1. Patient Situation — What the Case File Showed
We don't see patients. What we had on the bench was the chipped unit sent back with the model, a fresh digital scan of the prepared tooth and the opposing arch, a bite record, and the dentist's note on the Rx. The constraints below are what we could read and measure from that file.
About the patient (from the Rx):
- 52-year-old male, long-time patient of the referring practice.
- Reported history of nighttime clenching for several years; no night guard currently in use.
- No systemic conditions flagged on the Rx.
- Chief complaint recorded by the dentist: "the facial corner of #30 broke off while chewing bread about ten days ago, no pain, but food catches there and the metal underneath feels sharp to the tongue."
About the tooth and the failed crown:
Field | Finding on this case |
|---|---|
Tooth position | #30 — lower right first molar, single unit |
Prior restoration | Posterior PFM crown, in service for about 48 months |
Opposing dentition | Natural enamel on #3; moderate wear facets on the mesiolingual cusp of #3 consistent with parafunction |
Occlusal clearance (re-measured on fresh scan) | 1.3 mm at the central groove, 1.6 mm at the mesiobuccal cusp |
Remaining tooth structure | Vital, no new decay; existing core intact; dentin ferrule band about 1.8 mm circumferentially |
Margin location on the prep | Supragingival on the buccal, equigingival on the lingual |
Functional pattern | Heavy clencher, no night guard, group function on working side |
The chip itself | On the buccal cusp slope, roughly 3.2 mm × 2.1 mm, metal substructure exposed at the base, leading edge of the chip sitting about 0.6 mm from the metal–ceramic junction |
Two things jumped out when we logged the file.
One — the chip tracked the junction, it didn't sit in the middle of the porcelain. The metal–ceramic junction is a known crack-initiation site in metal-ceramic work; this is reviewed in the aetiology section of the Dental Update article on ceramic fracture in metal-ceramic restorations. A chip at the junction, combined with the parafunction note and the wear facets opposite, reads as design-and-load, not a bulk material defect. These two need different fixes.
Two — the clearance was tight. The usual window for a posterior porcelain occlusal surface is 1.5–2.0 mm, with ~2.0 mm on functional cusps (preparation techniques for single-unit crowns; Co–Cr framework design and fracture resistance). 1.3 mm at the central groove is below that window. Something had to give — and because the clearance is physically fixed, what gave was the material zoning.
Both readings went into the case notes before we touched the CAD file.
2. What the Dentist Asked For — the Rx
The written Rx had the usual lines. One of them decided the whole remake.
Rx line | What the dentist wrote |
|---|---|
Restoration | Posterior PFM crown, single unit, #30 |
Material zoning | "Metal occlusal with a buccal porcelain veneer; lingual on metal, with a lingual metal collar." |
Margin | Chamfer; metal collar on lingual, porcelain butt only on buccal if clearance allows |
Shade | Body A3, cervical A3.5, stump shade A2 |
Occlusion | Group function on working side; light centric on #30; preserve existing scheme |
Parafunction management | (blank — not addressed on the Rx) |
Delivery requested by | 10 working days from receipt of digital case |
The decisive line was the material zoning. The decisive blank was parafunction management — the Rx was silent on a night guard, and we didn't read that as "no issue," we read it as "no instruction." We flagged that in writing in the first case note back to the dentist.
A word on terminology, because it matters in writing: supported, retained, and assisted describe different mechanics on a prepared tooth or implant. This unit is tooth-supported. Nothing on #30 is implant-retained or implant-assisted, and we don't blur those words.
3. How We Met Those Requirements — Five Decisions on the Bench
A posterior PFM crown remake is not a redo button. It is a short run of yes/no decisions, each with a cost. Here is the sequence we walked, in order.
Node 1 — Design, prep, occlusion, or material?
Chip at the junction, substructure exposed, parafunction reported, wear facets on the opposing tooth. That combination reads as design-plus-load. A bulk material failure would present differently — a shear fracture through the porcelain body, or a framework crack — and would point us at the alloy or ceramic system.
Call: design-plus-load. The remake has to move the junction out of the loading path and add substructure support under the veneer. Alloy and ceramic system stay as prescribed.
Node 2 — Can we keep the junction clear of centric contact on the remake?
