My cavity is deep. Can't it be fixed with resin?

If the damage is small and enough tooth structure remains, a resin filling often works. However, deep decay between teeth or wide damage on surfaces that take heavy chewing force may call for an inlay or crown to restore shape and strength. The deciding factor is the extent of damage and remaining tooth structure, not the material itself.

I heard inlays make teeth more likely to crack. Is that true?

It cannot be decided by material alone. The risk of fracture after restoration depends on how much tooth remains, bite force and habits such as grinding. A tooth with thin remaining walls is under strain with any material, so covering it may be considered. It is judged case by case.

Different clinics told me resin, inlay or crown. Who is right?

When the depth and extent of decay are borderline, opinions can differ. If you bring your X-rays and other records and compare the views of 2 or 3 clinics based on the same data, you can see why they differ. Still, leaving active decay untreated can lead to a root canal, so simply putting off the decision is also risky.

Does health insurance cover cavity treatment?

It depends on the material. Amalgam and glass ionomer fillings are covered, and light-cured composite resin fillings are covered for permanent teeth up to age 12. Prosthetic restorations such as inlays and crowns are generally non-covered, so the cost structure differs by treatment method even for the same tooth.

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Resin, Inlay or Crown for a Cavity: Choosing by Extent of Damage, Tooth Removal and Why Diagnoses Differ

Q: Will an inlay do, or do I need a full crown?

The turning point is whether damage has spread to the cusps (corners of the chewing surface). If it is limited to part of the chewing surface, an inlay or onlay is used. If several cusps are lost or the tooth has been weakened by root canal treatment, a crown covering the whole tooth may be considered to prevent fracture.

Published August 27, 2026 Updated August 27, 2026 Based on official HIRA and Ministry of Health and Welfare data and public sources

In the analysis of patient comments about Prosthetics: Crowns, Inlay, resin or crown formed a question cluster of about 1,100 comments. Resin, inlay or crown depends on the extent of damage, remaining tooth and whether a cusp is affected. Also covers tooth removal, insurance coverage and why clinics diagnose differently. SOURCE Analysis of patient comments on YouTube dental content (DentStat) · public sources listed under References · Data as of June 28, 2026

Key facts

Deciding factors	Extent and depth of decay, amount of remaining tooth structure, whether the cusps (corners of the chewing surface) are affected ^[1]
Amount of tooth removed	Generally resin < inlay or onlay < crown: the larger the damage, the more likely the tooth is covered ^[1]
National Health Insurance	Amalgam and glass ionomer fillings are covered; light-cured resin is covered for permanent teeth up to age 12. Inlays and crowns are generally non-covered ^[2]
Main patient sentiment	Reluctance to grind down natural teeth and a wish to save them with resin: analysis of 1,100 related comments ^[3]

My cavity is deep. Will an inlay do, or do I need a full crown?

The turning point is not the material but the extent of damage and how much tooth structure remains [1]. When decay is limited to part of the chewing surface, a partial restoration (resin or inlay) is used. When the cusps (corners of the chewing surface) are lost or the tooth has been weakened by root canal treatment, the usual approach is a crown that covers the whole tooth to prevent fracture [1]. In other words, even for the same “cavity,” the options differ with depth, extent and location [1].

When DentStat analyzed 1,100 patient comments from YouTube dental content about choosing between resin, inlays and crowns, the largest share expressed reluctance to grind down natural teeth and a wish to save them, asking “can’t it be done with resin?” [3].

How do resin, inlays and crowns differ?

The three methods differ in the range of cases they suit, how much tooth is removed and how they are made [1].

	Resin filling	Inlay or onlay	Crown
Suitable for	Relatively small cavities [1]	Medium damage: made from an impression and fitted [1]	Extensive damage, teeth after root canal [1]
Tooth removed	Relatively little [1]	As much as the cavity shape requires [1]	All around the tooth [1]
Method	Filled directly the same day [1]	Made in a lab, then bonded [1]	Made in a lab, then placed over the tooth [1]
National Health Insurance	Covered for permanent teeth up to age 12; generally non-covered for adults [2]	Generally non-covered [2]	Generally non-covered [2]

None of the three can be called better in every case. Doing a large restoration when plenty of tooth remains and holding on with a small restoration when the damage is large both carry risks [1].

