Access in Endodontics – Why is it so Important?

Access in Endodontics – Why is it so important?

DISCLAIMER – How well you “see” influences your access design.

HOW you access canals is directly proportional to your ability to see. Naked Eye Dentists (NEDs- as they are colloquially called) or  2-5 x Loupe based Dentists need accesses that allow the greatest amount of  light into the canals, so they can see.  (Dedicated Headlights or not) It is disingenuous and deceitful for those selling endodontic products to omit the concept that they would never use the products they are selling or lecturing about ….without a Surgical Operating Microscope.

The biggest criticism I have of those who advocate “ extreme dentin conservation” or the “Ninja Access” is not with the access itself. These clinicians are often very skilled and experienced and would NEVER think of trying to perform these procedures without an SOM. Where I object, is the idea that they can advocate or market these products or ideas to those who do NOT use an SOM and who do NOT have that level of experience.

But you will NEVER hear Endodontic speakers ( many of whom receive millions of dollars in patent revenues and from instrument sales) say “I’m sorry. If you are doing Endo and want to get the results I show ….you MUST use an SOM.” That would eliminate 95% of audience and their targeted sales, because few Generalists use one.

Endodontics can be difficult. In many cases, clinicians make it more difficult than necessary by not creating a proper access that allows them straight line approach to the canals. This is especially true for Mesiobuccal canals in both Mandibular and Maxillary molars. Before dealing specifically with molars, lets examine a few access concepts that will allow us to reach the apex more successfully.

Concept # 1 – Most Files can safely only “do” two curves at a time
Although the development of heat treated NiTi metals has improved instrument flexibility, it is important to understand one basic fact about endodontic instruments: In vivo, they can only be expected to consistently negotiate two curves at a time, especially files greater than a size # 15 or 20. Because canals are curved both in a mesio-distal and bucco-lingual directions, we must initially provide as straight line access as possible in order to allow maximum freedom for the instrument in the more confined, difficult apical sections. Most endodontic cases that are ledged occur because the clinician is attempting to guide the instrument through too many curves. The instrument is unable to negotiate the final curve, resists, and then a ledge is created. Limited purposeful straightening of the cervical portion of the canal is the key to negotiating the final apical curves. This was the reason for the popularity of the “Crown-Down” technique that ushered in a new era of canal instrumentation.

Concept #2 – The access is complete when a DG 16 explorer can “stand” unaided in the canal.
How do we know when access is sufficient? I used to teach students to literally place a DG16 explorer in the canal and have it “stand up” (balanced in the canal orifice) without being held. That was for STUDENTS!  A conscious effort should me made to ensure that the explorer does not touch any other part of the access. When it “stands” on its own, access is sufficient. For less experienced clinicians or for clinicians who do endo less frequently, it is probably a good rule. For those advocating “minimalist” accesses, this concept is an anathema.

Concept #3. STRATEGIC  extension of the access
Strategic extension of the access is now the rule. By somtimes extending the access opening to “nontraditional areas” we allow for better direct line access to the deeper portions of the canal.  (For example in MB canals or madibular molars or MB2 in maxillary molars)

Concept #4. Creation of the “Glidepath”
General Dentists are often amazed at how quickly Endodontists treat their cases. Speed of treatment has very much to do with how easily and quickly instruments can consistently be placed in the canals. Dr. Ken Serota coined the term “Glidepath” with reference to how instruments are inserted into the canal orifice. The term describes the way that endodontic access is designed to

(a) allow for straight line access to the canal and

(b) allow the clinician to place instruments in the general vicinity of the orifice and have them passively led into the canal space as they are inserted.

i.e./ If the access is designed with the proper Glidepath, placing an instrument in “the vicinity” of the DB part of the access leads it directly into the DB orifice with no effort.

This dramatically decreases treatment time by :

(a) eliminating the need to “search” for the orifice with the file

(b) reduces the chance of acutely bent instruments that must be discarded

(c) allows for easier irrigation syringe insertion and better irrigation volume

Concept #5. Coronal tooth structure is not sacred
Endodontists who perform these type of accesses are occasionally criticized by Prosthodontists and Cosmetic dentists for being too aggressive in removal of sound coronal tooth structure. It is sometimes necessary to remind these clinicians that their restorative treatment depends on sound periapical health. (Both Endodontic and Periodontal) The best Prosthodontics is of absolutely no value in cases where the endodontic or periodontal treatment results are less than optimal. Straight line access is integral to successful endodontics. Having said that, excessive removal is not advocated.
My friend and colleague Dr. Terry Pannkuk put it perfectly when he coined the term “SEA – Strategically Extended Access”.  The SEA creates a balance between “Biomimetic” Dentistry (that may place undue emphasis on preserving tooth structure) and over-enlarging accesses to the point of weakening the tooth (simply because the clinician is unnecessarily destroying tooth structure to visualize the orifices or access) in their attempt to find or instrument canals.

If you ever  watch a skilled endodontist treat a case, you will invariably be impressed by the time invested in creation of the access cavity. Careful creation of smooth (unditched walls) and unhindered access to each canal pays handsome dividens later on when instruments, syringes, cones, heat carriers and pluggers are easily introduced into the tooth without the need to “finesse” them into the tooth.

