Clinical Sequence for Acrylic Partial Dentures

Chairside clinical sequence for an acrylic-based (mucosa-supported) removable partial denture — the tissue-borne alternative to the cast Co-Cr framework. Wrought-wire clasps are added after the acrylic is processed. Two pathways below: Sequence A = no OVD increase (confirmative, record at MIP); Sequence B = OVD increase (reorganised, record at a new vertical dimension). The companion cast-metal note is Clinical Sequence for Partial Dentures; the paste-ready chairside version is Acrylic RPD Clinical Sequence Template.

Acrylic RPD — when to choose it (indications & caveats)

• Interim / transitional: a provisional prosthesis to restore aesthetics/function while healing, during the control phase, or before a definitive appliance. Simple to make, easy to repair, and easy to add teeth to if further loss is expected. (Source: L1 Introduction to RPD — Interim RPD.)
• Immediate partial: fabricated pre-extraction and inserted immediately after extraction — eliminates the edentulous period, stabilises the clot, and maintains adjacent/opposing tooth position during healing. (Source: L1 Introduction to RPD.)
• Compromised abutments: acrylic is tissue-supported, distributing load to the mucosa rather than loading periodontally weak or mobile teeth — preferred when abutments cannot safely bear a cast framework. (Source: L3 Rests and Rest Seats — Free-End “missing four teeth” case study & Audio Appendix: acrylic is “tissue-supported… require no rest seat preparations… indicated when abutments are periodontally compromised”.)
• Cost / simplicity: cheaper and simpler to manufacture than Co-Cr, with lower laboratory fees and patient co-payments. (Source: L1 Introduction to RPD — Definitive RPD.)
• Limitations: bulkier; higher fracture risk; poorer retention and longevity than cast metal; tissue-borne loading. (Source: L3 Rests and Rest Seats Audio Appendix.)

• With severe loss of vertical dimension there may be insufficient prosthetic space for an adequate thickness of acrylic → a metal framework (or thin metal backing) is required instead. Reassess before committing to acrylic. (Source: L1 Introduction to RPD — the lecture states the principle, "insufficient space for adequate acrylic thickness; metal frameworks are required"; it gives no numeric minimum. The textbook anchor for denture-base material selection is McCracken 13e Ch 9, 11 9 - Denture Base Considerations, p.112–124.)

Key differences from the Co-Cr pathway

• No framework fabrication and no framework try-in visit — the master model is not duplicated, surveyed or cast. The MMR is recorded on a record base + wax rim built on the master model instead. (Source: L9 Clinical Sequence — the acrylic workflow has no duplication/investment/casting steps; the Co-Cr workflow explicitly adds them.)
• Generally no second-stage biomechanical mouth prep (rest seats, guide planes, height-of-contour changes, survey crowns) — only the control phase applies. (Clarification: L8 Mouth preparation for RPD frames the second, biomechanical stage around “the metal structure”; L3 Rests and Rest Seats states acrylic partials “require no rest seat preparations”. L8 does not state the acrylic exception in so many words — this is our synthesis of the two.) Acrylic partials may still carry wrought-wire clasps and occasionally simple rests, so it is not “zero tooth contact”.
• Clasps are added after acrylic processing (wrought-wire), not cast into a framework. (Source: L9 Clinical Sequence — Acrylic Workflow Notes: “Clasps are added after processing”.)
• Simpler lab prescription: master model + bite registration + lab slip (clasp positions, teeth to be replaced, shade). No study model with framework design, no major-connector/rest-location detail. (Source: L9 Clinical Sequence — Laboratory Requirements by Denture Type.)
• Facebow mounting and a new base & wax rim on the master model are still required. (Source: L9 Clinical Sequence.)

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Sequence A — Acrylic RPD, no OVD increase

Visit 1 — Preliminary impressions

• Preliminary alginate impressions of upper and lower arches (stock trays, periphery wax for support).
• Kennedy III / IV (no free-end saddle) → conventional bite registration; Kennedy I / II → digital bite reg (video all the contacts on your phone first).
• Lab: pour study models (type 3 gypsum); fabricate diagnostic base & rim if required (see callout).

