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Standardisation sequence protocol for polishing post processing of conventional heat cure made with vacuum mixing while packing and long curing cycle , 3d printed occlusal splints fabricated from form lab dental lt clear resin sla technique and pmma milled occlusal splint from 5axis milling machine . Write a write up in detail for thesis , and write the comparison table of all 3 tech

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Standardisation Sequence Protocol for Polishing and Post-Processing of Occlusal Splints: A Comparative Study of Conventional Heat-Cure (Vacuum Mixed, Long Curing Cycle), 3D-Printed (Formlabs Dental LT Clear Resin, SLA) and PMMA-Milled (5-Axis CAD/CAM) Fabrication Techniques

Chapter 1: Introduction

Occlusal splints are removable intraoral appliances used in the management of temporomandibular disorders (TMD), bruxism, and occlusal parafunctional habits. Their clinical success depends not only on accurate fit and adequate occlusal coverage but also on the surface quality delivered to the patient. Surface roughness above the critical threshold of Ra > 0.2 µm promotes microbial adhesion, plaque accumulation, gingival irritation, and material degradation, underscoring the clinical imperative for a well-defined and reproducible finishing and polishing protocol.
Historically, occlusal splints were fabricated exclusively using conventional heat-polymerized polymethyl methacrylate (PMMA) resin processed in a dental flask under pressure and heat. While this method remains the reference standard for flexural strength, two transformative manufacturing paradigms have entered routine dental laboratory and clinical practice: subtractive manufacturing (SM) through 5-axis computer-aided design/computer-aided manufacturing (CAD/CAM) milling of pre-polymerized PMMA pucks, and additive manufacturing (AM) through stereolithographic (SLA) 3D printing using photopolymer resins such as Formlabs Dental LT Clear Resin.
Each manufacturing pathway produces a unique surface texture, residual stress profile, and chemical composition that demands a specifically adapted post-processing and polishing sequence. Despite this, the literature has lacked a standardized, validated, and stepwise polishing protocol applicable across all three technologies. Recent comparative studies (Uma et al., 2025; Maleki et al., 2024; Bieger et al., 2023) have established that while unpolished splints from these three methods exhibit statistically significant differences in surface roughness, microhardness, and color parameters, a standardized polishing sequence can equalize surface quality to clinically acceptable levels across fabrication methods.
This thesis proposes and validates a standardization sequence protocol for polishing and post-processing for each of the three fabrication techniques, analyzing the rationale behind each step, the instrumentation employed, and the expected outcomes based on current evidence.

Chapter 2: Review of Literature

2.1 Conventional Heat-Cure Acrylic Resin (Vacuum Mixed, Long Curing Cycle)

Conventional heat-cured PMMA (ISO 20795-1:2013) has been the gold standard for removable prostheses and occlusal appliances for decades. The compression-molding technique involves mixing monomer and polymer under vacuum to minimize porosity, packing the dough-stage resin into a denture flask, and processing under a long curing cycle - typically 74°C for 8-9 hours followed by a terminal boiling stage at 100°C for 1-2 hours (or the modified 70°C/7-hour protocol). This long curing cycle minimizes residual monomer content, reduces polymerization shrinkage, and improves mechanical properties.
The as-processed surface emerging from the flask retains topographical irregularities from the plaster/stone investment surface, flash lines at the mold parting, and occasional resin blebs or voids due to air entrapment - despite vacuum mixing. The surface roughness (Ra) of unpolished heat-cured splints typically falls in the range of 0.5-1.5 µm, requiring systematic finishing and polishing to reach the clinical threshold of Ra < 0.2 µm. Heat-cured PMMA demonstrates the highest flexural strength and lowest vertical wear depth (approximately 27.5 µm) among compared materials (Maleki et al., 2024), and conventional polishing with pumice and high-shine compounds achieves predictable optical clarity.

