One Mouth, Two Teeth, Two Restorations: An E.max Inlay and Onlay Case

The Patient Situation

The dentist sent us an intraoral scan, bite record, two shade photos (A2 target, with a VITA tab in frame), and a short note. Everything here is anatomy-level only, no PII:

• Tooth #30 (lower right first molar). Previous root canal, large MOD defect with the mesiolingual cusp undermined. Remaining mesiolingual wall measured on the scan at about 1.6 mm at the thinnest point. Buccal wall thicker, around 2.3 mm. Clean enamel ring at the gingival margin on the buccal, slightly subgingival on the distolingual.
• Tooth #29 (lower right second premolar). A failed composite with recurrent decay underneath, defect contained in the occlusal fossa and the distal proximal box. No cuspal involvement. Pulp vital. Walls thick, no cracks visible on the scan.
• Opposing teeth not supra-erupted. Minor wear facets on #30, no night-guard yet, no reported bruxism, no reported pain.
• Shade target A2, body shade, matched off #28 and #31.

So we are looking at two posterior teeth, same quadrant, same patient, same visit, but with completely different biomechanical stories. One tooth has already been through a root canal and lost cusp support. The other one is still structurally intact and only needs the hole filled with something harder and better-fitting than another composite.

This is the first thing the case page is here to show: ceramic inlays and onlays are not a single product. They are two different design intents, and the choice between them is made on remaining wall thickness and cuspal coverage, not on patient preference or price.

For #30, cusp coverage was indicated. For #29, it was not. The reasoning is lifted straight from the posterior ceramic literature on remaining cusp wall thickness, and from the clinical consensus that endodontically treated molars benefit from cuspal protection, even though dentists themselves do not always agree on when exactly it becomes mandatory.

What the Dentist Asked For

The written Rx was short. We like short. Fewer places for a dropped assumption. The requirements, decoded:

Why One Tooth Got an Inlay and the Other Got an Onlay

Here is the single call that defined the whole case. The in-house rule we work by:

An inlay is for a mid-sized posterior defect that stays inside the fossa or extends into one proximal box, with cusps still intact, pulp vital, and walls thick enough to carry occlusal load on their own. An onlay steps up when one or more cusps are undermined, when the tooth has been root-treated, or when the remaining wall is thin enough that a wedge-shaped inlay would act like a splitter on function.

For #29 the defect sat inside the fossa with the mesial marginal ridge intact and the distal box depth under 3 mm. Cusps carried load fine. A porcelain inlay onlay decision was straightforward: inlay only.

For #30 the picture was different. Root-treated molars lose structural integrity, and the mesiolingual wall was already down to 1.6 mm. That sits below the 2.0 mm minimum that in-vitro work on remaining cusp wall thickness in adhesively bonded ceramic restorations identifies as the point where enamel crack formation rises sharply under load. Leave that cusp unprotected and we are building a well-fitting ceramic wedge inside a tooth that has already lost its own support. So we extended the design, reduced the mesiolingual and distolingual cusps by 2.0 mm occlusally, and carried a butt-joint margin onto the lingual. That is an onlay.

Same block of E.max, same shade, same bonding plan. Two different envelopes.

A dental ceramic inlay and a ceramic onlay on the same patient is also a nice teaching case for the clinician's own records, because the restored teeth sit side by side on the final photo and the design logic is visible in the geometry alone.

How We Made Them

Our workflow for this case lived entirely inside our own Shenzhen facility. No outsourced step. Istar runs a full in-house line: CAD, model print, press, crystallization, stain and glaze, QC, packing. On a two-unit E.max press case, eight pairs of hands see the work before it ships, in this order: case coordinator, CAD designer, press technician, finishing technician, ceramist, glaze technician, QC inspector, packing operator. All logged, all signed.

1. Design

• Scan imported. Margins traced on both preps. Clear buccal margin on #30, slight sub-gingival wrap on the distolingual that needed careful tracing.
• Path of insertion defined. Axial wall divergence set at 10°–12°, the convergence window recommended for ceramic inlay preparations, with the box walls flaring occlusally by at least 10° so the scanner and the press can both reach them.
• Geometry is not cosmetic on a posterior unit: in molar onlays, cavity design measurably shifts stress distribution and fracture resistance. That is why the two preps were not drawn to a single template.
• Minimum thickness check:
  • #29 inlay: isthmus 2.2 mm, proximal box floor 1.8 mm, cavosurface butt joint, no bevel.
  • #30 onlay: occlusal thickness over covered cusps 2.0 mm, lingual wrap 1.8 mm, mesial box floor 1.8 mm.
• Internal line angles rounded on both. No sharp corners inside the ceramic.
• Occlusal anatomy copied from the contralateral teeth in the same arch (#19 and #20 in the submitted scan were used as morphology reference).

The design was sent for dentist approval before pressing. Approval came back the same evening. Thirty-six hours after case receipt.

2. Pressing the E.max

Press ceramic, not milled. For lithium disilicate inlays and onlays we press, because the ingot behaves more predictably at thin cross-sections than a milled bulk block. Ingot: IPS e.max Press, LT (low translucency) for a body-shade A2 posterior.

• Investing, burnout, pressing in the Programat EP press furnace.
• Divest, cut-off, light bead blasting of the surfaces that will see cement.
• Crystallization already handled inside the pressing cycle for Press ingots.
• Both units checked under 10× magnification for marginal chips. Clean on first pass.

