US 6241521

I'll search for information about this specific patent number and any related litigation.

Let me run additional targeted searches for any CAFC or district court litigation and to confirm bibliographic details.

Summary: U.S. Patent 6,241,521 B1

Search results

I searched the USPTO/Google Patents records and web sources. No CAFC (Federal Circuit) appeal or 2026 docket entries involving this patent were found. Two near-miss results appeared and were excluded per your instruction not to return similar/coincidental numbers:

• A CourtListener entry with docket number "6241521" is an unrelated district-court docket ID for Young Living Essential Oils v. Sumner (2:17-cv-01284, D. Utah) — a trademark case, not this patent.
• A CAFC case article referencing "'521号专利" concerns U.S. Patent 9,031,521 (Dali Wireless, CommScope v. Dali, 2020-1817/1818) — a different patent.

If a CAFC 2026 matter exists for this patent, it did not surface in these searches; treat that as unverified rather than confirmed absent.

Bibliographic data (per USPTO/Google Patents records)

• Title: Bite block
• Patent / publication no.: US6241521B1 (US 6,241,521 B1)
• Inventor: John E. Garrison
• Assignee / original assignee: Individual (i.e., no corporate assignee listed; current assignee shown as "Individual")
• Application: US 09/304,200, filed May 3, 1999 (a continuation of PCT/US1998/014476, filed July 13, 1998 — the claimed priority date)
• Issue date: June 5, 2001
• Legal status: Expired – Lifetime (maintenance fees paid through year 12 in 2012; anticipated expiration July 13, 2018)
• Classifications: A61B1/24 (mouth instruments/props); U.S. class 433/140 per citing references

Abstract (verbatim)

"A bite block for facilitating a dentist's access to a patient's mouth includes an open-ended, U-shaped body having a pair of arms extending from a bight portion, thereby defining a void 40 that is bounded in part by the arms and the bite portion, whereby when the bite block is positioned between upper and lower teeth of the patient's mouth the dentist will have access to the patient's mouth through the void."

Independent claims — plain-language overview

The patent has 18 claims; the independent claims are claims 1 and 12 (claims 2–11 depend from claim 1; claims 13–18 depend from claim 12).

• Claim 1 — An open-ended, U-shaped bite block with two arms extending from a bight portion, so the arms and bight partly enclose a void. The bight includes strengthening ribs extending between the arms. When placed between the patient's upper and lower teeth, the void gives the dentist access into the mouth. (Core idea: a U-shaped block with ribs that keeps the jaws apart while leaving a large open working area.)

• Claim 12 — Nearly the same scope as claim 1 but drafted with slightly different wording: an open-ended U-shaped body with a pair of arms extending from a "bite portion", defining a void bounded in part by the arms and the bite portion, with "at least one" strengthening rib extending between the arms, giving the dentist access through the void when positioned between the teeth.

Notable literal-text caveats (not auto-corrected)

• In the issued text, claim 12 reads "bite portion" (and "arms in the bite portion") where claim 1 reads "bight portion" — this appears to be a typographical inconsistency in the printed claim, but I flag it literally rather than assuming correction.
• Dependent claim 15 in the Google Patents rendition begins "A bite block according to claim 14 therein the plastic polymer…" — again likely a typographical artifact ("wherein"), flagged literally.
• Some OCR/secondary copies render the material name "santoprene" inconsistently (e.g., "sandoprene"/"sandrogene"); the authoritative specification reads santoprene (a thermoplastic elastomer) bonded over a polypropylene base via two-step overlay injection molding.

Key technical features described (specification, for context)

• Resilient thermoplastic (polypropylene) body whose bight flexes like a spring hinge to accommodate different mouth openings (arm free-end spacing ≈ 1.125–1.500 in.; spacing at the bight ≈ 0.250–0.750 in.).
• Outer convex side has a channel (bottom portion + sidewalls) with a textured exterior surface (serrations, optionally knurling) for tooth traction; the sidewalls restrain the teeth laterally.
• The channel/soft surface is a softer-durometer material (santoprene) than the arms (polypropylene), typically formed by a two-step overlay injection molding process.
• A thin flexible portion of the bight, flanked by strengthening ribs on the outer edges, balances flexure with resistance to biting forces.
• The central void maximizes dentist/assistant working room and access from any direction.

Uncertainty note: The bibliographic facts above are well corroborated by Google Patents, FreePatentsOnline, Justia, and the USPTO image PDF. However, I could not confirm any CAFC 2026 docket activity for this specific patent; no authoritative source located indicates post-issuance litigation specific to U.S. Patent 6,241,521.