2.2 3D-Printed SLA Occlusal Splints (Formlabs Dental LT Clear Resin)

Stereolithographic 3D printing builds the appliance layer-by-layer (typically 50-100 µm layer resolution) by selectively photopolymerizing a liquid methacrylate-based resin with a UV/visible-light laser. Formlabs Dental LT Clear Resin (V2) is a Class IIa biocompatible photopolymer approved for long-term intraoral use (U.S. 510(k) and EU MDR). It is formulated to be fracture-resistant, optically clear, and color-stable.
Critical to SLA post-processing is a mandatory dual-step post-curing: first, thorough washing in isopropyl alcohol (IPA) to remove uncured surface resin (in Form Wash, 10-15 minutes), followed by drying and secondary UV post-cure (Form Cure, wavelength 405 nm, 60°C, 30-60 minutes depending on resin lot). Incomplete post-curing leaves oxygen-inhibited uncured resin on the surface, producing a tacky, biocompatible-compromised layer with elevated surface roughness (Ra values as high as 2-5 µm in the as-printed, unpolished state). The staircase stepping artifact from layer-by-layer construction is the dominant source of surface roughness and is directly correlated to print orientation.
Research by Abdulai et al. (2026, J Dent) demonstrated that printing orientation and post-polymerization time significantly influence color stability, gloss, surface roughness, and Vickers hardness. Bieger et al. (2023, J Prosthet Dent) evaluated fibroblast behavior on SLA-printed, milled, and conventionally processed splint materials and found that surface treatment profoundly affects cytocompatibility, reinforcing the biological imperative for adequate polishing.

2.3 PMMA-Milled Occlusal Splints (5-Axis CAD/CAM)

Subtractive manufacturing mills occlusal splints from pre-polymerized, industrially homogenized PMMA discs/pucks (e.g., Ivoclar ProArt CAD Splint, Dentsply Cercon, Vita CAD-Temp) using 5-axis CNC milling centers. The industrial pre-polymerization process yields a homogeneous, dense, low-porosity PMMA blank with consistent mechanical properties superior to laboratory-mixed conventional PMMA in terms of porosity and residual monomer. The 5-axis milling capability allows undercut reproduction, complex curvatures, and intaglio surface accuracy that 3-axis systems cannot achieve.
The milled surface typically exhibits a characteristic "orange peel" or tool-mark texture with regular periodic scratch patterns corresponding to the final milling tool path (typically 0.2-0.5 mm step-over). The as-milled Ra is approximately 0.5-1.0 µm. The industrial pre-polymerization means no curing post-processing is required - unlike both conventional and 3D-printed methods - though a sequential polishing protocol is still mandatory. Milled PMMA splints show vertical wear depth of approximately 30.5 µm, comparable to heat-cured controls (Maleki et al., 2024), and represent the most dimensionally accurate method due to the absence of polymerization shrinkage.

Chapter 3: Materials and Methods - Standardization Protocol

3.1 Rationale for Standardization

Standardizing the polishing sequence across three fabrication technologies requires that the protocol:
  1. Address the specific surface defects unique to each manufacturing process
  2. Progress systematically from gross reduction to fine polishing
  3. Use instruments and materials that are universally accessible in dental laboratories
  4. Achieve a final Ra < 0.2 µm (the threshold below which bacterial adhesion is not significantly increased)
  5. Be reproducible by trained laboratory technicians without specialized equipment beyond standard dental lab setup
Uma et al. (2025, Natural and Life Sciences Communications) demonstrated that a standardized polishing sequence using 600-, 800-, and 1000-grit sandpaper followed by pumice and tallow resulted in comparable surface roughness across heat-cured, milled, and 3D-printed groups, despite their significantly different unpolished Ra values. This finding forms the scientific backbone of the protocol described below.

Chapter 4: Detailed Polishing and Post-Processing Protocols

4.1 Protocol A - Conventional Heat-Cure PMMA (Vacuum Mixed, Long Curing Cycle)

Phase 1: Pre-Polishing Preparation (Laboratory Stage, Post-Deflasking)

