Dental laboratories increasingly rely on precise strength testing to ensure the durability and safety of dental ceramic restorations, according to experts.
Dinesh Sinha, BDS, PhD, recently interviewed Nathaniel C. Lawson, DMD, PhD, director of the Division of Biomaterials at the University of Alabama at Birmingham School of Dentistry, about current testing methods.
“Dental ceramics account for up to 90% of fixed restorations in many labs. Understanding their strength helps dentists determine proper use, including minimum thickness, connector dimensions, and placement in the mouth,” Lawson explained.
Most laboratories follow International Standards Organization (ISO) protocols to standardize testing.
ISO 6872:2015 specifies three key methods: 3-point bend flexural, 4-point bend flexural, and biaxial flexural (piston-on-3-balls) tests.
The 3- and 4-point bending tests use bar-shaped specimens loaded at the center or between two indenters, while the biaxial test uses a disc-shaped specimen supported on three balls and loaded at the center.
Ceramics are brittle due to their atomic lattice structure, which prevents bending and causes cracks to propagate. Zirconia is an exception, as it can halt crack progression through transformation toughening.
Lawson noted differences between specimen types: bar-shaped specimens may develop edge chips, creating stress points that trigger cracks, known as the edge effect. ISO recommends beveling these edges to reduce this issue.
Disc-shaped specimens avoid edge effects and often register higher strength. However, because real restorations have edges, testing bar-shaped specimens may better reflect clinical performance.
These findings highlight the importance of careful material testing in dental laboratories to optimize restoration longevity and patient safety.
