The effectiveness of completely and incompletely sealed first permanent molars on caries prevention

Abstract Fissure sealants are effective caries preventive measure. However, a dilemma has been expressed more than once, whether incompletely sealed fissures provides sufficient protection against caries. Dental examinations were performed in 88 children, aged 8 and then 4 years later at 12 years. All first permanent molars (FPMs), as diagnosed at the age of 8, were divided into three groups: nonsealed, incompletely and completely sealed. Four years later caries incidence and changes in presence and quality of fissure sealant were analyzed. At the age of 8 and 12 mean DMFT were 0.73 ± 1.24 and 3.48 ± 3.04, respectively. 71.59% of the 8‐year‐olds and 78.41% of the 12‐year‐olds had at least one sealed FPM. At the age of 8, 154 FPMs were completely sealed and 42 FPMs were incompletely sealed. Four years later, 81.17%, 71.43% and 69.4% of FPMs were healthy (sound or with noncavitated caries) in the baseline groups completely sealed, incompletely sealed and nonsealed FPMs, respectively. Incompletely sealed fissures were more susceptible to caries development than completely sealed fissures. It is important that incompletely sealed fissures are resealed as soon as possible.


| INTRODUCTION
Over the last decades, there has been a decline in dental caries prevalence among children and adolescents. Nevertheless, dental caries is still a major health problem worldwide (Ahovuo-Saloranta, Forss, Hiiri, Nordblad, & Makela, 2016), affecting as many as 60-90% of children (WHO, 2017). While some decrease in caries prevalence has been observed, the number of caries lesions developed on occlusal surfaces remains high (Hiiri, Ahovuo-Saloranta, Nordblad, & Makela, 2006), the lower the caries incidence in the population, the higher the proportion of occlusal caries (Batchelor & Sheiham, 2004).
The occlusal surfaces of both the first permanent molars (FPMs) and the second permanent molars (SPMs) have the greatest risk of caries development (Demirci, Tuncer, & Yuceokur, 2010). Although the occlusal surface represents only 15% of all dental surfaces, as much as 88% of all caries lesions develops in pits and fissures of FPMs and SPMs (Rethman, 2000). In 18-year-olds, almost half of all surfaces affected by caries are on the occlusal surface (Norrisgaard, Qvist, & Ekstrand, 2016).
Occlusal caries start in pits and fissures, which are particularly susceptible for caries development due to their complex morphology, that prevents both natural cleaning by saliva and mechanical cleaning by toothbrush (Bromo, Guida, Santoro, Peciarolo, & Eramo, 2011;Disney et al., 1992). The highest probability of occlusal caries development is during the time of a tooth's eruption (Carvalho, 2014). Dental plaque accumulates more abundantly on the occlusal surfaces of not fully erupted molars, compared to molars with proper occlusal contact (Carvalho, 2014). Additionally, post-eruptive mineralization of the outer enamel of a not fully erupted tooth is not completed (Kataoka, Sakuma, Wang, Yoshihara, & Miyazaki, 2007).
In children and adolescents, fissure sealants are suggested to be effective and safe in preventing the development of dental caries (Ahovuo-Saloranta, Forss, Walsh, et al., 2013), sealed fissure systems effectively prevent caries development or slows down and even stops further progression of initial caries lesion (Wright et al., 2016a). The purpose of fissure sealing is to protect the FPM as soon as it erupts.
Fissures, tightly sealed with a resin-based sealer, make a physical barrier that prevents nutrients entering the fissures. It limits the growth and metabolism of microorganisms present in the fissure, therefore excretion of acids is reduced (Ahovuo-Saloranta et al., 2016). With fluorides added, as for example, in GIC sealers, fluorides contribute to the remineralisation of initial caries lesions as they are released from the sealing material (Zhou et al., 2012).
Effectiveness of pits and fissures sealing in preventing dental caries has often been reported. Two systematic reviews, which pool data on the effectiveness of fissure sealing from 38 studies and from 23 studies (Wright et al., 2016b), found strong evidence that supports the benefits of sealing permanent molars in children and adolescents. Results of the first above mentioned systematic review showed that resin-based sealants reduced caries by between 11% and 51% compared to nonsealed teeth, reevaluated after 24 months . Results from the second abovementioned systematic review showed a 76% risk reduction in the development of new carious lesions in participants who received sealants compared with those whose teeth were not sealed, after 2-3 year follow up (Wright, Tampi, et al., 2016b). After a 7 year follow-up, children and adolescents with sealed teeth had a caries incidence of 29%, whereas in those without sealed dental fissures caries incidence was 74% (Wright, Tampi, et al., 2016b). A protective effect of pit and fissure sealants, particularly for children and adolescents at high caries risk, is further confirmed by meta-analysis of 19 studies (15 RCT and 4 systematic reviews) (Neusser, Krauth, Hussein, & Bitzer, 2014).
A dilemma has been expressed more than once regarding the fissure sealing; whether in incompletely (partially) sealed fissures the risk of caries development is increased. Yet, publication on the risk for caries development in partly sealed fissures is scarce. Some studies conclude that sealant loss is not associated with risk of caries (Muller-Bolla, Courson, Lupi-Pegurier, et al., 2018;Simonsen, 1991). Analysis of the results of seven studies concludes that teeth, in which the sealing was partially or completely lost, did not have an increased risk of caries development compared to unsealed teeth. The authors conclude that fissure sealants are indicated even if there is no possibility for a regular check-up (Griffin, Gray, Malvitz, & Gooch, 2009). On the other hand, it has been reported that incompletely sealed fissure systems present an increased risk for caries development compared to completely sealed teeth, which indicates that sealants should be regularly monitored and reapplied whenever necessary, to be effective (Chestnutt, Schafer, Jacobson, & Stephen, 1994;Ismail & Gagnon, 1995;Veiga, Ferreira, Correia, & Preira, 2014). Generally, it is accepted that all sealed tooth surfaces should be monitored regularly; whenever found defective, sealers should be reapplied in order to maintain the marginal integrity (Welbury, Raadal, & Lygidakis, 2004).
The aim of this study was to determine caries morbidity as well as the extent and quality of fissure sealing placement on FPMs in the group of children, aged 8 and then at the age of 12. Furthermore, we evaluated what was the protective effect of fissure sealing against dental caries over the 4-year period; especially regarding the quality of placed sealing.