Step 1 - Deflasking and Flash Removal After completion of the long curing cycle and bench-cooling to room temperature (minimum 30 minutes - do not quench in cold water as thermal shock causes warpage), the flask is opened and the splint is carefully deflasked using chisels. Flash resin at the mold parting line is identified. Using a straight handpiece (20,000-30,000 rpm) with a tungsten carbide acrylic trimming bur (cross-cut fissure, ISO 166, medium grit), remove excess flash and resin blebs. Keep the bur moving at all times to prevent localized heat generation and surface crazing.
Step 2 - Gross Contouring and Occlusal Adjustment Mount the splint on the articulator. Evaluate occlusal contacts using articulating paper (8 µm shimstock). Adjust premature contacts using a round acrylic bur. Maintain the designed occlusal plane. Do not over-reduce - the objective is removing polymerization irregularities, not recontouring the occlusal surface.
Step 3 - Pumice Slurry Wet Grinding (Coarse Pre-Polish) Using the dental lathe at 2,000-2,500 rpm with a rag wheel (muslin) charged with medium pumice-water slurry, systematically work across all external surfaces. Keep the splint moving with gentle, sweeping motions. Pumice slurry abrades residual stone contamination, surface irregularities from the flask investment, and minor porosity. Duration: 3-5 minutes continuous coverage. Rinse thoroughly under running water.
Step 4 - Sequential Abrasive Paper Reduction Using a wet bench polisher or handpiece with abrasive disc mandrel:
  • 600-grit wet/dry silicon carbide paper: Address remaining surface irregularities and scratches from gross trimming. Work in parallel strokes; rinse between papers.
  • 800-grit: Refine the surface; scratches from 600-grit paper should be eliminated before proceeding.
  • 1000-grit: Final pre-polish. Surface should appear uniformly matte-grey without visible tooling marks.
  • Rinse and dry completely between each grit change.
Step 5 - Fine Pumice Polish (Lathe) Using a clean rag wheel (muslin) with fine pumice slurry on the dental lathe (2,000-2,500 rpm), polish all surfaces for 2-3 minutes. The surface should begin to acquire a semi-translucent appearance. Rinse with water; dry with air.
Step 6 - High-Shine Compound (Lathe) Using a dry flannel or chamois wheel charged with a high-shine acrylic polishing compound (e.g., Acrysheen, Hi-Shine, or equivalent laboratory-grade compound), polish all surfaces at 2,000-2,500 rpm for 2-3 minutes. The surface should achieve optical clarity and high gloss. Do NOT use pumice and high-shine compound on the same wheel; cross-contamination negates the high-shine effect.
Step 7 - Final Inspection and Quality Control Examine under magnification (x3.5 loupes or equivalent). Check for:
  • Residual surface porosity or voids - if present, repeat Steps 5-6
  • Sharp edges or spicules - remove with rubber abrasive point (medium grit) and re-polish
  • Confirm occlusal contacts with shimstock
  • Measure surface roughness (Ra) with contact profilometer if available; target Ra < 0.2 µm
Step 8 - Ultrasonic Cleaning and Disinfection Place the polished splint in an ultrasonic cleaner with neutral detergent solution for 5 minutes. Rinse. Immerse in 2% glutaraldehyde or 70% IPA for 10 minutes (surface-compatible disinfection). Rinse. Package for delivery.

4.2 Protocol B - 3D-Printed SLA Occlusal Splint (Formlabs Dental LT Clear Resin V2)

Phase 1: Mandatory Post-Cure Processing (Before Any Mechanical Polishing)

CRITICAL NOTE: Mechanical polishing of SLA parts MUST NOT begin before complete post-cure. The as-printed surface contains an oxygen-inhibited, uncured resin layer. Polishing before washing and post-curing will smear uncured resin, embed abrasive particles, compromise biocompatibility, and produce an unacceptable surface.
Step 1 - Part Removal from Build Platform Using the removal tool, carefully separate the printed splint from the build platform. Handle with nitrile gloves; uncured resin is a skin sensitizer. Inspect for print failures, delamination, or incomplete sections. Discard if structurally compromised.
Step 2 - Washing (Form Wash or Manual IPA Wash)
  • Primary wash: Submerge in fresh IPA (isopropyl alcohol, minimum 96% purity) in the Form Wash for 10 minutes with agitation (or manual wash in two sequential IPA baths, 5 minutes each with gentle agitation).
  • Secondary wash: Transfer to a second clean IPA bath for 5 minutes if using manual method.
  • Air-dry in open air for minimum 30 minutes until all solvent evaporates. Do NOT post-cure while wet with IPA - solvent entrapment causes surface crazing and compromised mechanical properties.
Step 3 - UV Post-Curing (Form Cure) Place the clean, dry splint in the Form Cure unit. Recommended parameters for Dental LT Clear Resin V2:
  • Temperature: 60°C
  • Duration: 30 minutes (Form Cure)
  • Ensure all surfaces receive uniform light exposure; rotate/reposition for complex geometries if needed
  • Refer to the current Dental LT Clear Resin Manufacturing Guide for lot-specific parameters
After post-curing, the surface will be tack-free and fully polymerized. The splint is now biocompatible for intraoral use, but mechanical polishing is still required to address staircase stepping artifacts.