Example Case 1- The Maxillary Lateral Incisor
Higher failure rates are associated with treatment of the maxillary lateral incisor. We know that the apical section of this root curves both distally and palatally in most cases. This is not a particularly difficult tooth to treat when proper access is made. However, when access is small and poorly designed, the final palatal curve is almost impossible to negotiate. The result is that these cases are often ledged, filled short or perforated at the final curve.  This happens less frequently with today’s more flexible Ni-Ti files.

Example Case 2- The Mandibular Incisor with 2 Canals
Buccal extension of the access is not a new concept. Some clinicians have even suggested that anterior teeth with two canals ( such and mandibular incisors and Cuspids) should actually be accessed from the buccal surface! They claim that this produces straighter line access to the often missed lingual canals and they are correct. These lingual canals are missed because most incisor accesses are made at the cingulum. The instrument must first be placed toward the buccal as it is negotiated into the buccal canal orifice. But with the lingual canal, It must immediately make a sharp transition toward the lingual to get into the lingual orifice. The classic endodontic access in the mandibular incisor often does not take this into account. That is why when an Endodontist opens a suspected two canal lower anterior tooth, you will often see the access is moved very far labially, In many cases it incorporates the lingual dentin and enamel all the way to the incisal edge. We may be criticized for the aesthetics of this type of access but it is the only way that these cases can be treated successfully by non-surgical means.

Example Case 3- MB canals of Mandibular Molars
We can also extend these principles to the molars. Mesiobuccal canals of mandibular molars have a particular characteristic that often is not noticed by clinicians performing endodontics. Whereas the the Mesiolingual orifice is centered under the mesiolingual cusp, the mesiobuccal canal orifice is often located much further buccally than anticipated. The “Classic” trapezoidal endodontic access preparation does not take this into consideration.

Unless accommodation is made, the file shaft often is quite close to the MB cavosurface margin of the access or orifice and may be deflected by it. The file must first “negotiate” this curve as it enters the orifice. This happens even before it again must curve toward the lingual aspect of the tooth where it sometimes joins the mesiolingual canal on its way to the apical foramen. In most cases the file is able to negotiate two of these turns but as the final curve occurs either mesially or distally, there is so much tension on the instrument that, as in the maxillary lateral incisor, the canal often ledges. The clinician becomes frustrated and the case is filled short of the apical foramen.

The best way to prevent this is by modification of the access by buccal extension. This is done by again extending the principles of “Triangle1 and 2” by removing the cusp tip of the mesiobuccal cusp. In some cases where CL V buccal restorations have been placed, the orifice may be even further down the root than anticipated. In that case a “slot” is actually cut in the MB cusp that allows for straight line placement of the file into the orifice. You will notice immediately that the “first curve” that you negotiate is no longer high up in the area of the orifice,it is further down the canal. This allows you instrument to negotiate the two turns that are required to reach the terminus, the lingual curve and the M-D curve ( depending on the root curvature).

Example Case 4 – MB1 canals of Maxillary Molars
Good direct visibility is paramount. This may include removal of the ENTIRE MB cusp in molars. The Buccal canals are often tucked far to the buccal and you will NEVER see them if you don’t do this. They also often have multiple curves ( bucco-lingual and Mesio distal) You’ll never negotiate those unless you get as straight line access to the orifice as you can. I sometimes even use a “slot” type access that moves the opening very far buccally. Cameras or scopes won’t help you if this is not done correctly. (2) The creation of a “Glide Path” is essential to smooth shaping. You really should be able to place instruments into the canals WITHOUT LOOKING. If you are constantly picking up your mirror to get an instrument into the canal, you are wasting time and causing much unnecessary stress. The problem in that case is that the access is gouged or ledged and the instruments to not naturally glide down the prepared access walls right into the canal. i.e./ place the instrument “somewhere” in the MB of the orifice, and it goes directly down the canal. Same for DB, palatal etc. This may seem like an obvious concept but the access cavity is much like a crown prep in that it has to be refined and contoured properly to be effective.

Example Case – MB2 canals of Maxillary Molars
The MB2 of maxillary molars is most often very small. Recent studies have shown that at least 90 % of first molars have these canals. Fortunately, many of them are joined to MB1. In those cases it may be possible to just treat MB1 without even knowing about MB2 because sealing the common formen is often enough. But do we want to take that chance in a necrotic molar ?

Location of MB2 is a whole topic in itself and I will address that in another area of the web site. Having found MB2, it is important to get direct line access in this canal because of the minimal diameter of the canal and the tendency for their to be a “proximal lip” that covers the canal from the mesial aspect. If this mesial “lip” is not removed, the file will be deflected distal upon initial insertion. Just like the other canals mentioned above, this initial bend will make it difficult to negotiate the file as it moves buccally to join MB1 and then distally as the root curves. Creation of a proper Glidepath for this canal also solves the problem of repeated inadvertent entrance to MB1 when what you to do is insert the instrument into MB2.

Exceptional or Unusual Anatomy
In the case of bayonet or dilacerated canals, there may be another curve that can be very challenging even with adherence to the above principles. I believe that these cases should be radiographically anticipated before treatment and referred before the clinician ledges the case or breaks an instrument. cbCT imaging has been extremely helpful in determining and assessing anatomy previously impossible to image with 2D conventional radiography.