Most dental sealants are thin plastic coatings built from a handful of synthetic resin monomers, inorganic filler particles, light-activated curing agents, and small amounts of additives for color or fluoride release. The exact recipe varies by brand and type, but the overwhelming majority of sealants used today fall into two broad chemical families: resin-based and glass ionomer-based, with resin formulations dominating clinical use. The chemistry behind each family is surprisingly different, and the ingredient list matters more than most patients realize, particularly when it comes to questions about bisphenol A (BPA) exposure.
The Resin Backbone
The core of a resin-based dental sealant is its monomer system, the molecules that link together into long polymer chains when the sealant hardens. The single most common monomer in resin-based dental materials is BisGMA (bisphenol A-glycidyl methacrylate), found in more than half of all resin-based dental products analyzed in a large materials survey. Other frequently used monomers include UDMA (urethane dimethacrylate), TEGDMA (triethylene glycol dimethacrylate), and HEMA (hydroxyethyl methacrylate).1PubMed Central. Analysis of Resin-Based Dental Materials’ Composition Depending on Their Clinical Applications These monomers each bring different properties to the final material. BisGMA provides stiffness and strength but is extremely viscous on its own, so manufacturers blend it with thinner monomers like TEGDMA to make the sealant flow easily into the pits and grooves of a tooth before curing.
Some newer sealant formulations skip BisGMA entirely and rely on combinations of UDMA and TEGDMA instead. Roughly three in ten resin-based dental materials on the market contain no BPA-derivative monomers at all.1PubMed Central. Analysis of Resin-Based Dental Materials’ Composition Depending on Their Clinical Applications For parents concerned about BPA exposure from their child’s sealants, BPA-free formulations do exist, and a dentist can usually identify which product they stock.
How Sealants Harden
A sealant sitting in its syringe is a liquid or paste. It turns solid through a process called polymerization, where those individual monomer molecules cross-link into a rigid network. In light-cured sealants, which are the most common type, this reaction is kicked off by a photoinitiator system. The standard combination is camphorquinone paired with a tertiary amine. When a dental curing light (usually a blue LED) hits the sealant, camphorquinone absorbs the light energy and reacts with the amine to produce free radicals, which then attack the double bonds in the resin monomers and start the chain reaction that locks everything together.2PubMed. ESR study of camphorquinone/amine photoinitiator systems using blue light-emitting diodes
Camphorquinone is responsible for the slightly yellow tint some sealants have before curing. It is present in very small amounts, typically well under one percent of the total material. A few sealant brands use alternative photoinitiators to achieve a whiter or more translucent appearance, but camphorquinone remains the industry workhorse. There are also self-curing (chemically activated) sealants that harden on their own once two components are mixed, though these are less popular in practice because the dentist has less control over working time.
Fillers and Why Some Sealants Are “Filled”
Dental sealants are often described as either “filled” or “unfilled.” The distinction matters. An unfilled sealant is essentially just cured resin, while a filled sealant contains tiny inorganic particles mixed into the resin matrix. Common filler materials include ground glass, quartz, and fumed silica. These particles increase the sealant’s resistance to wear, improve its handling properties, and can reduce the amount of resin that shrinks during curing.
The filler particles do not bond to the resin on their own. To make them stick, manufacturers coat the particles with silane coupling agents, chemicals that act as a bridge between the inorganic filler and the organic resin. Silanes chemically bond to the silica-based surface of the filler particle on one side and to the resin matrix on the other, creating a unified material rather than a loose mixture of glass in plastic.3PubMed. Silane adhesion mechanism in dental applications and surface treatments: A review
Filled sealants are slightly more resistant to abrasion, which sounds like an obvious advantage. The trade-off is that they are thicker and harder to flow into narrow fissures. Because sealants only work when they fully seal the groove, an unfilled sealant that penetrates deep into a fissure can outperform a filled sealant that sits on top without reaching the bottom. Many clinicians choose unfilled sealants for exactly this reason, especially on teeth with very narrow grooves.
