Tooth fillings compared: amalgam, composite, glass ionomer
Three materials, three very different trade-offs in cost, looks, and lifespan. Here is what each filling actually does in your mouth, what the research says about safety, and the one stage where you can still skip the drill entirely.
Amalgam is the toughest and cheapest filling but silver-grey and now banned in the EU as of 2025. Composite looks natural and bonds to the tooth but costs more and wears faster, typically lasting 5 to 10 years. Glass ionomer releases fluoride and bonds chemically, but its softness limits it to low-stress spots, root surfaces, and kids. Enamel ranks 5 on the Mohs scale and cannot regrow once a hole forms, but softened pre-cavity enamel can still re-harden. Treat early white-spot lesions with remineralization before they ever need a drill.
This guide is by Minvelle. For the exact window this article describes we make a remineralizing gum, 5.7 mg nano-hydroxyapatite per piece, one piece a day, dose published.
When decay goes deeper than a filling can fix, the next step is different: see when a root canal is actually needed.
What actually happens in the chair, step by step?
Most people only register the drill and the numbness, but a tooth-colored filling is a sequence of small, technique-sensitive steps, and how carefully each one is done has more to do with how long the filling lasts than which brand of resin came out of the tube. Knowing the steps also explains why a composite costs more and takes longer than the silver fillings your parents got: there is simply more to do, and almost none of it can be rushed.
After the local anesthetic takes hold, the dentist removes the decayed tissue and shapes the cavity. Then comes the part that separates a good composite from a failing one: isolation. The tooth has to be kept completely dry, because composite that touches saliva before it sets does not bond reliably. That is done with a rubber dam, a thin sheet clipped around the tooth, or with cotton rolls and suction. This is not a minor detail. A Cochrane review of rubber dam isolation found low-certainty evidence that direct restorations placed under a rubber dam had a lower failure rate at six months than those placed with cotton-roll isolation, though at other time points the evidence was very uncertain (Cochrane Library). The signal points the same direction every dentist will tell you: a dry field matters.
Next, the dentist etches the prepared surface with a mild phosphoric-acid gel for roughly fifteen seconds, then rinses it off. That micro-roughens the enamel so the adhesive can grip it. A thin bonding resin is brushed on, worked into those microscopic pores, and hardened with a blue light. This forms the so-called hybrid layer, the chemical handshake between tooth and filling that gives composite its retention without the deep mechanical undercuts amalgam needs.
Only then does the actual filling go in, and it goes in slowly. Composite is placed in thin layers, often around two millimeters at a time, with each layer cured before the next is added. The dentist is effectively rebuilding the tooth's anatomy in miniature: the grooves, the cusps, the points where it touches its neighbors. Layering is not fussiness. All composites shrink slightly as they cure, and packing too much in at once concentrates that shrinkage stress, which can pull the resin away from the cavity wall and leave a microscopic gap. Research on recurrent caries describes how polymerization shrinkage and the resulting marginal gap are a recognized weak point of resin restorations (PMC). That gap is exactly where the next problem starts.
Local anesthetic, then the decayed tissue is removed and the cavity is shaped.
Rubber dam or cotton rolls keep saliva off the tooth, because moisture wrecks the bond.
Acid gel roughens the surface, then adhesive resin is brushed in and light-cured.
Composite is built up in thin increments, each one hardened before the next to control shrinkage.
The filling is trimmed, polished, and adjusted so it does not sit high when you close.
Why do fillings fail, and what makes one last longer?
No filling is forever, and the data is blunt about it. A large share of a dentist's restorative work is not new cavities at all, it is replacing fillings that have already failed. Research describes secondary caries, the decay that forms at the margin of an existing restoration, as still the main reason restorations get replaced, which is why understanding why they fail is more useful than chasing a material that supposedly never does (PubMed).
The two materials fail in different ways, and the research is fairly consistent on the split. A systematic review comparing amalgam and composite in permanent posterior teeth reported median survival times exceeding 16 years for amalgam, against roughly 11 years for composite, with secondary caries the most common cause of composite failure and fracture the primary reason for amalgam replacement (PMC). The headline number flatters amalgam, but it comes with an asterisk: those figures sit in controlled studies, and the same review notes that patient factors such as oral hygiene and grinding move the outcome more than the material label does.
Composite on its own is far from fragile when it is placed well. A separate systematic review of posterior composite restorations in adults found an overall failure rate of about 1.55 lost restorations per 100 restoration-years, with secondary caries and fracture again the main culprits, and most secondary caries showing up only after three years or later (PubMed). Translated into plain terms, that is a very low annual failure rate, and it means the average well-placed back-tooth composite is doing its job for many years before anything goes wrong. The gap between that statistic and the folk wisdom that composite fillings fall out is mostly a story about technique, isolation, and how big the cavity was to begin with.
