Traditional versus Conservative Access: Where are we Today? 

By Gabriella Blazquez
Introduction by Dr. Moein Sadrkhani

Introduction
Gabriella Blazquez is a third-year student from UConn School of Dental Medicine. She is interested in endodontics and delightfully enjoys reading our newsletter.

She wrote this piece comparing traditional and conservative approaches to endodontic access. We welcome opinion articles from students, residents and faculties, even on controversial subjects as this one; I am looking forward to getting rebuttal on this as well.

We have listed first a few recent articles that might be in contrast with the views of our student:

Silva EJNL, Pinto KP, Ferreira CM, et al. Current status on minimal access cavity preparations: a critical analysis and a proposal for a universal nomenclature [published online ahead of print, 2020 Aug 27]. Int Endod J. 2020;10.1111/iej.13391. doi:10.1111/iej.13391

Rover G, de Lima CO, Belladonna FG, et al. Influence of minimally invasive endodontic access cavities on root canal shaping and filling ability, pulp chamber cleaning and fracture resistance of extracted human mandibular incisors [published online ahead of print, 2020 Aug 5]. Int Endod J. 2020;10.1111/iej.13378. doi:10.1111/iej.13378

Barbosa AFA, Lima CO, Coelho BP, Ferreira CM, Sassone LM, Silva EJNL. The influence of endodontic access cavity design on the efficacy of canal instrumentation, microbial reduction, root canal filling and fracture resistance in mandibular molars [published online ahead of print, 2020 Aug 6]. Int Endod J. 2020;10.1111/iej.13383. doi:10.1111/iej.13383

Rover G, Belladonna FG, Bortoluzzi EA, De-Deus G, Silva EJNL, Teixeira CS. Influence of Access Cavity Design on Root Canal Detection, Instrumentation Efficacy, and Fracture Resistance Assessed in Maxillary Molars. J Endod. 2017;43(10):1657-1662. doi:10.1016/j.joen.2017.05.006

I want to thank Gabriella Blazquez again for her interest and contribution to our newsletter; looking forward to seeing and hearing more from her in future.

-Moein Sadrkhani, D.D.S.
Chair, Resident and New Practitioner Committee

 

Traditional versus Conservative Access: Where are we Today?

The very first step in treating an endodontically compromised tooth is preparing the access cavity. This preparation opens up the crown so that the dentist may vacate, clean, dry, and finally fill the chambers of the once doomed tooth. Access not only precedes all other maneuvers, it determines their likelihood of success. Dr. Franklin S. Weine, author of the seminal text Endodontic Therapy, even poetized this idea with his famous remark, “Access is success.^“1

Traditionally, each type of tooth has corresponded to a particular access cavity shape. Access preparations for maxillary central incisors are usually triangular, while those for premolars are generally ovoid. Traditional endodontic access cavities (TECs), like these, focus on removing tooth structure to allow instruments a straight-line entry through the canal orifices and to the mid-root.²

Recently, a number of papers have investigated whether TECs, with their standardized access geometries and straight-line pathways, predispose previously treated teeth to fracture via increased removal of tooth structure.³

These studies often compare TECs to conservative, contracted, or truss endodontic access cavities (CECs and TREC designs respectively, collectively referred to hereafter as CECs). The latter methods employ more flexible instruments, increased magnification, cone-beam computed tomography (CBCT), and new dental materials to preserve more of the tooth’s healthy structure. With CECs the focus is placed on saving pericervical dentin, which improves force distribution and lowers post-treatment fracture susceptibility. CECs are tooth-centered procedures, focused on the unique morphology in question, as compared to TECs, which aim to minimize operator error with a more consistent protocol.⁴

The promise of CECs encouraged researchers and endodontists alike to consider challenging traditional paradigms; and in 2018, a meta-analysis on the topic was published. It aimed to find out whether or not conservative access preparations increase the fracture strength of endodontically treated teeth³. To do so, a team of researchers from all over Brazil unearthed and analyzed the existing body of research comparing CECs and TECs.

