A review of the different methods of applying chlorhexidine in the oral cavity.

ABSTRACT

Chlorhexidine or CHX (chemical name 1.6-bis-4-chloro-phenyldiguanidohexane) is a synthetic cationic detergent, which has broad anti-microbial activity. (1) In numerous studies since the 1970s, chlorhexidine has been shown to be an effective anti-plaque and anti-gingivitis agent and there is extensive literature about chlorhexidine for the treatment of gingivitis. Some studies have demonstrated the efficacy of chlorhexidine using different concentrations and formulations. Others have studied chlorhexidine in various forms, such as mouthwashes, gels, and sprays. Chlorhexidine has also been applied with trays, fingers, toothbrushes, toothpicks, dental floss, foam brushes, and biodegradable chips. The study populations have also been extensive, ranging from children to adults, with and without periodontal disease, as well as with and without mechanical or surgical interventions. This article provides an overview of the anti-plaque and anti-gingivitis properties of chlorhexidine, with an emphasis on the different methods of application in the oral cavity.

Key words: chlorhexidine, dental plaque, gels, gingivitis, mouthwashes, vehicles

RESUME

La chlorhexidine (nom chimique : 1,6-bis-4-chloro-phenyldiguanidohexane) est un detergent cationique synthetique, dont l'activite antimicrobienne est vaste. Depuis les annees 1970, de nombreuses etudes ont montre que cette substance etait un agent anti-plaque et anti-gingivite efficace. La documentation au sujet de la chlorhexidine est abondante. Des etudes ont demontre l'efficacite de la chlorhexidine en differentes concentrations et selon differentes formules. D'autres ont etudie la chlorhexidine sous diverses formes, tels les rince-bouches, les gels et les aerosols. La chlorhexidine a aussi ete utilisee dans la fabrication de plateaux, de doigts, de brosses a dents, de cure-dents, de soie dentaire, de brosses en mousse et de puces biodegradables. Par ailleurs, les populations etudiees sont considerables : elles vont des enfants aux adultes, victimes ou non de maladie parodontale et ayant subi ou non une intervention mecanique ou chirurgicale. Cet article donne un apercu de la chlorhexidine et met l'accent sur les differentes methodes d'application dans la cavite buccale.

INTRODUCTION

CHLORHEXIDINE (CHEMICAL NAME 1.6-BIS-4-chloro-phenyldiguanidohexane) is a synthetic cationic detergent, which has broad anti-microbial activity. (1) Chlorhexidine (CHX) is effective against gram-positive and gram-negative bacteria, yeasts, dermatophytes, and some lipophilic viruses. (1,2) It was first marketed under the trade name "Hibitane" in 1953 as an antiseptic cream (1) but was eventually found to be effective for plaque control in the oral cavity in 1970. (3) In a short-term, experimental gingivitis model study, Loe and Schiott in 1970 demonstrated that twice-daily rinsing with a 0.2% concentration of chlorhexidine was effective in completely preventing plaque formation without mechanical interventions. (3)

The anti-bacterial mode of action of chlorhexidine is by damaging the cytoplasmic membrane of the bacteria so that the osmotic equilibrium is no longer maintained. (1,2) Chlorhexidine has two effects on bacteria. At the bacteriostatic level, the cationic chlorhexidine binds to anionic compounds, such as free sulfates, the carboxyl and phosphate groups of the pellicle, and salivary glycoproteins. (1,4) This results in fewer proteins available at the tooth surface for the formation of the dental pellicle, the precursor to dental plaque. (1) Coating the salivary bacteria with chlorhexidine also affects the ability of bacteria to adhere to the tooth surface. (1) The bacteriostatic phase is prolonged so that chlorhexidine, bound to salivary proteins, is released in active form even 8-12 hours later. (4) Substantivity, which is the prolonged bacteriostatic characteristic of chlorhexidine, is an important feature because it provides continuing anti-microbial effects even with reduced frequency of applications. However, during the bacteriostatic stage, the bacteria can still recover if the chlorhexidine is neutralized. (2) Unlike the bacteriostatic phase, the bactericidal stage is non-reversible. At the bactericidal level, "there is coagulation and precipitation of the cytoplasm by the formation of phosphated complexes such as adenosine triphosphate and nucleic acids." (2) Long-term studies show that chlorhexidine does not lose its effectiveness over time nor does it create resistant bacterial strains. (1,5,6)

Since chlorhexidine is a strong cationic substance, it may be rendered inactive in the presence of anionic substances, such as phosphates, sulfates, and anionic detergents. (7) Although researchers and clinicians suggest that people wait a minimum of 30 minutes between the use of toothpastes and chlorhexidine to prevent a reaction between the sodium lauryl sulphate (the detergent found in toothpastes) and the chlorhexidine, Van Strydonck et al. in 2004 found that this interaction did not occur as long as the person rinsed with water after toothbrushing. (8) Blood, pus, calcium ions, and tannin may also inactivate chlorhexidine. (1) Tannins are found in tea and red wine. Both chlorhexidine and tannins are protein denaturants and hence may compete for the same sites on the enamel pellicle. (9) Denaturing pellicle proteins allows for the formation of iron or tin sulfides to form pigmented products on the teeth. (9) This theory is the most prevalent of the three possible mechanisms, which may explain the characteristic brown stain that appears on teeth and oral tissues after using chlorhexidine. (9)

Tooth stain is a common adverse effect of chlorhexidine use. Three out of four subjects will develop a brown stain on the teeth, tongue, and composite and porcelain restorations within a few days of using chlorhexidine. (1,3,10-13) The intensity and coverage of the tooth stain increases with the intake of tea, red wine, coffee, and tobacco. (9,13)