When a composite does start to fail at one corner, the old reflex was to drill the whole thing out and start over. That is changing. A systematic review and meta-analysis of repairing versus replacing partially fractured direct composite restorations found that repaired restorations showed better marginal adaptation and a lower incidence of secondary caries than fully replaced ones, which supports a more conservative, repair-first approach where it is feasible (PMC). Every time a tooth is re-drilled the cavity gets a little bigger, so a repair that buys years without sacrificing more tooth structure is usually the better deal for the tooth.
Cavity size is the quiet variable behind all of this. There comes a point where so much tooth is gone that a direct filling, no matter how skilfully layered, is being asked to do a job it was not designed for, and the failure rate climbs. Dental commentary on restoration choice makes the same point: once the loss runs past roughly half the distance from cusp tip to cusp tip, a direct restoration is no longer the conservative option and an onlay or crown becomes the more durable answer (Dental Economics). For a small or medium cavity, though, a well-placed composite is hard to beat on the balance of looks, tooth preservation, and longevity.
Good isolation protects the bond, and studies link it to lower early failure of composite restorations.
Small to medium cavities suit a direct filling; very large ones often last longer as an onlay or crown.
Oral hygiene and grinding affect longevity more than the choice of material itself.
Secondary caries usually starts at the edge, so the margin is where most fillings are eventually lost.
The part you control: protecting the margin every day
If secondary caries at the margin is the single most common way fillings die, then the most useful thing a person can do after the dentist is finished is to keep that margin clean and the surrounding enamel strong. The filling itself does not decay, but the living tooth right next to it does, and the join between the two is the weakest part of the whole structure. Plaque that sits along that edge, fed by frequent sugar, is what tips a sound margin into a new cavity, which is why the daily routine around a filling matters as much as the filling did.
Two levers do most of the work. The first is reducing how often the mouth is exposed to fermentable sugar, because each exposure drops the pH at the tooth surface and gives plaque bacteria the acid they use to demineralize enamel. The second is supporting the natural repair process. Enamel is not inert: in its early, softened stage, demineralized surface can take minerals back up, and chewing stimulates saliva, the body's own buffer and mineral carrier. This is the territory where a sugar-free chewing habit fits, by keeping saliva flowing after meals rather than leaving the mouth acidic and dry. Research on minerals like nano-hydroxyapatite suggests they can help support the surface during that early remineralization window, which is the mechanism Minvelle's nano-hydroxyapatite chewing gum is built around. It is a remineralizing chewing gum, not a toothpaste, and it is designed to back up brushing and the dentist's work rather than replace either.
None of this is a substitute for the basics that keep a margin sound: cleaning between the teeth where the filling meets its neighbor, not skipping the checkups that catch a leaking edge while it is still small, and flagging any sharp pain or a bite that feels high so it can be adjusted early. A filling is a repair, not a reset, and the tooth around it stays as vulnerable as any other. Treat the margin as the place that needs the most attention, support your saliva and your enamel between meals, and you give whichever material your dentist chose its best shot at lasting the long end of those survival curves rather than the short end.
Amalgam is the toughest and cheapest but silver-grey and now banned in the EU. Composite looks natural and bonds to the tooth but costs more and wears faster. Glass ionomer releases fluoride and bonds chemically, but it is the softest, so it gets used for low-stress spots, roots, and kids.
No filling beats not needing one. Caught early enough, softened enamel can re-harden before it ever becomes a hole.
Almost everyone gets one eventually. You sit in the chair, the dentist says "we'll need to fill that," and then comes the part nobody explains: which material goes in the hole, and does the choice actually matter? It does. The three common options behave so differently that the right pick changes with the tooth, your budget, where you live, and even your age.
This is a straight comparison of amalgam, composite, and glass ionomer: real strengths, real weaknesses, what the long-term studies show, and the safety questions that keep coming up. At the end, the part most filling articles skip entirely: the narrow window where a cavity can still be stopped without any filling at all.
What happens when a tooth needs a filling?
A filling is repair work, not a cure. A cavity is a hole left behind after acid-producing bacteria have dissolved the mineral out of your enamel and into the softer dentin beneath it. Enamel is roughly 97% hydroxyapatite by weight and ranks about 5 on the Mohs hardness scale, which makes it the hardest tissue in the body, but it has no living cells and no blood supply, so once a hole forms it cannot regrow.
