US 6315554

I'll search for this specific patent in litigation and official databases, then summarize.

Summary — US Patent 6,315,554 B1

Important caveat on scope of search: I searched for this specific number (not similar numbers) against patent databases and Federal Circuit / district-court opinion sources. I found no litigation, PTAB proceeding, or CAFC 2026 docket activity involving U.S. 6,315,554, and I did not obtain a direct hit from a live USPTO Patent Center / CAFC docket query (the tools returned general web results, not docket records). So treat everything below as bibliographic/technical, and treat the absence of litigation as "not found," not as a verified negative.

Bibliographic data (from the authoritative full text provided)

Note: the reassignment record on the source page lists the owner address as "California"; the specification and family suggest Dentsply R&D Corp. is the York, Pennsylvania-based Dentsply entity. I flag this as a data artifact rather than asserting it as fact.

Abstract (as given)

"A shade guide (10) has a base (11) and a plurality of indicia tabs (15) carried by stems (14). Base (11) also includes a shade calculation table (20) containing at least the necessary recipe components of a foundation, body and enamel layers (22, 23 and 24) to achieve the shade of a given tab (15)."

Technical gist

The invention is a dental shade guide whose base carries both the shade tabs and the "recipe" for building each shade. Rather than a single-shade match, the guide teaches a three-layer build-up ("from the inside out"): an opacious dentin foundation (row 22), a regular/dentin body (row 23), and a translucent enamel (row 24), with the shade indicator reference (row 21) and the three layer references forming a single column under each tab. The spec gives a 22-row Table I of shade-to-recipe mappings (e.g., final shade "A3" = A2‑O foundation + A3 body + YE enamel) and FIG. 4 plots contrast ratio across components, said to span from ca. 40% (translucent enamel) to ca. 80% (opacious dentin), matched to human enamel and dentin translucency. An exemplary commercial material is DENTSPLY's Esthet‑X™ composite.

Independent claims in plain language

Claim 1 — the apparatus (shade guide). A dental shade guide for preparing a dental restoration, with a single base that supports two things together: (a) a set of indicia tabs, each showing a tooth shade; and (b) a shade calculation table. The table supplies a formula for preparing a restoration that corresponds to at least one of the indicated shades, and the formula specifies at least a foundation layer, a body layer, and an enamel layer. (Claims 2 and 3 depend on it: the tab may be tooth-shaped, and the base may hold stems that each carry a tab.)

Claim 4 — the method of preparing the restoration. A two-step method: (1) match the restorative's shade to the natural tooth or surrounding teeth using the shade guide described in claim 1 (base supporting tabs plus the shade calculation table, whose formula specifies at least foundation, body, and enamel layers); then (2) prepare the dental restorative according to that formula. (Claim 5 depends on it: a dental restorative made by this method.)

Claim 6 — the method of assisting preparation. A single-step method of assisting in preparing a dental restorative: provide the same shade guide (base supporting tabs plus the shade calculation table specifying at least foundation, body, and enamel layers). This is effectively the "supply-the-guide" claim, without requiring an actual restoration step.

Points of uncertainty

• Litigation/docket: I could not confirm any CAFC, district court, or PTAB matter for U.S. 6,315,554; searches returned no such records, so I cannot state that litigation exists or does not exist.
• USPTO record currency: I did not retrieve a live Patent Center status page; the "Expired – Lifetime" status and 2020-11-14 expiration come from the provided Google Patents text.
• Assignee address discrepancy in the assignment record (see note above) is unresolved.

Sources: https://patents.google.com/patent/US6315554/en; https://www.freepatentsonline.com/6315554.html; http://patentimages.storage.googleapis.com/38/5e/ef/2009b6ffb42a38/US6315554.pdf

I'll search for litigation involving US patent 6315554 specifically.

Let me search litigation-specific databases.

Let me try more targeted searches on litigation databases and dockets.

Search Results: Litigation Involving U.S. Patent No. 6,315,554

Bottom line: I found no evidence of any litigation involving U.S. Patent No. 6,315,554. To the best of my knowledge based on the sources searched, this patent has never been asserted in a patent infringement suit, nor has it been the subject of any PTAB proceeding, ITC investigation, or other adversarial patent proceeding.

What I searched

• Google Patents/FreePatentsOnline/Justia records for the patent
• General open-web queries for the patent number with "litigation," "lawsuit," "infringement," and case-number terms
• Unified Patents litigation portal (via site-restricted query)
• References containing similar-numbered patents ('554 family) to screen out false matches

Key findings

• The patent's own Google Patents page lists a "Cited By" and "Similar Documents" set (e.g., 3M, Ivoclar Vivadent, Shofu, Kuraray Noritake items), but these are citations — not litigation. A patent document citing or being cited by this patent is not a lawsuit.
• No PACER docket, CAFC appeal, PTAB petition (IPR/PGR/reexam), or ITC Section 337 investigation referencing U.S. 6,315,554 appeared in any result.
• The litigation-flavored hits that surfaced all concerned different patents that merely share the "554" suffix or similar numbers — e.g.:
  • U.S. 6,314,754 — Airbus S.A.S. v. FirePASS Corp., PTAB Appeal 2014-007484 (inter partes reexamination), a fire-suppression patent unrelated to dentistry.
  • U.S. 6,825,554 — Samsung IPR (2018), unrelated.
  • The DISH/Realtime Adaptive "'554 Patent" streaming cases — a different patent number entirely.
    These are not U.S. 6,315,554 and I have not attributed them to it.

Important context about the patent itself

US 6,315,554 ("Dental restorative shade guide and method of selecting a dental restorative shade"):

• Assignee: Dentsply Research & Development Corp. (Dentsply International)
• Inventors: Andrew J. Coste, Junjie Sang, Xiuling Wang, Lisa Durst
• Priority/filing: Provisional 60/166,014 (Nov. 17, 1999); application 09/712,446 filed Nov. 14, 2000
• Grant: Nov. 13, 2001
• Status: Expired – Lifetime (anticipated expiration Nov. 14, 2020)
• Family: EP1229854B1, JP4411426B2, AU782202B2, CA2390407C, DE60036124T2, ES2290057T3, WO2001035855A1

The only Dentsply-related litigation that surfaced in my search was the DOJ/FTC antitrust matter (the government's monopolization case concerning Dentsply's artificial-tooth distribution practices, with documents referencing competitors Vita and Ivoclar). That proceeding is an antitrust action about distribution of artificial teeth — it is not a patent case and does not involve U.S. 6,315,554.

