INTRODUCTION

Caries-preventive measures—good oral hygiene, establishment of noncariogenic dietary habits, and regular fluoride supplementation—often are not sufficient to prevent the occurrence of new carious lesions in orthodontic patients with high caries activity. Beyond a certain caries activity level, neither an increase in the frequency of tooth-brushing nor an increase in the dosage of administered fluoride is suitable to effectively stop the demineralization process in high-risk individuals.12 Patients undergoing orthodontic therapy are subjected to oral ecologic changes that lead to increased numbers of Streptococcus mutans in saliva and plaque.34

It has also been shown that orthodontic treatment with fixed appliances results in enamel demineralization and an increased number of carious lesions, predominantly in sites adjacent to brackets.5 Therefore, preventive efforts in these risk group have concentrated on direct suppression of the cariogenic microflora by chemotherapeutics as an adjunct to improved oral hygiene.

Chlorhexidine is the most potent documented antimicrobial agent against Mutans streptococci (ms) and dental caries. Different modes of administration are recommended for caries prevention.6–8 It has been suggested that chlorhexidine application in the form of a varnish results in longer-lasting suppression of ms concentrations by chlorhexidine compared with other forms of application.9–11 High and low concentrations have been reported to reduce the number of ms in plaque and saliva for considerable periods of time.12–14 Numerous studies have examined highly concentrated chlorhexidine varnishes as supersaturated solutions of chlorhexidine diacetate in ethanol, stabilized by the natural resin sandarac.15–19 In these examinations, the optimal chlorhexidine varnish concentration suggested for suppression of ms amounted to 36% chlorhexidine, as represented by the varnish EC40® (Dentres, Nijmegen, The Netherlands).

The consensus of these studies was that ms were significantly suppressed for at least 4 weeks after a single chlorhexidine varnish application. This effect has been tested on teeth free of orthodontic appliances. On the other hand, studies performed in high-risk orthodontic patients with highly concentrated varnish treatment did not show any influence on the caries increment.20 A rapid recolonization of the teeth with ms and a return to baseline values was regarded as a possible reason for the failure of chlorhexidine treatment in orthodontic patients.

Orthodontic patients usually are seen at appointments every 4–6 weeks. Therefore, it is desirable that suppression of ms caused by antimicrobial treatment last for at least this period of time. Hence it is of interest to evaluate whether suppression of ms within a suitable, and for orthodontic patients common, recall interval is possible. Moreover, as yet it is not known whether highly concentrated chlorhexidine varnishes are effective in suppressing recolonization of ms when applied in patients with fixed orthodontic appliances.

Therefore, the objective of the present study was to investigate the time period in which ms in patients with densely colonized teeth and fixed orthodontic appliances return to baseline values after a single treatment with the 36% chlorhexidine varnish EC 40®.

MATERIALS AND METHODS

RESULTS

The statistical analysis was done as described above using relative treatment effects. For better illustration of the original data, the distributions of ms score changes during the 2-week interval are given in a cross-table (Table 1). The table demonstrates that a deterioration to higher scores occurred in 36 cases, whereas in 64 sites an improvement to lower scores took place. Scores for the other 52 sites remained unchanged. However, ms scores were below detection level (score 0) in only 34 sites at the end of the 2-week period.

TABLE 1. Cross-tabulated Number of ms Values Indicating Tooth wise Changes From Baseline to Two Weeks^a

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In Figure 1, the results of site-specific plaque samples on teeth with brackets at baseline (T0) and 2 weeks (T1) after varnish treatment are demonstrated. After 2 weeks, ms counts were reduced as compared to baseline values. The reduction did meet statistical significance, but only weakly (P = 0.049). In the design of the study, we intended to record ms levels in plaque every 2 weeks until ms values returned to baseline values. Because in nearly every subject recolonization with ms was already complete after 2 weeks of varnish application, recording of ms values was not continued.

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Nevertheless, we could observe intra-individual differences. The degree of reinfection varied considerably between different patients (Table 2). However, only 2 patients showed a distinct suppression of ms counts.

