Dental sealants are thin plastic coatings made primarily from synthetic resins or glass-based cements. The two main types, resin-based sealants and glass ionomer sealants, use very different chemistry to achieve the same goal: creating a protective barrier over the grooves of your teeth where cavities are most likely to form. Here’s what goes into each type and why it matters.
Resin-Based Sealants: The Most Common Type
The majority of dental sealants placed today are resin-based, meaning their core structure is built from liquid plastic monomers that harden into a solid polymer when exposed to a curing light. The backbone of most resin sealants is a monomer called Bis-GMA (bisphenol A glycidyl methacrylate), which provides strength and durability. About 50% of commercially available sealants contain Bis-GMA as a primary ingredient, typically making up 40 to 55% of the sealant by volume.
Bis-GMA on its own is thick and hard to work with, so manufacturers blend it with thinner monomers. The most common is TEGDMA (triethylene glycol dimethacrylate), found in roughly 46% of sealant products. TEGDMA thins the mixture so it flows easily into the tiny grooves and pits of a tooth. Another monomer, UDMA (urethane dimethacrylate), appears in about 63% of sealants and serves as either a companion to Bis-GMA or a full replacement for it. Some newer sealants use UDMA-based formulas specifically to avoid bisphenol A derivatives.
Mixed into this resin base are small amounts of filler particles, typically fine silica or glass, that add wear resistance. Sealants contain far less filler than a standard dental filling, which is part of what makes them flow so easily into tooth grooves before hardening.
How Resin Sealants Harden
Most modern sealants are “light-cured,” meaning the dentist shines a blue LED light on the material for several seconds to trigger hardening. This works because the sealant contains a photoinitiator, a molecule that absorbs light energy and kicks off a chemical chain reaction. The standard photoinitiator in dentistry is camphorquinone, which responds to blue light at a wavelength around 470 nanometers. When the light hits it, camphorquinone generates reactive molecules that link the individual monomers into a continuous, solid plastic network within seconds.
Some sealants are “self-curing” instead, using a two-part chemical system that hardens on its own once the components are mixed together. These are less common today because light-cured versions give the dentist more control over working time.
Glass Ionomer Sealants: The Fluoride-Releasing Alternative
Glass ionomer sealants use a completely different chemistry. Instead of plastic resins, they’re made from two components: a fine powder of fluoride-containing glass (fluoroaluminosilicate glass) and a liquid acid solution (polyacrylic acid, sometimes blended with other organic acids like tartaric or maleic acid to control how fast the material sets).
When the powder and liquid are mixed, the acid attacks the surface of the glass particles, releasing calcium, aluminum, and fluoride ions. These ions then cross-link with the acid chains to form a rigid, cement-like material that bonds directly to the tooth. This acid-base setting reaction is entirely chemical, so no curing light is needed.
The fluoride released during this reaction doesn’t stop once the sealant hardens. Glass ionomer sealants continue to release small amounts of fluoride into the surrounding tooth structure over time. The release follows a predictable pattern: a large initial burst on the first day as fluoride washes off the surface, followed by a slower, steady release over weeks and months as fluoride diffuses through tiny pores in the cement. This ongoing fluoride delivery is the main advantage of glass ionomer sealants, since fluoride strengthens enamel and helps resist decay.
How Resin and Glass Ionomer Sealants Compare
Resin-based sealants are significantly more durable. In a clinical study comparing the two types in schoolchildren, 60% of resin sealants were fully intact at six months with only 3.3% completely lost. Glass ionomer sealants showed 50% fully intact at the same time point, but a third of them (33.3%) had been lost entirely. Over longer periods, this gap widens further. Resin sealants routinely last several years on molars, while glass ionomer sealants tend to wear away faster because the cement is softer and more brittle than cured resin.
Glass ionomer sealants still have a role, though, particularly in situations where keeping the tooth perfectly dry during placement is difficult (common with young children or newly erupting molars). Glass ionomer bonds to slightly moist tooth surfaces, while resin sealants require a completely dry field. Even when glass ionomer sealants wear away, the fluoride they’ve deposited into the enamel continues to provide some protection.
The Etching Step Before Sealant Placement
For resin-based sealants, the tooth surface needs preparation before the sealant is applied. This involves painting a phosphoric acid gel, typically at a concentration of 37%, onto the chewing surface for 15 to 30 seconds. The acid dissolves a microscopically thin layer of enamel (roughly 5 to 27 microns deep, depending on concentration and time), creating a roughened texture with tiny pores. When the sealant resin flows into these pores and hardens, it locks mechanically onto the tooth, much like Velcro on a microscopic scale. The acid is rinsed off completely before the sealant is applied, so none of it remains on the tooth.
BPA in Dental Sealants
Because Bis-GMA is derived from bisphenol A (BPA), a chemical that can interfere with hormones at high exposure levels, parents sometimes ask whether sealants are a meaningful source of BPA. The short answer: sealants do release trace amounts, but the quantities are extremely small.
Lab testing of six commercial sealant brands found detectable BPA in all of them. At neutral pH (close to normal mouth conditions), the amount released within the first 10 minutes averaged 0.09 parts per million. Under acidic conditions (pH 3.0, similar to drinking something very sour), the release was higher at 0.35 ppm. These amounts are far below thresholds considered harmful. The release also drops quickly after placement, and rinsing or having your child spit after the sealant is placed reduces exposure further.
If BPA is a concern, sealants made with UDMA instead of Bis-GMA are available. These formulas are not derived from bisphenol A and don’t release it.
Allergic Reactions to Sealant Materials
Allergic reactions to dental sealants are rare but documented. The methacrylate monomers in resin sealants are the most common trigger. Contact allergy to methacrylate occurs in roughly 1% of the general population, and the chemical HEMA (2-hydroxyethyl methacrylate) is one of the more frequently identified allergens, showing up as a positive patch test in about 5.8% of people tested for dental material sensitivities. Symptoms can include redness or irritation of the gums and cheeks near the sealant, and in one reported case, a patient developed asthma and hives after sealant placement, with symptoms resolving completely once the sealant was removed. Dental professionals themselves face higher exposure risk from handling uncured resins repeatedly, making occupational contact dermatitis more common in that group than in patients.