Litigation Search Results: U.S. Patent 6,241,521 B1

No litigation involving U.S. Patent 6,241,521 B1 ("Bite block," inventor John E. Garrison) was found in any of the searched sources. I found no district-court complaints, PTAB proceedings, ITC investigations, or CAFC appeals naming this patent as an asserted or challenged patent.

Searches performed

• General web searches for "6241521" patent litigation bite block, "US6241521" lawsuit patent, and "6,241,521" patent case docket
• Searches combining the patent number with litigation keywords and with the inventor's name (Garrison)
• A targeted search of the Unified Patents portal domain (site:unifiedpatents.com 6241521), which returned no matching caselist entry

Near-miss results (excluded — not this patent)

Consistent with the prior analysis, several superficially similar hits surfaced and were excluded because they do not involve U.S. Patent 6,241,521:

1. CourtListener docket No. 6241521 — Young Living Essential Oils v. Sumner, 2:17-cv-01284 (D. Utah). The number "6241521" here is merely the CourtListener docket ID, not a patent number. The case is a trademark matter (voluntarily dismissed and terminated April 2018 per the Notice of Voluntary Dismissal and Report on Final Decision to the USPTO Director). It has no connection to this patent.

2. References to a "'521 patent" in Green Mountain Glass LLC v. Saint-Gobain Containers Inc. (D. Del., 1:14-cv-00392) and in Via Vadis, LLC v. Amazon.com, Inc. — in both, the "'521 patent" refers to a different patent (glass-recycling and data-storage patents respectively), not U.S. 6,241,521.

Context supporting the "no litigation" finding

• The patent expired in 2018 (anticipated expiration July 13, 2018) after maintenance fees were paid through year 12 (December 2012), so it is well outside its enforceable life as of the current date (April 26, 2026).
• The assignee is listed as an individual (John E. Garrison) with no corporate assignee of record, and no assignment activity suggesting assertion campaigns surfaced.
• No inter partes review, ex parte reexamination, or post-grant proceeding was identified in the search results.

Caveat

Litigation databases (PACER, Unified Patents, DocketNavigator, RPX, CourtListener) were not exhaustively queried page-by-page in this session — the searches were web-index based. If a matter exists that is not well-indexed (e.g., a sealed or very recent filing, or a state-court proceeding that never reached the federal dockets), it may not have surfaced. Based on all information available, however, I have no known litigation to report for U.S. Patent 6,241,521 B1, and I would not be able to provide plaintiff(s), defendant(s), jurisdiction, case number, filing date, or outcome/status for any case because none was located.

I'll verify the structured PTAB data with targeted web searches before concluding.

Initial searches return only patent database pages, no PTAB dockets. Let me run additional targeted checks against PTAB-specific sources.

No PTAB dockets surfaced yet. Let me try a couple more query variants to rule out proceedings indexed under slightly different naming.

Proceedings overview

Zero AIA trial proceedings exist on file for US 6,241,521 B1. The USPTO Open Data Portal ingest returns no IPR/PGR/CBM dockets, and independent web searches across USPTO PTAB, CourtListener, Unified Patents, and Google Patents surfaced no petition, institution decision, Final Written Decision, settlement, or Federal Circuit appeal naming this patent. The bottom-line defensive posture: this is a fully expired, never-challenged patent — all 18 claims remain exactly as issued, no estoppel binds anyone, and no damages are recoverable for any act after the patent expired on 2018-07-13.

For completeness, the only near-miss hit was CourtListener docket ID "6241521," which is the unrelated Young Living Essential Oils v. Sumner trademark case (2:17-cv-01284, D. Utah) — not a PTAB proceeding and not this patent.

No proceedings to report

There are no IPR, PGR, or CBM dockets to profile. The structural reason is worth stating plainly:

• PGR and CBM are statutorily unavailable. This is a pre-AIA patent (application filed 1999-05-03; priority date 1998-07-13), so post-grant review (first-to-file, effective filing date after 2013-03-16) does not apply, and CBM (financial-product claims) never applied to a dental bite block.

• Only IPR could ever have been brought against this patent, and none was ever filed. That is consistent with the patent's lifecycle: it expired by term on 2018-07-13 (20 years from the PCT priority date, maintenance fees paid through year 12), so the window for a meaningful IPR was closing just as IPR filings peaked — and a petitioner gains little from attacking a patent with no remaining prospective damages.

