New York University College of Dentistry (NYUCD) Assistant Professor of Biomaterials and Biomimetics Yu Zhang was recently awarded a 3-year, $750,000 grant by the National Institute of Dental and Cranofacial Research (NIDCR) at the National Institutes of Health (NIH) to study whether reformulating zirconia (a ceramic material used in crowns and bridges) as a glass-ceramic composite will increase its fracture-resistance.

Zirconia ceramic crowns and bridges are more aesthetically pleasing than those made from metal; however, an estimated 10% of zirconia restorations develop fractures within the first 3 years. Zhang believes that reformulating zirconia as a glass-ceramic composite will increase its durability and longevity. 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 can occur when the bottom of the restoration buckles under pressure," predicts Zhang, who joined NYUCD 2 years ago after working as a materials scientist at National Institute of Standards and Technology.

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 glass-ceramic composite restoration offers aesthetics comparable to a porcelain-veneered zirconia restoration, but since it is thinner, less healthy tooth structure must be removed to make room for it.

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 FDA approval.

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