Filling, inlay, onlay or crown: how is the choice made?

A cusp is one of the raised parts of a back tooth's chewing surface. Its strength depends on the supporting tissue underneath as well as its appearance. Decay, earlier preparation or a fracture can leave it less able to tolerate repeated loading. Filling the central space does not necessarily address that weakness.

The dentist examines the distribution of surviving enamel and dentine, the supporting ridges between surfaces and any suspected crack. Two defects of similar width may leave quite different structures. A percentage of missing tooth, quoted without this context, is not a complete way to choose a restoration.

An old restoration may hide part of the condition until it is removed. The initial plan may therefore be provisional. Ask what could change during treatment and what the alternatives would be if more decay, a crack or a weak wall is found. This is particularly relevant when comparing proposals made only from photographs or a brief scan.

The CARES clinical concept considers cusp coverage, adhesion, resistance form, appearance and subgingival management together. It is a clinical framework for decisions, not a trial proving that every tooth meeting one size threshold needs an onlay or crown.

An indirect restoration is fabricated outside the prepared cavity, in a laboratory or through an appropriate digital workflow, and then fitted and attached to the tooth. An impression or scan records the preparation. Depending on the system and work needed, a temporary stage or more than one appointment may be involved; the word digital does not guarantee a single-visit treatment.

An onlay may cover a weakened cusp while retaining other sound surfaces. An overlay usually describes broader chewing-surface coverage. These designs can offer protection without full circumferential preparation in selected teeth. The surfaces available for bonding, material thickness, margin location and biting contacts all influence whether that is feasible.

Indirect treatment still requires tooth preparation. It is not automatically non-invasive, and a smaller-looking restoration is not necessarily suitable if the supporting structure or attachment conditions are poor. Ask what sound tissue will be removed for the design and why that removal is needed.

The ADA review of indirect restorative materials explains that materials differ in mechanical properties, processing and clinical indications. Ceramic, composite and metal-based restorations are not interchangeable simply because they can be made to the same colour or shape.

The pulp is the living tissue inside the tooth. Deep decay, symptoms and test findings may require a separate decision about its condition. A large filling does not automatically require root canal treatment, and a new crown does not itself treat internal infection. Selected vital teeth may be candidates for pulp-preserving care, as explained in the deep-cavity guide.

After root canal treatment, the tooth still needs a coronal seal and structural restoration. The important factors include tissue already lost to decay and previous work, the access opening and surviving cusps. The root filling is not a reason to ignore these details and prescribe the same crown for every tooth.

A relatively intact front tooth may be restored differently from a heavily damaged back tooth. Where a back tooth needs cusp protection, an onlay may be considered in selected circumstances as well as a crown. The separate guide to crowns after root canal treatment addresses posts, remaining structure and the timing of that restoration.

If further canal treatment may be needed, access through an existing or proposed restoration also belongs in the plan. It is helpful to know whether a restoration is definitive or provisional and whether the tooth's diagnosis is settled sufficiently to proceed.

Studies often include teeth with different amounts of damage, and those differences influence both the restoration chosen and its outcome. A crown placed on a severely compromised tooth is not directly comparable with a small filling on an otherwise intact tooth. Reported years of service are not a warranty for another patient.

A 2024 systematic review comparing onlays and crowns for substantial posterior defects found only three studies meeting its criteria. The evidence was too limited and heterogeneous to establish a dependable universal winner. Descriptions of potentially different failure patterns were relevant, but did not justify prescribing an onlay for every large restoration.

A 2024 review of direct and indirect composite restorations included five randomised trials. Its pooled result favoured direct restorations for failure risk, but the certainty was very low and the trials had high risk of bias. That finding should not be rewritten as proof that indirect restorations are unnecessary, or that every larger cavity is best managed directly.

For root-treated posterior teeth, a 2024 systematic review reported comparable survival findings for full coverage and partial bonded porcelain restorations across included studies, while noting the limited evidence for the partial approach. The practical decision still needs the actual tissue loss, attachment conditions and follow-up considered.

Age, staining or a material's appearance is not a diagnosis of failure. The dentist assesses recurrent decay, fracture, unacceptable margins, symptoms, contact and function. A superficially discoloured but serviceable restoration poses a different question from a broken cusp or an open defect trapping food.

Ask whether monitoring, polishing or repair is appropriate before removing an entire restoration. Sometimes complete replacement is necessary; preserving defective work at any cost is not the goal. The reason and extent of intervention should be explained. The old-filling guide looks specifically at those choices.