conclusions strongly
suggested that:
“1)The dental pulp may be removed without causing
irreparable damage to the periapical tissues,
provided the following definite plan of operation is
carried out: a) surgically clean technic ; b) use of
only mild antiseptics, all caustics being eliminated; c)
avoidance of injury to soft tissue in the apical
foramina; d) removal of all true pulp tissue; (and) e)
filling of the canal with a bland, non-irritating,
non-absorbable filling material to near the site of
amputation.
2) Following the operation, there is begun, in the apical
region, a process of resorption that enlarges the
apical foramen, or a new channel may be cut that
more successfully meets the conditions within the
canal.
3) These resorptions may heal, with the formation of
calcified material resembling cementum.
4) Many of the apical foramina may be reduced in size
by repair calcification. But this reduction seldom
obliterates the canal. as sufficient space usually
remains for an efficient circulatory apparatus.
5) The filling material, when in contact with soft
tissues, excites a foreign-body reaction. Better results
are obtained in the cases that are slightly underfilled.”
(Blayney 1929b).
Similar findings were identified, and clinical tech-
niques to achieve these results were supported by a
multitude of individuals during that era. As early as
1922, Noyes echoed these same directives as follows;
however, he was also concerned with root fillings that
were too short (Noyes E 1922):
There is one more thing I want to say in regard to
these fillings that do not reach the ends of the canal.
It is my belief that we should in every case, wherever
we can possibly do so, get our filling to the end of the
PULP CANAL (Author’s Emphasis). In every one of
those cases in which I did not get there, you may
depend I spent an hour or more, may two or three, in
trying to get there. But the point I want to make
particularly is that we may ignore absolutely the
foramen through cementum if we can fill the pulp
canal to the end of the dentin. While you cannot fill a
minute foramen, which is as fine as a hair in some
cases, in my judgment a tooth is three or four or ten
times as safe if you fill the root to the end of the pulp
canal, leaving the fine foramen through the cementum
Fig. 7 Histological view of the root apex with root canal filling
terminating 2–3 mm from the end of the root. Note the tissue
below the root filling is periodontal in nature and the walls of the
canal in this area are covered with cementum. There is also a hard
tissue barrier that has formed adjacent to the root filling that may
have been induced by dentin chips or represents an osteocemental
response. This presentation amplifies the fact that in many teeth the
pulp and pulpal canal terminates far above the anatomical root end

of the root without meddling with it, as it would be if
you drilled through the foramen and carried the filling
to the end of the root and put a cape over the end of
it, as Dr. Rhein advocates. (Fig. 8) (Author’s note:
Dr. Rhein advocated filling beyond the end of the
root so the filling material would encapsulate the
apical 2–3 mm, thereby sealing off all the accessory
communications. He referred to this as “mortarization”
of the root end.) (Fig. 9)
However, Dr. Rhein had different opinions regarding
root canal therapy that stood in opposition to the main-
stream clinicians at that time, regarding procedural ac-
complishments (Rhein 1920):
The question of root-canal therapy is one that
embraces a very particular point, and that is, there is
no question that I know of, as a medical man, outside
of brain surgery, (and I would even include a large
amount of brain surgery) that requires the same
amount of skill, patience and time…When I show
hundreds of roentgenograms - some of them dating
back to work done almost 30 years ago (Author’s note:
which would be in the late 1890s), showing absolutely,
so far as a roentgenogram can show, normal tissue
(with) thorough encapsulation of gutta percha on the
apices of the roots - I definitely refute the essential
point of criticism of the essayist’s paper. (Rhein 1920)
(Author’s note: that root canals should only be filled
to the end of the dentinal canal and not impinge on
the cementum).
To rationalize his technique of encapsulation even
further, Dr. Rhein indicated that:
Where I have found re-infection in my own cases and
have had to extract teeth, I have also found invariably
extra foramina at some point that had not been
encapsulated, and which were the cause of the
recurrence of infection. (Rhein 1920)
The issue of necrotic remnants being left in apical
accessory canals and treatment failure still reverberates
in today’s clinical practice and provides the impetus for
the promotion of filling to the root apex, using a tech-
nique in which these canals may be filled. However, this
achievement may be flawed with regard to histologically
identified outcomes (Ricucci Siqueira 2010).
Interestingly, Grieves had fostered directives similar to
Blayney as early as 1914–1915 relative to the importance
of periapical pathosis, cemental repair, and apical healing
in the presence of the apical ramifications (Grieves
1914a; Grieves 1914b).
There is some evidence for believing that remaining
vessels and apical pulp-shreds, lying in touch with
surrounding vascularity, either become organized into
fibrous tissue or foramina are closed by deposits of
cementum or osteo-dentin. This can occur only in a
vital apex, not infected, nor saturated with chemicals,
nor PERFORATED AND OVER FILLED (Authors’
Emphasis); and only in one to which the
Fig. 8 Dr. Meyer L. Rhein—reproduced from J Dent Research
1933;13:100
Fig. 9 Maxillary molar that has root filing beyond the end of the
root that encompasses the root-end anatomy, as proposed by Rhein
with his “mortarization”

periodontium is physically attached. However, he goes
on to say, in his extensive treatise, “The vital apex is,
thus, the crux of all canal operations. Its maintenance
is worth any amount of time and effort. It cannot be
encapsulated (Author’s note: as per Dr. Rhein)
because periodontal fibers are everywhere attached to
it. There is, therefore, no denudation or hypoplasia in
which encapsulations may lie, unless they traumatically
protrude into the membrane, granulomata, or cysts.
