Comparison of surface roughness between 3D printed and heat-polymerized polymers for removable dentures

Problems of Dental Medicine 51 DOI: 10.3897/pdm.51.e175885 Research Article Copyright by Ivet Dzhondrova et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. 1 Comparison of surface roughness between 3D printed and heat-polymerized polymers for removable dentures Ivet Dzhondrova1, Todor Uzunov1, Dimitar Kirov1 1 Department of Prosthetic Dental Medicine, Medical University, Sofia, Bulgaria Corresponding author: Ivet Dzhondrova, Sofia, Country; Email: i.dzhondrov[email protected]ofia.bg Received: 23 October 2025  Accepted: 10 November 2025  Published: 17 November 2025 Citation: Dzhondrova I, Uzunov T, Kirov D, (2025) Comparison of surface roughness between 3D printed and heat-polymerized polymers for removable dentures. Problems of Dental Medicine 51: 1– 5. doi: 10.3897/pdm.51.e175885. Abstract Aim: This study aimed to compare the surface roughness of 3D-printed denture base and teeth polymers with conventional heatpolymerized acrylic resin to evaluate their clinical suitability. Materials and methods: Sixty cylindrical specimens (18 mm × 3 mm) were fabricated and divided into three groups: Group A – 3Dprinted Denture Base Resin; Group B – 3D-printed Denture Teeth Resin; and Group C – heat-polymerized Superacryl Plus (control). Specimens were processed following standardized protocols for polishing and post-polymerization. Surface topography and roughness parameters (Ra, Rq, Rmax) were measured using atomic force microscopy (AFM). Data were analyzed using descriptive statistics, and intergroup differences were assessed with the non-parametric Mann–Whitney test (p < 0.01). Results: Both 3D-printed resins exhibited higher surface roughness than the heat-polymerized control, with Group B showing the highest Ra and Rq values, followed by Group A. Rmax values followed a similar pattern (Group B: 328.84 nm; Group A: 286.83 nm; Group C: 77.93 nm). No significant differences were found between the two 3D-printed resins. Despite variations, all materials remained within clinically acceptable roughness limits, although none reached the threshold Ra of 0.2 µm. Conclusion: The present study demonstrated that conventional heat-polymerized acrylic resin exhibits significantly lower surface roughness compared to 3D-printed denture base and teeth resins. Among the 3D-printed materials, the one used for the teeth showed the highest roughness values, followed by the material for denture bases. These findings highlight the influence of manufacturing technique and material type on surface properties, which may impact microbial colonization and denture hygiene. Keywords 3D printing, 3D printed dentures, surface roughness, atomic force microscopy Introduction One of the main limitations of denture base resins is their surface characteristics, which allow the accumulation of microorganisms, food debris, and stains. Surface roughness directly affects both the biological compatibility and longevity of dentures, as well as patient comfort [1]. A rough surface promotes bacterial and fungal adhesion, potentially leading to tissue irritation and denture stomatitis, while also compromising aesthetics through discoloration [2-4]. Ivet Dzhondrova et al. 2 Problems of Dental Medicine I 2025 I Vol. 51 Polishing is a key step in the fabrication process aimed at minimizing surface irregularities. Studies have shown that well-polished acrylic surfaces reduce bacterial colonization and lower the risk of denture stomatitis [5]. For 3D-printed dentures, some authors recommend applying a thin resin coating to further smooth the surface, although this method does not always provide better results than conventional polishing alone [6]. Due to the layer-by-layer nature of additive manufacturing, the surface properties of 3D-printed polymers have been extensively studied. While some reports indicate that their roughness values are clinically acceptable [7, 8] others show that 3D-printed resins exhibit higher roughness compared to milled or heatpolymerized materials [1, 9, 10, 11]. Printing orientation and post-processing protocols are also significant factors influencing surface quality [12, 13]. Efforts to improve these properties—such as incorporating zirconia, fluorinated glass, or silicon dioxide nanoparticles—have yielded mixed results, enhancing mechanical performance but not always improving smoothness [14, 15]. According to Cortes-Sandoval et al. [16], the methods used to evaluate the surface properties of materials can be classified into three main categories - mechanical contact methods, optical profilometry and scanning probe microscopy. One of the most frequently used techniques for assessing the surface characteristics of polymers is Atomic Force Microscopy (AFM) [14]. AFM is widely preferred in research due to its ability to precisely analyze the surface topography of various materials and biological tissues—including ceramics, metals, polymers, and even human cells and DNA molecules—under both air and liquid environments. The device represents a combination of a Scanning Tunneling Microscope and a profilometer and belongs to the group of Scanning Probe Microscopes (SPM). A key feature of AFM is a sharp probe mounted on an oscillating (spring-like) cantilever, which scans the specimen surface without causing scratches or damage [17]. Other essential components include a deflection detection and control system, a scanning unit, and specialized software that converts the obtained data into