Multi-cyclic loading in water-a test measuring how many chewing-like cycles of force a crown can withstand before it fractures-is the most reliable guide for assessing the long-term durability of all-ceramic posterior crowns, according to 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, and Dr. Van Thompson, Professor and Chair of the Department of Biomaterials & Biomimetics. Dr. Rekow and Dr. Thompson are the co-principal investigators on a 10-year, $10 million, NIH-funded study of zirconia and alumina crowns and esthetic porcelain veneers that is scheduled to conclude in spring 2008.
The test closely simulates the oral environment in which a posterior crown is placed by submerging the ceramic in water and repeatedly contacting it with a ball about the size of a biting tooth. The crown chips or fractures occur when the cracks caused by this process grow or join together.
Dr. Rekow is urging dental crown manufacturers to adopt the test and to make the results available to dental practitioners, through such mechanisms as product packaging or product inserts.
In the final phase of their study, Drs. Rekow and Thompson are overseeing multi-cyclic loading tests on ceramic configurations that closely resemble the actual complex shape of a crown.