Effectiveness of Chlorhexidine Varnish on the Prevention of Root Caries: A Narrative Review

Introduction

Many developed countries’ growing elderly populations are expected to retain their teeth into old age.¹ As age advances there may be reduced manual dexterity in an individual, making it increasingly difficult to maintain good oral health.² Quantity of dental plaque, diet, composition, flow of saliva, and fluoride exposure are associated with the development of root caries. Accessibility, root morphology, and the rate of caries progression pose limitations on the therapy of root caries lesions. Methods for preventing and treating root caries are required to improve the quality of life of the elderly while also reducing the overall cost of treatment provision. These methods for controlling existing root caries should require as minimal patient and professional involvement as possible. Chemotherapeutic agents applied topically may have the potential to reduce the severity of existing root caries lesions and reduce the need for both restorative care and tooth extraction.²

Mechanical plaque control effectiveness is influenced by the individual’s manual ability and motivation. There is great interest in the use of antimicrobial agents to replace or be adjuncts to mechanical methods. Chemical agents could represent a valuable complement to mechanical plaque control.³ Chlorhexidine(CHX) has been recognized as the primary agent for chemical plaque control. It is one of the most widely studied and efficacious compounds. It is the gold standard antimicrobial agent against which the efficacy of other antimicrobial and antiplaque agents are assessed.⁴

Varnishes are sustained release delivery systems applied to the teeth. They are the most effective professional application of CHX. The effect of varnishes containing CHX provides optimal protection for enamel and dentine.⁵ Chlorhexidine varnish has been shown to inhibit the growth of more than 99% of bacterial species isolated from subgingival plaque. The incorporation of CHX, and more specifically CHX varnishes, in the control of root caries have been effective, to a greater or lesser degree.⁶

Thus the article aims to review the literature pertaining to root caries and its prevention using Chlorhexidine varnish.

Root caries

Root caries lesions have been described as having a distinct outline and presenting with a discolored appearance in relation to the surrounding non-carious root. As defined by Hazen “it is a soft, progressive lesion that is found anywhere on the root surface that has lost its connective tissue attachment and is exposed to the environment”.⁷

The most common reason for the occurrence of root caries is gingival recession, though other causes can also be present. Gingival recession increases with age, leaving the root surface exposed to the oral environment and increasing the root caries rate. All extensive periodontal surgery for pocket elimination should place a person in a higher risk category for root caries for the rest of their lives.⁷

Root caries is more common in males than females. Most commonly seen in mandibular molars, followed by premolars, canines, and incisors. This order is reversed in the maxilla.⁸ Katz et al. estimated that individuals going into their 30s have about 1 out of 100 surfaces with recession and root caries; when they leave their 50s, about 1 out of 5 exposed surfaces are involved. The roots of the mandibular molars and mandibular incisors are at the greatest, and least risk, respectively.⁹ According to epidemiologic studies, root caries are prevalent among patients with treated and untreated periodontal disease.¹ Table 1 shows the country-wise prevalence, root decayed filled surfaces (RDFS), and root caries index (RCI) of root caries.

Management

Management of root caries, as in other diseases, generally comprises primary, secondary, and tertiary prevention. Practices and procedures carried out before the onset of root caries are referred to as primary prevention. Secondary root caries prevention focuses on people who are early in the disease process to arrest or reverse the process. Tertiary prevention (restorative treatment) focuses on root caries lesions that cause complications such as cavitation, function loss, and pain.¹³

Several primary and secondary prevention strategies have been proposed. These include control of dietary carbohydrate intake; oral hygiene improvement (active biofilm control); antimicrobial agents; chewing gums; fluoride-containing toothpaste; fluoridated water, salt or milk; professionally-applied topical fluoride (gels, CHX varnish, solution of silver diamine fluoride, etc.); arginine-based toothpaste; amorphous calcium phosphate and casein phosphopeptide (ACP-CPP); and ozone applications.¹³

When the structural integrity of demineralized dentine has been lost, restorative treatment should be considered. The conventional approach of ‘drilling and filling’ is the treatment most commonly used for the restoration of cavitated root surface caries lesions. The Atraumatic Restorative Treatment (ART), glass ionomer cement (GIC), resin-modified glass ionomer cement (RMGIC), modified polyacid resins (‘compomers’), or composite resins are frequently used to restore root caries lesions.¹³