an image [18]. This technology enables the acquisition of three-3 dimensional representations of surface structures, allowing precise comparisons among different materials. Materials and methods Methods To evaluate the surface texture of the tested materials, a total of 60 cylindrical specimens were fabricated, each with a diameter of 18 mm and a height of 3 mm(Fig. 1).. The specimens were divided into three groups according to the material used: • Group A (n = 20): Resin for 3D printing - Denture Base Resin (Formlabs, Somerville, MA, USA). • Group B (n = 20): Resin for 3D printing - Denture Teeth Resin (Formlabs, Somerville, MA, USA). • Group C (n = 20): Heat-polymerized acrylic resin Superacryl Plus (Spofa Dental, Czech Republic), used as the control group. Fig. 1. Specimens Specimens Preparation Group А and B (3D-printed Denture Base Resin) - A digital prototype of a cylinder with the specified dimensions was created using specialized 3D modeling software (Blender v. 3.5). The file in STL format was exported to PreForm, and the specimens were printed using a stereolithography (SLA)-based 3D printer (Form 2, Formlabs Inc., USA). Post-processing included washing with 95% isopropyl alcohol in an ultrasonic bath (Form Wash) and additional polymerization in a curing unit (Form Cure) for 30 minutesat 80 °C under ultraviolet light (wavelength 405 nm). Specimens were stored in distilled water at room temperature until laboratory testing. Group C (Heat-polymerized resin) - For the fabrication of the heat-polymerized acrylic resin specimens, a silicone mold containing six cylindrical cavities was used. After the mold was packed into a flask, the resin was mixed, placed into the cavities, pressed, and polymerized according to the manufacturer’s instructions for 2 hours. The dimensions of all specimens were verified at three points using an electronic caliper. Until testing, the specimens were stored in a container with distilled water at room temperature. Surface Roughness Analysis The surface texture of the specimens was evaluated using an Atomic Force Microscope (AFM) Multimode V with a NanoScope V controller (Bruker Inc., Germany) in non-contact dynamic mode (tapping mode) under ambient air at room temperature (fig. 2). The silicon cantilevers used (Tap3000AI-G, BudgetSensors®, Innovative Solutions Ltd., Bulgaria) featured an aluminum coating 30 nm thick with a tip radius of less than 10 nm according to the manufacturer’s specifications. Scanning was performed at a rate of 0.2–1 Hz, with a scanned area of 2 μm × 2 μm and a resolution of 256 × 256 pixels, recorded in JPEG format. Surface topography and roughness were analyzed using NanoScope software. Surface roughness was quantified using the following parameters: • Ra – arithmetic mean roughness • Rq – root mean square roughness • Rmax –the maximum vertical distance between the highest and lowest points Comparison of surface roughness Problems of Dental Medicine I 2025 I Vol. 51 3 All measurements were performed in duplicate, and results are presented as mean ± standard error of the mean (SEM). Fig. 2. (A) Scanning process of the laboratory specimen in non-contact dynamic mode (tapping mode); (B) image from the video camera. Results The surface texture of the specimens, as measured by atomic force microscopy, is summarized in Table 1. Descriptive statistical parameters, including mean, minimum and maximum values, median, and standard deviation, were calculated for each group. Table 1. Descriptive statistics of the surface roughness measurements for specimens from Groups A, B, and C The highest mean values of arithmetic mean roughness (Ra) and root mean square roughness (Rq) were observed in Group B (Denture Teeth Resin, Formlabs) (Fig. 4), followed by Group A (Denture Base Resin, Formlabs)(Fig. 3). The lowest values for both parameters were recorded in the control Group C (Superacryl Plus, Spofa Dental)(Fig. 5). A similar trend was observed for Rmax, with Group B exhibiting the highest value at 328.84 nm, followed by Group A at 286.83 nm, and Group C at 77.93 nm. Normality of the data was assessed using the Kolmogorov-Smirnov test, which indicated that the data were not normally distributed. Therefore, a nonparametric Mann-Whitney test was performed to compare Ra, Rq, and Rmax values between all groups. Statistically significant differences were observed at p < 0.01 (Table 2). Table 2 Comparative analysis between each group using the Mann–Whitney test Fig.3.Image of the scanning process (A) and 3D surface topography (B) of a specimen from Group A. Fig.4.Image of the scanning process (A) and 3D surface topography (B) of a specimen from Group B. Fig.5.Image of the scanning process (A) and 3D surface topography (B) of a specimen from Group C. Ra (nm) Rq (nm) Rmax (nm) A/B p=0.41794 p=0.13888 p=0.20408 A/C p<0.00001 p<0.00001 p<0.00001 B/C p<0.00001 p<0.00001 p<0.00001 Group Parameter Ra (nm) Rq (nm) Rmax (nm) A N=20 x 36,20 45,56 286,83 Min 5,18 8,27 76,2 Max 191 191 1001 Median 20,9 28,3 265 SD 37,25 41,83 211,21 B N=20 x 39,62 50,79 328,84 Min 5,95 8 74,8 Max 108 124 642 Median 27,45 38,4 280 SD 31,79 37,65 182,17 C N=20 x 5.39 7.18 77.93 Min 3.19 3.95 35.2 Max 8.72 10.6 118 Media 5.31 7.605 79.6 SD 1.629 2.054 20.152 А ) B ) A B ) А A B Ivet Dzhondrova et al. 4 Problems of Dental Medicine I 2025 I Vol. 51 Discussion Surface roughness of materials used for removable dentures is often associated with denture stomatitis, as rough surfaces provide a favorable environment for microbial colonization. The biocompatibility of 