The goal of this clinical trial is to is to assess the antibacterial effect of sodium hypochlorite heated inside root canals of necrotic teeth using various activation techniques

The main question it aims to answer is:

Does the antibacterial effect vary following various standardized techniques of intracanal heating of sodium hypochlorite in endodontic treatment?

Root canal treatment success depends on the removal of necrotic and vital pulp tissues and bacteria and bacterial byproducts from the root canal system.

Mechanical cleansing and removal of necrotic or vital pulp tissue lead to the formation of a layer of debris called " Smear layer," which is made of organic and inorganic substances that should be removed from the root canal system with the help of irrigants.

The presence of complex anatomy like isthmi and anastomoses makes chemical cleansing of the root canal system difficult because they are filled with the smear layer.

The ideal features of root canal irrigants include cleansing, lubrication of endodontic instruments and root canal system, dissolution of inorganic and organic tissues, antimicrobial properties, absence of cytotoxicity without alteration of dental microstructure. Sodium hypochlorite (NaOCl) has been the most widely used irrigant in endodontics due to its antimicrobial and tissue-dissolving action.

Due to the presence of complex anatomy inside the root canal system, activation of irrigation is essential to improve the cleaning of such a complex system. Ultrasonic activation is presently the most popular method for activation of irrigation. It delivers the irrigant farther into areas of the root canal system untouched by instruments, and it improves the mechanical cleaning by increasing the wall shear stress.

NaOCl is used in concentrations between 0.5% - 6%. In high concentrations, it may have a faster dissolution capacity, but it is associated with toxicity in cases of extrusion; thus, methods to improve the action of less concentrated solutions become relevant, such as agitation of the irrigant, constant refreshment and volume, and heating of the solution. Using NaOCl solution at high temperature is related to an increase in reactivity and, therefore, a reduction in bacterial counts and bacterial biofilm dissolution. Although the dentin acts as a thermal insulator, the excessive increase in temperature could dissipate to the periapical tissues, causing damage to the bone tissue .

Initially, it was suggested to heat NaOCl before inserting it into the canals, but this was of little effectiveness .

Woodmansey demonstrated that NaOCl solution can dissolve pulp tissue 210 times faster at boiling temperature (90-120°C) than at room temperature. However, this method remained limited due to the lack of studies confirming its safety until Simeone et al. confirmed that when NaOCl solution is heated inside the canals at a temperature of 150°C for 10 seconds, the temperature of the periodontal tissues does not rise above 42.5°C, which is within the acceptable limits for the periodontal tissue.

Intracanal heating to 180°C using System-B Heat Source shows better antibacterial efficacy than preheated sodium hypochlorite at 60°C. Also, it has been suggested to use low-concentration NaOCl at elevated temperature to report the evidence for better antimicrobial and tissue dissolution properties.

A combination of these two activation methods by ultrasonic agitation of sodium hypochlorite, followed by intracanal heating, may have promising results with regard to the removal of bacteria.

Patients frequently encounter postoperative pain after root canal treatment, and one of the causes is that NaOCl at a higher concentration is irritant to surrounding tissue, particularly in the case of extrusion. Irrigation using lower concentration NaOCl was effective in reducing postoperative pain.

Based on the previous studies, studying the effect of irrigation using low concentration NaOCl (2.6%), which can be activated to increase its reactivity, could give predectible antibacterial effect while reducing postoperative pain and toxicity associated with extrusion.

Inclusion Criteria:

For patients:

• adult male or female patients
• medically free.

For selected teeth:

• asymptomatic necrotic single rooted teeth
• teeth with mature root
• restorable teeth.

Exclusion Criteria:

For patients:

• Patients with dental related symptoms
• patients with chronic or systemic diseases
• pregnant females.

For selected teeth:

• multirooted teeth
• vital teeth
• teeth with incompletely formed roots
• teeth with internal or external resorption
• previously root canal treated teeth