RESUMO
The restoration of endodontically treated teeth requires the fabrication of a post and core; to provide retention and support for the final crowns. The purpose of this study was to evaluate fracture resistance of endodontically treated teeth restored with prefabricated zirconia post (CP), milled zirconia post (MZ), pressable ceramic post (PC) and cast metal post (Ni-Cr) of 1.4 and 1.7 mm diameter. 48 freshly extracted human maxillary central incisors were used for this study. The teeth were distributed in four groups of 12 teeth each. From each group, 6 teeth were selected for 1.4 mm diameter post and rest of the 6 teeth, is selected for 1.7 mm diameter post. All teeth were restored with metal crowns. Each specimen from the group was subjected to "load to fracture" in universal testing machine at 130° angle and the maximum load at failure was recorded. Statistically significant difference was found between the failure load of the groups studied. In group I (Ni-Cr)-1.4 mm diameter post and core recorded a maximum fracture load of 534.83 ± 1.28 N and 1.7 mm diameter post and core showed 294.33 ± 1.02 N. In group II (PC)-1.4 mm diameter post and core recorded a maximum fracture load of 205.33 ± 1.61 N and 1.7 mm post and core showed 375.00 ± 1.57 N. In group III (CP)-1.4 mm diameter post and cores recorded a maximum fracture load of 313.00 ± 0.73 N and 1.7 mm post and core showed 638.67 ± 0.81 N. In group IV (MZ)-1.4 mm diameter post and cores recorded a maximum fracture load of 312.00 ± 0.86 N and 1.7 mm post and core showed 415.00 ± 0.89 N. Prefabricated zirconia post (1.7 mm) with pressable ceramic core (Cosmo post)-exhibited higher fracture resistance. Milled zirconia and prefabricated zirconia post-showed same value with 1.4 mm diameter post. Pressable ceramic post and core showed satisfactory result with 1.7 mm post, but showed lesser values with 1.4 mm diameter post.
RESUMO
The Mn0.5Zn0.5Fe2O4 nanoparticles has been synthesized using citrate-gel-precursor method. The direct mixing of nitrates and acetates yields homogeneous nanoparticles. Phase formation and crystal structure of the synthesized powder were examined through the X-ray diffraction (XRD). Fourier transform infrared (FTIR) spectra of the sample confirm the spinel structure. The average particle size was determined by transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). The average particle size is found to be about 13 nm. Superparamagnetic-like nature of the nanoparticles of Mn0.5Zn0.5Fe2O4 has been revealed through various dc and linear and non-linear ac magnetization measurements. However, the nanoparticles do not behave like ideal non-interacting superparamagnets. The magnetic particle size is found to be about 8 nm with saturation magnetization about 18.1 emu/g. The blocking temperature (T(B)) of the nanoparticle assembly is found to be about 150 K as observed from dc and ac magnetization measurements. The frequency dependence of the blocking temperature (T(B)) is found to follow Vogel-Fulcher law. The associated characteristic time tau0 is found to be 10(-5) s. This value is different from that generally found for non-interacting superparamagnetic (SPM) systems (tau0 = 10(-9)-10(-10) s).