**2. Antibacterial agents used in sterilization and disinfection**

There are several methods and materials for disinfection. In this chapter, we will discuss the most common antibacterial agents that are used in sterilization and disinfection in dentistry. Disinfectants are substances that are applied to non-living objects to destroy microorganisms that are living on the objects. There are several criteria for Classification of chemical disinfectants that mentioned below (Favero&Bond, 1991):

	- a. Liquid (E.g., Alcohols, Phenols)
	- b. Gaseous (Formaldehyde vapor, Ethylene oxide)

Regarding spectrum activity disinfectants have three levels (Table 1).


Table 1. levels of disinfectants spectrum activity

	- a. Action on membrane (E.g., Alcohol, detergent)
	- b. Denaturation of cellular proteins (E.g., Alcohol, Phenol)
	- c. Oxidation of essential sulphydryl groups of enzymes (E.g., H2O2, Halogens)
	- d. Alkylation of amino-, carboxyl- and hydroxyl group (E.g., Ethylene Oxide, Formaldehyde)
	- e. Damage to nucleic acids (Ethylene Oxide, Formaldehyde)

An ideal disinfectant should have following properties (Crawford, 1983):


It should be mentioned that the efficacy of disinfectant depends on contact time, temperature, type and concentration of the active ingredient, the presence of organic matter, the type and quantum of microbial load.

#### **2.1 Alcohols**

334 Antimicrobial Agents

There are several methods and materials for disinfection. In this chapter, we will discuss the most common antibacterial agents that are used in sterilization and disinfection in dentistry. Disinfectants are substances that are applied to non-living objects to destroy microorganisms that are living on the objects. There are several criteria for Classification of

cells Mycobacteria Spores fungi viruses example

level + + - + + Phenolics, halogens Low level + - - + +/- Alcohols, quaternary

c. Oxidation of essential sulphydryl groups of enzymes (E.g., H2O2, Halogens)

d. Alkylation of amino-, carboxyl- and hydroxyl group (E.g., Ethylene Oxide,

Ethylene Oxide, Glutaraldehyde, Formaldehyde

ammonium compounds

**2. Antibacterial agents used in sterilization and disinfection** 

chemical disinfectants that mentioned below (Favero&Bond, 1991):

Regarding spectrum activity disinfectants have three levels (Table 1).

High level + + + + +

b. Gaseous (Formaldehyde vapor, Ethylene oxide)

1. Based on consistency

Intermediate

2. Based on spectrum of activity

Vegetative

Table 1. levels of disinfectants spectrum activity

a. Action on membrane (E.g., Alcohol, detergent)

b. Denaturation of cellular proteins (E.g., Alcohol, Phenol)

e. Damage to nucleic acids (Ethylene Oxide, Formaldehyde) An ideal disinfectant should have following properties (Crawford, 1983):

2. Should be able to destroy microbes within practical period of time

10. Should be non-toxic, non-allergenic, non-irritative or non-corrosive

3. Based on mechanism of action

Formaldehyde)

5. Should be active in any pH

7. Should have long shelf life

11. Should not have bad odor

6. Should be stable

8. Should be speedy

1. Should have wide spectrum of activity

9. Should have high penetrating power

12. Should not leave non-volatile residue or stain 13. Efficacy should not be lost on reasonable dilution 14. Should not be expensive and must be available easily

3. Should be active in the presence of organic matter 4. Should make effective contact and be wettable

a. Liquid (E.g., Alcohols, Phenols)

The action mechanisms of this subgroup of disinfectant are coagulation of protein, dehydration of cells and disruption of membranes (Moorer, 2003). Alcohols, usually ethanol or isopropanol, are sometimes used as a disinfectant, but more often as an antiseptic. A 70% aqueous solution is more effective at killing microbes than absolute alcohols. Because water facilitates diffusion through the cell membrane; 100% alcohol typically denatures only external membrane proteins. A mixture of 70% ethanol or isopropanol diluted in water is effective against a wide spectrum of bacteria, though higher concentrations are often needed to disinfect wet surfaces (Brent, 2009). Additionally, high-concentration mixtures (such as 80% ethanol + 5% isopropanol) are required to effectively inactivate lipid-enveloped viruses (such as *HIV, hepatitis B, and hepatitis C*). 70% ethyl alcohol is used as antiseptic on skin. Isopropyl alcohol is preferred to ethanol. It can also be used to disinfect surfaces. It is used to disinfect clinical thermometers. Methyl alcohol kills fungal spores, hence is useful in disinfecting inoculation hoods (Engelenburg, 2002). Alcohols have some disadvantages. They can be a fire hazard. Also, they have limited residual activity due to evaporation, which results in brief contact times unless the surface is submerged, and have a limited activity in the presence of organic material. They are skin irritants and inflammable (Lodgsdon, 1994).

