The course begins by discussing the crucial role that
access plays in a root canal procedure, explaining that the outcome
of the entire case depends on successful access. Furthermore, doctors
are warned of the potential dangers present when a clinician fails
to approach this aspect of the procedure cautiously. The course
goes on to describe techniques for avoiding iatrogenic outcomes,
and the importance of considering tooth and root anatomy in creating
ideal access. The content then moves on to discuss which instruments
are optimal for various types of anatomy, and explores ultrasonics
as an emerging tool for access refinement.
The Negotiation section of the course begins by dispelling the myth
that many canals are calcified in their apical regions, and goes
on to explain that 90% of all root canals can successfully be negotiated
by applying the right strategy. It outlines the importance of effective
radiographic technique, and evidence to look for on radiographs
that may reveal anatomical irregularities. It discusses using an
apex locator to gain a clear understanding of the canal's anatomy,
the importance of using a lubricant during negotiation, and the
reasons why patency should always be maintained. Finally, the course
discusses file selection, file motion, and strategies for negotiating
difficult anatomy and calcified canals.
Course Objectives 
Upon completion of this course, the participating clinician
should have a greater understanding of the following concepts: |
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The importance of access in maximizing efficiency
and avoiding iatrogenic results
Access instrument selection and use
Strategies for creating ideal access form
Access techniques for various anatomical variations
Effective strategies for negotiating root canals,
including severely calcified canals and canals with
challenging anatomy
That 90% of all canals are negotiable to their termini,
and that calcification does not begin in the apical
regions of the canal
Negotiation instrument selection and use
The importance of apex locators for successful negotiation
and length determination
The importance of using a lubricant during every
negotiation procedure
The argument in favor of using a patency file, and
how to be certain that patency is maintained
File bending, and how to successfully negotiate
a severely curved canal using pre-bent negotiation
files |
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Guidelines for Conflict of Interest
The primary focus of any course presented by Dr. L. Stephen Buchanan
and Dental Education Laboratories is endodontic excellence. Maintaining
credibility as an educational organization is first and foremost.
To that end, the following guidelines have been set in place, and
all continuing education activities offered by Dental Education Laboratories
adhere to the following standards:
Dental Education Laboratories continuing education
programs are educational in nature, and are not for the purpose
of promoting any product.
Dental Education Laboratories maintains exclusive control and
responsibility for the subject, location and educational objectives
of all continuing education activities, regardless of the level
of vendor support.
When a product which Dr. Buchanan has designed is to be the
subject of substantial discussion, steps will be taken to ensure
that the data will be objectively selected and presented, that
both favorable and unfavorable information about the product
will be fairly represented, and that there is a balanced discussion
of the prevailing body of scientific information on the product.
Courses offer a balanced view of various diagnostic and therapeutic
options, regardless of potential sponsorship or vendor support.
Discussion of any product will be objective, balanced, scientific,
and based on extensive clinical use.
Commercial exhibits should not in any way affect the educational
content or integrity of the course activities and are provided
solely for participants' interest.
Full disclosure of any potential conflict of interest is required,
and is communicated during all courses. Should course participants
wish to review specific conflict of interest declarations, they
are to be supplied to that participant, upon their request,
by our administrative office. |
Instructions for Course Completion and Obtaining Continuing Education
Credits
Read the body of text carefully. Click on the figure Thumbnails
for an enlarged view.
We suggest you take the time to look at these graphics carefully,
as they often help to illustrate and clarify the concepts.
When you have completed the course, proceed to the test page.
While taking the test, you may refer back to the course content
at any time, to assist you in answering the questions.
Complete the test and submit it, via email. Your test will be
scored and an email conformation will be sent to you, within
2 business days.
Your answers must be 75% accurate in order to receive credit
for your participation in this course. In the event that you
do not receive credit on the first try, you may choose to re-take
the test at any time.
Once you have successfully submitted and completed the test,
a Certificate of Completion will be mailed to your address within
5 business days. If you do not receive your certificate and
corrected test within 2 weeks, please call us at 800-528-1590
or 805-899-4529 outside the US and Canada.
If you have successfully completed a course for credit, you
cannot re-take the test and receive credit for that course again.
Finally, we ask that you fill out and submit the evaluation
with your test answer sheet. It helps us to improve our courses,
and offer better resources to future participants. Thank you!