• Defensive value: There is no PTAB estoppel under § 315(e)(2) against anyone, because no petition was ever instituted. Every prior-art ground that could have been raised in an IPR remains fully available in district court. But the dominant fact is not PTAB history — it is expiration: the last possible infringing act occurred no later than 2018-07-13, and under 35 U.S.C. § 286 damages are limited to the six years before suit. A complaint filed today (2026-09-08) reaches back only to 2020-09-08 — after expiration — meaning there is no recoverable damages window at all, and injunctive relief is unavailable for an expired patent.

Strategic summary

Claims CANCELED: None. Claims SUSTAINED in AIA trial: None (untested). Claims UNTESTED: All 18 (claims 1–18 remain in their original issued form, including both independent claims 1 and 12 and every dependent claim). No PTAB panel has ever construed, much less invalidated, any claim of this patent.

Estoppel landscape: Clean slate. Because no IPR was ever filed, no petitioner (or privy) is estopped under § 315(e)(2), and no one is barred from raising any § 102/§ 103 ground in district court. A defendant today can run any prior-art defense — including the references the examiner already considered (e.g., Via U.S. 3,722,101; Osborn U.S. 5,009,595; Flynn U.S. 5,421,327; plus the full table of 19 cited references) and any newly located art — without worrying about a PTAB record collaterally estopping or narrowing the fight.

Pattern signals: None. There is no serial petitioner, no Unified Patents or defensive-aggregator involvement, and no aggressive patent-owner PTAB litigation history, because there is no PTAB history at all. The patent owner is listed as an individual (John E. Garrison), and the "Cited By" list shows the patent was cited as background in later bite-block filings (e.g., D682431, D963863, US 8,535,056) — routine examiner citations, not assertion activity. The absence of IPR activity here is a weak signal at most: the patent expired in 2018, which is itself the best explanation for why no one bothered.

Recommended next steps

• Lead with expiration, not PTAB. If you are a defendant facing a demand letter on US 6,241,521 B1 today, the dispositive defenses are (1) expiration — the patent expired by term on 2018-07-13, so no injunction is possible; and (2) 35 U.S.C. § 286 — with suit filed after 2024-07-13, the six-year lookback cannot reach any act that occurred during the enforceable life of the patent, so zero damages are theoretically recoverable. State both in any motion to dismiss or summary judgment papers.
• Confirm there is no pending litigation deadline. There are no active PTAB proceedings, so there is no institution-decision deadline, oral-hearing date, or statutory one-year FWD deadline to calendar.
• Preserve prior-art defenses in court. Since no IPR was ever instituted, no § 315(e)(2) estoppel applies. If the patent owner somehow clears the expiration/limitations hurdles (e.g., suit over pre-2018 conduct filed within the lookback), you can assert any § 102/§ 103 combination — the 19 references of record plus uncited art — with no PTAB record to overcome. There is no FWD to quote because there is no FWD; do not let opposing counsel imply the claims were "confirmed" by the Board — they were never tested anywhere.
• Verify the procedural status independently before filing. The structured USPTO ODP data and my web searches agree there is no PTAB activity, but PTAB records are only authoritative at the Board. If you want a citable confirmation, run the patent number in the USPTO PTAB Trial Search (developer.uspto.gov/ptab-api or the PTAB E2E interface) and print the empty result — that is the cleanest way to put "no proceeding on file" in the record.

Caveat on confidence: The "zero proceedings" finding rests on the USPTO ODP ingest provided in the prompt plus web searches that returned no PTAB dockets, no FWDs, and no CAFC appeals naming this patent. I did not find any proceeding — but absence in search results is not an affirmative USPTO certification; if the stakes are high, a formal PTAB records check (and a USPTO Assignment/patent status report confirming the 2018 expiration and maintenance-fee history) is worth the cost before you rely on this analysis in litigation.

I'll research the assignment history for US 6,241,521. Let me start by querying USPTO assignment records and cross-referencing databases.

Initial searches show no assignment records. Let me verify directly against USPTO assignment databases and related indexes.

No assignment events appear in Google Patents' legal-events feed (only grant, certificate of correction, and fee payments). Let me check RPX/Unified Patents and inventor-related company records, plus try the USPTO assignment index directly.

Inventors

• John E. Garrison — sole named inventor (US 6,241,521 B1, "Bite block").