3D-printed polymers remains a topic of debate, with conflicting opinions regarding the risk of denture stomatitis compared to conventional heat-polymerized PMMA or pre-polymerized milling resins. Many authors suggest that Candida spp. colonization may be more pronounced on 3Dprinted polymers due to the additive manufacturing process and the layer-by-layer structure of the denture base and teeth [19]. The results of the present study demonstrated a statistically significant difference between 3D-printed polymers and heat-polymerized acrylic resin. Conventional heat-polymerized resin outperformed 3Dprinted materials in terms of surface roughness. These findings are consistent with those of Zeidan et al. [9], who also employed atomic force microscopy (AFM) to measure roughness, reporting an Ra value of 47 nm ± 7.01 for 3Dprinted specimens. Other studies using alternative surface measurement techniques, such as profilometry, have reported similar trends [1, 10, 11]. In contrast, Fiore et al. [20] reported no differences in surface roughness among the materials they tested (3Dprinted, milled, and heat-polymerized resins) and observed no variation in microbial adhesion between these polymer types. Conversely, Al-Dwairi et al. [8] concluded that heatpolymerized resins exhibited the highest mean surface roughness compared to various 3D-printed polymers, a finding supported by another in vitro study by Gad et al. [12]. According to their results, although 3D-printed resins demonstrated lower flexural strength, impact strength, and hardness than heat-polymerized resins, they exhibited superior surface roughness. In the present study, a strict protocol for surface finishing and polishing was applied to all specimens by a single operator to ensure consistency across groups. Despite this, none of the tested materials achieved Ra values at or below the clinical threshold of 0.2 μm, although all were considered clinically acceptable, supporting the findings of Çakmak et al. [7]. No statistically significant difference was observed between the matetials for 3D printed denture bases and teeth in terms of surface roughness parameters (Ra, Rq, and Rmax). Both 3D-printed materials exhibited similar topographical characteristics, suggesting that the composition and printing process result in comparable surface qualities for denture bases and teeth. This finding indicates that, despite differences in intended clinical function, the two resins perform equivalently with respect to surface smoothness. Increasingly, research is focused on improving the properties of existing materials by modifying their composition. For instance, Alshaikh et al. [21] reported that 3D-printed polymers exhibit inferior mechanical and surface properties compared to heat-polymerized resins, but these properties can be enhanced through the incorporation of zirconia nanoparticles (ZrO2NPs). Similarly, Al-Bakri et al. [14] suggested that adding fluorinated glass fillers to PMMA could reduce microbial colonization without adversely affecting the polymer’s surface characteristics. The main limitations of the present study include the lack of oral condition simulation and long-term water storage. Additionally, thermocycling was not performed, which may influence results depending on the type of resin and 3D printer used. Conclusion The present study demonstrated that conventional heatpolymerized acrylic resin exhibits significantly lower surface roughness compared to 3D-printed denture base and teeth resins. Among the 3D-printed materials, the one used for the teeth showed the highest roughness values, followed by the material for denture bases. Despite differences in surface texture, all tested materials remained clinically acceptable, though none reached the Ra threshold of 0.2 μm. These findings highlight the influence of manufacturing technique and material type on surface properties, which may impact microbial colonization and denture hygiene. Future studies should incorporate oral condition simulation, thermocycling, and long-term storage to better reflect clinical performance. Additional information Funding statement None. Ethical compliance Not applicable. Conflict of interest The authors declared that no clinical trials were used in the present study. The authors declared that no experiments on humans or human tissues were performed for the present study. The authors declared that no informed consent was obtained from the humans, donors or donors’ representatives participating in the study. The authors declared that no experiments on animals were performed for the present study. Comparison of surface roughness Problems of Dental Medicine I 2025 I Vol. 51 5 Author contributions • Conceptualization – T.U • Methodology – I.D and T.U • Investigation – I.D • Resources – I.D • Formal Analysis – I.D • Visualization – I.D • Writing – Original Draft – I.D • Writing – Review & Editing – D.K • Supervision – T.U and D.K References 1. Alfouzan AF, Tuwaym M, Aldaghri EN, Alojaymi T, Alotiabi HM, Taweel SMA et al. Efficacy of Denture Cleansers on Microbial Adherence and Surface Topography of Conventional and CAD/CAM-Processed Denture Base Resins. Polymers. 2023; 15(2):460. doi:10.3390/polym15020460 2. Bollen, C. M., Lambrechts, P., & Quirynen, M. Comparison of surface roughness of oral hard materials to the threshold surface roughness for bacterial plaque retention: a review of the literature. Dental materials, 1997, 13(4), 258–269. doi:10.1016/s01095641(97)80038-3 3. 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