Metal Inlay & Onlay Fabrication | Istar Dental Lab

When a Metal Inlay or Onlay Is the Right Choice

Inlay vs. onlay vs. crown

The decision follows how much sound tooth structure is left:

Our indication for a cast inlay is a small-to-moderate posterior defect that does not involve the cusp tips, with sufficient remaining tooth structure, a healthy pulpal wall, and the defect confined to the proximal surfaces or the occlusal fossa. Where a cusp is undermined, the case moves to an onlay. Where almost nothing is left above the gingival margin, a crown is the more honest recommendation — we will say so rather than press an onlay into a case it does not suit.

Metal vs. direct composite

Two large, independent datasets support the durability of cast gold:

• A retrospective evaluation of 1,314 cast gold restorations placed by a single practitioner and followed for 1 to 52 years reported an overall survival rate of 95.4%, with 97% still in service at 9 years. Most of the restorations had been cemented with zinc phosphate.
• A 2023 systematic review and meta-analysis compared intracoronal gold restorations with indirect resin composite and found that the composite restorations failed at a rate roughly 18 percentage points higher over 5–7 years of service.

That second finding needs its caveat stated plainly: the review's own authors rated the underlying evidence as limited and the observation window as short. Gold is not a magic material — it is simply the material with the longest and densest clinical record behind it.

Alloy Selection: Noble, Base Metal and What It Means

How alloys are classified

Dental casting alloys are grouped by their noble-metal content. The categories used in North America are set out in the ADA guidance on materials for indirect restorations:

The material requirements these alloys have to meet — mechanical properties, corrosion behaviour, release of metal ions, packaging and labelling — are specified in ISO 22674:2022, Dentistry — Metallic materials for fixed and removable restorations and appliances.

What actually drives the choice

The single most relevant property of a casting alloy for biologic safety is how much it corrodes — not simply whether it is labelled "precious". A review of the biocompatibility of dental casting alloys makes this point directly: systemic and local toxicity, allergy and carcinogenicity all follow from elements being released into the mouth during corrosion, and the practical conclusion is to prefer high-noble or noble alloys with low element release. The same review notes that nickel and cobalt have a relatively high potential to cause allergy, and that it is prudent to avoid alloys containing them where possible.

In practice, the trade-offs look like this:

• High-noble gold or platinum alloys — corrosion-resistant, easy to finish and burnish, and the best-supported choice for margins and long-term evidence. Visible, so normally limited to posterior teeth.
• Noble palladium-silver alloys — good corrosion behaviour, harder than gold, more economical. Palladium is worth thinking about separately (see the allergy section below).
• Cobalt-chromium — the strongest and most economical option, but much harder to adjust and polish, and the least esthetically forgiving.

The alloys we actually cast

Our casting alloys are cobalt-chromium, palladium-silver, gold and platinum. None of these is a nickel-based alloy. We will supply the exact elemental composition of the alloy used on your case on request — worth asking for if a patient has a documented metal allergy, because under ADA/ISO labelling conventions an alloy sold as "nickel-free" may still contain a trace of nickel below the labelling threshold, and "high noble" does not automatically mean "palladium-free".

How We Make Them: Casting and Milling

Lost-wax casting

Lost-wax casting is our primary route for metal inlays and onlays, and it is still the standard industrial method for casting precision dental restorations: a wax pattern is formed, invested, burned out, and the molten alloy is cast into the mould before finishing and polishing. It is the same fundamental process described in the casting chapter of a standard dental materials text.

In our production line the sequence is:

1. Scan the model or import your intraoral scan
2. Design the restoration in CAD
3. Produce the pattern (printed resin or milled wax)
4. Invest and burn out
5. Cast the alloy
6. Divest, cut the sprue, finish and polish
7. Inspect and pack

The reason we keep casting alongside milling is that wax and molten alloy are not limited by the diameter of a cutting bur. Narrow concavities, sharp internal angles and fine detail can be reproduced that a mill physically cannot reach. PFM metal frameworks are produced by casting and by milling, and both routes run on the same line.

CAD/CAM milling

We mill metal restorations from cobalt-chromium and other millable alloys. Milling removes the waxing, investing and casting steps, which makes the workflow more repeatable and easier to schedule, and it lets us store and re-cut a design if a unit has to be remade.

Does milling actually fit better than casting?

