Surface Effects of Regenerative Heat Treatment on Zirconia

Objectives: Developing a regenerative heat treatment (RHT) for zirconia (Y-TZP) after a grinding procedure is an alternative to convert the material into a more stable phase, but the effects of this treatment on the material surface are not yet completely known. The aim of this study was to evaluate the surface of Y-TZP after grinding with diamond stone followed by different RHT.
Methods: Y-TZP specimens (Lava^TM) were divided into 6 groups: sintered (control, C), ground (G), grinding + RHT of 700°C for 60min (G700/60), grinding + RHT of 800°C for 60min (G800/60), grinding + RHT of 900°C for 60min (G900/60) and grinding + RHT of 1000°C for 30min (G1000/30). Grinding (0.3mm) was performed on the specimens surface in a standardized device using diamond stone (MasterCeram®) at low speed under irrigation with distilled water. The heat treatment was carried out in a conventional oven for ceramics (AluminiPress) according to the experimental groups; the specimens’ cooling was performed at room temperature after the furnace opening. The surfaces were evaluated by scanning electron microscopy (SEM, 10,000x) and optical profiler (area of 2mm × 2mm). The SEM images and 3D profilometry were submitted to a descriptive analysis.
Results: The 3D profilometry analyses showed a large increase of scratches and superficial valleys after ground. Moreover, it was observed more regular surfaces after RHT. The D1000/30 treatment was the most efficient providing less rough surfaces. The SEM images showed the presence of longitudinal grooves parallel to the grinding direction, surface plastic deformation, surface chipping and microcracks for ground groups. After heat treatment at 1000°C for 30min there was a lower concentration of surface microcracks and smoothing of structures derived from the grinding procedure.
Conclusions: It was concluded that the regenerative heat treatment at 1000°C for 30 min was the most effective to let a smooth surface and seal surface microcracks.