A sealant shuts the deep grooves on the chewing surface of a back tooth. Fluoride varnish coats every surface of every tooth for a few hours and helps the enamel resist acid. They guard different parts of the mouth, so for many children the useful question is not which one, but which teeth need what.
Grooves and smooth surfaces decay for different reasons
The biting surface of a molar is not flat. It has pits and fissures that can be too narrow for toothbrush bristles to reach the bottom. Plaque packs into the bottom of these grooves and stays there, which is why a large share of decay in children's adult molars starts on the chewing surface. Fluoride helps here, but the shape of the groove works against it.
The smooth sides of teeth and the contacts between them are a different problem. Plaque on these surfaces can be brushed or flossed off, and fluoride is very effective at helping enamel there recover from acid. Early white spots on the front teeth or along the gumline usually respond to fluoride, not sealants.
How each one is put on
For a sealant, the dentist or OHT cleans the groove, keeps the tooth dry, applies a conditioning (etching) gel, rinses it off, then flows a liquid resin into the fissures and sets it with a curing light. No needle or drilling is needed. Keeping the tooth dry matters for the seal to hold, so a molar that is only half through the gum may be sealed later or with a different material. Our article on dental sealants for children goes into more detail.
Varnish is quicker. The teeth are dried, the varnish is brushed on, and it sets when saliva reaches it. The coating is gone after a day of eating and brushing, so it is repeated, often every three to six months for children at higher risk. You can read more about safety in our article on whether fluoride is safe for teeth.
Side by side
| Fissure sealant | Fluoride varnish | |
|---|---|---|
| Teeth covered | Usually adult molars, sometimes premolars or deep-grooved baby molars | All teeth present |
| How it protects | Blocks plaque from settling in grooves | Helps enamel resist acid and repair early damage |
| How long it lasts | Several years, checked at each visit | Hours on the tooth, effect builds with repeat visits |
| When it is usually done | Soon after the adult molars come through, often around 6 and 12 years | From the first baby teeth, repeated through childhood |
| Needs a dry tooth | Yes, which can be harder in very young children | Not as critical |
The research has no clear winner
Several trials have compared the two head to head. A Cochrane review by Kashbour and colleagues (2020) concluded that the evidence was of very low certainty and did not show clearly whether sealants or varnish prevent more decay in permanent molars. There was also very low-certainty evidence that adding sealants to varnish may reduce decay more than varnish alone. Given that, most clinicians decide by looking at the child in front of them rather than following a fixed rule.
What tips the decision for a particular child
Deep, sticky grooves on newly erupted molars, a sibling with lots of fillings, or early decay already in the grooves of baby molars point towards sealing. White spots on smooth surfaces, frequent snacking, braces, or a toddler too young to keep a tooth dry point towards regular varnish. A child with a high risk of decay will often have both, along with advice on diet and brushing. At home, some children are also advised to use products such as tooth mousse as an extra step.
None of this replaces twice-daily brushing with fluoride toothpaste. Sealants protect only the grooves, and varnish only adds to what toothpaste does every day.
Questions we are often asked
Does the Child Dental Benefits Schedule cover these?
Fissure sealants and fluoride applications are among the preventive services the CDBS can cover for eligible children, within the scheme's benefit cap. Our team can check your child's eligibility at the visit.
Can a sealant trap decay underneath?
A sealant placed over a sound groove or very early decay that has not formed a hole can slow or stop that decay. The tooth is checked before sealing, and the sealant is reviewed at check-ups so any loss can be repaired.
Do adults ever have them?
Yes, both are used in adults with a higher risk of decay, although sealants are most common in children and teenagers.
Planning prevention for your child
At a check-up our dentists and oral health therapists look at each molar and your child's overall risk, then suggest sealants, varnish, both or neither. To book, use our contact page, ask about a family dental visit, or see current deals for new patients.
This article is general information and is not a substitute for individual advice. A dentist can recommend the right prevention for your child.