This gets asserted in both directions, so it is worth looking at the evidence rather than the marketing. A systematic review and meta-analysis of single metal copings compared milled copings with lost-wax cast copings and found similar overall marginal and internal accuracy between the two, with lost-wax casting showing better absolute marginal-gap results in the pooled analysis. There was no clear overall precision advantage for CAD/CAM.

The Honest Picture on Longevity

What the studies show

Cast gold inlays and onlays have one of the longest clinical records of any indirect posterior restoration. Three cohorts, reported separately:

Why they fail

When cast metal restorations do fail, the cause is usually biological or retention-related rather than bulk fracture. In a dental-school series of 3,518 cast gold restorations, the reasons recorded were secondary caries (33.7%), loss of retention (32.7%), endodontic problems (29.6%), insufficient marginal adaptation (3.1%) and extraction (1%). The Norwegian cohort above reported a similar pattern — secondary caries 41.3%, lost inlay 25.4%, fracture 23.8%.

Design, Thickness and Preparation Requirements

Minimum thickness

The material has to be thick enough to survive the load, and the numbers are not negotiable. Our working minimums are:

• Anterior: 0.5–1.5 mm depending on the material
• Posterior: 0.8–2.0 mm depending on the material

For metal substructures we check an as-cast thickness of 0.3–0.5 mm with calipers, and where a metal framework carries veneering ceramic, the porcelain is built to a controlled 1.0–1.5 mm anterior / 1.5–2.0 mm posterior so it is neither starved nor over-thick at the load-bearing areas.

Margin design

High-strength materials, including gold alloys, are prepared with a shallow chamfer or a feather edge. The margin should be continuous and clearly readable on the scan — that is a preparation requirement, not a laboratory one, and it is the single most common reason we have to ask for a rescan.

What we need with the case

For a routine fixed case, the essentials are the physical impression and bite registration, or the intraoral scan data. For inlays and onlays specifically:

• Scans: STL, PLY, OBJ, DCM and native CAD design files. We work with 3Shape TRIOS, Medit, iTero, CEREC, Shining3D Aoralscan and Planmeca, and with any scanner that exports standard open formats.
• Conventional impressions: addition-cure VPS (our preferred material), condensation silicone and polyether, supported by stone models, sectioned models with dies, implant models or 3D-printed resin models.
• Occlusion: the opposing arch, the prepared arch, and a bite registration, plus the adjacent two or three teeth around the preparation.
• Identification: a patient name is not required. A clinic case number is enough, as long as it identifies the case unambiguously.
• Occlusal space: if space is tight, please note it on the prescription and tell us the remaining thickness so we can flag reduction or a thinner-section design.

If you want to see the design before we mill or cast, ask for design approval — we will send the design file for sign-off, but it adds 1–2 days to the schedule. Preferences you set once — occlusal feel, contact tightness, margin handling — are recorded against your account and applied to later cases, and any change has to be confirmed in writing to take effect.

Cementation and Surface Treatment

Conventional cementation or adhesive bonding?

This is one place where metal differs from glass-ceramic. Within our own protocol, resin-bonded adhesive cementation is used for E.max and veneers, while zirconia, PFM and metal restorations are considered better suited to conventional cementation. That fits the material logic: a well-retained metal inlay on a sound preparation does not depend on adhesion for retention, and conventional cementation is far less sensitive to moisture control than an adhesive protocol.

If you do want to bond a metal restoration, the adhesive gap should be controlled to 20–50 µm, with the surfaces clean and dry, uniform seating pressure, and full removal of excess cement before curing.

The cement itself should match the alloy, the retention form of the preparation and the isolation you can actually achieve in that quadrant rather than following a single default.

Surface preparation

Metal surfaces that will carry ceramic are prepared by abrasive blasting with a dedicated blasting medium such as alumina at a controlled pressure, followed by ultrasonic cleaning to remove oils and residue, and then pre-oxidation in a vacuum or inert-gas atmosphere to develop the oxide layer that the ceramic bonds to.

Finished metal restorations are polished in graded steps — coarse grinding, fine grinding, then polishing compound — followed by blasting, ultrasonic cleaning and steam blasting to remove all dust and oil before packing.