No employer or corporate affiliation at the time of filing is determinable from the patent record: the issued patent names no assignee, and the application (US 09/304,200, a continuation of PCT/US1998/014476) lists the inventor as an individual. The subject matter (a dental mouth prop) and the absence of any corporate assignee suggest an independent/dentist-inventor rather than a corporate R&D filing, but I have no reliable source establishing his employer. Unusual-pattern check: a single-inventor, no-assignee filing shows none of the "all inventors depart the assignee within 12 months" pattern — that pattern is inapplicable because there was never a corporate original assignee to depart from.

Original assignee

None recorded — the patent issued to the individual inventor. Google Patents lists both "Original Assignee" and "Current Assignee" as "Individual" (i.e., John E. Garrison). No corporate assignee appears on the face of the patent, in the USPTO bibliographic data, or in any secondary database surfaced.

• Product embodying the claims: No evidence located that Garrison (or any licensee) commercialized a bite block under this patent. This is an absence of evidence, not a confirmed negative.
• Primary line of business: Not applicable — an individual inventor; no operating company of record.
• Current status: The patent's maintenance fees were paid through year 12 (last payment recorded 2012-12-05), and the patent reached its anticipated expiration on 2018-07-13 (now expired/lifetime). The inventor's current status is not determinable from these records.

Assignment timeline

No recorded assignments were found for US 6,241,521 B1.

My search method and its limits, stated plainly:

• USPTO Patent Assignment Center / legacy assignment index (assignmentcenter.uspto.gov; assignment.uspto.gov) is a JavaScript application not directly crawlable by web search, so I could not execute a live reel/frame query in this session. No reel/frame entries for this patent are indexed by any search engine or secondary database I queried.
• The USPTO/Google Patents legal-events feed for this patent contains only: STCF (grant, 2001-05-17), CC (certificate of correction, 2002-02-19), and three FPAY fee-payment entries (2004-12-02, 2008-11-14, 2012-12-05). There is no assignment event of any kind — no Assignment, Security Agreement, Merger, Change of Name, License, Release, or Correction of inventorship.
• FreePatentsOnline and Justia copies likewise show no assignee and no assignment history.

Finding: This patent has no recorded post-issuance (or pre-issuance) assignment chain. That is itself a meaningful finding: the absence of any recorded transfer indicates the patent remained with the original owner — the individual inventor, John E. Garrison — from issuance (June 5, 2001) until it expired by operation of law (July 13, 2018).

Per the operating instruction for this workflow ("If the Assignment Center has no records for this patent, say so plainly and stop after this section"), I am stopping here. Because there is no assignment chain, the NPE/troll-pattern signals, ownership timeline diagram, and verdict sections are inapplicable: there is no shell-entity transfer, no asserter assignee, no correspondent recurrence, no cascading transfers, no bankruptcy sale, and no defensive-aggregator terminus to analyze. There is also no litigation record naming this patent (see the prior Litigation summary), consistent with an expired, never-asserted, inventor-held patent.

Verification: USPTO Assignment Center — https://assignmentcenter.uspto.gov/ (search by patent number 6241521); Google Patents legal events — https://patents.google.com/patent/[US6241521B1](/patent/US6241521B1)/en.

Caveat: If a paper assignment was executed but never recorded with the USPTO, it would not appear in any of the sources above; unrecorded assignments are not visible in the public record and cannot be ruled out.

I'll research the prior art cited against US 6,241,521 by examining the USPTO/Google Patents records for each cited reference.

I've confirmed the cited-reference list. Now let me verify details of the individual citations, starting with the older and less familiar references.

I've reached the limit of available search steps for this session, so I'll complete the analysis using the authoritative USPTO/Google Patents record for US 6,241,521 (provided in full above), the verified search results for key references (Via '101, Osborn '595, Flynn '327, McKesson '674), and clearly-flagged knowledge where confidence is lower.

Prior Art Analysis — U.S. Patent 6,241,521 B1 ("Bite block," Garrison)

0. Verification of the citation list

The USPTO/Google Patents record for US6241521B1 lists 19 "Patent Citations" (all examiner/third-party cited references; the only other listed publication, WO2000002493A1, is the parent PCT application of the same inventor disclosing the same invention — not prior art, and it published after the US filing date, so it is excluded from the § 102 analysis).

Statutory frame: Because the application was filed before March 16, 2013, pre-AIA § 102 governs. The effective filing date is no later than May 3, 1999 (US filing; priority claimed to PCT/US1998/014476, filed July 13, 1998). Every one of the 19 cited references issued/published between 1908 and January 7, 1997 — i.e., before the earliest critical date (July 13, 1997, if priority is honored; May 3, 1998, if not). Every reference is therefore prior art under pre-AIA § 102(a) and, on either critical-date theory, also § 102(b) (statutory bar). No § 102(c)–(g) issues arise from this list.

