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Introduction

In the permanent dentition of young children, carious lesions most frequently develop in pits and fissures of 1st molars. Sealing those pits and fissures is considered the most effective way of interfering with the development of carious lesions over a long period . In a well-structured oral health service system, failed sealants can be resealed and thus continue to exercise their caries-preventive action for an indefinite period . In contrast, in low and developing market economies, where a recall system is usually unavailable, sealants, once placed, continue to function without the possibility of repair if this is needed. To ensure a high level of sealant effectiveness over long periods in such countries, a sealant material should be used that bonds to the enamel surface longer than those currently used.

Resin- and glass-ionomer-based materials are used for sealing pits and fissures. Glass-ionomer-based sealant materials have evolved from a low-viscosity type used in the seventies and eighties, to a high-viscosity type used since the mid-nineties . Not too long ago, a high-viscosity glass-ionomer with an elevated powder-liquid ratio was marketed. This was assigned higher physical–mechanical properties, including a higher level of adhesion to enamel, than the previous ones . Changing the application procedure by adding heat to the setting high-viscosity glass-ionomer through the use of a high energy curing light, was also found to increase the retention, and consequently the longevity, of sealants . An additional option for a sealant material with increased retention was introduced through the marketing of a novel glass-ionomer-based material, fluorapatite-containing glass-carbomer, with powder particles reduced to nano size .

China is a country in transition. Its economy has increased tremendously over the last decades. Although the caries prevalence and severity in permanent dentition of young children has been relatively low and stable for decades , there are signs that caries severity is increasing in 1st molars of young children . The National Association of Preventive Oral Health, recently recommended, as part of a wider program, that caries prevention in children in China should focus on the application of sealants and on self-care through plaque control with a toothbrush and fluoride-containing toothpaste.

The aim of the present study was to investigate the caries-preventive effects of high-viscosity glass-ionomer sealants with an elevated powder-liquid ratio, of having energy added to this glass-ionomer, and that of glass-carbomer, in comparison with those of resin-composite sealants. The hypotheses tested were: (1) the cumulative survival rate of caries-free pits and fissures of glass-carbomer sealants is higher than those of high-viscosity glass-ionomer sealants, with and without energy supplied, and of resin-composite, after 2 years; (2) the cumulative survival rate of caries-free pits and fissures, of high-viscosity glass-ionomer sealants with energy supplied is higher than that of high-viscosity glass-ionomer sealants without energy supplied, after 2 years.

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Materials and methods