The end point of cleansing, shaping, and obturation procedures: where to, when to

By Richard E. Mounce, DDS

In my global lectures, I am commonly asked where endodontic treatment should be terminated and if this point is different for vital and necrotic teeth. I wrote this article to answer these questions in a clinically relevant manner.

While literature-based opinions may differ, I cleanse, shape, and obturate canals to the minor constriction (MC) of the apical foramen whether the tooth is vital or necrotic. For me, all rotary nickel titanium (RNT) shaping files, irrigants, and obturation materials cease at the MC whether the case is vital or necrotic.

The MC is a natural termination point of endodontic treatment. Cleansing, shaping, and obturation to the MC fulfills one of the key objectives of canal preparation — to keep the MC both at its original position and size during treatment. Leaving the MC at its original position and size provides the clinician an apical capture zone into which the obturation is predictably placed. Leaving the MC in place is predictive of uneventful treatment.

Alternatively, transportation of the MC through forceful instrumentation that is inappropriately carried out is predictive of postoperative pain and iatrogenic events of all types. Once violated, management of a clinical case is made much more difficult than it would otherwise be. Violation of the MC is consistent with fractured RNT file fragments, extrusion of irrigants and obturation material, and apical bleeding among many potential problems. In my hands, patency files (small hand K files, and #6-10) are the only things that pass beyond the MC. It is unproductive and unnecessary to pass RNT files through the MC. Such extrusion of RNT files is consistent with apical transportation, greater remaining debris, and extrusion of irrigants and obturation materials.

To discuss the rationale for this termination point of cleansing and shaping procedures, it has value to consider, in a larger context, many of the patient- and tooth-related factors that will promote the best clinical outcome and avoid iatrogenic issues, which are discussed below in the context of endodontics vs. implants.

Once observed and appreciated, these risk factors should guide clinicians to strategies for their correct management especially with regard to achievement and maintenance of apical patency, determination of the position of the MC, and preparation of the correct master apical diameter. The greater the number of complicating (risk) factors that are present in a clinical case from the lists (below) of periodontal, patient-, and tooth-related factors to be considered in the examination, the more challenging it will be to reach the MC and treat the tooth to the highest standard.

Succinctly stated (Munib Derhalli, DMD, MS, MBA, Richard E. Mounce, DDS, Clinical Decision Making Regarding Endodontics and Implants: Part 1, in manuscript): “Treatment options for either modality (endodontics vs. implants) in the most general sense should be based on case complexity, patient factors, tooth factors, periodontal status, systemic health, the intended functional and strategic value of the tooth, the esthetic desires of the patient, and financial considerations, among others. These factors are elaborated on below. These factors complicate treatment planning significantly and have an impact on case outcome. The risk factors are marked as I (implants) and E (endodontics) or both if they will have an impact on treatment planning implants, endodontics, or both.”

Patient-related (among others):

Dental anxiety (I/E)
Medical history (I/E)
Limited opening (I/E)
Gag reflex (I/E)
Inability to be reclined (I/E)
Financial restrictions placed on various options (I/E)
Lack of patient cooperation (I/E)

Tooth-related (among others):

Tipping, rotation, buccal, and lingual positioning relative to the alveolar ridge, crowding (E)
Short roots (E)
Long roots (E)
Calcified roots and pulp chambers (E)
Resorption of all types (E)
Third molars (E)
Atypical anatomy (dens in dentae, fused roots, etc.) (E)
Trauma cases of all types with luxation and replantation (E)
Blunderbuss apices (E)
Previous root canal treatment (E)
Presence of iatrogenic events (E)
Periapical and lateral root lesions (E)
Access through crowns and bridges (E)
Perio-endo combined lesions (E)

In addition (taken from the same article above) the following periodontal considerations should be taken into account.

“Factors in determining periodontal risk assessment:

a) Available alveolar bone support
b) Degree of furcation involvement
c) Tooth position in the arch
d) Genetic factors
e) Previous periodontal history
f) Crown-to-root ratio
g) Clinical mobility
h) Oral hygiene compliance
i) Tobacco utilization
j) Remaining dentition
k) Systemic health status
l) Endodontic status
m) Occlusal status
n) Status of periodontium
o) Age of patient”

One part of the comprehensive subjective and objective examination discussed above is the radiographic assessment. Knowing both where to terminate endodontic treatment and assess the anticipated ideal master apical diameter starts with a correct diagnosis of the initial preoperative radiographs. Ideally the clinician should take two to three preoperative radiographs of the tooth, if possible, from the mesial, the distal, and the buccal. To use only one radiographic image risks missing vital information that can have a long-term impact on treatment success. For example, many lower molars have three roots. Unless multiple radiographic angles are taken, it is easy to miss the third root.

Radiographs should be assessed, among many risk factors, for:

• Tooth length
• Curvature
• Canal calcification
• Degree of apical maturation (open apex, fully closed, etc.)
• Resorption, especially apically
• Presence of a cervical dentinal triangle
• Access challenges (making access through a crown where the chamber is obscured)

Fig. 1: The Elements Diagnostic Unit* (electronic apex locator)RNT files are then inserted to this length and after the first RNT file reaches the TWL, the length can be assessed again electronically. This degree of control should be contrasted with an approach where the clinician has no idea what the TWL is and blindly inserts an RNT repeatedly trying to make apical progress. A lack of apical control is highly predictive of iatrogenic events and postoperative discomfort. In addition to the above, if patency has been maintained appropriately, the clinician should be able to take a paper point to the TWL and obtain a small spot of moisture or hemorrhage. If the spotting is consistent over several paper points, and the length determined is the same as the electronic length and EWL, the position of the TWL is verified. The EWL is one piece of evidence in the determination of TWL along with an electronic length, bleeding point, tactile feel, and possibly radiographic means. These various means of determining TWL should confirm each other, and none of these means is definitive on its own. In other words, the clinician would not rely entirely on electronic means or the bleeding point alone (Figs. 2A-2B).