College of Dentistry's Yu Zhang Awarded NIH Grant to Develop Fracture-Resistant Crowns and Bridges

By Ami Finkelthal

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.

Yu Zhang, assistant professor of biomaterials and biomimetics at the NYU College of Dentistry, believes that reformulating zirconia as a glass-ceramic composite will increase its fracture-resistance. Zhang was recently awarded a three-year, $750,000 grant by the National Institute of Dental and Cranofacial Research at the National Institutes of Health to test his hypothesis.

The new composite will have a predominantly glass surface with underlying layers that gradually become more densely packed with ceramic. According to 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 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 can occur when the bottom of the restoration buckles under pressure," says Zhang, who joined the college 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 Zhang at NIST, where he was a co-investigator on a $5.9 million NIH grant. Led by Dianne Rekow, professor and chair of the Department of Basic Science and Craniofacial Biology and director of Translational Research, and Van Thompson, professor and chair of the Department of Biomaterials and Biomimetics, the grant examined the causes of ceramic fractures. Thompson and Brian Lawn, an NIST Fellow, are co-investigators on the new grant.

Zhang and his co-investigators 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.