Phase 2: Mechanical Post-Processing

Step 4 - Support Removal Using flush cutters (included in Formlabs Finishing Tools Kit) or a handpiece with a carbide bur, remove all support structures. Begin with flush cutters close to the support base; avoid tearing, which creates deep divots. Supports on the intaglio (tissue) surface are particularly damaging if torn - always cut with instruments.
Step 5 - Touchpoint Smoothing Using a straight handpiece at medium speed (15,000-20,000 rpm) with:
  • Medium Scotch-Brite wheel, OR
  • Green stone silicone carbide bur, OR
  • Medium rubber silicone abrasive point Smooth all residual touchpoint nubs flush with the appliance surface. Work carefully around occlusal areas to preserve designed contacts.
Step 6 - Staircase Artifact Reduction (Surface Contouring) SLA-specific step. The layer-by-layer build process leaves micro-stepped ridges on curved and angled surfaces (most prominent on the polished labial/buccal surfaces). Using:
  • Silicone diamond disc (pre-polish disc) in handpiece at 15,000-20,000 rpm
  • Smooth the surface with controlled, overlapping strokes perpendicular to the step orientation
  • Follow with a soft abrasive rubber wheel (grey/pink, fine grit) This step reduces Ra from the as-printed range (~2-5 µm) to approximately 1-2 µm.
Step 7 - Sequential Abrasive Paper Reduction As per Protocol A Step 4:
  • 600-grit wet silicon carbide paper - address remaining step artifacts and touchpoint areas
  • 800-grit - refine and blend
  • 1000-grit - final pre-polish; surface should be uniformly matte
Step 8 - Handpiece Pre-Polish Using felt wheel (hard felt, lathe or handpiece) at 8,000-12,000 rpm with a high-gloss composite/acrylic polishing compound:
  • Pre-polish phase with medium compound and felt wheel
  • Follow with soft felt or wool wheel using fine compound Duration: 2-3 minutes per surface.
Step 9 - Lathe Final Polish (for Maximum Transparency) For optimal optical clarity (Dental LT Clear Resin is designed to achieve high optical transparency after polishing):
  • Rag wheel charged with pumice-water slurry: 2 minutes at 2,000 rpm
  • Clean chamois/flannel wheel with dry high-shine acrylic compound: 2-3 minutes at 2,000-2,500 rpm The final surface should be optically clear and glossy.
Step 10 - Inspection and Quality Control As per Protocol A Step 7. Additionally, inspect for:
  • Any delamination at layer interfaces (indicates incomplete post-cure; discard)
  • Subsurface voids or bubbles (discard if present over functional occlusal surfaces)
  • Uniform transparency confirming complete polymerization
Step 11 - Final Cleaning and Disinfection Ultrasonic cleaning in neutral detergent (5 minutes), rinse, then disinfect with 70% IPA or surface-safe disinfectant. Note: avoid prolonged immersion in IPA after post-cure (>30 minutes) as it may affect surface quality.

4.3 Protocol C - PMMA-Milled Occlusal Splint (5-Axis CAD/CAM)

Phase 1: Pre-Polishing Assessment (Post-Milling)

Step 1 - Removal from Milling Disc and Inspection After milling completion, carefully remove the splint from the PMMA puck using flush cutters to sever the retention sprue(s). Inspect for:
  • Incomplete milling (undercuts that the 5th axis could not access)
  • Tool marks or chatter (vibration artifact from worn burs)
  • Surface consistency of the intaglio surface
  • Integrity of spruing attachment areas
No curing step is required for milled PMMA. The industrial pre-polymerization is complete. Proceed directly to mechanical finishing.
Step 2 - Sprue/Connection Point Removal and Gross Contouring Using a tungsten carbide trimming bur in a straight handpiece (20,000-30,000 rpm), remove the sprue connection points flush with the appliance surface. The as-milled surface is characterized by regular periodic tool-path marks - parallel grooves from the finishing ball-end mill. These require systematic abrasive reduction, but no flash removal is needed (unlike conventional).
Step 3 - Occlusal Verification Mount on articulator. Milled splints typically require minimal occlusal adjustment due to the high dimensional accuracy of 5-axis milling (no polymerization shrinkage). Check shimstock contacts. Any minor adjustments: use a round acrylic bur with minimal stock removal.

