The Effect Of Repeated Infiltration Firing On The Flexural Strength Of Alumina-Glass Complex

Compared with PFM restorations , all-ceramic restorations have superior aesthetics and compatibility . Many modern all-ceramic products had been introduced since the 1970s, and among which the In-Ceram system developed by VITA corporation is the most outstanding one. It was reported that the bend strength of In-Ceram restoration is over 446Mpa and is about three times of that of the other all-ceramic system. The fabrication of In-Ceram restoration use primary sintering to get the net-shape Alumina, during the infiltration sintering , the molten glass penetrates and eliminate into the spaces in the net and form the Alimona-Glass Composite. Then the veneer porcelain is applied and the final restoration is completed. The infiltration sintering is a critical step in the fabrication of In-Ceram restoration. The variations of the infiltration sintering procedure may affect the strength of the final restoration. So , it is important to improve the infiltration sintering technique to ensure the long-term performance .This study investigate the effect and the mechanics of multiple infiltration sintering on the biaxial bend strength of the AGC. The primarily sintered Alumina substructure is infiltrational sintered for 1,2,3,4 times respectively to fabricate the disc-shape AGC samples. The VITA In-Ceram kit is used and the recommended sinter procedure of the manufacturer was observed. The AGC samples are tested with universal test machine and the method of piston-on-three-ball is utilized. SEM observations of the fracture surfaces are also performed. The biaxial strength of group1,2,3,4 is 424.21 ± 56.40Mpa, 447.43 ± 65.33Mpa, 451.41 ± 44.97Mpa, 444.65 ± 60.32Mpa, respectively. There is statistically difference between the strength of group1 and group2,group1 and group3,and group1 and group4. The SEM photographs show that the bubbles in group1 and 2 is more and larger that those of the group 3 and 4. But it appears that more closed-bubbles are presented in the latter 2 groups .The fracture pattern of 4 groups are both trans-crystal and break-crystal. Some Alimina particles are pulled out of the glass phase. But in group1 and 2, the fracture is mainly trans-crystal, while in the group 3 and group 4, the fracture is mainly break-crystal. The fracture surface of the Alumina particles are presented. Within the limitation of this study, the conclusions below can be drawn: Multiple infiltration sintering may improve the co-molten of the Alumina particles and the elimination of the bubbles and improve the strength of AGC. But too much sintering may introduce more closed bubbles and subsequently reduced the strength. Additionally, because the multiple infiltration sintering may affect the transparency of the material, so the effect of multiple infiltration sintering on the aesthetics of the restoration must also be considered.