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The Effect of a Bi-annual Professional Application of APF Foam on Dental Caries Increment in Primary Teeth: 24-month Clinical Trial
1 Department of Preventive Dentistry, School of Stomatology, Wuhan University, China; and Correspondence: * corresponding author, phs301{at}vip.163.com
The purpose of this study was to evaluate the effect of a bi-annual professional application of acidulated phosphate fluoride (APF) foam on caries increment in the primary dentition over a two-year period in the People’s Republic of China. In a double-blind, cluster-randomized, placebo-controlled trial, 392 children aged 3–4 years from 15 classes were randomly assigned to two groups on a school class basis. The experimental group (8 classes) received a bi-annual APF foam application, and the control group (7 classes) received the placebo. The mean increment of dmfs in the experimental group was 24.2% lower than that in the control group (p < 0.05). The significant caries reduction was observed on approximal surfaces in the experimental group compared with the control group (p < 0.01), but there were no differences on occlusal surfaces (p > 0.05). A bi-annual professional application of APF foam was effective in reducing the increment of dental caries in the primary teeth.
Key Words: clinical trial • acidulated phosphate fluoride • fluoride foam • caries prevention
Acidulated phosphate fluoride (APF) is an effective cariostatic agent that was widely investigated in the last half-century. In recent decades, APF gels have been frequently used in dental clinics and prevention programs in schools in many countries (Hawkins et al., 2003; Marinho et al., 2003). The effects of APF gel in caries prevention were recently confirmed by 2 review articles (van Rijkom et al., 1998; Marinho et al., 2003). The meta-analysis of clinical studies showed that the overall caries-inhibiting effect of APF gel treatment was 21% (95%, CI = 14–28%) (Marinho et al., 2003). However, almost all of the clinical trials evaluated the preventive effect of fluoride gel on dental caries in the permanent teeth in 6- to 15-year-old children. Excessive ingestion of fluoride during gel applications in children under 5 yrs old is likely to result in acute toxicity (Duxbury et al., 1982; Ripa, 1990). Therefore, the use of APF gel in young children is not recommended. APF foam is a relatively recent product, with the same concentration of fluoride (1.23%) and pH (3–4) as conventional APF gel. The 2 APF products are also similar in terms of their abilities to deposit fluoride on the enamel surface (Whitford et al., 1995). However, compared with the gel, APF foam requires only about one-fifth as much material by weight for adequate coverage of the teeth, which significantly reduces fluoride exposure and retention by the patient (Wei and Chik, 1990). To our knowledge, until now, no clinical studies have investigated the preventive effect of APF foam on caries development in the primary teeth. The purpose of the present study was to evaluate the effect of a bi-annual professional application of APF foam on caries increment in the primary dentition in Chinese kindergarten children over a two-year period.
This was a double-blind, cluster-randomized, placebo-controlled trial aimed at Chinese kindergarten children. The study protocol was approved by the Ethics Committee of the School of Dentistry, University of Wuhan, in the People’s Republic of China, prior to the implementation of the study. The study was carried out in the Hongshan District of Wuhan City, Hubei Province, which is located in central China. Fluoride concentration in the drinking water in the district is 0.1–0.3 ppm. No organized oral health care programs for kindergarten children were available in the district. The minimum sample size required was 148 per group. The size of the sample was calculated to have an 80% power of demonstrating a significant difference between groups at the 5% level, if a difference was as high as 25%. In total, 392 children aged 3–4 years from 4 kindergartens were recruited into the 24-month clinical study. The children were randomly allocated to the two groups on a school class basis. Each child had an equal chance to be allocated to either class in every kindergarten, because assignment was not based on academic ability or family income level. Fifteen classes from 4 kindergartens made up 15 clusters. Randomization was performed, with a table of random numbers, by a researcher not involved in the study. Fifteen classes were randomly assigned to the fluoride group (n = 8 classes) and the placebo control group (n = 7 classes). All the children in these classes were included in the study. The subjects were blinded to the group assignment. The parents of these children were informed by letters explaining the purpose and procedures of the study. Meanwhile, short questionnaires were sent to the parents following the letters. The children’s parents completed them at baseline. The