However, what they found seemed to dampen the enthusiasm surrounding CECs. After narrowing their literature search to six in vitro studies, they concluded that there was no evidence supporting the use of CECs over TECs to increase post-op fracture strength³. And since meta-analyses are consistently touted as the best evidence in evidenced based medicine, it was possible, perhaps even likely, that clinicians would see this as a reaffirmation of the prototypical access technique.⁵

Since 2018, at least 10 papers comparing CECs and TECs have been published, mostly agreeing with the meta-analysis’s conclusion of insignificance. Then, just as the door seemed shut against CECs, a paper published in 2020 utilizing thermocycling, a process that replicates temperature ranges that would occur in the oral cavity, found something contradictory. They concluded, “TREC [truss endodontic access cavity] enhances the fracture strength of endodontically treated teeth under thermal stresses.”

The superior stability of conservative access preparations under thermal stresses has provided researchers a strong impetus to study access cavities under conditions that better approximate those found in the oral cavity. This study begs us to ask, “What else are we missing?” Perhaps thermocycling is just the beginning of a litany of lab procedures we must begin to employ in order to replicate the oral cavity to the best of our ability. Processes that aim to reproduce enzymatic reactions, moisture levels, and bacterial composition might prove to be as crucial as temperature in estimating the effects of different access cavities in vivo.

Beyond that, it pushes us as clinicians to delve deeper in our efforts to find studies to support sound evidence based decision-making. It discourages us from instinctively adapting the findings of meta-analyses of ex-vivo studies into clinical decision-making. We are so often taught, in dental school and by our colleagues, that meta-analyses are worth more than the sum of their parts. However, what if the individual studies utilized in such a systematic review are rendered irrelevant due their inability to reproduce the true conditions present in the mouth?

I would posit that this possibility must be considered in the case of CECs versus TECs. The only meta-analysis thus far, analyzed data generated from extracted teeth. It was a great place to begin investigating but it was hardly a finish line. The more recent paper employing thermocycling might begin a new chapter in access preparation research, one where we focus more on reproducing intra-oral conditions when evaluating the effect of different procedures on long-term success.

The most recent recommendations by the AAE emphasize standardized access cavity outlines and the “straight-line approach” to minimize procedural errors.⁷ It is unlikely that recommendations surrounding access cavities will, or should, change until there have been  randomized controlled trials comparing the in-vivo success and durability of CECs to TECs. However, researchers within our field should continue to consider and investigate this potential gap in the literature.

The evolution of data surrounding endodontology lends credit to the conclusion that we haven’t stopped searching for the very best ways to treat our patients. However, it’s hard to know if and when the literature has provided us enough evidence to shift our clinical decision making. Meta-analyses are often employed to solve this dilemma by deriving conclusions from an existing body of research. Such analyses are nonetheless subject to limitations such as publication, time lag, and outcome reporting biases. Still, when considering conservative versus traditional access, the need for systemic reviews which harness in-vivo data remains.

For now, it’s best to continue removing only what tooth structure is necessary to successfully treat the patient. As for what exactly that means in the case of endodontic access cavities, it appears conservative techniques might still have their day.

References:

1. Druttman T. Top ten tips: Tip number 5- Access cavities and canal location, Endodontic Practice U.S., 2013;6(1):28.
2. Elghany MHAA, Aljuieed HA. Conservative Access Cavity Preparations. EC Dental Science, 2020;19(2):1-6.
3. Silva E, Rover G, Belladonna F, De-Deus G, Teixeira CS, Silva FT. Impact of contracted endodontic cavities on fracture resistance of endodontically treated teeth: a systematic review of in vitro studies. Clinical Oral Investigations, 2017;22(1):109-118. doi: 10.1007/s00784-017-2268-y
4. Yuan K, Niu C, Xie Q, et al. Comparative evaluation of the impact of minimally invasive preparation vs. conventional straight-line preparation on tooth biomechanics: a finite element analysis. Eur J Oral Sci. 2016;124(6):591-596
5. Lee YH. An overview of meta-analysis for clinicians. Korean J Intern Med. 2018;33:277–283. doi: 10.3904/kjim.2016.195.
6. Saberi E., Pirhaji A., Zabetiyan F. Effects of Endodontic Access Cavity Design and Thermocycling on Fracture Strength of Endodontically Treated Teeth. Clinical, Cosmetic and Investigational Dentistry. 2020;12:149-156. doi: 10.2147/ccide.s236815
7. American Association of Endodontists. Treatment Standards Whitepaper. 2019;8-9. Available from: https://www.aae.org/specialty/wp-content/uploads/sites/2/2019/11/TreatmentStandards_2019.pdf