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surface roughness denture base resin milled 3D printed conventional

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"surface roughness" CAD-CAM 3D printing dental resin polishing

Results

Surface roughness (Ra, µm) was measured for three groups of polished specimens (n = 15 per group): Group I – conventional (heat-cured, hand-polished) resin; Group II – CAD-CAM milled resin; and Group III – 3D-printed resin. Using the individual values reported in the table, the calculated mean ± standard deviation for each group was:
  • Group I (Conventional, polished): 0.363 ± 0.011 µm (range 0.345–0.388)
  • Group II (Milled, polished): 0.093 ± 0.005 µm (range 0.085–0.105)
  • Group III (3D-printed, polished): 0.300 ± 0.012 µm (range 0.280–0.320)
The rank order of surface roughness from lowest to highest was Group II < Group III < Group I. The milled group showed roughness values roughly one-quarter of those recorded for the conventional group and about two-thirds lower than the 3D-printed group, with minimal intra-group scatter (SD ≤ 0.012 µm) in all three groups.
A one-way ANOVA performed on the raw data (df = 2, 42) yielded F ≈ 2898, indicating a highly significant difference among the three groups (p < 0.001). Because the between-group mean differences (0.207–0.270 µm) were an order of magnitude larger than the pooled within-group standard deviation (≈0.010 µm), all three pairwise comparisons (Conventional vs Milled, Conventional vs 3D-printed, Milled vs 3D-printed) were unambiguously significant. Only the milled group achieved a mean Ra below the widely cited 0.2 µm clinical threshold associated with minimal bacterial/plaque retention on intraoral materials; both the conventional and 3D-printed groups exceeded this threshold even after polishing.

Discussion

The present findings show that fabrication method has a marked and statistically significant effect on the final surface roughness of polished dental resin specimens, with subtractively milled (CAD-CAM) specimens producing the smoothest surface, additively manufactured (3D-printed) specimens showing intermediate roughness, and conventionally processed (heat-cured, hand-finished) specimens showing the highest roughness. This pattern is broadly consistent with recent comparative literature on denture base and CAD-CAM resins. Nejatidanesh et al. reported superior surface properties for milled denture base material compared with 3D-printed and conventional resins, attributing this to the homogeneous, highly cross-linked industrial polymerization of milling blanks (1). Singh et al. similarly found CAD-CAM milled PMMA denture base resin to have the lowest surface roughness among conventional heat-polymerized, milled, and 3D-printed groups (2), which mirrors the ranking observed in the present dataset.
The mechanistic explanation for the milled group's superiority relates to the manufacturing process itself. Milling blanks are manufactured industrially under high pressure and temperature with minimal residual porosity and a high degree of monomer-to-polymer conversion; the subtractive milling process removes material uniformly, and this homogeneous, void-free substrate responds more predictably and evenly to mechanical polishing, yielding a consistently smoother finish (1,4). Conventional heat-cured resin, by contrast, is polymerized in bulk via compression molding and finished largely by hand; this manual step introduces greater operator-dependent variability, and residual monomer, porosity, and inconsistent polishing pressure can leave a comparatively rougher surface, consistent with the highest Ra observed in Group I (2,5).
The intermediate roughness of the 3D-printed group is explained by the additive, layer-by-layer nature of stereolithography/DLP-based fabrication, which inherently produces a "stair-step" surface texture at each printed layer interface. Even after polishing, residual layer lines, incompletely light-cured surface resin, and print-orientation-dependent topography can persist, which several studies have linked to comparatively higher and more variable roughness relative to milled resin (3,6,7). Alharethi specifically demonstrated that build orientation significantly influences the surface roughness of 3D-printed denture base resin relative to milled resin, reinforcing that printing parameters (and not just the polishing protocol) are a major determinant of final surface quality (3). Al-Dulaijan et al. and Alfouzan et al. also confirmed that 3D-printed resins retain measurable surface irregularity and roughness sensitivity to post-processing and aging, which may explain why, despite polishing, Group III in the present study did not reach the smoothness achieved by the milled group (7,8).
Clinically, surface roughness below approximately 0.2 µm is generally regarded as the threshold beyond which bacterial adhesion, plaque accumulation, and staining increase substantially on intraoral prosthetic surfaces. In this study, only the milled group fell below this threshold; both the conventional and 3D-printed groups remained above it even after polishing, suggesting a potentially higher risk of biofilm accumulation, denture stomatitis, and discoloration for restorations fabricated by these two methods unless additional or repeated polishing/glazing protocols are employed. This aligns with recent work showing that polishing protocol selection substantially affects the final roughness of CAD-CAM and 3D-printed materials, and that some printed resins require more aggressive or multi-step polishing to approach the smoothness achievable with milled substrates (9,10).
Several limitations should be considered. This was an in vitro, single-time-point evaluation without simulated aging, thermocycling, or mechanical/chemical brushing challenge, all of which are known to alter surface roughness over time (8). A single polishing protocol was applied uniformly to all groups, whereas roughness outcomes are highly sensitive to polishing technique, abrasive sequence, and operator skill; different protocols could narrow or widen the gaps observed here (9,10). Sample size per group (n = 15) is adequate for detecting large effect sizes such as those found here but may be underpowered for finer comparisons (e.g., across different 3D-printing technologies or build orientations). Only Ra (arithmetic mean roughness) was assessed; other parameters (Rz, Rq) and surface topography via SEM/profilometry would provide a more complete picture, as used in several of the cited comparative studies (4,7). Finally, correlating roughness with actual microbial adhesion or clinical staining was outside the scope of this study and would strengthen the clinical relevance of the findings.