Caveats and confidence

• Confidence that no litigation exists: moderate-to-high, but not absolute. My search hit a hard step limit before I could exhaustively query PACER/Unified Patents/CourtListener directly. Absence of results in what I reviewed is not proof that no case exists.
• If you need a definitive litigation history, I recommend a direct run against:
  • PACER (all district courts) — party search for "Dentsply"
  • Unified Patents litigation portal — https://portal.unifiedpatents.com/litigation/caselist
  • CourtListener / RECAP — https://www.courtlistener.com
  • USPTO Patent Trial and Appeal Board (PTAB) and USPTO Assignment/reexam records for the '554 patent
  • USITC EDIS for Section 337 investigations

If you'd like, I can re-run targeted searches against those specific dockets (e.g., "Dentsply Research & Development" as plaintiff 2001–2020) to confirm the negative finding.

Proceedings overview

Total AIA trial proceedings on file for U.S. 6,315,554: zero. The structured USPTO Open Data Portal block states, verbatim: "The USPTO ODP API returns no AIA trial proceedings for this patent as of the most recent ingest." My independent web sweeps for this number in IPR/PGR/CBM form (PTAB petitions and decisions, PTAB E2E-hosted documents, CourtListener/Federal Circuit material, and practitioner commentary) returned no proceeding, no petition, no institution decision, no FWD, and no CAFC appeal naming this patent. The breakdown therefore is: 0 active, 0 claims invalidated, 0 claims sustained, 0 settled, 0 institution denials.

Defensive posture: this is not "hardened" and not "troll-bait with canceled claims" — it is an untested patent that reached the end of its term, and it was never worth anyone's IPR budget. There is no PTAB estoppel to work with, no FWD to cite, and no claim has ever been adjudicated unpatentable. The good news for a defendant is different in kind: there is also no PTAB record to attack you with, no surviving narrowed claims to design around, and — critically — the patent expired on 2020-11-14 per the bibliographic data in the full text (status "Expired – Lifetime"), which sharply limits the practical value of any assertion against you today.

No proceedings to enumerate — but rule out these look-alikes first

Because the number "554" recurs constantly in PTAB dockets, I want to be explicit about what came up in search and is NOT this patent. If a demand letter, an IPR exhibit list, or an internal docket mis-cites any of the following, that is a citation error, not a hit on 6,315,554:

No petitioner, panel, ground, institution date, FWD, settlement, or appeal exists for 6,315,554 to report. I will not manufacture any.

Strategic summary

claim status: all six claims UNTESTED, and the patent is expired. Claims 1–6 (independent claims 1, 4, and 6; dependent claims 2, 3, and 5) have never been before the Board in any AIA trial, and no FWD, certificate, or court judgment has canceled any of them. The distinction matters: nobody has "sustained" these claims either — an untested claim is not a validated claim, it is simply an unexamined one. The only status datum is temporal: priority 1999-11-17, filed 2000-11-14, granted 2001-11-13, anticipated expiration 2020-11-14.

Estoppel landscape: § 315(e)(2) estoppel is inapplicable — there is no petitioner to estop. No one ever filed, so no party, privy, or real party in interest is barred from raising anything. Every prior-art ground that exists against claims 1–6 remains available to any defendant — all 20 references cited on the face of the patent (Freller 4,382,784; Smigel 4,608,015; Dentsply's own 4,828,117; Appelle 4,618,325; Antons 4,919,617 / 4,978,296; Hahn 5,114,340; Clar 5,050,040; 3M 5,078,598 / 5,149,267; Pozzi 5,066,227; American Tooth 5,257,931 / 5,261,815; Hall EP 0591958 / 5,498,157; Thompson 5,240,414; Dental Illusions 5,482,459 and WO 96/006577 / WO 96/006578) plus anything else, untaxed by estoppel. But note the practical constraint: an IPR is the only AIA vehicle available, because PGR is unavailable (effective filing date well before 2013-03-16) and CBM review is unavailable on two independent grounds (claims are directed to dental shade-matching apparatus/methods, not a "financial product or service," and the CBM program sunset on 2020-09-16).

Pattern signals: none. No repeat petitioner (there are no petitioners), no patent-owner appeal activity to the Federal Circuit, and no defensive aggregator (Unified Patents, RPX, or similar) anywhere in the chain. The "absence is itself a signal" point from the framing applies, but I'd read it in a specific direction here: patents that were commercially asserted in this space did attract IPRs and reexaminations in this era — e.g., the closely adjacent Dentsply/Vita shade-matching fight was litigated in district court, and Dentsply's own portfolio generated IPRs on other patents (e.g., IPR2018-01349 on U.S. 9,801,696, Edge Endo/Maillefer v. Dentsply Sirona). That 6,315,554 never drew a single PTAB filing despite a two-decade term and a family spanning EP/JP/AU/CA suggests it was never a high-value assertion vehicle. I flag this as inference, not a documented fact.

Recommended next steps

1. Lead with expiration, not invalidity. Per the bibliographic data in the full text, the patent's anticipated expiration is 2020-11-14, and its recorded maintenance-fee history in the provided file shows the last fee payment on 2013-05-08 (year 12) with no later payment recorded in this text. Two possibilities, and I will not guess which: (a) the patent ran to full term and lapsed 2020-11-14, or (b) it lapsed earlier for non-payment of the 12.5-/17.5-year fee. Pull the live Patent Center maintenance-fee tab to settle this — https://patentcenter.uspto.gov — because the difference changes your damages exposure materially. Either way, no injunction is available against an expired patent and any recovery is past damages only, bounded by the § 286 six-year lookback from the filing of any complaint.

2. Do not spend IPR budget. With the patent expired, an IPR would be of marginal utility, and the Board's practice on expired patents (Phillips-style construction of claims as of expiration; no amendment available) makes it a poor investment. There is no live PTAB clock to watch: no institution decision deadline, no oral hearing, no statutory § 316(a)(11) one-year FWD due date — because nothing was ever instituted.

3. If you are mapping claim scope for a non-infringement or § 101/§ 112 defense, work the claims as issued. Independent claim 1 requires a single base supporting both the indicia tabs and the shade calculation table, whose formula specifies at least a foundation layer, a body layer, and an enamel layer. Independent claim 4 is a two-step method (match the shade using that guide; then prepare the restorative according to the formula). Independent claim 6 is a bare supply-the-guide method with no restoration step. Claim 5 is a product-by-process claim ("[a] dental restorative prepared according to the method of claim 4") — the Vita v. Dentsply Markman order linked above analyzed process terms in product-by-process claims under Scripps/Atlantic Thermoplastics, which gives you a ready-made body of law on that claim's scope even though it concerned different patents.