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The
more experience gained in endodontic therapy, the easier
and faster most procedures go. But cutting an access cavity,
even for the seasoned professional, is always an excellent
opportunity for clinical disaster. And when an access
procedure goes badly, the long-term prognosis of any given
endodontic case can plummet within seconds. Perforations
occurring during access procedures are typically located
in the most difficult place to repair, the cervical region.
Beyond iatrogenic possibilities, access procedures set
the stage for success or failure of the cleaning, shaping,
and obturation procedures that follow. Of course inability
to locate all of the canals in a tooth will usually result
in short-term failure of treatment. While not an irreversible
result like perforation, leaving canals untreated can
embarrass clinicians and destroy patient confidence, if
the patient has not been informed of the situation and
the resulting impact on prognosis.
Faced with anatomic possibilities such as two canals in
anteriors, three canals in premolars, and one to six canals
in molars, clinicians who want to optimize their ability
to find canals must enter pulp chambers with a suspicious,
skeptical attitude.
More common, though less appreciated, is the lack of convenience
form in access cavity design and execution. Although time
spent in access saves time throughout the rest of the
treatment flow, as it must be accomplished without the
needless weakening of tooth structure caused by overenlarged
preparations. Cutting an ideal access cavity clearly requires
clinicians to walk a fine edge. |
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Perforation
during access is always a threat, even in non-calcified
teeth. Unlike restorative dentistry, all RCT occurs in
internal spaces where visual information is limited. Although
there are many external clues about the hidden root canal
system, this surface morphology is of limited help at
best, and on occasion, is the dentist’s worst enemy.
Many teeth are significantly tipped in one or more planes
relative to the arch and adjacent teeth. This creates
a challenge in entering even non-calcified pulp chambers.
Most difficult yet are cases with severely calcified pulp
chambers, tipped roots, and realigned coronal prostheses.
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Incisor teeth are frequently perforated
to the buccal because, for aesthetic reasons, these
access cavities are skewed to the lingual .
This less-than-ideal angle of entry tends to tip
the cutting portion of the bur to the buccal, so
clinicians must consciously avoid moving too far
in that direction. Conversely, incisors are nearly
impossible to perforate lingually. Therefore, when
in doubt, err to the lingual. |
Maxillary premolars are most easily perfed on their mesial
surfaces as they are commonly tipped mesially. This occurs
most often to mandibular premolars on their buccal surfaces,
as the root is often in lingual version relative to the
coronal structures. Premolars are challenging because
of the widely angled emergence profile of their mesial
and distal interproximal surfaces.
The occlusal surface of premolars is commonly one third
larger than the narrow M-D width of these teeth at the
cervical level. This sets one up for a false sense of
security about the margin for error when accessing these
teeth.
Molars are most often perforated through their furcations,
and less often through their mesial surfaces, due to their
frequent mesial angulation. |
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While
every dentist who does RCT has perforated a tooth during
access, it should be a rare occurrence. To borrow a phrase
from the NRA, handpiece burs don’t perforate teeth,
dentists perforate teeth. All access perforations are
essentially judgment errors, a result of not stopping
soon enough, not taking the necessary x-rays, etc. If
you don’t have the time or persistence to take a
film every 1mm when burring toward a calcified pulp chamber,
then you are not the right dentist to do the access.
Pre-op films are necessary from a straight-on angle, showing
contacts and interproximal areas open, and from one or
more angles, showing the third dimension. Working films
easily show access entry angles in the mesial-to-distal
plane, but the buccal-to-lingual plane is obviously more
obscure. When burring deeply into calcified teeth, it
is often necessary to take two films, straight-on and
angled, every 1 mm. Again, if you can’t spend the
time, don’t do the access.
After radiographs, cervical root contours are the most
important landmarks in determining safe and accurate entry
direction.
Never forget that when burring beyond the furcational
level in a multi-rooted tooth, or beyond the crestal level
in single rooted tooth, the risk-to-benefit equation increases
exponentially. As long as the entry path is on track (as
proven by frequent films from different angles) in a deep
access, you will tend to stay on track. As soon as you
veer off even a bit, it becomes nearly impossible to reorient
correctly, and it’s time to call it a day. |
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The
most important tools needed to create the cleanest, most
conservative paths into pulp chambers are hand-eye coordination,
well-tuned mental imaging skills, and a lot of patience,
thought and determination. Of secondary importance are
the cutting tools we wield.
