**3. Antibacterial agents used in dental treatments**

Microorganisms are the main cause of pulpal and priapical diaeases. The primary endodontic treatment goal is root canal disinfection and prevention of re-infection of root canal system (Basmadji-Charles et al., 2002; Shahi et al., 2007; Zand et al.,2010). Besides of aseptic principles like rubber dam placement and correct mechanical instrumentation, root canal irrigants are the important aspect to eradication of microbes from root canals. To increase efficacy of mechanical preparation and bacterial removal, instrumentation must be supplemented with active irrigating solutions. Irrigation is defined as washing out a body cavity or wound with water or medical fluid. The objective of irrigation is both mechanical and biologic. The biologic function is related to their antimicrobial effect and mechanical one

Antibacterial Agents in Dental Treatments 339

solutions as they are used in endodontics have a pH of 12 , and thus the entire available

hypochlorous acid is more bactericidal than hypochlorite (Zehnder et al., 2002). One way to increase the efficacy of hypochlorite solutions could thus be to lower the pH. It has also been surmised that such solutions would be less toxic to vital tissues than non-buffered counterparts (Kamburis et al., 2003). However, buffering hypochlorite with bicarbonate renders the solution unstable with a decrease in shelf life to less than 1 week. Depending on the amount of the bicarbonate in the mixture and therefore the pH value, the antimicrobial efficacy of a fresh bicarbonate-buffered solution is only slightly higher or not elevated at all compared to that of a non-buffered counterpart (Costigan, 1936). Another approach to improve the effectiveness of hypochlorite irrigants in the root canal system could be to increase the temperature of low-concentration NaOCl solutions. This improves their immediate tissue-dissolution capacity (Abou-Rass &Oglesby, 1981). Furthermore, heated hypochlorite solutions remove organic debris from dentin shavings more efficiently than

Chlorhexidine is a strong base and is most stable in the form of its salts. The original salts were chlorhexidine acetate and hydrochloride, both of which are relatively poorly soluble in water (Foulkes, 1973). Hence, they have been replaced by chlorhexidine digluconate. It has a cationic molecular component that attaches to negatively charged cell membrane area and causes cell lysis. Chlorhexidine is a potent antiseptic, which is used as a mouth rinse and endodontic irrigant. The later application is based on its substantivity and long-lasting antimicrobial effect which arise from binding to hydroxyapatite. Aqueous solutions of 0.1 to 0.2% concentrations are recommended for that purpose, while 2% is the concentration of root canal irrigating solutions usually found in the endodontic literature (Zamany et al., 2003). It is commonly held that chlorhexidine would be less caustic than sodium hypochlorite (Spngberg et al., 1973). A 2% chlorhexidine solution is irritating to the skin (Foulkes, 1973). As with sodium hypochlorite, heating chlorhexidine of lesser concentration could increase its local efficacy in the root canal system while keeping the systemic toxicity low (Evanov et al., 2004). Despite its usefulness as a final irrigant, chlorhexidine cannot be advocated as the main irrigant in standard endodontic cases, because: (a) chlorhexidine is unable to dissolve necrotic tissue remnants (Naenni et al., 2004), and (b) chlorhexidine is less effective on Gram-negative than on Gram-positive bacteria (Hennessey,1973). In a randomized clinical trial on the reduction of intracanal microbiota by either 2.5% NaOCl or 0.2% chlorhexidine irrigation, it was found that hypochlorite was significantly more efficient than chlorhexidine in obtaining negative cultures (Ringel, 1982). Most important CHX disadvantage is its inability of to dissolve necrotic tissue remnants and chemically clean the

Iodine potassium iodine is a traditional root canal disinfectant with wide-spectrum antimicrobial activity. It is used in concentrations ranging from 2% to 5%).The oxidizing agent of this substance, iodine, reacts with free sulfhydryl groups of bacterial enzymes cleaving the disulfide bonds. It was manifested that calcium hydroxide–resistant

. However, at identical levels of available chlorine,

chlorine is in the form of OCl-

**3.2 Chlorhexidine** 

canal system.

