Crystallization and Dielectric Properties of BaO-SrO-PbO-TiO2-Nb2O5-SiO2 Glass-Ceramic Composites with La2O3 Addition

Glass-ceramic composite samples with different La2O3 content were prepared via melt-quenching followed by controlled crystallization. X-ray diffraction(XRD) analysis reveals that when the addition amount of La2O3 in the glass sample is less than 1mol%, two phases of perovskite structure and tungsten-bronze structure are formed after annealing at 1000°C for 3h. When the addition amount of La2O3 in the glass sample is increased to 2mol%, a new phase of pyrochlore structure is formed. Moreover, the addition of La2O3 causes the change in the lattice parameters of the glass-ceramic crystal phase. The microstructure observed that the ceramic phase grain size is in the nanometer level. The shape of some grains becomes an elongated structure when the La2O3 content in the sample increases to 2 mol%, and the grain size is increased significantly. The dielectric constant of the BaO-SrO-PbO-TiO2-Nb2O5-SiO2 glass-ceramic system is decreased with the increase of La2O3 addition, and the dielectric loss of the sample is decreased to the range of 0.003-0.008. The electric field stability of the dielectric constant was significantly improved with the addition of La2O3, indicating that adding a certain proportion of La2O3 to the BaO-SrO-PbO-TiO2-Nb2O5-SiO2 glass-ceramic system can effectively improve the dielectric properties, and it has a promising application as a dielectric material.

Microdontia treatment with orthodontics and indirect restoration: clinical case

Objective: This case report aims to present the microdontia treatment of tooth 35 through pre-prosthetic orthodontics, followed by re-anatomization with an indirect restoration. Case report: A 21-year-old female patient presented with microdontia in tooth 35, with a distalized and vestibularized crown. In addition, tooth 34 was gyroverted with mesial diastema. Orthodontic mechanics with segmented arch were used to centralize tooth 35 in the alveolar ridge, close the diastema in the mesial of tooth 34, and correct its gyroversion. For lingualization of tooth 35, a first-order fold (in set) was performed, and for mesialization, an open-coil spring was used between teeth 35 and 36. A closed-coil spring was used to delimit the movement of tooth 35 to mesial. The force applied by the open spring for mesialization of tooth 35 was transmitted to tooth 34, through the closed spring, resulting in its mesialization; this, closed the diastema between teeth 33 and 34 and corrected the gyroversion. Subsequently, the coronary preparation was performed with diamond tips 1014 and 3146, and confection of the temporary crown in acrylic resin. For the ceramic system, IPS™ e.max Press was used. The ceramic crown was luting using the adhesive technique, followed by light curing for 40 seconds on each face of the tooth. Conclusion: It can be concluded that the re-anatomization of a small tooth should be the first treatment option. However, pre-prosthetic orthodontic treatment may be necessary.