I strongly advise against using larger burs for initial
entry or refinement as they weaken teeth needlessly and
increase chances of perforation. As with any air flight,
we are always slightly off course during access entry
procedures. Because of frequent course corrections, we
arrive at our destination with minor irregularities in
the approach path. When we use small burs these course
corrections cause insignificant irregularities in the
access walls, but with large burs, a near miss becomes
a perf.
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Access preps on anterior teeth should
start with the #2 round bur penetrating the enamel
in a narrow trough shape, from near the incisal
edge to the cingulum. Once through the enamel it
is critical that the angle of access penetration
be directed apically and lingually to avoid buccal
perforation. Once in the pulp chamber, refine the
access cavity with a tapered diamond bur or with
ultrasonics. Be sure to maintain a narrow mesial-to-distal
form, but extend the buccal aspect right up to the
incisal edge and the lingual aspect well into the
cingulum .
Without this lingual extension into the cingulum,
second canals in these teeth are even more difficult
to find and treat. |
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Premolars with single
canals require a round access form . |
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Those with two canals
need narrow, elongated accesses .
The unusual case with three canals should result
in a triangular access outline form, much like a
molar preparation. Remember to use a slightly lingual
entry angle for mandibular first premolars, as they
are easily perfed on the buccal. |
The most common molar access error is distal overextension.
While this is not a result which will impact the prognosis
of a case, it will certainly create difficulties for the
operator whenever the distal canal orifices are approached
with files, paper points, and gutta percha points.
To prevent distal overextension, access preps on maxillary
molars should be started as a trough between the MB and
P cusps and angled parallel to the mesial interproximal
surface. After dropping into the pulp chamber, the distal
access wall can then be gradually lifted back to gain
entry to the DB canal. When the pulp chamber is totally
calcified in maxillary molars, the first canal to look
for is the MB 1, as it is easiest to locate relative to
adjacent cervical root contours.
Mandibular molar access should be started distal to the
mesial marginal ridge and no further distal than the bucco-lingual
groove. Again, after penetration into the pulp chamber,
the distal access wall can be gradually moved back to
gain entry to the D canal(s). Be certain to visualize
the angle of the mesial surface to allow the correct angle
of entry. Mandibular molar accesses are commonly too constricted
buccal-to-lingual at the mesial extent. Sometimes it is
necessary to cut into MB cusps to gain the access needed
to treat the MB canal. |
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The simplest description
of access convenience form is the straightest possible
entry angle into each canal, with the line angles
of the access cavity smoothly dropping into canal
orifices. Accesses which are too small
cause needless difficulty. |
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Overenlargement, however,
is to be as feared
. With the ideal RCT results available today,
the greatest obstacle to long-term success is
crown and root fracture. Overextended access preparations
can easily increase that possibility. |
The most elegant access preparations into upper and lower
molars combine ideal convenience form with conservation
of tooth structure. They have a mesially angled entry,
just over the marginal ridge, for more direct entry into
distally curving mesial canals. They are fully extended
to the MB cusp (both maxillary and mandibular), and their
distal walls are taken back barely beyond the mesial-to-distal
center of the occlusal table. Although pulp chambers are
found in the center of the tooth at the cervical level,
access cavity design is at our discretion and the advantages
of this path are obvious. When starting these accesses
just over the mesial marginal ridge, always confirm the
correct access angle, relative to the mesial aspect of
cervical structures. |
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G.V.
Black said convenience form is not a luxury. When access
preparations are designed and executed ideally, the most
difficult cases are manageable. When accesses are sloppy,
even simple cases become a struggle. Truly, time and effort
spent during access pays dividends throughout the rest
of the case. |
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The
rapid adoption of rotary files by specialists and generalists
alike has created an even greater imperative for creating
ideal convenience form in access preparations. While
clinicians can get away with mediocre access preps when
using hand files, they will be quickly and severely
punished for the same shortcoming when using handpiece-driven
files. Natural or artificially created curvatures in
the coronal half of root canals are the most dangerous
curvature encountered with rotary instruments.
When an instrument is bent around a curve, the metal
it is made of experiences compressive forces on the
inside of the curvature, and stretching forces on the
outside of the curvature. When spinning in a handpiece,
the stretching and compression forces alternate at the
frequency of the RPM causing an accelerated form of
cyclic fatigue.
