Surface structure and mechanical properties of impaction-modified Y-TZP

Objectives

The objectives of the study were to describe the surface structure and the chemical surface composition of Y-TZP ceramics produced by using the modified additive technique and to evaluate the flexural strength of Y-TZP with or without surface modification and with different pretreatments: etching before or after sintering combined with or without an adhesive cement system.

Methods

Y-TZP discs were used for surface analysis (n = 48) and for biaxial flexural strength testing (n = 200). The specimens were divided into groups depending on the cementation surface of Y-TZP: unmodified, sandblasted or glass-modified Y-TZP surfaces, and according to the production process: etching before or after sintering.

Results

The surface structure and the chemical composition of glass-modified Y-TZP differ; a rougher surface and phase transformation was identified compared to unmodified Y-TZP.The unmodified Y-TZP groups showed significantly higher flexural strength compared to the glass-modified groups (p < 0.001) and showed increased flexural strength after sandblasting (p < 0.001). Furthermore, by adding cement to the surface, the value increased even further in comparison with the sandblasted non-cemented specimens (p < 0.01). After thermocycling, however, the cement layer on the unmodified and the sandblasted surfaces had air pockets and regions with loose cement.

Significance

A rougher surface structure, superficial glass remnants and a higher content of m-phase was present in the cementation surface of glass-modified Y-TZP. The glass modification creates a bondable cementation surface that is durable. By etching the glass-modified Y-TZP before sintering, a more homogenous surface is created compared to one that is etched after sintering.