A critical analysis of research methods and experimental models to study apical extrusion of debris and irrigants

During root canal treatment, intra-canal content as well as irrigants and root filling materials may be extruded into the periapical tissues, leading to undesirable consequences such as delay of healing and flare-ups. Although apical extrusion of debris is an inherent occurrence of root canal treatment and no instrument or technique has totally solved this problem, attempts are underway to minimize the harm exerted to periapical tissues with the development of new techniques. This has led researchers to continuously evaluate new instruments and methodologies in terms of apical extrusion. New research on extrusion is frequently published some of which utilize traditional experimental designs and others assessing extrusion using modified or innovative methodologies. This review focuses on the research methods and experimental models to study apical extrusion of debris and irrigants by making a critical analysis of each technique. A PubMed and Scopus search was conducted and 144 articles relevant to apical extrusion were retrieved from 1968 until 2021. The methodologies used in every research article were evaluated and a classification was created. Each methodology is described with the general outlines and advantages and drawbacks of each technique summarized with a critical approach. It appears that the collection of debris in a vial still serves as a method chosen by authors even in most recent studies. On the other hand, development of experimental models that include multiple factors considering the drawbacks of the existing study designs is essential to draw more reliable conclusions on the apical extrusion phenomenon.