Superconducting gap structure and pinning in disordered MgB2 films

We have performed a comparative study of two thin films of magnesium diboride (MgB2) grown by different techniques. The critical current density at different temperatures and magnetic fields was evaluated from magnetisation curves, the structure of superconducting order parameter was obtained from point-contact spectroscopy, and the scattering rates were evaluated by fitting the temperature dependent normal-state resistivity to the two-band model. The films have similar critical temperatures close to 39 K, but the upper critical fields were different by a factor of 2 (5.2T and 2.5 T at 20 K). We have found that the film with higher Hc2 also had stronger scattering in the sigma band and smaller value of the superconducting gap in this band. As the scattering in sigma band is primarily due to the defects in boron plane, our results are consistent with the assumption that disordering the boron planes leads to enhanced Hc2 and better pinning properties in magnetic field.Comment: Paper presented at EUCAS'0

Surgical crown lengthening: a 12-month study - radiographic results

OBJECTIVE: The purpose of this study was to perform a radiographic follow-up evaluation after a 12-month healing period, following crown lengthening surgery. MATERIAL AND METHODS: Twenty-three periodontally healthy subjects (mean age 32.5 years) that required crown lengthening surgery in premolars were recruited. In a total of 30 premolars, full thickness flaps, osseous resection, and flap suturing were performed. The restorative margin was defined in the pre-surgical phase and maintained unaltered during the healing period, serving as a reference point. Standardized bitewing radiographs were taken before and after osseous reduction, and at 2, 3, 6, and 12-month healing periods. RESULTS: Intact lamina dura was observed at both mesial and distal alveolar crests only from the 3rd month. At 12-months, all alveolar crests presented lamina dura. The overall mean distance from the restorative margin to the alveolar crest achieved after osseous resection was 3.28±0.87 mm at mesial and 2.81±0.51 mm at distal sites. No significant radiographic changes in the bone crest were observed during a 12-month healing period. CONCLUSION: The findings of this study suggest that the radiographic proximal bone level observed on bitewing radiographs following crown lengthening surgery can be used as a reference to predict the future level of the healed alveolar crest