The Etching Step
Before a resin sealant is applied, the tooth surface needs to be roughened so the sealant can grip. This is typically done with phosphoric acid, usually at a concentration of about 37 percent. The acid dissolves tiny amounts of the enamel’s mineral structure (hydroxyapatite), creating a microscopically rough surface full of tiny pores and projections. When the liquid sealant flows over this roughened surface, it seeps into those pores and, once cured, forms resin “tags” that physically lock the sealant to the tooth.4PubMed Central. Evaluation of Resin Penetration Depth in Enamel Surface for Orthodontic Bonding Exposed to Five Types of Enamel Conditioning Methods
Phosphoric acid is rinsed off completely before the sealant is placed, so it does not remain as a permanent ingredient. But it is a critical part of the process, and skipping or shortening the etch can dramatically reduce how long the sealant stays bonded. Some newer “self-etching” sealant systems incorporate acidic monomers like 10-MDP (10-methacryloyloxydecyl dihydrogen phosphate) that condition the enamel and bond to it chemically at the same time, eliminating the separate acid-etch step. These monomers form insoluble calcium salts with the hydroxyapatite in enamel, creating both a chemical and a micromechanical bond.5PubMed Central. Evaluation of the Bond Strength of Self-Etching Adhesive Systems Containing HEMA and 10-MDP Monomers Self-etch sealants are faster to place and less technique-sensitive, which is appealing in pediatric dentistry where keeping a child’s mouth dry and cooperative for a multi-step procedure can be a challenge.
Glass Ionomer Sealants
Not all sealants are resin-based. Glass ionomer sealants use an entirely different chemistry. Instead of monomers that polymerize under light, glass ionomer materials consist of a fluoroaluminosilicate glass powder and a water-soluble polyacrylic acid liquid. When the two are mixed, an acid-base reaction takes place: the acid attacks the glass, releasing metal ions (mainly aluminum and calcium) that cross-link with the polyacrylic acid chains. As these metallic salts form, the material gels and eventually sets into a hard cement.6Journal of Yeungnam Medical Science. Current aspects and prospects of glass ionomer cements for clinical dentistry
The big selling point of glass ionomer sealants is fluoride. Because the glass component is loaded with fluoride, the set material slowly releases fluoride ions into the surrounding tooth structure over time. This sustained low-level fluoride exposure can help remineralize enamel and resist acid attacks from bacteria. Glass ionomer sealants release significantly more fluoride initially and recharge more effectively after exposure to topical fluoride treatments compared to resin-based sealants.7PubMed Central. Fluoride release and recharge from different materials used as fissure sealants That fluoride recharging ability means the sealant can act as a small reservoir, absorbing fluoride from toothpaste or professional treatments and then gradually releasing it back to the tooth.
The downside is durability. Glass ionomer sealants are softer and more brittle than resin sealants, and they wear away or chip off more quickly. Recent reviews found that resin sealants have retention rates up to about 80 percent at two years, while glass ionomer sealants sit around 44 percent.8PubMed Central. A concise review of dental sealants in caries management Even so, some evidence suggests that the fluoride left behind after a glass ionomer sealant falls off continues to protect the tooth, partly compensating for the lower retention. Glass ionomer sealants also do not require the phosphoric acid etching step, which makes them simpler to apply in difficult clinical situations, like sealing a tooth that has not fully erupted and is hard to keep dry.
Hybrid Materials
There are also materials that blur the line between resin and glass ionomer. Resin-modified glass ionomer cements (RMGICs) add light-curable resin monomers like HEMA to a glass ionomer base, giving the material both an acid-base setting reaction and a light-cured polymerization reaction. Compomers are another hybrid, essentially resin composites with some acid-reactive glass filler added. Both types try to combine the fluoride release of glass ionomers with the better wear resistance and adhesion of resins.