Conclusion

Within the limitations of this in vitro study, the fabrication technique significantly influenced the surface roughness of polished dental resin specimens. CAD-CAM milled resin produced the smoothest surface (mean Ra 0.093 µm), well below the clinically relevant 0.2 µm threshold, followed by 3D-printed resin (0.300 µm) and conventional heat-cured resin (0.363 µm), both of which remained above this threshold despite polishing. These results support milling as the superior technique for achieving a clinically favorable, plaque-resistant surface finish, while suggesting that 3D-printed and conventionally fabricated resins may require enhanced or repeated polishing protocols to achieve comparable surface quality. Further studies incorporating aging simulation, varied polishing systems, and correlation with microbial adhesion are recommended to validate the long-term clinical performance of these materials.

References

  1. Nejatidanesh F, Savabi O, Khodaei M. Comparative evaluation of surface properties of milled, 3D-printed, and conventional denture base materials: implications for clinical use. Int J Prosthodont. 2025. PMID: 40694394.
  2. Singh B, Jain S, Bhasin N. Comparative evaluation of surface roughness, wettability, and hardness of conventional, heat-polymerized, computer-aided designed and milled, and three-dimensionally printed polymethyl methacrylate denture base resins: an in vitro study. Cureus. 2025. PMID: 40585711.
  3. Alharethi NA. Evaluation of the influence of build orientation on the surface roughness and flexural strength of 3D-printed denture base resin and its comparison with CAD-CAM milled denture base resin. Eur J Dent. 2024. PMID: 37295454.
  4. Yu HJ, Kang YJ, Park Y. A comparison of the mechanical properties of 3D-printed, milled, and conventional denture base resin materials. Dent Mater J. 2024. PMID: 39414438.
  5. El Samahy MM, Abdelhamid AM, El Shabrawy SM. Evaluation of physicomechanical properties of milled versus 3D-printed denture base resins: a comparative in vitro study. J Prosthet Dent. 2023. PMID: 37121625.
  6. Zeidan AAE, Abd Elrahim RA, Abd El Hakim AF. Evaluation of surface properties and elastic modulus of CAD-CAM milled, 3D printed, and compression moulded denture base resins: an in vitro study. J Int Soc Prev Community Dent. 2022. PMID: 36777013.
  7. Al-Dulaijan YA, Alsulaimi L, Alotaibi R, et al. Comparative evaluation of surface roughness and hardness of 3D printed resins. Materials (Basel). 2022. PMID: 36234163.
  8. Alfouzan AF, Alotiabi HM, Labban N, et al. Effect of aging and mechanical brushing on surface roughness of 3D printed denture resins: a profilometer and scanning electron microscopy analysis. Technol Health Care. 2022. PMID: 34250915.
  9. Limpuangthip N, Apiromwijit S, Salimee P. Effect of chairside polishing systems on the surface roughness of different CAD-CAM denture base materials. J Prosthet Dent. 2025. PMID: 39645436.
  10. Büyükpolat M, Aydin N, Karaoğlanoğlu S. Effects of different polishing systems on the surface roughness, microhardness and gloss of 3D-printed resins. BMC Oral Health. 2025. PMID: 41351045.
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flexural strength 3D printed milled conventional denture base resin ISO 20795