Prevention

Root caries is a preventable disease that can be arrested at any stage of development by changing the oral cavity environment from one that promotes demineralization of tooth tissue to one that promotes remineralization. Control and reduction of dietary carbohydrates, modification, and reduction of cariogenic dental biofilm, or application of chemical agents such as fluoride, CHX varnish, or ACPCPP could inhibit demineralization and promote remineralisation.¹³

Evolution of chlorhexidine

Researchers used polybiguanides that established a broad antimicrobial spectrum to develop antimalarial agents. In the 1940s Imperial Chemical Industries developed CHX in England. In 1950 it was promoted as an antiseptic for general use. A polyguanide study in 1954 discovered that certain bisbiguanides had a very broad antimicrobial spectrum and arrived at CHX, with the greatest bactericidal and bacteriostatic properties, through structural variation. In 1957 it was approved for human use as a skin antiseptic in Britain.³ Initially, it was used in dentistry for pre-surgical mouth disinfection and Endodontics. Schroeder investigated plaque inhibition for the first time in 1969. However, in a definitive study conducted by Loe and Schiott in 1972, everyday application of CHX resulted in complete plaque inhibition and gingivitis prevention.⁴ In the year 1986, The American Dental Association’s Dental Therapeutics Council approved CHX as an antimicrobial and antigingivitis agent. There are three forms of CHX currently available: Hydrochloride salts [poorly soluble in water], CHX Digluconate [water soluble], Acetate [water soluble].³

Mechanism of action

CHX is a bisbiguanide antiseptic, which means it’s an asymmetrical molecule with four chlorophenyl rings and two biguanide groups connected by a hexamethylene bridge in the middle. It has a broad spectrum of activity, as well as viruses including HBV (hepatitis B virus), HIV (Human Immuno deficiency Virus), yeast, fungi, and dermatophytes. CHX has antimicrobial activity that is membrane-active, which means it harms the inner cytoplasmic membrane. Interestingly, at different concentrations, CHX has different effects. The agent has bacteriostatic properties at low concentrations and bactericidal properties at high concentrations.³

Bacterial cells are characterized by their negative charge. The negatively charged bacterial cell surface gets rapidly attracted towards the positively charged CHX molecule, where it binds to phosphate-containing substances with precision and strength. The bacterial cell membrane’s integrity is disrupted. CHX gets attracted to the inner cell membrane and attached to phospholipids in the inner membrane, increasing permeability and allowing low molecular weight compounds like potassium ions to leak through it. The effects are reversible at the bacteriostatic stage. As the concentration increases, the membrane suffers progressively greater damage, resulting in leakage of cytoplasmic components with low molecular weight, reflecting cytoplasm coagulation and precipitation caused by the formation of phosphate complexes such as nucleic acids and adenosine triphosphate.³

CHX is an effective antibacterial agent. This, however, is insufficient to explain its antiplaque activity. According to a review, plaque inhibition occurs only when CHX adsorbs to the tooth surface. The possible anti-plaque mechanisms of CHX are given below.³

• It forms bonds with hydroxyapatite in laboratory studies. CHX’s affinity for acidic proteins in the pellicle, plaque, calculus, oral mucosa, and on the surface of bacteria is now thought to be more clinically significant than on its affinity for hydroxyapatite. Adsorption of salivary glycoprotein acidic groups to hydroxyapatite and the formation of acquired pellicles are reduced when their acidic groups are effectively blocked.

• It adsorbs capsules or glycocalyces of their extracellular polysaccharides and reduces the capability of bacteria to attach to tooth surfaces. The cell coatings will absorb a greater amount of the drug, leaving less available to act on the cell membrane and kill the microorganisms directly.

• CHX is more likely to compete with calcium ion plaque agglutination factors.³

• It adsorbs hydroxyapatite and inhibits the colonization of the bacteria. CHX exhibits substantivity where the agent is gradually released in inactive within a period of 12 to 24 hours of binding.¹⁴ As the substantivity of an antiplaque agent decreases, the frequency of use needs to be increased.

