Glass Ionomer Sealant Versus Fluoride Varnish Application to Prevent Occlusal Caries Among Preschool Children - a Randomized Controlled Trial
Phase: NA
Conditions: Pit and Fissure Caries, Glass Ionomer Cements, Tooth, Deciduous, Child
Sponsor: The University of Hong Kong

 
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RESEARCH PROTOCOL  
Version no.1; Date: 17th January 2018  
Primary Investigator: Prof. Cynthia KY YIU 
Co-investigators: Prof. Edward CM LO, Dr. Gillian HM LEE 
 
a) Title:  
Glass ionomer sealant versus fluoride varnish application to prevent 
occlusal caries among preschool children - A randomized controlled 
trial. 
 
b) Introduction:  
Problems encountered in clinical work  
Dental caries has been considered as a significant public health 
problem worldwide (Selwitz et al., 2007; Peterson 2005). Despite 
that its prevalence might have declined in many developed countries 
(Selwitz et al., 2007), epidemiological data have shown a 
considerable rise in global caries rate, posing a significant point of 
issue in public health (Bagramian et al., 2009; Peterson 2005). 
 
In Hong Kong, the problem of dental caries among preschool 
children remains unsolved and the severity has exacerbated. The 
number of decayed, missing and filled teeth among pre-school 
children had increased from 2.3 in 2001 (Hong Kong Department of 
Health, 2002) to 2.5 in 2011 (Hong Kong Department of Health, 
2012). The latest government oral health survey found that more 
than 50% of the preschool children had caries experience, with over 
90% of the decayed teeth being untreated and that one in every 20 
children had even developed dental abscesses from extensive 
carious teeth (Hong Kong Department of Health, 2012).  
 
Preventing caries development in primary molars is especially 
important, as they would remain in the oral cavity for more than 10 

 
2 
years before exfoliation. Premature loss of primary molars can 
seriously affect the development of permanent dentition, including 
space loss and malocclusion. Moreover, second primary molars 
were reported to be the most susceptible to caries development at 
the 4 and 5-year-olds in studies conducted in different countries 
around the globe (Elfrink et al., 2006; Autio-Gold & Tomar, 2005; 
Holt, 1995, Holland & Crowley, 1982), with a predilection for their 
occlusal surfaces (Douglass et al., 1995; Bimstein et al., 1981). Pits 
and fissures on the occlusal surface of permanent molars are 
considered to favor biofilm formation and retention, which the rate of 
occlusal caries development and progression are comparatively 
higher than that of smooth surface caries (Batchelor et al., 2004; 
Brown, 1995). In primary second molars, the generally deeper pits 
and fissures, as well as the presence of buccal pits and palatal 
fissures at mandibular and maxillary second primary molars 
respectively, may also contribute to its caries prevalence (Bimstein 
1981).  
 
Incipient carious lesions occur when minerals from the enamel 
subsurface are being lost initially, which may progress to cavitated 
carious lesions requiring restorations if left untreated. Calcium and 
phosphate ions can be redeposited to demineralized enamel via the 
process of remineralization as crystal voids, enhancing the strength 
by creating a net mineral gain (Cochrane et al., 2010). 
Remineralization with appropriate agents has proven effective to 
treat incipient carious lesions (Mohd Said et al., 2017; Cochrane et 
al., 2010). The use of fluoride promotes the remineralization in 
incipient carious lesion. Fluoride facilitates adsorption of calcium 
ions to demineralized enamel surface, as well as substituting 
hydroxyl ions (OH-) to form fluorapatite, that have a strong acid 
resistance against demineralization (Featherstone, 1999). 
 
Topical fluoride varnish (TFV) with 5% sodium fluoride in its content 
has proven effective in preventing caries among children and 

 
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adolescents (Marinho et al., 2009; Marinho et al., 2002). Its 
reduction in DMFT is well supported by Cochrane reviews and 
clinical trials (Ahovuo-Saloranta et al., 2016; Marinho et al., 2013). 
When the varnish containing high concentration of fluoride 
(22,600ppm) is applied to the tooth surface, it forms a fast-setting 
base that releases fluoride subsequently (Marinho et al., 2002). It 
also increases the retention of fluoride on tooth surface, allowing a 
continuous flow of fluoride ions to enamel, dentine, plaque and 
saliva (Mohd Said et al., 2017). However, its effect in preventing pit 
and fissure caries in primary dentition has not been assessed 
(Ahovuo-Saloranta et al., 2016).  
 