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flexural strength CAD-CAM denture base resin comparison

Results

Flexural load-at-fracture values (N) were recorded for three groups of denture base specimens (n = 15 per group): Group I – conventional (heat-cured) resin; Group II – CAD-CAM milled resin; and Group III – 3D-printed resin. Descriptive statistics calculated from the individual specimen values were:
  • Group I (Conventional): 130.55 ± 11.01 N (range 113.5–147.5)
  • Group II (Milled): 543.50 ± 24.64 N (range 496.5–580.0)
  • Group III (3D-printed): 403.66 ± 24.49 N (range 348.0–445.5)
The rank order of mean flexural load from highest to lowest was Group II > Group III > Group I. The milled group withstood, on average, more than four times the load tolerated by the conventional group and roughly 35% more than the 3D-printed group, while the 3D-printed group withstood roughly three times the load of the conventional group.
A one-way ANOVA on the raw data (df = 2, 42) yielded F ≈ 1495, indicating a highly significant difference among the three groups (p < 0.001). Because the between-group mean differences (all ≥ 140 N) greatly exceeded the pooled within-group standard deviation (≈ 21 N), all three pairwise comparisons (Conventional vs Milled, Conventional vs 3D-printed, Milled vs 3D-printed) were unambiguously significant, confirming that fabrication method was the dominant source of variance in flexural performance.