Literal-text flags (not auto-corrected):

• The specification says prior art is shown in "U.S. Pat. No. 500,959 issued to Osborn." Read literally that is No. 500,959; the record, however, cites US5009595A ("Dental mouth prop," Osborn, 1991), and the specification's surrounding description matches the '595 patent. Flagged rather than corrected.
• Google Patents shows US2220674A inventor as Martha F. McKesson; a Justia rendition of the '521 cited list writes "Bloomheart." The authoritative Google Patents record (and independent search confirmations above) attributes the "Mouth prop" patent to Martha F. McKesson; I use that and flag the Justia divergence.

1. Claim elements used for the mapping

Independent claim 1 elements:

• 1A: open-ended, U-shaped body
• 1B: pair of arms extending from a bight portion
• 1C: a void bounded in part by the arms and the bight portion
• 1D: the bight portion includes strengthening ribs extending between the arms
• 1E: positioned between upper/lower teeth, dentist gains access through the void

Independent claim 12 is the same combination, with "at least one strengthening rib" (and the literal-text "bite portion" typo, flagged in the prior summary). Dependent claims 2–11 and 13–18 add: ribs on opposite outer edges of the bight (2); textured exterior surface for traction (3, 13); different-durometer polymer plastics (4, 14); softer-durometer surface (5, 15); santoprene/polypropylene (6, 16); serrations (7, 10, 17); serrations or textured surface flanked by transverse side walls to restrain teeth (8, 9, 11, 18).

For anticipation, one single reference must disclose every element of the claim at issue; a dependent claim additionally incorporates its base claim.

2. The 19 cited references — full citations, dates, descriptions, and § 102 claim assessment

§ 102 conclusion on this list: No cited reference, taken alone, discloses the full combination of either independent claim (1 or 12) — an open-ended U-shaped body whose arms extend from a bight portion and partly bound an open void, with strengthening ribs extending between the arms. That combination is precisely what the specification distinguishes from Via, Osborn, and Flynn. Consequently, no dependent claim is anticipated either, since each incorporates claims 1 or 12. The listed references are best characterized as § 103 obviousness references, not § 102 anticipations — which is consistent with the examiner having allowed claims 1 and 12 over this same list.

3. Most relevant prior art (ranked)

1. US5009595A (Osborn, 1991) — closest in purpose and the one that most nearly addresses working access (its window ≈ a partial 1E analogue); still a solid block, lacking 1A–1D. Strongest § 103 starting point for a "void/access" motivation.
2. US5421327A (Flynn, 1995) — closest in geometry language (arms 14/16 and inverted-U finger spaces 50) but in an endoscopic, flange-and-tube configuration; strongest § 103 art for the "arms flanking an open space" idea.
3. US3722101A (Via, 1973) — closest in the dental bite-block field; teaches teeth-gripping/locking and fixed openings but a solid polygon, teaching away from an open void; § 103 art for the traction concept behind claims 3/13.
4. USD297665S (Neeley, 1988) — design evidence of bite-block geometry (functional limitations not anticipatable).
5. US4975057A (Dyfvermark, 1990) / US2823455A (Sprague, 1958) / US4887965A (Fox, 1989) — plausible U-shaped or adjustable bite props; potentially relevant to 1A–1C but unverified this session as to any rib disclosure (1D).
6. US2220674A (McKesson, 1940), US1143515A (Dunlop, 1915), US1229595A (Du Brul, 1917), GB180607A (Hoare, 1922) — early jaw-openers/mouth props; background art only.
7. US886522A, US903344A, US2651109A, US4356821A, US4944313A, US5152300A, US5466153A, US5590643A — remote fields (speculums, lip/cheek guards, cotton-roll holders, airways, annular mouthpieces, intubation airways); no material § 102 or § 103 overlap with the claimed combination.

4. Caveats and confidence statements

• Verified this session (high confidence): the citation list itself; the full text and claims of '521; and the substantive content of Via '101, Osborn '595 (including its claims 1–10, which I reviewed via EveryPatent), Flynn '327 (reviewed via FreePatentsOnline/Google Patents), and the McKesson attribution of '674.
• Title/classification-level only (lower confidence): Dunlop '515, Du Brul '595 (no — '959), Hoare GB180607, Sprague '455 ('345), Rind '821 ('6821), Fox '965, E-Z-Em '313, Dyfvermark '057, Poindexter '153, Flam '643. For these I have not confirmed internal structure this session; where I described possible U-shape geometry I said so explicitly and did not assert anticipation.
• Discrepancies flagged (not auto-corrected): the spec's "U.S. Pat. No. 500,959" vs. the record's US5009595A; the McKesson/Bloomheart attribution variance for US2220674A on Justia; and the claim-12 "bite portion" / claim-15 "therein" typographical artifacts discussed in the earlier patent summary.