Preventing cross-contamination

Different alloys are processed in zoned areas with dedicated tools and separate blasting and polishing equipment, with segregated recycling and strict cleaning between jobs, so that alloy composition stays stable and the case remains traceable. Recycled casting alloy is used only up to a capped proportion of the charge, topped up with new alloy to the manufacturer's specification, with periodic composition testing to confirm that mechanical properties and biocompatibility are unaffected.

Allergy and Biocompatibility

Nickel

Nickel is the most common metal allergen in dentistry. In a patch-test analysis of patients who already had metal restorations, nickel produced the highest positive rate at 22.8%, and women reacted significantly more often than men to both nickel and palladium.

That is the reason we do not cast nickel-based alloys, and the reason we ask you to tell us about a documented allergy before we start rather than after. If a patient has reacted to jewellery, watch backs or metal spectacle frames, say so on the prescription.

Palladium

Palladium deserves its own line, because "palladium-silver" is a noble alloy and it is easy to assume noble means problem-free. A review of palladium allergy found that palladium contact allergy is nearly always seen together with nickel allergy, because the two metals cross-react, while palladium sensitisation without nickel sensitisation is uncommon. So nickel allergy is a flag to look at the palladium content too — and a high-noble alloy can still contain palladium.

If you need to go further

For a fuller clinical picture of reactions to dental materials — including why patch testing has a limited role in choosing replacement materials, and that cobalt-chromium allergy in the mouth is rare — the Australian Dental Association's clinical spotlight on dental material allergies is a useful, readable summary.

Turnaround Times

• Routine fixed restorations, including inlays and onlays: 2–3 days from receipt of complete data.
• Complex implant or full-arch cases: 5–7 working days.
• Design approval, if requested: adds 1–2 days.

Three things define "the clock": it starts when we have complete data, not when you send the first file; time spent waiting on your design approval or on a reply to a question is excluded; and we do not produce over Chinese weekends and public holidays.

Rush cases are not surcharged while your monthly rush volume stays under 10 units. Above that we will quote it as a separate arrangement rather than quietly absorb it or quietly drop it.

Cases ship by DHL, FedEx, UPS and SPIDER, with DHL as our usual international carrier. If you would rather use your own account, or ship under ours, either works.

Quality Control

Every case passes three inspection points:

Incoming check of the case data and prescription

In-process spot checks between production stages

Final inspection, released by a dedicated QC technician who does not produce the work and is independent of the technicians who made it

The final check covers margin fit, internal surface quality, seating and passive fit, contact tightness, centric/protrusive/lateral occlusion, form and contour, and polish, all against the confirmed prescription.

Our final-inspection first-pass rate is about 95% — that is the proportion of cases released at the first final inspection, excluding anything that failed once and was corrected before dispatch. Our overall rework rate, including customer complaints and internal non-conformances, is 2–3%, tracked per customer and analysed case by case to bring it down.

Casting, printing and heat-treatment equipment is validated through installation, operational and performance qualification — furnace temperature uniformity, vacuum and protective atmosphere, dimensional and porosity checks on test coupons, and mechanical verification of stress relief.

Rework and Warranty Policy

We would rather set this out precisely than leave it to be argued about later.

Free rework — our responsibility: margin void, open contact, high occlusion, a restoration that will not seat, wrong shade, an obvious esthetic defect, or poor form. Transit damage is also covered free if it is reported within 24 hours with an unboxing video showing the courier waybill, the damaged unit and the original packaging kept intact.

Not free: a change of shade or material requested by the clinician, or a request to proceed with an impression you already know is deficient. A case built on an impression the clinician flagged as poor is a clinical decision, and we will build it if you ask us to — but it is not a workmanship failure on our side.

How the process runs: problems should be reported within 24 hours of receipt. Every rework starts with a root-cause analysis and confirmation of the cause with you before anything is remade, because remaking a case without knowing why it failed simply repeats the failure. Free rework does not cover return shipping or implant component costs. If repeated reworks still fail to resolve the case, we will refund rather than keep cycling it.

Please try the restoration in before you cement it. Once a metal inlay is cemented, we cannot evaluate the fit, and a claim becomes very hard to resolve fairly for either side.

Regulatory Status

For the United States, our custom dental restorations — including inlays and onlays — are covered by FDA establishment registration and product listing. The scope covers custom crowns, fixed bridges, inlays/onlays, veneers, custom implant abutments, implant-supported frameworks, full and partial dentures and temporary restorations; it does not cover the implant body itself. The relevant regulatory framework is the Class II Special Controls guidance for dental noble metal alloys.