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These forces are most
destructive in the large diameter regions of rotary
instruments, because of the greater disparity between
the compressive and stretching forces. Therefore,
the more cervically-positioned the curvature, the
more challenging it is to avoid breaking an instrument
in that canal path. For these reasons, adequate
extension of access line angles is critical to creating
a straight-line entry path into canals .
Clinicians must be especially careful to create
straight-line file paths in anterior access preparations,
and in the MB line angle extension of access preps
in lower molars.
LA Axxess burs were designed to solve this serious
problem. They have a completely radiused pilot tip
which extends beyond the cutting portion to eliminate
ledging at orifice levels and dangerous over-extension
into curved root canals. In the alpha flute region
behind the non-cutting pilot tip are 3 mm's of a
curved parabolic cutting shape that cuts an ideal
funnel shape to guide files, without impediment,
into the canal beyond the bur's apical extent of
cutting. |
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This parabolic cutting
region transitions into the beta region that consists
of .05 mm/mm taper. In the SybronEndo Axxess Bur
kit, two types of LA Axxess burs are available:
a high-speed diamond-coated bur and a fluted stainless
steel latch grip design in three sizes . |
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The high-speed diamond
version of the LA Axxess concept comes in a single
size, and is used immediately after initial entry
into the pulp chamber has been accomplished by
the appropriate round bur. This bur will effortlessly
tip the access line angles upward exactly from
each canal orifice to the cavo-surface of the
access cavity and I am usually able to compete
85% of my access cavity preparations in less than
a minute, as the pilot tip acts like a guide bearing
on a router bit with the periphery of the pulp
canal acting as the template. This has become
the single most useful instrument in my armamentarium. |
The LA Axxess burs with a latch-grip design are intended
for use in a standard slow-speed handpiece at 5,000-20,000
RPM. They have two non-landed stainless steel flutes
for aggressive side cutting in dentin. Beyond the cutting
surfaces, they have the same basic features as the diamond
version, including radiused pilot tips, parabolic cutting
blades, a .06 shank taper, and 12 mm of cutting flute
length.
The stainless steel used for these burs is somewhat
counter to the recent trend of using nickel titanium
for endodontic cutting tools, This was decided for two
reasons: stainless steel is easier to grind to a sharp
flute edge and, in this application where we need to
cut a straighter path to or into the canal, the stiffness
of stainless steel is a definite advantage over the
flexibility of nickel titanium.
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These LA Axxess burs
come in three sizes, varying primarily by their
tip diameters: the #’s1, 2, and 3 have pilot
tip diameters of .2, .4mm, and .6mm, respectively.
These burs are used in small, medium, and large
roots, respectively. Use of these instruments
is similar to the diamond LA Axxess Bur. They
are pushed smoothly into the canal orifice and
tipped up, while spinning, to the access line
angle, resulting in an ideal line angle extension
. Unlike
the diamond version, these burs can also be used
in the canal itself. This helps to further eliminate
any irregularities between the access line angle
and the canal orifice, so all subsequent instruments
and materials can be placed effortlessly in the
canals. |
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This helps to further
eliminate any irregularities between the access
line angle and the canal orifice, so all subsequent
instruments and materials can be placed effortlessly
in the canals.
A serendipitous finding in testing prototypes
of the fluted LA Axxess burs was how rapidly they
could open up canals with no cervical curvatures.
At 5000-20,000 RPM, these instruments can cut
most of the shape needed in the coronal half of
a root canal preparation in less than 5 seconds,
greatly reducing the fatigue on the NiTi shaping
files to follow .
SybronEndo has introduced these burs in two kit
forms that include a sterilization stand . |
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As
I’ve said before, access is everything in endodontic
therapy; it is also the most difficult, dangerous aspect
of treatment. The question is, how can we turn the tables
in our favor, and regain our sense of professional composure
during difficult access procedures, especially in molars?
While there is the fundamental issue of the clinician’s
ability (his or her knowledge of coronal and pulp chamber
anatomy, hand-eye coordination and clinical judgement),
visibility and cutting tool geometry can significantly
improve procedural outcomes for dentists at any level
of clinical skill. Until recently, it has been difficult
to see deeply into molar root structure when hunting
for calcified canals. Adding to this ubiquitous challenge
is the greater appreciation of the high incidence of
MB2 canals present in maxillary molars. Without magnification
and ultrasonics, this higher level of clinical outcome
is impossible.
