Chlorhexidine – A Gold Standard in Chemical Plaque Control.

Chlorhexidine is a chemical antiseptic with outstanding bactericidal and bacteriostatic properties. It is  well tolerated and long lasting, which is not neutralized by soaps, body fluids or other organic compounds. It has proved to be the most effective anti-plaque and anti-calculus agent.

CHEMICAL STRUCTURE

Chlorhexidine is a symmetrical molecule consisting of four chlorophenyl rings and biguanide groups connected by a central hexamethylene bridge.

Chemical Structure of Chlorhexidine Molecule

The compound is a strong base and dicationic at pH levels above 3.5 with positive charges on either side of a hexamethylene bridge. Indeed it is the dicationic nature of chlorhexidine, making it extremely interactive with anions, which is relevant to its efficacy, safety, local side effects and difficulties with formulation in products.

Available in three forms:

Digluconate – Most commonly used, and Water soluble

Acetate – Water soluble.

Hydrochloride salts – sparingly water soluble.

MECHANISM OF ACTION

A. Antimicrobial Activity –

Wide spectrum of activity encompassing gram positive and gram negative bacteria yeasts dermatophytes and some lipophilic viruses. Chlorhexidine(CHX) shows different effects at different concentrations. The agent is bacteriostatic,whereas at higher concentration the agent is rapidly bactericidal.

Cationic CHX molecule + Negatively charged Bacterial Cell Wall

Instant adsorption of CHX to Phosphate containing Compounds

Bacterial cell wall integrity disrupted

CHX binds with the phosholipids in the inner cell membrane.

Leakage of lesser molecular weight components, viz. potassium ions

(This is the sub-lethal stage of Chlorhexidine. The action can be reversed. This marks the bacteriostatic property of CHX)

If the the concentration is increased and the action continues, the Chlorhexidine becomes bactericidal in nature.

Intracellular coagulation.

Slows down leakage of intracellular components

Cytoplasmic Coagulation

Irreversible damage (Bactericidal)

B. Antiplaque Activity –

Three mechanisms for inhibion of plaque by chlorhexidine.

  • The effective blocking of acidic groups of salivary glycoproteins will reduce their adsorption to hydroxyapatite and formation of acquired pellicle.
  • The ability of bacteria to bind to tooth surfaces may be reduced by adsorption of CHX to the extracellular polysaccharides of their capsules or gylcocalyces.
  • The chlorhexidine may compete with calcium ions for acidic agglutination factors in plaque.

What makes it so Unique?
  • What sets Chlorhexidine apart from the rest of antiplaque agents, is its persistent, long lasting bacterostatic action, also termed as ‘Substantivity’.
  • The action lasts for as long as 12 hours in the oral cavity after a single rinse.
  • The Dicationic CHX molecue, attaches to the pellicle by one cation, and to the bacteria attempting to colonize the tooth surface with the other. This is called the ‘Pin-Cushion Effect’.
  • This prolongs the action of Chlorhexidine.

USES

  1. As an adjunct to oral hygiene measures and professional prophylaxis
  2. Post oral surgery care including periodontal surgery or root planing .
  3. In patients with inter maxillary fixation
  4. For oral hygiene and gingival health benefits in physically and mentally handicapped.
  5. Medically compromised individuals predisposed to oral infections.
  6. High caries risk patient
  7. Recurrent oral ulceration
  8. Removable and fixed orthodontic appliance wearers.
  9. Treatment of denture stomatitis and dry socket .
  10. As an immediate prophylactic rinse in the prevention of post – extraction bacteremia and decrease bacterial content of aerosal spray.

ADVERSE EFFECTS

1) Extrinsic staining - Dark yellow or brownish stain seen on both artificial and natural teeth after few days of use of chlorhexidine preparation, more severe in higher concentrations of chlorhexidine. Possible  Mechanisms,

  • Carbohydrates and amino acids containing compounds present in acquired pellicle undergo series of polymerization reactions to produce pigmented substances called melanoidins such browning reactions are catalyzed by chlorhexidine, which produces a thick pellicle containing more amino groups than ordinary pellicle.
  • Degradation of CHX molecule to release parachloraniline –appears not to occur on storage or as a result of metabolic process.
  • Chlorhexidine denatures the proteins in pellicle by splitting sulphide bridges to produce free sulphydryl groups .The sulphydryl groups then react with iron or tin ions to produce brown or yellow pigmented products.
  • Chlorhexidine reacts with ketones and aldehydes in dietary breakdown or intermediatotry products to form insoluble, coloured compounds.

2) Taste perturbation where salt taste appears to be preferentially affected.

3) Oral mucosal erosion –appears to be idiosyncratic reaction and concentration dependent.

4) Enhanced supragingival calculus formation. This effect may be due to precipitation of salivary proteins on to the tooth surface, thereby increasing the pellicle thickness and or precipitation of inorganic salts on the pellicle layer.

OPTIMIZING THE USE OF CHLORHEXIDINE

  • In the absence of mechanical tooth cleaning, rinsing for 60s twice daily with 10ml of a 0.2% chlorhexidine di gluconate solution reduces the plaque accumulation by approximately 60% and severity of gingivitis by 50-80%.
  • CHX does not distinguish between bacterial protein and other proteins found in mature plaque, hence extraneous protein professional scaling must be performed before starting with the mouthrinse regimen.
  • CHX reacts with anionic species hence should not be used with surfactants.
  • CHX and Sodium Lauryl Sulphate(SLS) which is a major component in dentifrices can act as antagonists. Hence the time between a chlorhexidine rinse and tooth brushing with a SLS containing dentifrice should atleast be 30 min to enhance the antimicrobial activity of Chlorhexidine.
  • To reduce chances of CHX staining,  intake of coffee & tea immediately after morning rinse should be avoided.
  • Use of the mouthwash as the last thing at night recommended.

CHLORHEXIDINE PRODUCTS

  1. Mouth rinses – Aqueous / Alcohol  solutions of 0.2% – first used.  0.1% and 0.12% concentrations are also available .
  2. GEL – 1% CHX gel usually delivered in tooth brush or trays. Recently, 0.2% and 0.12% gels are also available.
  1. Sprays -  0.1% and 0.2%. Useful for handicapped patients.
  2. Tooth pastes – Not routinely used because of inactivation or competition for oral retention sites by tooth paste components like anionic detergents and Calcium Ions (Barkvoll 1989).
  3. Varnishes – Used mainly for prophylaxis against caries, but recently found to have plaque inhibitory effect.
  4. chewing gums
  5. Periodontal Dressings – CHX incorporated in periodontal dressings, decreases the bacterial load, during the post surgical phase.
  6. Subgingival Plaque control – i. Irrigation

– Subginigval Irrigation

–  Pulsated Jet Irrigation

ii.  Slow releasing devices – Periochip.

CONCLUSION

After so many years of use by dental profession, Chlorhexidine is recognized as gold standard against, which other antiplaque and antigingivitis agents are measured. Although other mouth rinses may show either purely immediate effect or limited persistence, the degree of Chlorhexidine persistence of effect at the tooth surface is the basis of its clinical efficacy.

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