Accordingly, a variety of implements have been marketed and used to facilitate the mechanical removal of plaque, including toothbrushes of varying shapes and configurations, dental floss, inter-dental brushes and toothpick holders.² It has been demonstrated in clinical studies that more frequent or intense episodes of instruction in plaque control can help control the onset or progression of periodontal diseases.^3–5 Experience in actual clinical practice, however, can be quite different. In fact, most patients often are not able to maintain adequate plaque control levels using mechanical methods alone, despite efforts to educate them about preventive procedures.

The experiences of individual practitioners are reflected in epidemiologic data from the United States and other countries that reveal that gingivitis was present in a majority of the people examined. For example, in the United States, 63 percent of dentate people examined in the Third National Health and Nutrition Examination Survey had gingivitis, as indicated by gingival bleeding on probing⁶; this prevalence likely is an underestimate of the true prevalence, since only two sites (the mesiobuccal and midbuccal) on each tooth in two randomly selected quadrants were assessed. In a Swedish study in which a random sample of 600 adults in six age groups from 20 to 70 years were examined in 1973, 1983 and 1993, researchers found that the levels of plaque accumulation and gingivitis in the 20-year-olds actually increased between 1983 and 1993.⁷ A survey in Ireland revealed that gingivitis was present in 77 percent of people in the 16- to 24-year-old group and in 91 percent of the people in the 55- to 64-year-old group.⁸ In a study conducted in the United Kingdom, researchers found visible plaque in 72 percent of adults; even when subjects cleaned their teeth immediately before their examinations, plaque still was seen on close to one-third of their teeth.⁹ While these are just a few examples, a high prevalence of gingivitis and periodontal diseases can be seen in many countries worldwide.¹⁰

Bacteria in biofilms are different from those of the same species freely floating in a tube of culture medium.

Thus, from both clinical experience and population-based studies, it is clear that mechanical plaque control methods that in theory are able to maintain adequate levels of oral hygiene are in actuality not being employed sufficiently by large numbers of the population. The need for additional help in the control of bacterial plaque provides the rationale for the use of antimicrobial mouthrinses with clinically proven antiplaque and antigingivitis effectiveness as adjuncts to patients’ mechanical oral hygiene regimens.¹¹

	EVIDENCE FOR EFFECTIVENESS

TOP EVIDENCE FOR EFFECTIVENESS CLINICAL STUDY DESIGNS CLINICALLY PROVEN MOUTHRINSES CONCLUSIONS

 
A variety of study types ranging from laboratory studies to long-term clinical trials have been used to support the effectiveness of antimicrobial mouthrinses. Given this range, it is necessary to consider what constitutes sufficient evidence to support clinical effectiveness of antiplaque and antigingivitis mouthrinse formulations. In this article, I consider the conclusions that can be drawn from the types of studies that have been conducted. I am not, however, presenting a rigorous evaluation of the literature that is typical of the evidence-based approach to clinical decision making that has become the cause célèbre of clinical practice.

To appreciate fully the kind of information that can be obtained from various study designs, it is important to recognize that dental plaque is just one example of a category of adherent, organized microbial communities referred to as biofilms.^12–16 Bacteria in biofilms are different from those of the same species freely floating in a tube of culture medium, so-called "planktonic organisms." Once bacteria adhere to a surface, they develop a phenotype that is altered from the one they had while floating freely. For example, they may start to produce an extracellular matrix and synthesize and release molecules that enable them to "communicate" with other bacteria within the mass (for example, quorum-sensing molecules). Bacteria in biofilms usually are more resistant to antimicrobial agents than are planktonic organisms, as they are encased in an extracellular matrix that impedes access of the agent to the bacteria and because the phenotypic changes themselves may render the bacteria more resistant.¹⁷ This is relevant to antimicrobial mouthrinse studies, as it suggests that assessments based on a mouthrinse’s effect on planktonic organisms may not be indicative of the effectiveness of the mouthrinse against the plaque biofilm under actual-use conditions.

