Inlays and Onlays

What Inlays and Onlays Are

An inlay and onlay dental lab produces indirect restorations that rebuild part of a posterior tooth rather than covering it completely. An inlay fits within the prepared cavity between the cusps, while an onlay extends over one or more cusps to restore a wider area, and both are made outside the mouth and then cemented into place. KC Dental Lab supports these workflows by reviewing the preparation, margin design and occlusion before the restoration is designed, so the delivered unit seats accurately and supports the remaining tooth structure.

The distinction between an inlay and an onlay matters because it changes the amount of coverage the restoration provides. An onlay carries more of the occlusal load and protects weakened cusps, while an inlay stays within the walls the clinician has prepared. Because both are indirect, the review stage confirms margin clarity, isthmus width and wall thickness before production. Each unit is checked against the preparation and the supplied bite record so that proximal contacts and occlusal contacts follow the clinician’s plan rather than an approximate fit.

Who It Suits

This service suits clinicians, laboratories, distributors and dental groups that want conservative posterior restorations delivered to a written prescription. It is appropriate where the treating clinician assesses the remaining tooth structure and the laboratory reproduces the design from the supplied records. The model also helps practices that want to place esthetic posterior work externally while keeping patient contact and clinical decisions in house. Laboratory partners can manage uneven demand by outsourcing inlay and onlay fabrication while retaining the prescription and shade choices, and a single-unit trial case shows how the laboratory reads margins and contacts before a larger batch is committed.

• Clinics restoring posterior teeth conservatively
• Laboratories outsourcing ceramic inlay and onlay fabrication
• Distributors and agents serving restorative-focused practices
• Dental groups standardising a posterior restoration protocol

Indications Commonly Considered

Inlays and onlays are usually considered where a posterior tooth has enough sound structure to support a bonded restoration. Typical requests include the following.

• Posterior teeth with sufficient remaining structure
• Replacement of failing or discolored direct restorations
• Conservative cavity preparations that do not need a full crown
• Onlay cases where one or more cusps need coverage
• Cracked-tooth cases where cusp protection is indicated
• Cases where a digital or conventional route is available

Material and Design Options

The material and design choices for an inlay or onlay follow the remaining tooth structure and the loading the restoration must carry. A ceramic option suits a visible posterior tooth where appearance matters, while zirconia is selected where higher strength is preferred. The design itself is defined by whether the restoration stays within the cavity walls or extends over one or more cusps, and the options below describe how those choices are specified before production begins.

• Lithium disilicate for an esthetic posterior restoration
• Zirconia where higher strength is preferred
• Inlay design for coverage within the cavity walls
• Onlay design where cusp coverage is indicated
• Cut-back layering, staining and characterization for visible areas

What the Case Needs

A complete submission shortens the review stage and reduces the risk of a remake. The following details help the laboratory plan the restoration accurately.

• Tooth number and whether an inlay or onlay is intended
• Preparation records showing the margin and remaining walls
• A bite registration for the occlusal relationship
• Target shade and notes on the adjacent teeth
• Isthmus width and wall thickness information where relevant
• Any characterization or esthetic request stated before production

Digital Workflow Requirements

• STL, PLY or OBJ scan with clear, continuous margin capture
• Opposing arch and a bite registration for occlusion
• Adequate isthmus and wall thickness in the preparation
• Notes on the intended inlay or onlay design
• Shade and surface references where esthetic match matters

Compatibility to Confirm

• Whether the case suits an inlay or requires onlay coverage
• Material selection against the loading the tooth will carry
• Whether a digital or conventional workflow is intended
• Margin position and clarity before the case is accepted

Quality Checkpoints

Every inlay and onlay passes a defined set of checkpoints before dispatch, because an indirect posterior restoration depends on fit, contacts and occlusion as much as on appearance. The reviews below confirm that the unit seats correctly, respects the remaining tooth structure, and follows the supplied bite record, and any point that cannot be confirmed is raised with the requesting party rather than assumed.

• Marginal and internal fit checked against the preparation
• Proximal contact tightness assessed against the adjacent teeth
• Occlusal contact distribution matched to the bite record
• Thickness and structural integrity confirmed for the design
• Surface finish, polish and cleanliness reviewed
• Prescription consistency checked before packaging

Turnaround Variables

Inlay and onlay scheduling depends on the material, the unit count and confirmation of margin and occlusion details rather than a fixed interval. Ceramic and zirconia routes each follow different internal steps, and any cut-back layering or characterization adds bench time. Margin clarity and the completeness of the bite record both shape the confirmed schedule, because an unclear preparation may need clarification before production.

Where several posterior units are submitted together, additional review time is reflected in the confirmed timing. A single-unit case usually moves through fewer stages than a quadrant of restorations, and the schedule is confirmed once the prescription, files and shade information are complete. KC Dental Lab discusses the expected sequence with the requesting party before production begins, and reports any record issue that could affect the result.

Common Questions

How is an inlay different from an onlay?

An inlay sits within the prepared cavity and stays between the cusps, while an onlay extends over one or more cusps to cover a wider area. The choice follows the remaining tooth structure and the loading the restoration must carry.

What material is used?

Inlays and onlays are commonly produced in lithium disilicate or zirconia, with the selection following the esthetic target and the strength required. The clinician confirms the material on the prescription.

Are digital scans supported?

Open digital scans in STL, PLY or OBJ are supported when margins are continuous and the bite record is supplied. Scanner compatibility is confirmed before the first case.

What if the margin is unclear?

An unclear margin may need clarification before production, because the fit of an indirect restoration depends on a well-defined preparation. Record quality is reviewed at the intake stage.

Next Step

Send your inlay or onlay case files with preparation records, a bite registration and the target shade so the design can be reviewed before production. You can review the crown and bridge workflow or the E.max crown service for related cases, read the cementation guide for delivery context, or send a case to start a review.