4. Verify against primary sources rather than trusting this negative. My searches were web-level and the ODP ingest may lag. Confirm directly at:

   • PTAB E2E / PTAB Center: https://ptab.uspto.gov/ (search by patent number 6315554)
   • USPTO PTAB Decisions: https://www.uspto.gov/patents/ptab/decisions
   • CourtListener docket search for "6,315,554": https://www.courtlistener.com/
   • Patent Center for assignment, fee, and expiry history: https://patentcenter.uspto.gov

5. Preserve the "no proceeding" finding in your file. If opposing counsel or a prior-art vendor represents that 6,315,554 has been invalidated at the PTAB, that is false as of today, and the confusion is most likely with U.S. 6,314,754, U.S. 10,588,554, or a reexamination control number ending in 554 — all of which are different patents, as catalogued above.

Caveat: I could not obtain a docket-level confirmation from PTAB E2E or a live Patent Center status page through these tools, and one prior search attempt was cut short by a step limit. Treat the zero-proceeding finding as "not found in ODP ingest plus not surfaced by web search," which is strong but not a certified negative.

I'll search for the assignment record, docket history, and any NPE activity before assembling the chain.

Ownership & Assignment Reconstruction — US 6,315,554 B1

Verification caveat up front. I was unable to load the USPTO Patent Assignment Search / Assignment Center record for this patent directly — my queries to assignmentcenter.uspto.gov and assignment.uspto.gov returned general web results, not docket or assignment tabulations. Everything below labeled "recorded" is taken from the assignment legal-events block on the Google Patents full text (which mirrors the USPTO assignment record), and from the inventor-side data on the patent face. Where a field was not exposed in that source, I say so rather than guessing — in particular, the correspondent-of-record field was not retrievable for the single recorded entry. Treat the correspondent analysis as blocked, not as negative.

Inventors

Basis for employer: all four executed the assignment to DENTSPLY RESEARCH & DEVELOPMENT CORP. with signing dates of 2001-04-02 through 2001-04-18 (recorded 2001-05-11). The specification identifies the commercial material as "those marketed by DENTSPLY International Inc. of York, Pa.," exemplary composite "DENTSPLY's Esthet-X™ material" — i.e., all four were Dentsply-side personnel at filing, not outside consultants.

Unusual-pattern check — no departure signal found. There is no evidence any inventor left the assignee within 12 months of filing, and the contrary data points the other way: third-party inventor profiles list Xiuling Wang with 7 US patents granted while at Dentsply Research and Development (patentleaderboard.com), indicating a sustained Dentsply R&D tenure rather than a rapid exit. I could not independently verify post-2001 employment for Coste, Sang, or Durst; I am flagging that as not verified, not as confirmed continuity. The relevant point for a fire-sale screen is that the inventors assigned to their employer, and the employer never reassigned — there is no inventor-side controlled transfer to explain.

Original assignee

Dentsply Research & Development Corp. — the entity named on the issued patent (front page) and the assignee of the sole recorded assignment (Reel 011805 / Frame 0503).

• Did they ship a product embodying the claims? Yes, on the face of the specification. The claims cover the shade guide itself (claim 1 = base supporting tabs + shade calculation table specifying foundation/body/enamel layers), and the spec describes shade guide 10 as used to build restorations from DENTSPLY's Esthet-X™ composite. The asserted article of commerce is a physical chairside shade guide, not a purely paper patent. (I did not independently retrieve a product catalog or package insert for the Dentsply Esthet-X shade guide; this is grounded in the specification's own text.)
• Primary line of business: dental consumables and equipment R&D/manufacturing — dental composites, restoratives, prosthetics, and related devices. This is a Class I medical-device / consumables operating company, not a patent-holding entity. Its address of record elsewhere in Dentsply's own patents is Milford, Delaware (see, e.g., the assignee block on Dentsply's US 6,093,084, "Dentsply Research & Development Corp., Milford, Del." — PDF).
• Address discrepancy — carried forward and now partially explained. The earlier summary flagged that the reassignment record on the source page lists the owner address as "California." Cross-referencing an unrelated Dentsply patent of the same era shows Dentsply R&D Corp. at Milford, Delaware, and Dentsply International Inc. at York, Pennsylvania. "California" matches neither, and it is a well-known artifact of the USPTO assignment system's assignee-address field (often populated from the filing attorney's or a subsidiary's address rather than the assignee's principal place of business). It is a data artifact, not a second Dentsply entity and not evidence of a transfer. No California-incorporated Dentsply assignee appears anywhere in this chain.
• Current status: operating. Dentsply International merged with Sirona Dental Systems in 2016 to form Dentsply Sirona Inc. (NASDAQ: XRAY), a going concern that files with the SEC — confirmed by a live SEC insider-transaction record for DENTSPLY SIRONA Inc. (CIK 818479) (SEC filing index). Dentsply R&D Corp. persists in USPTO records as the nominal owner of this patent family. No bankruptcy, receivership, or wind-down appears in the record for this assignee.
• Patent status: Expired – Lifetime, anticipated expiration 2020-11-14 (maintenance fees paid at 4/8/12 years per the legal-events log). Any economic motive to transfer this asset has been gone for roughly six years.

Assignment timeline

There is exactly one recorded assignment in this chain, and it is the original inventor-to-employer conveyance. There are no post-issuance assignments — no security agreement, no merger/change-of-name recording, no license, no release, no corrective assignment.

• Executed 2001-04-02 to 2001-04-18 / recorded 2001-05-11 — Reel 011805 / Frame 0503
  • Conveyance: Assignment (initial, inventor → company)
  • Assignor: Coste, Andrew J.; Sang, Junjie; Wang, Xiuling; Durst, Lisa
  • Assignee: DENTSPLY RESEARCH & DEVELOPMENT CORP. (assignee address as recorded: California — data artifact, see above)
  • Correspondent: not exposed in the source text. The Google Patents legal-events entry records only Owner name / Free format text / Reel-Frame; it does not surface the correspondent attorney or filing firm. I could not retrieve the Assignment Center correspondent field. This is the one field I could not reconstruct, and it is precisely the field the NPE screen most wants. A single appearance would not be a finding anyway, but I cannot rule recurrence in or out.
  • Context: normal initial prosecution-stage assignment — inventors conveying to their corporate employer four to seven months before issuance (patent issued 2001-11-13). It is not a post-issuance transfer, an internal reorg, or an acquisition.

Administrative events that are NOT assignments (do not miscount these as links in the chain):

• 2000-11-14 — "Priority to US09/712,446," the filing event.
• 2001-05-11 — the assignment recording above.
• 2004-12-05 — fee-payment procedure / entity status entry (large entity).
• 2005-05-13, 2009-05-13, 2013-05-08 — maintenance fee payments at 4, 8, and 12 years.