Quite the reverse: the denuded apex, necrotic by
whatever means, is not worth a moment’s effort, no
matter how medicated nor how well filled (Author’s
note: this reflects the impact of focal infection). One
of the gravest mistakes of dentistry is the stubborn
belief that correct root-canal filling will cure apical
disease.” (Author’s note: this same concept is present
today when clinicians say they are treating periapical
lesions or apical periodontitis) The most perfect
canal operation is never curative, but only a preventive
procedure. (Grieves 1920)
Quite vocal in this controversy of where to terminate
the root canal filling and the issue of retaining pulpless
teeth was Dr. Rodrigues Ottolengui (Fig. 10) of New
York City (Ottolengui 1922):
There be dentists who conscientiously believe that a
pulpless tooth is a dead tooth; that every dead tooth is
doomed to infection; and that all infected teeth are a
menace to the health of the individual. to such
practitioners this communication is not addressed.
There be others who believe that a pulpless tooth may
be so treated that it will not only be tolerated by the
human body, but may be made to serve its function of
mastication, and aid in the initial step of digestion,
thus becoming an important factor in metabolism and
an ultimate contributor to the health of the subject.
From such as subscribe to these tenets I crave
attention, trusting that I may deliver to them a
message which may in some small degree render their
efforts to minister to suffering humanity more certain
and more effacious. (Ricucci Siqueira 2010)
To do so, Ottolengui dictated his doctrines for root
canal filling procedures (Ottolengui 1922):
“1.Any radiographic evidence of gutta percha beyond
the apex of the root, is a protrusion of the filling
material…
2. The protusion of gutta percha beyond the apex
demands space for its occupation.
3. …any appearance of gutta-percha beyond the apex
of a healthy root is an evidence of a fault in the
technique.
4. In the presence of infected apical areas…and the
gutta percha has been forced beyond the apex…
whether such infection, both of the area and of
the protruding foreign body can be overcome,
will be determined solely by the vital responses
of the patient in each instance. Sometimes a
cure will be accomplished in spite of the gutta
percha. It is inconceivable, however, that the
protruded material can act as a curative factor.”
(Ottolengui 1922)
Transitions in thought and reaffirmation of clinical
directives
In the late 1930s, Dr. Bernhard Gottlieb (Fig. 11) pub-
lished a monograph entitled “Dentistry in Individual
Phases” (Gottlieb 1938). In this monograph, he dis-
cusses the challenges that are present in dealing with
root canal procedures, i.e., instruments and medica-
ments, that may come in contact with the periapical tis-
sues during treatment. He indicated that he had no
concept as to the response of these tissues to the treat-
ment procedures, while at the same time hoping to
control any inflammatory responses that may prevent
healing with calcified tissues. To these purposes, he
used a dog model in his investigations:
Fig. 10 Dr. Rodriguez Ottolengui—reproduced from Prinz H. Dental
Chronology, Lea Febiger, Philadelphia, 1945. Also found in Dent
Cosmos 1934; 76(1):158

…in the case of extraction of the pulp it was or
importance to establish, how any given method would
operate when the pulp canal was in direct connection
with the periapical connective tissue. In the case of
the dog, on account of its ramifications the pulp
tissue is without exception separated from the
connective tissue, so that no connection is
established with the periapical connective tissue
throughout the manipulation in the canal. We
now had to drill through the tooth to this area,
and at once it was evident that we must use a
much more pretentious method, if we are to come
in direct contact the periapical tissue and if we
were to care for injuries to the connective tissue.
This change made in the procedure of the
experiment by this drilling was necessitated by
the fact that in the human mouth it was not at
all uncommon to come in contact with the
periapical connective tissue during pulp extraction.
(Gottlieb 1938)
Gottlieb understood the challenges faced with human
teeth that required the removal of a viable dental pulp,
but he also realized the importance of this same set of
clinical circumstances in the presence of an infected
pulp or necrotic pulp:
The claims that we had to satisfy in the treatment of a
periapical focus of infection took an a much more
complicated form, and aspects developed that we
could in nowise anticipate. We could form no clear
picture of what happened to the necrotic root
surfaces, nor could we imagine what might be
expected from branchings of the root canals that
harboured dead tissue. It was demonstrated that soon
after sterilizing and freeing these dead tissue of germs,
the neighbouring inflamed connective tissue regained
health, and almost at once deposited cementum upon
the necrotic surfaces of the tooth. This cementum
may also close up the apical foramen, and thus
produce a complete surface consisting of living
cementum, which removes completely every doubt
concerning retention of such a tooth. (Gottlieb 1938)
In his assessment, Gottlieb defies the tenets of focal
infection, indicating that properly performed root canal
procedures, with retention of root-filling materials inside
the canal in the presence of a necrotic pulp, will result
in biologic healing of the periapical tissues and the for-
mation of a cementum closure of the canal apically
(Fig. 12). Furthermore, he was quite adamant about
where to terminate these procedures, especially in the
presence of a vital, yet possibly inflamed, pulp, indicating
that “surgical common sense forbids it” (that is, going
past the apical foramen). He indicated that there are
healthy tissues at the point of severance apically, and
therefore, the use of caustic drugs was prohibited, files
must not penetrate the foramen (present day concept of
patency filing), and any damage to the periapical tissues
may well prevent the healing of these tissues with the
cementum (Davis 1923). He published his findings in
1928 and presented them at the 8th International Dental
Congress—FDI in 1931 in a special session that featured
world-class authorities who addressed the controlling of
root canal treatment procedures (Gottlieb et al. 1928):
Once a piece of foreign material has penetrated
through the foramen, no favorable condition of any
kind can induce the closure of the entrance by the
formation of a hard wall. (Gottlieb et al. 1950)
Gottlieb’s philosophies went far beyond where to ter-
minate both instrumentation and obturation. Being one
of the stalwarts from the Vienna School of Medicine,
who came to the USA (Gutmann 2013; Kremenak
Fig. 11 Dr. Bernhard Gottlieb—reproduced from Gutmann JL.