Other adverse effects of chlorhexidine are a bitter metallic taste (12%), changes in taste sensation (88%), and occasional epithelial desquamation (6%). (10,14,15) Desquamations have been observed in subjects using concentrations of 0.2% or more. (1,2,16,17) Increased calculus formation has also been noted in chlorhexidine studies. (11,18-22) Flemmig et al. in 1990 noted a four-fold increased in calculus formation in subjects using a 0.06% chlorhexidine mouthrinse compared with control subjects. (19)

Long-term studies have shown that chlorhexidine is safe. (1,5,6) In toxicological evaluations in animal models, chlorhexidine has been found to be non-effective against systemic infections with parenteral dosing. (23) It was therefore concluded that chlorhexidine was only to be used for prophylactic antisepsis by topical or oral applications. (23) Tests that were conducted in animal models for reproductive effects, skin sensitizations, and eye irritations were found to be satisfactory, i.e., no tumours or other toxic manifestations were found. (23) Retrospectively, chlorhexidine has been used orally since the 1950s with no reports of ill-effects following ingestion. (23) Since chlorhexidine is poorly absorbed in the gastrointestinal tract, it has very low toxicity in humans and animals. (1) There are few reported cases of anaphylaxis from chlorhexidine. Krautheim in 2004 reported one subject who had an anaphylactic reaction to chlorhexidine, but it was thought that the reaction was made more severe by applying the chlorhexidine to broken skin, thus introducing chlorhexidine into the blood stream. (24) Generally, the sensitization rate of chlorhexidine is thought to be less than 2%, with prolonged and repeated contact required to develop the contact sensitivity. (24) Overall, the intra-oral use of chlorhexidine is safe.

Chlorhexidine has been used in the oral cavity since the 1970s for the treatment of gingivitis. (1,3) Although gingivitis can be treated by mechanical methods, such as toothbrushing and flossing, (3,25-27) subjects may be unwilling or unable to effectively remove the dental plaque (28-34) that is responsible for the gingival inflammation. (35,36) Many studies have tested the effectiveness of chlorhexidine as a chemical adjunct or replacement for mechanical procedures in the treatment of gingivitis. (3,5-7,11,16-21,29-35,37-66) Chlorhexidine has been shown to effectively inhibit de novo plaque formation or newly forming plaque and to reduce the bleeding and inflammation associated with gingivitis. (3,5-7,11,16-21,29-35,37-66)

In the literature, studies have used various methods of introducing the chlorhexidine into the oral cavity. The most common method of application has been the mouthrinse, followed by gels, sprays, and other novel methods. The purpose of these different methods of application has been two-fold. One aim was to find a method that would enhance subject compliance in using the product. The second was to find a method that would enhance the anti-plaque and anti-gingivitis properties of chlorhexidine while simultaneously minimizing its side effects.

CHLORHEXIDINE MOUTHRINSES

Chlorhexidine has been traditionally dispensed as a 0.2% mouthrinse, a method of application that is easy and accepted by subjects. Long considered the gold standard, the 0.2% chlorhexidine is effective at inhibiting new plaque formation and controlling the clinical signs of gingivitis. (2) The 0.2% concentration was chosen by Loe and Schiott in the initial clinical trial because this concentration was used to irrigate the eyes and was therefore felt to be safe. (3,40) Numerous studies have since supported the claim that 0.2% chlorhexidine is an effective anti-plaque and anti-gingivitis agent. (3,12,38,43,46,50,53) In experimental gingivitis studies, 0.2% chlorhexidine has been found to be effective in returning subjects to gingival health. (3,12,46,53) The 0.2% chlorhexidine mouthrinse was significantly more effective (p < 0.05) than manual tooth-brushing in resolving the experimental gingivitis within four days. (38) However, subject compliance for the long-term use of the 0.2% chlorhexidine mouthrinse has been poor because of the extrinsic brown stain that forms on the teeth and oral tissue within a few days of use. (9-13) Hence, recent studies have explored the possibility of lower concentrations of chlorhexidine, the use of an oral irrigator, toothbrush, or foam brush to apply the chlorhexidine solution, and different formulations of chlorhexidine solutions to address the staining issue, whilst maintaining chlorhexidine's anti-plaque and anti-gingivitis properties.

Lower concentrations of chlorhexidine rinses

One of the attributes of 0.2% chlorhexidine that makes it the gold standard is substantivity. (2) Substantivity is the ability of chlorhexidine to adsorb from the oral tissues in active form, resulting in a lingering bacteriostatic effect hours after the initial dose. (1,2) Whether a lower concentration of chlorhexidine also had this attribute was explored. A study conducted by Bonesvoll, Lokken, and Rolla in 1974 demonstrated that the retention of chlorhexidine in the oral cavity was proportional to its concentration. (4) For example, "the mean amount of chlorhexidine retained in the oral cavity ranged from 1.8 mg ([+ or -] 0.4) at the 0.05% concentration to 10.5 mg ([+ or -] 3.4) at the 0.4% concentration." (4) Other studies explored the effectiveness of lower concentrations of chlorhexidine on oral bacteria. Sreenivasan et al. in 2004 explored the effect of 0.03%, 0.06%, and 0.12% chlorhexidine rinses on oral bacteria and found that a significant dose-dependent effect occurred. (51) For example, the 0.12% chlorhexidine rinse had significantly stronger effects on oral bacteria than the 0.06%, and the 0.06% concentration had stronger effects than the 0.03% concentration. (51) In another study, 0.05% chlorhexidine was compared with a placebo for microbiological effects. (49) The lower concentration of chlorhexidine was found to be effective in significantly reducing the bacteria in the oral flora (p < 0.05), especially for Porphyromonas gingivalis (p = 0.01), compared with a placebo. (49)

Lower concentrations of chlorhexidine mouthrinses: short-term studies

In short-term studies, 0.12% chlorhexidine has been compared with other agents or placebo for effectiveness in plaque and gingivitis inhibition. In an experimental gingivitis study comparing 0.12% chlorhexidine, triclosan, and placebo, the chlorhexidine had significantly lower plaque scores, but not gingival and gingival crevicular fluid scores. (48) In another study, 0.12% chlorhexidine was compared to an amine and stannous fluoride solution in post-surgical subjects. (16) No differences were found between the two treatment groups in this three-month study. The fact that these subjects had just received periodontal surgery and were probably quite motivated with their oral hygiene may account for the lack of differences between the two treatment groups. A multi-centre, general dental practice study demonstrated that a 0.12% chlorhexidine rinse was effective in reducing plaque and gingival bleeding sites over three months compared with placebo. (41) Although the baseline plaque and gingival scores were already low for these study subjects, it was interesting that the chlorhexidine was still able to exert a noticeable effect.

