2026-07-15 · 9 min
Dental inlays: what they are and when they beat a crown
A badly damaged tooth almost always has more than one technical solution. What separates a good decision from a mediocre one is a single variable: how much healthy tissue is still standing once the treatment is done. Inlays and crowns differ in material, technique, and number of appointments, but the difference that actually matters ten or twenty years out is how much tooth had to be ground away to fit them. Here's what each one is, when we prefer one over the other, and how they're made today in a single visit, with no impressions and no temporaries.
What a dental inlay is
A dental inlay (or onlay) is a restoration made outside the mouth, milled from a block of ceramic or composite, then bonded onto the prepared tooth. It replaces the destroyed part of the tooth and leaves the rest alone. There are two types, and the difference between them is purely anatomical:
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Inlay: sits inside the tooth, between the cusps, without covering any of them. It's the option when damage is confined to the centre of the tooth.
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Onlay: covers one or more cusps in addition to the inner surface. It's indicated when a wall is left too weak to withstand chewing on its own.
It makes more sense placed between the two options that flank it. On one side is the composite filling, which the dentist builds directly in the mouth, layer by layer, in the same appointment: excellent for small and medium cavities, but it loses precision at the contact point and shape stability once the cavity gets large. On the other side is the crown, which wraps the entire tooth. The inlay covers the middle ground: cavities too extensive to trust to a direct composite, in teeth still too healthy to justify a crown.
Inlay or crown: how much tooth you keep
A dental crown is a cap that covers the whole visible portion of the tooth, all 360 degrees of it. To make room for it, every surface of the tooth has to be reduced and a margin created right around it, usually near the gum. The tooth ends up as a stump onto which the crown is cemented.
That detail drives nearly everything else. An inlay removes the tissue that's already diseased, plus the minimum needed for retention and a clean margin. A crown also removes healthy enamel and dentine from every wall, including the walls that had nothing wrong with them. On a living tooth, that circumferential reduction brings the preparation closer to the pulp and raises the odds of post-operative sensitivity, or of the tooth eventually needing root canal treatment. That difference has been measured: a prosthodontics study that weighed the tissue removed by each preparation design on posterior teeth found roughly 5.5% to 27.2% of structure taken away for adhesive and inlay preparations, against 67.5% to 75.6% for complete crowns. At the extremes, the most invasive crown preparation removed nearly fourteen times more tooth than the most conservative inlay.
There's a second consequence, less visible and more important long term: the restorative cycle. No restoration lasts forever. Every time one is replaced, a little more tooth goes with it. A tooth that starts with a composite, moves to an inlay, and years later receives a crown has worked through that cycle with room to spare. One that jumps straight to a crown at thirty has no steps left at forty or fifty. Preserving structure today is preserving options tomorrow, and it's the same logic we apply when deciding between keeping a tooth and replacing it with an implant.
So when a tooth still has enough sound walls, we prefer the inlay. The crown is reserved for teeth that can no longer support a partial restoration predictably. The rule we use in the office is easy to state and demanding to apply: the most conservative preparation that solves the problem predictably.
Types of dental crowns and materials
Crown and inlay materials overlap considerably. These are the ones in routine use today:
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Zirconia: the most fracture-resistant. Used mainly on molars, in patients with heavy chewing loads, and for crowns on implants. Today's translucent versions look considerably better than the first generations, which came out opaque.
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Lithium disilicate (e.max): the most widely used balance of aesthetics and strength. Its translucency mimics natural tooth well, which makes it the first choice for visible teeth and for most premolar and molar inlays.
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Porcelain-fused-to-metal: a metal substructure covered in porcelain. It was the standard for decades and still works, but it tends to show a grey line at the margin once the gum recedes, and it demands more tooth reduction than the ceramic alternatives. We rarely indicate it now.
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Composite and hybrid ceramics: less rigid materials, useful for specific inlays and where it helps for the restoration to absorb part of the load.
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Provisional resin: the temporary crown that protects the tooth while the definitive one is made in a conventional lab workflow. It isn't a long-term solution, and in a single-visit digital workflow it simply isn't needed.
Material is chosen tooth by tooth. It depends on how much structure is left, where the tooth sits in the arch, the force it takes when you chew, and how visible it is. A molar in a bruxist patient and a premolar that shows when you smile don't get solved with the same block.
When each one is indicated
The situations that put an inlay or a crown on the table are fairly recognisable:
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Extensive decay. When the cavity is wide enough that a direct composite would be left without adequate support, the inlay restores shape and contact point with a precision the direct technique can't match. If the decay has also destroyed most of the walls, the crown becomes the sensible call.
