Effect of temporal width pulse of Er:YAG laser on surface characteristics, bond strength and mechanical properties of zirconia

Author(s)

Beatriz Togoro Ferreira da Silva

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Faculdade de Odontologia (FO/SDO)
• Defense date: 2019-08-12

Examining board members

Paulo Francisco Cesar; Marina da Rosa Kaizer; Erick de Lima; Adriana Bona Matos

• Advisor: Paulo Francisco Cesar

Abstract

This study evaluated the effect of different irradiation pulse width with Er:YAG laser on surface characteristics (morphology, phase transformation, surface roughness, surface loss), adhesive interface bond strength formed by the irradiated zirconia and luting cement system (Panavia F 2.0, Kuraray, Okayama, Japan) and mechanical properties (flexural strength) of zirconia. Blocks of pre-sintered 3Y-TZP were cut providing 350 standard samples which were divided by surface treatment as follows (n=50): GC untreated (control); G50 (80mJ/2Hz/50?s); G100 (80mJ/2Hz/100?s); G300 (80mJ/2Hz/300?s); G600 (80mJ/2Hz/600?s); GUNTC (tribochemical silica coating before sintering); GTC (tribochemical silica coating after sintering). Specimens were sintered according to the manufacturer\'s recommendations. Except for GTC, all specimens were sintered prior to surface treatment. The specimens were evaluated by different methods: morphological analysis by scanning electron microscopy (SEM) (n=3); surface roughness and surface loss by a 3D optical profilometer; the immediate (24 h) and long term (8 months) bond strength by microshear test (?SBS) (n=8); evaluation of phase transformation of zirconia, by Xray diffractometry (XRD) (n=1) and biaxial flexural strength (BFS) (n=30). SEM evaluation indicated that irradiation of Y-TZP with Er:YAG laser promoted an effective ablation irrespective of the pulse width, ending in an irregular surface without cracks or carbonization. The roughness and surface loss values obtained from G50, G100, G300 and G600 groups were significantly higher than those obtained from GTC e GC. A satisfactory roughness with little surface loss was detected in GUNTC. Regarding immediate ?SBS, the highest value was recorded in GTC followed by G300. On the other hand, G50, G100, G600 groups showed an intermediate ?SBS, while the lowest bonding value was obtained in GUNTC and GC groups. After aging, all experimental groups presented similar and very low bond strength, irrespective of the surface treatment. While, the bonding of GC and GUNTC showed spontaneous debonding after 8 months of water storage. XRD detected only tetragonal phase in all groups, except for GTC where monoclinic phase was observed. The best surface treatment concerning to BFS was tribochemical silica coating after sintering (GTC). On the other hand, a significant decrease was observed after laser treatments. Intermediate BFS were observed in untreated zirconia (GC) and tribochemical silica coating before sintering (GUNTC). Er:YAG laser treatment is not recommended to be used with 3Y-TZP. Although it did not cause phase transformation, the zirconia specimen strength decreased, bonding do not resist to water storage and also created a rough surface with great surface loss. Tribochemical silica coating was the most effective surface treatment method because, although it caused phase transformation and the bond strength did not remain stable over time; this treatment caused little surface loss and increased flexural strength of the material. (AU)

• FAPESP's process: 16/13117-1 - Effect of temporal width pulse of Er:YAG laser in zirconia morphology, roughness and bond strength
• Grantee: Beatriz Togoro Ferreira da Silva
• Support Opportunities: Scholarships in Brazil - Doctorate