Comparisons between mechanical plaque removal and lower concentrations of chlorhexidine mouthrinses have also been reported. Caton et al. in 1993 compared the adjunctive use of 0.12% chlorhexidine and mechanical cleaning to mechanical cleaning alone in the treatment of interdental gingivitis. (39) Interdental cleaning and tooth-brushing alone were found to be effective in significantly reducing bleeding sites compared with chlorhexidine and toothbrushing. (39) While this supports previous findings that toothbrushing alone is ineffective in cleaning the interdental area, (26,27) it also highlights the inability of chlorhexidine mouthrinses to penetrate the interdental area, (39) an area where gingivitis is more prevalent. (67,68)

For many short-term studies, the effects of chlorhexidine on plaque formation and gingivitis may appear to be only slightly better or not at all compared with other test solutions, placebos, or mechanical cleaning. Often the Hawthorne effect (i.e., the subjects in the study perform better oral hygiene than usual because they know they are being assessed) and lingering effects from the initial professional prophylaxis play a significant role in the results. (11,43,45,46)

Lower concentrations of chlorhexidine rinses: long-term studies

Studies of six months or longer have several advantages over short-term studies. According to Overholser (1988), the advantages of a long-term study are as follows: (11)

** A period of six months simulates a common recall interval in private practice, something a subject may be familiar with.

** Subjects will likely begin and end the study with a professional prophylaxis. Having all the subjects begin with a plaque score near or at zero facilitates later comparisons between the treatment groups.

** The effects of the initial scaling and root planing will have been mitigated by six months.

** The development of toxic and other adverse effects is more likely to become known.

** Qualitative and quantitative changes in the subject's oral flora can be monitored, especially for the emergence of gram negative, anaerobic, or motile bacteria. Six months also allows researchers to determine if the treatment produces resistant forms of bacteria.

** The initial Hawthorne effect will gradually lessen over time.

In long-term studies, 0.12% chlorhexidine rinses have been found to be effective in reducing plaque and gingivitis compared with a placebo. (18,19) When compared with a placebo, 0.12% chlorhexidine significantly reduced gingival (18.2%, p < 0.001) and plaque (21.6%, p < 0.001) scores. (18) However, there was no significant difference in plaque and gingival scores between 0.12% chlorhexidine and an essential oil mouthrinse (Listerine[TM]). (18) Over the six-month period, the chlorhexidine group had significantly more calculus (0.45) and stain (2.08) compared with the essential oil rinse (0.24 and 0.33, respectively) and placebo groups (0.21 and 0.01, respectively). (18) The authors suggest that the 0.12% chlorhexidine mouthrinse be used for short-term use only to reduce the side effects and that the essential oil rinse be used for long-term use since the anti-plaque and anti-gingivitis effects are similar without the side effects of the chlorhexidine. (18)

In another large study (n = 430), subjects used either a 0.12% chlorhexidine mouthrinse or placebo rinse for six months. (20) Compared with the placebo, the chlorhexidine group had a 37% reduction in gingival occurrence, 39% reduction in gingival severity, 44% reduction in gingival bleeding, and 61% reduction in plaque scores. (20) Although both groups started the study with a professional prophylaxis, the beneficial effect of the prophylaxis slowly diminished, as indicated by gingival severity increasing with time in the placebo group. (20) The authors noted that calculus and stain increased in the chlorhexidine group, but there were no indices included in the study design to indicate that these parameters were actively assessed. (20)

Two other long-term studies used a 0.06% chlorhexidine mouthrinse to test for plaque and gingivitis inhibition. (19,44) The larger study (n = 222) examined the application of 0.06% chlorhexidine as a mouthrinse and by an oral irrigator. (19) The chlorhexidine was compared against two controls, water irrigation and toothbrushing. (19) The six-month results of Flemmig et al.'s 1990 study can be found in table 1. The results for the toothbrushing group remained constant over the six months. At the three- and six-month assessments, the chlorhexidine groups (via mouthrinse or oral irrigator) and the water irrigator group all had significant reductions in the gingival index and bleeding on probing compared with the toothbrushing group (p [less than or equal to] 0.05). The group using the oral irrigator and the 0.06% chlorhexidine had a greater reduction in the gingival index and bleeding on probing scores compared with the other treatment groups at six months.

Interestingly, the water irrigation control was found to have beneficial clinical effects. The authors speculated that specific bacteria may have been reduced or toxic by-products of the plaque washed away, although this is unknown since microbiological tests were not conducted as part of this study. The other speculation was that the mechanical stimulation of the gingiva with the oral irrigator could have played a role in the positive clinical effects seen. (19)

Another six-month study (n = 85) compared 0.06% chlorhexidine mouthrinse with 0.06% chlorhexidine with 250 parts per million sodium fluoride. (44) Both positive (0.1% chlorhexidine) and negative (250 parts per million amine fluoride with stannous fluoride and water) controls were used (44) (see table 2).

As shown in table 2, the researchers noted a strong Hawthorne effect that lasted for three months. This effect was noticeable because the results at three months were better than the results at six months. Longer studies clearly indicate the initial positive effects of the professional prophylaxis and Hawthorne effects and how these confounding effects diminish over time to allow the true treatment effects to be known. Side effects are also more likely to be known in long-term studies, especially when using lower concentrations or dosages of chlorhexidine.

