Edentulism remains a significant oral health concern worldwide, particularly among elderly populations¹. Complete dentures continue to be the most common rehabilitative treatment for fully edentulous patients. Among available denture base materials, polymethyl methacrylate (PMMA) remains the gold standard because of its favorable esthetics, ease of processing, cost-effectiveness, and biocompatibility². Despite these advantages, PMMA possesses inherent mechanical limitations, particularly low impact and fatigue resistance³. Denture base fractures are frequently reported in clinical practice and may occur either due to accidental dropping (impact failure) or repetitive intraoral loading (fatigue failure)⁴,⁵. Flexural fatigue, especially in maxillary dentures, is a primary cause of midline fractures⁵. Flexural strength is one of the most clinically relevant mechanical properties of denture base materials. It reflects the material’s ability to resist deformation under bending stresses, which simulate masticatory loading conditions⁶. Various manufacturers have introduced modified heat-cure acrylic resins claiming improved mechanical performance. However, comparative evaluation under standardized conditions remains essential for objective assessment. Previous investigations have shown variability in flexural strength among commercially available denture base resins⁷–⁹. Differences in polymer-to-monomer ratio, cross-linking agents, residual monomer content, and polymerization cycles may influence mechanical performance³,¹⁰. Given the clinical importance of selecting a denture base resin with optimal mechanical properties, the present in vitro study was undertaken to compare the flexural strength of four commercially available heat-cured denture base resins fabricated without reinforcement. OBJECTIVE To comparatively evaluate the flexural strength of four commercially available heat-cured denture base resins fabricated without reinforcement.

Study Design: An in vitro experimental study conducted in 2016 at Department of Prosthodontics, Jaipur Dental College in collaboration with Central Institute of Plastic Engineering & Technology. Materials Tested • Lucitone 199 (Dentsply) • Acralyn-H (Asian Acrylates) • Pyrax (Pyrax Polymers) • DPI Heat Cure (Dental Products of India) Specimen Preparation: A custom-fabricated metal die was used to standardize specimen dimensions (40 × 40 × 3 mm). A total of 40 wax patterns were fabricated (10 per material group). Specimens were invested using conventional flasking technique and processed according to manufacturer instructions. A standardized short curing cycle was used: • 73°C for 90 minutes • Terminal boil at 100°C for 30 minutes Specimens were bench cooled, retrieved, finished, polished, and dimensionally verified using a digital vernier caliper. Flexural Strength Testing: Flexural strength was evaluated using a three-point bending test on a SHIMADZU-AGS universal testing machine. Testing parameters: • Crosshead speed: 1 mm/min • Span length: 20 mm • Central loading until fracture Flexural strength was calculated using: Flexural strength = 3pl / 2bd2 Where p - is the peak load l -is the span length b - is the sample width and d - is the sample thickness Statistical Analysis: Data were analyzed using SPSS 17.0. One-way ANOVA was applied to detect intergroup differences, followed by Tukey’s post hoc test. Statistical significance was set at p<0.05. A B C D E F A) Armamentarium; B) Lucitone 199; C) Acralyn-H; D) Pyrax; E) DPI Heat Cure; F) Load Applied on the Specimen

Table 1: Mean Flexural Strength Without Mesh Reinforcement Group n Mean (MPa) Std. Deviation P-value Lucitone 10 64.6917 17.46058 Pyrax 10 46.3333 19.03437 Acralyn-H 10 63.7583 18.85264 DPI 10 54.4500 14.23357 Overall p-value 0.080 Lucitone showed the highest mean flexural strength (64.6917 MPa). Pyrax showed the lowest (46.3333 MPa). Lucitone demonstrated 39.6% higher mean flexural strength than Pyrax; 18.8% higher than DPI; and 1.46% higher than Acralyn-H. However, the overall difference was statistically non-significant (p=0.080). Table 2: Post Hoc Tukey Test Comparison Mean Difference P-value Lucitone vs Pyrax 18.35833 0.107 Lucitone vs Acralyn-H 0.93333 0.999 Lucitone vs DPI 10.24167 0.564 Pyrax vs Acralyn-H -17.42500 0.135 Pyrax vs DPI -8.11667 0.729 Acralyn-H vs DPI 9.30833 0.637 All pair wise comparisons were statistically non-significant (p > 0.05).

The present study evaluated and compared the flexural strength of four commercially available heat-cured denture base resins fabricated without reinforcement. Although Lucitone 199 exhibited the highest mean flexural strength, statistical analysis revealed no significant intergroup differences. Flexural strength is a combined measure of tensile, compressive, and shear stresses acting simultaneously⁶. During mastication, dentures experience bending forces that may lead to fatigue failure over time⁵. Therefore, evaluating flexural performance under standardized laboratory conditions is critical. Lucitone 199 demonstrated the highest mean value (64.6917 MPa). These findings are consistent with Flinton and Neihart⁷, who reported superior fracture toughness of Lucitone 199 compared to other materials. Thomas and Latta⁸ also observed higher flexural strength values for Lucitone 199 among tested materials. Acralyn-H exhibited flexural strength comparable to Lucitone (difference only 1.46%), suggesting competitive mechanical performance. Chandra Patel et al.⁹ similarly reported that high-quality heat-cure acrylics demonstrate comparable transverse strength values under standardized conditions. Pyrax demonstrated the lowest mean flexural strength (46.3333 MPa), approximately 39.6% lower than Lucitone. Variations in polymer formulation, cross-linking density, and residual monomer content may explain these differences³. However, the ANOVA p-value (0.080) indicated that differences were not statistically significant. This suggests that under standardized curing and testing conditions, commercially available heat-cure denture base resins may perform comparably in terms of flexural strength. Craig and Powers³ emphasized that polymerization cycle and residual monomer levels significantly influence mechanical properties. Standardized processing in the present study minimized confounding variables, ensuring valid comparison. Clinically, the absence of statistically significant differences implies that material selection may depend on other factors such as cost, availability, handling characteristics, and clinician preference. Limitations include the in vitro design and absence of fatigue cycling. Long-term clinical studies would better reflect intraoral conditions.

Within the limitations of this in vitro study: • Lucitone 199 demonstrated the highest mean flexural strength. • Pyrax showed the lowest mean flexural strength. • However, no statistically significant difference was observed among the four heat-cured denture base resins without reinforcement. • All tested materials exhibited clinically acceptable flexural strength values. ACKNOWLEDGEMENT The authors acknowledge Jaipur Dental College and the Central Institute of Plastic Engineering & Technology for laboratory support. The authors also thank The VAssist Research team (www.thevassist.com) for its contribution in manuscript editing and submission process. Conflict of Interest: None declared. Source of Funding: No external funding was received.

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