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RESEARCH REPORT |
1 Key Laboratory of Oral Biomedical Engineering (Wuhan University), Ministry of Education and Department of Endodontics, School and Hospital of Stomatology, Wuhan University, Wuhan, 430079, P.R. China;
2 Department of Preventive and Restorative Dentistry and
3 WHO Collaborating Centre for Oral Health Care Planning and Future Scenarios, Radboud University Nijmegen Medical Centre, the Netherlands
* corresponding author, zhangqimary{at}yahoo.com.cn
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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KEY WORDS: caries prevention • chlorhexidine • varnish • randomized controlled trial
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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In recent years, varnish formulations have become available for prolonged chlorhexidine release to eliminate mutans streptococci and inhibit mineral loss in a demineralization model (for review, see Matthijs and Adriaens, 2002). When the present study was initiated, there were only 3 published clinical trials evaluating the long-term effects of chlorhexidine varnish treatment on caries prevention (Bratthall et al., 1995; Petersson et al., 1998; Fennis-Ie et al., 1998). Bratthall et al.(1995) used a split-mouth design to measure the effects of 1% chlorhexidine varnish (Cervitec®) on fissure caries of permanent molars of seven- to eight-year- and 12- to 13-year-old children. Cervitec® was applied at baseline, and after 3 to 4 and 8 to 9 months. The results indicated that Cervitec® significantly reduced caries increment on fissures after 2 yrs. In the study by Petersson et al.(1998), semi-annual applications of a chlorhexidine/fluoride varnish mixture (Cervitec® + Fluor Protector®) for 3 yrs had no additional preventive effect on approximal caries in 12-year-old children, as compared with the application of Fluor Protector® alone. Fennis-Ie et al.(1998) selected five-to six-year-old and 11- to 12-year-old children for investigation of the anti-caries effect of a semi-annual application of 40% chlorhexidine varnish (EC40) on fissures of permanent molars. A borderline statistically significant 36% reduction of caries was found 3 yrs later in the children who harbored high mutans streptococci counts at baseline. However, no significant caries reduction was seen in the whole sample. These results were controversial, which might be due to the differences in the study populations, surface sites, chlorhexidine varnish concentrations, frequencies of application, and study design. Hence, there was a need for further clinical studies on the caries-inhibiting effect of chlorhexidine varnish. We conducted a clinical trial among children in Wuhan, China. These children did not receive any caries-preventive program, and it was expected that the relatively simple application of chlorhexidine varnish would have a caries-inhibiting effect in pits and fissures of permanent first molars.
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MATERIALS & METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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From all 1st grade, six- to seven-year-old children from nine primary schools of Hongsan District in Wuhan City, we selected 905 children who had at least one pair of contralateral, completely erupted first permanent molars without dentinal caries or fillings, or not missing due to caries. Of these, we selected 461 children who had more than 2 decayed primary molars. These 461 children, who were considered to represent the high-caries-risk fraction of the child population, were enrolled in the clinical trial. These selection procedures resulted in 778 pairs of contralateral, completely erupted first permanent molars, 417 pairs in the lower jaws and 361 pairs in the upper jaws.
The children received no additional health care advice. Drinking water in Wuhan city contains 0.25 ppm fluoride. The study was approved by the Ethics Committee of the Dental School, Wuhan University. The schools granted permission for the study, and informed consent was obtained from parents or legal representatives of all participating children.
The sample size estimation was based on the assumption of a 0.2 mean increment of dentinal caries in fissures and pits of a pair of permanent molars per child, and a standard deviation of 0.2 over the period of six to nine yrs of age (Petersen and Esheng, 1998), with a power of 80% (ß = 0.20), and a difference in mean caries increment of 30%. With 
= 0.05 as the significance level, the sample size was calculated to be 174 pairs. Since the presumed annual dropout rate is about 10%, the sample size was about 230 pairs per group.