The 5% sodium fluoride varnish containing 22,600 ppm fluoride is 
the only fluoride agent that is considered safe-to-use for children 
aged below 6 years (Maguire, 2014; Weyant et al., 2013; American 
Dental Association Council on Scientific Affairs, 2006). As the 
quantity of fluoride contained in a single application dose of 5% 
sodium fluoride varnish is relatively small (5.65mg in 0.25mL), it is 
well below the probable toxic dose (5mg/kg) (Lee, 2015). Comparing 
with fluoride gels or other fluoride agents, the potential risks 
associated with inadvertent ingestions in young children is also 
reduced (Weyant et al., 2013; American Dental Association Council 
on Scientific Affairs, 2006). The current recommended dosage of 5% 
sodium fluoride varnish for children between 2-5 years old is 0.25mL, 
applying at intervals of every 3-6 months, depending on the caries 
risk assessed (Lee, 2015; American Dental Association Council on 
Scientific Affairs, 2006). 
 
Pit and fissure sealants have been a recommended procedure in 
preventing pit-and-fissure caries development in permanent molars. 
Both resin-based and glass-ionomer sealant serve as a physical 
barrier between enamel and the oral environment, reducing plaque 
retention by sealing occlusal pit and fissures (Nunn et al., 2000). 
Multiple systematic reviews and clinical trials have concluded that 

 
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fissure sealants are significantly more effective than topical fluoride 
varnishes in preventing occlusal caries in permanent molars (Levy, 
2012; Liu et al., 2012). However, a recent Cochrane review 
suggested that there was still insufficient evidence to determine 
superiority of resin or glass ionomer fissure sealants over topical 
fluoride varnishes for occlusal caries prevention, due to the lack of 
reliable results and low quality of evidence (Ahovuo-Saloranta et al., 
2016).  
 
Also, most studies were conducted on permanent first molars among 
school children (Ahovuo-Saloranta et al., 2016), whom cooperation 
and moisture control can be easily achieved. However, application of 
fissure sealants, especially resin-based sealant, in very young 
children can be a technique-sensitive procedure. Compared with a 
mean treatment time of less than 3 minutes for varnish application, 
application of resin-based sealants required over 15 minutes (Splieth 
et al., 2001). Moisture control is also of paramount importance for 
the retention and success of resin-based sealants (Gooch et al., 
2009), which may be difficult among young preschool children.  
 
Glass-ionomer sealants can chemically bond to enamel and are 
more tolerable to inadequate moisture control (Antonson et al., 
2012). As its application requires less clinical steps, glass-ionomer 
sealant is comparatively more acceptable to younger patients and 
can be used in outreach settings with a large number of participants. 
The fluoride releasing ability is also beneficial in preventing caries 
especially at adjacent tooth surfaces (Cagetti et al., 2014). However, 
its retention rate is significantly lower than that of resin-based 
sealants (Antonson et al., 2012), its success rate in preventing 
fissure caries in very young patients is still unknown.  
 
 
 
 

 
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c) Aims and Hypotheses to be Tested:  
Aims  
To compare the efficacy of glass ionomer fissure sealant versus 
topical application of 5% sodium fluoride varnish in prevention of 
occlusal caries among preschool children. 
 
Hypotheses to be tested  
Greater reduction in occlusal caries in preschool children by glass 
ionomer fissure sealant compared to topical application of 5% 
sodium fluoride varnish. 
 
d) Plan of Investigation:  
 
 
(i)  Subjects 
The proposed study will be conducted in kindergartens in Hong 
Kong. The communal water supply in Hong Kong is fluoridated at 
a concentration of 0.5 ppm. Most child formula toothpastes 
available in Hong Kong contain fluoride at a concentration of 500–
600 ppm. Generally healthy children aged between 3-4 years with 
no remarkable medical history will be invited to participate in this 
study. Children with at least one of the following criteria, deemed 
to be at moderate to high caries risk (American Academy of 
Paediatric Dentistry, 2013), will be included in this study: 
 
Moderate risk 
The child is a recent immigrant. 
The child has plaque on teeth. 
High risk 
The parent/ caregiver has low socioeconomic 
status. 
The child has >3 between meal 
sugar-containing snacks or beverages per 
day. 
The child is put to bed with a bottle containing 
natural or added sugar. 
The child has >1 decayed/missing/filled 

 
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surfaces. 
The child has white spot lesions or enamel 
defects. 
The child has visible cavities or fillings. 
 