Phase 2: Sequential Polishing

Step 4 - Sequential Abrasive Paper Reduction Milled PMMA tool marks are regular and periodic, making abrasive paper reduction highly efficient:
  • 400-grit (optional preliminary step if heavy tool marks are present from rough milling pass)
  • 600-grit wet silicon carbide paper - working parallel and then perpendicular to existing tool marks
  • 800-grit
  • 1000-grit - final pre-polish
  • Optional: 1200-grit for particularly demanding optical transparency requirements (e.g., where the patient requests maximum aesthetics) Rinse and dry between each grit.
Step 5 - Pumice Slurry Pre-Polish (Lathe) Rag wheel (muslin) with medium pumice slurry at 2,000-2,500 rpm for 3 minutes. The milled PMMA surface polishes faster than conventional heat-cured material due to lower porosity and greater material homogeneity. Rinse.
Step 6 - High-Shine Final Polish (Lathe) Clean flannel or chamois wheel with high-shine acrylic compound at 2,000-2,500 rpm for 2-3 minutes. Milled puck PMMA achieves excellent optical clarity due to its industrial pre-polymerization and homogeneous microstructure. The result should be high gloss with Ra < 0.2 µm.
Step 7 - Handpiece Touch-Up (Selective Areas) For concave intaglio surfaces and palatal curvatures that the lathe wheel cannot access:
  • Use rubber abrasive points (fine, then extra-fine)
  • Felt points with polishing compound
  • Wool buff attachment in handpiece for final shine in inaccessible areas
Step 8 - Inspection and Quality Control As per Protocol A Step 7. Milled splints should exhibit the most dimensionally accurate intaglio surface; evaluate tissue-fit on the study model. Minor milling chatter marks on non-occlusal areas are acceptable if polishing removes surface roughness below threshold.
Step 9 - Ultrasonic Cleaning and Disinfection As per Protocols A and B.

Chapter 5: Key Parameters, Threshold Values, and Scientific Basis

5.1 Clinical Significance of Surface Roughness (Ra)

The threshold Ra of 0.2 µm for dental prosthetic materials is established based on the correlation between surface roughness and Streptococcus mutans and Candida albicans adhesion. Surfaces with Ra > 0.2 µm demonstrate exponentially increased microbial colonization, which in the context of occlusal splints - worn nightly and often for extended periods - represents a significant infection risk and potential cause of mucosal inflammation.
Uma et al. (2025) demonstrated that:
  • Unpolished heat-cured specimens: Ra significantly variable (0.5-1.5 µm range)
  • Unpolished 3D-printed specimens: highest Ra among all groups (2-5 µm, staircase artifact)
  • Unpolished milled specimens: intermediate Ra (0.5-1.0 µm, tool-mark pattern)
  • All groups after standardized polishing protocol (600/800/1000-grit + pumice + tallow): Ra values converged to comparable and clinically acceptable levels

5.2 Effect of Polishing on Microhardness

Polishing was found to decrease Vickers Hardness Number (VHN) in heat-cured and 3D-printed groups, while milled PMMA showed less pronounced hardness reduction. This is explained by removal of the harder surface skin of heat-cured PMMA and removal of any residual oxygen-inhibited surface in SLA-printed parts. The clinician should be aware that excessive polishing beyond the recommended sequence could compromise surface hardness, particularly in SLA-printed splints.

5.3 Color and Optical Clarity

The polishing sequence (L* > a* > b* trend) improves lightness (L*), optical clarity, and reduces yellowing (b*). Milled PMMA B (ML-B) demonstrated the best overall performance - highest L*, near-zero b*, and lowest Ra post-polishing. Dental LT Clear Resin achieved clinically acceptable transparency after the full polishing sequence, confirming its optical formulation is activated by polishing. Heat-cured PMMA polishes to a predictable milky-clear appearance.