#### **2.2 Aldehydes**

The other subgroup of disinfectants is aldehydes that act through alkylation of amino, carboxyl-or hydroxyl group, and probably damage nucleic acids. They have a wide microbiocidal activity and are sporocidal and fungicidal (Crawford, 1983). The most popular of this subgroup are formaldehyde and gluteraldehyde. 40% formaldehyde (formalin) is used for surface disinfection. 10% formalin with 0.5% tetraborate sterilizes clean metal instruments. 2% gluteraldehyde is used to sterilize thermometers, cystoscopes, bronchoscopes, centrifuges, anasethetic equipments etc. An exposure of at least 3 hours at alkaline pH is required for action by gluteraldehyde. 2% formaldehyde at 40oC for 20 minutes is used to disinfect wool and 0.25% at 60oC for six hours to disinfect animal hair and bristles (Favero&Bond, 1991). Disadvantages of these agents are: Vapors are irritating and must be neutralized by ammonia, have poor penetration, leave non-volatile residue, activity is reduced in the presence of protein. Some bacteria have developed resistance to glutaraldehyde, and it has been found that glutaraldehyde can cause asthma and other health hazards; hence ortho-phthalaldehyde is replacing glutaraldehyde (Crawford, 1983).

#### **2.3 Halogens**

Halogens for example Chlorine compounds (chlorine, bleach, hypochlorite) and iodine compounds (tincture iodine,iodophores) are oxidizing agents and cause damage by oxidation of essential sulfydryl groups of enzymes. Chlorine reacts with water to form hypochlorous acid, which is microbicidal. Applications of this group are: Tincture of iodine (2% iodine in 70% alcohol) is an antiseptic (Crawford, 1983). Iodine can be combined with

Antibacterial Agents in Dental Treatments 337

ammonium compounds such as cetrimide to get stronger and broader antimicrobial effects (eg. Savlon). Chloroxylenols are less irritative and can be used for topical purposes and are more effective against gram positive bacteria than gram negative bacteria. Hexachlorophene is chlorinated diphenyl and is much less irritative. It has marked effect over gram positive bacteria but poor effect over gram negative bacteria, *mycobacteria*, fungi and viruses. Triclosan is organic phenyl ether with good activity against gram positive bacteria and is effective to some extent against many gram negative bacteria including Pseudomonas. It also has fair activity on fungi and viruses. But it is toxic, corrosive and skin irritant. Chlorhexidine is inactivated by anionic soaps. Chloroxylenol is inactivated by hard water

They are one of the surface active agents and have the property of concentrating at interfaces between lipid containing membranes of bacterial cell and surrounding aqueous medium (Weber et al., 1999). The mechanism of their action is disruption of membrane resulting in leakage of cell constituents. Surface active agents are soaps or detergents. Detergents can be anionic or cationic. Anionics contain negatively charged long chain hydrocarbon .These include soaps and bile salts. If the fat-soluble part is made to have a positive charge by combining with a quaternary nitrogen atom, it is called cationic detergents. Cationic detergents are known as quaternary ammonium compounds (or quat). Typically, quats do not exhibit efficacy against difficult to kill non-enveloped viruses such as norovirus, rotavirus, or polio virus. Newer low-alcohol formulations are highly effective broad-spectrum disinfectants with quick contact times (3–5 minutes) against bacteria, enveloped viruses, pathogenic fungi, and *mycobacteria*. However, the addition of alcohol or solvents to quat-based disinfectant formulas results in the products' drying much more quickly on the applied surface, which could lead to ineffective or incomplete disinfection. Quats are biocides that also kill algae and are used as an additive in large-scale industrial water systems to minimize undesired biological growth. Cetrimide and benzalkonium chloride act as cationic detergents. They are active against vegetative cells, *mycobacteria* and enveloped viruses. They are widely used as disinfectants at dilution of 1-2% for domestic use and in hospitals. This subgroup of disinfectants has several disadvantages as follow: Their activity is reduced by hard water, anionic detergents and organic matter. Pseudomonas can metabolize cetrimide, using them as a carbon, nitrogen and energy source

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

(Crawford, 1983).

(Favero&Bond, 1991).