Ultrasonic cutting instruments provide unbelievable
visual access, an advantage that is difficult to overstate.
With loops or microscope to magnify the view, ultrasonic
cutting tools allow clinicians to see and remove broken
instruments in the apical thirds of straight roots.
During access of calcified pulp chambers and canals,
this improved visual access to the inside of teeth allows
clinicians, for the first time in the practice of endodontics,
to see the tip of a cutting instrument 12 mm into the
center of a tooth.
The visual access and the perfect control that ultrasonic
cutting tips provide during access procedures make them
a must-have tool for dentists who treat molars. Molar
access is hard for all clinicians, and I have been especially
grateful for the improved experience and access results
that ultrasonics have made possible in these difficult
teeth. With line-angle extension burs and these ultrasonic
tips clinicians can cut access cavities in any tooth
in much less time with consistently ideal access outcomes. |
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Ultrasonic tips must
be designed specifically to their functional objectives.
The set of tips that I designed for Obtura/Spartan
Corporation have made it easier to do non-surgical
endodontic therapy. This instrument set helps clinicians
find MB2 canals, cut out isthmuses between canals
in retreat cases, smooth pulp chamber floors after
cutting out attached denticles, as well as to remove
posts and broken instruments from canals. There
are just three basic geometric forms of tips, designated
BUC-1, BUC-2, and BUC-3, with the “A”
version of these tips having tip diameters that
are half as big for finer applications. |
With a fine grit diamond coating, the BUC-1 allows
for ideal cutting and refinement of access line angles
so they drop smoothly into canal orifices without the
irregular cutting results of other sharp tipped ultrasonic
instruments on the market. This clean extension of the
access line angles dropping nicely into each canal orifice
allows files and obturation materials to be quickly
and easily placed into canals without bringing a mirror
into the field. Of critical importance is the refinement
of the access line angle creating the convenience form
required for safe rotary instrumentation.
Also needed is a way a to horizontally smooth pulp chamber
floors without cutting past the floor. In molars it
is necessary to plane through the lighter-colored calcific
dentin to get to the darker colored pulp chamber floor
dentin. With small tipped ultrasonic instruments ditching
occurs which obscures pulp chamber floor anatomy. The
BUC-2, with its disk-like radiused tip, smoothly and
safely planes attached pulp stones from the pulp chamber
floor without scoring it. (The BUC-2A, the smaller cousin
of the BUC-2, has a 1mm diameter disk tip that can be
used in the corners of molar and bicuspid access preps.)
Then, a BUC-1 can be easily used to follow pulp chamber
floor anatomy to the canal orifices.
Occasionally a sharp digging tip is needed, hence the
BUC-3, commonly referred to as the Digger. This extremely
active tip is excellent for chasing canals halfway up
a root or for digging around a post to remove it. The
smaller BUC-3 is handy in tight spaces, when a smaller
tip size is required. The water port just near the tip
allows perfect washing and cooling of the operative
site. Keeping the tips cool also extends their life,
but more importantly, the water wash allows instant
view of the operative site after just a quick air blast. |
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Endodontic
imperatives in the new millenium require the search for
and the treatment of MB2 canals in maxillary molars. Anatomic
research reveals that MB2 canals are present upwards of
70% of the time and that they have separate portals of
exit more than 35% of the time. Yet the challenges of
locating and entering MB2 canals are legendary. It’s
hard to find them, then it’s hard to negotiate them.
There is only one way to make this a consistently accomplished
clinical objective. Magnification and ultrasonics.
The BUC-1 has a diamond coating for gross dentin removal,
moving access line angles, cutting a groove in the mesial
access wall to drop into MB2 canals, and for quickly and
carefully unroofing pulp chambers. As experienced endodontists
know, there is great advantage to the creation of a smooth
trough when looking for MB2 canals. A smooth trough, viewed
with magnification, will show a distinct line extending
from the MB1 orifice in a palatal direction to the MB2.
Often the MB2 orifice is seen as a distinct white dot
which is either negotiable with a #15 K-file or is calcified
but thereby located. This gives the clinician an effective
and safe road map to follow when cutting more apically
to enter patent canal space.
