Crystallization Effect on The Elastic Modulus of a Lithium Disilicate

Objectives: Appropriate mechanicals analyses of dental ceramics require a suitable elastic modulus. The aim of this study was to determine the elastic modulus of a new lithium disilicate glass-ceramic material developed at Vitreous Materials Laboratory (LaMaV) under different times and temperatures of nucleation and evaluates the influence of crystalline fraction.
Methods: The experimental material (LaMaV CAD) was prepared by individual reagents weighing, homogenization, melting at 1450^oC for 3h, and annealing at 380^oC. Blocks were cut into bar-shape specimens (20mm X 4mm X 3mm) and treated with different times/temperatures of crystal nucleation: 1h30min/500^oC (G1), 3h/500^oC (G2), 6h/480^oC (G3) and 6h/500^oC (G4), with 3 specimens per group. All specimens were treated for lithium metasilicate and disilicate crystal growth following the same condition. E.max CAD (Ivoclar) composed the control group (G5, n=3). Elastic modulus (E, in GPa) was determined using the ultrasonic pulse-echo technique, following the recommendations of ASTM E 494-95. Quantification of the crystalline fraction (CF) was performed using the Image J software, obtaining the estimated percentage for the glass and the crystalline phase and analyzed descriptively. Data for E were statistically analyzed with Kruskal-Wallis and Dunn post test (α=0.05).
Results: The mean values for E (GPa) were: G1=94.38 ± 0.94; G2= 96.18 ± 1.09; G3=98.02 ± 2.25; G4=87.0 ± 4.14 and G5=105.71 ± 0.80. The E of the tested materials differed significantly among groups (p< 0.0001). G5 was different from all the experimental groups; only G3 was equal to G5. G5 has the major CF (≈ 60%) and was similar only to G1 in CF and morphology; G3 showed more nucleation and crystals with small size.
Conclusions: It was concluded that the group that showed the elastic modulus closest to the e-max CAD was the group that was heat treated at 480^oC for 6h, which also showed higher nucleation and crystal growth.