They are thus qualified to receive fissure sealants and topical 
fluoride application regularly every 3 months (Lee, 2015; AAPD, 
2013). 
 
The following will be excluded from this study: 
1. 
Children with the presence of caries of ICDAS code 3, 4, 5, or 6 
on other primary teeth. 
2. 
Children who had received professional fluoride application in 
the past 6 months. 
3. 
Children with serious systemic disease or taking long term 
medication. 
4. 
Children who are uncooperative or refuse the treatment.  
5. 
Second primary molars that are (i) with caries in dentin indicated 
by ICDAS code 4, 5 or 6; (ii) partially erupted; (iii) with fillings and/or 
sealants; and (iv) hypoplastic or hypomineralized. 
 
   (ii)  Methods   
Sample size calculation  
The primary outcome of this clinical trial is carious cavity 
development into dentin (ICDAS code 4,5 and 6) on occlusal 
surfaces of primary second molars. Sample size is calculated to be 
256 children with a type I error of 0.05 and a power of 90%. This is 
based on the results of a previous study on primary molars (Honkala 
et al., 2015), where the real difference between fluoride varnish and 
sealant effect on occlusal caries reduction was 30%. Calculating with 
a 5% statistical significance level and a 90% power, a minimum of 
102 children in each group will be required. To allow for loss of 
power due to drop-out, the initial sample size should be around 25% 

 
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larger, i.e. 128 children are needed in each group at the beginning of 
the study. Thus, the total initial sample size will be 256 (128 x 2 
groups). 
 
Ethical approval   
Ethical approval will be obtained from the Institutional Review Board 
of the University of Hong Kong/Hospital Authority Hong Kong West 
Cluster and the trial will be registered in the HKU Clinical trials 
registry.  
 
Recruitment and screening   
Children studying in kindergarten 1 and Nursery 2 will be invited to 
participate in this proposed study. An invitation letter will be sent to 
their parents, explaining the objectives and procedures of the study. 
Only those children whose parents have signed the informed 
consent will be included in this study. Children will be screened for 
the following aspects: 
1. 
Plaque assessment using visible plaque index (VPI) (Ainamo & 
Bay, 1975) 
2. 
Overall tooth status with diagnostic criteria recommended by 
WHO in 2013, in the form of: 
Classification 
Description 
Decay (d) 
presence of dentin carious lesion(s) with or without 
a restoration. 
Missing (m) 
the tooth is extracted due to caries. 
Filling (f) 
presence of a temporary or permanent filing due to 
caries with no decay. 
 
3. Dental caries status based on ICDAS code score (International 
Caries Detection and Assessment System Coordinating 
Committee, 2009; Ismail et al., 2007), which is summarized 
below: 
 

 
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Code Classification 
Description 
0 
Smooth & intact 
tooth surfaces 
No evidence of dental caries or 
questionable changes in translucency of 
enamel after prolonged drying (around 5 
seconds). 
1 
Visual change in 
enamel 
Color changes due to caries which is not 
consistent with the clinical appearance of 
sound enamel, which is seen only after 
prolonged drying. 
2 
Distinct visual 
change 
Carious opacity (white spot lesion) and/or 
brown carious discoloration which is 
wider than the natural fissure/fossa that 
is not consistent with the clinical 
appearance of sound enamel, when seen 
wet and after drying. 
3 
Localized enamel 
breakdown due to 
caries with no 
visible dentin or 
underlying 
shadow 
The tooth viewed wet might have a clear 
carious opacity and/or brown carious 
discoloration which is wider than the 
natural fissure/fossa that is not consistent 
with the clinical appearance of sound 
enamel.  
 
4 
Underlying dark 
shadow from 
dentin with or 
without localized 
enamel 
breakdown 
The carious lesion appeared like a 
shadow of discolored dentin appeared 
through an apparently intact enamel, 
which might show signs of localized 
breakdown. 
5 
 
Distinct cavity with 
visible dentin 
Cavitation in opaque or discolored 
enamel exposing the dentin beneath, 
involving less than half of the tooth 

 
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surface. 
6 
 
Extensive distinct 
cavity with visible 
dentin 
Cavitation in opaque or discolored 
enamel exposing the dentin beneath, 
involving at least half of the tooth surface. 
Obvious loss of tooth structure and 
dentin is clearly visible on the walls and 
at the base in a cavity that involved at 
least half of the tooth surface. 
 
