Crown, Onlay, or Filling: Why Your Dentist Chose That Restoration
A filling, onlay, and crown all "fix" a damaged tooth — but they cover different amounts of structure and last different lengths of time. The choice isn’t opinion; it’s how much healthy tooth is left. Here’s the rule your dentist is following.
In short
Roughly: if less than 50% of the tooth’s coronal (visible) structure is damaged, a filling or inlay is enough. Between 50% and 70% damage, an onlay that partially covers the cusps is the right choice. More than 70%, or a tooth that has had a root canal, needs a full crown. This isn’t arbitrary — it’s based on how much healthy tooth must remain to resist biting forces without fracturing. Your dentist assesses this when looking at the cavity after clean-out.
The 50% threshold — the rule behind the choice
Roughly: if less than 50% of the tooth’s coronal (visible) structure is damaged, a filling or inlay is enough. Between 50% and 70% damage, an onlay that partially covers the cusps is the right choice. More than 70%, or a tooth that has had a root canal, needs a full crown. This isn’t arbitrary — it’s based on how much healthy tooth must remain to resist biting forces without fracturing. Your dentist assesses this when looking at the cavity after clean-out.
Filling — the least invasive option
A composite (tooth-coloured) or amalgam (silver) filling places material directly into the prepared cavity and cures in the chair. No lab, one visit. Cost in Muscat: OMR 25–55 depending on surface count. Lifespan: 7–10 years for composite with good hygiene; amalgam often 15–20 years but aesthetically dated. Appropriate for cavities that haven’t undermined the cusps of the tooth. No dentist should drill beyond the damaged tissue to "make room" for a bigger restoration than the cavity needs.
Inlay and onlay — the middle ground
Inlays (inside the cusps) and onlays (covering one or more cusps) are lab-fabricated ceramic or gold pieces bonded into the tooth. They’re stronger than a large composite filling and more conservative than a crown. Cost in Muscat: OMR 140–220. Lifespan: 15+ years for ceramic onlays. Ideal for medium-to-large back-tooth cavities where a filling would be too weak but a crown removes more tooth than the damage justifies. Underused in Oman because they need a good ceramist and an extra visit; many clinics jump straight to crowns.
Crown — when the tooth needs wrapping
A crown covers the entire coronal portion of the tooth and is the right answer when structure is so compromised that any biting force would split the remaining tooth without full coverage. Required: after a root canal (the tooth is dried out and brittle), severe cracks, very large old fillings that have fractured, and teeth worn below the gum line. Cost in Muscat: OMR 160–280 depending on material (see our separate article on crown materials). Lifespan: 15–20+ years.
What to ask if you’re being sold a crown
If a dentist recommends a crown when you feel your cavity isn’t huge, ask three questions. One: "Can I see a photo of the cavity after cleaning, before preparation?" A legitimate clinician will show you. Two: "Would an onlay work instead?" A good dentist will have already considered this. Three: "What’s your plan if we try a large composite first and it fails?" The honest answer is "we upgrade to a crown later, but we start minimal." A clinician who can’t explain why a crown is needed in your specific case is overtreating.
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