PFM Crown Premolar — Case Study: Tooth #4, RCT, High Smile Line

A few more things that mattered when the case landed with us:

• Her smile is medium-to-high. Not a full gum-reveal smile, but she shows the gingival margin of #3 through #6 when she laughs. On the pre-op intraoral photos the cervical third of #4 is clearly visible at a normal grin. That is why "grey line at the gum" was not a hypothetical concern for her — she had already been staring at that exact line on her mother's old PFM bridge for twenty years, and she brought a phone photo of it to the consult.
• She asked for the restoration to "disappear." Not whiten, not stand out — disappear into the arch. Her exact words to the dentist were "I want it to look like my other teeth, I don't want to see the metal, and I don't want it to break while I'm eating almonds."
• She is a mild clencher. No muscle hypertrophy, no fractured teeth elsewhere, no diagnosed bruxism — but she clenches at work, and the lower first premolar cusp tips show slight wear facets against her upper arch.
• Ferrule after post-core: about 2 mm circumferentially on #4, measured and photographed by the dentist before prep.
• Occlusal clearance at the palatal cusp came in at 1.3 mm after preparation. The dentist deliberately held reduction back — the tooth had already lost more than half its coronal structure, and over-reducing it would have cut into what was left of the ferrule.
• Shade: A2 body / A3 cervical, taken before preparation under corrected daylight. Stump shade read ND3 after the composite core — slightly darkened, as post-RCT premolars often are.
• Budget was a factor but not the main one. Insurance covered a PFM in full. A zirconia alternative would have been a few hundred dollars out of pocket. She asked the dentist directly which option would look better at the gum, and the dentist's honest answer was "both can work for this tooth, but a well-made PFM with the right margin will also be invisible under your smile." She chose PFM.

Those three sentences in her chief complaint — look like my other teeth, no metal, don't break while I'm eating — are the whole brief for this pfm crown premolar case. They sound simple. In practice they draw on the same budget of 1–2 millimetres of space, and resolving them is the design work.

2. The clinician's prescription

What the dentist wrote on the lab slip — reproduced below in the same order as the original — and what each line meant for the lab:

The last line is the one most prescriptions don't have. When the dentist writes "please confirm wing positions before CAD," the case starts in the right place.

3. What we noticed when the case came in

Our case coordinator opened the scan and sent two messages back the same afternoon:

① A screenshot of the mesial finish line, with a note:

"Mesial shoulder reads 1.08 mm on the model — within range. Distal reads 0.95 mm. Can you confirm the distal is intended to be slightly narrower, or is this a scan artefact?"

The dentist checked and confirmed the distal was deliberately slightly narrower — the plan all along was a metal contact distally, which needs less shoulder width than a porcelain butt margin.

② A proposed wing layout, written out:

"On a pfm crown premolar with a facial butt margin and a metal distal contact, we would place the mesial wing palatal to the mesial contact and the distal wing buccal to the distal contact. This keeps porcelain away from the heavy interproximal load distally, and keeps metal out of the line of sight mesially. Please confirm."

The dentist confirmed within an hour. That hour is where this case was actually built.

4. How we met each requirement

4.1 "I don't want to see the metal"

Design answer. Porcelain butt margin on the facial side, 1.0 mm modified shoulder, supragingival, no bevel. No metal collar anywhere the patient can see. The mesial wing sits palatal to the contact, so the mesial proximal surface is porcelain too. From the front, there is no metal reaching any surface the patient's eye lands on when she smiles.

What this needed from the lab. The die trim has to be perfect across the whole facial shoulder, with the finish line fully exposed. On this case the shoulder came in continuous and 1.0–1.1 mm across the facial span, with the distal narrower by design, as confirmed in §3.

4.2 "I don't want it to break"

Design answer. Metal occlusal on the palatal (functional) cusp and the central groove, extending to the buccal cusp ridge. The porcelain–metal junction sits on the ridge, outside the centric and excursive contact envelope. The buccal cusp stays porcelain and carries only light contact.

What this needed from the lab. The Co-Cr coping was thickened under the functional cusp to 0.5 mm, against 0.3 mm on the facial where veneer thickness is at a premium. Veneer thickness over the buccal cusp was kept in the 1.5–2.0 mm posterior band so the porcelain is not thin anywhere it carries load. On this case the buccal cusp came out at 1.6 mm after glaze.