The dentist removes the decayed tissue, cleans the cavity, and packs it with a material that restores the tooth's shape and seals out bacteria. That is the whole job. The disagreement between materials is about how well each one does four things: how long it lasts, how natural it looks, how strongly it bonds, and whether it gives anything back to the tooth over time.
Molars absorb chewing forces that can exceed those on front teeth several times over, so durability and wear resistance dominate the material choice there.
A filling on a visible tooth is judged on appearance first, which rules amalgam out for most people regardless of how strong it is.
Amalgam: the silver workhorse of the last 150 years
Dental amalgam is a mix of liquid mercury (roughly half by weight) bound with a powdered alloy of silver, tin, and copper. It has been used since the 1800s for one simple reason: it works, and it keeps working for a long time. Amalgam tolerates moisture during placement, packs into a cavity easily, and stands up to grinding molars better than almost anything else. Cochrane evidence has consistently found amalgam restorations to be highly durable in load-bearing teeth.
It is also the cheapest of the three, which is why it stayed the standard for back teeth across most of the world for over a century. The downsides are equally real. It is silver-grey, so it never blends in. It requires the dentist to remove some healthy tooth structure to create a mechanical lock, because amalgam does not bond to enamel, it wedges into place. And then there is the mercury question, which gets its own section below.
Exceptional durability under heavy chewing, low cost, fast placement, and forgiving in a damp field. Often lasts 10 to 15 years or longer.
Visibly grey, requires removing more healthy tooth, no bond to enamel, and now banned in the EU for environmental reasons. Carries the lingering mercury debate.
Are composite fillings worth the extra cost?
Composite resin is the tooth-colored filling most people get today. It is a blend of a plastic resin matrix and fine glass or ceramic filler particles. The dentist shade-matches it to your enamel, bonds it directly to the tooth, and cures it hard with a blue light. A good composite filling is genuinely difficult to see, which is why it has largely replaced amalgam for both front and back teeth where appearance matters.
The bonding is the underrated advantage. Because composite adheres to enamel and dentin, the dentist can remove less healthy tooth structure than amalgam requires. The trade-offs: it costs more, it takes longer to place because the cavity has to stay completely dry, and it has historically worn faster than amalgam on heavy chewing surfaces. Reviews in the Journal of Dentistry put typical posterior composite lifespans in the 7 to 10 year range, with newer materials closing the durability gap. The other known weakness is shrinkage during curing, which, if the technique is sloppy, can leave tiny gaps where new decay can start.
Natural appearance, bonds to the tooth, conserves healthy structure, mercury-free, and repairable. The default choice for visible teeth.
More expensive, technique-sensitive, needs a perfectly dry field, can stain at the edges over years, and shrinks slightly on curing. Wears faster than amalgam under heavy load.
What is glass ionomer, and where does it shine?
Glass ionomer cement is the quiet specialist of the group. It is made from a fluoride-containing glass powder mixed with an organic acid, and it does two things the others cannot. First, it bonds chemically to tooth structure without needing a separate adhesive, even in slightly moist conditions. Second, it releases fluoride into the surrounding tooth over time, which research in the European Journal of Dentistry has linked to a protective effect against new decay at the filling margin.
That fluoride release and moisture tolerance make it the go-to for situations the other materials handle poorly: root-surface cavities, fillings that sit below the gumline, baby teeth, and as a liner placed underneath a composite or amalgam to seal the deep part of a cavity. It is also central to atraumatic restorative treatment, a minimally invasive approach used widely in children and in settings without a drill. The catch is mechanical: glass ionomer is the softest and most brittle of the three, so it wears down and fractures under heavy chewing. For a large filling on an adult molar, it usually is not the first pick.
Chemical bond to the tooth, ongoing fluoride release, tolerates moisture, and ideal for roots, gumline cavities, liners, and children's teeth.
Softest and most brittle of the three, lower wear resistance, and not ideal for large fillings on adult chewing surfaces. Shorter lifespan in high-load spots.
How do amalgam, composite, and glass ionomer compare?
Here is the head-to-head on the metrics that actually change the decision. Read it by tooth and by priority, not as a search for one universal winner, because there isn't one.
Note on numbers: lifespan figures are population averages from review studies, not guarantees. Your own fillings depend heavily on your dentist's technique, your bite, your diet, and how well you keep the margins clean.
Feed your enamel the mineral it is made of
Minvelle is a nano-hydroxyapatite chewing gum built around the exact mineral in your enamel, plus xylitol to starve the bacteria that start cavities. Sugar-free, natural gum base, designed for the part of the day a toothbrush never reaches.
See the formula →Is the mercury in amalgam something to worry about?
