TREATMENTS
Fillings, inlays and onlays
A damaged tooth may need a filling, inlay, onlay or crown.
SHORT ANSWER
A damaged tooth may need a filling, inlay, onlay or crown. The aim is to restore what is lost while preserving sound tooth structure whenever possible.
Direct fillings: Composite fillings are placed directly in the tooth and can work well for many small and moderate defects when moisture control, remaining tooth structure and bite are favourable.
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Direct fillings
Composite fillings are placed directly in the tooth and can work well for many small and moderate defects when moisture control, remaining tooth structure and bite are favourable.
Inlays and onlays
Indirect ceramic or composite restorations are made outside the mouth and bonded to the tooth. An onlay can cover one or more cusps without necessarily preparing the whole tooth for a crown.
When a crown enters the discussion
If the tooth is extensively weakened, cracked, heavily restored or lacks sufficient structure for a more limited restoration, broader coverage may be considered. The choice should be based on the actual defect rather than the age of the filling alone.
Old fillings do not have an expiry date
A restoration should not be replaced simply because it is old. Marginal breakdown, recurrent decay, fracture, symptoms and structural concerns are more useful reasons for intervention.
Cuspal protection is a structural decision
When decay or an old restoration has undermined a cusp, an onlay can cover and protect that cusp while preserving other tooth surfaces. A full crown may be unnecessary if enough sound structure remains.
Cracks complicate the decision
A cracked tooth can be difficult to diagnose because symptoms may be intermittent. The extent and direction of the crack, remaining structure and pulpal status influence whether a direct restoration, onlay, crown, root canal treatment or extraction is considered.
Adhesive dentistry is technique-sensitive
Bonded restorations depend on moisture control, material selection and preparation design. “No crown” is not automatically more conservative if the smaller restoration is unlikely to survive the functional load.
Questions to ask
- What part of the tooth is actually weakened?
- Why is a filling, onlay or crown being recommended?
- Is any crack suspected?
- How much sound tooth tissue will remain after treatment?
Frequently asked questions
Is an onlay stronger than a filling?
It can provide broader coverage and cuspal protection when needed, but strength depends on indication, design and bonding rather than the name alone.
Should every old amalgam filling be replaced?
No. Replacement should be based on clinical findings such as fracture, recurrent disease or other specific concerns.
The border between filling and onlay is not a fixed size
Two cavities of similar size can behave differently depending on which cusps remain, how deep the defect is, whether a crack is suspected and how the tooth is loaded. That is why restoration choice cannot be reduced to a percentage of tooth loss without context.
Material choice
Direct composite, indirect composite and ceramic each have different handling, thickness and repair considerations. The material is selected after the structural design is understood—not before.
Long-term strategy
Complete replacement generally removes additional tooth tissue. If an existing restoration can be repaired predictably rather than completely replaced, that option may preserve structure. A conservative philosophy therefore includes repair when appropriate, not only smaller first-time restorations.
References and verification links
- FDI policy statement: repair of restorations
- Survival and Complication Rates of Ceramic Partial Coverage Restorations (PCRs) and Ceramic Laminate Veneers Made of Different Types of Ceramics. Consensus Statement From SSRD, SEPES, and PROSEC Conference on Minimally Invasive Restorations (2025)
- https://www.ada.org/resources/ada-library/oral-health-topics/materials-for-indirect-restorations
- Survival and Success Rates of Endodontically Treated Teeth Restored with Full Veneer Crowns or Full Cuspal Coverage onlays: A Systematic Review (2024)
- Accuracy of Intraoral Scanner Systems for Fabricating Inlay, Onlay, and Veneer Restorations: A Systematic Review and Meta-Analysis (2024)
- Restorative and Periodontal Outcomes of Deep Margin Elevation in Posterior Teeth: A Systematic Review (2025)
- Effect of Deep Margin Elevation on the Pulpal and Periodontal Health of Teeth: A Systematic Review (2024)
- Survival of direct resin composite onlays and indirect tooth-coloured adhesive onlays in posterior teeth: a systematic review (2022)
- Long-term Clinical Performance of Composite Resin or Ceramic Inlays, Onlays, and Overlays: A Systematic Review and Meta-analysis (2021)
- Remaining Tooth Structure and Prognosis of Restored Endodontically Treated Teeth: A Systematic Review (2025)
This page provides general information and does not replace an in-person dental examination, diagnosis or an individual treatment plan.