Lower concentrations of chlorhexidine mouthrinse applied with different tools

In 1973, Cumming and Loe tested various concentrations of chlorhexidine as mouthrinses and in an oral irrigator to determine if a lower concentration was effective in controlling plaque formation. (40) They discovered that concentrations as low as 0.075% were effective as a mouthrinse, provided that the total volume of solution used was increased. (40) For example, 100 ml of 0.075% chlorhexidine was just as effective in controlling plaque formation as the gold standard of 20 ml of 0.2% chlorhexidine. (40) The use of an oral irrigator was also effective, with 700 ml of 0.05% chlorhexidine producing a plaque score of 0.2. (40) However, since the volumes were so large, it was assumed that most subjects would not comply with this regime over time. The authors suggested 50 ml of 0.075% to 0.1% chlorhexidine by rinsing or 400 ml of 0.025% to 0.05% chlorhexidine by oral irrigator as reasonable alternatives for controlling plaque formation. (40) The lower concentrations minimized the characteristic bitter taste of chlorhexidine and appeared to minimize the amount of staining, although nine days may not have been long enough for the stain to appear on the teeth. (40)

Various lower concentrations of chlorhexidine have also been applied with a toothbrush or foam swab. (60,63,64) Both 0.10% and 0.15% chlorhexidine solutions applied with a toothbrush were effective in reducing plaque scores (66% and 72%, respectively) compared with the placebo. (60) However, the tested concentrations (0.05%, 0.10%, and 0.15%) were unable to completely inhibit plaque formation. (60) Mean gingival index scores were reduced by 58% for the 0.15% concentration and 57% for the 0.10% chlorhexidine concentration compared with the placebo. (60) Stain intensity increased with increasing concentrations and increasing utilization of chlorhexidine. (60) For example, 92% of the 0.15% chlorhexidine group had tooth staining compared with 17% of the subjects in the 0.05% group. (60) Although brushing the chlorhexidine onto the teeth did not eliminate tooth staining, burning sensations and desquamative lesions were absent in this study. (60) The author speculates that using a toothbrush to apply the chlorhexidine resulted in less contact with the mucosal membranes compared with a mouthrinse and thus mucosal adverse effects were absent. (60)

Similarly, chlorhexidine solution has been applied with a foam brush in subjects unable to use a conventional toothbrush. (63,64) Although these studies demonstrated an effect on plaque and gingivitis, there were significant carry-over effects as the subjects were crossed over from one treatment to the next. (63,64)

Different formulations of chlorhexidine mouthrinses

Research has also been conducted using different formulations of chlorhexidine mouthrinses to minimize or eliminate the adverse effects of tooth staining and poor taste. A study by Addy et al. in 1991 compared the efficacy of 0.12% chlorhexidine and a new reformulated 0.1% chlorhexidine rinse (Pierre Fabre, Castres, France). (37) The anti-plaque and anti-gingivitis properties of the 0.1% chlorhexidine rinse appeared to be reduced compared with the 0.12% rinse. (37) Unfortunately, due to the small sample size and significant crossover effects in the study, the effects of the 0.1% formulation on plaque scores is not clear. The authors discuss how 0.1% concentrations of chlorhexidine have been shown in vivo and in vitro to produce no staining in exchange for limited anti-plaque activity. (37) However, the design of this study did not include any measurements for staining. Therefore, comparisons between the 0.1% and 0.12% chlorhexidine rinses were incomplete.

Another study added 0.5% sodium fluoride to 0.5% chlorhexidine to determine if this formulation would result in less stain, while continuing to have an effect on plaque formation and gingivitis. (45) After eight weeks, the chlorhexidine and fluoride group had a mean plaque score of 0.4 [+ or -] 0.2, p < 0.001 and a mean bleeding score of 0.1 [+ or -] 0.1, p< 0.001 compared with placebo 0.95 [+ or -] 0.35 and 0.45 [+ or -] 0.30, p<0.05, respectively. (45) At eight weeks, the initial professional prophylaxis was continuing to exert a positive influence on gingival health because the control group demonstrated significant reductions in gingival bleeding. (45) A longer study might have demonstrated a difference between the two treatment groups. Another weakness in this study was that the test group had a significantly higher baseline stain score than the control group, even after both groups had received the initial prophylaxis. This complicates the comparison between treatment groups, especially when it is already known that chlorhexidine causes extrinsic tooth staining. Unfortunately, this study does not clearly indicate that a 0.5% chlorhexidine and 0.5% sodium fluoride combination is effective in treating gingival bleeding or reducing the amount of staining usually associated with chlorhexidine.

Different formulations of chlorhexidine have also been produced to improve the characteristic bitter taste of the 0.2% chlorhexidine mouthrinse. According to Lang et al. in 1988, a subject's taste sensation for "salty" was impaired within one day of using a 0.2% chlorhexidine mouthrinse. (14) This alteration in taste sensation was found to be transient and subjects reported normal taste sensations upon stopping the chlorhexidine. (14)

