Fissure sealants are done to prevent fissure caries (decay). Natural teeth have grooves, pits and fissures that form in the enamel as a normal part of the tooth anatomy. In some patients, these can be very deep and accumulate stains and plaque that cannot be removed by brushing or even professional cleaning.
If you are at high risk for tooth decay (which is something that can be assessed by your dentist), then you may be at an increased risk for cavities developing in these fissures. This is especially if oral hygiene is not maintained thoroughly and the diet is high in sugar and fermentable carbohydrates. Also when a tooth first erupts, the enamel is immature and has not yet reached full hardness. This is why children tend to be at risk of developing fissure caries compared to adults.
Microscopically, the anatomy of a fissure can be very complex. Most of the stains accumulate below the immediate enamel surface and cannot be accessed by surface cleaning alone. This is also why fluoride (toothpaste, mouth rinse, professionally applied varnish) is not a very useful agent for preventing the development of fissure caries, compared to a smooth surface (e.g. in between the teeth) caries.
At the moment, Singapore does not have any clinical guidelines for dentists to use in selecting teeth that would benefit from fissure sealants. It may be difficult to predict which teeth will go on to develop fissure caries and which will not unless a period of observation is followed. Ireland 
, France and the European Union have published guidelines for their dentists to follow when selecting which teeth would benefit the most from fissure sealants. The Cochrane Review, the premier source for reviews of the evidence, has also published a review on how effective sealants are in preventing tooth decay in permanent teeth 
1. Irish Oral Health Services Guideline Initiative. PIT AND FISSURE SEALANTS Evidence-Based Guidance on the Use of Sealants for the Prevention and Management of Pit and Fissure Caries.; 2010. Accessed January 15, 2020.
2. Ahovuo-Saloranta A, Forss H, Walsh T, Nordblad A, Mäkelä M, Worthington HV. Pit and fissure sealants for preventing dental decay in permanent teeth. Cochrane Database of Systematic Reviews. July 2017. doi:10.1002/14651858.cd001830.pub5
Dr Jaclyn TohELITE DENTAL GROUP
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