3. Shade, stain, and glaze

Posterior shade work on E.max is where most of the final look is decided. The protocol on this case:

• Body shade A2, confirmed under D65 before and after each firing.
• Light occlusal staining in the central fossa of #30 to carry a touch of chroma into the covered cusps.
• No incisal translucency work (these are posterior units, so no translucent halo, no mamelons).
• Glaze firing, cooled slowly, re-checked under daylight-balanced light.

Shade memory is kept in the case folder. If the dentist calls back next year with a crown next door, we pull the same stain recipe.

4. QC before packing

Our QC checklist on an E.max inlay-onlay case:

Marginal gap under the microscope sat in the low tens of micrometres on both units, which is well inside the clinically acceptable range reported in the ceramic restoration literature for pressable lithium disilicate.

5. Packing

Both units went into a foam-lined box with the printed die for the dentist to try the fit on before taking them to chairside. A short case note went in the same box: material, shade, press batch, suggested cement, HF concentration and etch time, silane dwell, and a single-line reminder that the restorations are a ceramic inlay and a ceramic onlay from the same ingot and should be bonded under rubber dam.

The Final Restorations

Delivery state as it left the bench. Not "the patient was happy", because we do not see the patient. What we can report:

• #29 ceramic inlay. MOD-like contained inlay, A2 body, butt-joint margin all around, isthmus 2.2 mm, polished occlusal with light anatomy, light staining in the central groove to break the monochrome, contact tight on distal, light on mesial by the dentist's request. Pre-cementation marginal gap measured in the low tens of µm range.
• #30 ceramic onlay. Full cuspal coverage on the mesiolingual and distolingual cusps, 2.0 mm thickness over the covered cusps, butt-joint margin on the lingual wrap, slightly subgingival on the distolingual, cleaned up without over-reduction. Shade matched the submitted A2 photo under D65. Occlusion mapped on the mounted model with no supra-contact at MIP.

Two different products, one patient, same ingot batch, same shade recipe. The dentist booked a 60-minute slot for cementation under rubber dam.

Bonding Notes We Sent With the Case

We do not cement. The dentist does. But because a lithium disilicate inlay or onlay only performs if the bond is right, we always ship with a short bonding note in the box. For this case, the suggested protocol follows the current adhesive literature on silane application time for lithium disilicate bonding:

• Isolation: rubber dam. Non-negotiable on an E.max inlay or onlay. Saliva at the bonding interface and the whole mechanical argument for ceramic inlays and onlays collapses.
• Try-in: use clear glycerin try-in paste, not the final cement, to check the shade match.
• Intaglio: 5% HF, 20 seconds for lithium disilicate. Rinse 30 seconds, air-dry.
• Silane: fresh single-bottle silane, 60 seconds dwell, warm air-dry.
• Universal adhesive, light-polymerized per manufacturer instructions.
• Resin cement: light- or dual-polymerized, dentist's preference. We suggested a dual-polymerized cement for #30 because of the deeper lingual margin.

Some mild post-op sensitivity in the first week on a bonded ceramic restoration is not unusual. In the published posterior ceramic data, post-op sensitivity drops sharply from the first week to the fourth, so we flagged this in the note so the dentist's chair conversation with the patient could be grounded in that pattern instead of in guesswork.

What This Case Shows About Our Dental Ceramic Inlay Workflow

A single case is a single case. But the design calls on this one are not case-specific. They are the ones we make on every pressed lithium disilicate partial restoration that comes through the bench.

• We read the scan before the Rx. If the preparation geometry does not match the restoration the dentist wrote on the Rx, we pick up the phone before pressing. On this case the geometry matched. Sometimes it does not, and the WhatsApp message goes out that evening.
• We write down the thickness numbers. Isthmus, occlusal, wall. Numbers end arguments at remake time.
• We press rather than mill lithium disilicate inlays and onlays. Press ingots behave more predictably at the 1.4–2.0 mm cross-sections typical for partial-coverage ceramic restorations.
• We keep the shade recipe. Next unit in the same mouth matches the first.
• We send a bonding note with every ceramic inlay and ceramic onlay case. The restoration is only half the job. In a retrospective that followed partial ceramic restorations for up to 24.8 years, ceramic fracture was the most frequent technical complication at 6.7%, ahead of secondary caries at 4.7% and debonding at roughly 2% (long-term performance of ceramic in-/onlays). The 27-year chairside follow-up shows the same shape: when these restorations fail, they fail by fracture. Thickness discipline and a clean bond are the two levers we hold before the box leaves the bench.

A porcelain inlay onlay case is simple to describe and hard to make well. The difference between a well-made one and a struggling one lives in the millimetres and the micrometres, which is the part the patient will never see and the part the dentist pays us to get right.

Send Us a Case Before You Send Us an Order

We would rather look at your scan and tell you if the preparation is restorable than quote on an Rx we have not read. For a ceramic inlay and onlay case, send us:

1. Intraoral scan or scanned impression of both arches, with the bite.
2. Shade photos with a shade tab in frame, under D65 light if possible.
3. One line on each tooth: what you want (inlay / onlay / overlay), target material (E.max, zirconia, hybrid), and the margin location.

We will come back with a design-level reply, not a price-level reply. If the prep needs a tweak, we will say so before pressing anything. Send the case to our desk, or read how a case moves through our lab before you start.

Case facts at a glance