Speed-sintering protocol and blank type affect optical properties and strength of 3-5 mol% yttria-stabilized zirconia

To investigate whether the blank type of two materials for in-office and lab-side use, layer and sintering protocol influences optical, mechanical and surface properties multi-layered zirconia blanks.

Specimens were fabricated from 3 to 5 mol% yttria-stabilized zirconia (IPS e.max ZirCAD Prime (PR)) and (IPS e.max ZirCAD MT Multi (MT)) from blocs and discs of 4 different layers and subsequently sintered with conventional or different speed-sintering protocols. Optical properties, flexural strength, grain size and surface properties were obtained.

For material MT and PR the blank type, layer and sintering protocol significantly affected translucency values. Flexural strength values of MT were overall significantly higher for discs than blocs while no difference was observed for PR. Flexural strength values within layers varied, depending on the yttria content. Using conventional sintering, higher flexural strength values were overall achieved. Speed-sintering of 55 min revealed acceptable translucency and strength results for MT blocs and speed-sintering protocols < 30 min for PR blocs as an alternative to conventional sintering. A linear correlation was established between flexural strength and yttria content of conventionally sintered specimens.

The blank type having different compositions despite same trade name, layer and sintering protocol influence optical, mechanical and surface properties of 3-5 mol% yttria-stabilized zirconia. Using a speed-sintering protocol can be a valid alternative to conventional sintering, however, the respective material needs to be specifically developed and approved for this processing.