For the European Union, custom-made dental restorations are risk-classified as Class IIa but do not go through ordinary Notified Body certification. They follow the MDR Annex XIII custom device route: a custom-made device statement is issued per case under the prescribing dentist's written prescription, and the custom device notification is lodged with the EU competent authority, with technical documentation retained and an authorised representative assisting with EUDAMED reporting. Standardised, mass-produced IIa dental consumables, Class III custom implantable devices and the implant body itself are all outside that scope.

Our Facilities and Capacity

We are a manufacturing laboratory, not a trading company. Design, casting and milling, finishing and inspection all happen at our own sites in Shenzhen and Huizhou, which means no third-party handoffs and no waiting on a subcontractor's queue.

• Founded: 2012
• Team: approximately 460 staff — about 100 in design, 70 in milling, 70 in the ceramic and metal group, 25 in QC, plus coordination and a backup pool of roughly 50 to absorb peak-season load
• Capacity: in low season, about 8,000 zirconia single crowns per month; in peak season, about 15,000, alongside bridge, All-on-X and removable volume on the same lines
• Metals: casting alloys of cobalt-chromium, palladium-silver, gold and platinum, plus Bego alloys for PFM
• Experience: 50 dental laboratories, 100 clinics and 400 directly partnered dentists to date
• Markets: the United States, the Netherlands, Germany, France, Belgium, Austria, the United Kingdom, Luxembourg and Switzerland

Visits to the production floor are welcome, and we can arrange a video factory tour for overseas clients.

Frequently Asked Questions

Do dentists still place metal inlays?

Yes, though not in the numbers they once did. The shift has been driven mainly by esthetics and by same-day workflow economics rather than by any clinical inferiority of cast metal. When dentists discuss the choice for their own teeth, the durability argument still comes up repeatedly — a long-running thread in r/Dentistry on whether they would choose a filling or an inlay/onlay for themselves contains the common view that a well-made inlay/onlay should outlast a composite filling, along with the equally common caveat that it is more technique-sensitive.

Will the metal be visible?

Yes. A cast metal restoration is fully visible, which is why we treat it as a posterior-material decision and will say so if the restoration would sit in a visible area. For anterior teeth or an exposed buccal cusp, a ceramic or composite option is usually the better answer, and we would rather tell you that than fill the order.

Can a metal inlay cause a metallic taste or a galvanic reaction?

It can, when dissimilar metals sit in contact in the mouth. Practical ways to reduce the risk: keep to one alloy family where several restorations are present, and avoid placing a cobalt-chromium restoration directly against a high-noble gold one. High-noble and noble alloys have low galvanic potential. A persistent metallic taste without dissimilar metal contact is worth investigating as corrosion or allergy rather than ignoring.

How should patients maintain them?

No special regime is needed. Normal brushing, daily flossing and routine professional cleaning are enough. The metal does not stain or discolour. The one thing worth telling patients is not to use the tooth as a tool — opening packaging with a restored molar is a common way to fracture the tooth around an otherwise intact inlay.

Can an existing metal inlay be repaired or replaced?

A debonded inlay can often be re-cemented if both the preparation and the restoration are still intact. A fractured or worn one usually needs replacing. We can make a replacement from a new impression without needing the original inlay back, and if you tell us the alloy of an existing restoration we will match the family.

Request a Quote

To price a metal inlay or onlay case, tell us:

1. Alloy — cobalt-chromium, palladium-silver, gold or platinum, or "your recommendation"
2. Case type and units — inlay or onlay, surfaces involved, and how many units per month you expect
3. Turnaround — standard 2–3 days, or rush, with your monthly rush volume

Send it through your account manager, by email or on WhatsApp, or through the enquiry form on this site. If you are evaluating us for the first time, we will build a single sample unit so you can judge the fit and finish on a real case before committing to volume — contact us to arrange it.

Further Reading

Where this page makes a clinical claim, the source is linked at the point of the claim. The following are additional general references you may find useful:

• American College of Prosthodontists — Inlays and Onlays
• Cleveland Clinic — Dental Fillings: Types and Materials
• MouthHealthy (ADA) — Fillings (Gold Inlays)
• British Dental Journal — Dental material allergies and oral soft tissue reactions