Measures of antimicrobial effectiveness that are conducted on planktonic organisms include the kill kinetics assay, which assesses the percentage of organisms killed within a given period, and minimal inhibitory and bactericidal concentration determinations, which provide information about the lowest concentration of the mouthrinse exerting a growth inhibitory or outright killing effect. These measures provide important information about the antimicrobial spectrum and the potency of mouthrinse formulations. By themselves, however, they are not predictive of clinical effectiveness. When a quantity of mouthrinse is added to a tube containing planktonic organisms, the mouthrinse quickly mixes with the fluid culture medium and gains access to the suspended microorganisms to exert its effect. It is not clear, however, that the mouthrinse will behave the same way when encountering the plaque biofilm, since it will have to penetrate the biofilm matrix to carry the active agents to the more densely packed bacteria within the brief period of a 30- or 60-second rinse. Thus, mouthrinses that might be effective against planktonic organisms may not be comparably effective against the same organisms contained within a biofilm.¹⁸ Laboratory tests using biofilm models have been developed that help explain the differences among formulations, as well as mechanisms of action, and that may be more predictive of clinical effectiveness.^19–24

There are a number of factors that might be important during the actual use of a mouthrinse that cannot be simulated in the laboratory.

There are a number of factors that might be important during the actual use of a mouthrinse that cannot be simulated in the laboratory and thus provide a requirement for clinical studies. They might include the contribution of substantivity to a product’s effectiveness, interactions between salivary components and the active ingredient that might reduce its activity, and inhibitory interactions between a mouthrinse’s active ingredients and the components of other oral hygiene products such as dentifrice.

	CLINICAL STUDY DESIGNS

TOP EVIDENCE FOR EFFECTIVENESS CLINICAL STUDY DESIGNS CLINICALLY PROVEN MOUTHRINSES CONCLUSIONS

 
A wide range of clinical studies has been presented over the years in support of the effectiveness of therapeutic antimicrobial mouthrinses. At the least rigorous end of the spectrum are open trials, or so-called "pragmatic clinical trials," in which a test group of subjects uses a product according to label directions with full knowledge of what the product is. In these trials, there is no true control group, as the test group is compared with a group of people who have done nothing in addition to their usual oral hygiene procedures. Since it is known which product the test subjects used, such a design does little to minimize investigator bias and, in the absence of a true negative control group, does not allow for the factoring out of improvement resulting from a "Hawthorne effect," which will be discussed later. Trials using this protocol design have only limited value in determining the effectiveness of a given mouthrinse formulation.

There are four characteristics that are essential in assessing which types of clinical studies are the most credible:

– the trial should be controlled with a negative control group to which the test group can be compared;

– the trial should be blinded so that the examiner and all other personnel involved in evaluating data or laboratory specimens are not aware of which group a given subject is in;

– subjects meeting entry criteria should be assigned randomly to treatment and control groups;

– the trial should be prospective; that is, the protocol, entry criteria, random assignments and method of statistical analyses should be determined in advance of the actual treatment phase.

A number of blinded, randomized, prospective study designs have been used to demonstrate antimicrobial mouthrinse effectiveness. These include studies looking at salivary bacterial counts,^25,26 studies looking at plaque regrowth over a 24-hour²⁷ or four-day period^28–31 and studies using an experimental gingivitis model^32,33 based on Löe and colleagues’ study.¹ These all have limitations that preclude their providing sufficient information about antiplaque and antigingivitis effectiveness for use in clinical decision making. Some investigators consider studies of subjects’ salivary bacterial counts at various times after rinsing with test mouthrinses or placebos to be a surrogate for antiplaque activity. Such studies, however, do not assess the mouthrinse’s activity against bacteria in biofilms and, of course, do not assess gingivitis. Four-day and 24-hour plaque regrowth studies may serve as a screening method or provide preliminary information about antiplaque activity, but they only evaluate short-term effects in the absence of mechanical oral hygiene and do not assess gingivitis. While experimental gingivitis studies look at both plaque and gingivitis, they are short-term (14–21 days) and, because they do not involve usual oral hygiene procedures, cannot reveal interactions that may occur between the mouthrinse and components in other products such as dentifrices. In addition, none of these study models allows for longer-term assessment of the oral flora or the occurrence of adverse effects under normal-use conditions.

