The objective of this study is to investigate "clinically" the effectiveness of Glycyrrhizin based intracanal medication compared to the commonly used intracanal medicaments (calcium hydroxide Ca(OH)2 and Ledermix) on the levels of bacteria and inflammatory cytokines in root canals and periradicular tissues of teeth with apical periodontitis.

Periodontitis is a dynamic inflammatory process located at the periapical region, the type of immune-inflammatory response to periapical periodontitis is determined by a network of chemical mediators produced by immune cells in response to the stimulus caused by the action of microorganisms and/or virulence factors. This may result in damage to the tissues and in the development of endodontic signs and symptoms (1-3).

In infected root canals, the destruction of periapical tissues is mediated by tumor necrotizing factor (TNF-α) and interleukin-1β (IL-1β) that appears to be directly related to high levels of infectious content present in the root canal (4). Arachidonic acid metabolism plays a key role in many inflammatory diseases, one of its products is the prostaglandin E2 (PGE2) which has been also shown to potentially stimulate bone resorption and to inhibit reparative bone formation in vitro and in vivo (5). Particularly, IL-1β, TNF-α, and PGE2 have been detected in periapical tissues (6-9), being considered as an important inflammatory biomarker in the periapical disease (1, 2, 5, 7, 10).

To identify a specific inflammatory mediator as a diagnostic marker of disease status, the mediator should not only be present or elevated in disease and absent or low in health, but it should also longitudinally increase during active disease progression and subside following therapy (5).

Although instrumentation may be assumed to be of greater importance in the clinical practice, the use of intracanal medication has been proven to optimize the root canal disinfection (11-14). As root canal medicaments can come in direct contact with periapical tissues, in addition to having good antibacterial ability and being biocompatible, so a wide variety of intracanal medications have been proposed. In selecting root canal medicaments, it is necessary to consider their therapeutic benefits against their potential cytotoxic effects. Ideal root canal medicaments should have strong antibacterial properties and minimal cytotoxic effect on the host tissues (11-16).

Calcium hydroxide (Ca(OH)2) has been used extensively in dentistry since the 1920s (17). Today, it is still the most commonly used endodontic medicament throughout the world(18).Ca(OH)2 also inactivates lipopolysaccharide so it can assist in periapical tissue repair (19).

Corticosteroids have also shown to interfere with the repair process. This interference includes an inhibition of fibroblastic proliferation and a decrease in polymorphonuclear leukocyte locomotion. In addition, corticosteroids interfere with the immune response, which could disseminate bacteria leading to infectious disease. Considering these potential pitfalls, some investigators have advocated supplemental use of an antibiotic to help control infection. As a result, ledermix paste was used where it consists of both a corticosteroid "triamcinolone" and an antibiotic "dimethyl chlortetracycline" (20, 21).

Herbs have been used in clinical medicine for thousands of years. Recently researchers have been able to employ scientific methods to prove the efficacy of many of these herbs and to provide a better understanding of their mechanisms of action (22).

Glycyrrhiza glabra which is known as licorice belonging to the Fabaceae, is native to southern Europe and parts of Asia including Iran (23). Licorice roots have been used as a remedy for cough, constipation, menopausal hot flashes, peptic ulcer, and viral diseases (24). Licorice contains more than 20 triterpenoids and nearly 300 flavonoids. Among them, glycyrrhizin, 18 β-glycyrrhetinic acid, liquiritigenin, licochalcone A, licochalcone E and glabridin are the main active components which possess antimicrobial, antioxidant and anti-inflammatory activities (25-27). Badr et al. (28) reported that Licorice extract either separately or as Liquorice/Ca(OH)2 mixture had a potent bactericidal effect against Enterococcus faecalis and retained compatibility with fibroblasts in tissue culture compared to the commonly used root canal medicament Ca(OH)2.

Glycyrrhizin (an oleanane-type triterpenoid glucuronide), the main active and important constituent in licorice, is 50 times sweeter than sugar (29) and is used in large quantities as a well-known natural sweetener and as a pharmaceutical (30). It is a conjugate of two molecules of glucuronic acid and glycyrrhetinic acid and is found chiefly in roots and stolons but not in aerial parts (31). Glycyrrhizin possesses anti-allergic (32), anti- diabetic (33), anti-inflammatory (34), anti-ocular hypertension (35), immune-modulatory (36), anti-cholestasis (37), hepatoprotective (38) and neuroprotective pharmacological activities (39). It also has protective effect on the respiratory system (40).

So based on the above mentioned data, it is believed to be of interest to investigate clinically the use of Glycyrrhizin as an intracanal medication.

Inclusion Criteria:

• Single-rooted with pulp necrosis and apical periodontitis.

Exclusion Criteria:

• Receiving antibiotic treatment within the preceding 3 months.
• Reporting systemic disease.
• Teeth that could not be isolated with rubber dam.
• Teeth with periodontal pockets deeper than 3 mm.