Flexural strength: one of the key values when evaluating the durability of a material
Flexural strength is a term frequently used in the dental lab world. It is expressed in the metric system as megapascals or MPa. Megapascal is the mega unit used to measure the intensity of pressure or force per unit area that a material is able to withstand before breaking. Every manufacturer of dental materials provides MPa values that indicate flexural strength. With good reason: flexural strength is a key value when it comes to the durability of a material such as zirconium oxide.
Note: Measuring methods vary!
From a scientific point of view, flexural strength is the resistance of a material to breakage or fracture. Flexural strength indicates how much force is required to break a test sample of a defined measurement diameter.
As soon as this value is exceeded, the test specimen breaks. The higher the value, the more impacting forces the material can withstand. However, the flexural strength determined during a test depends heavily on the measuring method used and the surface preparation of the test samples, for instance on whether a material is polished or ground.
Comparisons between different materials are therefore not always definitive and values measured with different measuring methods are not comparable. For the values to be comparable, they must be obtained using the same measuring method. Current research is pushing towards an industry standard, but that has not been currently achieved.
Advantages of high flexural strength
Materials with high flexural strength offer advantages with these applications in particular:
- Extensive or long-span restorations. The more strength a material offers, the more units a restoration can include. The more extensive the restoration is, the stronger the material should be.
- High flexural strength is essential for stress-bearing restorations such as posterior crowns. When high pressure/stress is exerted on the material or restoration, especially on bruxism patients, flexural strength determines which a material should be used.
- Minimally invasive treatment options with thin wall thicknesses. High flexural strength also benefits the thickness of the restoration walls. A high-strength material allows a low wall thickness. This means a material that offers high flexural strength and high fracture resistance allows very thinner restorations to be produced and is therefore well suited for minimally invasive treatment options.
Zirconium Oxide: The champion when it comes to strength
Zirconia is probably the best-performing all-ceramic material in dentistry in terms of flexural strength. Lower translucency dental zirconias have a flexural strength of approximately 1,200 MPa. Among the translucent zirconia materials, flexural strength ranges from 600 to 900 MPa. The relationship between strength and translucency in the oxide ceramic material currently available is inversely proportionate.
The higher the translucency of a material, the lower the flexural strength and the higher the flexural strength of a material, the lower its translucency.