Effects of Glass-Ceramic-Spray-Deposition on Shape and Morphology of Zirconia Disks

Objectives: A new glass-ceramic-spray-deposition (GCSD) technique has been developed to modify zirconia surface and improve the resin-zirconia bonding. Contrarily to traditional glazing, GCSD has been claimed to generate an ultra-thin lithium silicate coating. The purposes of this study were to compare GCSD and traditional glazing in affecting the shape of zirconia restorations and find out their optimal etching time.
Methods: Zirconia (VITA XT) disks were divided into two groups: glaze and GCSD. At first, these disks were examined by optical coherence tomography (OCT) to determine the thickness of coating layers and shape deformation. Secondly, these disks receive 9% hydrofluoric (HF) acid (Ultradent™ Porcelain Etch) etching for 20s, 40s, 60s, 90s, 120s, 150s. The surface morphology and compositions of the materials were examined by SEM and EDS. The surface roughness was examined by a profilometer, and the hydrophilicity was examine using a contact angle test.
Results: The OCT analysis of all groups revealed that the thickness of glaze on zirconia surface were 18.7µm, and GCSD coating layers were 13.5µm thick. No warping of disk edges or obvious deformation was seen under OCT. GCSD group showed rod-like crystals under SEM, while glaze group showed dense coating layers. GCSD coatings with or without etching treatments were more hydrophilic than their respective glaze groups. The hydrophilicity increased with HF etching time only in GCSD groups. The unetched GCSD and glazing treatments generated comparable surface roughness values. The etched GCSD coating presented decreased roughness values, which did not vary with etching time. Contrarily, 90-s etching generated the highest roughness in glaze group.
Conclusions: In this study, 150-s and 90-s HF acid etching is suggested for GCSD and glaze coating respectively. GCSD generated thinner coatings than traditional glazing which is favorite in clinical applications to prevent restoration unfitness.