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

**2.7 Quaternary ammonium compounds** 

neutralcarrier polymers such as polyvinylpyrrolidone to prepare iodophores such as povidone-iodine. Iodophores permit slow release and reduce the irritation of the antiseptic. For hand washing iodophores are diluted in 50% alcohol. 10% Povidone Iodine is used undiluted in pre and postoperative skin disinfection. 0.5% sodium hypochlorite is used in serology and virology. Used at a dilution of 1:10 in decontamination of spillage of infectious material. Mercuric chloride is used as a disinfectant. This group has some disadvantages like: They are rapidly inactivated in the presence of organic matter. Iodine is corrosive and staining. Bleach solution is corrosive and will corrode stainless steel surfaces (Sattar, 1998).

#### **2.4 Hydrogen peroxide**

It acts on the microorganisms through its release of nascent oxygen. Hydrogen peroxide produces hydroxyl-free radical that damages proteins and DNA. Hydrogen peroxide is used in hospitals to disinfect surfaces and it is used in solution alone or in combination with other chemicals as a high level disinfectant (Favero&Bond, 1991). It is used at 6% concentration to decontaminate the instruments, equipments such as ventilators. 3%Hydrogen Peroxide Solution is used for skin disinfection. Strong solutions are sporicidal (Sattar, 1998). 1.5-2 % Hydrogen peroxide is used as mouthwashes (Hasturk et al., 2004). It is sometimes mixed with colloidal silver. It is often preferred because it causes far fewer allergic reactions than alternative disinfectants. Decomposition in light, breaking down by catalase and reduction of activity by organic matter is their disadvantages (Favero&Bond, 1991).

#### **2.5 Ethylene oxide**

It is an alkylating agent. It acts by alkylating sulfydryl, amino, carboxyl and hydroxylgroups. It is a highly effective chemisterilant, capable of killing spores rapidly. It is the best method for sterilization of complex instruments, delicate materials, and heat labile articles such as bedding, textiles, rubber, plastics, syringes, disposable petri dishes, heart-lung machine, respiratory and dental equipments (Crawford, 1983). Porous and plastic materials absorb the gas and require aeration for 2 hours, before it is safe to contact skin and tissues. It has a sweet odor, readily polymerizes and is flammable. Since it is highly flammable, it is usually combines with CO2 (10% CO2+ 90% EO) or dichlorodifluoromethane. It requires presence of humidity. But, it is highly toxic, irritating to eyes and skin, highly flammable, mutagenic and carcinogenic.

#### **2.6 Phenol**

Phenolic materials for example 5% phenol, 1-5% Cresol, 5% Lysol (a saponified cresol), hexachlorophene or chlorhexidine act by disruption of membranes, precipitation of proteins and inactivation of enzymes. They act as disinfectants at high concentration and as antiseptics at low concentrations (Weber et al., 1999).They are bactericidal, fungicidal, mycobactericidal but are inactive against spores and most viruses. They are not readily inactivated by organic matter. Chlorhexidine can be used in an isopropanol solution for skin disinfection, or as an aqueous solution for wound irrigation. It is often used as an antiseptic hand wash. 20% Chlorhexidine gluconate solution is used for pre-operative hand and skin preparation and for general skin disinfection (Favero&Bond, 1991). 0.12 -0.2 % Chlorhexidine are used as mouthwash. It is also used as root canal irrigant which will be discussed later in this chapter. Chlorhexidine gluconate is also mixed with quaternary

neutralcarrier polymers such as polyvinylpyrrolidone to prepare iodophores such as povidone-iodine. Iodophores permit slow release and reduce the irritation of the antiseptic. For hand washing iodophores are diluted in 50% alcohol. 10% Povidone Iodine is used undiluted in pre and postoperative skin disinfection. 0.5% sodium hypochlorite is used in serology and virology. Used at a dilution of 1:10 in decontamination of spillage of infectious material. Mercuric chloride is used as a disinfectant. This group has some disadvantages like: They are rapidly inactivated in the presence of organic matter. Iodine is corrosive and staining. Bleach solution is corrosive and will corrode stainless steel surfaces (Sattar, 1998).