Bottom line: After examining all 19 USPTO citations for US 6,241,521, none individually anticipates any claim under § 102. The three references discussed in the specification — Via, Osborn, and Flynn — are the most relevant prior art, but only as § 103 combination material, because none discloses the claimed open-ended U-shaped body with arms extending from a ribbed bight portion bounding an open dental-access void.

I'll verify a few structures the Prior Art section flagged as "unverified" — those are the references that could supply the "bight portion" element, which is where the § 103 attack will either succeed or fail.

Two useful confirmations came back (Osborn's wedge/concavity structure; Poindexter's ridged, flanged bite surfaces with a rubber cap). Let me pin down the two references that could supply the U-shaped "bight" element, plus re-check the design patent's geometry.

Obviousness Analysis — U.S. Patent 6,241,521 B1 (Garrison, "Bite block")

Statute: Pre-AIA 35 U.S.C. § 103(a) (application filed 1999-05-03; priority 1998-07-13, via PCT/US1998/014476). Obviousness is judged as of the effective filing date, from the perspective of a person of ordinary skill in the art (POSITA), under Graham v. John Deere and KSR Int'l Co. v. Teleflex Inc., 550 U.S. 398 (2007).

Building on the Prior Art section: That section concluded no single cited reference anticipates any claim under § 102. That conclusion is unchanged here. This section takes the next step: treating the same 19 references as § 103 combination material and identifying which combinations a POSITA would have been motivated to make.

Note on the earlier sections: The previously generated sections show inconsistent working dates (the Litigation summary says April 26, 2026; the PTAB summary says 2026-09-08; the header says 2026-09-10). I flag this discrepancy rather than reconcile it; nothing in the analysis below turns on the date.

Literal-text flags carried forward (not auto-corrected): the specification's "U.S. Pat. No. 500,959 issued to Osborn" vs. the record's US5009595A; claim 12's "bite portion" and claim 15's "therein."

1. The hypothetical POSITA

A person of ordinary skill in this art would be a mechanical/industrial designer or dental professional with ~2–3 years' experience developing intraoral devices, familiar with (a) the existing mouth-prop/bite-block art, (b) thermoplastic molding (including multi-shot/overlay molding and spring-hinge behavior of molded plastics), and (c) the routine mechanics of tooth retention (ridges, serrations, flanges/side walls). This level of skill matters: the more routine the design modifications, the more KSR's "predictable variation" rationale bites.

2. Element chart for the independent claims

Claim 1: 1A open-ended U-shaped body; 1B pair of arms extending from a bight portion; 1C void bounded in part by arms and bight; 1D strengthening ribs extending between the arms; 1E teeth-on-block → dentist access through the void.
Claim 12: same, with "at least one strengthening rib" (and the literal "bite portion" typo).

Immediate consequence: no single reference maps 1A–1D, so this is an imperfect but viable § 103 case, not a § 102 case — with element 1D (ribs) as the contested center.

3. Reference characterizations (updated from the searches)

Newly verified this session:

• US5009595A (Osborn '595) — confirmed: tapered, unitary, wedge-shaped pliable polystyrene block; long/short ends; straight top/bottom sloping tooth-resting surfaces; cheek-side flanges 24/26 extending above/below the tooth surfaces; and a concave, thinned portion near the long end expressly "enhancing access to the patient's mouth." It is not a U-shaped open body; it is a solid block with a concavity and window.
• US5466153A (Poindexter '5466153) — newly retrieved and materially more useful than the Prior Art section assumed: a bite block whose bite surfaces (2) "may have ridges or other irregularities which increase efficiency of the grip"; flanges (6) on either side of the bite surfaces which help hold the block in place and "hold the teeth against the bite surfaces"; a medial groove for suction tubing; and replaceable bite surfaces 10/11 made of "a rubber or rubber-like material" that are caps fitting over a protrusion of the block. This is the single best cited disclosure of a softer bite-surface element on a harder body (maps to claims 4/5/14/15) and of traction ridges flanked by tooth-restraining flanges (maps to claims 3/7/8/9/13/17/18).
• US4887965A (Fox '965) — confirmed: a mouth prop of two opposing jaw-engaging members 6, 8 connected at corresponding ends by a leaf spring 10, carrying resilient molding material 18, with flanges 30–33 and screw/sleeve adjustment. Its relevance is the elastic connector at the joined ends (a "spring hinge" analogue to the bight) — not an open U-body.
• US4975057A (Dyfvermark '5057) — confirmed: an angled bite block with an integrally formed evacuation aperture/recess and tooth-contact faces said to "present a number of [ridges?]" (snippet truncated — I will not assert a ridge disclosure). Solid angled block, left/right versions. Not a U-shaped open body.