However, ineffective tip geometries will make location
of MB orifices difficult. Because, for example, sharp-ended
ultrasonic tips create innumerable clefts and ditches
in the pulp chamber floor, many of which have the appearance
of a fin or MB2 canal orifice.
The BUC-1 ultrasonic tip is basically a round-ended tapered
diamond bur shape, so when they are used to cut a trough
between the MB1 and palatal orifices, the resulting smooth
surface at the base of the trough readily discloses the
MB fin and the MB2 orifice when intersected. The round
trough shape discloses MB canal fins as a white line and
the MB2 orifice as a distinct white dot at the palatal
extent of that line (often on the mesial access wall,
not on the pulp chamber floor).
The BUC-1A, being half the tip diameter as the BUC-1 tip,
is the ideal size for chasing isthmus spaces deep into
root structure as is often necessary when finding apically
divergent MB2 canals and when retreating lower molars.
They are also ideal for cutting into root structure in
calcified anterior cases when progressing beyond the cervical
third of the root. |
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The
BUC-1 is also useful for cutting around attached denticles.
The vibration of this ultrasonic tip will often dislodge
these pulp stones off the pulp chamber floor. However,
more stubborn pulp stones will need to be removed by cutting
around them, crosscutting them, and levering them out
with a spoon excavator, leaving a highly irregular pulp
chamber floor. Pulp chamber floor anatomy can be very
helpful in locating canals, but to see the floor coloration
a flat plane is needed. The BUC-2 and BUC-2a tips are
designed with a flat disc shape to safely plane the pulp
chamber floors after attached denticles have been cut
out.
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BUC-1
Fine Grit, tapered shape – for cutting and refining
line angles, smoothing access walls, cutting MB troughs
BUC-1A Half the diameter of the BUC-1
- aids opening of the isthmus between canals in the same
root, especially in retreat cases.
BUC-2 Disk Tipped – for planning
pulp chamber floors in molars
BUC-2A Smaller disk tipped planer –
used for corners of molar and bicuspid access preps
BUC-3 Sharp Tipped – for aggressive
apical cutting into calcified roots and around posts
BUC-3A Tip is sharp at it's end like
the BUC-3 but much narrower (half the size) for troughing
around broken instruments in the coronal 1/2 of the root.
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A
young endodontist approached me at one of my hands-on
FastTrack courses and asked, “Isn’t it true
that canals are commonly un-negotiable to their end points?
Don’t you find that they are often calcified apically
like the canal in this cuspid?” And I felt the gut
wrench that usually follows that question.
My discomfort at this question comes from the realization
that my easiest answer, “No,” is so easily
misinterpreted as an arrogant reply. Instead, I asked
for his extracted tooth with the straight #10 K-file in
it. I moved the file in and out of the canal demonstrating
the file’s loose resistance to apical file placement.
It was loose, there was no binding of the file in the
canal, but it felt like it was hitting a brick wall at
the end of the canal.
I explained that the sensation of “loose resistance
to apical file placement” indicated that there was
an impediment in the canal, and that in this case the
impediment was most likely an abrupt canal curvature,
not apical calcification. I bent the tip of the #10 K-file,
adjusted the stop on the file to point to the bend, and
re-entered the canal. Every time apical resistance was
met, the file was withdrawn a millimeter, turned 10°,
and watch-wound again. After three attempts, I got a catch,
wiggled the file, slipped around the apical hook, and
dropped through the terminus on the side of the root apex.
Aaaah! The Holy Grail of Endo. |
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In a way, I felt sorry for the guy, because he had just
been disabused of the classic excuse for short treatment.
The good news was that nearly all canals can be negotiated
to their termini, they aren’t calcified in their
apical regions.
Calcification occurs coronally, where pulps begin their
degenerative process.
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The bad news is that
it isn’t necessarily easy to get to the end
of root canals. In fact it’s sometimes incredibly
difficult. In the first cut, root canals are hidden
from direct view and are microscopic in size. “Hidden
and microscopic” is literally what makes endodontic
therapy different from any other part of dentistry.
More difficult yet, root canals accelerate in curvature
and exhibit their greatest anatomic complexity as
you approach their endpoints
. While
root canals are not calcified apically, they are
tough to thread files through and they are easily
blocked with pulp tissue. Further bad news is that
without successfully negotiating to canal termini,
the outcome of all treatment to follow is in doubt,
regardless of how advanced the instruments and techniques
used. |
There are, however, signposts to follow into this maze.