TABLE 2. Exemplary Plaque ms Scores (0–3) in a 13-Year-Old Girl and a 14-Year-Old Boy at Baseline and 2 Weeks After Treatment Given for the Respective Teeth at Which Plaque Samples Were Tak en^a

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DISCUSSION

The ms counts in the present study were evaluated with a commercial available S. mutans test, namely the chair-side Strip-mutans-Dentocult® test.31 The reliability of this method has been proven by numerous studies. There is a significant correlation between conventional analysis with MSB agar32 and the Strip-mutans® test.3334 Intra-individual differences with the Strip-mutans® method were investigated by El-Nadeef and Bratthall.35 They observed that tests that were repeated in one subject usually showed no differences. Tests varied in more than one category in very rare cases. Therefore, with good handling, the Strip-mutans® method is a very reliable method.

If fluoridation measures and dietary counseling are not considered, the use of antimicrobials is currently the only promising alternative to improved oral hygiene. However, it must be noted that studies performed in high-risk orthodontic patients did not find significant differences in caries increment after repeated application of high- or low-concentration chlorhexidine varnishes.3637 In contrast to these findings, other investigations with orthodontic patients have documented a reducing effect of chlorhexidine and/or fluorides on caries increment and S. mutans.38–42 However, in contrast to the present investigation, in these studies patients taking part in the trials were not preselected with regard to caries risk, caries activity or levels of ms in plaque and saliva, respectively,

In a former study it was proved that the efficacy of a highly concentrated varnish is reduced by bands and brackets.43 In this split-mouth–designed study, recolonization on teeth with orthodontic appliances occurred significantly faster than on teeth without appliances.

It was assumed that the duration of ms suppression depends partly on the extent to which any retention niches are coated with varnish. In a previous study by Jenatschke et al,44 ms counts were assessed only at baseline and 8 weeks, so the definite time point of the recolonization was not discernible. In that study, the varnish was applied on the day of bracket placement and was repeated at 8-week intervals, while the fixed appliances were in place. As mentioned above, in this investigation the caries increment was not reduced despite the use of chlorhexidine varnish treatment. It can be assumed that the recolonization must have taken place during this time interval (ie, 8 weeks) so that recolonization with ms and caries development could not be avoided.

The recolonization with ms after antimicrobial therapy in highly colonized teeth was investigated in the present study. We could show that ms counts had nearly returned to baseline values after 2 weeks. Because only a weak significant difference between baseline and 2-week values was observed, the reduction of ms is assumed to be not clinically relevant. This suggestion is corroborated by the fact that most of the samples were not below detection level 2 weeks after varnish treatment.

Additionally, it could be assumed that a complete recolonization would have taken place within a short period after completion of the 2-week interval chosen in the present study. This finding may act as an explanation of why no effect on caries increment was achieved in former studies. On the other hand, an application modus applying the varnish even more often, eg, once a week, is not practicable. A more effective application mode must be found to hamper the fast recolonization of ms in orthodontic patients.

Emilson and Lindquist45 evaluated the coherence of the infection level of ms and recolonization of teeth after chlorhexidine treatment and observed that tooth surfaces with a high level of infection are more rapidly colonized by ms. This was true even if these microorganisms had previously been suppressed to undetectable levels after antimicrobial treatment. This observation makes clear that a slow recolonization pattern and higher efficacy more presumably can be achieved in teeth with low levels of colonization.

Unfortunately, patients with a fast recolonization pattern are more likely to develop carious lesions after application of fixed orthodontic appliances. Therefore, an effective way of suppressing ms should be found for these patients. An effective way could be to apply the varnish immediately before bracketing and banding of the teeth. It may be hypothesized that this results in a slower recolonization of ms. Afterwards, the exact recolonization time after varnishing has to be determined to set an application interval and to suppress ms during the entire therapy with fixed appliances. Another focus should be set on the cleaning of the tongue, because the tongue may act as an infection source, possibly favoring the recolonization pattern on the teeth. Of course, it can also be assumed that in the present study no suppression at all could be achieved. This is speculative, because no ms counts were assessed right after varnish treatment. The authors had expected suppression for at least 4 weeks, and because of this assumption, the ms counts were investigated after a 2-week interval.

Therefore, development of more effective therapy modes and identification of reasons for lack of effectiveness need to be investigated in further studies. Furthermore, interdisciplinary work between the cariologist and orthodontist should be intensified to develop caries prevention strategies for orthodontic patients, because these patients are at a high caries risk.46

CONCLUSIONS

• A single 36% chlorhexidine varnish application is not effective in suppression of ms counts to a clinically relevant degree in patients with fixed orthodontic appliances and highly colonized ms salivary counts.