Flexural Strength in 3D-Printed Composite Resins for Permanent Crowns and Bridges

At Custom Resin Solutions, we developed a next-generation 3D-printed composite resin for permanent dental restorations. CRS Composite Resin is engineered for high flexural strength, strong dimensional stability, durability under occlusal stress, and verified biocompatibility—supporting both digital workflow efficiency and long-term clinical performance.

Why Mechanical Performance Matters in Permanent Restorations

In restorative dentistry, mechanical performance is a key predictor of long-term success. Permanent restorations such as crowns and bridges must withstand repeated chewing forces and cyclic loading over years of use. For polymer-based restorative materials, flexural strength is widely used as a core benchmark to evaluate resistance to bending stresses that occur during function.

According to ISO 10477, polymer-based crown and veneering materials must achieve at least 50 MPa flexural strength. In clinical practice—especially for load-bearing restorations—higher flexural strength values are generally preferred to provide a greater safety margin against fracture and long-term degradation.

Understanding Flexural Strength

Flexural strength (bending strength) is the maximum stress a material can tolerate before fracture under bending forces. In dentistry, it is a critical performance indicator because restorations experience repeated occlusal loads that can initiate microcracks over time. Materials with higher flexural strength generally show better resistance to crack initiation and fracture under functional stresses.

Flexural strength is commonly measured by a three-point bending test, where a bar-shaped specimen is supported at two points and loaded at the center until failure.

The test setup is illustrated in Figure 1.

Figure 1: Illustration of the three-point bending test

Clinical Importance of Flexural Strength

Permanent restorative resins must tolerate masticatory forces, temperature variations, and chemical exposure in the oral environment. During mastication, restorations are subjected to bending stresses—especially in posterior regions where occlusal forces are highest. If flexural strength is insufficient, microcracks may initiate and propagate through repeated chewing cycles, ultimately leading to failure.

For this reason, high flexural strength is often associated with improved durability, fewer fractures, and better long-term outcomes—particularly in load-bearing crowns and bridges.

Benefits of Selecting High Flexural Strength Restorative Resins

Choosing a resin that significantly exceeds the minimum flexural strength requirement can offer practical clinical advantages, including:

• Improved load-bearing capacity: Higher resistance to bending stresses reduces fracture risk under heavy or accidental loads.
• Lower likelihood of catastrophic failure: Stronger materials are less prone to cracking in high-stress zones.
• Enhanced longevity: Better crack resistance may reduce replacement and repair frequency over time.
• Greater design freedom: Higher strength can support thinner geometries where appropriate, while maintaining mechanical reliability.

While flexural strength is a key benchmark, other properties—such as fracture toughness, elastic modulus, fatigue resistance, and wear behavior—also influence long-term performance. Nevertheless, consistently high flexural strength remains one of the most widely accepted predictors of functional durability in polymer-based restorative materials.

Method: Three-Point Bending Test (Zwick Z250)

All materials in this evaluation were prepared according to the manufacturers’ instructions for use. A total of six specimens were prepared from resins intended for permanent dental restorations. Mechanical testing was performed using a three-point flexural test on a Zwick Z250 universal testing machine (ZwickRoell, Yokohama, Japan), with a crosshead speed of 5 mm/min.

The alternative resins are presented anonymously (manufacturer initial + country), while the CRS Composite Resin is identified as the in-house material developed in Turkey.

• Sample A: Switzerland-based manufacturer (name starts with “S”).
• Sample B: U.S.-based manufacturer (name starts with “R”).
• Sample C: Custom Resin Solutions (Turkey).

Results: Flexural Modulus and Flexural Strength

Table 1: Three-Point Bending Test Results (Sample A)

Figure 2: Three-Point Bending Test Graphs (Sample A)

Table 2: Three-Point Bending Test Results (Sample B)

Figure 3: Three-Point Bending Test Graphs (Sample B)

Table 3: Three-Point Bending Test Results (CRS Composite Resin)

Figure 4: Three-Point Bending Test Graphs (CRS Composite Resin)

Figure 5: Average Flexural Strength Values of Tested Resins

Key Finding

Among the tested materials, CRS Composite Resin showed the highest average flexural strength (144.05 MPa). This indicates stronger resistance to bending forces compared to the other tested alternatives and suggests a wider safety margin against fracture under occlusal loading for load-bearing crowns and bridges.

• Greater reliability: Increased resistance to crack initiation during function.
• Potential for broader applications: High flexural strength may support more demanding restorative designs where higher stresses are expected.

Conclusion

This evaluation reinforces that flexural strength is a critical mechanical parameter for the success of 3D-printed dental restorations. CRS Composite Resin demonstrated the highest average flexural strength (144.05 MPa) among the tested materials, indicating strong mechanical reliability for load-bearing applications such as posterior crowns and bridges.

Following CE certification under the MDR framework, CRS Composite Resin has been used and monitored in clinical cases, and feedback has been consistent with laboratory performance. Further long-term in vivo studies can provide additional insight into clinical outcomes over extended service periods.

References

1. Amin, F., Farhan, T., Kumar, N., & Mahmood, S. J. (2020). Exploration of the Customized Fixtures for the Evaluation of Three-point Bending Strength of Dental Resin Composites. JDMT, 9(1), 51–55. https://doi.org/10.22038/JDMT.2020.44057.1320
2. Rauch, A., et al. (2023). Aging and Fracture Resistance of Implant-Supported Molar Crowns with a CAD/CAM Resin Composite Veneer Structure. Journal of Clinical Medicine, 12(18), 5997. https://doi.org/10.3390/jcm12185997
3. ISO 10477:2020 Dentistry — Polymer-based crown and veneering materials. https://www.iso.org/standard/80007.html
4. Characterization of temporary and permanent 3D-printed crown and bridge resins. Biomaterial Investigations in Dentistry. https://doi.org/10.2340/biid.v12.43584
5. Basheer, R. R., et al. (2024). Evaluating flexure properties... BMC Oral Health, 24(1). https://doi.org/10.1186/s12903-024-04333-3
6. Banerjee, S., et al. (2024). Flexural Strength of Different Commercially Available Auto-Polymerizing Acrylic Resins. Cureus, 16(10), e71905. https://doi.org/10.7759/cureus.71905

 

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