Bernhard Gottlieb’s impact on contemporary endodontology.
J Hist Dent 61:(2)85-106, 2013. Erratum 61:(3) 128, 2013. (http://
www.alumni-meduniwien.at/news/medizin+im+bild/bernhard+
gottlieb). (http://www.alumni-meduniwien.at/news/medizin+im+
bild/bernhard+gottlieb)

Squier 1997), his focus in dentistry was highly biological
and he devised a method to ensure the development of
hard tissue (cementum) at the root apex following root
canal procedures. His method to achieve apical healing
with cementum was simple. He used dentin from teeth
that had been ground fine and sterilized. After mixing
the dentin powder with sulfathiazole or restorative ce-
ment, it was applied to the apical portion of the root
canal prior to obturation. The success of his approach
was demonstrated in an animal model (Fig. 13) and
Fig. 12 Root apex showing cemental coverage following root canal procedures and subsequent healing. A represents the root filling; C is the
original cementum, while D is the new cementum; B is the junction of the two tissues; and E is the inflammation-free periodontal ligament.
Gottlieb B. From data accumulated on Professor Gottlieb from the Gottlieb Collection presently located at the Baylor College of Dentistry, Dallas, TX
Fig. 13 Healing at the root apex with cementum following the use of a dentin-cement root canal filling in the apical portion of the root. Gottlieb
B. From data accumulated on Professor Gottlieb from the Gottlieb Collection presently located at the Baylor College of Dentistry, Dallas, TX

clinically was advocated for patient use in his mono-
graph published in 1938 (Gottlieb 1938). Although not
having the molecular biological investigative capabil-
ities available today, Gottlieb’s concept was to induce
healing through the use of substances (calcium salts
and protein matrices—for which the dentin was not
to be sterilized with heat to prevent the destruction
of the proteins) within the dentin, which today we
now know as specific growth factors, such as bone
morphogenic proteins, fibroblast growth factors,
insulin-like growth factors, and epidermal grow fac-
tor, in addition to dentin matrix collagenous and
non-collagenous proteins, such as dentin sialopho-
sphoproteins, osteocalcin, bone sialoproteins, serine-
rich phosphoproteins, dentin matrix proteins, and so
forth, the latter of which has been identified in the
induction of cementoblasts and the formation of ce-
mentum (Rutherford Fitzgerald 1995; D’Souza
et al. 1997). In essence, he had begun the concept of
tissue engineering to promote predictable healing
(regeneration) following root canal procedures.
While some authors had identified other materials,
such as ivory and bone powder for the induction of
hard tissue, Gottlieb focused on dentin powder but
indicated that there were two requirements for any
material to be successful:
…first, it must be resorbable, and second, it must
stimulate the connective tissue to form new additional
hard tissue which will replace it. (Gottlieb et al. 1928)
While the philosophy of using dentin chips packed in
the apical preparation to enhance periapical healing with
hard tissue formation was used by Göllmer (Fig. 14) in
the 1930s (Göllmer 1936), and Mayer in the 1940s
(Mayer 1949), its popularity dwindled until it was re-
vived somewhat in 1967 by Engström and Spångberg
(Engström Spångberg 1967) and in 1978 by Tronstad
(Tronstad 1978). Using monkey teeth, Tronstad found
that a plug of dentin chips was well tolerated by the tis-
sues, serving as an effective apical barrier. Further stud-
ies by Oswald and Friedman in 1980 demonstrated the
presence of cementum formation with minimal inflam-
mation in the apical tissues of the maxillary canines of
cats (Oswald Friedman 1980). To the contrary, how-
ever, Holland and co-workers found that the presence of
dentin chips at the apical extent of the root canal in
monkey’s teeth did not influence healing (Holland et al.
1983), and in particular, when the dentin chips were in-
fected, the outcome was totally unfavorable (Holland
et al. 1980).
The philosophies of root canal treatment and where to
terminate not only both enlargement and shaping but
also obturation permeated the early 1900s in a plethora
of published papers and dental meeting presentations.
The biological principles of root canal procedures had
been formulated, even to the point of enlisting “Mother
Nature” to put the finishing touch on the treatment ren-
dered (Fig. 15). Furthermore, they formed the basis for
the principles that were developed at the First World
Conference on Endodontics in 1953, as very little
Fig. 14 Formation of cementum sealing and healing of the root apical tissues following the placement of dentinal chips. Göllmer L. Die Wurzelfϋllung
auf Grund der preparativen Fähigkeit der Wurzelhaut (The use of dentin debris as a root canal filling). Ztschr f Stomatol 1936;34:761

changed in treatment parameters in the previous
40 years. Ironically, no mention of Gottlieb’s efforts in
promoting these biological principles were made at this
initial conference in 1953, and his contributions to the
principles of endodontics were not even recognized.
Even though he had provided significant research to
support the science of endodontics (endodontology),
there is no mention of him in the early 1940s during the
organization and formation (originally the American
Root Therapy Association, which became the American
Society of Endodontists) of the present day American
Association of Endodontists (AAE) (Milas 1968). Iron-
ically, Gottlieb’s student and colleague, Balint Orban,
was the first editor of the Journal of Endodontia in
1946, which was the initial and official voice of the
organization that became the AAE.
