A comparative evaluation of the mechanical and surface properties of reinforced 3D printed polymethylmethacrylate and CAD CAM polymethylmethacrylate - An in-vitro study

International Journal of Dental Science and Innovative Research (IJDSIR) IJDSIR : Dental Publication Service Available Online at:www.ijdsir.com Volume – 8, Issue – 6, November – 2025, Page No. : 99 - 110 Corresponding Author: Vinitha S Kumar, ijdsir, Volume – 8 Issue - 6, Page No. : 99 - 110 Page99 ISSN: 2581-5989 PubMed - National Library of Medicine - ID: 101738774 A comparative evaluation of the mechanical and surface properties of reinforced 3D printed polymethylmethacrylate and CAD CAM polymethylmethacrylate - An in-vitro study 1Vinitha S Kumar, Postgraduate, Department of Prosthodontics and Crown and Bridge, Vokkaligara Sangha Dental College and Hospital, Rajiv Gandhi University of Health Sciences (RGUHS), Bengaluru, India. 2Archana Shetty, Reader, Department of Prosthodontics and Crown and Bridge, Vokkaligara Sangha Dental College and Hospital, Rajiv Gandhi University of Health Sciences (RGUHS), Bengaluru, India. 3Surendra Kumar G.P, Professor and Head, Department of Prosthodontics and Crown and Bridge, Vokkaligara Sangha Dental College and Hospital, Rajiv Gandhi University of Health Sciences (RGUHS), Bengaluru, India. 4Anupama N M, Professor, Department of Prosthodontics and Crown and Bridge, Vokkaligara Sangha Dental College and Hospital, Rajiv Gandhi University of Health Sciences (RGUHS), Bengaluru, India 5Jnanadev K R, Professor, Department of Prosthodontics and Crown and Bridge, Vokkaligara Sangha Dental College and Hospital, Rajiv Gandhi University of Health Sciences (RGUHS), Bengaluru, India Corresponding Author: Vinitha S Kumar, Postgraduate, Department of Prosthodontics and Crown and Bridge, Vokkaligara Sangha Dental College and Hospital, Rajiv Gandhi University of Health Sciences (RGUHS), Bengaluru, India. Citation of this Article: Vinitha S Kumar, Archana Shetty, Surendra Kumar G.P, Anupama N M, Jnanadev K R, “A comparative evaluation of the mechanical and surface properties of reinforced 3D printed polymethylmethacrylate and CAD CAM polymethylmethacrylate - An in-vitro study”, IJDSIRNovember – 2025, Volume – 8, Issue – 6, P. No. 99 – 110. Copyright: © 2025, Vinitha S Kumar, et al. This is an open access journal and article distributed under the terms of the creative common’s attribution non-commercial License. Which allows others to remix, tweak, and build upon the work non-commercially, as long as appropriate credit is given, and the new creations are licensed under the identical terms. Type of Publication: Original Research Article Conflicts of Interest: Nil Abstract Introduction: Polymethylmethacrylate (PMMA) denture bases fabricated through 3D printing technology are proven to be better in comparison to its digital counterpart, the subtractive CAD CAM technique, in terms of cost effectiveness, reduced wastage, better detail reproduction and ability to print complex geometries. However, the mechanical and surface properties of 3D printed denture bases are found to be inferior to both conventional and CAD CAM techniques. Therefore, it is necessary to enhance the properties of 3D printed PMMA resin to make it a viable alternative to conventional and CAD CAM techniques. Aim: To compare and evaluate the mechanical and surface properties of reinforced 3D printed PMMA with CAD CAM PMMA. Method: A total of 72 samples of dimensions 64x10x3.3mm were divided into 4 groups (n=18), Group Vinitha S Kumar, et al. International Journal of Dental Science and Innovative Research (IJDSIR) ©2025 IJDSIR, All Rights Reserved Page100 Page100 Page100 Page100 Page100 Page100 Page100 Page100 