"Base & rim — only if needed" (why it's conditional)

The diagnostic record base + wax rim exists for one job: to let the lab mount the study casts (record the maxillo-mandibular relationship). You only need one when the remaining teeth can’t register the bite on their own:

• Tooth-bounded (Kennedy III / IV, stable MIP) → the existing occlusion is your registration → hand-relate the casts with a simple bite reg; no rim needed. (Source: L9 Clinical Sequence — “Class 3 cases: models may be hand-related with normal bite registration material”.)
• Free-end saddles (Kennedy I / II) or large spans → no posterior tooth contacts to stop the bite → you need a rigid base carrying a wax rim built to the correct occlusal plane and OVD to hold the vertical stop while you register. (Source: L9 Clinical Sequence — a base is required to mount “Kennedy Class I, II and extensive Class IV” cases.)
• Missing anterior teeth → the leaf gauge can’t be used → base + rim with extraoral references (base of nose → chin). (Source: L9 Clinical Sequence — “Establishing OVD Without Anterior Teeth”.)
• Raising the OVD (Sequence B) → the wax rim is where the new vertical dimension is set. (Source: L9 Clinical Sequence, Sequence B.)

For record-base periphery and wax-rim dimensions/registration technique, the transferable complete-denture reference is L4 Base Rim MMr.

Visit 2 — Jaw relations & tooth selection

• Try in the diagnostic base & rim; check adaptation and stability. (chairside technique: Registration Sequence for a Removable Partial Denture)
• Record jaw relations: centric relation (leaf gauge, confirmative approach, record at MIP — don’t bite too hard); facebow (maxillary cast) and protrusive record.
• OVD = RVD − freeway space; verify with closest-speaking-space (“Mississippi 66” — sibilants shouldn’t click).
• Mark landmarks on the rim (midline, canine lines, smile line).
• Select prosthetic tooth shade and mould.
• Lab: mount study models on a semi-adjustable articulator.

Visit 3 — Design & special tray

• Plan the design: clasp positions and which teeth to replace (shade/mould already chosen at Visit 2). No framework survey/design/cast (tissue-supported).
• Note any minimal tooth modification only if genuinely needed — usually none.
• Lab: fabricate special (custom) tray on the study model.

Visits 2 and 3 are commonly combined for straightforward acrylic cases

The split mirrors the Co-Cr sequence, where Visit 3 carries real chairside content — reviewing the lab’s diagnostic wax-up and surveying/designing the metal framework against the mounted casts. Acrylic has no framework to survey and usually no wax-up, so “design” shrinks to deciding clasp positions and which teeth to replace — desk/chairside work that doesn’t need the mounted casts back. The special tray is a lab step made on the Visit-1 study cast, so it doesn’t depend on Visit 2 either. In practice you can record jaw relations + select teeth + note the clasp plan in one appointment, send the casts for mounting + special tray, and next see the patient at the final impression (Visit 4). (L9 Clinical Sequence’s acrylic workflow lists only mouth prep → special tray → final impression, with the base-&-rim/MMR folded into the study-model workup.) Keep them separate when you want a wax-up/try-in preview, need tooth-modification decisions against mounted casts, or for lab/clinic scheduling. The copy-pastable checklist below merges them.

Why acrylic usually skips the biomechanical mouth-prep stage

Mouth preparation has two stages: a first (control) phase — perio, endo, restorative, surgical — that restores oral health, and a second (biomechanical) phase — rest seats, guide planes, height-of-contour recontouring, survey crowns. The second phase exists to optimise the fit of the metal framework against the abutment teeth. (Source: L8 Mouth preparation for RPD — Objectives of Mouth Preparation; the biomechanical stage is described as serving “the metal structure”.) Because an acrylic partial is tissue-supported and “requires no rest seat preparations” (L3 Rests and Rest Seats), it generally needs only the control phase.

