16 February 2022

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Ultra-conservative endodontic access cavity and its influence on the shaping of straight oval canals

Lara Figini

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The correct design of the access cavity is essential to provide adequate visibility, facilitate the identification of canal orifices and reduce the risk of complications, such as instrument fracture, apical transport and perforations.
A new concept has been proposed for the preparation of endodontic access cavities which involves minimal removal of the coronal tooth structure and the preservation of a portion of the pulp chamber roof and pericervical dentin and this to avoid excessive removal of dental tissue. which predisposes the tooth to fracture.
However, an ultraconservative endodontic access cavity can hinder the visualization and identification of root canal orifices and limit the action of endodontic instruments, thus determining large regions of unprepared canal walls and compromising the decontamination process.
In particular, shaping of oval-shaped root canals has always been considered a challenging procedure, so much so that computed tomography (micro-CT) studies have revealed that a substantial part of the dentinal walls in oval-shaped root canals remain unprepared after root canal instrumentation. Oval shaped root canals with unprepared surfaces can 'protect' bacterial biofilms, which can be a source of persistent infection that can lead to post-treatment endodontic disease.

Materiasl and methods
In an in vitro study, published in the International Endodontic Journal of January 2022, the authors evaluated the influence of endodontic access cavity design on the percentage of unprepared areas of the canal walls and the flexural fatigue of motion-activated instruments. alternating in the oval root canals of the extracted teeth.
Forty-two mandibular incisors with oval canals were scanned by a microcomputerized tomography (micro-CT) device for selection and homogeneous distribution of samples. Then, the teeth were divided into two groups (n = 21) based on the design of the access cavity under consideration:

Group 1, in which an ultraconservative endodontic access cavity (UltraAC) was performed;

Group 2, where a traditional access cavity was made.

All canals were reached with the aid of an operating microscope, instrumented with the WaveOne Gold Medium system and irrigated with 2.5% NaOCl and 17% EDTA. Unprepared areas of the canal wall were analyzed by superimposing images before and after instrumentation and expressed as percentages. The data provided by the micro-CT were analyzed using the t-test, the Mann-Whitney and Wilcoxon test. The endodontic instruments used during the instrumentation were subjected to static flexural fatigue tests using a stainless steel artificial canal with a bend angle of 60 ° and a radius of 5 mm, located 5 mm from the tip of the instrument. The instruments were activated until the fracture occurred and the time in seconds to the fracture was recorded using a digital timer. The number of cycles to fracture was statistically calculated and analyzed. For the flexural fatigue data, an ANOVA test supplemented by a Tukey gamma test was used. The 5% significance level was used for all analyzes.

Results
There was no significant difference between the two groups in areas not prepared by the instrument during root canal shaping (p> .05). The difference in flexural fatigue strength between the two groups was also not significant.

Conclusions
From the data of this study, which must be confirmed in other similar works, it can be concluded that the design of the UltraAC ultraconservative endodontic access cavity does not interfere with the quality of the root canal instrumentation at the level of the mandibular incisors extracted with straight and oval canals and not even in the resistance to flexural fatigue of endodontic instruments.

For additional information: Influence of conservative endodontic access cavities on instrumentation of oval-shaped straight root canals.