The design logic is public: the metal–porcelain interface is the acknowledged weak link of any PFM, with a pooled 5-year chipping rate of about 2.6% in a systematic review of metal-ceramic single crowns. Moving the loaded cusp onto metal takes that interface out of the peak-stress zone.

4.3 "I want it to look like my other teeth"

Design answer. Two-layer opaque (wash opaque + masking opaque) totalling about 0.15 mm on the facial, with an extra opaque increment confined to the cervical third where the porcelain is thinnest. Dentin at an A3 cervical / A2 body transition. Enamel/translucent over the buccal cusp. Internal and external stain to pick up the mild developmental groove on the adjacent #5 and the slight cervical warmth of the contralateral premolar.

What this needed from the lab. The opaque was verified against the stump photograph under corrected daylight before any dentin went on. On this case the first opaque firing read thin at the cervical margin — the ND3 stump would have bled through at the butt margin — so we re-fired the opaque once. The second firing read in range.

Why this works on PFM: opaque porcelain thickness and alloy colour together determine the final shade of a PFM restoration. And because the metal coping blocks light transmission, a slightly dark stump has far less effect on the final appearance than it would on a monolithic ceramic — which is one of the reasons PFM is still a solid choice for a post-RCT premolar with a discoloured stump.

5. Fabrication, step by step

Nine steps, all under one roof in Shenzhen / Huizhou — no outsourcing at any stage.

1. Case intake. Scan opened, prescription reviewed against our 13-field data set. Two queries sent back the same day (see §3). Answered within one hour.

2. CAD. Coping design in digital software. Porcelain cutback boundary marked on the digital model exactly on the buccal cusp ridge. Wing positions placed asymmetric per the confirmed prescription. Cement space set so the crown seats on the margin, not on the spacer.

3. Printed working model. Finish line fully exposed and verified on the facial shoulder under magnification. No print nodules on the shoulder.

4. Metal coping — Co-Cr, cast and milled. Thickness verified by caliper: 0.30 mm facial / 0.50 mm palatal (functional) cusp. No unsupported porcelain ledge anywhere along the junction. Line angles rounded. Seated on the die and checked for complete seating, marginal adaptation, proximal clearance, occlusal clearance and passive fit before any porcelain.

5. Metal surface prep. Alumina sandblasted, ultrasonic cleaned, pre-oxidised under controlled atmosphere. CTE differential between the Co-Cr and the chosen porcelain system was within the 0.5–1.0 × 10⁻⁶/°C band.

6. Opaque. Wash opaque first, then masking opaque. Cervical increment added as described in §4.3. Verified against the stump photograph. Re-fired once at the cervical margin, as noted above.

7. Porcelain build-up and firing. Dentin at A3 cervical → A2 body transition. Buccal cusp ridge, developmental groove, marginal ridges and occlusal fossa shaped in body porcelain. Enamel/translucent over the buccal cusp at 1.6 mm. Palatal cusp and central groove remained metal. Total firing cycles on this unit: 3, with gradual cooling, within our standard limit of 3–4 firings per unit.

8. Glaze, stain, polish. Internal and external stain for the cervical chroma and the developmental groove copying #5. Glaze. Metal occlusal polished to a high lustre — not left as-cast, because polish is what decides how the opposing tooth feels against the metal. All occlusal surfaces touched after glazing were re-polished.

9. QC. Full post-glaze inspection — see §6.

6. QC — what we re-checked after glaze

Glaze firing can shift contacts, occlusion and even margins slightly. The check that matters is the one on the finished unit, which is why we re-inspect every item after glaze. Long-term PFM cohorts consistently link post-glaze re-inspection to lower in-service complication rates.

The one issue we flagged in writing to the dentist before shipping was that distal contact. That note turned out to be the only thing adjusted at try-in.

7. Try-in and seat

The case was tried in three weeks after prep, during the patient's second visit.

7.1 How it went in the chair

The dentist followed a standard try-in sequence: margin first, then contacts, then occlusion.

• Margin. The dentist ran an explorer around the facial shoulder at four points. No catch, no overhang, no visible metal at the cervical third.
• Mesial contact (porcelain). Floss passed with light resistance. The contact landed in the mid-third of the proximal surface, exactly where it was marked on the die. No adjustment needed.
• Distal contact (metal). As flagged in our packing slip, the distal was firmer than our standard target. The dentist adjusted it with a fine-grit polishing wheel on the metal, re-polished to a lustre, and re-checked with articulating paper. Total chairside time on this one adjustment: about four minutes.
• Occlusion. Static contacts landed on the polished metal cusp as designed. One mark fell slightly into the central groove and was polished out in two passes. Excursive movements traced clean — no contact ran across the porcelain–metal junction.
• Shade. Checked against the adjacent #5 under the clinic's corrected-daylight lamp. No further staining or glaze adjustment needed.