Questionnaire survey  
Parents are required to complete a validated questionnaire before 
the baseline examination, which consists of the following sections: 
(1) The child’s personal information - gender, age, place of 
birth, medical history of systemic disease and long term 
medication 
(2) The child’s oral health-related behaviors – snacking habit, 
frequency of toothbrushing, parent’s supervision in 
toothbrushing, use of toothpaste and night bottle habit 
(3) The child’s dental history – past dental treatment received 
(4) The child’s socio-economic background - parents’ age, 
education level, household income and number of children 
 
(iii) Study design  
Clinical exam 
Clinical examination will be carried with the child lying supine on 
table provided by the kindergarten.  
 
The Visible Plaque Index (VPI) (Ainamo & Bay, 1975) will be used to 
measure the oral hygiene status of the child. Buccal and palatal/ 
lingual surfaces of 6 index teeth (teeth 55, 51, 63, 71, 75, 83) will be 
examined. The presence or absence of visible plaque on the tooth 
surfaces mentioned above will be recorded as “1” or “0” respectively. 
The VPI score of the child will be obtained by dividing the number of 

 
10 
tooth surfaces recorded as “1” with the total number of tooth 
surfaces recorded as “0” and “1”, i.e.  
    
VPI= 
number of tooth surfaces recorded as “1” 
total number of tooth surfaces recorded as “0” and “1” 
  
b. 
Tooth status 
All tooth surfaces will be first wiped clean and dry by clean gauze 
and cotton swab for visual inspection of caries. A basic dental 
charting will be first performed, which the overall primary dentition 
will be further assessed and recorded based on the presence of 
decayed (d) missing (m), and filled (f) teeth, as recommended by the 
WHO in 2013. 
 
Then the ball end of the CPI probes will be used to slide through the 
pits and fissures of primary molars to detect any enamel cavities or 
discontinuities. The status of the occlusal surfaces of primary molars 
will be recorded based on the ICDAS coding system (International 
Caries Detection and Assessment System Corrdinating Committee, 
2009; Ismail et al., 2007).  
 
Children who do not meet all the inclusion criteria will be given an 
examination report. Parents will be informed regarding the carious 
teeth and will be advised to seek treatment from private dental 
practitioners or specialist paediatric dentists promptly. Children with 
second primary molar(s) that fulfill all the criteria will be included in 
the study. 
 
The occlusal fissures of each of the upper and lower molars included 
in the study will be assessed, and the fissure morphology 
(deep/shallow) and ICDAS score will be recorded.  
 
Randomization and treatment allocation 

 
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By using the random numbers generated by stratified block 
randomization method in a personal computer, children will be 
randomly allocated to one of the two study groups: 
(1) NaF varnish   
— Application of a 5% NaF varnish (Duraphat, Colgate-Palmolive 
Ltd, Waltrop, Germany) on the occlusal surfaces of primary second 
molars and all other teeth, every 3 months during the study period; 
(2)  GI sealant  
-- Glass ionomer sealant (GC Fuji VII® (pink)) on all primary second 
molars included in the studies, with no further repair/replacement of 
the sealant 
 
Interventions 
Immediately after the oral examination, a chair-side dental assistant 
will prepare the materials respective to the groups allocated on the 
random allocation list.  
 
For the sealant group, glass ionomer sealants will be applied using the 
finger pressure technique described in the WHO manual for 
atraumatic restorative treatment (ART) (Frencken et al.; 1997). The 
primary second molars included in the study will first be cleaned and 
dried by wiping with gauze and cotton pellets. Following the 
manufacturer’s instructions, further cleaning of the fissures will be 
performed by applying GC cavity conditioner with micro-applicator for 
10-15 seconds, then clean with wet cotton pellets for several times. 
The surface will be dried with cotton pellets. The dental assistant will 
mix the glass ionomer sealants (GC Fuji VII) in a standardized 
proportion with an amalgamator. Glass ionomer sealants will be 
applied to the occlusal surface with blunt end of an applier and slightly 
overfilled. A gloved finger with petroleum jelly will be used to push and 
rub the materials into the pits and fissures, as well as removing the 
excess sealants from the tooth surfaces. The sealants will be covered 
and protected by a layer of petroleum jelly (Vaseline ®). 

 
12 
 
In the NaF varnish groups, 0.25mL (one drop) of the varnish will be 
placed in a plastic dappen dish. A disposable microbrush will be used 
to apply the varnish onto the second primary molars included in the 
study and all other teeth. The child will be instructed not to eat or drink 
after the application of varnish for at least half an hour.  
 