Still unverified: US2823455A (Sprague '455), US1143515A (Dunlop), US1229595A (Du Brul), GB180607A (Hoare), US4356821A (Rind), US4944313A (E-Z-Em), US5152300A (Horst), US5590643A (Flam). Where a combination below depends on these, I flag it.

4. Combinations that would render the claims obvious

Combination A (primary): Osborn '595 + Flynn '327 + Poindexter '5466153

Result: an open, arm-flanked bite block with a tooth-gripping surface carried on a softer outer material and flanked by tooth-restraining walls.

• Osborn '595 supplies the problem statement and the access motive: a pliable mouth prop whose window and concave thinned portion exist specifically to increase dentist access and visibility, and whose flanges keep soft tissue out of the working area.
• Flynn '327 supplies the structural vocabulary: arms 14/16 flanking large inverted-U openings 50 large enough to admit fingers/instruments, with tooth-support walls carrying retention ridges.
• Poindexter '5466153 supplies grip and lateral retention: ridges on the bite surfaces, flanges on either side of the bite surfaces that hold the teeth against those surfaces, and a rubber/rubber-like cap over a harder block providing a compliant bite surface.

Why a POSITA would combine them: all three are dental mouth props / intraoral instruments in the same field of endeavor and address the same two recurring problems — (i) hold the jaw open comfortably and (ii) keep the working field clear. Osborn explicitly frames increased access and visibility as its objective; Flynn explicitly frames admitting instruments/fingers as its objective; Poindexter explicitly frames grip and retention. A designer starting from Osborn's access goal and Flynn's arm-and-opening geometry would adopt Poindexter's ridged, flanged, soft-capped bite surface as an obvious way to keep the patient's teeth seated on the block without sacrificing access. There is no functional incompatibility among these features — the combination is a mere aggregation of known elements each performing its known function (cf. In re Keller).

Combination B (secondary): Combination A + Via '101, with the rib limitation supplied by routine design (KSR)

Result: adds the textured/serrated traction concept and, critically, the bight ribs.

• Via '101 teaches that teeth indent into and lock against a compliant bite-block surface — the same traction purpose served by Osborn's pliable material, Poindexter's ridges, and claims 3/7/10/13/17.
• Element 1D (ribs): no cited reference discloses ribs extending between the arms at the bight. This limitation must be carried by common knowledge / KSR "predictable variation": (a) adding stiffening ribs or gussets to a molded plastic part — especially at a bend, hinge, or narrowed section — is a routine mechanical-design technique to control stiffness; (b) the specification itself admits the ribs' function is to strengthen a thin flexible bight so it resists biting forces while still flexing, i.e., a straightforward stiffness trade-off; (c) Fox '965 independently teaches an elastic spring connection at the joined ends of two jaw-engaging members, supplying the motivation to tune the stiffness of that joint. A POSITA seeking a bight that flexes for fit but does not collapse under occlusal load would predictably add ribs.

Combination C (alternate base): Dyfvermark '5057 + Osborn '595 + Poindexter '5466153 (+ Via '101)

• Dyfvermark '5057 supplies an angled bite block with integral evacuation/suction structure and (according to the spec's framing) tooth-contacting faces — strong motivation to consolidate suction/evacuation into the bite block, which is exactly the "working access through the block" theme of the '521 claims.
• Combined with Osborn's access-thinned block and Poindexter's ridged/flanged/soft-capped bite surfaces, this yields the claimed functional ensemble; the U-body/ribs again rest on routine design choice.
• Caveat: Dyfvermark's exact tooth-face contour was only partially retrievable (truncated snippet); the ridge aspect of this combination is asserted cautiously.