| Study population
Hundred and twenty-three school children, 58 boys and 65 girls, all 8 years old were invited to the study. Children included in the study had no systemic disease, neither motor nor cognitive impairment. Prior to any examination, written informed consent was obtained from all participants and their parents. The study was approved by the Slovenian National Committee for Medical Ethics (No. 0120-34/2017/4).
The first examination was performed on 123 children. Of these, 14 participants were subsequently excluded due to molar-incisor hypomineralization (MIH). Four years later, 109 children were recalled.
Of those, 88 of the then 12-year-old children (37 boys and 51 girls) responded positively to the invitation and were included in the study ( Figure 1).

| Examination procedures
The first dental examination was performed by three dentists who were calibrated. Four years later, the second dental examination of Interexaminer reproducibility also showed excellent to perfect agreement regarding surface condition assessment (weighted kappa 0.86-1.00) and caries presence (weighted kappa 0.64-0.94).
All dental examinations were done in a dental office on a dental chair, under artificial light, using dental mirrors and blunt probe.
Before starting with the dental examination, the dentist performed professional tooth cleaning with a professional dental brush and toothpaste. After the cleaning procedure, all the dental surfaces were initially examined wet. Then, the surfaces were dried with air for 5 s and checked again.
Signs of dental caries were recorded in accordance with ICDAS, and later on these results were converted to DMFT (number of decayed-D, missing-M and filled-F permanent teeth) and dmft (number of decayed-d, missing-m, filled-f primary teeth). For cavitated caries presence, ICDAS codes 3-6 were recorded as decayed-D in DMFT, and ICDAS codes 0-2 as "healthy" (i.e., sound or noncavitated caries lesion). If a tooth was filled and decayed, it was recorded as decayed. At the first examination, missing primary canines and molars were recorded as lost due to caries. If a primary tooth and its permanent successor were present, only the permanent tooth was taken into consideration.
At the baseline, in 8-year-olds, each FPM's occlusal surface was evaluated in respect of the presence of signs of caries and/or dental treatment (i.e., sealing or filling). Given the average eruption time of FPMs, these teeth could have been sealed at any time during the previous 2 years. All teeth were sealed with a resin-based sealer, and sealings had been placed by different dentists. After excluding the filled FPMs, FPMs were divided into three groups in relation to the presence of sealing: (a) nonsealed (ICDAS codes 00, 01 and 02), (b) not completely sealed (ICDAS codes 10, 11 and 12) and (c) completely sealed FPMs (ICDAS codes 20, 21 and 22). Four years later (in 12-year-olds), all FPMs were reevaluated.

| Data analysis
The statistical analysis was conducted with IBM SPSS 23.0 and the p value was set at .05 or higher. Friedman's nonparametric test was used to detect differences in occurrence of caries at the age of 8 and at the age of 12 on the occlusal surfaces of FPMs in comparison to other surfaces. Furthermore, we used Wilcoxon's signed-rank test to check for differences in the number of cavitated carious lesions on individual surfaces of FPMs in 8-and 12-year-olds. The Pearson chisquare test was used to detect statistically significant associations between the two examinations (at the baseline and the second one); to determine a possible association in the clinical status of the FPMs (sound, noncavitated or cavitated caries lesion), the presence of fillings on FPMs, and the number and the quality (incompletely or completely sealed) of FPMs' sealing. A two way analysis of variance was used to test the difference between the two examinations according to the quality of the fissure sealing at age 8 and caries at age 12. For each of the three groups of FPMs (nonsealed, incompletely or completely sealed FPMs), proportions of healthy teeth, teeth with noncavitated and cavitated caries lesions, filled or extracted teeth were calculated. Based on the results of the first and the second examination, relative risk and odds ratio of deterioration due to caries in each of the three groups were calculated.

