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.

CO2 Laser Glazing Treatment of a Veneering Porcelain: Effects on Porosity, Translucency, and Mechanical Properties

“…The observed increase in microhardness for irradiated specimens may be explained by the increase in leucite content and size after continuous CO 2 laser irradiation, as described in a previous study. 20 On the other hand, the differences observed among the mean values of fracture toughness did not follow any logical trend. It is believed that the different heat treatments applied to the porcelain surface resulted in significantly different distributions of residual stresses, which affected the crack growth that originated from the corner of the Vickers indentations during the IF test.…”

“…Irradiance and time were chosen based on a previous study. 20 For surface porosity determination, three images per specimen were obtained at 1003 magnification (HMV, Shimadzu, Singapure). Micrographs were analyzed with Image J software (National Institutes of Health, Bethesda, MD, USA) for determination of the area fraction and Feret diameter of pores.…”

“…The advantages of CO 2 laser glazing are 1) the possibility of reducing the number of appointments that they offer, since laser application is a chairside technique, and 2) the higher processing speed, which is approximately four times faster than that of the conventional technique. 20 To the authors' knowledge, the effects of CO 2 laser glazing on porosity and translucency have not yet been determined. Therefore, this study evaluated the surface porosity, masking ability, microhardness, and apparent fracture toughness of a commercial veneering porcelain submitted to CO 2 laser glazing.…”

“…When light propagates within a material and reaches a pore, it deviates from its normal path as a result of the difference in refraction index between the pore medium (air) and the porcelain material. 18 Alternative glazing treatments have been suggested in the literature (eg, microwave oven 19 and CO 2 laser sintering 20 ), with promising results. Continuous CO 2 laser irradiation of ground porcelain discs resulted in surface roughness similar to that of autoglazed specimens.…”

Comparison of surface roughness between CO2 laser and typical glazing on two types of porcelain vita and ivoclar

“…Remaining sample of each type of porcelain was glazed in the usual way of furnace glazing and accord-ing to glazing manufacturer's instructions, also standard polished group was prepared with sandpaper bysame grits according to recommendation of American Academy of Cosmetic Dentistry (P360, P400 and P1200) (Fairhurst 1992).To investigate surface roughness, a profi lometer (Mitutoyo Surf Test 402 Analyser; Mitutoyo crop, Kawasaki, Japan) was used with a pen diameter 12.5 mμ, pen power 10mg (Prasad 2009) and movement speed of co2 laser on the surface was 10 mm /min (Sgura 2015) and manually, and the entire sample length was scanned by profi lometer (Mitutoyo Surf Test 402 Analyser; Mitutoyo crop, Kawasaki, Japan).…”