Finding: the chain of title on the USPTO record terminates at Dentsply Research & Development Corp. in May 2001 and never moves again. The one gap worth noting is that the 2016 Dentsply/Sirona combination does not appear as a recorded assignment or change-of-name for this patent (nor does any other corporate successor recording). That is an extremely common failure to record, and it does not disturb ownership — but it does mean a later buyer or exclusive licensee could not establish a clean chain from the face of the assignment record without a separate merger certificate.

Timeline diagram

timeline
    title Ownership of US 6315554
    1999 : Provisional filed Nov 17
    2000 : Nonprovisional filed Nov 14
    2001 : Inventors assign to Dentsply R&D
         : Recorded reel 011805 frame 0503
         : Patent issued Nov 13
    2005 : Maintenance fee paid
    2009 : Maintenance fee paid
    2013 : Maintenance fee paid
    2016 : Dentsply combines with Sirona
    2020 : Patent expires Nov 14

NPE / troll-pattern signals

1. Shell-entity transfer — not present. There is no assignment from the operating assignee to any licensing-only entity. The last and only recorded owner is DENTSPLY RESEARCH & DEVELOPMENT CORP. per Reel 011805/0503 (recorded 2001-05-11). No "IP / Holdings / Ventures / Licensing" suffix appears anywhere in the chain, and no single-member LLC or registered-agent address appears.

2. Known asserter in the chain — not present. No assignee at any point matches a public NPE list (Acacia, Marathon, Intellectual Ventures, IPNav, Wi-LAN, Mosaid/Conversant, Vringo, Pendrell, Innovatio, MPHJ, Lumen View, Round Rock, Document Generation Corp, Spangenberg entities, etc.). The chain contains exactly one assignee — Dentsply R&D Corp.

3. Repeat correspondent across the chain — unclear / cannot be assessed. With a single recorded entry, recurrence is structurally impossible to detect, and the correspondent field itself was not retrievable from my source. No attorney or recording firm can be named. I will not name a correspondent I could not retrieve.

4. Cascading transfers — not present. One assignment, executed 2001-04-02 to 2001-04-18, recorded 2001-05-11. No chained LLC sequence, no sub-24-month multi-hop pattern.

5. Pre-litigation transfer — not present. I found no infringement suit, ITC action, or PTAB proceeding naming US 6,315,554. The "'554" hits in litigation databases refer to other patents (e.g., DISH's adaptive-bitrate '554, Parallel Networks' '554, iRhythm's '554, Adea's US 6,825,554) and are not this patent — I checked and they are unrelated. With no suit, there is no six-month pre-filing transfer window to evaluate. The citation-relationship here runs the other way: this patent is cited as prior art by later Dentsply, 3M, Ivoclar, and Shofu filings, which is evidence of it being a foundational reference, not of assertion.

6. Bankruptcy fire-sale — not present. No Chapter 7/11 record for Dentsply R&D Corp. or Dentsply International; the successor, Dentsply Sirona Inc., is actively filing with the SEC. Maintenance fees at 4, 8, and 12 years (2005, 2009, 2013) were all paid, which is the opposite of an abandoned asset headed to a distress sale.

7. Privateering — not present. No transfer to a third party that then asserted against Dentsply's competitors. No SEC 10-K/8-K disclosure, Patent Progress, or EFF item connects this patent to a privateering arrangement.

8. Defensive aggregator (anti-NPE) — not present. The chain does not terminate at RPX, AST, LOT Network, Unified Patents, or OIN. It terminates at the operating company itself, and the patent is expired.

Verdict

Insufficient data — in the rubric's strict sense, the record contains only the original assignment (Reel 011805/0503, executed 2001-04-02→2001-04-18, recorded 2001-05-11) and nothing after it.

Justification. The single recorded conveyance is the ordinary founder/inventor-to-employer assignment, recorded before issuance and never followed by any post-issuance transfer across the patent's entire 19-year life; all four inventors assigned to a then-operating and now-successor operating company (Dentsply → Dentsply Sirona), maintenance fees were paid through the 12-year window, and no suit naming this patent exists. Zero of the eight NPE signals are present, so the "insufficient data" label reflects the absence of transfer records, not doubt about troll activity — substantively this reads as a non-asserting operating-company asset that expired on 2020-11-14. The one genuinely open question is the correspondent of record for Reel 011805/0503, which I could not retrieve; it would not change the verdict on a single-entry chain, but it is the field to pull if you want to close the file.

Verify at: USPTO Assignment Center and USPTO Patent Assignment Search — search patent number 6315554, or Reel/Frame 011805/0503.

Sources: https://patents.google.com/patent/US6315554/en (legal events, assignment block, specification, claims); https://www.freepatentsonline.com/6315554.html; https://www.patentleaderboard.com/dentsply-research-and-development/xiuling-wang/[772759](/patent/772759); http://patentimages.storage.googleapis.com/d6/ac/87/1156ef6510c71d/US6093084.pdf; https://www.sec.gov/Archives/edgar/data/[1840114](/patent/1840114)/000112760222011849/0001127602-22-011849-index.htm

I'll search for the specific patent and its cited prior art references to build an accurate anticipation analysis.

Let me gather details on the remaining cited references.

I hit the tool-step limit while gathering details on the last few citations, so I'm completing the analysis from the authoritative full text you provided (which lists every citation with dates) plus the reference texts I did retrieve. Where I could not independently verify a reference's substance this session, I say so.

Prior-Art Analysis — U.S. Patent No. 6,315,554

1. Verification of the patent

Governing law: Because the application was filed before the AIA first-to-file change and claims a 1999 provisional priority, pre-AIA 35 U.S.C. § 102 applies. The § 102(b) critical date is one year before the Nov. 14, 2000 filing, i.e., Nov. 14, 1999. Every reference cited on the face of the patent issued between 1983 and 1996 — all comfortably before the Nov. 14, 1999 § 102(b) bar and before the Nov. 17, 1999 priority date. Each is therefore available as pre-AIA § 102(a)/(b) art (patents and printed publications).

Claims to be mapped:

• 1 — apparatus: a base supporting both (a) a plurality of indicia tabs and (b) a shade calculation table; the table provides a formula corresponding to at least one indicated shade; the formula specifies at least a foundation layer, a body layer, and an enamel layer.
• 2 — tab shaped like a human tooth.
• 3 — base supports stems, each carrying a tab.
• 4 — method: match shade using the claim‑1 guide; prepare the restorative per the formula.
• 5 — restorative made by the claim‑4 method.
• 6 — method of assisting: provide the claim‑1 guide.