Discussion

The results demonstrate that fabrication technique exerts a marked, statistically significant effect on the flexural strength of denture base resin, with CAD-CAM milled specimens performing best, 3D-printed specimens intermediate, and conventionally heat-cured specimens weakest. This hierarchy is consistent with recent comparative literature. Alshali et al. directly compared printed and milled denture base resins and reported significantly higher flexural strength for milled material, attributing this to the industrially polymerized, defect-free nature of milling blanks compared with the layer-wise architecture of printed resin (1). Yu et al. similarly found milled resin to outperform both 3D-printed and conventional groups across mechanical parameters including flexural strength and elastic modulus (2). El Samahy et al. and Zeidan et al. reported comparable trends, with milled PMMA consistently exceeding 3D-printed material in flexural strength and elastic modulus in vitro (3,4).
Mechanistically, milling blanks are fabricated under high pressure and temperature with a high degree of monomer conversion and minimal residual porosity; the subtractive process removes material from this pre-formed, homogeneous, defect-poor block without introducing new internal flaws, yielding superior load-bearing capacity (1,2). Conventional heat-cured resin, polymerized by manual compression molding, is more susceptible to porosity, incomplete polymerization, and residual monomer, all of which act as stress concentrators and crack initiation sites under flexural loading, plausibly explaining the markedly lower values recorded in Group I of this study (3). The intermediate performance of the 3D-printed group reflects the additive, layer-by-layer photopolymerization process: interlayer bonding, degree of conversion between layers, print orientation, and post-curing protocol all influence the resulting flexural strength, and incomplete interlayer fusion or void formation between printed layers can act as preferential fracture planes, limiting strength relative to milled material despite exceeding conventional resin (5,6). Gad and Fouda's systematic review on factors affecting the flexural strength of 3D-printed resins confirmed that printing angle, layer thickness, post-curing time, and resin composition are all significant modifiers of the mechanical outcome, which may explain the variability (SD ≈ 24 N) observed within Group III in the present study (6). Alharethi likewise showed that build orientation significantly affects both surface roughness and flexural strength of 3D-printed denture base resin relative to milled material, reinforcing that printing parameters, not only material chemistry, drive this gap (7). A recent network meta-analysis by Kunnath Menon et al., pooling in vitro comparisons of CAD-CAM versus conventional denture bases across strength, hardness, toughness, and elastic properties, similarly concluded that milled resins generally exhibit superior mechanical performance to both printed and conventional resins (8), corroborating the pattern found here. Li et al. further showed that even after clinically relevant modifications such as hard reline application, the relative ranking of conventional, printed, and milled materials in flexural strength was largely preserved, supporting the robustness of milling's mechanical advantage across clinical scenarios (9).
Clinically, ISO 20795-1 specifies a minimum flexural strength requirement for denture base polymers, and although the present study reports raw load-at-fracture (N) rather than converted stress (MPa), the wide separation between groups suggests that all three materials are unlikely to be equally close to this margin under equivalent geometry; conventional resin in particular would be expected to have the least safety margin against clinical fracture under functional loading, especially in thin sections such as the palatal region of a maxillary denture or around post-dam and frenal notch areas where stress concentrates. The comparatively lower and more variable performance of 3D-printed resin relative to milled resin also carries implications for long-term serviceability, particularly given that printed resins are known to be sensitive to post-curing protocol, storage conditions, and aging, factors not evaluated in the present in vitro, single-time-point design (5,6).
Limitations of this evaluation include the absence of specimen dimension data needed to convert load (N) into true flexural stress (MPa) per ISO 20795-1/ISO 178 formulae, which restricts direct comparison with strength thresholds reported elsewhere in the literature. The study also did not incorporate thermocycling, water storage, or fatigue loading, all of which are known to reduce flexural strength over time, especially in printed resins with residual unreacted monomer (5,6). A single brand/printer or milling system and a single post-processing protocol were used, whereas flexural outcomes are highly sensitive to printer technology, resin formulation, build orientation, and post-cure regimen (6,7). Larger multi-material, multi-batch samples with standardized specimen geometry and wet aging protocols are needed to confirm the generalizability of these findings.

Conclusion

Within the limitations of this in vitro study, fabrication method significantly affected the flexural performance of denture base resin specimens. CAD-CAM milled resin demonstrated the highest flexural load-bearing capacity (543.50 ± 24.64 N), followed by 3D-printed resin (403.66 ± 24.49 N), while conventional heat-cured resin showed the lowest values (130.55 ± 11.01 N). These findings support milled CAD-CAM resin as the mechanically superior option for denture base fabrication, with 3D-printed resin representing an intermediate alternative that may still require optimization of printing and post-curing parameters to approach milled-material performance. Conventionally processed resin showed the weakest mechanical resistance among the three groups, warranting caution in load-bearing or thin cross-sectional areas. Further studies standardizing specimen geometry for true stress calculation, incorporating aging and fatigue protocols, and evaluating multiple printing/milling systems are recommended before firm clinical recommendations can be generalized.

References

  1. Alshali S, Basunbul G, Basunbul A. Comparison of the flexural strength of printed and milled denture base materials. BMC Oral Health. 2024. PMID: 39127617.
  2. Yu HJ, Kang YJ, Park Y. A comparison of the mechanical properties of 3D-printed, milled, and conventional denture base resin materials. Dent Mater J. 2024. PMID: 39414438.
  3. El Samahy MM, Abdelhamid AM, El Shabrawy SM. Evaluation of physicomechanical properties of milled versus 3D-printed denture base resins: a comparative in vitro study. J Prosthet Dent. 2023. PMID: 37121625.
  4. Zeidan AAE, Abd Elrahim RA, Abd El Hakim AF. Evaluation of surface properties and elastic modulus of CAD-CAM milled, 3D printed, and compression moulded denture base resins: an in vitro study. J Int Soc Prev Community Dent. 2022. PMID: 36777013.
  5. Al-Qarni FD, Gad MM. Printing accuracy and flexural properties of different 3D-printed denture base resins. Materials (Basel). 2022. PMID: 35407742.
  6. Gad MM, Fouda SM. Factors affecting flexural strength of 3D-printed resins: a systematic review. J Prosthodont. 2023. PMID: 36629333.
  7. Alharethi NA. Evaluation of the influence of build orientation on the surface roughness and flexural strength of 3D-printed denture base resin and its comparison with CAD-CAM milled denture base resin. Eur J Dent. 2024. PMID: 37295454.
  8. Kunnath Menon R, Yew HX, Chen Tze Wei B, et al. CAD-CAM vs. conventional denture bases: a systematic review with network meta-analysis of in vitro studies comparing strength, hardness, toughness, and elastic properties. Front Dent Med. 2025. PMID: 40861085.
  9. Li R, Malik D, Sadid-Zadeh R. Effect of adding a hard-reline material on the flexural strength of conventional, 3D-printed, and milled denture base materials. J Prosthet Dent. 2023. PMID: 37121624.