This is the question that ended amalgam in Europe, so it deserves a careful answer. Yes, amalgam contains mercury, and it does release a tiny amount of mercury vapor, mostly during chewing and grinding. The disagreement is over whether that amount matters for your health.
Major health authorities have repeatedly concluded that amalgam is safe for the general population. The European Scientific Committee on Health, Environmental and Emerging Risks (SCHEER) and the American Dental Association have both stated that existing amalgam fillings do not pose a health risk and should not be removed solely over mercury concerns, since drilling out an intact filling actually releases more vapor than leaving it alone. Some regulators advise caution for specific groups, such as pregnant women and young children, as a precaution rather than a proven harm.
The EU ban that took effect on 1 January 2025 was driven primarily by the environment, not patient safety. Mercury from dental clinics and crematoria is a known source of environmental contamination, and the bloc has been steadily reducing all mercury use under international agreements. So the honest framing is this: the ban is about mercury in rivers and air, not a verdict that your existing fillings are dangerous.
Dental bodies advise the opposite for intact, functioning fillings. Removal exposes you to more vapor in one sitting and sacrifices healthy tooth structure. Replace them when they actually fail, not on principle.
Composite and glass ionomer avoid mercury, but they have their own trade-offs in durability and edge sealing. Better looking is not the same as objectively better for every tooth.
Every filling has a lifespan and every margin is a spot where new decay can start. Fillings buy you time and function, they do not make the tooth permanently invincible.
Which filling is right for your situation?
There is no single best material, only the best fit for a specific tooth and a specific person. Use these scenarios as a starting point, then have the real conversation with your dentist, who can see what the tooth actually needs.
Composite. Shade-matched, bonds to the tooth, and effectively invisible. The standard of care for anything in the smile zone.
Composite, with amalgam as the historic alternative. Modern composites handle moderate loads well. Where amalgam is still legal, it remains a durable budget option for large back-tooth restorations.
Glass ionomer. Bonds in a damp field, tolerates the awkward location, and releases fluoride right where root surfaces are most vulnerable.
Glass ionomer. The fluoride release and quick, drill-light placement suit primary teeth that will be lost anyway and patients who struggle to sit still.
Can you avoid fillings altogether?
Sometimes, and only at the very start. Decay does not jump straight to a hole. It begins as a white-spot lesion, a patch of enamel that has lost mineral but whose surface has not yet broken. At that stage the damage is reversible: minerals from saliva and from what you put in your mouth can flow back into the softened crystal and re-harden it. This is remineralization, and it is the only window where a forming cavity can be stopped without a drill.
The mechanics are pH driven. Enamel starts dissolving when the mouth drops below a pH of 5.5, and plenty of everyday things blow past that line: coffee sits around 4.8, wine near 3.5, citrus juice around 2.5. Resting saliva at about 7.4 slowly brings the mouth back up and redeposits mineral, but if acid attacks come faster than saliva can recover, the balance tips toward decay. Anything that raises pH and supplies repair minerals during the day shifts that balance back.
Two ingredients keep showing up in this research. Fluoride is the classic one. The newer one is nano-hydroxyapatite, the nanoparticle form of the same mineral your enamel is built from. It has been used in Japanese oral care since 1980, was approved there as an anti-cavity agent in 1993, and was assessed as safe for oral care by the European Scientific Committee on Consumer Safety (SCCS) in 2023. A 2022 systematic review in Clinical Oral Investigations found nano-hydroxyapatite showed potential comparable to fluoride under laboratory remineralizing conditions. Xylitol plays a supporting role: clinical trials have shown it can reduce Streptococcus mutans, a key cavity bacterium, by up to 75%.
Important context: remineralization works on early, surface-intact lesions only. Once enamel has cavitated into an actual hole, no gum, paste, or rinse can refill it. That is exactly when you need one of the three fillings above. The honest goal of any remineralizing product is to widen the gap between checkups where nothing has progressed to that point.
This is the logic behind Minvelle, our nano-hydroxyapatite chewing gum. Chewing sugar-free gum stimulates saliva, which raises mouth pH on its own, and the gum delivers nano-hydroxyapatite and xylitol during the long stretch of the day when you are nowhere near a sink. To stay honest, as our research standards demand: most branded remineralizing gums, ours included, are supported by ingredient-level research rather than independent trials of the finished product. The evidence supports the ingredients. It is a daytime prevention habit that sits on top of brushing, flossing, and seeing your dentist, not a replacement for any of them. You can read more in our remineralizing gum guide or check your own risk with the enamel quiz.
Frequently asked questions
How long do tooth fillings last?
