What Is Bis-GMA and Why Is It Used in Dental Bonding?

If you have a tooth-coloured filling, a bonded veneer or a bonded bridge, there is a strong chance a molecule called Bis-GMA is doing much of the structural work.

It was developed in the early 1960s specifically for dentistry, and it solved a problem that had blocked tooth-coloured restorations for years: how to make a material that behaves like a workable paste in the mouth, hardens only when the dentist decides, bonds to tooth structure, and then survives being chewed on.

It is worth understanding, partly because it is genuinely interesting chemistry and partly because it comes up in online discussions about BPA in dental materials, often with more heat than accuracy.

What is the material, in plain terms?

Bis-GMA — bisphenol A-glycidyl methacrylate — is a large, viscous resin molecule with a reactive methacrylate group at each end. Those reactive ends allow individual molecules to link into a rigid three-dimensional network when activated. In a composite filling, this resin network forms the matrix that holds together the glass or ceramic filler particles which give the material its strength and wear resistance.

The molecule has a rigid aromatic core with a reactive group at either end. That structure explains most of its behaviour:

• The rigid core gives the set material stiffness and strength

• Two reactive ends per molecule allow extensive cross-linking, producing a durable network rather than a soft polymer

• Its large size means fewer molecules per unit volume, which reduces how much the material shrinks as it sets — a significant advantage, since shrinkage is the source of most composite problems

• Hydroxyl groups along the molecule make it relatively resistant to water uptake and give it good wetting behaviour on tooth surface

The drawback is that it is extremely viscous — thick and sticky. Practically unusable on its own. So it is always blended with lower-viscosity co-monomers such as TEGDMA, which thin it to a workable consistency and allow filler particles to be incorporated. The ratio of the two is one of the main things manufacturers adjust between products.

It sets on command. A photoinitiator, usually camphorquinone, absorbs blue light at around 470 nanometres and starts the polymerisation reaction. This gives unlimited working time to shape the material, followed by rapid hardening. Before light-cured materials, dentists worked against a chemical clock.

It cross-links well. Two reactive ends per molecule produce a densely linked network, giving hardness and resistance to solvents.

It shrinks less than smaller monomers would. All resins shrink as they polymerise, and shrinkage stress is the main cause of marginal problems — as discussed in our article on layering techniques that reduce composite chipping. Bis-GMA's size limits this.

It accepts high filler loading. Modern composites contain a large proportion of glass, quartz or ceramic filler by weight, which provides strength, wear resistance and radiopacity. The resin has to accommodate it.

It can be pigmented and shaded, allowing composites in a wide range of shades and opacities.

It has a long clinical record, which counts for something in a field where materials are in service for decades.

Bis-GMA is the matrix, but the bond to tooth structure comes from a specific sequence.

To enamel. The surface is etched with phosphoric acid, creating a microscopically roughened pattern. Low-viscosity resin flows into it and is cured, locking mechanically into the surface. This bond is reliable and durable.

To dentine. More difficult, because dentine is wet and contains organic material. Etching removes mineral and exposes a mesh of collagen fibres. A primer carries resin into this mesh, and when cured the result is a hybrid layer of resin reinforced with collagen. The bond is genuinely good but more technique-sensitive and less durable over time than the enamel bond.

This is why isolation matters so much. Moisture contamination during bonding is one of the most common causes of early failure, and it is also why bonding protocols are product-specific and not interchangeable.

This is the part people search for, so it deserves a straight answer.

The BPA connection. Bis-GMA is manufactured using bisphenol A as a starting material. It is not BPA, and BPA is not an ingredient in composite. However, trace amounts of BPA can be detected in some materials as a manufacturing residue, and some related monomers can release very small quantities of BPA when broken down by salivary enzymes.

What studies have found. Measurable exposure occurs primarily in a short window immediately after placement, and detected levels have generally been far below established safety thresholds. Regulatory and professional bodies in the UK, Europe and the United States currently consider composite restorations safe for general use, including in children, while supporting continued research.

Reducing exposure. Rinsing thoroughly after placement, wiping the surface with pumice, and adequate curing all reduce residual unreacted monomer. Under-curing leaves more unreacted material, so proper curing is both a strength and a biocompatibility matter.

Allergy. Methacrylate allergy exists and is uncommon but well documented, occurring more often in dental staff with repeated handling exposure than in patients. If you have a known methacrylate sensitivity, tell your dentist so alternatives can be considered.

Pulp sensitivity. Unreacted monomer reaching a deep cavity floor can irritate the pulp, which is one reason deep cavities may be lined before restoration.

Materials science has moved on in several directions:

• UDMA-based composites, which omit Bis-GMA entirely and are used in a number of current products

• Silorane and other low-shrinkage chemistries, developed to reduce polymerisation stress

• Bis-EMA, a related monomer without the hydroxyl groups, which absorbs less water

• Ormocers, using an organically modified ceramic network

• Glass ionomer and resin-modified glass ionomer, which release fluoride and are useful in specific situations though generally less wear-resistant

• Ceramic restorations such as porcelain veneers, crowns and onlays, though these are still typically cemented with resin

If avoiding Bis-GMA specifically matters to you, ask — several current materials do not contain it.

Arrange an assessment if:

• You have tooth decay or a suspected cavity

• A filling has chipped, fractured or fallen out

• You have pain when biting on a restored tooth

• A restoration has stained around its margin

• You have tooth sensitivity after a filling that is not settling

• You have a known methacrylate allergy and need restorative treatment

• You want the material options for a planned restoration explained

• Brush twice daily with fluoride toothpaste and a soft brush

• Clean between the teeth daily, especially around restoration margins

• Limit staining exposure in the first 48 hours after placement

• Avoid abrasive whitening pastes, which dull the polished surface

• Do not bite hard objects, ice or packaging

• Wear a night guard if you grind

• Attend routine check-ups and hygiene appointments so margins are monitored

Our white fillings page covers what treatment involves.

• Bis-GMA is a resin monomer that forms the matrix of most composite materials

• Its size and structure give strength, cross-linking and reduced shrinkage

• It is too viscous alone and is always blended with thinner co-monomers

• Light curing gives controlled working time followed by rapid setting

• The bond to enamel is mechanical and reliable; the dentine bond is more technique-sensitive

• Bis-GMA is made from BPA but is not BPA; detected exposure is transient and low

• Bis-GMA-free composites exist if you prefer to avoid it

The NHS guidance on caring for teeth and gums covers day-to-day oral care.

Bis-GMA is one of those quiet pieces of engineering that made a whole category of treatment possible. It is why a filling can be shaped at leisure, set in seconds, and still be there years later.

The BPA question is reasonable to ask, and the honest answer is that measured exposure is small and short-lived, while alternatives exist if you would rather avoid it entirely. Either way, it is worth asking what is being placed and why.

To discuss restorative treatment, arrange an appointment at 22 Wimpole St, London W1G 8GQ, or call 020 7183 0692.

Dental symptoms and treatment options should always be assessed individually during a clinical examination.

This article is for general educational information only and is not professional dental advice, diagnosis, or a treatment recommendation. Information here is general and cannot replace an in-person assessment by a qualified, GDC-registered dental professional. Symptoms, suitability, fees, timelines, and outcomes vary according to individual clinical circumstances. If you have pain, swelling, or other concerning symptoms, seek prompt professional dental care. Always request a written treatment plan and cost estimate before proceeding with treatment.

Written Date: 1 September 2026 Next Review Date: 1 September 2027