5.4 Role of Vacuum Mixing and Long Curing Cycle

Vacuum mixing (reduced pressure during dough preparation) minimizes air inclusion, resulting in fewer subsurface pores that can open at the surface during polishing and create "craters" resistant to polishing. The long curing cycle (74°C + 100°C terminal stage) ensures more complete polymerization than short cycles, minimizing residual monomer that can soften the surface and interfere with high-shine polishing. For thesis documentation, the specific curing cycle should be recorded: water bath temperature, duration, and bench-cooling protocol are all variables that affect the polishability of the final appliance.

Chapter 6: Comparison Table - All Three Technologies

Table 1: Comprehensive Comparison - Conventional Heat-Cure vs. 3D-Printed SLA (Formlabs Dental LT Clear) vs. PMMA-Milled (5-Axis CAD/CAM)

ParameterConventional Heat-Cure PMMA (Vacuum Mixed, Long Cure)3D-Printed SLA (Formlabs Dental LT Clear Resin V2)PMMA-Milled (5-Axis CAD/CAM)
Manufacturing MethodCompression moulding in dental flask; heat-polymerizationStereolithography (SLA); photopolymerization layer-by-layer (50-100 µm layers)Subtractive CNC milling from pre-polymerized PMMA disc/puck
Resin/MaterialPMMA powder-liquid system (heat-cure type); ISO 20795-1Formlabs Dental LT Clear Resin V2 (dimethacrylate-based photopolymer); Class IIa biocompatiblePre-polymerized industrial PMMA disc (e.g., ProArt CAD Splint, Vita CAD-Temp)
Curing CycleLong cycle: 74°C/8-9 hr + 100°C/1-2 hr terminal boil (or 70°C/7 hr protocol)Print + mandatory IPA wash (10-15 min) + UV post-cure at 60°C, 30 min (Form Cure)No curing required (industrial pre-polymerization complete)
Mixing MethodVacuum mixing (reduces porosity and air inclusion)Not applicable (liquid resin in cartridge)Not applicable (pre-polymerized solid blank)
Dimensional AccuracyModerate; affected by polymerization shrinkage (~0.3-0.5%) and flask deformationGood; ~50-100 µm layer resolution; supports affect intaglio accuracy; print orientation dependentHighest accuracy; 5-axis eliminates shrinkage; tolerances ~20-50 µm
Polymerization ShrinkagePresent (~0.3-0.5%); compensated by packing pressurePresent during post-cure; layer-by-layer minimizes bulk effect but internal stresses accumulateNone (pre-polymerized blank)
PorosityLow (vacuum mixing reduces; still higher than milled)Very low subsurface porosity; oxygen-inhibited surface layer present before post-cureLowest porosity; homogeneous industrial polymerization
As-Fabricated Surface Roughness (Ra)0.5-1.5 µm (stone/plaster investment texture + mold flash)2-5 µm (staircase stepping artifact from layer-by-layer build; highest among three methods)0.5-1.0 µm (regular periodic tool-path marks from finishing mill)
Post-Cure Processing Required?No (bench-cooling only)YES - mandatory IPA wash + UV post-cure before any polishingNo
Support Removal Required?NoYES - flush cutters + bur smoothing of touchpointsNo (sprue removal only)
Flash/Sprue RemovalYES - flash at mold parting line; trim with carbide burNot applicable (supports differ from flash)YES - sprue connection points at disc holder
Dominant Surface Defect for PolishingFlask investment texture; mold parting flash; occasional voidsStaircase stepping artifact from layer orientation; support touchpointsRegular periodic tool-path grooves from ball-end milling bur
Polishing Sequence (Step 1)Pumice slurry on rag wheel (lathe, 2,000-2,500 rpm); gross pre-polishSupport removal + touchpoint smoothing (Scotch-Brite/silicone bur)Sprue removal + gross contouring (carbide bur)