Enter empiricism as the endodontist’s mantra
In 1953, an article was published by Bernard Berg that
served as the basis for new concepts in root canal prep-
aration that focused on the importance of canal shaping
along with thorough obturation to the root apex (Berg
1953). There was no discussion of where to terminate
activities in the root canal other that at the root apex.
The concepts within this publication served as the basis
for the principles that were extolled by Dr. Herb
Schilder 14 years later in 1967, in his seminal publica-
tion on canal obturation (Schilder 1967) and in 1974 on
cleaning and shaping the root canal system (Schilder
1974). Regardless of all the research that had been done
on the biological ramifications of the position where to
terminate both the canal preparation and obturation in
the early part of the 20th century, neither author pro-
vided any references to the empirical claims that were
made regarding the instrumentation techniques prof-
fered within these publications. When it came to obtura-
tion, the publications by the latter author questioned the
importance of the vertical extent of the filling material,
focusing more on the concept of “three-dimensional fill-
ing.” He even went so far as to refer to the cementodent-
inal junction as being the “theoretical…point which
divides the pulp tissues from the tissue of the periodon-
tal ligament,” a concept that had been affirmed histo-
pathologically for decades (Grove 1916; Noyes 1921).
Fig. 15 a Advertisement that appeared in Trans Ill State Dent
Soc—29th Annual Meeting, The Dental Review Co., HD Justi Son
1893 that extolled the value of normal healing with a connective
tissue scar that will gradually calcify. This was placed to support Dr.
W Clyde Davis’s approach to “pulp canal surgery” that did not have
a sound biological and clinical basis at that time; b Dr. W. Clyde
Davis, archival print reprinted with permission from the American
Association of Endodontists, from Milas, VB. A History of the
American Association of Endodontists 1943–1968, General Printing
Co. Chicago, 1968

While recognizing that filling to the theoretical apical
end of the root canal was the point that may best en-
courage a physiological closure with cementum, that
doing so “is not an unmixed blessing” due to the great
degree of variability that exists in this anatomical loca-
tion. Furthermore, he claimed that
…the closure of the root end with cementum,
while both possible and desirable, is demonstrable
much more readily in animal experimentation that
in human patients, and is unnecessary for the
health and function of the apical periodontium.
(Schilder 1974)
Rather than acknowledging that cemental deposition
played a role in histological healing, closure, and sealing
of the root canal system and clinical success, Schilder
chose to relate the clinical success achieved to his phil-
osophy of three-dimensional obturation:
The enormous success which has followed filling root
canals to their radiographic apices or beyond has led
some to theorize that healing of large periapical
radiolucencies may be stimulated by root canal filling
material outside the confines of the canal. While this
may be possible, it is more likely that, as in the case of
filling to the cementodentinal junction, continued
success results from the thoroughness of the three-
dimensional filling along the major extent of the root
canal and not on the fractional overextension or
underextension of the filling. The wise old suggestion
to slightly underextend root canal fillings in case of
vital extirpation and to fill to the radiographic apex or
slightly beyond in cases of pulpal necrosis and
gangrene is probably more meaningful in terms of
patient comfort that in terms of the ultimate result.
(Schilder 1974)
In many respects, these empirical comments cast a
dark shadow on many years of histopathological re-
search and in-depth investigations by the few bio-
logically motivated clinicians who fought the fight
against both focal infection and the inadequacies that
permeated clinical practice. In doing so, this ushered
in the “look or thrill of the fill” on the two-
dimensional radiographic, and as long as the filling
material was positioned at the extent of the root, and
one or more accessory or lateral canals evidenced
some type of filling with puffs or buttons of sealer or
gutta-percha along the root surface, success was con-
sidered inevitable and the focus of treatment was on
new instruments and new techniques.
Ironically, Schilder’s article on obturation was pub-
lished 7 years prior to his paper on cleaning and shaping
of the root canal. In this latter publication, he does ad-
dress the issue of apical termination of the root canal
preparation and filling:
…it will be understood that the instruments are, in
most cases, slightly beyond the confines of the root
canal in the adjacent periodontal ligament space. This
position will be reached from time to time with
appropriate caution, to ensure both a complete
debridement of tissue debris and to maintain the
patency of the canal. Deliberate instrumentation short
of this point without occasional probing of the apical
opening predisposes to dentin mud accumulation at
the apex, thereby increasing the risk of inadvertent
blockage of the primary canal. This major source of
frustration for inexperienced operators can be avoided
by probing to or near the radiographic apex sufficiently
often to keep dentin mud from accumulating there.
(Schilder 1967)
This was the first indication that “patency filing”
was being advocated over attempting to retain instru-
ments within the “pulp canal,” while other authors
who recognized the possibility of packing debris and
dentin mud advocated apical clearing without going
beyond the confines of the pulp canal (Walton
Torabinejad 1989).
In the late 1980s, due to the plethora of advances
in enlarging and shaping techniques and enhanced in-
struments and the focus on a more thorough cleaning
of the root canal system, patency filing was advocated
as a routine clinical procedure (Buchanan 1989), al-
beit empirical, which gained acceptance, especially in
many of the dental schools in the USA (Cailleteau
Mullaney 1997). Claims were made that the removal
of accumulated debris in the apical portion of the
canal was essential for both cleaning the apical for-
amen and ensuring success through a more thorough
canal obturation. Since then, while there have been
numerous publications that have addressed the value
of this procedure, it has been accepted globally by
many with the exception of the some areas in North-
ern Europe and Scandinavia (Goldberg Massone
2002; Cemal-Tinaz et al. 2005; Araújo Souza 2006;
Gonzalez Sanchez et al. 2010). In a recent random-
ized controlled trial that addressed the effect of main-
taining apical patency on post-treatment pain in
posterior teeth with necrotic pulps and the presence
of apical periodontitis, no significant differences were
noted between patency filing and no patency filing
(Arora et al. 2016).