Study Design
A split-mouth design was used, with one first permanent molar as the test tooth and one contralateral first permanent molar as the control in the same jaw. Left or right side was selected randomly for test or control.
The 461 participating children were randomly selected within different classes and assigned to three different application groups by pupil registration number: that is, from each class, number one to group C, number two to group B, number three to group A, number 4 to group C, and so on. Group A included 150 children with 241 pairs of first permanent molars, group B had 155 children with 272 pairs, and group C had 156 children with 265 pairs.
Application of Varnish
The test tooth received chlorhexidine application on fissures and pits. Chlorhexidine varnish was applied to the test molar of group A at baseline, 6, 12, and 18 mos. In group B, the test molar received chlorhexidine varnish treatment at baseline, 3, 12, and 15 mos. In group C, 1 test molar received chlorhexidine varnish with the application frequency of group A, and the contralateral molar received the chlorhexidine varnish with the application frequency of group B. No placebo varnish was applied to the control molar.
Chlorhexidine varnish was applied by one of two dentists. The first permanent molar to be treated was isolated from saliva with the use of cotton rolls. The fissures and pits were cleaned by means of a probe moving through the fissures and pits, and were scrubbed with cotton pellets. The surfaces were then dried with a blast of compressed air. Chlorhexidine varnish, 40% (w/w) chlorhexidine diacetate with a sandarac resin base and dissolved in water-free alcohol, was packed in glass ampoules. A dentist injected it, via a syringe with a blunt needle, into the fissures and pits. The occlusal surfaces and palatal pits on palatal surfaces of the upper first permanent molars and occlusal fissures and buccal pits on buccal surfaces of lower first permanent molars were treated. Children were instructed not to eat and drink for 10 min following varnish application.
Caries Diagnosis
Caries diagnosis, distinguishing enamel caries (D1; white or brown discoloration of fissure and pit and/or some loss of enamel), and dentinal caries (D2; cavity visible in dentin, or the presence of a filling, or tooth missing due to caries), was carried out independently by two examiners at baseline and after 1 and 2 yrs. After 2 yrs, it was decided to reevaluate groups A and B 1 yr later.Caries score D1 was assigned as sound in the analysis. The two examiners were calibrated against a ‘gold standard’ examiner (WHvPH). Each palatal surface of upper first permanent molars and buccal surface of lower first permanent molars was divided into two sections: pits and smooth. The examiners were blinded to the assignment of the groups and the test molars. The surfaces were dried with cotton rolls and examined visually with an intra-oral fiber-optic light and a mouth mirror.
Statistical Analysis
We applied actuarial survival analysis to estimate the percentage of molars free of caries. (Free of caries is here defined as sound or with a D1 condition.) The prevented fraction was calculated as the difference between the increment of dentinal caries in the control and test molars, divided by the increment of the control molars. For statistical testing of differences, the child was the unit of analysis. Since, in many children, two pairs of molars were included in the study, the data cannot be considered statistically independent. As a result, variance estimates will be biased. We used the ‘Jackknife method’ of omitting one patient (Efron, 1982) to calculate the standard error of the survival percentages and of the prevented fraction. T-values were calculated as t = difference/SE (difference) and could be used to calculate p-values according to the normal standard distribution. Data analysis was performed by the use of the SPSS-12 statistical package.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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Of the 461 children at baseline, 48 children did not appear for further examinations. At the second-year evaluation, another 20 children had dropped out, and at the third evaluation, 11 children did not appear. Due to longitudinal inconsistencies in recorded data files, 13 children were excluded from the analysis. Of the participating children, 7% missed one EC40 application during the course of the study.
