Minimally Invasive Endodontics: Finding the Right Balance Between “Too Much” and “Not Enough”

Since the goal of endodontic therapy is microbial elimination (control), it is important to determine if this goal can be achieved with minimal dentin removal given the available technology. Unfortunately, some level of dentin removal is necessary because disinfection of the root canal without direct manipulation of dentin is currently not possible. The shaping process facilitates irrigation and obturation, and access is required to achieve each of these aspects. The real question is where should clinicians draw the line in terms of achieving their treatment goals while simultaneously being less invasive. In other words, what is the appropriate balance to routinely achieve stated objectives without over- or under-doing it?

The purpose of access preparation is to find all canal orifices and allow for their full disinfection (including those canals hidden from view). Therefore, making the access too minuscule may have unintended consequences. If the desire to be minimally invasive leads to an increase in the rate of procedural errors such as missed canals, ledging, perforation, or instrument separation, the benefit may well be outweighed by the poor outcome. Being more conservative than the standard microsurgical access preparation might save some dentin/enamel, but perhaps at too high of a cost.

Moreover, histological studies have shown that the natural diameter of root canals requires a biologically sound apical preparation size (wide enough to clean the biofilm).^1-3 These biological sizes combined with effective irrigation can increase clinicians’ chances of success. The addition of new and innovative 3-dimensional (3-D) finishing instruments may help improve canal cleaning without aggressive dentin removal. This area is highly promising for the near future and may save on dentin removal at the apical third.

Thus, when considering the third phase of dentin removal, namely root flaring, clinicians may at last be able to save considerable dentin without potential compromise. Historically, the approach has been to flare and remove dentin in this area of the canal to accommodate condensers and pluggers for warm vertical and lateral condensation techniques. However, with the availability and increased popularity of bonded obturation (bioceramic cements) using synchronized hydraulic condensation, the need for over-flaring to fit pluggers and spreaders deep in the apex is no longer necessary. This minimally invasive technique will surely preserve dentin by not requiring unnecessary flaring (a size 0.04 constant taper is all that is required for irrigation and bonded obturation^4,5).

In conclusion, while clinicians should strive to be minimally invasive (on balance), some aspects of MIE, such as micro-access preparations, may fade away as their potential for negative consequence is compared with their benefits. In any case, removing what dentin and enamel is necessary for predictable success—and not more or less—remains the objective of care.

To paraphrase Ericson, minimally invasive dentistry includes “a systematic respect for the original tissue” and “preventing or treating disease with as little loss of original tissue as possible.”⁶ These aims are logical and almost obvious if taken in the correct context. Ericson does not claim that respecting original tissue is more important than preventing or treating disease, but rather that the disease prevention/elimination should be performed without sacrificing unnecessary original tissue.

There are three aspects of clinical endodontics that are essential for biological success (ie, no periradicular disease) and survivability of the tooth:

• Biological success is achieved by prevention or removal of microbes, particularly in the apical 3 mm to 4 mm of the canal.

• Long-term survivability of the tooth is improved with the minimal removal of original tissue in the coronal two thirds of the root.

• Access to the root canal (both coronal and apical) is critical.

Let’s examine the future of minimally invasive endodontics (MIE) regarding these three aspects (according to the author’s opinion).

1. Biological success. Dentistry is entering a new era in endodontics with the introduction of disinfection systems that do not require changing the non-round canal to a round shape. Previously, clinicians either had to sacrifice cleaning or remove too much original tissue. Now, files and finishers are able to adjust to the original shape of the canal, scrape biofilm similar to periodontal scalers, and then allow irrigants to work against exposed microbes. These systems will continue to advance, allowing clinicians to leave greater amounts of original root structure while more effectively removing inflammatory stimulants.

2. Survivability. Here again the future looks bright. Until recently, the preparation of the coronal two thirds of the canal was designed to facilitate placing pluggers to within 4 mm of the working length in order to create hydraulic forces for heated gutta-percha. This required large tapers that are destructive to the original root with little benefit to microbial removal. Today, cold hydraulics with bioceramic sealers allow for improved sealing of the canal without the need for removal of excessive coronal root structure.