Page100 Page100 Page100 Page100 Page100 Page100 Page100 Page100 Page100 Page100 Page100 I CAD CAM PMMA, Group II unmodified 3D printed PMMA, Group III 1wt% Al2O3 reinforced 3D printed PMMA and Group IV 2.5wt% ZrO2 reinforced 3D printed PMMA. Immediate flexural strength, surface hardness and surface roughness were tested after immersion in distilled water for 24 hours. Delayed flexural strength, surface hardness and surface roughness were tested after immersion in artificial saliva for 30 days followed by 5000 cycles of thermocycling simulating 6 months of intraoral use. Results: The statistical analysis was performed using Kruskal-Wallis test and Wilcoxon signed-rank with significance set at p value < 0.05. Statistically significant differences (p < 0.05) were found among all groups. CAD CAM PMMA (Group I) had the highest immediate (116.20 ± 1.28 MPa) and delayed (108.25 ± 0.98 MPa) flexural strength, hardness (24.38 ± 0.64 VHN immediate; 22.82 ± 0.33 VHN delayed), and lowest roughness (0.66 ± 0.02 μm immediate; 0.74 ± 0.02 μm delayed). Zirconium oxide reinforcement (Group IV) showed higher flexural strength than Aluminum oxide (Group III), whereas Aluminum oxide reinforcement yielded the lowest surface roughness among the 3D printed groups. Conclusion: Reinforcing 3D printed PMMA denture base resin with 2.5 wt% aluminum oxide or 1 wt% zirconium oxide significantly improved its mechanical and surface properties. While CAD-CAM PMMA remains superior, nanoparticle reinforcement offers a viable path to enhance the clinical performance of 3D printed resins. Keywords: 3D printed PMMA, nanoparticles, Zirconium oxide, Aluminium oxide Introduction The increase in life expectancy has led to a rise in the geriatric population, with edentulism being a prevalent oral health problem.1 Edentulous patients face functional, esthetic, and psychosocial challenges, and complete denture rehabilitation remains the most common treatment modality. The success of complete dentures depends on patient factors, the choice of material, and the fabrication method.2 Polymethylmethacrylate (PMMA), introduced by Walter Wright in 1936, has been the material of choice for denture base fabrication due to its favorable mechanical, physical, and esthetic properties. Conventional heat polymerization techniques such as compression molding and injection molding are widely used but have drawbacks such as porosity, polymerization shrinkage, surface roughness, and processing errors.1,3 Advancements in digital dentistry have introduced CAD CAM and 3D printing technologies for denture fabrication. CAD CAM milling uses pre-polymerized PMMA blanks fabricated under high temperature and pressure, providing superior mechanical and surface properties with minimal porosity and reduced microbial adhesion. However, the subtractive method involves significant material wastage and high fabrication costs.4,5 3D printing, an additive manufacturing technique, offers advantages such as reduced material waste, lower cost, faster production, and the ability to produce complex geometries. Nevertheless, 3D printed PMMA resins exhibit inferior mechanical and surface properties compared to conventional and CAD CAM PMMA. 4,5 Reinforcement of heat cured PMMA with metal oxides nanoparticles has been shown to improve the mechanical, surface, and antimicrobial properties.6 Limited literature exists on nanoparticle reinforcement of 3D printed PMMA denture base resins. This study aims to evaluate and compare the immediate and delayed mechanical and surface properties of reinforced 3D printed PMMA with CAD CAM PMMA Vinitha S Kumar, et al. International Journal of Dental Science and Innovative Research (IJDSIR) ©2025 IJDSIR, All Rights