informed written consents signed by parents of all children were obtained prior to the implementation of this study. APF foam (1.23% APF, Laclede, Inc., Rancho Dominguez, CA, USA) or placebo (fluoride-free foam, Laclede, Inc., Rancho Dominguez, CA, USA) was professionally applied at the 4 kindergartens by two dentists and two assistants, who were blinded to fluoride exposure because the bottles of APF foam and placebo were identified only with ‘1’ and ‘2’. The subjects did not receive professional prophylaxis prior to the application. Appropriately sized sponge-lined trays (upper and lower) were used for the treatment procedure. If the tray was not suitable for the child, it was trimmed by the operators. The moderate amount of APF foam (0.6–0.8 g) placed in the upper or lower tray was approximately one-third of the tray’s volume. The upper and lower trays were then inserted into the child’s month separately, and the child was instructed to close the jaws. The teeth were allowed to be in contact with the foam or placebo for 4 min. During that time, the child was seated in an upright position with the head inclined forward and downward to reduce swallowing. Meanwhile, the children were told not to swallow but to allow the saliva to drop directly onto a recyclable plastic plate. At the end of the treatment, the tray was removed from the mouth, and each child was told to expectorate the mixture of saliva and foam for up to 1 min. The children were cautioned to refrain from rinsing, eating, and drinking for at least 30 min after the treatment (Wei and Chik, 1990). The treatments were provided at approximately six-month intervals over 2 yrs. The maximum number of applications that a child could receive was 4. Oral examination at baseline was carried out in September, 2000, and the follow-up examination took place in October, 2002. The children were examined by two examiners (dentists), who were blind to the children’s group allocation throughout the study. The dentists conducted the clinical examinations in classrooms, under natural daylight, using sharp explorers and mouth mirrors. Examination criteria for caries diagnosis followed the WHO guidelines. As a test of intra-examiner reliability, about 10% of the children were re-examined randomly on the same day in all examinations. The kappa values of the duplicate examinations were over 0.90 at baseline and follow-up evaluations. All data were entered into the computer and analyzed by means of the SPSS 12.0 system for Windows (SPSS 12.0, SPSS Inc., Chicago, IL, USA). We used cluster-specific methods for the primary outcome, because classes rather than individuals were randomized. The analysis of caries increment was based on the class as the unit of analysis. We performed independent-sample t tests to compare the differences in caries indices at baseline and caries increments between the two groups. Chi-square tests were conducted for descriptive variables. The level of statistical significance was set at 0.05.
Originally, 392 children were included in the study. There were 209 (mean age, 3.6 ± 0.4 yrs) children in the APF foam group and 183 (mean age, 3.5 ± 0.6 yrs) in the placebo control group. After 2 yrs, 167 children (90 boys, 77 girls) in the experimental group and 151 (82 boys, 69 girls) in the placebo control group completed the study. The drop-out rate was 20% and 17%, respectively, which was similar between the two groups (P-value = 0.51). Most children who were lost from the study transfered to other kindergartens.
Only those children who were present at the baseline examination, 4x treatments, and follow-up examination were included in the analysis. There was no statistically significant difference between the two groups in terms of potential confounding factors such as gender, age, toothbrushing frequency, use of fluoride toothpaste, dental visits, and family’s economic status. No significant differences in dental caries experience (dmft, dmfs) were observed between the experimental and placebo control groups at baseline (Table 1
About 38% of the children in the experimental group and 27% of those in the placebo control group showed no increments in the dmfs index at the end of the study (Table 2  ). Table 3 shows the two-year surface-specific caries increments of children in the two groups. The mean caries increment in the experimental group was 3.8 dmfs, while it was 5.0 dmfs in the placebo control group, resulting in 24.2% caries reduction (P-value = 0.03). The experimental group had a 37.6% caries reduction on approximal surfaces compared with the placebo control group (P-value = 0.002). Although the mean dmfs increment of bucco-lingual surfaces was lower in the experimental group than in the control group, it was not statistically significant (P-value = 0.054). No significant difference in the mean caries increment was observed on occlusal surfaces between the two groups (P-value = 0.75).
No clinical side-effects such as nausea and vomiting were reported in the present study.