The vehicles most often used to administer CHX are mouth rinses, sprays, gels, and varnishes.¹⁵

Comparative evaluation of 1%, 10%, and 40% CHX varnish

CHX varnish is available as 1%, 10% and 40% concentrations. It can be useful in decreasing the number of S.mutans in dental plaque when applied on root surfaces as a varnish because they are particularly sensitive to this compound. A persistent reduction of S.mutans depends on the concentration of CHX.¹

CHX varnishes affect root caries as stated previously. Chlorhexidine varnish (CHX-V) may be useful in preventing and controlling this process: CHX varnishes have been shown to penetrate and seal tubules in the dentine; they can lower the S.mutans counts in the plaque of exposed root surfaces and; there is a decreased mineral loss in situ and dentin lesion depth.⁶

1% CHX-V

Six studies used 1%^2,5,6,16-17CHX- V. In a study involving elderly people aged ≥ 85 years living in residential homes the texture of approximately 15% of the lesions in both groups was worse after 12 months than at the commencement of the study while in the Test group 42% were better compared with 30% in the Placebo group that improved in a 1-year placebo-controlled randomized trial. The applications of varnishes were repeated at 6, 13, 26, and 39-week intervals. ²

Another study conducted among elders aged 78 years living in residential and nursing homes found 57%, 64%, 71% of new caries lesion among CHX-V 1% Fluoride, sodium, and SDF respectively after 3 years suggesting of significant reduced caries development CHX-V. The application was repeated every 3 months.⁵

A study was conducted among institutionalized elderly aged ≥65 years living in residential homes years over 12 months. Significantly (p = 0.039) lower mean number of new root caries lesions were detected in the 1% CHX + 1% thymol group (0.67±0.73) than in the placebo group (1.32±1.22). Varnish was applied twice in the first week of the study and was reapplied at 1, 3, 6, 9, and 12 months. ⁶

One study compared the effects of four different dental varnishes containing 1% CHX and 1% thymol, a custommade 1% thymol, 1% sodium fluoride and Duraphat (5% sodium fluoride) among patients aged 37-81 years for 6 months and found that treatment with varnish containing 1% CHX and 1% thymol significantly reduced the numbers of mutans streptococci from baseline (1371 MS/ml) and 1 week (659 MS/ml) (p = 0.013), and 1 month (833 MS/ml) (p = 0.034). The application was done at baseline and after 1 week. ¹⁸

A parallel single-blinded study conducted among physically dependent patients aged 69 years for 18 months comprised professional mechanical tooth cleaning and the application of a varnish containing 1% thymol and 1% CHX (Cervitec) or a combination of Cervitec and 0.1% fluoride varnish (Fluor Protector). No statistically significant differences could be demonstrated among the three treatment groups. Varnish treatment was carried on two occasions within 10 days, at three-monthly intervals for 18 months.¹⁶

An in-vitro study found no significant difference in bacterial counts (p>0.05) among the study groups the groups with copper removed and the not treated group had significantly greater total lesion area and total fluorescence than the copper varnish without removal group and the chlorhexidine group suggesting copper and CHX-V have anti-cariogenic model has tested on this model.¹⁷

10% CHX- V

Four studies used 10%^19-20CHX-V. A one-year study conducted among adult patients aged 45-75 years with xerostomia reported statistically significant lower root caries increment (0.45± 0.74) (p=0.02) as compared to placebo (0.97±1.19) and Sham (0.96±1.60). CHX-V treatment consisted of a once-weekly, two-stage application over four consecutive weeks and then a single reapplication after six months.¹⁹

A 13-month trial in 45-75-year-old xerostomic individuals group had significantly fewer root surfaces with caries (40.8%) (p ≤ 0.02) and coronal surfaces with caries (14.4%) (p ≤ 0.06) relative to the placebo coating group. The first 4 treatment applications occurred weekly in the first month after randomization, followed by a fifth treatment 6 months later.²¹

A study conducted for 18 months caused a significant reduction in the number of S.mutans from baseline (5.43±0.43) to post-treatment (1.95±1.91) when compared to placebo baseline (5.50±0.44) to posttreatment (5.26±0.45). The applications were applied once weekly for four weeks.²²