These hybrid materials do release some fluoride, though generally less than a conventional glass ionomer. They also release small amounts of unreacted monomer, as all resin-containing dental materials do. Lab testing has shown that RMGICs and compomers can leach HEMA and TEGDMA into surrounding fluid, and some formulations reduced the survival of fibroblast cells in culture.9PubMed Central. Residual HEMA and TEGDMA release and cytotoxicity evaluation of resin-modified glass ionomer cement and compomers cured with different light sources Whether this matters clinically, in a living mouth rather than a petri dish, is less clear. The concentrations involved are extremely low, and the mouth is constantly flushed with saliva.
Additives for Color and Visibility
A sealant that is completely clear can be hard to evaluate at a follow-up appointment, since the dentist cannot easily see whether it is still intact. Many sealant brands add opacifiers or tints so the material is visible on the tooth surface. Titanium dioxide is a common opacifying agent, giving some sealants a white or off-white appearance. Even small amounts have a meaningful effect on the material’s optical properties; research has shown that as titanium dioxide concentration approaches about half a percent, it nearly completely blocks the transmission of fluorescence signals through the sealant.10Pediatric Dentistry. An In Vitro Evaluation of the Effect of Sealant Characteristics on Laser Fluorescence for Caries Detection That is worth knowing because some caries-detection devices use fluorescence to spot decay underneath sealants. An opaque sealant can mask what is going on below.
Other sealants are tinted pink or contain color-change indicators that shift from one color to another during curing, helping the clinician confirm the material has fully hardened. These pigments are present in trace amounts and are generally considered inert.
The BPA Question
BPA (bisphenol A) concerns are probably the single most common worry parents have about dental sealants. The connection exists because BisGMA, the dominant monomer in resin sealants, is synthesized from BPA. However, BisGMA itself is not BPA. It is a much larger molecule, and once polymerized, it is locked into the resin matrix. The real concern involves a related monomer called BisDMA (bisphenol A dimethacrylate), which some older sealant formulations used. BisDMA breaks down rapidly in the presence of saliva enzymes, and lab studies have shown that within 24 hours, saliva incubated with BisDMA saw a sharp drop in the monomer concentration alongside a significant rise in free BPA.11PubMed. Stability of bisphenol A, triethylene-glycol dimethacrylate, and bisphenol A dimethacrylate in whole saliva
Products based on BisGMA are far less likely to release BPA through this pathway, because BisGMA resists that enzymatic breakdown much more effectively than BisDMA does.12Pediatrics. Bisphenol A and Related Compounds in Dental Materials Most modern sealants have moved away from BisDMA. If you are concerned, ask your dentist which specific product they use and check whether it is BisDMA-free. In practice, even for sealants that do release trace BPA, the amounts are orders of magnitude below the levels associated with any known health effects, and the exposure is a brief spike right after placement rather than a sustained dose.
What Leaches Out After Placement
No polymerization reaction converts 100 percent of the monomer into polymer. Some unreacted monomer and small breakdown products inevitably leach out of the cured sealant into saliva, especially in the first hours and days. Researchers who analyzed the eluates (the substances washed out) from pit-and-fissure sealants found a cocktail of organic compounds including TEGDMA, HEMA, camphorquinone residues, the antioxidant BHT (butylated hydroxytoluene), and the stabilizer MEHQ (hydroquinone monomethyl ether), among others. TEGDMA was the most abundant leached monomer. Higher concentrations were measured after 40 days of storage in solution compared to shorter periods, and the chemical profiles differed between brands.13PubMed. Investigation of the chemical profile and cytotoxicity evaluation of organic components eluted from pit and fissure sealants
In cell culture, these eluates did reduce cell viability. That finding sounds alarming, but it is worth keeping in perspective. A cell culture sits in a fixed pool of liquid; your mouth produces about a liter of saliva a day, constantly diluting and washing away whatever leaches from a tiny sealant. The clinical relevance of lab-measured cytotoxicity is debated, and decades of widespread sealant use have not produced evidence of systemic harm. Thorough light curing and wiping the sealant surface with a cotton pellet immediately after placement can reduce the initial burst of unreacted monomer on the surface.
