When an onlay may be discussed for a broken filling
Many broken fillings can be replaced with a new direct filling. An onlay enters the conversation when the remaining tooth walls are thin, a cusp has broken or cracked, the filling is already large or has failed repeatedly, or the dentist wants the restoration to cover and hold the weak cusps rather than sit between them.
The exam, not the size of the hole alone, decides.
What changes the answer
How much sound enamel and dentin remain, whether a crack is present (AAE), decay under the old filling, bite forces and grinding, the position of the tooth, and whether the nerve is healthy.
The three usual options
| Direct filling | Onlay or overlay | Full crown | |
|---|---|---|---|
| Made | In the mouth, in one piece | Outside the mouth, bonded on | Outside the mouth, cemented or bonded |
| Covers | The cavity | The cavity plus weak cusps | Everything |
| Keeps | Most tooth | Most sound walls | Least |
| Usually chosen when | Walls thick enough to support it | Walls thin or a cusp weak, but enough to bond to | Little wall remains |
The American Dental Association describes direct filling materials and when indirect restorations are used (ADA); the FDA lists options for treating decay (FDA).
What the research shows
Reviews comparing direct and indirect composite restorations in large back-tooth cavities report similar fracture resistance and mixed longevity findings, with a high risk of bias. Neither choice is automatic, so the decision rests on the tooth's findings.
Why cusp coverage matters
A thin cusp beside a large filling flexes with every bite and can crack. Covering it ties it to the rest of the tooth. The studio's biomimetic approach favors bonded restorations that keep sound structure (studio).
Questions to ask
How much wall is left? Is there a crack? Why an onlay rather than a filling, or a crown rather than an onlay? What happens if the new filling breaks again?
Next step: Request a consultation or call (805) 565-5111. A request is not a confirmed appointment; the office confirms times during its listed hours (Monday to Thursday, 8 am to 5 pm, plus select Fridays).
Filling-onlay-crown decision sheet
| Finding on my tooth | Filling | Onlay | Crown |
|---|---|---|---|
| Walls thick, no crack | Usual | ||
| One cusp thin or cracked | Usual | Sometimes | |
| Filling large or failed repeatedly | Sometimes | Usual | Sometimes |
| Little wall remains | Usual | ||
| Nerve involved | Depends | Depends | Depends |
Dentist's recommendation and reason: ________
Guides are general education; an examination is needed for individual advice.
Sources
- Six Things You Need to Know About Stress-Related Tooth Injuries Like Cracked Teeth (Aug 2021) — American Association of Endodontists
- MouthHealthy: Dental Filling Options — American Dental Association
- Treatment Options for Dental Caries — U.S. Food and Drug Administration
- Clinician statement — Loul Dental Studio
- Loul Dental Studio: Biomimetic Dentistry — Loul Dental Studio
Sources were current when this guide was last updated.
Educational content, not a diagnosis. Please contact the studio to discuss your own situation.