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ePaper created 2015-10-28, 09:28:35 | version 1.38.0
Dental Tribune U.S. Edition | November 2015A4 AD INDUSTRY NEWS Nanoscale fiber strengthens composites NovaPro Flow, designed and created by Nanova Biomaterials, is the first com- mercial dental composite reinforced by nanofibers. The in-house made hydroxy- apatite nanofibers, composed of calcium phosphate minerals, are the secret to NovaPro Flow’s high strength, great han- dling properties and esthetic effects, ac- cording to the company. Teeth, bones and nanofibers have the same structure, all composed of a hard inorganic mineral in a soft organic ma- trix. For example, the enamel of a tooth is made up of high-volume, needle-like mineral crystals (approximately 15–20 nanometers thick and 1,000 nanome- ters long) in a small-volume, soft protein matrix. Bone and dentin are made up of plate-like crystals (approximately 2–4 nanometers thick and up to 100 nano- meters long) embedded in a collagen- rich protein matrix. By comparison, the nanofibers have a thickness under 100 nanometers in diameter, or 1,000 times smaller than human hair. Most dental composites comprise only nanoparticles, while NovaPro Flow reinforces the composites with nano- fibers, adding several advantages. The strength found in the nanofibers is due to its one-dimensional nature and large surface area. If you apply a shear force to a bunch of nanoparticles, it is easier for the particles to slide by each other. A fiber, on the other hand, has a solid connection that is stronger to resist bending, shear and tensile forces. In com- parison, synthetic bulk hyd r ox y ap at it e typically has a tensile strength of approximate- ly 50 MPa, which would not be able to reinforce a dental composite. The large size would also lead to polishing problems. The larger surface area of nanofibers provide better transfer of strength for the fiber and the dental composite alike. During World War I, A. A. Griffith discovered the correlation between strength and the small size of ceramic materials, such as enamel, by testing dif- ferent thicknesses of glass. According to the Griffith theory, these needle-like mineral crystals can reach their theoretical strength, or maximum strength, of a material (several or tens of GPa) when their diameters are in the nanoscale. Microscopic flaws cause a ma- terial to fail, so by creating a nanoscale fiber, statistically, it limits the amount of flaws and provides the ability to reach the material’s maximum strength. In addition, such mineral crystals at na- noscale are not sensitive to cracks or stress concentration, which typically degrades when produced on a micro or macro scale. The fibers are able to bend without breaking. The high strength and low sensitivity to cracks found in natural nanocomposites are the same advantag- es provided by the nanofiber reinforced NovaPro Flow. (Source: Nanova Biomaterials) NovaPro Flow, the first composite to add nanofiber technology to today’s nano-hybrid composite to significantly improve mechanical perfor- mance. Photo/Provided by Nanova Biomaterials Result is described as stronger, longer-lasting — and with low shrinkage stress