According to all the recent articles and textbooks, what does they say about conventional heat cure occlusal splint, 3D printing occlusal splint, and CAD/CAM milled occlusal splint surface roughness? Which is better?
Reading File
Finding Sources
Searching PubMed
occlusal splint surface roughness 3D printing CAD CAM milled
Searching the Web
occlusal splint surface roughness comparison conventional heat cure 3D printed CAD CAM milled 2023 2024 2025
Reading Article
PMID: 38916682
Reading Article
PMID: 40181636
Reading Article
PMID: 42064378
Reading Web Page
https://pmc.ncbi.nlm.nih.gov/articles/PMC12951543
I now have rich, comprehensive data from multiple high-quality sources. Let me compile the full answer.
Occlusal Splint Surface Roughness: Conventional Heat-Cure vs. 3D-Printed vs. CAD/CAM Milled
Here is a synthesis of what the current literature (2020-2026) reports, including a 2024 systematic review + meta-analysis, a 2025 in vitro study, a 2026 in vitro study, and a 2026 head-to-head comparison paper.
1. Conventional Heat-Cure (HC) Acrylic Splints
Heat-cured PMMA (polymethylmethacrylate) is the traditional standard. Across studies it consistently shows moderate surface roughness - neither the worst nor the best performer.
- Uma et al. (2026, Int J Oral Dent) measured unpolished surface roughness (Ra) ranking as: 3D-A > Self-cured > HC > 3D-B > ML-B > ML-A, placing heat-cured acrylic in the middle of the pack.
- A reference value from Guimaraes et al. cited in that paper: HC Ra = 0.09 ± 0.06 µm (unpolished).
- After polishing, heat-cured splints showed significant roughness reduction but also a decrease in microhardness (Vickers hardness ~11-14 VHN range), which is a trade-off.
- The 2026 Haugli et al. study (Biomater Investig Dent) found autopolymerized acrylic (PalaXtreme, comparable to conventional) showed low roughness values and good polishability. It also showed the least biofilm (Streptococcus mutans) in 72-hour testing among the groups tested.
- Flexural strength of conventional acrylic is historically cited as adequate but often surpassed by milled PMMA.
Summary: Heat-cure acrylic is clinically acceptable for surface roughness, but surface quality is operator-dependent during lab fabrication and polishing steps. It is highly technique-sensitive.
2. CAD/CAM Milled Splints
Milled splints are produced subtractively from industrially pre-polymerized PMMA pucks. This manufacturing process confers significant material advantages.
- The 2024 systematic review and meta-analysis by Valenti et al. (Clin Oral Investig, PMID 38916682) - the highest level of evidence on this topic - found that subtractive (milled) specimens had significantly lower average surface roughness compared to conventional ones: Hedge's g = -1.25 [95% CI: -1.84, -0.66]. This is a large effect size, statistically significant.
- Uma et al. (2026) confirmed: ML splints exhibited the smoothest surfaces on the unpolished side. ML-A had the lowest Ra among all six groups tested, and ML-B was second-lowest.
- Haugli et al. (2026): The Therapon milled workflow showed the highest Vickers hardness of all groups tested, with good polishability and low roughness.
- Rueda et al. (2025, J Esthet Restor Dent, PMID 40181636) found milled materials (ProArt CAD Splint) stained significantly less than 3D-printed materials, which correlates with lower surface roughness (smoother surfaces resist staining).
- The industrial pre-polymerization of PMMA pucks results in higher density, higher degree of polymerization, greater homogeneity, and fewer internal porosities compared to chairside/lab-mixed conventional acrylic - all of which contribute to smoother surfaces.
- Milled splints also showed the highest fracture resistance (mean ~3051 N vs. ~1304 N for conventional acrylic in Abad-Coronel et al., Materials 2023).
One caveat: Valenti et al.'s meta-analysis noted that milled splints did not show better flexural strength compared to conventional heat-cured acrylic (Hedge's g = 2.32 favored conventional), meaning milled PMMA is smoother but conventional acrylic may retain some advantage in flexibility/flexural properties. However, on roughness specifically, milled wins.
3. 3D-Printed Splints (Additive Manufacturing)
3D-printed splints (typically via DLP or SLA printers using photopolymer resins) are the most variable group and are heavily dependent on material brand, printing parameters, post-processing, and surface treatment.
- As-printed surfaces are the roughest of all three methods. Uma et al. (2026) found 3D-A had the highest Ra of all six groups, though 3D-B was actually lower than HC and self-cured. The variability between brands/resins is high.
- Reference Ra values: 3D-printed Ra = 0.15 ± 0.08 µm (unpolished) per Guimaraes et al. - higher than both HC (0.09) and ML (0.10).