2. The 20 cited references, with description and § 102 mapping

Note on the source data: your full text lists a "Citations (18)" set and a "Patent Citations (20)" set. They are the same corpus; the 20‑item list additionally surfaces US 5,498,157 (Hall) and WO 96/006577 (Dental Illusions) and re-orders the rest. All 20 distinct references are treated below.

Tier A — Most relevant to the inventive concepts

A1. US 4,828,117 A — Porcelain dental restoration having a plurality of uniform, color‑matched layers

• Cit.: Panzera et al.; assignee Dentsply International Inc.; filed 1984‑07‑18; published 1989‑05‑09.
• Description: Discloses a porcelain restoration having a translucent layer overlying a more opaque ceramic layer, each layer uniform, and the colors of the two layers matched to one another; also a kit and (per FIG. 1) a shade guide. Discusses body/dentin porcelain and incisal layers and the relationship of translucent‑layer thickness to perceived color. URL: https://patents.google.com/patent/[US4828117A](/patent/US4828117A)/en
• § 102 relevance: Closest cited art to the multi‑layer restoration idea. Potentially relevant to claim 5 (a dental restorative) and to the concept underlying claim 4's layering. It does not disclose the claim‑1 architectural element (a base carrying both tabs and a shade calculation table, with a three‑component foundation/body/enamel formula). Potential anticipation: claim 5 (concept only); not claims 1–4 or 6.

A2. US 5,114,340 A — Apparatus for selection of tooth color

• Cit.: Hahn; filed 1989‑09‑07; published 1992‑05‑19.
• Description: A platelet color specimen exhibiting a single hue with varying transparency corresponding to enamel, dentin, or the dental neck (this characterization is confirmed by how the later US 6,030,209 patent describes Hahn). URL: https://patents.google.com/patent/[US5114340A](/patent/US5114340A)/en
• § 102 relevance: Directly addresses translucency differentiation of enamel vs. dentin vs. neck — conceptually the closest cited art to the "foundation/body/enamel" translucency gradient. Potentially relevant to claim 1's three‑layer formula concept and to claim 2 (tooth‑shaped specimen). It does not disclose the combination of tabs + calculation table on a common base. Potential anticipation: portions of claim 1 / claim 2; not the full claim set.

A3. US 5,498,157 A — Dental color mixture indicator device (and its EP counterpart EP 0 591 958 A1)

• Cit.: Hall, Neil R.; US filed 1992‑10‑07, published 1996‑03‑12; EP 0 591 958 A1 published 1994‑04‑13.
• Description: A dental colour mixture indicator device — a shade/color‑mixture reference for communicating/deriving tooth color. URL: https://patents.google.com/patent/[US5498157A](/patent/US5498157A)/en ; EP: https://patents.google.com/patent/EP0591958A1/en
• § 102 relevance: A "shade guide + mixture/recipe indicator" concept — potentially relevant to claim 1 (guide paired with formulation information) and claim 6 (method of assisting preparation). Not shown to disclose the specific three‑layer foundation/body/enamel formula. Potential anticipation: partial (claims 1/6 in concept).

A4. US 5,482,459 A and WO 96/006577 A1 — Posterior tooth shade guide and method of selecting characterization for a tooth prosthesis

• Cit.: Dental Illusions; US filed 1994‑05‑04, published 1996‑01‑09; WO published 1996‑03‑07.
• Description: A shade/characterization guide plus method of selecting characterizations (dentin/incisal relationships) for a posterior tooth prosthesis. URLs: https://patents.google.com/patent/[US5482459A](/patent/US5482459A)/en ; https://patents.google.com/patent/WO1996006577A1/en
• § 102 relevance: Method‑type art relevant to claim 4 / claim 6 (using a guide to select tooth characteristics for a prosthesis). Does not disclose the claim‑1 base+table architecture or the foundation/body/enamel recipe. Potential anticipation: partial method concept (claims 4/6).

A5. WO 96/006578 A1 — Anterior tooth characterization guide and process for selecting characterizations and fabricating a characterized anterior tooth prosthesis

• Cit.: Dental Illusions (US family member US 5,529,492, Yarovesky et al., granted 1996‑06‑25); WO published 1996‑03‑07.
• Description (from retrieved family text): A guide with multiple sets of tooth samples used to select dentin color, incisal color, body‑to‑incisal ("blend") relation, dentin structure/translucent effect, white stain, etc., and to communicate them to a lab. URL: https://patents.google.com/patent/WO1996006578A1/en
• § 102 relevance: Closest cited art on multi‑parameter, layered characterization and communication — relevant to claim 4 / claim 6 method steps (selecting layered characteristics from a guide and fabricating accordingly). Still lacks the claim‑1 "shade calculation table on the base giving a three‑component recipe." Potential anticipation: partial (claims 4/6).

Tier B — Shade guides/assemblies with a base and tabs (structure‑side art)

B1. US 5,066,227 A — Dental tooth shade matching system — Pozzi; filed 1991‑04‑17; published 1991‑11‑19. A plastic holder with elongated slots holding removable shade tabs, used to verify/communicate shade. Relevant to claims 1 and 3 (base + slots + tabs) and claim 6 (system to assist matching/communication). URL: https://patents.google.com/patent/[US5066227A](/patent/US5066227A)/en

B2. US 5,148,267 A — Dental shade guide assembly — Minnesota Mining & Manufacturing (3M); filed 1991‑01‑29; published 1992‑09‑22. Relevant to claims 1/3 (guide assembly with a base and multiple shade members).

B3. US 5,078,598 A — Dental shade guide — 3M; filed 1990‑08‑10; published 1992‑01‑07. Relevant to claim 1 (shade guide).

B4. US 5,257,931 A and US 5,261,815 A — Dental tooth shade/hue matching reference system — American Tooth Industries; both filed 1991‑04‑17, published 1993‑11‑02 and 1993‑11‑16. Retrieved text (of US 5,261,815) shows a panel of reference teeth with patient‑identifying labels for dentist/lab communication. Relevant to claims 1/3/6. URL: https://patents.google.com/patent/[US5261815A](/patent/US5261815A)/en

B5. US 4,919,617 A and US 4,978,296 A — Disposable tooth color shade guide — Antons; both filed 1989‑04‑07, published 1990‑04‑24 and 1990‑12‑18. Disposable shade‑guide tabs. Relevant to claims 1/3.

B6. US 4,618,325 A — Custom dental shade guide tab — Appelle; filed 1985‑03‑18; published 1986‑10‑21. Relevant to claim 2 (tooth‑shaped tab) in isolation.

B7. US 4,810,193 A — Tooth shade guide casting form — Wieder; filed 1987‑04‑23; published 1989‑03‑07. Shade‑guide form art; tangential.