Contemporarily, four philosophies tend to permeate
the clinical world of endodontics regarding where to ter-
minate enlarging, shaping, and obturation: (1) those

based strictly on the anatomical studies; (2) those
based strictly on prognostic studies and outcomes of
treatment; and (3) those based on empirical direc-
tives… “it works for me.” Using one of these first
three positions as arguments, it is conceivable that
every endodontist or dentist who performs root canal
procedures can use all three for a given case or a se-
lective, whichever was convenient, to exercise cogni-
tive dissonance (Seltzer Bender 1965). According to
Simon and associates, “…differences represent con-
flicting opinions concerning the apical limit of prepar-
ation and overall differences in concepts.” (Simon
et al. 2009). Possibly the most influentional concepts
within this dilemma of where to terminate both the
enlarging and shaping and obturation lie in the status
of the dental pulp at the time of the procedure. How-
ever, even this can create consternation due to the in-
ability of the clinician to determine without question
the viability of the dental pulp and/or the mere pres-
ence of bacterial species or bacteria and their associ-
ated biofilms, along with the location of such. Finally,
(4) those based on the status of the dental pulp and
periapical tissues may be the determining criteria for
many clinicians, but the exactness of such is severely
wanting.
Anatomical studies
The anatomical findings apically have been enhanced
tremendously with the advent of micro-CT and SEM.
The ability to view in depth the apical variations and
challenges presented has opened a whole new world
of appreciation regarding the issues that this anatom-
ical region poses for the clinician in all phases of
treatment (Figs. 16 and 17). This is especially true in
not only the unusual morphological variations but
also the presence of bacterial species and their
accompanying biofilms (Siqueira Lopes 2001;
Richardson et al. 2009). These findings, if studied
further, may result in an alteration of techniques to
better determine working length and position of the
canal material apically. While electronic apex locators
have enhanced the procedures of working length
determination (Simon et al. 2009; Martins et al.
2014), they cannot account for the high variability
that is present apically (Figs. 18 and 19). Furthermore,
additional definitive research most likely may result in
newer, more biologically formulated materials for root
canal obturation. Moreover, the anatomical findings
with the new technologies have provided a better un-
derstanding as to why both biologically based and
clinically based treatment parameters of treatment
may fall short of ideal in many cases.
One of the more interesting publications (two parts)
that addressed the focus of this paper appeared in 1998,
before the availability of micro-CT (Ricucci 1998;
Ricucci Langeland 1998). Part 1, which was a litera-
ture review, confirmed what the previous prognostic
studies had indicated, that the practice of staying short
of the apex with a homogeneous root canal filling
yielded the highest success rate (90–94 %), when done
by or under the supervision of a specialist. However, re-
sults in the general population resulted in a greater fail-
ure rate (50 %) (Martins et al. 2014). Furthermore, the
author indicated that it was impossible to instrument
accessory canal ramifications and that, when these
ramifications appeared filled on the radiograph, it was
only due to the forcing of root canal sealer into the
tissues located in these ramifications, which was veri-
fied in a later study (Ricucci Siqueira 2010)… an
outcome that was frowned up decades earlier (Grieves
1914a; Grieves 1914b).
In part 2 of the study, Ricucci and Langeland per-
formed histological analysis of teeth that had been root
treated and extracted after different observation periods
(Ricucci Langeland 1998). They found that the most
favorable histological conditions occurred when instru-
mentation and obturation remained at or short of the
apical constriction, whether the pulp had been vital or
necrotic, and even if some bacteria were present in the
periapical tissues. Furthermore,
When the sealer and/or gutta-percha was extruded
into the periapical tissues, the lateral canals and the
apical ramifications, there was always a severe
Fig. 16 Micro-CT scans of a mandibular molar from multiple angles that show the highly irregular root canal anatomy from the orifice to the
apex (courtesy, Mr. Stephen Rigsby)

inflammatory reaction including a foreign body
reaction despite the absence of pain. (Ricucci
Langeland 1998)
These observations are juxtaposed to those of Khayat
(Khayat 2005) and Tamarut et al. (Tamarut et al. 2006),
both of which will be discussed below under prognostic
studies.
In a unique study that addressed tooth anatomy risk
factors that influenced root canal working length acces-
sibility, Tang et al. (Tang et al. 2011) found that tooth
type, root canal curvature, canal calcification, and
retreatment were primary risk factors in an independent
factor analysis. However, using a multiple-factor regres-
sion model, root curvature and canal calcification were
found to most significantly influence working length ac-
cessibility and ultimate treatment success. In particular,
as the extent of the canal calcification increased, the dif-
ficulty in reaching the root canal constriction increased
sevenfold, whereas an increase in canal curvature only
increased the difficulty twofold.
Prognostic studies and treatment outcomes
The majority of prognostic studies have been summarized
in the publications cited below as to outcomes and dic-
tates, and therefore, these studies do not warrant individ-
ual discussion here. Hasselgren in 1994 (Hasselgren 1994),
in discussing “Where shall the root filling end?”, cited a
plethora of studies that every endodontist should be famil-
iar with from 1956 to 1990 that resulted in one finding
common to all, and that being, an overfill will markedly
decrease the success rate;
“The optimal result was to end the root filling one to
two mm inside the radiographic apex - exactly the
same recommendation that emerged from the
anatomical studies (in the early 1900s). If the root
filling is shorter than that, the success rate will drop;
but overfills will yield an even poorer results.