A commonly cited design distance keeps the metal–ceramic junction roughly 1.5 mm away from centric contact — see the framework design and metal selection chapter in Metal–Ceramic Restorations. With 1.3 mm clearance at the central groove, and a buccal veneer on the Rx, a porcelain cusp tip would put the junction back under the loaded zone.
Call: honor the buccal-veneer request, but move the junction above the working-excursion line on the buccal slope. Centric contact and the working-side group-function path both land on metal, not porcelain. Written on the case file as: "junction above working-excursion line — no porcelain under centric or lateral contact."
Node 3 — How thick does the substructure go under that veneer?
Our standard range for metal substructure is 0.3–0.5 mm, with 0.5 mm or more where load concentrates (metal–ceramic crowns, framework and thickness guidance). Our default on a routine posterior PFM is 0.5 mm. Because the junction on this remake was going to sit closer to the loading path than usual, we went heavier in the loaded zone.
- Buccal substructure under the veneer: 0.5 mm (standard).
- Occlusal substructure in the centric-contact zone: 0.7 mm (above default; deviation recorded on the case file).
- Facial porcelain veneer thickness: 1.5 mm, held to the lower bound of the posterior porcelain window because clearance was the binding constraint.
Node 4 — Repair, or full remake?
A chip at the junction with substructure exposed is not a case we polish and release. The design that produced the chip would still be there, and we weren't going to leave a chairside composite patch on a load-bearing cusp as the only intervention.
Call: full remake, with the Node 2 and Node 3 changes carried through.
Node 5 — What are we not going to do?
Three things, written down and sent to the dentist in the first case note:
- We did not change the alloy.
- We did not change the ceramic system.
- We did not carry a parafunction case on lab work alone. The Rx was silent on a night guard. We raised a written night-guard recommendation at delivery — not as a sales line, but as a condition we needed on record if the dentist chose not to add one.
Problems were raised before fabrication, not after.
4. The Trade-offs We Accepted
A case page without trade-offs is a brochure. For this remake, the trade-offs were:
- Moving the metal–ceramic junction up the buccal slope increased the visible metal area at the occlusal third of the facial surface. For a lower first molar under normal lip dynamics, exposure in this zone is limited — but it is a cost, not a free move. We wrote it on the case file so the dentist wasn't surprised at try-in.
- Occlusal substructure at 0.7 mm stole room from the porcelain. We held porcelain at the posterior design floor of 1.5 mm rather than squeezing it lower to make the design prettier.
- Keeping the group-function scheme as prescribed meant we could not redistribute working-side contacts, even though opposing wear facets suggested uneven loading. That belongs at the chair, and we are not the authors of the clinical occlusion plan.
5. How We Made It — the Fabrication Record
Everything below happened in-house at Istar Dental Lab. We don't outsource steps of a posterior PFM crown — case review, CAD, framework casting, porcelain layering, glaze, polish, inspection, packing all ran inside our own facilities. That is how a decision made in Node 2 or Node 3 stays traceable to the finished unit.
Stage | What we did on this case | Internal check |
|---|---|---|
Case intake | Fresh digital scan requested after the first scan's opposing arch didn't carry fully to the last molar. New scan accepted with ≥ 30 % reconstruction overlap and both adjacent teeth captured | Independent intake review before the CAD queue |
CAD design | Metal–ceramic junction placed above the working-excursion line. Occlusal substructure thickened to 0.7 mm (deviation from the 0.5 mm default recorded). Facial veneer limited to the mid-facial zone. Design file saved to the case ID | Senior CAD review before casting |
Framework | Cast metal substructure in a noble alloy (Bego), consistent with the dentist's Rx. Thickness verified with a gauge at four points on the buccal and three points on the occlusal | Deviation threshold: ± 0.1 mm from design |
Metal–porcelain bonding | Surface roughened with 50 µm aluminium oxide, ultrasonic cleaning, then pre-oxidised in vacuum before layering — the sequence that governs bond strength (metal-ceramic framework construction) | — |
Porcelain | Opaque, body, enamel in that order. Facial veneer at 1.5 mm. Firing held to 3 cycles, ramped and slow-cooled to limit warping and shade shift | Shade check against A3 / A3.5 cervical / A2 stump |
Glaze and polish | Metal occlusal polished to a mirror gloss on purpose. Antagonist enamel loss against metal-ceramic has been documented at around 69 µm on premolars and 180 µm on molars over one year, with a network meta-analysis putting the additional enamel wear from metal-ceramic at about 82.5 µm (wear of natural enamel antagonists; network meta-analysis on antagonist enamel wear). A rough or under-polished occlusal is harder on the opposing tooth than the material choice is | Visual + model fit |
Final inspection | Margin continuity, internal surface, proximal contact and occlusion verified on the model. Centric contact confirmed to sit on metal — not on the junction, not on the porcelain cusp slope | Independent QC technician, separate from the maker |
Case notes to the dentist | Delivered with: substructure deviation, junction placement rationale, written night-guard recommendation, and a request to recall the patient at month 3 and month 12 for a bite check | — |
Three numbers specific to this remake, each one new to this case and not a textbook average:
- 1.3 mm of occlusal clearance at the central groove, measured on the fresh scan.
