Root canal treatment diagnoses as pulpitis irreversible can be treated in a non-vital condition with devitalization material. Arsenic is one of devitalization material that used in inflammatory pulp tissue before it is going to endodontic treatment. The long-term use of it or the leak of using this arsenic can cause the toxic effect of the pulp tissue. The case is going to report is about the damage of gingival tissue and alveolar that caused by the uncarefullness using of arsenic. Inappropriate arsenic applications cause the leak that able to spread to gingival tissue and will become necrosis. Now a day, the using of arsenic begin to leave because of the toxicity sad effect. This report is going to report how much the damage using arsenic trioxide (As2O3) and the effort from the leakness.

Cleaning and shaping of the root canal as the foundation for successful endodontic therapy. Cleaning of the root canal as the removal of all the contents of the root canal systems before and during shaping. Mechanical cleaning as the most important part of the root canal therapy. Instrumentation of the apical region has long been considered to be an essential component in the cleaning and shaping process. The apical area as the critical zone for instrumentation. The apical portion of the root canal system can retain microorganisms that could potentially cause periradicular inflammation. The nickel-titanium rotary instrumentation system to facilitate the cleaning and shaping process. Larger instrumentation sizes not only allow proper irrigation but also significantly decrease remaining bacteria in the canal system. How the larger apical sizes preparation must be achieve to clinical success. This paper will describe about the major factors impacting the selection of final apical size, the factors are the anatomy of the apical constriction, root canal diameter, apical instrumentation, and bacteria in dentin tubuli.