A critical analysis of research methods and experimental models to study root canal fillings

Abstract

Canal filling materials and techniques have been one of the most studied topics in Endodontics. A simple search using the mesh term “root canal filling” in PubMed revealed more than 11 000 articles, an impressive number that is much higher than “root canal disinfection” (5544 articles) or even the popular “root canal preparation” (8527 articles). The overriding importance attributed to root filling procedures is not merely intuitive. It derived from the appealing relevance given by the appearance of the white lines in common radiographs grounded on retrospective clinical data that had identified the quality of a root filling as one of the major causes of treatment failure (lack of healing). Since the publication of the Washington study, impressive efforts have been made for the release of new materials and techniques, as well as, for the development of a plethora of laboratory methods to assess the quality of root filling procedures. This narrative review aims to address and discuss the most relevant laboratory methods to assess the root canal filling. As filling quality improvements have not translated into higher success rates, as reported in longitudinal clinical studies, more than to deliver a simple methodology‐based review, this paper aims to present an in‐depth critical view on the assessment of laboratory methods used to study the filling materials and techniques. Recent data indicate that the long‐term dimensional stability/degradation over time of endodontic sealers plays a central role in the treatment outcome. In this context, laboratory methods should be developed focusing on predicting, at least to some degree, the long‐term clinical behaviour of root canal fillings, rather than simply ranking different materials or techniques.

The Influence of Thermomechanical Compaction on the Marginal Adaptation of 4 Different Hydraulic Sealers: A Comparative Ex Vivo Study

“…According to De-Deus et al, the interfacial gap evaluation through sectioning/microscopy has several limitations [40]. First of all, it is a destructive method, with the possibility of specimen damage, such as partial loss of the sample and heat generation, which could jeopardize the SEM observation of the obturation materials.…”

“…Despite this, in the present methodological setup, the root sections were realized following procedures that guaranteed the absence of materials overheating. Moreover, due to the variable pressure scanning electron microscope Hitachi SU-3500, dehydration of the specimen and application of an ultra-thin coating of an electrically conducting metal were not needed to allow for SEM observation, reducing the damage caused by preparation procedures [40]. Moreover, another limitation of interfacial gap measurement through digital software is the difficulty in establishing an overall value for each root section.…”

Effect of the Modified Methacrylate-Based Root Canal Sealer in Single-Cone Technique

“…CLSM with fluorescent organic dyes (such as rhodamine B) was a standard way to evaluate sealer penetration, as it is not dependent on surface quality, and no surface preparation that could cause artifacts is necessary which is superior to SEM [ 36 , 37 ]. However, rhodamine is a hydrophilic dye, so the sealer penetration may be overestimated especially in bioceramic sealers [ 38 ]. On the contrary, we did not find an unusually high dentin permeability in iRoot SP.…”

Dimensional changes of endodontic sealers—An in vitro model simulating a clinical extrusion scenario during 18 months

“…Some of the methodological issues associated with the standard tests are the evaporation of the mixing liquid during the drying of the sample (Vivan et al, 2010 ), the use of water for immersion media instead of body fluids (Gandolfi et al, 2016 ), and the fluid uptake by set sealers (Grga et al, 2011 ). Additionally, current standard tests do not seem appropriate for calcium‐silicate‐based sealers, as their dimensional stability does not seem to comply with the tests advocated in international standards (De‐Deus et al, 2022 ). As these tests are often set up differently than the clinical procedures, the solubility values derived from them cannot easily be extrapolated to in vivo situations (De‐Deus et al, 2022 ; Razdan et al, 2019 ) such as sealer extrusion.…”

“…Additionally, current standard tests do not seem appropriate for calcium‐silicate‐based sealers, as their dimensional stability does not seem to comply with the tests advocated in international standards (De‐Deus et al, 2022 ). As these tests are often set up differently than the clinical procedures, the solubility values derived from them cannot easily be extrapolated to in vivo situations (De‐Deus et al, 2022 ; Razdan et al, 2019 ) such as sealer extrusion. Various authors have already highlighted the need for alternative methods for assessing sealer dissolution (Gandolfi et al, 2016 ; Grga et al, 2011 ; Ha et al, 2017 ; Silva et al, 2016 ; Vivan et al, 2010 ) and for detailed reporting on in vitro studies (Nagendrababu et al, 2019 ).…”