Good to know: flexural strength and why it is important
Surely you have already come across the term ‘flexural strength’. What exactly do we mean by ‘flexural strength’? Why is flexural strength important? Which values are considered good? Find out some of the most important things you should know about this topic.
Flexural strength: one of the key values for evaluating the stability of a material
Flexural strength is a term that is frequently used in the dental world. Every manufacturer of dental materials provides values that refer to this feature. With good reason: flexural strength is considered to be a key value when it comes to the stability of a material - such as zirconium oxide.
Note: Measuring methods vary!
From a scientific point of view, flexural strength informs about the resistance of a material against deformation, i.e. flexural strength indicates how much force is required to break a test sample of a defined diameter. As soon as this value is exceeded, the test specimen breaks. The higher the value, the more impacting forces the material is able to withstand. However, the flexural strength determined during a test depends heavily on the measuring method used and the surface preparation of the test samples, i.e. on whether a material is polished or ground, for instance. Comparisons between different materials should therefore always be taken with a pinch of salt. Values measured with different measuring methods are not comparable. For the values to be comparable, they have to be obtained using the same measuring method.
The actual advantages of high flexural strength
Materials with high flexural strength offer advantages with regard to two applications in particular:
A) Extensive or long-span restorations
High flexural strength is essential for stress-bearing restorations, when high pressure/stress is exerted on the material or restoration. As a result, flexural strength also determines the indications for which a material can be used:
- The more strength a material offers, the more units a restoration can include.
- Or, if put the other way round: The more extensive the restoration is, the stronger the material should be.
▸ The strength values required for specific restorations or indications are detailed in the relevant standards.
B) Minimally invasive treatment options with thin wall thicknesses
High flexural strength also affects the thickness of the restoration walls. A high-strength material allows a low wall thickness. For instance, if you use the IPS e.max ZirCAD MO or LT zirconium oxide, you can reduce the wall thickness to 0.4 mm for anterior teeth and to 0.6 mm for posterior teeth. If you use IPS e.max ZirCAD MT or MT Multi, you can limit the wall thickness to 0.8 mm for anterior teeth and to 1 mm for posterior teeth. This means:
- A material that offers high flexural strength and high fracture toughness allows very thin restorations to be produced
- and is therefore well suited for minimally invasive treatment options.
Zirconia & Co.: the champions when it comes to strength
Zirconia is probably the best-performing all-ceramic material in dentistry in terms of flexural strength. An example: IPS e.max ZirCAD LT (Low Translucency) has a flexural strength of 1,200 MPa, which is a very high value indeed.
Among the translucent zirconia materials, IPS e.max ZirCAD MT and MT Multi offer high stability at a flexural strength of 850 MPa. These materials offer attractive esthetic possibilities for high-strength monolithic treatment options.
In the field of glass-ceramics, IPS e.max Press and CAD also offer high flexural strength values. Mean values of 470 and 530 MPa have been measured over more than ten years and are testimony to the high flexural strength of these materials.
Strength and translucency: carefully coordinated
Generally speaking, the relationship between strength and translucency is closely intertwined in the oxide ceramic materials currently available.
- The higher the translucency of a material, the lower the flexural strength.
- Or, to put it the other way round, the higher the flexural strength of a material, the lower its translucency.
▸ You can achieve sound, esthetically pleasing restorations with the help of an ideally matched translucency concept that enables both a maximum level of natural esthetics and translucency as well as high strength.