Reserved Page101 Page101 Page101 Page101 Page101 Page101 Page101 Page101 Page101 Page101 Page101 Page101 Page101 Page101 Page101 Page101 Page101 Page101 Page101 Materials and Methodology A total of 72 samples of dimensions 64x10x3.3mm were digitally designed and divided into 4 groups (n=18) Figure 1: STL file of sample design  Group I: CAD CAM PMMA  Group II: Unmodified 3D printed PMMA  Group III: 2.5 wt% Aluminum oxide–reinforced 3D printed PMMA  Group IV: 1 wt% Zirconium oxide–reinforced 3D printed PMMA Specimen Preparation Group ICAD CAM specimen preparation: 18 CADCAM specimen were designed in the dimensions of (64 × 10 × 3.3mm) and milled to be tested for flexural strength, surface hardness and surface roughness. The specimens were cleaned using isopropyl alcohol bath with 99% purity for 10 minutes. Figure 2: CAD CAM specimen preparation Group IIUnmodified 3D printed PMMA specimen preparation: 18 unmodified 3D printed PMMA specimen with dimensions of (64 × 10 × 3.3 mm) were printed at 90o orientation to be tested for flexural strength, surface hardness and surface roughness. The 3D printing process was followed by thorough washing of specimens in an isopropyl alcohol bath with 99% purity for 10 minutes. Figure 3: Unmodified 3D printed PMMA specimen preparation Group III2.5wt% Aluminium oxide nanoparticles reinforced 3D printed PMMA preparation: Nanocomposite was prepared by gradual incorporation of 2.5wt% of Al3O2 nanoparticles into the 3D printed PMMA solution under continuous magnetic stirring (Remi 1 MLH) for 30 minutes followed by mechanical mixing for 30 minutes at low frequency. The resultant resin was then used to print 18 aluminium oxide reinforced 3D printed PMMA specimen with dimensions of (64 × 10 × 3.3 mm) at 90o orientation to be tested for flexural strength, surface hardness and surface roughness. The 3D printing process was followed by thorough washing of specimens in an isopropyl alcohol bath with 99% purity for 10 minutes Vinitha S Kumar, et al. International Journal of Dental Science and Innovative Research (IJDSIR) ©2025 IJDSIR, All Rights Reserved Page102 Page102 Page102 Page102 Page102 Page102 Page102 Page102 Page102 Page102 Page102 Page102 Page102 Page102 Page102 Page102 Page102 Page102 Page102 Figure 4: 2.5wt% Aluminium oxide nanoparticles reinforced 3D printed PMMA preparation GROUP IV1wt% Zirconium oxide nanoparticles reinforced 3D printed PMMA preparation: Nanocomposite was prepared by gradual incorporation of 1wt% of ZrO2 nanoparticles into the 3D printed PMMA solution under continuous magnetic stirring (Remi 1 MLH) for 30 minutes followed by mechanical mixing for 30 minutes at low frequency. The resultant resin was then used to print 18 zirconium oxide reinforced 3D printed PMMA specimen with dimensions of (64 × 10 × 3.3 mm) at 90o orientation to be tested for flexural strength, surface hardness and surface roughness. The 3D printing process was followed by thorough washing of specimens in an isopropyl alcohol bath with 99% purity for 10 minutes. Figure 5: 1wt% Zirconium oxide nanoparticles reinforced 3D printed PMMA preparation Figure 6: Samples categorized into respective groups Artificial ageing: Twelve specimen from each group were stored in artificial saliva at 37oC for 30 days and subjected to thermocycling for 5000 cycles between 5oC to 55oC with dwell time of 30 seconds each, equivalent to 6 months of intraoral exposure. Figure 7: Storage in artificial saliva for delayed testing Figure 8: Thermocycling of samples for delayed testing Testing for flexural strength: A three-point bending test was used to evaluate the flexural strength. The load was applied at the centre of the specimen until fracture. The fracture load (N) was