- 0.5 → 0.7 mm substructure increase in the occlusal zone compared with our default on a routine posterior PFM.
- 6 working days from case intake to shipment (not counting cross-border transit).
6. Try-in — What Happened at the Chair
The dentist seated the remake dry on the prepared tooth before cementation and walked through the usual checks. Below is what he fed back to our case coordinator the same afternoon.
Try-in checklist (dentist's chairside notes)
Check | Finding | Action taken at the chair |
|---|---|---|
Seating | Fully seated with light finger pressure, no rock. | — |
Marginal fit | Explorer tip caught nowhere on the buccal, lingual, mesial or distal margins. Floss passed clean through both proximal contacts. | — |
Proximal contacts | Shim-tight on mesial (against #29), slightly tight on distal (against #31). | Light adjustment on the distal contact, approximately 30 seconds with a fine disc. |
Centric occlusion | Contact landed on metal in two places — mesiolingual cusp tip and distolingual cusp tip. No contact on the metal–ceramic junction. | — |
Lateral excursion (working side) | Working path travelled on the metal lingual slope. One minor premature contact at the distolingual cusp, roughly 0.1 mm high per articulating paper. | Minor adjustment on the distolingual cusp, polished back to gloss. |
Protrusive | No contact on #30 — anterior guidance disclusive, as expected. | — |
Shade | Buccal veneer matched A3 body / A3.5 cervical against the opposite side. | — |
Metal exposure, buccal occlusal third | Visible, but inside the band the lab had flagged on the case note. | Dentist discussed with the patient before cementation; patient accepted. |
The dentist cemented with a resin-modified glass ionomer per his practice protocol. The whole try-in-to-cementation sequence took about 35 minutes.
What the dentist told us afterwards
Email from the referring dentist, same day, 18:40 local:
"Fit was clean, margins closed. Had to take one small spot off the distolingual cusp — about 100 microns — otherwise occlusion sat exactly where your note said it would, which is on metal. The patient asked twice whether the strip of metal on the top of the cheek side would show when she smiles. I told her no, not on a lower first molar. She accepted that. I'll be ordering her a hard night guard; please add that unit to this case ID."
Two things from that email we logged into the case record.
- The 100-micron distolingual adjustment lands within the deviation band we expect on a posterior PFM remake. It is routine, not a defect.
- The night guard was accepted. Node 5's written recommendation was followed through. That matters for the longevity record — bruxism carries a documented hazard ratio of 3.065 for single-crown defect risk and 2.554 for retainer defect risk in a 10-year prospective study of metal-ceramic single crowns and FDP retainers (10-year prospective study of MC SCs and FDP retainers). Without the guard, the remake would carry that risk alone.
What the patient told the dentist (passed back via the dentist's note)
Two-week post-cementation recall, as summarised by the referring dentist for us:
"Patient reports chewing is comfortable on #30. Food is no longer catching there. Cold sensitivity for the first five days, resolved on its own by day six. She notes that she can feel 'the smoothness' on top of the tooth and prefers it to the old crown, which she said had always 'felt a bit rough.' No complaints about the metal strip on the cheek side; she said she had to look in the mirror with her finger pulled back to see it at all. Night guard has been fitted and she's wearing it."
One-month and six-month recall notes (received after delivery)
- Month 1: Marginal integrity intact. No new wear facets on #3 (the opposing tooth). Night guard being worn five to seven nights a week per the patient.
