Chlorhexidine Gluconate (CHX) [6]

Molecular Structure

CHX is a strongly basic molecule with a pH between 5.5 and 7 that belongs to the polybiguanide group and consists of two symmetric fourchlorophenyl rings and two biguanide groups connected by a central hexamethylene chain. CHX digluconate salt is easily soluble in water and is very stable [25].

Mode of Action

Chlorhexidine, because of its cationic charges, is capable of electrostatically binding to the negatively charged surfaces of bacteria [14], damaging the outer layers of the cell wall and rendering it permeable [33, 36, 37]. CHX is a widespectrum antimicrobial agent, active against gram-positive and gram-negative bacteria and yeasts [16].

Depending on its concentration, CHX can have both bacteriostatic and bactericidal effects. At high concentrations, CHX acts as a detergent and exerts its bactericidal effect by damaging the cell membrane and causes precipitation of the cytoplasm. At low concentrations, CHX is bacteriostatic, causing low-molecular-weight substances (i.e., potassium and phosphorous) to leak out from the cell membrane without the cell being permanently damaged.

Substantivity

Due to the cationic nature of the CHX molecule, it can be absorbed by anionic substrates such as the oral mucosa and tooth structure [54, 73, 92]. CHX is readily adsorbed onto hydroxyapatite and teeth. Studies have shown that the uptake of CHX onto the teeth is reversible [34]. This reversible reaction of uptake and release of CHX leads to substantive antimicrobial activity and is referred to as substantivity. This effect depends on the concentration of CHX. At low concentrations of 0.005Ð0.01 %, only a constant monolayer of CHX is adsorbed on the tooth surface, but at higher concentrations, a multilayer of CHX is formed on the surface, providing a reservoir of CHX which can rapidly release the excess into the environment as the concentration of CHX in the surrounding environment decreases [19].

Time and concentration of CHX can inßuence the antibacterial substantivity and the conclusions are inconsistent. Some studies demonstrated that 4 % CHX has greater antibacterial substantivity than 0.2 % after 5 min application (332). Other studies stated that CHX should be left for more than 1 h in the canal to be adsorbed by the dentin [50]. Komorowski et al. [45] suggested that a 5-min application of CHX did not induce substantivity, so the dentin should be treated with CHX for 7 days. However, when Paquette et al. [63] and Malkhassian et al. [55] in their in vivo studies medicated the canals with either liquid or gel forms of CHX for 1 week, neither of them could achieve total disinfection. Therefore, residual antimicrobial efÞcacy of CHX in vivo still remains to be demonstrated.

Chlorhexidine as an Endodontic Irrigant

CHX has been extensively studied as an endodontic irrigant and intracanal medication, both in vivo (Barbosa, Linkgog, Manzur, Paquette, Malkhassian) and in vitro [4, 5, 9, 10, 51, 56].

The antibacterial efÞcacy of CHX as an irrigant is concentration dependent. It has been demonstrated that 2 % CHX has a better antibacterial efÞcacy than 0.12 % CHX in vitro ([10]). When comparing its effectiveness with NaOCl, controversial results can be found. NaOCl has an obvious advantage over CHX with the dissolution capacity of organic matter that CHX lacks; therefore, even though in vitro studies suggest some advantages with the use of CHX, as soon as organic and dental tissue is added, NaOCl is clearly preferable.

The antibacterial effectiveness of CHX in infected root canals has been investigated in several in vivo studies. Investigators [70] reported that 2.5 % NaOCl was signiÞcantly more effective than 0.2 % CHX when the infected root canals were irrigated for 30 min with either of the solutions.

In a controlled and randomized clinical trial, the efÞcacy of 2 % CHX liquid was tested against saline using culture technique. All the teeth were initially instrumented and irrigated using 1 % NaOCl. Then either 2 % CHX liquid or saline was applied as a Þnal rinse. The authors reported a further reduction in the proportion of positive