Final answer:
The smear layer present on the root canal wall after cleaning and shaping is best removed using EDTA, which is a chelating agent that binds to calcium ions in dentin.
Step-by-step explanation:
The smear layer present on the root canal wall after cleaning and shaping is best removed by using EDTA (ethylene diamine tetraacetic acid). EDTA is a chelating agent that effectively removes the smear layer by binding to the calcium ions in dentin. This action demineralizes the smear layer and the surface layer of dentin, which allows for better adhesion of sealants during the root canal procedure. Other options like hydrogen peroxide, chlorhexidine, and isopropyl alcohol do not have the same efficacy in removing the smear layer as EDTA does.