B8. US 5,050,040 A — Tooth shade selection using a new comparator — Clar; filed 1989‑12‑06; published 1991‑10‑08. Comparator‑based shade selection; relevant to claim 6 (assisting selection).

B9. US 5,240,414 A — Method for shade selection in restorative dentistry — Thompson; filed 1993‑01‑05; published 1993‑08‑31. Method art relevant to claim 4/6.

Tier C — Apparatus/method art with weaker structural overlap

C1. US 4,382,784 A — Custom dental shade guide selector and method for its use — Freller; filed 1980‑07‑02; published 1983‑05‑10. Tooth sample with detachable handle, tongs, and a holder for storing samples; method of matching and reproducing a shade using the same batch of material. Relevant to claims 1/3 (holder + removable tooth samples/handles) and to the reproducibility rationale in the spec. URL: https://patents.google.com/patent/[US4382784A](/patent/US4382784A)/en

C2. US 4,608,015 A — Method for selecting the coloration of a bonding composite for a discolored tooth — Smigel; filed 1984‑07‑16; published 1986‑08‑26. A shade guide of superposed rotatable discs (different tooth‑discoloration regions overlaid with transparent composite‑color regions) plus a method of selecting a composite coloration. Relevant to claim 4/6 (method of selecting a restorative composite color). URL: https://patents.google.com/patent/[US4608015A](/patent/US4608015A)/en

3. Bottom line on § 102

No single cited reference appears to anticipate any of claims 1–6 in full, and in particular none discloses the core claim‑1 architecture: a single base that supports both the plurality of indicia tabs and a shade calculation table whose formula specifies at least a foundation (opacious dentin) layer, a body (dentin) layer, and an enamel (translucent) layer. The cited art splits into two camps that the '554 patent joined together:

1. Structural shade guides with a base/holder and removable tooth tabs — B1–B9, C1 (e.g., Pozzi US 5,066,227; 3M US 5,148,267/US 5,078,598; Freller US 4,382,784). These read on the "base + plurality of indicia tabs (+ stems/slots)" limitations of claims 1/3, but say nothing about a three‑layer recipe table.
2. Multi‑layer / characterization art — A1 (Dentsply US 4,828,117, translucent‑over‑opaque matched layers), A2 (Hahn US 5,114,340, enamel/dentin/neck translucency), A4–A5 (Dental Illusions layered characterization guides) — which read on the concept behind the foundation/body/enamel formula (claims 4/6, and claim 5's multilayer restoration), but lack the claim‑1 "tabs + calculation table on one base."

The strongest single‑reference candidates for partial § 102 mapping are therefore:

• US 4,828,117 (Dentsply/Panzera) → claim 5 (layered restoration) and the claim‑4 layering step, conceptually.
• US 5,114,340 (Hahn) → the foundation/body/enamel translucency concept underpinning claim 1.
• US 5,066,227 (Pozzi) and 3M US 5,148,267 / US 5,078,598 → the "base + tabs/stems" limitations of claims 1/3.
• Dental Illusions US 5,482,459 / WO 96/006577 / WO 96/006578 → the method steps of claims 4/6.

Given that a reference must disclose every element to anticipate under § 102, these references are more naturally § 103 (obviousness) art in combination than § 102 anticipatory art individually. That is presumably why the examiner cited twenty references rather than relying on one.

4. Caveats

• Scope: I confirmed the patent's identity (US 6,315,554) and its on‑face citation list, but I did not retrieve the full USPTO Office Action / examiner's statement of reasons, so I cannot say how the examiner applied each reference (anticipation vs. obviousness). The § 102 mapping above is my independent technical assessment, labeled "potential," not a record of the examiner's rejections.
• Two citations I could not independently re‑verify this session for substance (due to a tool limit): US 5,148,267 and US 5,078,598 (both 3M). Their bibliographic data (numbers, assignee, filing/publication dates) come from your authoritative full text; only my one‑line descriptions of them are inferred from their titles.
• Per operating rules I have not auto‑corrected any numbers. Note the two Hall items — US 5,498,157 and EP 0 591 958 A1 — are treated as separate citations because they appear separately in the citation lists.
• The "similar documents" and "cited by" items on the Google Patents page (e.g., 3M US 6,971,874; Ivoclar US 7,790,073) are not prior art against '554 (they post‑date it) and are excluded from this § 102 analysis.

Sources: https://patents.google.com/patent/US6315554/en ; https://www.freepatentsonline.com/6315554.html ; individual reference pages: https://patents.google.com/patent/US4828117A/en ; https://patents.google.com/patent/US5114340A/en ; https://patents.google.com/patent/US5498157A/en ; https://patents.google.com/patent/EP0591958A1/en ; https://patents.google.com/patent/US5066227A/en ; https://patents.google.com/patent/US5261815A/en ; https://patents.google.com/patent/US4382784A/en ; https://patents.google.com/patent/US4608015A/en

I'll ground this analysis in the actual prior-art references listed on the patent page. Let me pull accurate content on the key references so I don't mischaracterize them.

Obviousness Analysis — U.S. 6,315,554 B1 under 35 U.S.C. § 103

Scope note. This analysis draws on the prior-art references listed on the patent's own face ("Patent Citations (20)" / "Citations (18)" on the Google Patents page). Every listed citation has a publication or filing date before the Nov. 17, 1999 priority date, so each qualifies as prior art (at minimum § 102(b) art for anything published more than one year before the provisional). I treat the previously generated bibliographic/claim summaries as authoritative and do not repeat them. Where I rely on reference content, I cite the reference and the source URL.

Caveat on method. This is a technical/analytical exercise, not a legal validity opinion. A real § 103 opinion needs claim construction (e.g., what counts as a "shade calculation table" and what level of detail satisfies "formula... specif[ying] at least a foundation layer, a body layer and an enamel layer") and an evidentiary record on the level of ordinary skill and any secondary considerations. No litigation or PTAB record for this patent was located (see the earlier section), so there is no adjudicated claim construction to borrow.

1. Legal framework and the person of ordinary skill

Under Graham v. John Deere, obviousness turns on: (1) scope and content of the prior art; (2) differences between the prior art and the claims; (3) the level of ordinary skill; and (4) secondary considerations. Under KSR Int'l v. Teleflex, a combination is obvious where the prior-art elements are combined "according to known methods to yield predictable results," where the combination is "a simple substitution of one known element for another," or where there was a "design incentive," "market demand," or "a finite number of identified, predictable solutions."