Follow-up evaluation 
Children in the NaF varnish group will be recalled at the 3rd, 6th, 9th, 
12th, 15th,18th, 21st and 24th months for reapplication of fluoride varnish. 
Similar to baseline, 0.25mL (one drop) of the 5% sodium fluoride 
varnish will be applied using a disposable microbrush. At the 6th, 12th, 
18th and 24th months, a clinical examination will be performed for all 
children in both groups. During the follow-up examination, overall VPI 
and dmft will be recorded. ICDAS score will be recorded for each 
primary second molar included in the study.  
 
Sites with sealant will be evaluated in the following aspects: 
Aspect 
Code 
Classification 
Description 
Retention 
0 
Fully intact 
Sealants are fully intact 
without apparent loss of 
materials. 
1 
Partial loss 
Sealants are retained with 
partial loss  
2  
Total loss 
No sealant materials are 
found on tooth surface. 
Caries 
0 
No caries 
No caries found at the 
margin of the sealants. 
1 
Presence of 
caries 
Evidence of caries found 
at the margin of the 
restoration. 
 

 
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A 10% random sample will be re-examined during every examination to 
monitor intra-examiner reproducibility.  
 
An oral health talk will be given to the parents of the participants. During 
the talk, the parents will be instructed to choose fluoridated toothpastes 
and child toothbrushes throughout the period of study. In case of any 
adverse event during the study, the parents will be advised to contact 
the principal investigator.  
 
Outcome measures 
The primary outcome measure is carious cavity development into dentin 
(ICDAS code 4, 5 and 6) on the occlusal surfaces of primary second 
molars over time. 
 
Only one registered dentist will be the examiner in the kindergarten 
throughout the whole 24-month study period. She will receive training 
and calibration by epidemiologists before examining the subjects. The 
following dental equipment will be used: 
(1) 
Disposable dental mirror attached to a handle with light-emitting 
diode intra-oral illumination  
(2) 
World Health Organization CPI periodontal probe(405/WHO 
probe) 
 
A 10% random sample will be re-examined during every examination to 
monitor intra-examiner reproducibility. The ICDAS score will be recorded 
based on the index proposed by Ismail et al., 2007. 
 
Parents will be notified about the development of carious lesions. Advice 
on oral hygiene maintenance and seeking private dentists for respective 
dental treatments will be given to the parents in the form of a detailed 
report.  
 

 
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The proposed study will be a randomized controlled trial with 2 parallel 
groups. The unit of randomization will be each individual participant, but 
not each tooth of the mouth.  
 
(iv)  Data processing and analysis  
Data analysis will be performed using SPSS® Statistics version 23.0 
(SPSS Inc, Chicago, IL, USA). All children with missing data resulting 
from loss to follow-up or unrecorded data will be excluded from the 
analysis. Data proof-reading will be performed after data entry to identify 
and correct any errors before analyzing the data. An intention-to-treat 
analysis will be undertaken. Intra-examiner agreement in the diagnosis 
of dental caries will be assessed by Cohen’s Kappa statistics. 
 
Chi-square test will be used to assess the difference between groups 
according to the distribution of children’s demographic characteristics 
such as gender, place of birth, oral health-related behavior, use of 
fluoride toothpaste, snacking habit, parents’ education and family 
income. 
 
The outcome measures are the mean change in the overall dmft scores 
and ICDAS code in primary second molars over time. Within-group 
comparison of changes in mean overall dmft scores and ICDAS scores 
at 24 months and mean change in overall dmft scores and ICDAS 
scores will be assessed by applying repeated analysis of variance 
(ANOVA) (or Friedman test for non-parametric data). 
 
Student’s t-test will be applied to differentiate the comparability between 
the treatment groups according to the subject’s baseline conditions, 
including the child’s age, dmft score and VPI score.  
 
Since more than one molar will be included from one child, GLIMMIX 
procedure will be used to adjust for the clustering effect. The first level 
and second level will be the primary second molar and the subject 

 
15 
respectively. This analysis accounts for the correlation (clustering) 
between observations of multiple molars from the same child. 
 
A multi-level logistic regression analysis will be performed to analyze the 
effects of independent variables on the ICDAS scores at the 6, 12, 18 
and 24 month examinations. The independent variables included the 
child’s demographic characteristics, oral health-related behaviors and 
clinical characteristics (gender, place of birth, frequency of tooth 
brushing, use of fluoride toothpaste, snacking habits, mother’s education, 
father’s education, family income, VPI score, dmft score and the 
treatment group). The level of statistical significance for all tests will be 
set 5%.   
 
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