Therefore, to increase subject compliance with chlorhexidine mouthrinses, other studies were undertaken to improve the taste of the mouthrinse. In particular, 0.5% cetylpyridinium chloride (CPC) was used instead of alcohol. (47,49) In an experimental gingivitis study, 0.12% chlorhexidine rinse with cetylpyridinium chloride was compared with 0.2% chlorhexidine rinse with alcohol (the gold standard and positive control), 0.12% chlorhexidine with alcohol (positive control), and 0.12% chlorhexidine with 0.05% sodium fluoride. (47) Both the 0.12% chlorhexidine rinses with either CPC or alcohol were just as effective clinically and microbiologically as the 0.2% gold standard in retarding new plaque formation. (47) The 0.12% chlorhexidine with 0.05% sodium fluoride did not completely retard plaque inhibition, similar to the results found by Joyston-Bechal et al. in 1993. (45,47) Subjects had the opportunity to rinse with all four rinses in the study by Quirynen et al. in 2001 and were asked to complete a subjective questionnaire regarding the taste of each rinse, loss of taste sensation, sensations on the tongue, staining on the teeth, and any other side effects. (47) The subjects preferred the taste of the new 0.12% chlorhexidine rinse with cetylpyridinium chloride compared with the other rinses (p < 0.01). (47) There were no significant differences among the tested chlorhexidine rinses for teeth staining. (47) Other studies support the findings of Quirynen et al., that is, rinsing with 0.12% chlorhexidine with cetylpyridinium chloride is not significantly different than 0.12% chlorhexidine rinse with alcohol on plaque accumulation and bacterial counts. (49,52) The only advantage the 0.12% CPC chlorhexidine had over the other formulations was better taste.

Although chlorhexidine applied as a 0.2% mouthrinse has been clinically and microbiologically proven to be effective as an anti-plaque and anti-gingivitis agent, adverse effects such as tooth staining, changes in taste perception, and poor taste of the solution have limited its long-term use. The lower concentrations of chlorhexidine mouthrinses have been shown to provide similar anti-plaque and anti-gingivitis effects as the 0.2% concentration and in particular, the cetylpyridinium formulation was shown to have a better taste. The method of applying the chlorhexidine solution, such as using an oral irrigator or brushing it on, may also reduce the potential adverse effect of epithelial desquamations by localizing the solution to the teeth. Regardless of the concentration or method of applying the chlorhexidine solution, tooth staining remains a concern for long-term use in subjects.

CHLORHEXIDINE GELS

Over the years, other methods of applying chlorhexidine were devised. The 1% chlorhexidine gel was developed as a means of incorporating the chlorhexidine into a subject's oral hygiene habits by substituting the subject's toothpaste with the gel. This method of application is thought to provide adjunctive benefits to mechanical oral hygiene, such as toothbrushing and flossing, in the prevention and treatment of gingivitis. To determine if a gel formulation of chlorhexidine would be retained intraorally, Bonesvoll in 1978 tested 1% chlorhexidine gel with various concentrations of chlorhexidine mouthrinses. (56) Results from the study indicated that 4 mg of chlorhexidine was retained after toothbrushing with 1 gram of 1% chlorhexidine gel, similar to the results of rinsing with 10 ml of 0.1% chlorhexidine mouthrinse for one minute. (56) The length of brushing time had little influence on the chlorhexidine gel retention, with times as short as 15 seconds having high retention levels. (56) According to Gjermo, Bonesvoll, and Rolla in 1974, the plaque-inhibiting effect of chlorhexidine is related to the amount of chlorhexidine retained. (69)

Chlorhexidine gels: short-term studies

Different study populations were used in the chlorhexidine gel studies, ranging from children to adults, with and without good oral hygiene habits. In an eight-week double-blind trial, children ranging in ages from 9 to 17 years old were instructed in toothbrushing techniques using either the 1% chlorhexidine gel or placebo. (59) There were no significant differences between the chlorhexidine gel and placebo for plaque and gingival scores after eight weeks. (59) The researchers speculate that both groups had reductions in plaque and gingival scores because of the intensive oral hygiene instruction and professional prophylaxis. However, the study did demonstrate marked tooth staining in the chlorhexidine group compared with the placebo, with 45% of the chlorhexidine subjects exhibiting staining. (59)

A 1975 study by Hansen et al. used young adults to compare the efficacy of 1% chlorhexidine gel with placebo on plaque and gingival scores. (57) The chlorhexidine gel lowered the mean plaque index scores compared with placebo and mechanical oral hygiene, but this was noticeable only for the first four weeks, after which the scores rose to the levels of the controls. (57) The chlorhexidine gel had no effect on gingivitis but did cause more tooth staining than the placebo. (57)

In another study using an adult population, the 1% chlorhexidine gel appeared to have no effect on plaque index scores, gingival crevicular fluid, gingival index scores, and pocket depths compared with placebo over four weeks. (54)

The short-term studies on chlorhexidine gel generally demonstrate negative or inconclusive results. There may be various reasons that explain this lack of results, one of which may have been not to allow enough time for the positive effects of the initial professional prophylaxis to have mitigated. A literature search was therefore conducted for long-term studies using chlorhexidine gel.

Chlorhexidine gels: long-term studies

In a 1977 study by Cutress et al., nursing staff brushed the teeth of mentally challenged children with either a 1% chlorhexidine gel or placebo. (29) No clinical or statistical difference was noted between the chlorhexidine gel and the placebo for plaque or gingival scores over the six-month period. (29) The only significant difference was found for tooth staining, with 79% of the chlorhexidine group exhibiting stain compared with 41% of placebo subjects. (29) The researchers speculated that results were unfavourable due to the nature of the population, which made proper application of the chlorhexidine gel challenging.

