title: Surface treatment of dental porcelain: CO2 laser as an alternative to oven glaze.
abstract: This work tested continuous CO2 laser as a surface treatment to dental porcelain and compared it to oven glaze (auto-glaze) by means of roughness and color parameters. Three commercial veneering porcelains with different crystalline content were tested: VM7, VM9, and VM13. Porcelain discs (3.5 × 2.0 mm, diameter × height) were sintered and had one side ground by a diamond bur (45 μm) simulating a chairside adjustment in a clinical office. Specimens (n = 7) were divided into the following groups: C--control (no treatment), G--auto-glaze (oven), and L--surface continuous irradiation with CO2 laser (Gem Laser, Coherent; λ = 10.6 μm). Laser was tested in three exposure times (3, 4, or 5 min) and two irradiances (45 and 50 W/cm(2)). Roughness parameters (Ra, Rz, and Rpm/Rz) were measured using a rugosimeter (Surftest 301, Mitutoyo). Color differences (ΔE) between the G and L groups were calculated (VITA Easyshade); ΔE values up to 3.3 were considered as not perceivable. A surface analysis was conducted by stereomicroscopy (Olympus SZ61) and SEM (Stereoscan 440, LEO). Crystalline content of specimens from groups C and L (50 W/cm(2), 5 min) was assessed by X-ray diffraction and then compared. Surface roughness (Ra and Rz) observed for laser-irradiated groups was similar to G for all studied porcelains. Rpm/Rz ratios were near 1.0 for all groups that indicated a sharp ridge profile for all specimens. Only one laser condition studied (50 W/cm(2), 3 min) from VM7 porcelain resulted in color difference (ΔE = 3.5) to G. Specimens irradiated with 50 W/cm(2) for 5 min presented the smoother surface observed by SEM, comparable to G. X-ray diffraction data revealed an increase in leucite crystallite size for VM9 and VM13 porcelains after laser treatment. Regarding roughness, continuous CO2 laser applied on porcelain surface was as effective as conventional oven auto-glaze.
authors.affiliation: Departamento de Materiais Dentários, Faculdade de Odontologia, Universidade de São Paulo, Av. Prof. Lineu Prestes, 2227, Cidade Universitária "Armando Salles de Oliveira", São Paulo, SP, CEP 05508-900, Brazil.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Sgura
authors.forename: Mariana Cavalcante
authors.initials: MC
authors.lastname: Reis
authors.forename: Antonio Carlos
authors.initials: AC
authors.lastname: Hernandes
authors.forename: Márcia Carvalho
authors.initials: MC
authors.lastname: de Abreu Fantini
authors.forename: Marcello Rubens Barsi
authors.initials: MR
authors.lastname: Andreeta
authors.forename: Igor Studart
authors.initials: IS
authors.lastname: Medeiros
mesh_terms: D000538:Aluminum Silicates; D002245:Carbon Dioxide / Q000737:chemistry*; D003116:Color; D003460:Crystallization; D003775:Dental Polishing; D003776:Dental Porcelain / Q000737:chemistry*; D007834:Lasers; D054020:Lasers, Gas; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D013499:Surface Properties; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D000538:Aluminum Silicates; D003776:Dental Porcelain; C078519:leucite; D002245:Carbon Dioxide