Visit 4 — Mouth prep & final impression (key visit)

• Complete the control phase first (perio / endo / restorative / surgical).
• Generally no rest-seat / guide-plane preparation (mucosa-supported — see callout above).
• Try the custom tray in the mouth; check it is not overextended; retract lips/cheeks to copy frenula. (Source: L9 Clinical Sequence — Impressions and Master Cast.)
• Impression: border-mould with putty → light-body PVS → heavy-body PVS in the tray → seat and take the final elastomeric impression.
• Lab: bead, box and pour the master model (no duplication, no framework); make a new base & wax rim on the master model.

Visit 5 — MMR on record base (replaces the framework try-in)

• Try in the new record base & wax rim built on the master model; check adaptation and stability.
• Record the MMR (facebow + CR at the established OVD).
• Confirm midline / occlusal plane / lip support on the rim.
• Lab: cross-mount the master models; set up teeth.

Where the acrylic record base attaches (vs Co-Cr)

For a Co-Cr case, the acrylic base + wax rim for the MMR is added to the saddle region of the framework; for an acrylic case there is no framework, so the base & wax rim is built on the master model itself. (Source: L9 Clinical Sequence — Acrylic Workflow Notes vs Maxillo-Mandibular Relationship Recording.)

Altered-cast (corrected-cast) technique — recording the free-end saddle under functional compression — is indicated for mandibular Kennedy Class I & II distal-extension cases (finger pressure on the rests only, never on the saddle). It is not used for the maxilla or Class III. Its stated indication is by arch/Kennedy class, not by material. (Source: L9 Clinical Sequence — Altered Cast Technique.)

Visit 6 — Wax try-in

• Check occlusion (even across the arch), OVD, aesthetics and neutral-zone position.
• Prefer to move teeth rather than grind them at this stage; get patient approval.
• Lab: process the denture, then add the wrought-wire clasps after processing.

Wrought-wire clasps & undercut engagement

Acrylic partials are retained by wrought (drawn) stainless-steel wire clasps, which are more flexible than cast clasp arms and are embedded into the acrylic after the denture is cured — not cast into a framework. (Source: L9 Clinical Sequence; flexibility from L10 RPDs Summary / L11 RPD Lecture Recap.) The retentive tip engages a 0.75 mm undercut (the standard depth for stainless/wrought wire; cf. CoCr 0.25 mm, cast gold 0.50 mm). (Source: L6 Dental Surveyor, L7 Survey and Design — undercut depths by alloy.)

Visit 7 — Insertion

• Inspect the base before insertion: voids/porosity (→ return to lab), nodules/sharp projections (remove chairside), overextensions (trim), round sharp edges.
• Seat and assess: retention, stability, base extension, occlusal contacts (articulating paper), reassess OVD (processing can shift teeth), appearance.
• Check/adjust the wrought-wire clasp engagement (bend to adjust — do not over-tighten).
• If poor saddle adaptation: reline with PVS / ZOE using the rests-only pressure technique; for a chairside reline pickup, record the bite registration before the pickup impression.
• Give denture care, cleaning and adaptation instructions.

Visit 8 — Review (~2 weeks; earlier if symptomatic)

• Assess adaptation; address complaints.
• Don’t over-adjust at insertion — confirm true pressure points at review using fit checker / light body (perforations = strong contact); trim gradually with an acrylic bur in a straight handpiece.
• Re-check clasp retention; add teeth later if further extractions occur.

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Sequence B — Acrylic RPD, with OVD increase

Same skeleton as Sequence A — only the early steps differ. The OVD increase is established and stabilised before the final impression, then the case rejoins Sequence A from Visit 4 onward.

Visit 1 — Preliminary impressions

• Identical to Sequence A (alginate prelims → lab study models, base & rim). Here the base & rim is effectively always needed, because it carries the new vertical dimension.