It appears that the length of the chlorhexidine gel studies has no effect on the study outcomes. Another possible explanation for the inconclusive or lack of positive results may be the inactivation of the chlorhexidine in the gel vehicle. Yet, in both the 1997 Cutress et al. study and the 1975 Hansen et al. study, the chlorhexidine in the gel was found to be active. (29,57) Although the chlorhexidine gel was active, the studies did not demonstrate the anti-plaque and anti-gingivitis properties found in chlorhexidine mouthrinses. In all of the above studies, the subjects used the chlorhexidine gel only once a day, which may not have been a sufficient dosage. The anti-plaque and anti-gingivitis effect of chlorhexidine is dose-dependent, (51) with the optimal dosage being 40 mg a day. (2)

In comparison, in studies during which subjects have brushed with the chlorhexidine gel twice a day, the gel has been found to be effective in reducing plaque and gingivitis. Bassiouny and Grant in 1975 reported significant differences between a 1% chlorhexidine gel and placebo in plaque reduction and gingival index scores in adults wearing partial dentures. (17) Tooth staining was reported by 37% of the subjects in the chlorhexidine group and this was most visible on approximal surfaces and exposed roots. (17) Lie and Enersen in 1986 also reported significant reductions in plaque and bleeding sites in maintenance care subjects with poor oral hygiene. (30) Tooth staining increased from 0.39 to 1.33 (p < 0.01) in the chlorhexidine group and was most evident in non-smokers. (30)

Different methods of applying chlorhexidine gel

Although applying the chlorhexidine gel by toothbrush has been the most popular method, the gel has also been applied to the teeth by finger, toothpicks, and trays. In one study, 1 gram of the 1% chlorhexidine gel was applied with the subject's index finger to all the teeth. (58) The chlorhexidine gel was compared with placebo gel, 0.2% chlorhexidine mouthrinse, and Neem extract gel (Azadirachta indica, a plant found in India and southern Asia, that is commonly used for oral health care). (58) Table 3 shows the six-week results for plaque and gingival scores.

This study was conducted as an open labelled study, which is not ideal because of the potential for researcher bias in the interpretation of the results. Although tooth staining was not assessed in this study, it would have been interesting to see if there was any difference between the chlorhexidine gel and the mouthrinse.

Chlorhexidine gel has also been applied to the teeth with toothpicks. In a pilot study, seven subjects applied 1% chlorhexidine gel or placebo to the interproximal sites for one week. (55) There was no significant difference in plaque scores between the chlorhexidine gel and the placebo. The authors speculated that the mechanical cleaning effect of the toothpick and the motivation of the subjects resulted in the overall reduction in plaque in both groups. (55) There was the additional problem of the chlorhexidine gel accumulating on the buccal surface rather than being carried into the interproximal area, which may have affected the interproximal dental plaque scores. (55)

A 2003 study by Pannuti et al. used 0.5% chlorhexidine gel in trays twice a day and found significant reductions (22.4%, p < 0.001) in interdental bleeding after eight weeks compared with placebo. (31) The interdental bleeding increased by 6.1% in the placebo group. (31) In this study, a total daily dose of 120 mg was provided to the subjects. (31) The chlorhexidine group had significantly more tooth staining (81.8% of the subjects) than the placebo group, which had one person present with staining after the placebo gel application. (31)

Francis et al. in 1986 compared 1% chlorhexidine gel in trays to 0.2% chlorhexidine mouthrinse and 0.2% chlorhexidine spray in handicapped children. (70) The chlorhexidine was applied twice a day, regardless of the application method, for four weeks followed by a three-week washout period. (70) In this crossover study, each group received all three methods of chlorhexidine application. (70) Although all three methods were effective in reducing plaque and gingival bleeding scores, the gel was significantly more effective. (70) This difference was attributed to better coverage of the teeth and a higher dosage with the chlorhexidine gel. (70) The tray method has the advantage of providing complete and consistent coverage of the teeth, especially in subjects who are unable to rinse for one minute. (70)

Chlorhexidine gel may provide a convenient mode of application for some subjects but to achieve good anti-plaque and anti-gingivitis effects, the gel must be used twice a day to ensure an optimal dose. Unfortunately, chlorhexidine gel does not eliminate tooth staining.

CHLORHEXIDINE SPRAY

Chlorhexidine has also been applied with a non-aerosol spray. Chlorhexidine spray had originally been used in handicapped populations because of their inability to rinse with chlorhexidine for one minute. Spraying twice a day delivers approximately 1.4 to 2 ml of chlorhexidine, which is one-seventh of the optimal mouthrinse dose of 0.2% chlorhexidine. However, it has the same effect on plaque formation and gingival bleeding as the mouthrinse. (70-72) Twice-a-day spraying of a 0.2% chlorhexidine significantly reduced plaque and gingival bleeding scores compared with placebo in handicapped children and adults. (70,71)

A study comparing the anti-plaque and anti-gingivitis properties of 0.2% stannous fluoride and 0.2% chlorhexidine sprays in handicapped children demonstrated that both sprays were effective in reducing plaque and gingival scores. (33) However, the chlorhexidine spray was significantly better than the stannous fluoride (p < 0.05). (33) When a 0.2% chlorhexidine spray is used as an adjunct to mechanical oral hygiene procedures, the chlorhexidine continues to have noticeable clinical and statistically significant reductions in plaque and bleeding scores compared with toothbrushing alone and placebo. (73)

A lower concentration of chlorhexidine spray has also been studied. A 0.12% chlorhexidine spray, in addition to the oral hygiene procedures being provided to the subjects from residential caregivers, significantly reduced plaque (p = 0.002) and improved gingival colour (p = 0.09), tone (p = 0.02), and bleeding (p = 0.03) compared with placebo in institutionalized subjects. (32)

For some population groups, twice-a-day spraying of chlorhexidine is not feasible, especially in situations where a caregiver is responsible for the subject's personal hygiene. (34,74) There have been controversial results with a once-a-day spraying of 0.2% chlorhexidine. Although Dever in a 1979 study states that a daily 0.2% chlorhexidine spray produced statistically significant reductions in plaque and gingival inflammation compared with placebo, he discusses the possibility that 5 ml of a 0.2% chlorhexidine spray may not be clinically significant. (34) This may have been due to the initial high plaque and gingival scores, which were not treated with a preliminary professional prophylaxis. (34) Studies have shown that chlorhexidine is more effective on de novo plaque than mature plaque. (2)