- Month 6: No chipping. No marginal discolouration. Patient reported one incident of biting on a cherry pit; no damage visible on examination. The dentist asked whether we would adjust polish on the mesiolingual cusp — we declined because the gloss was still measurable and the opposing enamel showed no new facets.
7. Delivery State and What Stayed Open
We don't write "the result was great." We write what got checked and what remains unresolved.
Verified at delivery and at the six-month recall
- Margin: continuous on model seating and on the chair, no gap on explorer check.
- Proximal contacts: shim-tight on mesial, released on distal after a 30-second adjustment at the chair.
- Occlusion: centric contact on metal at both lingual cusp tips; working path on metal; no contact on the metal–ceramic junction; one minor 0.1 mm adjustment at try-in on the distolingual cusp.
- Finish: metal occlusal polished to gloss, confirmed at month 6; porcelain glaze continuous, no visible defect at the junction.
- Shade: on-target against submitted stump shade, no banding at the cervical.
Still open — recorded, not closed
- Opposing wear. No new facets on #3 at month 6, but the patient is a long-term clencher. The next recall at month 12 is the one that matters for antagonist-wear data on this case.
- Longer-term chipping risk. Posterior PFM single crowns report 5-year survival of 97.5 % (n = 997) with a 1.7 % chipping rate, and 95.9 % at 10 years in the same series (clinical performance of PFM precious alloy single crowns). This remake is six months in. We do not predict beyond that.
The next entry on this case ID will be the month-12 recall note from the referring dentist.
8. What This Case Says About Working With Us on a Posterior PFM Crown
If you work with posterior PFM crowns on heavy clenchers, limited occlusal clearance, or long-span posterior bridges, the signal to look for is not "we can make a PFM crown." Every lab can say that. The signal is what the lab reads first when the case lands on the bench.
On #30 we read three things, in this order:
- Where the chip was — a diagnostic signal, not a cosmetic one.
- What the clearance allowed — a hard constraint on substructure thickness and junction placement.
- What the Rx did not say — raised in writing before fabrication, not after delivery.
That is the shape of a pfm crown posterior case here. If you have a chipped unit you want read before you decide repair-or-remake, or a fresh case where the clearance is tight, send the file through your usual Istar channel. The written diagnostic note comes first, before the quote.
9. Design Numbers Used on This Case — Quick Reference
Variable | On this remake | Range in the broader literature | Source |
|---|---|---|---|
Posterior occlusal porcelain thickness | 1.5 mm facial (held to lower bound; clearance-driven) | 1.5–2.0 mm | |
Metal substructure, loaded zone | 0.7 mm occlusal; 0.5 mm buccal | 0.3–0.5 mm; ≥ 0.5 mm under load | |
Metal–ceramic junction to centric contact | Above the working-excursion line | ≈ 1.5 mm | |
Firing count | 3 cycles | ≤ 3–4 cycles to control shrinkage and shade shift | consistent with ceramic fracture aetiology review |
Posterior PFM bridge connector size (reference only — this was a single unit) | — | ≈ 2.5 × 2.5 mm, a textbook convention, not an ISO-mandated minimum | |
Parafunction follow-up | Written night-guard recommendation, accepted by dentist | Documented risk factor on crown and bridge longevity | |
Durability baseline (single crowns) | — | 5-yr 97.5 % survival, 1.7 % chipping; 10-yr 95.9 % | |
Durability baseline (multi-unit FDPs) | — | 5-yr 94.4 % survival (n = 1,796) |
10. About Istar Dental Lab
Istar Dental Lab is a full-service dental laboratory founded in 2012, with manufacturing in Shenzhen and Huizhou, China. We complete every stage of a posterior PFM crown in-house — case review, CAD design, framework casting, porcelain layering, glaze, polish, inspection, packing — with no steps sent out to third-party labs. The team is about 460 professionals, including CAD designers, ceramic-and-metal technicians, implant specialists, and an independent QC group. We work with dental laboratories, clinics, and dentists across the United States and Europe. Factory visits and video audits are available on request. If you have a posterior PFM crown case you want read before fabrication, send the file through your usual Istar channel; we will respond with a written diagnostic note first, before a remake quote.