(Hasselgren 1994)
Most prognostic studies could only relate to radio-
graphic findings identified at the time of filling and
Fig. 17 Micro-CT scans of a maxillary molar from multiple angles that show the highly irregular root canal anatomy from the orifice to the apex
(courtesy, Mr. Stephen Rigsby)
Fig. 18 Micro-CT scan. a, b Apical termination of the buccal canals on two maxillary molars that show a vast array of canal configurations that
make working length determination most difficult (courtesy, Mr. Stephen Rigsby)

subsequent control or recall appointments. Therefore,
the issue of where the measurement was taken, to what
level the canal was “carefully instrumented” and the ul-
timate obturation, both vertically and laterally may be is-
sues that could never be resolved in the historical
studies. Furthermore, outcomes with teeth having
vital, inflamed pulps that had obturations that go be-
yond the confines of the canal may have been worse
than teeth with necrotic pulps that had obturations
within the canal confines and vice versa depending
the degree of canal cleaning and disinfection in each
situation. The scenario just addressed brings to the
forefront another important issue in these studies,
with that being there may be insufficient evidence to
support the clinical achievement of bacterial eradica-
tion prior to obturation at whatever level the filling
is placed. Studies do support better outcomes re-
gardless of the position of enlargement, shaping, and
obturation if the root canal is bacteria free. However,
two issues come to mind in that regard: (1) that the
presence or absence of bacteria at the time of obtu-
ration cannot be reliably determined at this point
and (2) not every root that contains bacteria at the
time of obturation will result in failure, again regard-
less of the position of the root canal procedures that
had been performed (Sjögren et al. 1997). Moreover,
and possibly most important, virtually all the studies
only used two-dimensional radiographic assessments,
which by today’s standards may be woefully substand-
ard, as there is substantial disagreements between
periapical and CBCT radiographs for assessing the
periapical status of molar teeth, especially for the
maxillary arch (Cheung et al. 2013). These findings
have serious implications in periapical diagnosis and
for evaluation of the outcomes of root canal proce-
dures (Cheung et al. 2013).
In 2000, Wu and co-workers did an extensive evalu-
ation of studies over the previous 50 years and arrived at
the following conclusion (Wu et al. 2000):
After vital pulpectomy, the best success rate has
been reported when the procedures terminated 2 to
3 mm short of the radiographic apex. With pulpal
necrosis, bacteria and their byproducts, as well as
infected dentinal debris may remain in the most
apical portion of the canal; these irritants may
jeopardize apical healing. In these cases, better
success was achieved when the procedures
terminated at or within 2 mm of the radiographic
apex (0 to 2 mm). When the therapeutic
procedures were shorter than 2 mm from or past
the radiographic apex, the success rate for infected
canals was approximately 20% lower than that
when the procedures terminated at 0 to 2 mm.
Clinical determination of apical canal anatomy is
difficult. An apical constriction is often absent.
Based on biologic and clinical principles,
instrumentation and obturation should not extend
beyond the apical foramen. (Wu et al. 2000)
When evaluating the technical aspects of treatment
in relation to treatment outcome, Kirkevang and
Bindslev arrived at similar conclusions (Kirkevang
Bindslev 2002):
Fig. 19 Micro-CT scan. Apical termination of the mesial-buccal root of this maxillary with significant variations in canal termination (courtesy, Mr.
Stephen Rigsby)

When the technical quality of the root-filling was
related to treatment outcome, the studies
demonstrated success rates of 70-100 %, if the
quality was assessed to be optimal. If the root-
fillings were short of the apex, a lower success
rate of 57 %-95 % was found, If extrusion of
root-filling material in periapical tissues were found, the
success rate was ever lower at 50 %-90 %. (Kirkevang
Bindslev 2002)
Similar findings were identified by Schaeffer and asso-
ciates in a meta-analysis designed to determine the opti-
mal obturation length (Schaeffer et al. 2005). Very few
studies, however, could be considered in this analysis
due to inclusion/exclusion criteria. While the data
was suggestive and it was considered as biologically
sound to obturate short of the radiographic apex, they
found that in reality, the length of the fill and success
are correlated. Interestingly, they noted that there is
opinion held by many clinicians that extrusion of root
canal sealer from the root apex (and accessory com-
munications—Author’s note) does not lower the prog-
nosis of root canal procedures. While clinically
desirable by many to see these puffs or buttons of
sealer radiographically, Ricucci and Siquiera (Ricucci
Siqueira 2010) found that
…vital tissue in the accessory communications was
not removed during canal shaping and cleaning and
although lateral canals appeared radiographically filled
they were actually not obturated, and the remaining
tissue in the ramification was inflamed and enmeshed
with the filling material. (Ricucci Siqueira 2010)
This finding supports the dictates of our forefathers,
discussed previously, who encouraged the preservation
of the tissues in these ramifications to allow normal
healing to occur.