recorded to calculate the flexural strength (MPa) using the equation FS = 3Fl/2bh2, where F= fracture load, l= length of specimen, b= width of the specimen and h= thickness of the specimen Vinitha S Kumar, et al. International Journal of Dental Science and Innovative Research (IJDSIR) ©2025 IJDSIR, All Rights Reserved Page103 Page103 Page103 Page103 Page103 Page103 Page103 Page103 Page103 Page103 Page103 Page103 Page103 Page103 Page103 Page103 Page103 Page103 Page103 Figure 9: 3-point bending test for flexural strength using universal testing machine Testing for surface hardness: Hardness was measured by Vickers hardness test and each specimen was subjected to a 50 N of load on three different sites. The final hardness (VHN) value of each specimen was arithmetically calculated by obtaining the average of the three readings. Figure 10: Vickers Hardness test for surface hardness Testing for surface roughness: A non-contact optical profilometer was used for the measurement of the specimens’ surface roughness. The specimens were radially scanned 3 times at different points with 0.01 mm resolution and the average surface roughness (µm) for each specimen was calculated. Figure 11: Non optical profilometer test for surface roughness Statistical analysis: All statistical analyses were performed using IBM SPSS Statistics for Windows, Version 20.0 (IBM Corp., Armonk, NY, USA). Descriptive statistics were utilized to summarize quantitative data, with continuous variables expressed as means and standard deviations (SD) or medians with interquartile ranges (IQR), based on data distribution as assessed by the Shapiro-Wilk test. For intergroup comparisons of flexural strength, hardness, and roughness at both immediate and delayed time points, the Kruskal-Wallis test was employed owing to nonparametric data distribution, followed by pairwise comparisons using the Mann–Whitney U test with Bonferroni correction to control for type I error. The differences between immediate and delayed values within each group were analyzed using the Wilcoxon Signed-Rank test to determine the effect of artificial aging and thermocycling on material performance. A pvalue of less than 0.05 was considered statistically significant. Vinitha S Kumar, et al. International Journal of Dental Science and Innovative Research (IJDSIR) ©2025 IJDSIR, All Rights Reserved Page104 Page104 Page104 Page104 Page104 Page104 Page104 Page104 Page104 Page104 Page104 Page104 Page104 Page104 Page104 Page104 Page104 Page104 Page104 Results Table 1: Overall comparison of immediate flexural strength among the study groups Groups Mean±SD Median (IQR) Range Chi-Square value; P value Group 1 116.20±1.28 115.85 (115.13-117.40) 114.90118.30 21.60; 0.001* Group 2 86.33±1.22 86.30 (85.25-87.40) 84.8088.00 Group 3 98.63±0.99 98.45 (97.82-99.40) 97.60100.30 Group 4 104.17±0.93 104.25 (103.32-105.05) 102.80105.20 Kruskal Wallis test; *statistically significant (p<0.05) Table 2: Overall Comparison of delayed flexural strength among the study groups Groups Mean±SD Median (IQR) Range Chi-Square value; P value Group 1 108.25±0.98 108.50 (107.30-109.12) 106.70109.20 21.60; 0.001* Group 2 76.80±0.89 76.75 (75.95-77.62) 75.80-78.00 Group 3 91.77±0.42 91.80 (91.40-92.07) 91.10-92.30 Group 4 98.35±1.01 98.60 (97.17-99.15) 97.10-99.60 Kruskal Wallis test; *statistically significant (p<0.05) Table 3: Comparison of immediate and delayed flexural strength Groups Immediate flexural strength Delayed flexural strength Z value; P value Group 1 116.20±1.28 108.25±0.98 2.201; 0.028* Group 2 86.33±1.22 76.80±0.89 2.207; 0.027* Group 3 98.63±0.99 91.77±0.42 2.201; 0.028* Group 4 104.17±0.93 98.35±1.01 2.207; 0.027* Wilcoxon Signed Ranks test; *statistically