Effects of cementation surface modifications on fracture resistance of zirconia

• Alumina coating and glass infiltration can be used to effectively modify the intaglio (cementation) surface of zirconia-based restorations.
• Glass infiltration significantly improves the flexural strength of zirconia.
• Alumina coating has no substantial effect on the load-bearing capacity of zirconia.
• Monolithic zirconia mechanically outperforms its porcelain-veneered zirconia and lithium disilicate glass–ceramic counterparts.

ObjectivesTo examine the effects of glass infiltration (GI) and alumina coating (AC) on the indentation flexural load and four-point bending strength of monolithic zirconia.MethodsPlate-shaped (12 mm × 12 mm × 1.0 mm or 1.5 or 2.0 mm) and bar-shaped (4 mm × 3 mm × 25 mm) monolithic zirconia specimens were fabricated. In addition to monolithic zirconia (group Z), zirconia monoliths were glass-infiltrated or alumina-coated on their tensile surfaces to form groups ZGI and ZAC, respectively. They were also glass-infiltrated on their upper surfaces, and glass-infiltrated or alumina-coated on their lower (tensile) surfaces to make groups ZGI2 and ZAC2, respectively. For comparison, porcelain-veneered zirconia (group PVZ) and monolithic lithium disilicate glass–ceramic (group LiDi) specimens were also fabricated. The plate-shaped specimens were cemented onto a restorative composite base for Hertzian indentation using a tungsten carbide spherical indenter with a radius of 3.2 mm. Critical loads for indentation flexural fracture at the zirconia cementation surface were measured. Strengths of bar-shaped specimens were evaluated in four-point bending.ResultsGlass infiltration on zirconia tensile surfaces increased indentation flexural loads by 32% in Hertzian contact and flexural strength by 24% in four-point bending. Alumina coating showed no significant effect on resistance to flexural damage of zirconia. Monolithic zirconia outperformed porcelain-veneered zirconia and monolithic lithium disilicate glass–ceramics in terms of both indentation flexural load and flexural strength.SignificanceWhile both alumina coating and glass infiltration can be used to effectively modify the cementation surface of zirconia, glass infiltration can further increase the flexural fracture resistance of zirconia.