**3.3 Iodine potassium iodine** 

unheated counterparts (Cunningham&Balekjian, 1980).

is due to flushing out effect (Cheung&Stock, 1993). The ideal irrigant should be germicide and fungicide, nonirritating to tissues, stable in solution, have prolonged antimicrobial effect, not interfere with tissue repair, relatively inexpensive, and non-toxic (Tay et al., 2006). There are several irrigants used in endodontic. In this chapter, we discuss about the properties of routine irrigants used in endodontic field.

#### **3.1 Sodium hypochlorite**

Hypochlorite solutions were first used as bleaching agents. Based on the controlled laboratory studies by Koch and Pasteur, hypochlorite then gained wide acceptance as a disinfectant by the end of the 19th century. In World War I, the chemist Henry Drysdale Dakin and the surgeon Alexis Carrel extended the use of a buffered 0.5% sodium hypochlorite solution to the irrigation of infected wounds, based on Dakin meticulous studies on the efficacy of different solutions on infected necrotic tissue (Dakin, 1915). Besides their wide-spectrum, nonspecific killing efficacy on all microbes, hypochlorite preparations are sporocidal, virucidal , and show far greater tissue dissolving effect on necrotic than on vital tissues ( Austin & Taylor, 1918) . These features prompted the use of aqueous sodium hypochlorite in endodontics as the main irrigant as early as 1920 (Grossman, 1943). In the endodontic field, NaOCl possesses a broad spectrum antimicrobial activity against microorganisms and biofilms difficult to eradicate from root canals such as Enterococcus, Actinomyces and Candida organisms. Furthermore, sodium hypochlorite solutions are cheap, easily available, and demonstrate good shelf life (Heling et al., 2001; Mahmudpour et al., 2007). Other chlorine-releasing compounds have been advocated in endodontics, such as chloramine-T and sodium dichloroisocyanurate. These, however, never gained wide acceptance in endodontics, and appear to be less effective than hypochlorite at comparable concentration (Dychdala, 1991).There has been controversy over the most suitable concentration of hypochlorite solutions to be used in endodontics. As Dakin original 0.5% sodium hypochlorite solution was designed to treat open wounds, it was surmised that in the confined area of a root canal system, higher concentrations should be used, as they would be more efficient than Dakin solution (Grossman, 1917). The antibacterial effectiveness and tissue-dissolution capacity of aqueous hypochlorite is a function of its concentration, but so is its toxicity (Spyngbergl et al., 1973). However, severe irritations have been reported when 5.25% concentrated solutions were inadvertently forced into the periapical tissues during irrigation or leaked through the rubber dam (Hismann& Hahn, 2000). Furthermore, a 5.25% solution significantly decreases the elastic modulus and flexural strength of human dentin compared to physiologic saline, while a 0.5% solution does not (Sima et al., 2001). This is most likely because of the proteolytic action of concentrated hypochlorite on the collagen matrix of dentin. The reduction of intracanal microbiota, on the other hand, is not any greater when 5% sodium hypochlorite is used as an irrigant as compared to 0.5% (Bystrm&Sundqvist, 1985). From in vitro observations, it would appear that a 1% NaOCl solution should suffice to dissolve the entire pulp tissue in the course of an endodontic treatment session (Sirtes et al., 2005). Hence, based on the currently available evidence, there is no rationale for using hypochlorite solutions at concentrations over 1% wt/vol. This concentration of NaOCl is also used for disinfection of Gutta-percha cones. Reactive chlorine in aqueous solution at body temperature can, in essence, take two forms: hypochlorite (OCL) in pH above 7.6 or hypochlorous acid (HOCl) in pH below 7.6. Both forms are extremely reactive oxidizing agents. Pure hypochlorite

is due to flushing out effect (Cheung&Stock, 1993). The ideal irrigant should be germicide and fungicide, nonirritating to tissues, stable in solution, have prolonged antimicrobial effect, not interfere with tissue repair, relatively inexpensive, and non-toxic (Tay et al., 2006). There are several irrigants used in endodontic. In this chapter, we discuss about the