Another study, with better controls, was undertaken in 2003 by Clavero et al. to compare the plaque and gingival efficacy of 0.2% chlorhexidine sprays applied once and twice a day in a geriatric population. (74) One group used the 0.2% chlorhexidine spray twice a day and the other group used the chlorhexidine once a day and a placebo spray once a day. (74) Both groups received an initial professional prophylaxis and continued their usual oral hygiene practices. (74) Study results indicated that the once-a-day spraying was just as effective as twice-a-day spraying on plaque accumulation and gingival inflammation. (74)

In most of the studies involving chlorhexidine spraying, there was no tooth staining or less tooth staining than with the chlorhexidine mouthrinse. (32-34,70,72,74) Only Francis et al.'s study in 1987 stated that the tooth staining from chlorhexidine was similar for mouthrinses, sprays, and gels in trays. (70) The reduction in tooth staining may have been the result of the overall lower dosages of chlorhexidine being applied by spray. (10,40)

The advantage of using a spray versus a mouthrinse or gel is the ease of application for a caregiver or parent when administering the chlorhexidine to the subject. (32,34,71-74) Since the spray method localizes the areas of the mouth to be treated by the chlorhexidine, adverse effects may be minimized. (72)

NOVEL METHODS OF APPLYING CHLORHEXIDINE

Most subjects routinely use a toothbrush and toothpaste to remove dental plaque. (28) Therefore, incorporating chlorhexidine into a toothpaste product could provide an easy substitution for subjects to incorporate into their daily oral hygiene regime. A study was conducted comparing toothpastes containing either 0.8% chlorhexidine and inorganic abrasives or 0.6% chlorhexidine and polymer particles with a placebo paste for two months. (7) The active toothpastes had significantly lower mean plaque index scores than the placebo, with a tendency for the differences to increase with time. (7) The chlorhexidine in the toothpaste was stable for up to six months and showed no changes in antibacterial activity in vitro. (7)

Other studies combined chlorhexidine with zinc citrate, sodium fluoride, or triclosan. (22,61,63) Combining 0.4% chlorhexidine with 0.34% zinc in an experimental dentifrice was effective in reducing plaque and gingivitis compared to a gum care dentifrice. (21) The addition of 1000 parts per million of sodium fluoride to a 1% chlorhexidine toothpaste also showed significant reductions in plaque, gingivitis, and gingival bleeding compared with placebo. (22) However, in both studies, increased supragingival calculus formation and tooth staining were reported with the toothpastes containing the chlorhexidine. (21,22) Jenkins et al. in 1990 experimented with 13 combinations of chlorhexidine and other active ingredients and compared these with water (negative control) and 0.2% chlorhexidine mouthrinse (positive control) to determine their antibacterial effects. (61) Although all the toothpaste combinations showed some anti-bacterial effects, the toothpastes were able to reduce the salivary bacterial counts only for a maximum of five hours compared with seven hours in the 0.2% chlorhexidine mouthrinse group. (61) The reduction in bacterial counts was better for the subjects using the 0.2% chlorhexidine mouthrinse (70%) compared with the subjects using the chlorhexidine toothpastes (35%). (61) Jenkins et al. conclude that there is little clinical benefit for subjects to use dentifrices containing chlorhexidine because the anti-microbial effect is reduced. (61) Toothpastes containing chlorhexidine are not commercially produced because tooth staining and increased calculus formation on the teeth are significant concerns for consumers. (22)

Dental floss is another tool that subjects are familiar with in their oral hygiene practices. However, the use of dental floss is considerably lower than toothbrushes. For example, only 22% of the Canadian population used dental floss on a regular basis in 1996. (28) Studies have shown that toothbrushing alone is ineffective in maintaining gingival health in the interproximal areas (26,27) where gingival inflammation is the most prevalent. (67,68) Dental floss has been found to be an effective mechanical method of treating and preventing interproximal gingivitis. (25-27) Kinane et al. in 1992 decided to combine the mechanical effectiveness of dental floss with the chemical effectiveness of chlorhexidine to determine if this device would be better at reducing gingival bleeding than dental floss alone. (62) A floss holder was designed to deliver 25 [micro]l of 0.1% chlorhexidine into each interdental embrasure while the floss was in position interdentally. (62) This was compared with a similar floss holder with placebo solution and conventional dental floss. (62) The percentage bleeding reduction after two weeks was as follows: 38.3% for conventional floss, 51.5% for the flossing device with chlorhexidine, and 51.4% for the flossing device with placebo. (62) The lack of significant inter-group differences was attributed to insufficient daily dose of chlorhexidine: 0.25 to 0.50 mg per day compared with the recommended 4 mg of sprayed chlorhexidine. (70-73) The authors concluded that higher concentrations, volumes, or twice-a-day usage could have improved the results of the study. (62) However, the method itself may have precluded the penetration of the chlorhexidine into the interproximal sites because as it was described in the article, the floss was already placed in the interproximal area then the chlorhexidine was sprayed. This may have resulted in most of the chlorhexidine being applied to the lingual and buccal surfaces of the teeth or at best to the line angles. There is no way to know, for the study only examined the interproximal sites. This may explain why the two flossing devices had similar results because only the mechanical plaque removal would thus be exerting an effect on the gingival bleeding. The better results for the flossing device compared with the conventional floss was attributed to ease of use and novelty of the device.

