Effect of ultrasonic vibration on the removal of posts cast in different metal alloys

The aim of this experiment was to evaluate the relative efficacy of ultrasonic instruments on the removal of posts cast in alloys with different stiffness (nickel-chromium and silver-tin alloys). Sixty roots of extracted bovine incisor teeth were sectioned, prepared and randomly divided into 4 groups (n=15): groups 1 and 2 received posts cast in Ni-Cr and groups 3 and 4 received posts cast in Ag-Sn. All posts were cemented with zinc phosphate cement. Groups 2 and 4 received ultrasonic vibration for 12 minutes. The force necessary for post removal was measured by an Instron universal testing machine. Data were statistically analyzed with ANOVA and when significant differences were found, means were compared using Tukey's intervals with a confidence level of 95%. The mean force (kgf) to remove posts of group 1 (67.84± 15.31) was statistically greater than groups 2 (46.95± 10.85), 3 (48.53± 8.49) and 4 (41.25± 11.40). There was no statistically significant difference among groups 2, 3 and 4. The ultrasonic vibration was effective in reducing the force required to remove posts cast in Ni-Cr (about 31% of reduction), but had little effect on posts cast in Ag-Sn (about 15% of reduction). Posts cast in Ni-Cr were also more retentive then posts cast in Ag-Sn when they were not submitted to ultrasonic vibration.

Influence of the finishing technique on surface roughness of dental porcelains with different microstructures.

UNLABELLED: This study compared the surface roughness of 4 dental porcelains with different microstructures (d.Sign-D, Finesse-F, Noritake-N and Symbio-S) using varied surface treatments. The porcelain surfaces were submitted to the following surface treatments: 1) g (glazing only); 2) rg (polishing with a rubber wheel before glazing); 3) 2g (reglazing); 4) r (rubber wheels); 5) rp (rubber wheels + diamond paste); 6) d (sandpaper discs) and 7) dp (sandpaper discs + diamond paste). Treatments 3 through 7 were performed after breaking the glaze layer with a diamond bur. Surface roughness (Ra, in m) was determined using a profilometer (n=10). Visual inspection was made using the scanning electron microscope. Microstructural characterization was also performed (hardness, leucite content and particle size). Reglazed specimens presented significantly rougher surfaces compared to glazed specimens. The use of a polishing paste after the sandpaper discs or after the rubber wheel resulted in a reduction of the Ra value for all materials (except for the dp group of porcelain S). Rubber or discs followed by diamond paste were the best surface treatments for porcelains D (D-rp: 0.21 +/- 0.06 microm and D-dp: 0.22 +/- 0.05 microm) and F (F-rp and F-dp: 0.17 +/- 0.03 microm). For porcelains N and S, both reglazing (2g) and the use of rubber or sandpa- per discs followed by diamond paste (groups rp and dp) resulted in similar roughness (N-2g: 0.22 +/- 0.03 microm; N-rp: 0.22 +/- 0.04 microm; N-dp: 0.20 +/- 0.04 microm, S-2g: 0.22 +/- 0.04 microm; S-rp: 0.19 +/- 0.04 microm; S-dp: 0.23 +/- 0.04 microm). CONCLUSION: The best choice of surface treatment for leucite-based porcelains depended on the material considered. Porcelains with lower leucite content (F and S) tended to present lower roughness compared to those with higher leucite content after being polished with rubbers or discs followed by diamond pastes.

Otimização de sobredentaduras implantossuportadas: relato de caso clínico / Optimization of implant-retained overdentures: case report

A utilização de implantes para suportar sobredentaduras está comprovada por vários autores na literatura. Inúmeros sistemas de abutments estão disponíveis no mercado; a escolha depende de fatores que variam de acordo com o quadro clínico presente. A retenção e a estabilidade são requisitos fundamentais a qualquer sistema. Em alguns casos, a facilidade de inserção da prótese em posição pelo paciente pode-se tornar um fator determinante nesta escolha. A descrição e a utilização de um novo abutment, o sistema Locator, são relatadas neste trabalho.