Inlays and onlays are types of indirect dental restorations used to repair teeth that have been damaged by decay or trauma but do not require a full‑coverage crown. They are fabricated outside the mouth—typically in a dental laboratory—from materials such as porcelain, composite resin, or gold alloy, and then bonded to the prepared tooth.
Definition and Classification
- Inlay: A restoration that fits within the biting surface of a posterior tooth, covering the cavity walls but not extending over the cusp tips.
- Onlay: A restoration that covers one or more cusp tips in addition to the cavity walls, providing more extensive coverage than an inlay but still less than a full crown.
Indications
- Moderate to large cavities in posterior teeth where sufficient tooth structure remains to support the restoration.
- Teeth with fractures confined to the cusps that can be reinforced by an onlay.
- Situations where a crown would remove excessive healthy tooth structure.
Materials
| Material | Typical Use | Notable Properties |
|---|---|---|
| Porcelain (ceramic) | Aesthetic restorations, especially in visible areas | High translucency, excellent color match, good wear resistance |
| Composite resin | Esthetic and cost‑effective option | Polished surface, easier adjustment chair‑side |
| Gold alloy | High‑strength, long‑term durability | Superior marginal adaptation, low wear on opposing teeth |
Clinical Procedure
- Tooth preparation: Removal of decayed tissue and shaping of the cavity to create proper retention and resistance form.
- Impression or digital scan: Capture of the prepared tooth morphology for laboratory fabrication.
- Fabrication: Laboratory or CAD/CAM production of the inlay/onlay.
- Try‑in and adjustment: Verification of fit, contacts, and occlusion; minor adjustments made if necessary.
- Cementation: Bonding of the restoration to the tooth using resin-modified glass ionomer or composite luting agents.
Advantages
- Conservation of more natural tooth structure compared with full crowns.
- Enhanced strength and precision from laboratory fabrication.
- Superior aesthetics when ceramic materials are used.
Disadvantages
- Requires multiple visits (unless CAD/CAM same‑day technology is employed).
- Potential for marginal leakage if preparation design is inadequate.
- Higher cost than direct composite fillings.
Comparison with Related Restorations
- Direct fillings (amalgam or composite) are placed intra‑orally in a single appointment but may lack the strength and marginal precision of indirect restorations for larger lesions.
- Crowns encircle the entire tooth and are indicated when extensive structural loss exists; they require more aggressive tooth reduction.
Current Guidelines
Dental professional bodies (e.g., the American Dental Association, the British Dental Association) recommend inlays and onlays as conservative options for restoring premolars and molars when the remaining tooth structure can provide adequate support. Selection of material and design should be based on functional demands, aesthetic requirements, and patient preferences.
References
- American Dental Association. Guidelines for Indirect Restorations, ADA Council on Scientific Affairs, 2020.
- S. R. Sturdevant, Sturdevant’s Art and Science of Operative Dentistry, 7th ed., Elsevier, 2022.
- G. Goodacre, “Ceramic Inlays and Onlays: Clinical Outcomes,” Journal of Prosthetic Dentistry, vol. 124, no. 3, 2021, pp. 456‑462.