In a 10-year clinical follow-up study, a group of in-
vestigators from Croatia identified success in compari-
son to length of root canal instrumentation and
obturation in 163 patients (Tamarut et al. 2006). In
this study, they used controlled over-instrumentation
(1.62 mm ± 0.92 mm) in all pulpal diagnostic states
and obturation to the physiological foramen or apical
constriction and found that it was not harmful to heal-
ing. Furthermore, slight overfilling did not impair
success. Keep in mind, radiographic evaluations were
done with traditional two-dimensional assessments
In another 10-year follow-up study of 15 single-rooted
teeth following root canal procedures from a population
of patients aged 25–40, the teeth were extracted due to
caries, resorption, or trauma. In order to obtain sur-
rounding apical bone for histological analysis, an apical
block dissection was performed (Khayat 2005). While
limited in sample size, the teeth had root fillings that
were extruded beyond the apex (47 %) or flush with the
radiographic apex (53 %). Radiographs showed that 8 of
the 15 had overfilling of gutta-percha and sealer, while 7
of the cases had gutta-percha and sealer to the root
apex. Healing activity was observed in all cases; how-
ever, active macrophage with phagocytic activity was
seen even in a case that was 10 years old, which
would imply some degree of persistent inflammation.
However, many studies of this nature show “healing”
in some areas of the periapical tissues, while chronic
inflammation can be present in other areas; addition-
ally, healing does not equate with healed (Glossary of
Endodontic Terminology 2012).
Most recently, Azim and associates reviewed radio-
graphically 422 roots from 291 root-treated teeth that
met an inclusion criteria of a mean follow-up period of
2 years (Azim et al. 2016). Roots instrumented apically
within 0.5 mm from the radiographic apex had a signifi-
cantly more favorable outcome (88 %). Those 2 mm
short from the radiographic apex had the least favorable
outcome (33 %). Teeth with overextended root fillings
showed delayed healing by almost 14 months.
To somewhat mollify the empirical approach to
working length determination that was either arbitrar-
ily based on a guesstimate of the apical constriction
or on a two-dimensional radiograph, the use of elec-
tronic apex locators (EALs) has been favored by most
academicians and clinicians (Mohammed et al. 2015).
Ironically, the very principles behind the use of the
EAL were proffered by Custer in 1918 (Fig. 20) who
understood clearly the nature of the canal termination
at the root apex (Custer 1918):
While it is true that the foramen is not always at the
extreme apex…there may be more than one foramen
to the root, the one method to be presented will meet
this condition with precision…an electrical method of
extreme delicacy and accuracy…The electrical method
is based upon the difference in the electrical
conductivity of a dry pulp canal or one filled with a
non-conducting liquid, and the conductivity of the
tissues just beyond the apical foramen. (Custer 1918)
While popular in its application for working length de-
termination, the EALs have not resolved issues as to the
apical limit for canal instrumentation and obturation
(Mohammed et al. 2015), as survey results of UK-trained
or qualified respondents indicated that the majority pre-
ferred to go to the same apical limit with all apical pro-
cedures. This is in deference to empirical directives that
may indicate that the status of the pulp and periapical
tissues may require variations in apical terminations. As

a confirmation of the former choice of relying on the
EALs for the working length in all cases, being the same
position for all procedures, Tsesis et al. (Tsesis et al.
2015) found the use of the EALs was not influenced by
the status of the pulp tissue, although the precision of
the length determination was based on the particular de-
vice and the type of canal irrigant. In contrast to this
issue, Martens and associates, in a systematic review of
the literature on the clinical efficacy of the EALs, noted
that in addition to using the EALs, and due to the fact
that the available scientific evidence base for efficacy is
minimal and at risk for bias, at least one radiograph con-
trol should be used to detect possible errors in the appli-
cation and interpretation of data from these devices
(Martins et al. 2014).
Empirical directives
There are no guidelines that can be identified with
this directive as they are all clinician-based and are
determined on a case-by-case basis; however, even
this would not be an accurate assessment, as many
clinicians manage their apical root canal procedures
in the same way for all teeth, that is instrumenting
and obturating to the same apical limit (Mohammed
et al. 2015), claiming complete success, as long as the
patient is comfortable. In this regard, most will follow
the dictates of a professor where they received their
education or grasp on to the directive given to them
in their most recent continuing educational pursuit
from those claiming to have the magic way to achieve
success. The hallmark of this approach usually is
characterized by the presence of root canal sealer
puffs and the extrusions of filling materials beyond
the root end, with claims of having achieved a perfect
seal of the canal system (using only two-dimensional
radiographic evaluations).
Status of the dental pulp and periapical tissues
The wide range of anatomical variables and technical in-
terpretations regarding the apical location for determin-
ing the working length and the position of the final
obturation have been identified. Furthermore, because
the actual location of this variable terminal position
has resulted in significant number of clinical opinions,
along with variable applications and advocacies, at
least two camps of polarized thought, along with a
vast array of outliers, have evolved. Advocates have
been driven by passion, concern for radiographic ap-
pearance, staunch adherence to the use of EALs,
strong advocacy for patency filing, and the incorpor-
ation of cognitive dissonance into their decision-
making and proffering (Seltzer Bender 1965). One
major philosophy is to retain all procedures within
the confines of the root, while the other philosophy
espouses the determination of working length, enlar-
ging, shaping, cleaning, and obturation to the ana-
tomical root apex or root length. In most teeth, while
overlap or agreement may occur in some cases, these
two philosophies are not compatible. However, in
light of this controversy, there seems to be a middle-
of-the-road position that most clinicians can travel
comfortably and that will yield success. While the
choices can vary, it would seem to be dependent on
the status of the dental pulp, access to the end of the
root, and the clinician’s skill and expertise, in addition
to experience that demonstrates that particular
choices provide positive outcomes in the majority of
cases. However, evidence-based data at the highest
level to verify this approach are not available, and
therefore, it is empirically driven.
If the dental pulp is vital (inflamed; irreversible pulpi-
tis), then the working length is established clinically as
close to the constriction as possible and attempts are
made to retain all procedures within the root canal.