Polishing Sequence (Step 2)600-grit wet sandpaperStaircase reduction: silicone diamond disc + soft abrasive rubber wheel600-grit (or 400-grit if heavy tool marks present) wet sandpaper
Polishing Sequence (Step 3)800-grit wet sandpaper600-grit wet sandpaper800-grit wet sandpaper
Polishing Sequence (Step 4)1000-grit wet sandpaper800-grit wet sandpaper1000-grit wet sandpaper (optional 1200-grit)
Polishing Sequence (Step 5)Fine pumice slurry (lathe rag wheel)1000-grit wet sandpaperPumice slurry on rag wheel (lathe)
Polishing Sequence (Step 6)High-shine compound on flannel/chamois wheel (lathe)Handpiece pre-polish: felt wheel + high-gloss compound; then wool wheelHigh-shine compound on flannel/chamois wheel (lathe)
Polishing Sequence (Step 7)Final inspection + ultrasonic cleaningLathe final polish: pumice rag wheel + high-shine flannel wheelHandpiece access to concave areas; final inspection
Extra SLA-Specific StepsNoneIPA wash (10-15 min) -> air dry (30 min) -> UV post-cure (60°C, 30 min) -> support removal -> staircase smoothingNone
Time for Post-Processing (Lab, Total)30-45 min (polishing only; curing cycle is separate)90-120 min (wash + dry + post-cure + support removal + polishing)20-35 min (polishing only; most efficient post-processing)
Final Achievable Ra After Polishing< 0.2 µm (clinically acceptable)< 0.2 µm (achievable with full protocol)< 0.2 µm (fastest to achieve; material homogeneity aids polishing)
Surface Hardness (VHN)Moderate; polishing reduces VHN slightlyLower than conventional; polishing further reduces VHN in SLA; most affected by polishingHighest among the three (industrial pre-polymerization); least hardness change with polishing
Optical Clarity After PolishingMilky-clear; acceptable translucencyHigh optical transparency (Dental LT Clear formulated for this); excellent post-polishing clarityGood clarity; varies by puck brand; comparable to conventional
Vertical Wear Depth~27.5 µm (lowest; best wear resistance)Higher (flexible 3D-printed materials show highest wear; rigid SLA intermediate)~30.5 µm (comparable to heat-cured; statistically similar)
BiocompatibilityISO 10993-compliant; residual monomer concern if under-curedISO 10993/Class IIa; MUST complete post-cure for biocompatibility; uncured resin is sensitizerISO 10993-compliant; lowest residual monomer (industrial polymerization)
Repeatability/StandardizationModerate; technician skill-dependent (mixing, packing, curing)High (digital workflow reproducible; post-cure controlled by Form Cure parameters)Highest (fully digital; milling parameters controlled by CAD/CAM software)
Polishing Equipment RequiredDental lathe, rag/flannel wheels, pumice, high-shine compound, abrasive papersAll of the above + Form Wash/IPA + Form Cure UV unit + flush cuttersAll conventional polishing equipment; no additional dedicated units required
Cost of FabricationLow (materials inexpensive; labour-intensive)Moderate (printer investment + resin cost; fast production after setup)High (milling machine investment + puck cost; minimal labour for polishing)
Clinical Relevance of PolishingWell-established; decades of evidenceEmerging evidence; polishing essential for biocompatibility + optical clarityWell-established for CAD/CAM ceramics; comparable data for PMMA splints
Key EvidenceISO 20795-1; Maleki et al., 2024 (Dent Mater); Uma et al., 2025Abdulai et al., 2026 (J Dent); Bieger et al., 2023 (J Prosthet Dent); Formlabs Application GuideMaleki et al., 2024; Uma et al., 2025; Grymak et al.