Fluoride-Releasing Resin Sealants
Some resin-based sealants incorporate fluoride-releasing additives to capture some of the anticaries benefit associated with glass ionomers while keeping the superior retention of resin. These products use various fluoride compounds blended into the resin matrix or filler system. Their fluoride release tends to be lower than that of a true glass ionomer, but it can be boosted. Applying a professional fluoride varnish over a sealant increases fluoride release from all types of sealants, and the enhancement from varnish is substantially greater than from other fluoride products like casein-based pastes.14PubMed Central. Fluoride release and uptake abilities of different fissure sealants In other words, fluoride-containing resin sealants can work as rechargeable fluoride stores, absorbing fluoride from external applications and then releasing it gradually to the tooth.
Experimental Ingredients on the Horizon
Researchers are actively trying to make sealants do more than just physically block bacteria. Two directions are especially active. The first involves bioactive glass particles, specifically mesoporous bioactive glass (MBG). Sealants loaded with MBG release calcium and phosphate ions that can help remineralize enamel around and under the sealant. Lab testing has shown that MBG-containing sealants significantly increased the hardness of enamel in contact with them, with imaging and crystallographic analysis confirming new mineral deposition on the enamel surface.15PubMed. Enhancing dental sealant performance: Effects of mesoporous bioactive glass and 10-MDP on adhesion and remineralization If this holds up clinically, it would mean sealants could actively repair early enamel damage rather than just preventing new damage.
The second direction targets bacteria directly. Antibacterial nanocomposites, such as silver bromide particles coated with a polymer shell, have been blended into experimental sealant formulations. These modified sealants showed contact-killing activity against Streptococcus mutans, the primary bacterium responsible for dental caries, outperforming two commercial sealants in laboratory tests regardless of whether the materials had been artificially aged.16PubMed. The antibacterial effect and physical performance of pit and fissure sealants based on an antibacterial core-shell nanocomposite Neither bioactive nor antibacterial sealants are widely available commercially yet, but they represent where the ingredient list is likely heading in the coming years.
How Material Choice Affects Longevity
The ingredients inside a sealant have a direct relationship with how long it lasts. Resin sealants, with their stronger bond to acid-etched enamel and greater resistance to wear, consistently outperform glass ionomers for long-term retention. That 80 percent versus 44 percent retention gap at two years reflects fundamental differences in material properties: resin is tougher, more water-resistant, and bonds more tenaciously to etched enamel than glass ionomer cement does.8PubMed Central. A concise review of dental sealants in caries management
But retention is not the whole story. A sealant that lasts five years on a low-risk tooth is less valuable than a sealant that lasts 18 months on a high-risk tooth during the critical window when the tooth is most vulnerable to decay. Glass ionomer sealants, despite lower retention, still show meaningful cavity prevention in high-risk populations, likely because their fluoride release continues to protect the enamel even after the bulk material is gone. Some clinicians use a staged approach: glass ionomer as a temporary sealant on a newly erupted molar that is still partly covered by gum tissue (making isolation difficult), followed by a resin sealant once the tooth has fully emerged and can be kept dry during placement.
Proper curing also matters enormously. An undercured resin sealant will leach more monomer, bond less effectively, and wear down faster. The light-curing unit must deliver sufficient intensity at the correct wavelength (camphorquinone absorbs blue light most efficiently around 468 nanometers) for the recommended exposure time. A weak or aging curing light can leave the sealant partially polymerized at the bottom, even if the surface looks and feels hard.
Reading a Sealant’s Safety Data Sheet
If you want to know exactly what is in the sealant your dentist uses, the manufacturer’s Safety Data Sheet (SDS) is the most reliable source. Every dental product sold commercially is required to have one, and dentists should be able to provide it on request. The SDS lists all hazardous components above certain concentration thresholds, along with their Chemical Abstracts Service (CAS) numbers. Look for the “Composition/Information on Ingredients” section. You will typically see entries for the base monomers (BisGMA, UDMA, TEGDMA, etc.), the photoinitiator, any filler types, and additives like fluoride compounds or pigments. Comparing your child’s sealant’s SDS to the ingredient categories described above gives you a concrete picture of what is actually being placed on their teeth, which is more reliable than searching for the brand name online and finding contradictory forum posts.