Patients hear material names in passing: "we'll do a zirconia crown," "this one should be e-max," "that old one is a PFM." The names go by quickly, and it can sound like branding. It isn't. Each of these is a genuinely different material with different physics, and the choice among them is a real clinical decision with consequences you'll live with for a decade or more.
This guide explains what the materials actually are and, more usefully, how we think when choosing one for a specific tooth. If you want the historical arc of how dentistry got this menu, start with our cornerstone guide, Why Dentistry Is Different Than You Remember. This one is the practical field guide.
- Crown and onlay materials differ in strength, toughness, beauty, required thickness, bondability, kindness to opposing teeth, and repairability. No material leads in all of them.
- Zirconia and lithium disilicate cover most modern situations; PFM, gold, and resin materials all retain legitimate places.
- Onlays live or die by adhesion, so onlay materials must bond — which quietly excludes some of the strongest options.
- What your restoration chews against matters nearly as much as what it's made of.
- The strongest material is not the best material. The matched material is.
The seven properties that actually matter
Before the materials, the yardsticks. When I'm choosing what a restoration will be made of, these are the questions in play:
- Strength — how much load it takes before it breaks. Necessary, but the most overrated number on this list.
- Toughness — resistance to cracks spreading. Ceramics are strong but brittle; metals bend before they break. Different virtues.
- Wear behavior — both how the material wears and what it does to the enamel chewing against it. A crown that outlasts everything while grinding down its opposing tooth has exported its failure.
- Esthetics — translucency and the way light moves through it. Natural enamel glows; opaque materials don't.
- Required thickness — how much room the material needs to be reliable. Thickness comes out of your tooth, so a material that works thin is a conservative material.
- Bondability — whether it can be adhesively bonded or must be conventionally cemented. Bonding unlocks onlays, veneers, and thin designs; cementation asks the preparation shape to do the holding.
- Repairability and serviceability — what happens in year nine when something chips.
The materials, honestly described
Zirconia — the tough one
Zirconia is a polycrystalline ceramic, milled from dense blocks, and it is the toughest tooth-colored material dentistry has. It comes in a family: the original formulations are extraordinarily strong but relatively opaque, best suited to back teeth and heavy bites; newer, more translucent versions trade a substantial share of that strength for much better looks. "Zirconia" on a treatment plan therefore isn't one decision but two — which zirconia, for which job. It's generally conventionally cemented (bonding to it is possible but less straightforward than to glass ceramics), it needs less thickness than PFM did, and in polished form it's gentler on opposing enamel than its reputation suggests. Its weakness is the flip side of its strength: when it does fail, it fractures rather than dents, and adjusting or repairing it chairside is limited.
Lithium disilicate — the balanced one
This is the material most patients know as e-max, a glass ceramic that's meaningfully strong while remaining genuinely beautiful — light passes through it the way it passes through enamel. Its defining ability is adhesion: etched and bonded, it becomes structurally one with the tooth, which lets it work in thinner sections and in partial-coverage designs. That's why it dominates onlays and veneers and is a mainstay for single crowns in the esthetic zone. Its limits are real: in the heaviest bites and longest spans, zirconia's toughness wins, and like all ceramics it wants proper thickness where forces are high.
Other glass ceramics and hybrids — the middle shelf
Around lithium disilicate sits a family of milled materials: leucite-reinforced ceramics, feldspathic blocks, and resin-ceramic hybrids that blend ceramic filler with resin matrix. The hybrids are notable for being kind — kind to opposing teeth, kind to mills, easy to adjust and polish, repairable with composite chairside. They give up strength and some long-term luster for that forgiveness, which makes them sensible in specific places: some onlays, some premolars, situations where wear-kindness or repairability leads the priorities.
Resin and printed materials — the newest shelf
Modern high-filled resins, milled or 3D printed, have earned a genuine place: provisionals, transitional restorations during complex care, and — with newer formulations carrying regulatory indications — selected definitive restorations at a price point that didn't previously exist. They are the most repairable materials on this page and the least proven over decades, and both halves of that sentence belong in the conversation. We've given them their own guide: 3D-printed restorations — when are they actually a good choice?
PFM — the incumbent
Porcelain-fused-to-metal carried restorative dentistry for half a century: a cast metal substructure for strength and fit, layered porcelain for appearance. Millions are in service right now, many superbly. Its compromises — opacity, the possibility of a grey margin line as gums recede, porcelain chipping off the metal, and the combined thickness both layers require — are what modern ceramics were engineered to solve. A sound existing PFM should be left alone. A new PFM is simply chosen less often now that materials exist which do its job with fewer trade-offs.