Write short introduction for this study on occlusal splints with 4 references only

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occlusal splint CAD-CAM milled 3D printed conventional comparison

Introduction

Occlusal splints are widely used in the management of temporomandibular disorders, bruxism, and parafunctional habits, as well as for occlusal stabilization following restorative and orthognathic treatment (1). Traditionally, these appliances have been fabricated using the conventional heat-cured or cold-cured acrylic resin technique, which, despite being simple and cost-effective, is prone to processing errors such as polymerization shrinkage, porosity, and operator-dependent variability that can compromise fit, surface quality, and mechanical durability (2). The introduction of digital workflows has enabled two principal computer-aided design/computer-aided manufacturing (CAD-CAM) alternatives: subtractive milling of pre-polymerized industrial resin blanks, and additive manufacturing via 3D printing. Both techniques have been reported to improve fabrication accuracy, reduce chair-side time, and offer greater reproducibility compared with the conventional approach (3).
However, the clinical performance of an occlusal splint depends not only on fit but also on its surface characteristics and mechanical strength, since a rough surface favors biofilm accumulation and staining, while inadequate strength predisposes the appliance to fracture under functional and parafunctional loading (4). Milled and 3D-printed splints differ fundamentally in their manufacturing principle, subtractive versus layer-by-layer additive fabrication, and this difference has been shown to translate into measurable variation in surface roughness, flexural strength, and overall clinical durability compared with conventionally processed resin (1,2). Despite growing adoption of digital techniques, comparative data across all three fabrication methods, conventional, milled, and 3D-printed, remain limited, and the material and mechanical trade-offs of each approach are not yet fully established. This study was therefore undertaken to compare the surface roughness and flexural strength of conventional, CAD-CAM milled, and 3D-printed occlusal splint materials, in order to provide evidence to guide material and technique selection in clinical practice.

References

  1. Abad-Coronel C, Ruano Espinosa C, Ordóñez Palacios S. Comparative analysis between conventional acrylic, CAD/CAM milled, and 3D CAD/CAM printed occlusal splints. Materials (Basel). 2023. PMID: 37763547.
  2. Gibreel M, Perea-Lowery L, Vallittu PK. Characterization of occlusal splint materials: CAD-CAM versus conventional resins. J Mech Behav Biomed Mater. 2021. PMID: 34530298.
  3. Reymus M, Hickel R, Keßler A. Accuracy of CAD/CAM-fabricated bite splints: milling vs 3D printing. Clin Oral Investig. 2020. PMID: 32436163.
  4. Orgev A, Levon JA, Chu TG. The effects of manufacturing technologies on the surface accuracy of CAD-CAM occlusal splints. J Prosthodont. 2023. PMID: 36227731.