While this position has been advocated as approximately
0.5–1.0 mm from the radiographic apex, this dictate is
flawed (Ricucci 1998). In essence, the thought behind
this approach is that the tissue that invaginates into the
Fig. 20 L. E. Custer—reproduced from Custer LE. Exact methods of
locating the apical foramen. J Natl Dent Assoc. 1918;5:815–819

canal from the periodontal ligament, and which is peri-
odontal in nature, is not disturbed by the subsequent
manipulations that are performed within these confines
(see Fig. 7) (Gutmann Reagan 1998; Gutmann 2005).
This recommendation is based on sound wound-healing
principles in that severance of the tissue at its narrowest
point will create the smallest wound possible for healing
(Ricucci 1998; Ricucci Langeland 1998). It also en-
courages the potential for tissue regeneration with the
formation of cementum as opposed to just fibrous con-
nective tissue repair or persistent chronic inflammation
(Gutmann 2005).
If the dental pulp is non-vital (obvious necrosis; pres-
ence of a periapical radiolucency), then the working
length is initially established as close as possible to the
canal exit or slightly short of the apical foramen to clean
the entire length of the canal (Shabahang et al. 1996),
thereby eradicating bacteria as much as possible and re-
moving the substrates that could encourage bacterial re-
growth and multiplication (Wesselink Bergenholtz
2003). This is an empirical and contemporary approach
to working length determination, in addition to enlar-
ging and shaping that is promulgated by many in today’s
practice of endodontics. However, because the root apex
can be highly irregular (Fig. 21), especially in the pres-
ence of obvious or even unidentified apical resorption
(Brynolf 1967), files placed to the apical extent of the
root as viewed radiographically will likely be outside the
confines of the canal and create potential damage to the
root anatomy at that point (Ricucci 1998; Ricucci Lan-
geland 1998). It is also possible that this technique may
serve to inoculate the apical tissues with bacteria and
material debris that may cause an adverse reaction or
result in persistent inflammation, a concept that was
considered as unacceptable by Ottolengui in 1922
(Ottolengui 1922) and highlighted by Yusuf and Love
and Firth, when examining biopsies from lesions from
teeth that required periapical surgery due to persist-
ent inflammation (Yusuf 1982; Love Firth 2009).
Here also, a middle-of-the-road philosophy has been
proposed, that is, cleaning and shaping the canal to
the entire length of the root and then backing up or
retreating into the canal sufficiently to develop a con-
striction or stop inside of the root where the dentin
terminates for further intracanal procedures (Simon
1994). However, even with this choice, the movement
of materials past the root apex into the periapical
tissues usually cannot be prevented.
Ironically, both of these philosophical and clinically
practiced positions provide no evidenced-based data to
support them as the ideal working-length technique for
instrumentation and obturation, and it is only when the
teeth are obturated can one conjecture where the exact
working length was terminated during the procedures.
Therefore, data to support either position contemporar-
ily are elusive and unfounded, except for information
gleaned from outcome studies that take into account all
phases of the root canal procedures. For example, ac-
cording to Gesi and Bergenholtz (Gesi Bergenholtz
2003), when no infection is present, it is hard to ration-
alize, as it is sometimes advocated that the apical for-
amen be pierced and root canals be overfilled with so
Fig. 21 Micro-CT of the root canal termination showing the anatomical challenges encountered in working length determination (courtesy, Mr. Stephen Rigsby)

called puffs. It would seem that overfills of this nature
actually reflect the inexactness of the obturation tech-
nique, whereas the clinician is hoping that the canal is
truly filled and sealed. Furthermore, an inadvertent over-
filling may not necessarily be harmful or cause a periapi-
cal lesion to form but may actually reflect a unfavorable
apical shaping and alteration of the normal anatomy,
which may put the apical tissues at risk for delayed heal-
ing or lack thereof (Bergenholtz et al. 1979). Many of
these studies that address these issues are retrospective
in nature, have questionable bearing on contemporary
practices, and are based on two-dimensional radio-
graphic assessment.
Conclusions
In the late 1800s, Cravens warned us that “beyond the
apex…danger lurks” (Cravens 1893), while in the early
1900s, Prinz (Fig. 22) made a bold statement regarding
the sanctity of the apical constriction: “The hermetic
sealing of the foramen without injury to the periapical
tissues is the unalterable prerequisite upon which the
future welfare of the tooth rests.” (Prinz 1928). Finally,
following lengthy and thorough assessments of the out-
comes relative to the termination of the root canal pro-
cedures, in the early 2000s, Gesi and Bergenholtz
echoed similar observations: “No scientific basis exists in
the literature to support the notion that the apical for-
amen should be pierced and root canals be overfilled for
a successful outcome.” (Simon 1994). Is it possible that
the lessons of history have gone unheeded or have been
obfuscated by contemporary clinical directives, or has
empiricism provided total disambiguation in the eyes
and minds of the contemporary clinician?
Competing interests
The author declares that he has no competing interests.
Acknowledgements
The author would like to thank the following individuals for their invaluable
professional assistance and guidance in procuring the necessary
documentation in support of the figures/photos in this manuscript.
Andrea Matlak, Archivist, American Dental Association, Library and Archives
Arlene Shaner, Historical Collections Librarian, The New York Academy of
Medicine
Dawn McInnes, Rare Book Librarian, Clendening History of Medicine Library,
University of Kansas Medical Center
Helen Jameson, Assistant Executive Director, American Association of
Endodontists
Joanna Goldberg, Information Services Librarian, The New York Academy of
Medicine
Nicola Perrini, Fondazione Castagnola, Milano
Tim Horning, University Archives, University of Pennsylvania
Received: 11 June 2016 Accepted: 14 June 2016
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