Gold — the quiet benchmark
Cast gold deserves its paragraph. It's tough without being brittle, wears at nearly the rate of enamel, is kinder to opposing teeth than any ceramic, works in thin sections, and its longevity record is measured in generations. What it can't do is look like a tooth, which is why it survives mainly on hidden back teeth for patients who prioritize function — a choice I respect whenever it's made.
The comparison, in one table
| Material | Strength/toughness | Esthetics | Bonds? | Kind to opposing teeth | Repairable in mouth | Typical home |
|---|---|---|---|---|---|---|
| Zirconia (high-strength) | Highest | Modest (opaque) | Limited | Good when polished | Limited | Molars, heavy bites, bridges |
| Zirconia (esthetic) | High | Good | Limited | Good when polished | Limited | Crowns needing strength + looks |
| Lithium disilicate | Moderate-high | Excellent | Yes — its superpower | Good | Limited | Onlays, veneers, esthetic crowns |
| Resin-ceramic hybrids | Moderate | Good | Yes | Very good | Yes | Selected onlays, wear-sensitive spots |
| Milled/printed resin | Moderate | Good | Yes | Very good | Yes — easiest | Provisionals, transitional, selected definitive |
| PFM | High | Moderate | Conventional cement | Porcelain can wear enamel | Limited | Existing work; selected new cases |
| Cast gold | High (tough, not brittle) | None (metal) | Conventional cement | Best of all | N/A — rarely needs it | Hidden molars, heavy grinders |
Simplified for orientation — formulations vary, and the row that fits your tooth is a clinical judgment, not a lookup.
So why doesn't everyone get the strongest one?
Strength solves one failure mode. Teeth offer several.
Run the logic on a real decision. An upper front tooth needs a crown: the strongest zirconia would essentially never break there — and would look like a beautiful piece of the wrong tooth, because front teeth fail esthetically long before they fail structurally. Lithium disilicate wins. A second molar in a grinder's mouth reverses it: nobody sees it, forces are enormous, and toughness is the whole job. High-strength zirconia, or for the right patient, gold. A premolar onlay needs a material that bonds, because adhesion is the onlay's entire mechanism — which is why the strongest non-bondable options never even make that shortlist, as our filling, onlay, or crown guide explains.
And in every case, the mouth itself votes: available thickness, what the opposing tooth is made of, gum position, and the forces recorded across the whole bite. The mouth is a hostile environment — heat, acid, enzymes, and hundreds of pounds of force — and the material is chosen for the case, not pulled from the drawer. That sentence has been house philosophy here long enough that we wrote it up separately.
Myth vs fact
- Myth: Zirconia is the premium option, so it's what I should want. Fact: Zirconia is the toughest option. On teeth where esthetics or adhesion lead the priorities, a glass ceramic is often the genuinely better material at similar cost.
- Myth: Metal-based crowns are obsolete. Fact: Sound PFMs should stay right where they are, and gold remains the kindest material to opposing teeth ever used in dentistry. Fewer new ones are made; that's different from obsolete.
- Myth: The material determines how long the crown lasts. Fact: The tooth underneath, the seal at the margin, the bite it lives in, and the hygiene around it usually decide longevity. Material failures are real but rank behind all of those — a theme covered in why dental work fails.
- Myth: Newer materials are always the safer bet. Fact: Newer materials are options with shorter track records. Sometimes that trade is right, sometimes the forty-year material is. The reasoning should be visible either way.
When to see a dentist
If a crown or onlay is on your treatment plan and the material hasn't come up, it's a fair question to raise — not because anything improper is happening, but because the answer reveals the reasoning. "Zirconia, because this molar takes heavy force and looks don't matter back there" is a plan. So is "lithium disilicate, because we can bond it and keep more of your tooth." What you're listening for is a match between material and situation. That's the conversation we have at every crown visit, and it's part of what a second opinion examines on larger plans.
Summary
Crowns and onlays are made from a real menu: zirconia in its strong and pretty variants, lithium disilicate and its glass-ceramic relatives, forgiving hybrids and resins, and the veteran PFM and gold. Each material is a bundle of trade-offs across strength, beauty, thickness, bondability, wear behavior, and repairability, and the bundle has to match the tooth — its location, its remaining structure, its opponents, and the bite it lives in. The right question for your dentist is never "what's the best material?" It's "why this material, for this tooth?"