Although zirconia all-ceramic crowns and bridges are more aesthetically pleasing than those made from metal, an estimated 10 percent of zirconia restorations develop fractures within the first three years.
Dr. Yu Zhang, an Assistant Professor of Biomaterials & Biomimetics, believes that reformulating zirconia as a glass-ceramic composite will increase its fracture resistance. Dr. Zhang was recently awarded a three-year, $1.2 million grant by the National Institute of Dental and Craniofacial Research (NIDCR) at the NIH to test his hypothesis.
The new composite will have a predominantly glass surface with underlying layers that gradually become more densely packed with ceramic. "A composite with glass-rich surfaces will be less susceptible to top-to-bottom fractures from direct contact with hard food as well as to ruptures that occur when the bottom of the restoration buckles under pressure," predicts Dr. Zhang, who joined NYUCD two years ago after working as a materials scientist at NIST, the Maryland-based National Institute of Standards and Technology.
The study is an outgrowth of research conducted by Dr. Zhang at NIST, where he was a coinvestigator on a $5.9 million NIH grant. Led by Dr. Van Thompson, Professor and Chair of the Department of Biomaterials & Biomimetics, and Dr. Dianne Rekow, Professor and Chair of the Department of Basic Science & Craniofacial Biology and Special Advisor to the President and the Provost on Engineering at NYU, the grant examined the causes of ceramic fractures. Dr. Thompson and Dr. Brian Lawn, an NIST Fellow, are coinvestigators on the new grant.
According to Dr. Zhang, fracture risk will also be reduced because glass-rich surfaces can be bonded with conventional etching, a less invasive process than sandblasting, which bombards all-ceramic surfaces with hard particles.
A glass-ceramic composite restoration offers aesthetics comparable to a porcelain-veneered zirconia restoration, but since it is thinner, less healthy-tooth structure needs to be removed to make room for it.
Dr. Zhang and his coinvestigators have patented a preliminary design for the glass-ceramic composite. If it proves more durable than all-ceramic formulations, a subsequent study examining the safety and efficacy of glass-ceramic composite restorations in human subjects would be required for Food and Drug Administration approval.