significant (p<0.05) Figure 12: Within-group comparison of immediate and delayed flexural strength CAD CAM PMMA (Group 1) showed the highest immediate flexural strength (116.20 ± 1.28 MPa), followed by ZrO₂ reinforced 3D-printed PMMA (Group 4, 104.17 ± 0.93 MPa), Al₂O₃ reinforced 3D-printed PMMA (Group 3, 98.63 ± 0.99 MPa), and unmodified 3D-printed PMMA (Group 2, 86.33 ± 1.22 MPa) as the lowest. After aging, flexural strength decreased in all groups. CAD CAM PMMA (Group 1) remained highest (108.25 ± 0.98 MPa), followed by ZrO₂ reinforced (Group 4, 98.35 ± 1.01 MPa), Al₂O₃ reinforced (Group 3, 91.77 ± 0.42 MPa), and unmodified 3D-printed PMMA (Group 2, 76.80 ± 0.89 MPa). Table 4: Overall comparison of immediate surface hardness among the study groups Groups Mean±SD Median (IQR) Range Chi-Square value; P value Group 1 24.38±0.64 24.40 (23.75-24.97) 23.6025.20 20.95; 0.001* Group 2 17.50±0.41 17.45 (17.20-17.87) 16.9018.10 Group 3 19.92±0.29 19.95 (19.65-20.15) 19.5020.30 Group 4 20.40±0.24 20.40 (20.17-20.62) 20.1020.70 Kruskal Wallis test; *statistically significant (p<0.05) Vinitha S Kumar, et al. International Journal of Dental Science and Innovative Research (IJDSIR) ©2025 IJDSIR, All Rights Reserved Page105 Page105 Page105 Page105 Page105 Page105 Page105 Page105 Page105 Page105 Page105 Page105 Page105 Page105 Page105 Page105 Page105 Page105 Page105 Table 5: Overall comparison of delayed surface hardness between the study groups Groups Mean±SD Median (IQR) Range Chi-Square value; P value Group 1 22.82±0.33 22.75 (22.50-23.15) 22.4023.30 19.71; 0.001* Group 2 16.15±0.19 16.15 (15.97-16.32) 15.9016.40 Group 3 18.95±0.33 18.85 (18.67-19.32) 18.6019.40 Group 4 19.08±0.15 19.05 (18.97-19.22) 18.9019.30 Kruskal Wallis test; *statistically significant (p<0.05) Table 6: Comparison of immediate and delayed surface hardness Groups Immediate surface hardness Delayed surface hardness Z value; P value Group 1 24.38±0.64 22.82±0.33 2.214; 0.027* Group 2 17.50±0.41 16.15±0.19 2.201; 0.028* Group 3 19.92±0.29 18.95±0.33 2.201; 0.028* Group 4 20.40±0.24 19.08±0.15 2.201; 0.028* Wilcoxon Signed Ranks test; *statistically significant (p<0.05) Figure 13: Within-group comparison of immediate and delayed surface hardness For immediate hardness, CAD CAM PMMA (Group 1) recorded the highest mean value (24.38 ± 0.64 VHN), followed by ZrO₂ reinforced 3D-printed PMMA (Group 4, 20.40 ± 0.24 VHN), Al₂O₃ reinforced PMMA (Group 3, 19.92 ± 0.29 VHN), and unmodified 3D-printed PMMA (Group 2, 17.50 ± 0.41 VHN) as the lowest. After thermocycling, all groups showed a decrease in hardness. CAD CAM PMMA (Group 1) remained hardest (22.82 ± 0.33 VHN), followed by ZrO₂ reinforced (Group 4, 19.08 ± 0.41 VHN), Al₂O₃ reinforced (Group 3, 18.95 ± 0.25 VHN), and unmodified 3D-printed PMMA (Group 2, 16.15 ± 0.19 VHN). Table 7: Overall Comparison of immediate surface roughness among the study groups Groups Mean±SD Median (IQR) Range Chi-Square value; P value Group 1 0.66±0.02 0.65 (0.64-0.67) 0.63-0.68 16.28; 0.001* Group 2 0.92±0.01 0.91 (0.91-0.93) 0.90-0.94 Group 3 0.91±0.02 0.91 (0.88-0.92) 0.88-0.93 Group 4 0.93±0.01 0.93 (0.92-0.94) 0.91-0.95 Kruskal Wallis test; *statistically significant (p<0.05) Table 8: Overall comparison of delayed surface roughness among the study groups Groups Mean±SD Median (IQR) Range Chi-Square value; P value Group 1 0.74±0.02 0.73 (0.72-0.75) 0.71-0.76 20.96; 0.001* Group 2 1.06±0.02 1.05 (1.03-1.07) 1.03-1.08 Group 3 0.94±0.02 0.94 (0.91-0.95) 0.91-0.96 Group 4 1.01±0.03 1.01 (0.98-1.03) 0.97-1.05 Kruskal Wallis test; *statistically significant (p<0.05) Table 9: Comparison of immediate and delayed surface roughness Groups Immediate surface roughness Delayed