Effect of Repeated Firings on Microtensile Bond Strength of Bi-layered Lithium Disilicate Ceramics (e.max CAD and e.max Press).
OBJECTIVE
To achieve acceptable contour, color, esthetics, and occlusal relations, the porcelain may be subjected to several firing cycles. This study sought to assess the effect of multiple firing cycles on the microtensile bond strength (MTBS) of lithium disilicate-based ceramics (e.max Press, e.max CAD).


METHODS
IPS e.max computer aided design (CAD) cores were fabricated using CAD/(Computer Aided Manufacturing (CAM)) technology, and IPS e.max Press cores were fabricated using the heat-pressing technique (12 × 12 × 4 mm(3)). Cores in each group were divided into three subgroups based on the number of firing cycles (three, five, and seven cycles). After porcelain application, the samples were sectioned into microbars and a total of 20 sound microbars in each group were subjected to tensile load in a microtensile tester at a crosshead speed of 1 mm/minute. Microtensile bond strength of the core to the veneering porcelain was analyzed using one-way analysis of variance (ANOVA). Pairwise comparisons were made using the Tukey's test (p < 0.05).


RESULTS
In the e.max CAD, the mean MTBS values were 22.07 ± 6.63, 34.68 ± 7.07, and 26.05 ± 10.29 MPa following three, five, and seven firing cycles respectively. These values for the e.max Press were 34.46 ± 9.28, 23.09 ± 5.02, and 31.26 ± 12.25 MPa respectively. There was significant difference in bond strength of e.max CAD (p < 0.003) and e.max Press (p < 0.002) based on the number of firing cycles.


CONCLUSIONS
Increasing the number of porcelain firing cycles decreased the bond strength of the core to the veneering porcelain in both ceramics.


CONCLUSIONS
It is better to decrease the number of firing cycle as much as possible.
Department of Prosthodontics, Dental Research Center Dentistry Research Institute, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran.
Hamid
H
Jalali
Department of Prosthodontics, School of Dentistry, Yazd Shahid Sadoughi University of Medical Sciences, Yazd, Iran.
Zeinab
Z
Bahrani
Assistant Professor, Department of Prosthodontics, Dental Research Center Dentistry Research Institute, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran, Phone: +982188095695, e-mail: somayeh.zeighami@gmail.com.
Somayeh
S
Zeighami
D003764:Dental Materials / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis; D006358:Hot Temperature; D066298:In Vitro Techniques; D008422:Materials Testing; D013718:Tensile Strength
D003764:Dental Materials; C520133:IPS e.max CAD LT; C508050:IPS e.max Press; C493120:lithia disilicate; D003776:Dental Porcelain
Bi-layered restoration; Glass ceramic; IPS e-max; In vitro study; Lithia disilicate; Microtensile bond strength; Repeated firing.