Abstract
Aim: This work evaluated dental porcelain sintering by CO2 laser irradiation. Methods: Two commercial veneering porcelains were used: VM7 and VM9 (VITA Zahnfabrik). Porcelain disks (0.35 mm dia. x 2.0 mm) were sintered by a continuous CO2 laser (Coherent, USA – 35 W e ?= 10.6 ?m) in two irradiances (20 and 23 W/cm2) and exposure times: 5 and 10 min. A control group was sintered in a conventional oven following manufacturer’s instructions. After sintering, one of the disks surfaces was mirror polished. Superficial pores (%) were assessed by images obtained in an optical microscope (100x) submitted to the software Image J analysis. Apparent density was measured by Archimedean’s method. Microhardness and fracture toughness (Indentation Fracture - IF) were determined with a Vickers indenter (Shimadzu). Results: Porosity ranged between 4.0 and 5.9% for irradiated specimens; control group had 6.0 and 4.7% of porosity for porcelain VM7 and VM9 respectively. Density of porcelain VM7 irradiated for 10 min. with irradiance of 23 W/cm2 was significantly higher than control group. Microhardness and fracture toughness of irradiated specimens were similar to control. The measurements of some irradiated groups were not possible to achieve because the tests revealed irregular marks after indentation. Conclusions: Porcelain sintering with CO2 laser in some fluences produced a material with superficial porosity similar to that obtained in conventional oven. Microhardness and fracture toughness could not be measured for all irradiated groups suggesting some subsuperficial defect caused by entrapped gases or cracks originated by temperature gradient along the specimen.
Highlights
I n modern dentistry, ceramics are an important material to the patient and professional when considering an esthetic procedure
Researchers look forward to new ceramic materials and manufacturing procedures that offer esthetic characteristics combined with sufficient mechanical properties to support the chewing efforts [2]
The hypothesis of this study was partially accepted because despite the fact that the porosity did not differ among the studied conditions, the density and the mechanical properties of some irradiated groups differed from the control group
Summary
I n modern dentistry, ceramics are an important material to the patient and professional when considering an esthetic procedure. The control group consisted of discs sintered in a conventional oven (Kerampress – Kota), following the porcelains manufacturer’s instructions (table 1) This methodology produced specimens with a high amount of superficial pores (up to 18%) compared to other previous studies [14] and to the control group (3.2 %). Five experimental conditions, for each commercial porcelain, were tested (n = 5): the laser fluences of 6000, 6900, 12000 and 13800 J/cm and the control group (oven sintered – sintering cycles are described in table 1) These specimens were mirror polished and characterized as described in the last topic regarding superficial porosity.
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