A one-year study was conducted among 34-73 year old individuals with exposed root surfaces. The study showed that the mean zone diameter of inhibition of the CHX-V discs was 11 mm for S. mutans and 18 mm for Actinomyces spp in disc test suggesting the CHX treatment was less effective in suppressing the Actinomyces viscosus/naeslundii species than the S.mutans. CHX-V was applied at 1, 5, and 26-week intervals.²⁰

40% CHX-V

A study conducted among patients aged 44.4 years treated at three-month intervals over one year period with 40% CHX-V reported fewer root caries surface of 0.75 lesions per patient in the CHX varnish group versus 1.53 lesions per patient in the control group. CHX-V was applied in three-month intervals over one year period.²³

1% and 40 % CHX-V

One study evaluated 1%, 40%, fluoride varnish with a control group on Actinomyces, S.mutans, and lactobacillus for 3 years among patients aged 53 years old and concluded that significant reduction in Actinomyces and S.mutans occurred among four groups whereas there was no significant difference in reduction of lactobacillus. CHX-V 40% and CHX 1% achieved the lowest reduction of Actinomyces and S.mutans respectively. The varnish was applied to the root surface every 3 months.²⁴

Application regimen

Treatment with 1% CHX-V over 12 months when applied 3- monthly intervals significantly reduced the incidence of new root caries lesions and the numbers of S.mutans. In existing lesions, there was a reduction in the rate of growth and prevented the progression of superficial root caries lesions. ^{5,6, 18}

Treatment with 10% CHX-V caused a significant reduction in the number of S.mutans and root caries increment when applied once-weekly, two-stage application over four consecutive weeks, and then a single reapplication after six months. ^19-20

Treatment with 40% CHX-V over 1 year when applied 3- monthly intervals significantly reduced root caries lesions.²³ Long-term statistically significant suppression of S.mutans was achieved after treatment with 40% CHX-V when compared to 1% CHX-V.²⁴

Within the limitations of this review, the application of 40% CHX-V applied every 3 monthly- intervals over a year was effective in the prevention of root caries.

Advantages, disadvantages, and adverse reactions

The advantage of chlorhexidine varnish use over chlorhexidine gel or mouth rinse is that varnish is easy to apply, and they stay in place for a longer time. They can be applied specifically on caries predilection sites, thus diminishing side-effects involved in the use of mouth rinses or gel applications, irritation of the mouth mucosa, and staining of teeth and tongue.²³ One disadvantage of CHX-V is the unpleasant flavor that can temporarily alter one’s sense of taste.¹

Adverse reactions associated with CHX-V seem to be minimal. The alcohol base can cause a burning sensation once the mucosal barrier has been disrupted. Dental staining has occurred but is reversible with good dental care.²⁵ The toxicity of CHX-V appears to be quite minimal, with no evidence of long-term retention in the body. CHX is slowly released from the varnish even at high concentrations, resulting in low salivary concentrations.²⁶

Recommendations

Well-designed multi-center trials with antibacterial intervention according to a standard protocol would be desirable, and special efforts should be made to select representative study groups with enough power to ensure firm conclusions.

To improve efficiency and compliance, it seems reasonable in the future to move from topical administrations by professionals to consumer products and homecare procedures, such as antibacterial constituents incorporated into dentifrices and chewing gums.²⁷ Further, studies on how to communicate the preventive health message and increase motivation in caries risk patients and vulnerable groups should be encouraged.

Moreover, the use of CHX-V does not require expensive equipment or support infrastructures, such as pipe water or electricity. Therefore, an inexpensive root caries prevention program can be easily implemented. Non-dental professionals, such as primary health care workers, can be trained to apply the agent.

Conclusion

CHX-V is effective in controlling S.mutans and managing root caries lesions. With professional guidance and patient cooperation, biological repair of a root caries lesion can be achieved in many cases as a desirable option given the difficulty and lack of success in restoring root caries via operative procedures. In the absence of regular professional tooth cleaning and oral hygiene instructions, CHX-V may provide a beneficial effect in patients in need of special care.

Conflicts of Interest

None