Postoperative Pain and Periapical Tissue Healing

The role of microorganisms in periradicular infection has been well established in endodontic literature, signifying that endodontic treatment will be afflicted with a higher chance of failure if microorganisms persist in the canals at the time of root canal Obturation .

Furthermore, anatomic complexities of the root canals as isthmuses, fins, ramifications, lateral Canals, and dentinal tubules make the situation much more difficult; bacteria harboring such areas become inaccessible to mechanical instrumentation, and protected by tissue residues, dentin, serum and dead cells that inactivate or diminish the efficiency of antimicrobial agents.

Sodium hypochlorite (NaOCl) is regarded as the most potent disinfectant in endodontics due to its excellent ability to dissolve vital and necrotic tissues in addition to its antimicrobial activity. However, intracanal irrigants are only effective when in contact with the surface, and they cannot penetrate deep into the surfaces because of anatomic barriers. NaOCl can penetrate into the dentinal tubules by 130 μm, whereas bacteria can penetrate into the dentinal tubules by 1000 μm.

Silver nanoparticles (AgNPs) can also be used for disinfection because of their optimal antimicrobial properties. They are effective against many microorganisms including E. faecalis . Nanomaterials has dimensions of 1- 100nm, presenting small sizes, large surface/area mass ratio and increased chemical reactivity , the small size of nanoparticles offers a larger surface area for a small volume of the particles. This allows them to exert action even when used in small quantities, the action of AgNPs differ according to size, concentration, and time of application. Moreover, the killing effect of AgNPs against gram-negative and grampositive bacteria increases with decreasing particle size.

Silver nano particles release silver ions which have an electrostatic attraction to sulfur proteins, that results in adherence and disruption of the bacterial membrane, Silver ions can also cause the denaturation of DNA and ribosomes directly. AgNPs can also interrupt signal transduction by dephosphorylation of tyrosine residues on the peptide substrates leading to cell death and apoptosis.

However, cell culture studies revealed that AgNPs are able to induce cytotoxicity in human cell lines including human bronchial epithelial cells, red blood cells, macrophages, liver cells, etc., particularly for those with sizes more than 10 nm, and the cytotoxicity of AgNPs has been reported to be contingent upon dose, size, and exposure time .

Since irrigant needs to reach and disrupt the biofilm matrix in less accessible areas of the root canal system, several agitation and activation methods have been proposed to improve efficacy, including sonic \& ultrasonic activation, negative apical pressure irrigation, laser activation and physical agitation using XP-Endo Finisher. Several studies have shown that compared to conventional irrigation, the application of ultrasonic activation or XP-Endo Finisher enhances the efficacy of NaOCl in reducing intra-canal bacteria and removing biofilms from the main canal lumen, the apical third root surface and shallow or deep layers of root dentine.

Pain following root canal treatment is an important patient-centered outcome that has been related to the patient's quality of life, with an incidence of 3-58% following treatment. It could be associated with mechanical and chemical injuries, along with the presence of microorganisms in the periapical region. However, Advancements in material science and metallurgy have improved the predictability and efficiency of delivering endodontic treatment either following single-visit or multiple-visit root canal treatment, even in teeth with necrotic pulps.