In the final analysis, the clinical effectiveness and safety of mouthrinses are best evaluated by using prospective, randomized clinical trials in which plaque and gingival indexes, the condition of the oral mucosal tissues and the composition of the oral flora are determined when the product is used according to the label directions and as an adjunct to usual mechanical oral hygiene procedures over a prolonged period. The ADA’s Council on Dental Therapeutics (currently the ADA Council on Scientific Affairs) developed guidelines for the design of such clinical trials.³⁴ Pivotal studies included in product submissions for the ADA Seal of Acceptance are required to meet the requirements of these guidelines (Box). These guidelines also have been adopted, in some cases with modifications, by other professional and governmental organizations that evaluate antiplaque and antigingivitis products; these organizations include the U.S. Food and Drug Administration, or FDA; the Canadian Dental Association; and the British Dental Association.

In addition, it usually is observed in these trials that all subjects will show some improvement, especially over the initial few months of the study. This generally is attributed to the so-called "Hawthorne effect," a tendency for subjects who know they are in a dental trial to unconsciously brush their teeth more thoroughly at first. This effect usually will diminish over time; if the mouthrinse is truly effective, subjects in this group will show significantly greater improvement than those in the negative control group during the latter phase of the study. Therefore, a comparison of the active group with the negative control group at six months will allow for an assessment of the true effectiveness of the mouthrinse in that it will factor out that portion of improvement resulting from the Hawthorne effect. There are several rationales for a six-month study duration: it is the "traditional" recall interval in dental practice, it provides sufficient time to determine if the product has any adverse effects such as tooth staining or mucosal irritation, and it provides enough time to determine whether the mouthrinse will have an adverse effect on the oral flora, such as allowing for the overgrowth of opportunistic pathogens.

Subsequent modifications to the guidelines³⁵ deal with issues of study design, such as making the need for randomization and blinding explicit; require a gingival bleeding component in the assessment of gingivitis; indicate methods for standardization of examiners; specify elements to be included in the statistical analyses; and establish a minimum acceptable effect level.

	CLINICALLY PROVEN MOUTHRINSES

TOP EVIDENCE FOR EFFECTIVENESS CLINICAL STUDY DESIGNS CLINICALLY PROVEN MOUTHRINSES CONCLUSIONS

 
Active ingredients and marketed products containing these ingredients that are backed by published studies satisfying the ADA’s guidelines are listed in the table.^36–45 Chlorhexidine and triclosan were approved by the FDA for use in oral care products in the United States by means of the New Drug Application route. Triclosan-containing dentifrices were approved in the United States by the FDA. Triclosan-containing mouthrinses are not marketed in North America but are in other countries worldwide. The Plaque Products Subcommittee, an FDA advisory panel that reviewed antiplaque ingredients as part of a process intended to determine the safety and effectiveness of ingredients in nonprescription products with a significant marketing history, has recommended that two ingredients, the fixed combination of essential oils and cetylpyridinium chloride, be placed in Category 1 (safe and effective).

Although the primary endpoints in the six-month studies are supragingival plaque and gingival indexes, mouthrinses—because they are liquid delivery devices—can deliver active antimicrobial agents throughout the mouth in the course of rinsing. Therefore, it is likely that they also may reduce bacterial levels in sites that might serve as reservoirs for dental plaque bacteria, such as the dorsum of the tongue. In fact, studies have reported that use of an antiseptic mouthrinse results in significant reductions of tongue bacteria levels.^46,47

	CONCLUSIONS

TOP EVIDENCE FOR EFFECTIVENESS CLINICAL STUDY DESIGNS CLINICALLY PROVEN MOUTHRINSES CONCLUSIONS

 
Thus, the data indicate that the adjunctive use of antimicrobial mouthrinses can provide significant benefits to patients who cannot maintain adequate levels of plaque and gingivitis control through mechanical methods alone. When recommending such products, dentists need to ensure that their patients understand that using a mouthrinse is not a substitute for mechanical oral hygiene procedures and that daily compliance with label directions and their professional recommendations are essential to the most successful outcome.