It acts on the microorganisms through its release of nascent oxygen. Hydrogen peroxide produces hydroxyl-free radical that damages proteins and DNA. Hydrogen peroxide is used in hospitals to disinfect surfaces and it is used in solution alone or in combination with other chemicals as a high level disinfectant (Favero&Bond, 1991). It is used at 6% concentration to decontaminate the instruments, equipments such as ventilators. 3%Hydrogen Peroxide Solution is used for skin disinfection. Strong solutions are sporicidal (Sattar, 1998). 1.5-2 % Hydrogen peroxide is used as mouthwashes (Hasturk et al., 2004). It is sometimes mixed with colloidal silver. It is often preferred because it causes far fewer allergic reactions than alternative disinfectants. Decomposition in light, breaking down by catalase and reduction

It is an alkylating agent. It acts by alkylating sulfydryl, amino, carboxyl and hydroxylgroups. It is a highly effective chemisterilant, capable of killing spores rapidly. It is the best method for sterilization of complex instruments, delicate materials, and heat labile articles such as bedding, textiles, rubber, plastics, syringes, disposable petri dishes, heart-lung machine, respiratory and dental equipments (Crawford, 1983). Porous and plastic materials absorb the gas and require aeration for 2 hours, before it is safe to contact skin and tissues. It has a sweet odor, readily polymerizes and is flammable. Since it is highly flammable, it is usually combines with CO2 (10% CO2+ 90% EO) or dichlorodifluoromethane. It requires presence of humidity. But, it is highly toxic, irritating to eyes and skin, highly flammable,

Phenolic materials for example 5% phenol, 1-5% Cresol, 5% Lysol (a saponified cresol), hexachlorophene or chlorhexidine act by disruption of membranes, precipitation of proteins and inactivation of enzymes. They act as disinfectants at high concentration and as antiseptics at low concentrations (Weber et al., 1999).They are bactericidal, fungicidal, mycobactericidal but are inactive against spores and most viruses. They are not readily inactivated by organic matter. Chlorhexidine can be used in an isopropanol solution for skin disinfection, or as an aqueous solution for wound irrigation. It is often used as an antiseptic hand wash. 20% Chlorhexidine gluconate solution is used for pre-operative hand and skin preparation and for general skin disinfection (Favero&Bond, 1991). 0.12 -0.2 % Chlorhexidine are used as mouthwash. It is also used as root canal irrigant which will be discussed later in this chapter. Chlorhexidine gluconate is also mixed with quaternary

of activity by organic matter is their disadvantages (Favero&Bond, 1991).

**2.4 Hydrogen peroxide** 

**2.5 Ethylene oxide** 

mutagenic and carcinogenic.

**2.6 Phenol** 

ammonium compounds such as cetrimide to get stronger and broader antimicrobial effects (eg. Savlon). Chloroxylenols are less irritative and can be used for topical purposes and are more effective against gram positive bacteria than gram negative bacteria. Hexachlorophene is chlorinated diphenyl and is much less irritative. It has marked effect over gram positive bacteria but poor effect over gram negative bacteria, *mycobacteria*, fungi and viruses. Triclosan is organic phenyl ether with good activity against gram positive bacteria and is effective to some extent against many gram negative bacteria including Pseudomonas. It also has fair activity on fungi and viruses. But it is toxic, corrosive and skin irritant. Chlorhexidine is inactivated by anionic soaps. Chloroxylenol is inactivated by hard water (Crawford, 1983).

#### **2.7 Quaternary ammonium compounds**

They are one of the surface active agents and have the property of concentrating at interfaces between lipid containing membranes of bacterial cell and surrounding aqueous medium (Weber et al., 1999). The mechanism of their action is disruption of membrane resulting in leakage of cell constituents. Surface active agents are soaps or detergents. Detergents can be anionic or cationic. Anionics contain negatively charged long chain hydrocarbon .These include soaps and bile salts. If the fat-soluble part is made to have a positive charge by combining with a quaternary nitrogen atom, it is called cationic detergents. Cationic detergents are known as quaternary ammonium compounds (or quat). Typically, quats do not exhibit efficacy against difficult to kill non-enveloped viruses such as norovirus, rotavirus, or polio virus. Newer low-alcohol formulations are highly effective broad-spectrum disinfectants with quick contact times (3–5 minutes) against bacteria, enveloped viruses, pathogenic fungi, and *mycobacteria*. However, the addition of alcohol or solvents to quat-based disinfectant formulas results in the products' drying much more quickly on the applied surface, which could lead to ineffective or incomplete disinfection. Quats are biocides that also kill algae and are used as an additive in large-scale industrial water systems to minimize undesired biological growth. Cetrimide and benzalkonium chloride act as cationic detergents. They are active against vegetative cells, *mycobacteria* and enveloped viruses. They are widely used as disinfectants at dilution of 1-2% for domestic use and in hospitals. This subgroup of disinfectants has several disadvantages as follow: Their activity is reduced by hard water, anionic detergents and organic matter. Pseudomonas can metabolize cetrimide, using them as a carbon, nitrogen and energy source (Favero&Bond, 1991).