It depends on the material and where the filling sits. Amalgam fillings often last 10 to 15 years or more because they tolerate heavy chewing forces well. Modern composite fillings typically last 7 to 10 years, though placement skill and bite location matter a lot. Glass ionomer is the shortest-lived of the three in load-bearing areas, which is why it is often used for low-stress spots, root surfaces, and children's teeth.
Are amalgam fillings being banned?
In the European Union, dental amalgam use was banned from 1 January 2025 under the EU mercury regulation, with narrow medical exceptions. The move was driven by environmental mercury concerns rather than a finding that existing fillings harm patients. Outside the EU, amalgam remains legal and in use in many countries. If you already have amalgam fillings, dental bodies including the ADA do not recommend removing intact ones.
Do composite fillings look more natural than amalgam?
Yes, by a wide margin. Composite resin is tooth-colored and can be shade-matched to the surrounding enamel, so a well-placed composite is hard to spot. Amalgam is silver-grey and visible whenever you open your mouth wide, which is the main reason most people now choose composite for front and visible back teeth even though amalgam can be more durable under heavy load.
Does getting a filling hurt?
The procedure itself is usually painless because the dentist numbs the area with local anesthetic before drilling. You may feel pressure and vibration but not sharp pain. Some sensitivity to hot, cold, or pressure is common for a few days afterward as the tooth settles, especially with deeper fillings. Sensitivity that lasts more than two weeks or gets worse is worth a call back to your dentist.
Can a cavity heal without a filling?
Only at the earliest stage. A white-spot lesion, which is softened enamel before the surface has broken, can re-harden through remineralization using minerals like calcium, phosphate, fluoride, or nano-hydroxyapatite. Once the surface cavitates into a hole, the structure cannot regrow and a filling is needed. The honest takeaway: prevention and early intervention can stop some cavities, but established holes need a dentist.
Is glass ionomer good for adults or just for children?
Both, but for specific situations. Glass ionomer bonds chemically to tooth structure and releases fluoride over time, which makes it useful for root-surface cavities, fillings below the gumline, and as a liner under other materials. It is widely used in children's teeth and in minimally invasive techniques. It is less wear-resistant than composite or amalgam, so dentists usually avoid it for large fillings on heavy chewing surfaces in adults.
The cheapest filling is the one you never need.
Minvelle is a nano-hydroxyapatite chewing gum with xylitol, built to support your enamel through the acidic middle of the day. Sugar-free, natural gum base, 30-day money-back guarantee.
Try Minvelle →- Cochrane Oral Health, systematic review of dental amalgam versus composite resin fillings for permanent posterior teeth.
- Scientific Committee on Health, Environmental and Emerging Risks (SCHEER), opinion on the safety of dental amalgam.
- American Dental Association (ADA), statement on dental amalgam safety and recommendations on removal.
- Journal of Dentistry, reviews of posterior composite resin restoration longevity.
- European Journal of Dentistry, research on glass ionomer cement fluoride release and anti-caries effect.
- Clinical Oral Investigations, 2022 systematic review of nano-hydroxyapatite remineralization potential compared to fluoride.
- Caries Research, studies on enamel demineralization, the critical pH of 5.5, and remineralization of white-spot lesions.
- European Scientific Committee on Consumer Safety (SCCS), 2023 assessment of nano-hydroxyapatite safety in oral care.
- Longevity of Amalgam Versus Composite Resin Restorations in Permanent Posterior Teeth: A Systematic Review (PMC)
- Longevity of Repair Versus Replacement of Partially Fractured Direct Composite Restorations: A Systematic Review and Meta-Analysis (PMC)
- Rubber dam isolation for restorative treatment in dental patients (Cochrane Library)
- Secondary caries and restoration replacement: an unresolved problem (PubMed)
- Current Strategies to Control Recurrent and Residual Caries with Resin Composite Restorations (PMC)
- Longevity of posterior resin composite restorations in adults: a systematic review (PubMed)
- Crown, onlay, or direct restoration? (Dental Economics)
Nano-hydroxyapatite vs fluoride: what's actually the difference? →
The two ingredients that can re-harden enamel, compared head to head.
How to remineralize teeth naturally →
What actually rebuilds softened enamel before it becomes a cavity.
The best remineralizing gum in 2026 →
An honest look at the nano-hydroxyapatite gums worth chewing.
Max, Founder of Minvelle. Reads dental research daily, not a medical professional. Every Minvelle post is fact-checked against primary sources, no LLM-generated content goes live unedited. More on how this brand started.
Last reviewed: June 2, 2026 by Max, Founder of Minvelle.