The future trend is towards professional dental placement of slow-release chlorhexidine chips or other implantable devices for the treatment of periodontal disease. (6,66) This method offers a controlled, localized approach for treating specific sites while virtually eliminating the common adverse effects of chlorhexidine. Soskolone et al. in 1997 placed a biodegradable chip containing 2.5 mg of chlorhexidine into periodontal pockets, which were previously treated with conventional scaling and root planing at baseline and again at three months. (6) These sites were compared with scaling- and root-planing-only sites in each subject. Probing depths were significantly reduced in sites treated with the chlorhexidine chip compared with scaling and root planing alone (1.16 mm [+ or -] 0.058 versus 0.70 mm [+ or -] 0.056, p < 0.0001, respectively). (6) Gingival index scores were significantly reduced in treated sites, but plaque and bleeding changes were negligible compared with the control sites. Since the chlorhexidine chips were placed subgingivally, tooth staining was not apparent. It was unfortunate that a scaling and root planing was not performed on the control sites at three months when the second chlorhexidine chip was inserted, to provide a better comparison between the sites at the six-month assessment because scaling and root planing also have positive gingival benefits. The positive effects of scaling and root planing wane after a few weeks and would not exert an influence six months later but could influence a gingival effect at three months. (25,43,46,60)

CONCLUSION

Concentrations of chlorhexidine that are lower than the gold standard of 0.2% has been shown to effectively inhibit plaque formation and reduce the bleeding and inflammation associated with gingivitis. Numerous modes of delivery have been explored to optimize the anti-plaque and anti-gingivitis properties of chlorhexidine while at the same time controlling or eliminating its unwanted adverse effects. The only mode of delivery successful at achieving this in the past was spraying the chlorhexidine onto the teeth. As the development of implantable, biodegradable systems matures, there is an increased likelihood that chlorhexidine will be delivered by this method because the use of localized techniques ensures optimal dosage of the chlorhexidine at the site, with minimal adverse effects and compliance from the subject. The success of any treatment will depend on an accurate diagnosis, appropriate choice of treatment for the oral condition and the subject's abilities, and subject compliance in following the appointed directions. It is the clinician's responsibility to choose the most appropriate method for his or her client.

ACKNOWLEDGEMENTS

The author would like to thank Dr. Markus Haapasalo, Professor, Faculty of Dentistry, University of British Columbia for his assistance in proofreading the manuscript.

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by Pauline Imai, CDA, DipDH, BDSc*

* MSc student, Faculty of Dentistry, University of British Columbia

                          Gingival index      Bleeding on probing

0.06% CHX oral irrigator  [down arrow] 42.5%  [down arrow] 35.4%
0.06% CHX mouthrinse      [down arrow] 24.1%  [down arrow] 15.0%
Water irrigator           [down arrow] 23.1%  [down arrow] 24.0%

                          Plaque index        Calculus index

0.06% CHX oral irrigator  [down arrow] 53.2%  [up arrow] 276.4%
0.06% CHX mouthrinse      [down arrow] 43.3%  [up arrow] 273.2%
Water irrigator           NSF                 [up arrow] 7.1%

                          Staining index    Pocket probing depth

0.06% CHX oral irrigator  [up arrow] 68.9%  [down arrow] 4.6%
0.06% CHX mouthrinse      [up arrow] 74.2%  NSF
Water irrigator           NSF               NSF

CHX = Chlorhexidine; [down arrow] = Percentage reduction in scores
compared with toothbrushing control; [up arrow] = Percentage increase
in scores compared with toothbrushing control; NSF = No significant
findings between treatment group and toothbrushing control

Table 1. Comparing the effects of 0.06% chlorhexidine administered by
oral irrigator or mouthrinse to water irrigation and toothbrushing on
gingival health using gingival index, bleeding on probing, plaque,
calculus, and stain indices, and pocket probing depths after six months
of treatment (from Flemmig et al.) (19)

                   Plaque index              Gingival index

Month              3 M          6 M          3 M         6 M
Water control      0.55         0.72         0.28        0.45
Amine fluoride +   0.23         0.29         0.15        0.36
stannous fluoride  *p = 0.0456  *p = 0.0150  *p = 0.287  NSF
0.06% CHX +        0.20         0.27         0.21        0.34
Sodium fluoride    *p = 0.0022  *p = 0.0130  *p = 0.151  NSF
0.06% CHX          0.14         0.25         0.16        0.29
                   *p = 0.0007  *p = 0.0077  *p = 0.183  NSF
0.10% CHX          0.15         0.13         0.14        0.15
                   *p = 0.0013  *p = 0.0007  *p = 0.045  *p = 0.003

                   Discolouration index

Month              3 M          6 M
Water control      0.50         0.38
Amine fluoride +   0.66         0.89
stannous fluoride  *p = 0.0109  *p = 0.0081
0.06% CHX +        0.83         1.06
Sodium fluoride    *p = 0.0001  *p = 0.0011
0.06% CHX          0.68         1.02
                   *p = 0.0642  *p = 0.0017
0.10% CHX          0.96         1.13
                   *p = 0.0000  *p = 0.0011

CHX = Chlorhexidine; * = Significant findings, p [less than or equal to]
0.05; NSF = No significant findings

Table 2. Comparing the effects of amine fluoride/stannous fluoride,
0.06% chlorhexidine with sodium fluoride, and 0.06% chlorhexidine to a
positive control of 0.10% chlorhexidine and a negative control of water
on gingival health using plaque, gingival, and discolouration indices
at three and six months (Hoffmann et al. (44)). Median scores and
P-values.

                     Mean plaque score   Mean gingival score

Control placebo gel  1.31 [+ or -] 0.20  1.140 [+ or -] 0.26
0.2% CHX mouthrinse  0.98 [+ or -] 0.20  0.92 [+ or -] 0.21
                     *p< 0.05            *p< 0.05
1% CHX gel           0.62 [+ or -] 0.29  0.52 [+ or -] 0.25
                     *p< 0.05            *p< 0.05
Neem extract gel     0.63 [+ or -] 0.24  0.60 [+ or -] 0.28
                     *p< 0.05            *p< 0.05

CHX = Chlorhexidine
* = Significant result compared with placebo gel,
p [less than or equal to] 0.05

Table 3. Comparison of 1% chlorhexidine gel and Neem extract gel with a
positive control of 0.2% chlorhexidine mouthrinse and a negative control
of placebo gel on mean plaque and gingival scores at six weeks in Pai et
al. (58) Mean scores [+ or -] standard deviation.