The actuarial survival analysis indicated that, in group C, no statistically significant difference had occurred in caries increment between molars treated according to EC40 application scheme A or B (Table 1
). Because there was no difference in caries-inhibiting effect between the two application schemes in group C, groups A and B were combined in the analysis, to increase the power of the study. The cumulative two-year survival rate of EC40-treated molars that remained free of dentinal caries was statistically significantly higher as compared with that of the control molars (Table 2). The prevented fraction of caries increment was 25% (95%CI, 1%, 49%, p = 0.04) after 2 yrs. At the three-year evaluation, which was 18 to 21 mos after the final EC40 application, the observed caries-inhibiting effect of EC40 had disappeared (Table 2). The prevented fraction at the three-year evaluation was 9% (95%CI, –11%, 29%, p = 0.20).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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In a parallel-group design, placebo treatment for control subjects is recommended, to neutralize a possible positive influence on the disease process caused by the provider’s attention. However, provider’s attention as a determinant for the disease process does not play a role in a split-mouth design, and therefore control molars in the present study did not receive a placebo treatment.
The overall dropout rate during the three-year course of the study was 17%, which was low. Adherence to the treatment protocol was good, since only 7% of the participating children missed one EC40 application.
Two different EC40 application frequencies were used in this study, either every 6 mos over a period of 18 mos (scheme A), or twice in the first 6 mos two times, at baseline and after 3 mos, and again after 12 and 15 mos (scheme B). The six-month interval application was in accordance with the prevailing follow-up dental care system in many countries. Previous studies have shown that a higher chlorhexidine varnish application frequency leads to a stronger suppression of mutans streptococci (Ie and Schaeken, 1993; Twetman and Petersson, 1997). That finding was the rationale for the EC40 application scheme B. However, the results in the present study indicated that these two application frequencies had no statistically significantly different caries-inhibiting effect.
The prevented fraction of caries increment at the one-year evaluation was 35%, but, due to the large confidence intervals, this substantial caries reduction was not statistically significant. The prevented fraction of caries increment was 25% (95%CI, 1%, 49%) in EC40-treated molars at the two-year evaluation. Statistical significance was reached because groups A and B were combined, which increased the sample size sufficiently for the necessary power. A prevented fraction of at least 30% was originally set for the sample size estimation, since a lower percentage was considered to have questionable clinical relevance in this low-caries-incidence child population. The small prevented fraction of 9% (95%CI, –11%, 29%) at the three-year evaluation, which was 1 yr after termination of the trial, was not statistically significant. Thus, the observed beneficial effect of EC40 had disappeared 1 yr later.
Until now, there have been only five studies focusing on the caries-inhibitory effect of chlorhexidine varnish application in the pits and fissures of permanent molars (Bratthall et al., 1995; Fennis-Ie et al., 1998; Joharji and Adenubi, 2001; Araujo et al., 2002; Baca et al., 2002). For molars treated with chlorhexidine varnish, the prevented fraction of caries increment was found to be 53% (Bratthall et al., 1995), 9% (Fennis-Ie et al., 1998), 64% (Johari and Adenubi, 2001), and 48% (Baca et al., 2002), whereas one study did not find any dentinal caries increment in a small sample of 16 children (Araujo et al., 2002). All the reported reductions in dentinal caries increment were statistically significant, except one (Fennis-Ie et al., 1998). Varnishes with various chlorhexidine concentrations were used, and different application frequencies were applied in the 5 studies cited. Despite these differences, significant reductions in dentinal caries increment were reported (except one) as a result of chlorhexidine varnish application. A prevented fraction of 25% in dentinal caries increment in the present study is in accordance with the previous results. However, the caries-inhibiting effect disappeared 1 yr later. The lack of a long-lasting effect was also recently reported in another paper (Baca et al., 2003).
In conclusion, the application of EC40 to the pits and fissures of permanent first molars of six- to seven-year-old children has a short-term caries-inhibiting effect, but its efficiency is questionable in a child population with a low caries incidence.
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ACKNOWLEDGMENTS |
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Received September 18, 2005; Last revision December 16, 2005; Accepted January 11, 2006
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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Araujo AM, Naspitz GM, Chelotti A, Cai S (2002). Effect of Cervitec on mutans streptococci in plaque and on caries formation on occlusal fissures of erupting permanent molars. Caries Res 36:373–376.[ISI][Medline]
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