The present study was a cluster-randomized, placebo-controlled trial, based on a two-year follow-up design. The drop-out rate was low after 2 yrs, and baseline characteristics were well-balanced. It was noteworthy that, among the children in the present study, 22% used fluoride toothpaste, almost three-fifths brushed their teeth less than once a day, and only one out of ten had seen a dentist within the preceding 12 mos. These potential factors of intervention should be considered not to confound the preventive effect of APF foam on dental caries in the primary teeth. Furthermore, results from intra-examiner agreement indicated excellent reliability of the examination. The examiners and operators were blind to the group affiliation of the children throughout the study. We also performed statistical analyses taking cluster randomization into account. In conjunction with the above observations, it was concluded that the findings were valid. The design of the present study was based on previously published reports evaluating the effect of APF gel on caries prevention in the permanent teeth (Olivier et al., 1992; Johnston and Lewis, 1995). We chose to apply APF foam bi-annually because of findings that APF gel was effective in reducing caries increment when applied at this frequency (van Rijkom et al., 1998). Routine prior prophylaxis was not undertaken in the present study. Johnston and Lewis (1995) reported that no statistically significant effects on caries reduction were found when prophylaxis was conducted before the patients were given a topical fluoride treatment. The one- four-minute application is recommended in the manufacturer’s instructions for Laclede APF foam. However, enamel fluoride uptake was significantly less when contact time was reduced to 1 min (Wei and Chik, 1990). The four-minute application of fluoride foam was thus chosen by the authors. The present study demonstrated that a bi-annual professional application of APF foam was effective in preventing dental caries in the primary teeth. The reduction of new dental caries development was 24%, when compared with that in the placebo control group, coinciding with a 21% reduction (95%, CI = 14–28%) in DFMS on the systematic meta-analysis of gel trials (Marinho et al., 2003). It is interesting to note that about 38% of the children in the experimental group and 27% in the control group show no increments in the dmfs index after 2 yrs. This implies that the percentage of children developing at least 1 new caries surface in the experimental group is lower than that in the control group. Recently, a randomized controlled study assessed the efficacy of 1.23% fluoride gel in reducing caries increment in low-caries children initially aged 4.5–6.5 yrs and found that fluoride gel had no statistically caries-inhibiting effect on dmfs. It was likely that the unexpectedly poor outcomes were caused by the prognostic factors ‘fluoride tablet’ and ‘toothbrushing frequency’ (van Rijkom et al., 2004). The significantly additive effect of the professionally applied gel treatment on caries prevention might be less when more fluoride tablets were used and the toothbrushing frequency was higher. In the present study, a bi-annual application of APF foam was significantly efficacious in reducing caries increment on approximal surfaces, but not significant on occlusal surfaces. This was consistent with the findings of Seppä et al.(1995), who showed that application of topical fluoride can ensure prevention on smooth surfaces but had limited effect on pits and fissures in teeth. Fluoride application in young children must be carefully monitored, because the children may be exposed to excessive ingestion levels of fluoride during topical application (Duxbury et al., 1982; Ripa, 1990). A previous study showed that a single dose of 1 mg F/kg body weight might cause early symptoms of acute fluoride toxicity (Spoerke et al., 1980). The acute toxic dose for a 3-year-old child weighing 13.5–14.5 kg would be in the range 13.5 to 14.5 mg F. The amount of APF foam sufficient to cover upper and lower teeth was approximately 0.6–0.8 g (7.38–9.84 mg F) (Wei and Chik, 1990). The maximum 9.84 mg F ingested by a child weighing 13.5 kg would mean a dose of 0.73 mg F/kg body weight, which was smaller than the lowest single dose required for acute poisoning (1 mg F/kg body weight). Meanwhile, if one takes into account the possible overestimation inherent in the method, it was in fact probable that the children could not receive such high doses of fluoride. Furthermore, numerous precautionary measures were taken by the operators in this study, such as using sponge-lined and well-fitted trays, limiting the amount of fluoride foam placed in the tray, seating the child upright with the head inclined forward and downward, and instructing the children to expectorate saliva for up to 1 min after tray removal. No clinical side-effects were reported after treatment in the present study. This suggests that APF foam therapy is a relatively safe caries-prevention procedure if the guidelines recommended are followed strictly. Caries prevalence in the primary teeth in China is high (Wong et al,. 2001). It is very important to find some effective prevention measures that could be readily implemented to change this situation. Based on the 24-month results of this study, it is concluded that APF foam is effective in reducing the increment of dental caries in the primary dentition in Chinese kindergarten children.
This study was supported by National Key Technologies R & D Program of the Tenth-five Year Plan, the Ministry of Science and Technology, China (2004BA720A24). We thank Dennis Pipenbring (Department for Community Dentistry and Graduate Studies, School of Dentistry, Faculty of Health Science, University of Copenhagen) for his help in data analyses. Received for publication July 1, 2004. Revision received November 9, 2004. Accepted for publication January 2, 2005.
Journal of Dental Research, Vol. 84, No. 3,
265-268 (2005) This article has been cited by other articles:
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ABSTRACT
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