Write introduction on uses of occlusal splint and how fabrication technique matters with few references added in Vancouver style

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occlusal splint therapy temporomandibular disorder bruxism indications

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digital workflow fabrication technique dental appliance accuracy fit clinical outcome

Introduction

Occlusal splints, also known as bite splints, night guards, or interocclusal appliances, are removable devices most commonly fabricated to cover the occlusal and incisal surfaces of the maxillary or mandibular teeth. They are among the most frequently prescribed conservative interventions in dentistry, primarily indicated in the management of temporomandibular disorders (TMD) and bruxism, where they help reduce abnormal loading of the temporomandibular joint, redistribute occlusal forces, decrease hyperactivity of the masticatory muscles, and protect the dentition from further attrition (1,2). Beyond TMD and parafunction, occlusal splints are also used for occlusal stabilization prior to and following restorative or prosthodontic rehabilitation, for diagnostic evaluation of a therapeutic jaw position before definitive treatment, as retention devices after orthodontic or orthognathic surgical correction, and as adjuncts in the management of sleep-related bruxism (3,4). Their broad clinical utility stems from their reversibility, relative simplicity of fabrication, and ability to be adjusted or relined as treatment needs evolve.
Traditionally, occlusal splints have been fabricated using the conventional heat-cured or cold-cured acrylic resin technique on stone casts, a method that is inexpensive and technically well established but is also time-consuming and susceptible to processing errors such as polymerization shrinkage, porosity, and dimensional inaccuracy introduced during boil-out, packing, and curing (5). The advent of digital dentistry has introduced two CAD-CAM-based alternatives, subtractive milling from pre-polymerized industrial resin blanks and additive manufacturing by 3D printing, both of which aim to reduce chairside time, improve reproducibility, and eliminate several of the manual errors inherent to the conventional workflow (5,6). However, fabrication technique is not merely a matter of convenience: it directly determines the internal structure, degree of polymerization, and surface finish of the resulting appliance, which in turn influence its fit accuracy, surface roughness, and mechanical strength (6,7). Lin et al. showed that a digital fabrication workflow produced occlusal appliances with significantly better fit accuracy than a conventional workflow, underscoring how the manufacturing route can affect clinically relevant outcomes such as intaglio surface adaptation and occlusal contact reproduction (7). Similarly, Orgev et al. demonstrated that different CAD-CAM manufacturing technologies (milling versus printing) yield measurably different surface accuracy in occlusal splints, while Gibreel et al. reported that CAD-CAM and conventional splint resins differ in flexural strength and surface characteristics important for long-term intraoral performance (5,6). These material and manufacturing differences are clinically significant because a splint with excessive surface roughness may favor biofilm accumulation, staining, and patient discomfort, whereas inadequate flexural strength predisposes the appliance to fracture under the sustained parafunctional loads for which it is prescribed (5,6). Given the increasing clinical adoption of digital workflows, a clear understanding of how fabrication technique, conventional, milled, or 3D-printed, affects the surface and mechanical properties of occlusal splints is essential to guide evidence-based material and technique selection.

References

  1. Dao TT, Lavigne GJ. Oral splints: the crutches for temporomandibular disorders and bruxism? Crit Rev Oral Biol Med. 1998. PMID: 9715371.
  2. Albagieh H, Alomran I, Binakresh A, et al. Occlusal splints-types and effectiveness in temporomandibular disorder management. Saudi Dent J. 2023. PMID: 36817028.
  3. Gray RJ, Davies SJ. Occlusal splints and temporomandibular disorders: why, when, how? Dent Update. 2001. PMID: 11476035.
  4. Abad-Coronel C, Ruano Espinosa C, Ordóñez Palacios S. Comparative analysis between conventional acrylic, CAD/CAM milled, and 3D CAD/CAM printed occlusal splints. Materials (Basel). 2023. PMID: 37763547.
  5. Gibreel M, Perea-Lowery L, Vallittu PK. Characterization of occlusal splint materials: CAD-CAM versus conventional resins. J Mech Behav Biomed Mater. 2021. PMID: 34530298.
  6. Orgev A, Levon JA, Chu TG. The effects of manufacturing technologies on the surface accuracy of CAD-CAM occlusal splints. J Prosthodont. 2023. PMID: 36227731.
  7. Lin R, Yan YQ, Sun J, et al. A comparison of the accuracy between a digital fabrication workflow and a conventional fabrication workflow for occlusal appliances: a pilot study. Int J Prosthodont. 2023. PMID: 37699192.
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