Evaluation of an experimental chelating agent for use in continuous chelation and its effects on different dental tissues, adsorption of chlorhexidine to dentin, prevention, and treatment of endodontic failure

Abstract

Due to the great anatomical complexity, the physical and chemical effects of irrigants are crucial for cleaning surfaces untouched by instruments and reducing the microbial load in endodontic treatments. Consequently, there is a growing interest in new irrigant solutions aimed at enhancing the cleaning and disinfection of the root canal system. Among them, etidronic acid (HEDP) has emerged as an alternative to EDTA. Its alkaline pH allows mixed use with sodium hypochlorite (NaOCl) throughout the biomechanical preparation, providing continuous chelation of smear layer without compromising the dissolution of organic matter by NaOCl and enhancing the antimicrobial action of this irrigant. Sodium gluconate (GS) also shows potential for this type of use, as it has the ability to remove calcium ions and stability at an alkaline pH. Additionally, irrigant solutions with residual antimicrobial activity, such as chlorhexidine (CHX), when used as a final irrigant, may hinder recolonization by microorganisms surviving instrumentation and the adherence of others that could cause secondary infections. Therefore, enhancing the substantivity of CHX is desirable to help prevent therapy failures. Upon diagnosis of failure and the need for endodontic retreatment, it is important to use irrigation protocols that favor the complete removal of obturation material, reduce the extrusion of contaminated debris, and the risk if instrument fracture, in order to avoid the negative impacts of these issues on the prognosis of retreatment. In periradicular surgeries, irrigant solutions with antimicrobial action and the ability to remove the smear layer without aggressing periapical tissues can improve retrocavity cleaning. However, due to the alterations it promotes in the dentin surface, the irrigation used may interfere with obtaining proper sealing between retrofilling material and dentin in the long term. In light of these considerations, this project aims to: Stage 1. Analyze different concentrations of GS when mixed with NaOCl regarding the free chlorine content and the organic matter dissolution capacity of this irrigant, the time for total smear layer removal, the alterations in dentin composition and microhardness, and calcium removal from dentin; Stage 2. Compare a mixture of GS with NaOCl to other irrigation protocols, associated with the final flush with CHX, regarding the amount of CHX adsorbed onto dentin immediately after irrigation and over time, and the prevention of biofilm formation by Enterococcus faecalis; and Stage 3. Compare a mixture of GS with NaOCl to other irrigation protocols in the treatment of endodontic failure regarding the volume of extruded debris, the remaining obturation material, resistance to torsional instrument fracture in retreatments, dentin cleanliness in retro-preparations, and the adhesion resistance of MTA cement to dentin in apical retrofillings in the short and long term. (AU)