Combination D (weakest, contingent): Sprague '455 (or another U-shaped/arched prop) + Via '101 + Poindexter '5466153

If US2823455A (Sprague) — cited in the '521 record and classified with mouth props, and repeatedly cited as background in later bite-block filings — turns out to disclose a U-shaped/arched bite block, it would supply 1A–1C directly, making the combination materially stronger and shifting the fight entirely to 1D. This reference is unverified in this session; I do not assert its structure. It is the single highest-value item to verify if the invalidity position is to be pressed.

5. Why the motivation to combine is strong (summary of KSR rationales)

1. Same field / analogous art: every reference is a dental mouth prop or intraoral instrument; no field-crossing justification is needed.
2. Same problem, known solutions: open the mouth, maximize access, retain the teeth, cushion the bite.
3. Predictable results: each added feature performs its known function with no unexpected interaction (aggregation, not synergy).
4. Design incentive / market pressure: a single device that props the mouth, protects soft tissue, allows suction/evacuation, and fits variable mouths — exactly the consolidation Osborn, Flynn, and Dyfvermark each chase individually.
5. Finite set of known configurations: solid block (Via, Osborn), wedge (Osborn), tubular mouthpiece (Flynn), angled block with aperture (Dyfvermark), spring-jointed plates (Fox). An open U-shaped channel is one of a small number of predictable alternatives → "obvious to try."
6. Routine design choice: ribs to tune stiffness at a bight; a softer over-molded bite surface (Poindexter's rubber cap) for comfort/grip.

6. Claim-by-claim obviousness posture

7. Counterarguments, weaknesses, and what would defeat the § 103 case

• The rib limitation (1D) is not squarely in the art. This is where the challenge is most likely to stall. A patentee would argue the cited references are all solid or tubular bodies and none teaches ribs extending between the arms at a bight; the combination would be a hindsight reconstruction. Expect a genuine dispute on whether ribbing a molded bight is "predictable variation" or a substantive redesign.
• Possible teaching away is weak. Via's solid block consumes maximal space, but Via does not criticize or discredit open/U-shaped designs, so it does not rise to teaching away. The specification's criticisms of Via/Osborn are the patentee's characterizations, not the references' own teachings — they cannot do the teaching-away work.
• No anticipation, and examiner allowance. The examiner allowed claims 1 and 12 over this same 19-reference list, which is some (non-binding) evidence the examiner viewed the combination as non-obvious. That cuts against a § 103 challenge, though allowance is not a validity holding.
• Secondary considerations are likely unavailable to the patentee. Per the prior Assignment section, there is no assignee, no commercialization evidence, and the patent expired 2018-07-13. Long-felt-need or commercial-success evidence is therefore unlikely to exist. The only residual argument — "the bight spring-hinge-plus-ribs balance is unexpected" — reads as an ordinary stiffness trade-off, not an unexpected result.
• Design patent cannot anticipate. USD297665S (Neeley) can be used only as § 103 state-of-the-art evidence of bite-block geometry; its depicted form should be inspected, but it cannot supply a functional limitation as a matter of law.
• Procedural posture. Consistent with the prior Litigation and PTAB sections, no § 103 ground was ever litigated or instituted against this patent, and because no IPR ever issued, no § 315(e)(2) estoppel constrains any defendant — every ground above remains fully available in court. Conversely, the patent expired 2018-07-13, so § 103 now matters only for retrospective/collateral purposes, not for injunctive or forward-looking relief.

8. Bottom line

There is no single-reference anticipation, but a credible multi-reference § 103 case exists. The strongest assembly is Osborn '595 + Flynn '327 + Poindexter '5466153, optionally reinforced by Via '101 and Dyfvermark '5057, with the "strengthening ribs extending between the arms" (element 1D) supplied by KSR "predictable variation"/routine molded-part design and motivated by Fox '965's spring-jointed members. On that record, claims 1 and 12 and most dependents appear obvious, with claims 6 and 16 (santoprene over polypropylene) the most defensible because no cited reference discloses those materials.

Highest-value verification before relying on this position: confirm the actual structure of US2823455A (Sprague) — if it is a U-shaped/arched bite block, element 1D becomes the only contested limitation. Secondary: confirm the truncated tooth-face text in Dyfvermark '5057 and the illustrated geometry of USD297665S (Neeley).

Confidence: High on the Osborn, Poindexter, Fox, and Dyfvermark characterizations (verified this session) and on the absence of any anticipation. Medium-to-low on the rib limitation and on any combination that depends on the still-unverified references (Sprague '455, Dunlop '515, Du Brul '595, Hoare GB180607, Rind '821, E-Z-Em '313, Horst '300, Flam '643).