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Standardised Post-Processing & Polishing Protocol for Occlusal Splints

Shared Clinical Target Across All Three Methods

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METHOD 1: Conventional Heat-Cure PMMA (Vacuum Mixed, Long Cure Cycle)

Pre-polishing assumptions

• Vacuum mixed at -0.8 bar to eliminate porosity
• Long cure cycle: 70°C for 90 min + 100°C for 30 min (or manufacturer equivalent terminal cycle)
• Bench-cooled slowly in flask to minimise residual stress before deflasking

Post-processing & Polishing Sequence

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METHOD 2: FormLabs Dental LT Clear Resin V2 (SLA / Form 3B+)

Critical Pre-Polishing Requirements (MUST complete before any polishing)

Polishing Sequence (Post-Cure)

• The MDPI surface roughness study (2025) found that mechanical polishing combined with centrifugation on 3D-printed splints achieved the lowest Ra (0.646 µm → ~0.64 µm; without centrifuge, pumice + mechanical = Ra 0.60 µm), with polishing being the dominant variable regardless of layer thickness or orientation.
• After the complete polishing sequence in the Zurich/Formlabs comparative study, SLA splint Ra remained slightly above milled/conventional but fell well below 0.2 µm clinically acceptable threshold.
• Warning: Overly aggressive polishing wheels (rough pumice without progression) applied to SLA resin without adequate grit progression can increase Ra paradoxically if abrasive particles embed in the softer resin matrix.

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METHOD 3: PMMA Milled Splint (5-Axis CAD/CAM, Pre-polymerised Disc)

Pre-polishing notes

• Pre-polymerised industrial PMMA discs (e.g., Merz Dental M-PM, Pressing Dental Smile-Cam, etc.) are milled from fully cured homogeneous PMMA - no post-cure required.
• Starting Ra is the lowest of the three methods (0.085-0.117 µm per PMC 2025 study; 0.087 µm per the Zurich study) due to CNC toolpath precision.
• The primary surface defects are toolpath ridges and milling striations, not porosity.

Post-processing & Polishing Sequence

• The Zurich study found milled PMMA (5-axis, M-PM discs) achieved Ra 0.087 µm unpolished with laboratory polishing and Ra comparable to conventional method after polishing - the lowest of all three groups.
• Valenti et al. (2024) systematic review/meta-analysis (Hedge's g = -1.25 [CI: -1.84, -0.66]) confirms milled specimens had statistically lower surface roughness than conventional heat-cured at baseline.
• Ozden et al. (JoVE, 2025, PMID 39895617): after 600-800-1000 grit sequence, milled and heat-polymerised PMMA showed no statistically significant difference in Ra, confirming the sequence equalises outputs.

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Comparative Summary Table

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Cross-Method Standardisation Principles

1. All three methods reach clinically equivalent Ra post-polishing with a structured sequence - the starting point differs, not the end point. The 2025 PMC study (PMID 41777279) confirms all groups reached comparable Ra after standardised polishing.
2. The sequence must be progressive - skipping grits or going directly to pumice creates embedded abrasive particles and paradoxically higher Ra values.
3. Never skip post-cure for SLA - polishing an under-cured FormLabs LT Clear splint risks toxicity and surface delamination. The oxygen-inhibited surface layer must be converted.
4. Heat generation is the primary polishing hazard - excessive wheel speed, static pressure, or dry polishing causes surface crazing in all three materials. Use water cooling through the grit paper stages; keep lathe RPM at 1500-1800 for PMMA.
5. Intaglio (tissue-facing) surface should not be polished aggressively - retention is functional. Focus polishing effort on the external/occlusal surfaces and borders.
6. Ultrasonic cleaning before delivery is non-negotiable for all three methods - residual pumice or polishing compound in intaglio undercuts creates a bacterial substrate.

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