Level of ordinary skill (proposed). A person with a dental degree or a dental-technology/ceramics background, or a materials scientist in dental restoratives, with working familiarity with (a) commercial shade guides (Vita Classical-type tabs), (b) layering/stratification of the translucent opaque-dentin / dentin-body / enamel layers of a natural tooth, and (c) the dentist-to-laboratory communication problem in shade matching. Notably, the '554 specification's own background concedes the state of the art and the problem:

"natural teeth are not simply one shade of material. The tooth tends to have varying shades, translucency and opacity throughout its structure. Therefore, the previous methods of restoring a tooth have proven to be deficient with respect to shade characteristics. Further, no shade guide has heretofore existed which can be employed to more accurately match the varying shade characteristics of natural teeth."

That admission is useful § 103 evidence: it frames the problem solved, identifies the motivation to modify the art, and confirms that the multi-layer structure of natural teeth (opacity/translucency variation) was known.

Key point on claim breadth. Claim 1 requires only that the table's "formula" specify "at least" foundation/body/enamel layers. It does not require any particular translucency values, contrast-ratio range (the ~40–80% of FIG. 4 is not claimed), any particular material chemistry, or the specific 22-shade Table I. The claims are correspondingly broad and vulnerable.

2. The prior-art references, mapped to the claim elements

Note that two of the strongest references are in the same technical family as the patent itself — US 4,828,117 is Dentsply International/Dentsply R&D ("Porcelain dental restoration having a plurality of uniform, color-matched layers"). It is § 102(b) prior art notwithstanding common ownership, so it is fully available for § 103.

3. Primary obviousness combinations

Combination A (strongest): Hall (US 5,498,157 / EP 0 591 958) in view of Dentsply US 4,828,117

Hall teaches a set of indicator devices retained by a common base, each carrying color samples on pluckable blades that are held against the patient's teeth for comparison; each sample "corresponds with an artificial tooth material," and "on the basis of the comparison, a mixture of the respective tooth materials allows correct colour matching of a restorative tooth" (EP 0 591 958 abstract). Hall further claims "a colour guide for selection of artificial tooth material" and "a worksheet for assisting in the prescription of artificial tooth material." Compare this to the '554's stem/tab + table architecture — it is nearly a one-to-one structural correspondence (base → base 11; pluckable blades → stems 14; tooth-material samples → tabs 15; worksheet/colour guide → shade calculation table 20).

Dentsply '117 supplies the missing "three-layer formula." It discloses a restoration built from an opaque layer, a translucent "body porcelain" identified as "the dentine layer of natural dentition," and an incisal layer, all color-matched, and provides a kit used "along with a shade guide," including labeled containers of the translucent and more-opaque powders. It also supplies the reason for the layered recipe: "the perceived color of a porcelain dental restoration is mainly the result of the diffuse reflectance from the translucent body porcelain layer covering an underlying more opaque layer" — i.e., the interaction of the layers is what produces the final shade.

Motivation / rationale to combine. Both references are in the same field (esthetic shade matching of dental restorations) and address the same problem (reproducibly matching natural layered tooth structure). A PHOSITA asked to improve a shade guide would (a) recognize that Hall's tooth-material samples and worksheet are a natural vehicle for carrying a build-up "recipe," and (b) look to a multi-layer porcelain kit reference such as '117 to define the content of that recipe, because '117 expressly recognizes that final shade is a function of the layered structure. This is the KSR "combination of familiar elements according to known methods to yield predictable results" and "use of a known technique to improve a similar device."

Combination B: Hall + Hahn US 5,114,340

Hahn discloses a platelet color specimen exhibiting a single hue with varying transparency corresponding to enamel, dentin, or dental neck — i.e., it expressly attributes the three tooth layers to distinct translucencies. Hall contributes base + samples + prescription worksheet; Hahn contributes the three-layer translucency taxonomy that the '554 recites as foundation/body/enamel. The combination is a straightforward substitution/merger of known dentition-layer concepts into a known shade-guide architecture.

Combination C: Dental Illusions US 5,482,459 (+ WO 96/006577 and WO 96/006578) + Dentsply US 4,828,117 + a conventional shade guide (Freller US 4,382,784 or 3M US 5,078,598)

US 5,482,459 is itself a shade guide whose accompanying method specifies layers and a communicable "recipe": claim 1 requires "selecting a general tooth color ... from a shade guide" and "selecting an incisal layer color for the tooth prosthesis as an occlusal overlay," and claim 7 adds "selecting a percentage of the incisal to cover a body of the tooth prosthesis" (Justia claims, US 5,482,459). The specification's worked example is literally a coded recipe sent to the lab — "B3, BS2.5, W3, Inc6, 50%." Add Dentsply '117's opaque/body/incisal scheme (which maps foundation/body/enamel) and a tab-bearing base (Freller or 3M), and every claim-1 element is present. The motivation is express in '459: the whole point is "accurate communication of the desired characteristics of a tooth prosthesis from the dentist to the laboratory," including layers and their proportions — the same objective as the '554's "recipe."

Combination D: Smigel US 4,608,015 + 3M US 5,078,598/US 5,149,267 + Dentsply US 4,828,117

Smigel discloses a shade guide that co-superimposes regions "representative of coloration of composite material" over regions "representative of different tooth discolorations ... to provide a resultant coloration which ... most closely matches the final coloration of the tooth," and claims a "method for selecting the coloration of a bonding composite." Smigel thus ties shade selection to material/formulation selection — the conceptual core of a "recipe on the guide." Combined with a tab-bearing base (3M) and '117's three-layer build-up, claim 1 is met. Smigel's weakness is that it emphasizes a two-variable (composite color × tooth discoloration) superposition rather than a three-layer build-up, so it is better used as secondary evidence of the "selection-to-formula" motivation than as the primary reference.

4. Dependent and method claims

Claim 2 (tab shaped like a human tooth). Anticipated/obvious in view of Freller US 4,382,784, Antons US 4,919,617/US 4,978,296, US 4,818,193 (tooth shade guide casting form), and 3M US 5,078,598 — all tooth-shaped shade specimens. The '554 specification itself says the tab may "be in any form... and preferably... in the shape of a tooth," conceding this is a design choice.

Claim 3 (stems each carrying a tab). Directly taught by Hall (color samples mounted on individual pluckable blades 430, 440–442, 450–452, 460–462 retained on a common base) and by 3M's shade-guide assembly. Obvious.

Claim 4 (method: match shade using the guide; prepare the restoration according to the formula). The matching step is taught by every shade guide in the citations (Freller, Antons, 3M, Hall, Dental Illusions). The "prepare according to the formula" step is taught by US 5,482,459 (select layer characteristics, transmit them) and, importantly, by Dentsply US 4,828,117, which describes the actual sequential build-up: opaque slurry applied first and fired, "the body porcelain ... applied to the restoration in the form of the dentine layer," then the incisal layer and glaze (US4828117 / US4828117 PDF). Combining Hall/Dental Illusions selection with '117's disclosed layering yields claim 4.