Hypochlorite solutions were first used as bleaching agents. Based on the controlled laboratory studies by Koch and Pasteur, hypochlorite then gained wide acceptance as a disinfectant by the end of the 19th century. In World War I, the chemist Henry Drysdale Dakin and the surgeon Alexis Carrel extended the use of a buffered 0.5% sodium hypochlorite solution to the irrigation of infected wounds, based on Dakin meticulous studies on the efficacy of different solutions on infected necrotic tissue (Dakin, 1915). Besides their wide-spectrum, nonspecific killing efficacy on all microbes, hypochlorite preparations are sporocidal, virucidal , and show far greater tissue dissolving effect on necrotic than on vital tissues ( Austin & Taylor, 1918) . These features prompted the use of aqueous sodium hypochlorite in endodontics as the main irrigant as early as 1920 (Grossman, 1943). In the endodontic field, NaOCl possesses a broad spectrum antimicrobial activity against microorganisms and biofilms difficult to eradicate from root canals such as Enterococcus, Actinomyces and Candida organisms. Furthermore, sodium hypochlorite solutions are cheap, easily available, and demonstrate good shelf life (Heling et al., 2001; Mahmudpour et al., 2007). Other chlorine-releasing compounds have been advocated in endodontics, such as chloramine-T and sodium dichloroisocyanurate. These, however, never gained wide acceptance in endodontics, and appear to be less effective than hypochlorite at comparable concentration (Dychdala, 1991).There has been controversy over the most suitable concentration of hypochlorite solutions to be used in endodontics. As Dakin original 0.5% sodium hypochlorite solution was designed to treat open wounds, it was surmised that in the confined area of a root canal system, higher concentrations should be used, as they would be more efficient than Dakin solution (Grossman, 1917). The antibacterial effectiveness and tissue-dissolution capacity of aqueous hypochlorite is a function of its concentration, but so is its toxicity (Spyngbergl et al., 1973). However, severe irritations have been reported when 5.25% concentrated solutions were inadvertently forced into the periapical tissues during irrigation or leaked through the rubber dam (Hismann& Hahn, 2000). Furthermore, a 5.25% solution significantly decreases the elastic modulus and flexural strength of human dentin compared to physiologic saline, while a 0.5% solution does not (Sima et al., 2001). This is most likely because of the proteolytic action of concentrated hypochlorite on the collagen matrix of dentin. The reduction of intracanal microbiota, on the other hand, is not any greater when 5% sodium hypochlorite is used as an irrigant as compared to 0.5% (Bystrm&Sundqvist, 1985). From in vitro observations, it would appear that a 1% NaOCl solution should suffice to dissolve the entire pulp tissue in the course of an endodontic treatment session (Sirtes et al., 2005). Hence, based on the currently available evidence, there is no rationale for using hypochlorite solutions at concentrations over 1% wt/vol. This concentration of NaOCl is also used for disinfection of Gutta-percha cones. Reactive chlorine in aqueous solution at body temperature can, in essence, take two forms: hypochlorite (OCL) in pH above 7.6 or hypochlorous acid (HOCl) in pH below 7.6. Both forms are extremely reactive oxidizing agents. Pure hypochlorite

properties of routine irrigants used in endodontic field.

**3.1 Sodium hypochlorite** 

solutions as they are used in endodontics have a pH of 12 , and thus the entire available chlorine is in the form of OCl- . However, at identical levels of available chlorine, hypochlorous acid is more bactericidal than hypochlorite (Zehnder et al., 2002). One way to increase the efficacy of hypochlorite solutions could thus be to lower the pH. It has also been surmised that such solutions would be less toxic to vital tissues than non-buffered counterparts (Kamburis et al., 2003). However, buffering hypochlorite with bicarbonate renders the solution unstable with a decrease in shelf life to less than 1 week. Depending on the amount of the bicarbonate in the mixture and therefore the pH value, the antimicrobial efficacy of a fresh bicarbonate-buffered solution is only slightly higher or not elevated at all compared to that of a non-buffered counterpart (Costigan, 1936). Another approach to improve the effectiveness of hypochlorite irrigants in the root canal system could be to increase the temperature of low-concentration NaOCl solutions. This improves their immediate tissue-dissolution capacity (Abou-Rass &Oglesby, 1981). Furthermore, heated hypochlorite solutions remove organic debris from dentin shavings more efficiently than unheated counterparts (Cunningham&Balekjian, 1980).
