65 - Evaluating Boron-Doped Soda Lime Glass for Finishing Dental Zirconias

Abstract

Even though monolithic restorations can be produced from dental zirconias, glaze and stains applications are routine procedures for a natural appearance result. Thus, this study evaluated the use of boron-doped soda lime glass as an alternative for finishing zirconia restorations. Disc-shaped samples of second and third generations zirconia were prepared: 3Y-TZP (ZPex, Tosoh) and 5Y-PSZ (Zpex Smile, Tosoh) (ISO 6872, diameter: 12 mm; thickness: 1.2 mm). The samples were polished with SiC #1200 sandpaper, sintered at 1550 C for 2 hours (Sirona inFire HTC speed) and randomly divided into 4 groups: 3Y-TZP with comercial glaze (3Y-G); 5Y-PSZ comercial glaze (5Y-G); 3Y-TZP with boro-doped soda-lime glass (3Y-SL) and 5Y-PSZ with boron-doped soda lime glass (5Y-SL). Then, glaze layer (Vita Akz 25, VITA Zahnfabrik, Germany) was mixed with the manufacturer building liquid, applied over the zirconia discs with a brush and fired at 950 C for 20 min. The boron-doped soda lime glass powder was mixed with propylene glycol, applied with a brush and fired at 1200 C for 20 min. The samples were subjected to surface roughness analysis in a contact profilometer for average (Ra) and ten-point-mean roughness (Rz) assessment. The biaxial flexural strength (MPa) was measured in a universal testing machine with a loading speed using the piston-on-three-ball method. The strength and roughness values (MPa) were analyzed by two-way ANOVA (α= 0.05). The glaze application led to slightly lower Ra values when applied over the 5Y-PSZ when compared to the other groups: 3Y-G (Ra-0.011; Rz-0.083), 3Y-SL(Ra-0.011; Rz-0.076), 5Y-G (Ra-0.008; Rz-0.054), 5Y-SL (Ra-0.011; Rz-0.076). However, no statistical difference was observed in Rz (p>0.05). The highest flexural strength values were observed for 3Y-TZP samples. The statistical analysis showed significant differences as follows: 3Y-SL (1026.99 MPa 130.04) > 3Y-G (818.401 MPa 89.63) > 5Y-SL (762.91 MPa 123.30) > 5Y-G (620.87 MPa 50.38). Although roughness values were similar among the experimental groups, boron-doped soda lime glass was able to improve flexural strength of both 3Y-TZP and 5Y-PSZ when compared to commercial glaze.