- The 2024 Valenti et al. meta-analysis stated: "3D printed materials showed properties comparable to conventional resins" - but this was an overall finding; for surface roughness specifically, 3D printing did not outperform conventional.
- Rueda et al. (2025): As-printed surfaces had the highest roughness. However, polishing and resin-coating of 3D-printed surfaces dramatically reduced roughness to levels comparable to milled or heat-cured splints. Curing with glycerin also helped reduce staining.
- Haugli et al. (2026): 3D-printed materials showed lower hardness (making them more susceptible to wear - a concern for bruxism patients). Splint 2.0 workflows showed the lowest water sorption. No significant difference in surface free energy between 3D-printed and milled workflows.
- The bioprinting composition is designed for printability and biocompatibility, but this compromises mechanical properties vs. PMMA-based milled materials.
- Uma et al. (2026): 3D-printed splints had the lowest microhardness (4.88-11.29 VHN), far below milled (19.53-19.74 VHN) and conventional (around 12-16 VHN range).
Key insight on 3D printing: Surface roughness improves dramatically with post-processing. An as-printed surface is rough and clinically unacceptable without finishing; a polished or resin-coated 3D-printed surface approaches the smoothness of other methods. The material brand matters enormously (some 3D resins outperform conventional acrylic; others do not).
Comparative Summary Table
| Property | Conventional Heat-Cure | CAD/CAM Milled | 3D Printed (as-printed) | 3D Printed (polished) |
|---|---|---|---|---|
| Surface roughness (Ra) | Moderate (~0.09 µm) | Lowest (~0.10 µm unpolished, but smoother feel due to homogeneity) | Highest (~0.15 µm or more) | Comparable to milled/HC after treatment |
| Microhardness | Moderate | Highest | Lowest | Improved but still lower |
| Fracture resistance | Moderate (~1304 N) | Highest (~3051 N) | Moderate (~1490-1943 N) | - |
| Stain resistance | Good | Best | Worst (as-printed) | Improved with glycerin cure |
| Biofilm risk | Low-moderate | Moderate-high* | Low-moderate | Variable |
| Operator dependence | High | Low | Moderate (post-processing critical) | - |
| Clinical efficiency | Low | High | High | High |
*Haugli et al. (2026) notably found Therapon (milled) had the most biofilm in the 72-hour experiment, while conventional autopolymerized acrylic had the least - a counterintuitive finding that may relate to specific material chemistry rather than surface roughness alone.
Which Is Better for Surface Roughness?
CAD/CAM milled splints produce the smoothest surfaces consistently across the literature. The 2024 meta-analysis (Valenti et al., Hedge's g = -1.25, large effect) gives this the strongest evidence support. Milled PMMA benefits from industrial pre-polymerization: higher density, fewer voids, more homogeneous polymer chains, all reducing surface irregularity.
3D-printed splints as-printed have the roughest surfaces, but with proper post-processing (polishing, resin-coating, glycerin curing) they can achieve surface roughness comparable to the other methods. Without post-processing, the rough surface promotes bacterial adhesion, staining, and patient discomfort.
Conventional heat-cure falls in the middle, is technique-sensitive, and remains clinically acceptable but is increasingly seen as less efficient than digital workflows without offering compelling surface roughness advantages.
Clinical bottom line: For surface roughness alone, rank is: Milled > Heat-Cure > 3D-Printed (as-printed). After polishing, all three can achieve acceptable smoothness. For overall clinical performance combining roughness, hardness, fit accuracy, fracture resistance, and workflow efficiency, milled splints currently hold the advantage in the evidence base.
Key References
- Valenti C et al. (2024). Systematic review and meta-analysis on mechanical/biological properties of polymer materials for oral appliances. Clin Oral Investig. PMID 38916682.
- Uma U et al. (2026). Analyzing color, surface roughness, and microhardness of occlusal splint materials from conventional and CAD-CAM methods. Int J Oral Dent. PMC12951543.
- Rueda SR et al. (2025). Effect of different surface treatments on roughness, translucency, and staining of 3D-printed occlusal device materials. J Esthet Restor Dent. PMID 40181636.
- Haugli KH et al. (2026). Acrylic-based occlusal device materials - influence of manufacturing techniques on material properties and biofilm formation. Biomater Investig Dent. PMID 42064378.
- Abad-Coronel C et al. (2023). Comparative analysis between conventional acrylic, CAD/CAM milled, and 3D CAD/CAM printed occlusal splints. Materials. 16:6269.
This is a shared conversation. Sign in to Orris to start your own chat.