I asked for resin. Why was I told it won’t work?

Resin has the advantage of removing less tooth, but it does not suit every case [1]. For deep decay between teeth or a wide cavity that takes heavy chewing force, the limits of filling material in strength and shape mean a lab-made restoration such as an inlay or crown may be considered [1]. Conversely, if the damage is small, the tooth is often saved with resin, so the depth and extent seen on X-rays are the basis for deciding [1]. The comment analysis included accounts of people diagnosed with an inlay who were then treated with resin at another clinic, as well as the reverse, which shows how judgment can differ in borderline cases [3].

Why do diagnoses differ from clinic to clinic?

When the depth of decay is borderline, opinions on how to restore it can differ [1]. Whether decay stays in the enamel or has reached the dentin, and whether the remaining walls can withstand chewing force, are judged by X-rays and visual examination. In unclear cases, both “let’s watch it conservatively” and “let’s restore it now” are possible opinions [1]. In that situation, bringing the records already taken and comparing explanations from 2 or 3 clinics on the same data can show why they differ [1]. However, leaving active decay for a long time can lead to root canal treatment or extraction, so simply putting off the decision out of distrust is also risky [1].

Common misconceptions and the facts

Concern sometimes raised	What the sources show
”Every cavity needs an inlay or crown”	When damage is small and enough tooth remains, it is often saved with a resin filling [1]
“Inlays make teeth crack, so avoid them”	Fracture risk depends more on remaining tooth structure and bite force than on material, and is judged case by case [1]
“Once a tooth is crowned, it will soon be lost”	That is not a set path. Some crowns last a long time depending on margin care and regular checkups [1]
“Resin can fix any cavity”	For deep decay between teeth or wide cavities, other restorations are considered because of resin’s limits in strength and shape [1]

Crown material choices and replacement timing are covered in the crown guide, the stages of tooth decay in the cavity guide, and regional clinic data in Find a dentist.

Frequently asked questions

My cavity is deep. Can't it be fixed with resin?: If the damage is small and enough tooth structure remains, a resin filling often works. However, deep decay between teeth or wide damage on surfaces that take heavy chewing force may call for an inlay or crown to restore shape and strength. The deciding factor is the extent of damage and remaining tooth structure, not the material itself.
Will an inlay do, or do I need a full crown?: The turning point is whether damage has spread to the cusps (corners of the chewing surface). If it is limited to part of the chewing surface, an inlay or onlay is used. If several cusps are lost or the tooth has been weakened by root canal treatment, a crown covering the whole tooth may be considered to prevent fracture.
I heard inlays make teeth more likely to crack. Is that true?: It cannot be decided by material alone. The risk of fracture after restoration depends on how much tooth remains, bite force and habits such as grinding. A tooth with thin remaining walls is under strain with any material, so covering it may be considered. It is judged case by case.
Different clinics told me resin, inlay or crown. Who is right?: When the depth and extent of decay are borderline, opinions can differ. If you bring your X-rays and other records and compare the views of 2 or 3 clinics based on the same data, you can see why they differ. Still, leaving active decay untreated can lead to a root canal, so simply putting off the decision is also risky.
Does health insurance cover cavity treatment?: It depends on the material. Amalgam and glass ionomer fillings are covered, and light-cured composite resin fillings are covered for permanent teeth up to age 12. Prosthetic restorations such as inlays and crowns are generally non-covered, so the cost structure differs by treatment method even for the same tooth.

Find a dental clinic

Compare dental clinics by area and treatment in the area shortlists, or see nationwide figures in dental clinic statistics for South Korea.

References

National Health Information Portal: Tooth Decay (Cavities) and Restorative Treatment · Korea Disease Control and Prevention Agency (KDCA)
National Health Insurance Coverage Criteria for Dental Fillings and Prosthetics (Including Coverage of Light-Cured Composite Resin) · Ministry of Health and Welfare · National Health Insurance Service (NHIS)
Analysis of Patient Comments on YouTube Dental Content: 1,100 Comments on Inlays, Resin and Crowns (Collected 2026-06-28) · DentStat (Osamil Inc.)

This content is general information based on public sources and does not replace diagnosis, prescription or treatment for any individual. If you have symptoms, consult a dentist.