3. Access. Unfortunately, minimally invasive access cavities have dominated the discussion of MIE. Context here seems to have been lost, and respect for original tissue has become more important than preventing or treating disease. As presented, it seems impossible for most dentists to predictably and safely prevent or remove microbes in the root canal. In addition, in teeth requiring root treatment, the shape and size of the access opening is usually dictated by caries or lost restorations. Moreover, the design and quality of the restoration has been shown to effectively make up for lost tooth structure. While removal of unnecessary dentin during access preparation should still be the aim, minimally invasive access preparations should have no future in our field. If the aim was changed from “removal of as little tooth structure as possible” to “removal of as little tooth structure as necessary,” I would be all for it.

The purpose of endodontics is to heal or cure lesions of endodontic origin. The question regarding the philosophy of minimally invasive technique and technology must be in the context of the rationale for endodontics: Endodontics has a 100% capacity for repair if the root canal system can be cleaned and sealed either nonsurgically or surgically.⁷ Do current minimally invasive thinking, techniques, and technologies produce more or less predictably successful endodontic outcomes?

In order to define minimally invasive endodontics (MIE), it is important to state what it is not. MIE should not mean being mechanically more conservative and yet clinically less successful. It should not mean making endodontic mechanics more difficult by “conservative” accesses or root canal system preparations. MIE, while sounding altruistic, can represent a false sense of endodontic security; it can place emphasis on a medical “buzzword” rather than what is biologically important.

Conceptually, minimally invasive seems noble: fewer traumas, better efficiency, and perhaps more predictability. But are these metrics of measurement for MIE biologically and structurally good or bad? Of course, the optimal “minimally invasive” approach is noninvasive or no invasion at all. Like most things in life, there is the give and the get. In endodontics, the get is treatment that may necessitate only minimal weakening of tooth structure while successfully eliminating the root canal system as a source when endeavoring to prevent or cure lesions of endodontic origin.

The terms minimally invasive and maximally appropriate require careful scrutiny when considering endodontics. For decades, root canal systems could not be sterilized, shaped, and 3-dimensionally sealed because the technology simply wasn’t available. Access cavities were designed without sufficient knowledge of mesiobuccal (MB) 2s and 3s in maxillary first molars or mid-third mesial canals of mandibular first molars. Triple-rooted maxillary premolars and appreciating 50% of two-canal mandibular lateral incisors, for example, were not on the endodontic radar except for Swiss physiologist Walter Hess’ discoveries in the 1920s that used vulcanite metal to map root canal systems. It took the operating microscope, the Tooth Atlas, digital radiography, and nickel titanium (NiTi) instrumentation to successfully address and treat the root canal system.

Some minimalists would have endodontics revert back to the dark ages (literally), when canals could not be found or treated. Today, elegant shapes can be predictably prepared to clean, shape, and obturate the root canal system. The size of the radicular shapes replicates nature’s original shapes that allow the tooth to be strong enough to last a human lifetime, as nature intended. The size of a natural root canal system’s canals range from a fifth to a third of the width of the root as the root canal nears its pulp chamber’s entrance.

Perhaps the most confusion over minimally invasiveness involves “overshaping” coronally, as cited in the buccal view of posterior teeth and, thus, ruining the ferrule. However, restorative literature clearly identifies the buccal and lingual dimension—not the mesial distal—as the critical ferrule location.⁸ Proponents of “over-instrumenting” in the mesial-distal dimension need only learn their restorative literature and compare shaping buccal and lingual results by using cone-beam computed tomography (CBCT) 3-D imaging.

Finally, being more conservative with tooth structure but less predictable in endodontic mechanics is a bad idea clinically. Root canal treatment is difficult enough as is. Treatment that is conducted through small access openings is more likely to result in undercleaned, undershaped, or underfilled root canal systems while increasing the probability of catastrophic breakdowns in technique. Maximally appropriate means optimizing current tools and technology. When properly interpreted and applied, minimally invasive and maximally appropriate are essentially the same in regards to thinking, technique, and preferred outcome.

Allen Ali Nasseh, DDS, MMSc
President, RealWorldEndo™
Wilmington, Delaware
Clinical Instructor
Department of Restorative Dentistry and Biomaterial Sciences
Harvard University School of Dental Medicine
Boston, Massachusetts
Private Practice
Boston, Massachusetts

Martin Trope, DMD
Clinical Professor of Endodontics
University of Pennsylvania School of Dental Medicine
Philadelphia, Pennsylvania
Private Practice
Philadelphia, Pennsylvania

John West, DDS, MSD
Founder and Director
Center for Endodontics
Tacoma, Washington
Past President
American Academy of Esthetic Dentistry
Past President
Academy of Microscope Enhanced Dentistry