surface roughness P value Group 1 0.66±0.02 0.74±0.02 2.207; 0.027* Group 2 0.92±0.01 1.06±0.02 2.220; 0.026* Group 3 0.91±0.02 0.94±0.02 1.841; 0.066 Group 4 0.93±0.01 1.01±0.03 2.214; 0.027* Vinitha S Kumar, et al. International Journal of Dental Science and Innovative Research (IJDSIR) ©2025 IJDSIR, All Rights Reserved Page106 Page106 Page106 Page106 Page106 Page106 Page106 Page106 Page106 Page106 Page106 Page106 Page106 Page106 Page106 Page106 Page106 Page106 Page106 Wilcoxon Signed Ranks test; *statistically significant (p<0.05) Figure 14: Within-group comparison of immediate and delayed surface hardness Immediately after fabrication, CAD CAM PMMA (Group 1) showed the least surface roughness (0.66 ± 0.02 µm), followed by Al₂O₃ reinforced 3D-printed PMMA (Group 3, 0.91 ± 0.02 µm), ZrO₂ reinforced (Group 4, 0.93 ± 0.01 µm), and unmodified 3D-printed PMMA (Group 2, 0.92 ± 0.01 µm) exhibited the highest surface roughness. After aging, surface roughness increased for all groups. However, CAD CAM PMMA (Group 1) still exhibited the lowest surface roughness (0.74 ± 0.02 µm), followed by Al₂O₃ reinforced PMMA (Group 3, 0.94 ± 0.02 µm), ZrO₂ reinforced PMMA (Group 4, 1.01 ± 0.03 µm), and unmodified 3D-printed PMMA (Group 2, 1.06 ± 0.02 µm) showed the highest roughness. Discussion The denture bases fabricated through 3D printing technology have proven to be better in comparison to their digital counterpart, the subtractive CAD CAM technique, in terms of cost effectiveness, reduced wastage, better detail reproduction and ability to print complex geometries.5,6 However, the mechanical and surface properties of 3D printed denture bases are found to be inferior to both conventional and CAD CAM techniques.1,7,8 Several studies aimed at enhancing the properties of heat cured PMMA have stated that reinforcing PMMA with various fibres, and nanoparticles have significantly improved their physical, mechanical and surface properties. The most commonly used fibres for reinforcement are glass fibres, polyamide, polyethylene and polypropylene and natural fibres. The fillers included aluminium oxide, zirconium oxide, titanium oxide, silver, gold, platinum, palladium, silicon dioxide, hydroxyapatite, mica, and carbon in micro and nanosizes.9,10, 11, 12, 13, 14 This in-vitro study evaluated the flexural strength, surface hardness and surface roughness of unmodified 3D printed denture base PMMA resin and 2.5wt% Aluminium oxide and 1wt% Zirconium oxide nanoparticle reinforced 3D printed denture base PMMA resin and compared them with CAD CAM denture base PMMA resin. The specimens were tested for immediate mechanical and surface properties after 24-hour immersion in distilled water. To evaluate the long-term performance, the specimens were also tested for delayed properties after undergoing artificial aging to. To simulate the dynamic intraoral conditions, the specimens were immersed in artificial saliva for 30 days, followed by 5000 thermocycling cycles, which approximates six months of intraoral use. Flexural strength represents the maximum stress a material can withstand before fracture under bending and is critical for denture durability. Consistent with earlier findings by Prpic et al7. and Gad et al.15, CAD CAM PMMA showed the highest strength due to dense prepolymerization under high temperature and pressure, producing a cross-linked, low-porosity structure. The unmodified 3D printed PMMA recorded the lowest strength, attributable to incomplete polymerization and weak interlayer adhesion during additive fabrication. Vinitha S Kumar, et al. International Journal of Dental Science and Innovative Research (IJDSIR) ©2025 IJDSIR, All Rights Reserved Page107 Page107 Page107 Page107 Page107 