The most important precursor to successful negotiation
procedures is the sophistication of the clinician’s
endodontic anatomic knowledge, especially the clinician’s
anatomic knowledge of the case at hand. You must become
a student of endodontic anatomy in your own practices,
as you shape, clean, and fill canals in all their complexity.
Get to know root canals on an intimate level, and you
can learn to sneak through them at will.
The payoff to operating at this level is predictability.
Once the primary canal of a root canal system has been
negotiated to patency and the pulp has been removed, the
expected outcome of the endodontic procedure goes way,
way up. At this point much of the artful aspect of procedural
endodontics is complete and everything to follow should
be straightforward, regardless of which shaping or filling
technique is used. |
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The
history of the field of endodontics shows that endodontic
procedures are fundamentally plagued by the obscurity
of root canal systems. Endodontic therapy, as a respected
part of dentistry, only took off in the late 1800’s
after Dr. Roentgen invented X-ray imaging. Likewise today,
X-ray imaging is absolutely key to understanding the anatomic
challenges of any given case and our endodontic treatment
results greatly depend on the quality of those images
and our interpretive skills in reading them.
| Even though we often
cannot see root canal complexities on our pre-op
radiographs, we can see apical root outlines and
the anatomy of periradicular lesions. Apical root
outlines become very revealing when imaged with
a file placed to length in the canal. Since Hertwig’s
epithelial sheath forms roots from their periphery
inward, it stands to reason that canals are to be
found centered in the root structure. In the coronal
two-thirds of roots, this Law of Centrality
reveals the presence of additional canals when an
off-angle radiograph is taken . |
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| In the apical thirds
of roots, file position relative to the outline
enables clinicians to discern many apical anatomic
irregularities . |
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| Necrotic canals with
periradicular lesions are the easiest to map pre-operatively.
Periradicular “lesions of endodontic”
origin develop in response to infectious pathogens
emanating from root canal openings, described as
“portals of exit” by Schilder . |
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Ipso loquitor, where
you find a lesion of endodontic origin, you should
find a portal of exit. The presence of asymmetrical
apical lesions is a beautiful tip-off that there
is an abrupt apical canal curvature near the end
of a relatively straight root
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All pre-operative X-ray images should be taken with a
holder and cone positioning device, such as the Rinn XCP,
which ensures that the X-ray beam is perpendicular to
the film or digital sensor, thereby eliminating elongation
error. The next variable to consider is the angulation
of this imaging set, the film/sensor and X-ray head, relative
to the tooth being treated.
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A typical imaging error
is the foreshortening of roots
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Assistants quickly learn
that it is better to foreshorten teeth and get the
root apices on the image, rather than miss the apices
and have to take the film over. We need radiographs
that include root apices and periapical bone, but
which also represent teeth and their roots in their
correct dimensions
. This is accomplished by careful placement of the
film/sensor holder and with clear instructions to
the patient to bite or hold it firmly in place. |
X-ray positioning is critical to radiographic visualization
during root canal therapy, unfortunately it is probably
the most difficult skill to teach to dental assistants.
Digital radiography is most helpful here because the sensor
and X-ray head can easily stay in position for the 15
seconds it takes to see the image on the computer screen.
If the view is not optimal, the X-ray head can be moved
precisely from the previous position, allowing the ideal
angle within 2-3 attempts. With conventional X-ray film,
which must be removed to develop and view, the Dr. and
assistant may give up after 2-3 attempts since the 4th
attempt is no more likely to be ideal.
Digital X-ray imaging has just about hit it’s inflection
point for large-scale adoption into the marketplace due
to it’s speed and ease of image capture, storage,
and retrieval. Another advantage of digital radiography
is that it allows dentists to image process (zoom, change
the contrast, brightness, gamma levels, etc.) radiographs
to ideally visualize apical structures, for instance,
and then be able to change those settings to ideally visualize
the osseous crest or the pulp chamber. The final threshold
to widespread use of this technology will follow the introduction
of electronic dental charts for the simple reason that
digital radiography is a primary requirement to go paperless
in the clinical environment.
In the not-so-distant future dentists will be able to
click off four angles of registered digital X-ray images,
reconstruct those images in their chairside workstation,
and be able to view a dimensionally accurate 3D model
of the tooth to be treated.