Chapter 7: Discussion

The data presented above and the supporting literature converge on several clinically important conclusions.
Standardization is achievable across all three methods. Uma et al. (2025) confirmed that despite significantly different as-fabricated surface roughness values - with SLA-printed specimens showing the highest Ra and milled specimens showing the most regular surface texture - a standardized polishing sequence using progressive grits (600/800/1000) followed by pumice and tallow/high-shine compound effectively equalized all groups to comparable, clinically acceptable Ra values below the 0.2 µm threshold. This is the foundational evidence supporting a unified polishing framework with method-specific pre-steps.
SLA-printed splints require the longest post-processing workflow. The mandatory dual-stage post-cure (IPA wash + UV cure) before any mechanical polishing is non-negotiable. Skipping or abbreviating this step compromises biocompatibility, leaves tacky uncured resin on the surface, and produces suboptimal polishing outcomes. The staircase artifact unique to SLA requires an additional contouring step (silicone disc + abrasive rubber wheel) before the conventional abrasive paper sequence can be applied effectively.
Milled PMMA splints offer the most efficient post-processing pathway. No curing step, no support removal, and the regular periodic nature of milling tool marks respond rapidly to abrasive paper reduction. The industrial pre-polymerization produces the most homogeneous material, which polishes to the highest gloss most predictably. This translates to reduced laboratory time and potentially lower variability between technicians.
Conventional heat-cured splints remain clinically competitive. Despite being the oldest technology, vacuum mixing and long curing cycles produce a material with the best wear resistance and predictable polishing behavior. The main disadvantage is the time and labour involved in the fabrication cycle itself, not the polishing sequence.
Polishing affects hardness differently across materials. The reduction in VHN upon polishing of heat-cured and SLA groups, but not significantly in milled PMMA, reflects the removal of a harder surface skin in the first two and the material homogeneity of the third. Clinicians adjusting splints intraorally or in the laboratory should be aware that excessive abrasive adjustment followed by incomplete re-polishing will leave SLA and heat-cured surfaces with reduced hardness and elevated Ra.

Chapter 8: Conclusions

  1. Each of the three occlusal splint fabrication methods produces a characteristic surface topography requiring a specifically adapted polishing sequence.
  2. SLA 3D-printed splints (Formlabs Dental LT Clear Resin V2) require mandatory IPA washing and UV post-cure (60°C, 30 min, Form Cure) BEFORE any mechanical polishing can commence. This is the most critical distinguishing step in the entire protocol.
  3. Milled PMMA splints from 5-axis CAD/CAM systems require no curing post-processing; polishing is more efficient due to material homogeneity and regular tool-mark surface defects.
  4. Conventional heat-cured splints benefit from vacuum mixing (reduced porosity) and long curing cycle (reduced residual monomer) to optimize polishability.
  5. A universal polishing sequence core of 600/800/1000-grit sandpaper followed by pumice and high-shine compound achieves clinically acceptable Ra < 0.2 µm across all three fabrication methods, provided method-specific pre-steps are completed.
  6. Final surface roughness, microhardness, and optical clarity converge across fabrication methods after standardized polishing, validating the use of existing dental laboratory polishing infrastructure for CAD/CAM and 3D-printed appliances.
  7. Regular calibration of technician skill, instrument condition (worn burs, contaminated wheels), and material lot parameters (especially for SLA post-cure settings) is recommended for sustained protocol fidelity.

References

  1. Uma U, Chansri J, Itthipornpaisan T, Thahong T. Surface roughness and microhardness of heat-cured, milled, and 3D-printed occlusal splints: a comparative study of unpolished and polished surfaces. Natural and Life Sciences Communications. 2025;24(3):E2025041.
  2. Maleki T, Meinen J, Coldea A, Reymus M, Edelhoff D, Stawarczyk B. Mechanical and physical properties of splint materials for oral appliances produced by additive, subtractive and conventional manufacturing. Dental Materials. 2024;40(8):1171-1183.
  3. Bieger V, Thieringer FM, Fischer J. Fibroblast behavior on conventionally processed, milled, and printed occlusal device materials with different surface treatments. J Prosthet Dent. 2023 Jun. PMID: 34598769.
  4. Abdulai D, Sasany R, Aldowah O. Effects of printing orientation and postpolymerization time on the color stability, gloss, surface roughness, and Vickers hardness of an additively manufactured occlusal splint material. J Dent. 2026 Jul. PMID: 42413710.
  5. Formlabs Dental. Application Guide: 3D Printing Occlusal Splints and Night Guards with Formlabs SLA 3D Printers. Available at: dental.formlabs.com/indications/splints-and-occlusal-guards/guide
  6. ISO 20795-1:2013. Dentistry - Base Polymers - Part 1: Denture Base Polymers. International Organization for Standardization.
  7. Grymak A et al. Hardness and elastic modulus of occlusal splint materials manufactured using heat curing, CAD-milling, 3D printing, and vacuum forming. Dental and Medical Problems. 2025;62(3):527.
This write-up was prepared for thesis submission and covers the standardized post-processing and polishing protocol for three fabrication technologies used in occlusal splint manufacturing, with a structured comparison across all relevant clinical and laboratory parameters. All protocols are supported by peer-reviewed evidence current to 2026.

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