Page107 Page107 Page107 Page107 Page107 Page107 Page107 Page107 Page107 Page107 Page107 Page107 Page107 Page107 Layer thickness, printing orientation, and post-curing directly influence mechanical outcomes, with thinner layers enhancing dimensional stability and polymerization.8,15 Reinforced 3D printed groups demonstrated improved flexural strength over unmodified PMMA. Al₂O₃ reinforcement (2.5 wt%) significantly increased strength, consistent with Vojdani et al.16, who attributed the improvement to crack-deflection mechanisms of alumina fillers. SEM analysis in previous studies confirmed uniform Al₂O₃ dispersion with minimal void formation at optimal concentrations, while excessive filler load (> 5 wt%) reduced strength due to agglomeration. Similarly, ZrO₂ reinforced PMMA (1 wt%) exhibited higher strength than both unmodified and Al₂O₃ reinforced resins, aligning with Alshaikh et al.1 and Azmy et al17. This can be explained by ZrO₂’s transformation from tetragonal to monoclinic phase, which absorbs crackpropagation energy and improves fracture resistance. In the present study, the ZrO₂ group surpassed the Al₂O₃ group for both immediate and delayed testing, demonstrating superior crack deflection and stability. Nevertheless, CAD CAM PMMA remained superior overall due to its pre-polymerized nature. Thermocycling decreased flexural strength in all groups owing to waterinduced polymer degradation. The least deterioration occurred in the ZrO₂-reinforced group, followed by Al₂O₃-reinforced, CAD CAM, and unmodified PMMA, indicating that nanoparticle reinforcement enhances resistance to thermal fatigue. Surface hardness determines a material’s resistance to wear and deformation. Low hardness can lead to surface abrasion, plaque retention, and color alteration, compromising longevity.1 CAD CAM and heat-cured PMMA generally exhibit higher hardness than 3D printed PMMA, which has been attributed to material composition, water sorption, layer thickness, and printing orientation.1,15 Incorporation of nanoparticles substantially enhanced hardness. In this study, CAD CAM PMMA showed the highest hardness, followed by ZrO₂ reinforced, Al₂O₃ reinforced, and unmodified 3D printed PMMA. The difference between ZrO₂ and Al₂O₃ groups was statistically significant. The intrinsic hardness of Al₂O₃ is ≈15 GPa, which is lower than ZrO2 which has a hardness of ≈20 GPa. This could explain the better results obtained by ZrO2 in comparison to Al₂O₃. However, in agreement with previous studies,9,10,17,18 the results confirm that both nanoparticles positively contribute to the improved surface hardness of 3D printed PMMA resin Thermocycling significantly reduced surface hardness in all groups due to water absorption acting as a plasticizer within the PMMA matrix.1,15 Among reinforced groups, Al₂O₃ reinforced PMMA demonstrated better retention of hardness than ZrO₂ reinforced PMMA after aging. The improved stability of Al₂O₃ may be attributed to its homogeneous dispersion and strong filler–matrix adhesion, which reduce filler debonding under stress. In contrast, phase transformation of ZrO₂ during thermal cycling can induce microstructural alterations that slightly compromise surface hardness Surface roughness directly influences plaque accumulation, microbial colonization, and mucosal irritation. Highly polished denture surfaces are clinically desirable, as values above 2.2µm promote bacterial retention.9 3D printed PMMA typically shows greater surface roughness than CAD CAM PMMA due to its layer-by-layer structure and potential for incomplete interlayer fusion. Factors such as printing orientation, polishing technique, and resin composition also affect the final surface texture.1,5,9,15