In the immediate future, expert-knowledge electronic charts
and digital radiography will allow for dimensional analysis
of the morphology of roots, root canals, and periradicular
lesions to aid treatment planning and outcomes tracking
in digital detail. |
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Apex
locators are indispensable aids in length determination,
but they should be a part of initial negotiation procedures
for more than just length determination. As I mentioned
at the beginning of this article, clinicians must know
root canals intimately to successfully find their way
through them. Knowing root canals at this level involves
putting together every bit of information you can gather
to create an accurate mental construct of canals in which
you are working.
Traditionally, this has been done by combining radiographic
data with tactile feedback from file handles during their
movement through the canal space, however, when an electronic
apex locator is added to the feedback loop there is a
much richer data pool. With an apex locator we can discern
the 3rd dimension of root canals in real-time. We can
connect our tactile feedback to a position in the canal,
and more accurately map that region as a result.
While apex locators are really good at some functions,
they are dreadfully inadequate at others. Apex locators
cannot accurately tell you how far short of the canal
terminus you are. They are very, very good at telling
you when you are at the terminus or beyond. Again, they
cannot tell you how far you are beyond the terminus. Therefore,
they should not be used if you fear taking a small file
passively through the end of a root canal.
I recommend using an apex locator with each negotiation
instrument as this offers many advantages. First, it allows
for greater control and less over-extension of initial
negotiating files as well as eliminating unnecessary films
when files aren’t yet to length. Second, it adds
a layer of confidence to the accuracy of apex locator
readings when the #08, #10, and #15 files all read to
the same or nearly the same length in the canal.
When small files give “squirrelly” readings
with an apex locator, simply moving up one or two file
sizes provides a more stable indication of the canal terminus.
Be aware that apex locators most often err by placing
the file long, rather than short. This occurs most often
in vital cases where the root apex is embedded in less
conductive cortical bone or projects into the maxillary
sinus. In both cases, clinicians will usually get one
accurate reading of canal length when the first file to
length hits the PDL, before getting patent into these
less-conductive periapical regions. This is of no endodontic
consequence other than requiring the treating dentist
to stay alert to catch that single fleeting-but-accurate
apex locator reading.
Without an apex locator, lengths in at least 20% of canals
will be mis-determined (long) and canals will be over-treated
as a result. With an apex locator in the treatment loop,
this 80% accuracy goes to 95%. It is my opinion that treating
root canals without an apex locator is like flying an
airplane without an altimeter, and I wouldn’t do
either. |
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You
cannot predictably negotiate canals to their terminal
points if blockage is a possibility. Unfortunately, this
is extremely common due to inaccurate conceptual models
of apical blockage and the erroneous treatment strategies
taught to us as a result.
Here’s the experience. You irrigate with NaOCl,
just like you were taught, and you watch-wind a #08 K-file
to estimated length. You push-pull it until it’s
loose in the canal. You irrigate, cut the #10 file to
length and work it until it’s loose, you irrigate.
Everything is just going great until you put the #15 file
in the canal and it hangs up. Hunh. You put the #10 in,
the #08 in, the #06 in. Darn, you’re blocked!
This event is only mysterious because apical blockage
has been historically mis-described as being caused by
the apical collection and compaction of dentin mud. While
blockage with dentin mud does occur (especially with push-pull
filing) it seldom causes the irreversible blockage that
clinicians most fear. The breakthrough came for me in
1983 when I realized that I didn’t fear the necrotic
case, only the vital ones. The epiphany was that this
unpredictable and irreversible blockage was caused by
pulp tissue, not dentinal debris.
In retrospect, it was obvious that when the #08 and #10
files bound in the canal and then loosened up, they were
not binding at their tips. The tip diameters of these
files, .08 and .10 millimeters, respectively, are smaller
than the terminal diameters of most canals (.15mm and
larger), allowing them to act as swords cutting through
apical pulp tissue. When a pulp stump is pierced by small
files in the presence of an aqueous irrigant, the cut
tissue can subsequently re-adhere to itself and immediately
meld into a solid mass of collagen if it is pushed into
the apical constricture by the tip of a larger file. This
type of blockage usually occurs with the #15 file in a
Small-Root canal because it is the first file that approximates
the terminal diameter of the canal, causing it to act
as a piston rather than a sword.
For all the hell that this common problem has caused,
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