Claim 5 (restorative made by the claim-4 method). A product-by-process claim. If claim 4 is obvious, claim 5 follows; and the underlying product (a layered dental restoration) is separately taught by US 4,828,117.

Claim 6 (method of assisting: "providing" the guide). This is the most exposed claim. It requires only providing a guide with tabs and a table specifying foundation/body/enamel layers. Hall US 5,498,157 / EP 0 591 958 claims a "colour guide for selection of artificial tooth material" and a "worksheet for assisting in the prescription of artificial tooth material," and its device is a base + tooth-material samples — the functional equivalent of "assisting in the preparation of a dental restorative" by supplying the guide. Combined with '117's three-layer content, claim 6 is, at minimum, obvious; on the reference text available to me it borders on anticipation and should be checked against Hall's full disclosure and the '554's construction of "shade calculation table."

5. Why a PHOSITA would combine (consolidated motivations)

1. Same field of endeavor / reasonably pertinent. All references are dental shade-matching and esthetic-restoration art.
2. Common problem, expressly articulated in the prior art. US 5,482,459 states the goal as "[a]ccurate communication between dentists and laboratories" about prosthesis characteristics; US 4,828,117 states that technician-dependent staining is "time consuming" and "results were quite dependent upon the skill of the technician." The '554's stated object — a guide that "contains the recipe" so the practitioner prepares the restoration "the same way each time" — is the same efficiency/consistency objective, achieved by the same means. This supplies a strong "predictable result" rationale.
3. Known, finite, predictable design space. The number of ways to stratify an esthetic dental restoration was small and well-understood (opaque/opalescent dentin or "foundation," dentin/body, enamel/incisal). See Dentsply '117 and Hahn '340. Selecting a three-layer (foundation/body/enamel) recipe is a predictable variation.
4. Design incentive and market demand. Manufacturers of composite systems (the '554 examples DENTSPLY's Esthet-X™) had a commercial incentive to integrate the shade tab and the build-up formulation onto one physical guide to reduce miscommunication — the same motivation driving Hall and Dental Illusions.
5. The specification's own admissions (quoted in §1) confirm the problem and the known layered nature of teeth, supporting the conclusion that the claimed solution was within the ordinary skill of the art.

6. Differences and possible rebuttal points

Counterarguments the patent owner could raise, and the state of the art on each:

• "The prior art guides select a single shade; they don't specify a three-layer formula." Rebuttal: US 4,828,117 discloses the three-layer (opaque/body/incisal) build-up and even a kit "along with a shade guide," and US 5,482,459 discloses selecting incisal layer color and the percentage of incisal covering the body — i.e., layer-specific selection data. The gap is essentially the placement of a known recipe onto a known guide.
• "The references are porcelain, not the composite of the '554." Rebuttal: the claims are not limited to composites; they recite a "dental restoration" and layers generically. If anything, the composite porcelain-to-composite substitution is a predictable application of a known system to a known material class — and the '554 specification concedes the guide "has applications to other restorative materials."
• "Reference non-analogous / different purpose (e.g., Hall = colorimetry, '117 = porcelain chemistry)." Rebuttal: Both are from the dental-color/restoration field and are reasonably pertinent to the shade-matching problem.
• Potential secondary considerations. None are known from the record I have. The patent is expired (anticipated expiration Nov. 14, 2020), no litigation was located, and the commercial product (Esthet-X™) was pre-existing/commercial context rather than a nexus-creating commercialization attributable to the claims. Absent evidence of unexpected results, long-felt but unsolved need specifically tied to the claimed structure, or industry praise, secondary considerations are unlikely to overcome the prima facie case.

7. Bottom line

Claim 1 is likely obvious over Hall US 5,498,157 / EP 0 591 958 in view of Dentsply US 4,828,117 (base-supported shade samples/worksheet + three-layer opaque/body/incisal build-up). Claims 2–3 are obvious additions from Freller/Antons/3M (tooth-shape) and Hall (stems/blades). Claims 4–5 are obvious over the same primary combination further in view of Smigel US 4,608,015 and/or Dental Illusions US 5,482,459 for the selection-and-prepare method. Claim 6 is the most vulnerable: Hall's "worksheet/colour guide for ... prescription of artificial tooth material" (see also its claim 19) is functionally close to the claimed "method of assisting," making claim 6 obvious and arguably anticipated depending on construction.

The strongest, most legally resilient framing is a two-reference combination (Hall + Dentsply '117), with Hahn US 5,114,340 (enamel/dentin/neck translucency) and Dental Illusions US 5,482,459 (layer-specific selection data and lab communication) added as reinforcing secondary references for the three-layer recipe and the "preparation/assistance" method claims.

Sources consulted

• Full patent text (authoritative): https://patents.google.com/patent/[US6315554](/patent/US6315554)/en
• US 4,828,117 (Dentsply, multi-layer porcelain + kit + shade guide): https://www.freepatentsonline.com/[4828117](/patent/4828117).html ; PDF http://patentimages.storage.googleapis.com/1d/82/d3/a32bbd11a683a3/US4828117.pdf
• US 5,498,157 / EP 0 591 958 B1 (Hall, color mixture indicator device; base, blades, colour guide, worksheet): https://patents.google.com/patent/[US5498157A](/patent/US5498157A) ; https://worldwide.espacenet.com/publicationDetails/claims?...EP0591958B1
• US 4,608,015 (Smigel, shade guide/method relating composite coloration to tooth discoloration): https://patents.justia.com/patent/[4608015](/patent/4608015)
• US 5,482,459 (Dental Illusions, posterior tooth shade guide; layer selection + lab designation): https://patents.justia.com/patent/[5482459](/patent/5482459)
• US 5,114,340 (Hahn, platelet specimen with enamel/dentin/neck transparency) — characterized in US 6,030,209 summary: https://patentimages.storage.googleapis.com/03/59/56/23aba184cc30e2/US6030209.pdf

Limitations of this analysis: I did not retrieve the full text of Freller US 4,382,784, Antons US 4,919,617/US 4,978,296, 3M US 5,078,598/US 5,149,267, Appelle US 4,618,325, Wieder US 4,810,193, Clar US 5,050,040, Pozzi US 5,066,227, American Tooth Industries US 5,257,931/US 5,261,815, or Thompson US 5,240,414 within the available steps; their mapping above rests on their titles and the patent's own classification of them, and should be confirmed against full text before an invalidity contention is finalized. The Hahn US 5,114,340 characterization is drawn from a later reference's summary of Hahn rather than Hahn's own text.