| RESULTS
Caries morbidity in the examined group of children was high (Table 1).
The number of "caries free" children (DMFT = 0) at the first and the second dental examination changed significantly (43.022, p = .000).
Similarly, a statistically significant difference was obtained when T A B L E 1 Number and proportion of children with teeth not affected by caries lesions at the first (8-year-olds) and the second (12-year-olds) examination respectively. Not only were many of the FPMs not sealed appropriately at the age of eight, but reapplication of dental sealers was very poor throughout the period of 4 years (Table 7). The association in proportions of cavitated caries lesions between the two observations was statistically significant (χ 2 =84.239, df = 9, p < .001). showed that the proportion of degradation differed significantly between the three groups. In the 12-year-olds, the highest proportion of filled FPMs was found in the group of at the baseline nonsealed FPMs (Figure 4). Moreover, two FPMs in this group had already been incompletely and completely sealed FPMs, respectively. On the contrary, Simonsen (1991)  e.g., poor oral hygiene and/or cariogenic diet. We would argue that in patients with higher risk for caries partially retained sealants pose an additional risk for caries development. Therefore, resealing of incompletely sealed fissures seems to be essential in patients with higher risk for caries development.
As observed in this study, the estimated odds ratio for a relative risk of deterioration over the 4-year time-period (i.e., change to caries cavitation, dental filling or tooth extraction) was slightly higher in the group of nonsealed FPMs (1.948) than in the group of incompletely which is an indication for dental sealing placement (Neusser et al., 2014;Welbury et al., 2004). In the examined group of children, high caries morbidity was already present in primary dentition. One of the risk factors for caries development in permanent dentition is the presence of nontreated cavitated caries in primary dentition (Skeie, Raadal, Strand, & Espelid, 2006). In mixed dentition, dental caries of primary molars may influence development of carious lesion on FPMs (Vanderas, Kavvadia, & Papagiannoulis, 2004). widely acknowledged and often exposed; the essential role of simultaneously preventive actions, undertaking by an individual, is every so often less highlighted. In order to reduce high morbidity, implementation of a variety of preventive measures should be incorporated.
Professional and individual preventive measures clearly need to be strengthened simultaneously. Some countries report good results when a specially designed national programme is achieved; e.g., Scotland and Portugal (Calado et al., 2017;Macpherson, Ball, Brewster, et al., 2010). In Slovenia, population based caries preventive measures started with the implementation of fluoride tablets in 1956, and was followed by the implementation of topical application of fluorides and fissure sealants in 1970 and in 1980, respectively. As a result, caries prevalence among children was reduced (Vrbic & Vrbic, 2016).
Although educational activities (e.g., promotion of individual good oral hygiene and noncariogenic diet) have also been applied, caries preventive action is likely to still be inadequate, and additional information about the importance of one's own role for maintaining good oral health is needed. Children and their parents need to be further educated and motivated about their own contribution in preventing caries and improving their own oral health. Further, it is necessary to identify which specific preventive activities need to be specifically reinforced at the national level, to gain a significant positive effect on improving the oral health of children.
In conclusion, caries morbidity in the examined group of children was high. At the same time, the children had a large proportion of sealed FPMs, predominantly inadequately sealed. The results of this study showed that incompletely sealed fissure systems were more susceptible to the development of caries than completely sealed fissure systems of the FPMs. In particular, in children with a higher caries risk, regular retention-check-up of sealed teeth is particularly important; and, whenever identified as incompletely sealed, such a tooth must be resealed.

| Why this paper is important to paediatric dentists
• Paediatric dentists are encouraged to implement a regular checkup of applied pit and fissure sealants and to reseal them, when found incomplete or lost.
• Application of fissure sealants is safe and effective however simultaneous emphasis on implementation of other preventive measures is also required, especially in a population with high caries prevalence.

ACKNOWLEDGMENTS
The authors thank the participating children and their parents as well as managements of primary schools for their cooperation that enabled this study. Further we would like to express our gratitude to Mrs.
Ruth Moody for English editing of the manuscript.

AUTHOR CONTRIBUTIONS
L.L.O collected data and wrote the manuscript; J.S. contributed to design of the study, carried out the statistical analysis and wrote the manuscript; A.P. conceived the idea of the study, conducted and wrote the manuscript, and was guide for the whole study.