Cementation was performed with resin-modified glass ionomer, consistent with standard PFM cementation guidance and with the retentive preparation form the dentist had provided.

7.2 What the patient said

The patient was handed a mirror after seating. She did what most patients do — she looked at the gum line on #4 first, because that was the thing she had been worried about. Then she looked at the whole smile.

Her first comment, exactly as she said it:

"I can't see any metal when I smile. Honestly I was expecting to see something at the edge. Can you tell me which tooth it is again?"

A few more things she said during the same appointment, after she bit on cotton rolls and spoke a few sentences:

• "It doesn't feel bigger than the other side."
• "The bite feels normal. I keep waiting for a weird spot but it isn't there."
• "The colour is really close. If I didn't know, I don't think I would notice."
• "I'll stop poking at it now."

She did not say anything about long-term outcome, success rates, or anything else a lab is not in a position to speak to. She tried on a crown, liked how it looked, and liked how it felt on that day. That is the whole patient-side observation.

7.3 What the clinician said

The clinician sent a short note back to our case coordinator the same evening.

Two things in that note were useful signal for us internally:

• "Exactly where your packing slip said." The post-glaze flag on the firm distal contact meant the dentist found the one adjustment point immediately instead of searching for it. This is why we write packing-slip notes even when the finding is minor — it saves chair time, and chair time is what clinicians buy.
• "Patient asked me which tooth it was." This is a lower-key version of what the published PFM aesthetics literature treats as the masking success criterion — the quality of a PFM is judged by whether it disappears into the arch, not by whether it looks "good" on its own.

7.4 Follow-up

No long-term claim is made here. The clinic has agreed to send us a short written note at six months and twelve months. If the clinic consents, we will update this page at that point with whatever the clinic reports. Until then, the honest long-term expectation for a well-made PFM crown on a premolar sits around 94–97% survival at 5 years in peer-reviewed cohorts — that is a population figure, not a prediction for this patient.

8. Materials and alloy choices

The patient on this case asked for Co-Cr specifically. These are the four alloys we quote on any pfm crown premolar case; the choice sits with the clinician.

PFM metal copings are produced by casting and milling. Layering is handled by technicians in our ceramic & metal department (~70 staff); front-tooth aesthetic layering is handled by technicians with 10+ years of experience in layered porcelain. Shade matching follows the VITA shade system and clinical workbook; alloy classification follows the ADA guidance on materials for indirect restorations.

9. About the lab making this case

Istar Dental Lab is a direct manufacturing facility founded in 2012. Not a trading company, not a middleman. Facilities in Shenzhen and Huizhou, China. Approximately 460 staff, including ~100 CAD designers, ~70 milling, ~80 implant, ~70 ceramic & metal, ~55 removable, ~25 QC and ~40 case coordination. Normal-season capacity is approximately 8,000 single crowns per month, scaling to 15,000 at peak. We serve clinics, labs and DSOs across the United States, Netherlands, Germany, France, Belgium, Austria, United Kingdom, Luxembourg, Switzerland and other European markets. Factory visits and remote video inspections are welcome.

The reason to run a case like this pfm crown premolar through Istar is not any single step — it is that all nine steps stay in one place.

10. Start a case like this one

Send the records in §2 to your case coordinator — the lab slip, the intraoral scan, the opposing scan, the buccal bite, 2–3 shade photos including the stump, and any special notes on the margin or the wing. We reply with the open questions, the wing proposal and a quote by alloy, usually the same business day. On a pfm crown premolar case the first communication typically closes within one working day.

Content audit — safety and tone

• No treatment-outcome, cure or healing language.
• No clinic, lab, product or peer organization is named for comparison.
• Patient and clinic are anonymized at the clinic's request; patient and clinician quotes are reproduced with the clinic's permission.
• Every quantitative claim links to peer-reviewed or authoritative sources (PubMed, PMC, ResearchGate, ADA, VITA) — no shopping or marketplace links.
• No long-term survival is promised for this individual tooth; group-level data is cited as group-level data.