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Fractured cusp. A molar that loses a cusp while the rest of its walls stay sound is the textbook case for an onlay: cover the compromised cusp, keep everything else. We cover the immediate handling of these situations in what to do with a broken or fractured tooth.
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Root-canal-treated tooth. An endodontically treated tooth is more brittle, largely because it has lost the roof of the pulp chamber and much of its internal structure. Covering the cusps reduces fracture risk. For years that meant an automatic crown. Today, if enough sound walls remain, a bonded onlay does the same protective job while keeping considerably more tooth. The crown remains the indication when destruction is extensive or the case needs a post.
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Wear from bruxism or erosion. Generalised wear is rarely solved one tooth at a time. Onlays let us rebuild the lost height without prepping crowns across the whole mouth, though the treatment fails if the cause goes unaddressed: bruxism or repeated contact with acidic drinks.
Same-day restorations: the digital workflow
The classic objection to inlays and crowns was time: two or three visits, an uncomfortable silicone impression, a two-week wait, and a temporary that came loose at the worst moment. The digital workflow removes that part of the problem. Here's how we work at the clinic in Vitacura, within a single appointment:
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Intraoral scan. We prepare the tooth and record it with an intraoral scanner. No tray, no silicone, and the file appears on screen immediately, so a poorly captured margin gets corrected in seconds rather than surfacing at the lab two days later.
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CAD design. We design the restoration in Exocad on the digital model, adjusting shape, contact points, and occlusion against the patient's own bite.
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In-clinic milling. The Primemill mill carves the piece from a ceramic block, lithium disilicate or zirconia depending on what the case calls for.
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Glazing and cementation. It's characterised and furnace-glazed, cemented definitively, and the occlusion is adjusted before you get out of the chair.
The full procedure takes two to three hours. No temporary, no second visit, and no lab transfer, which is historically where fit errors accumulated. The obvious doubt deserves an answer, because we get asked often: milling in the clinic doesn't compromise the result. A systematic review comparing manufacturing methods estimated 97% survival at five years and 89% at ten years for CAD/CAM restorations, in line with those made by conventional methods. The detail on the equipment, the materials, and their limits lives on the CAD/CAM and same-day restorations page. And the obvious caveat is worth stating: not every case fits into one visit. Extensive rehabilitations and high-demand aesthetics on front teeth still benefit from lab work, and we say so at the first evaluation.
How long they last
The honest answer starts by admitting that no restoration lasts forever, and that any published range is an average that may not describe your mouth. That said, the numbers support a reasonable expectation. A systematic review with meta-analysis in the Journal of Dental Research estimated 92% to 95% survival at five years (5,811 restorations) and 91% at ten years (2,154 restorations) for ceramic inlays and onlays. The most frequent failure was fracture or chipping (4%), ahead of endodontic complications (3%) and secondary decay (1%). With good hygiene and regular check-ups, both inlays and well-indicated crowns routinely work for more than a decade, and many stay in service well beyond that.
What's interesting is what moves that number, because almost all of it comes down to factors you can act on:
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How much sound tooth was there to start with. The single best predictor. A restoration on a tooth with solid walls behaves better than the same restoration on a hollowed-out one.
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The marginal seal. The point where the restoration meets the tooth is where recurrent decay shows up, and that's the most frequent reason for replacement. A margin your brush and floss can reach lasts longer than one buried under the gum.
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Bruxism. Clenching and grinding fracture ceramic, plainly. A bruxist patient without a nightguard wears down the restoration and, with luck, only the restoration.
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Hygiene and check-ups. The tooth underneath is still alive and can still get sick. Ceramic doesn't decay; the tooth holding it does.
How to care for them
Caring for an inlay or a crown looks a lot like caring for a healthy tooth, with two caveats. The first is the margin: it's the critical zone and it needs floss or an interdental brush daily, not just brushing. The second is load: if you clench or grind at night, a well-fitted nightguard is what separates a restoration that lasts ten years from one that fractures in two.
Add the predictable to that: brushing twice a day with fluoride toothpaste, keeping acid and sugar frequency in check, and regular reviews. At every check-up we look at the margin, the occlusion, and the state of the tooth underneath. Catching early leakage means we can act before decay forces a full redo of the restoration, which is exactly the step of the restorative cycle worth avoiding.
If one idea survives from all of this, make it this one: facing a damaged tooth, the useful question to ask your dentist is how much healthy tissue is coming out, why, and which more conservative alternative was ruled out. If the answer is clear and justified by the actual state of the tooth, you're in good hands. When a tooth still has enough sound walls, the inlay is usually the way: it fixes the damage and leaves the rest standing, which is what keeps your options open twenty years from now.