Visit 2 — Jaw relations at the new OVD (reorganised)

• Establish the target increased OVD on the wax rim (not simply MIP).
• Use extraoral references (base of nose → chin), RVD − freeway space, and confirm with phonetics / closest speaking space.
• Facebow + record jaw relation at the new vertical dimension.
• Select shade & mould; mark landmarks.
• Lab: mount at the new OVD.

Visit 3 — Diagnostic wax-up at the new OVD

• Wax up to the new OVD and confirm the occlusal plane.
• Plan composite build-ups and/or restorations to support the increased VD.
• Finalise the design (clasp positions, teeth to replace, shade — no framework).
• Lab: special tray.

Visit 3b/4 — Stabilise the new OVD (extra step vs Sequence A)

• Place composite build-ups and/or restorations to the planned OVD.
• Verify comfort, phonetics and occlusion; allow an adaptation period at the new VD.

• Heavily worn dentitions (the usual reason to raise OVD) often warrant prosthodontic referral — assess complexity before committing.

Visit 4 onward — rejoin Sequence A

• From the mouth-preparation/final-impression visit onward, follow Sequence A, Visits 4–8 unchanged. The acrylic denture is built to the increased OVD and can itself carry the interim OVD.
• Provisional composite build-ups may later be replaced with definitive restorations if planned.

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How this differs from the cast-metal pathway

See Clinical Sequence for Partial Dentures for the full Co-Cr sequence. In brief: the Co-Cr pathway adds a diagnostic wax-up + survey/design step, biomechanical mouth prep (rest seats, guide planes, survey crowns), master-model duplication + framework casting, and a framework try-in visit (at which the MMR is recorded on a base added to the framework). The acrylic pathway omits all of these — the MMR is instead recorded on a base & wax rim built on the master model, and clasps are added after processing.

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Copy-pastable checklist

(Chairside version — Visits 2 & 3 of the prose above are combined into one appointment.)

VISIT 1 — Preliminary impressions
- Alginate prelim impressions U/L (stock trays, periphery wax)
- Bite registration (Kennedy III/IV conventional; I/II digital + video contacts)
- Lab: study models (type 3 gypsum), base & rim if needed

VISIT 2 — Jaw relations, tooth selection & design
- Try in base & rim
- Record CR (leaf gauge, confirmative/MIP), facebow, protrusive
- OVD = RVD - freeway; verify "Mississippi 66" (closest speaking space)
- Mark midline / canines / smile line
- Select shade & mould
- Plan clasp positions + teeth to replace (NO framework survey/cast)
- Minimal tooth mod only if needed (usually none)
- Lab: mount on articulator; make special (custom) tray

VISIT 3 — Mouth prep & final impression (KEY)
- Complete control phase first (perio/endo/resto/surgical)
- Generally NO rest-seat / guide-plane prep (mucosa-supported)
- Try-in custom tray (not overextended); copy frenula
- Border-mould (putty) -> light-body PVS -> heavy-body in tray
- Take final elastomeric impression
- Lab: bead/box/pour master model (NO duplication, NO framework); new base & wax rim

VISIT 4 — MMR on record base (replaces framework try-in)
- Try in new base & wax rim on master model; check adaptation
- Record MMR (facebow + CR at established OVD)
- Confirm midline / occlusal plane / lip support
- Lab: cross-mount, tooth setting

VISIT 5 — Wax try-in
- Check occlusion, OVD, aesthetics, neutral zone
- Move teeth, don't grind; get patient approval
- Lab: process denture + add wrought-wire clasps after processing

VISIT 6 — Insertion
- Inspect base: voids (->lab), nodules/sharp edges (remove chairside), overextensions (trim)
- Check retention, stability, extension, occlusion (articulating paper), OVD, appearance
- Check/adjust wrought-wire clasp engagement (bend to adjust)
- Reline if poor saddle adaptation (bite reg BEFORE pickup impression)
- Care / cleaning / adaptation instructions

VISIT 7 — Review (~2 weeks)
- Assess adaptation, address complaints
- Identify true pressure points (fit checker / light body), trim gradually
- Re-check clasp retention; add teeth later if further extractions