Influence of straight versus angulated screw channel titanium bases on failure loads of two-piece ceramic and titanium implants restored with screw-retained monolithic crowns: An in-vitro study.

OBJECTIVE: To analyze the influence of titanium-base (straight [SSC]/angulated-screw-channel [ASC]) on failure-loads and bending-moments of two-piece ceramic and titanium-zirconium implants restored with monolithic-zirconia crowns after fatigue. MATERIALS AND METHODS: Thirty-two anterior monolithic-screw-retained zirconia crowns were divided into four groups (n = 8/group) according to the factors: (1) type of implant material: two-piece titanium-zirconium implant (Ti-Zr; control-group) versus two-piece ceramic implant (CI; test-group) and (2) type of titanium-base: SSC (0° angle) versus ASC (25°). An intact implant was used for field emission gun-scanning electronic microscopy (FEG-SEM) characterization and Raman spectroscopy for phase analyses and residual stress quantification. All samples were exposed to fatigue with thermodynamic loading (1.2-million-cycles, 49 N, 1.6 Hz, 5-55°C) at a 30° angle. Surviving specimens were loaded until failure (SLF) and bending moments were recorded. Failed samples were examined using light microscope and SEM. Statistical analyses included ANOVA and Mann-Whitney U-test. RESULTS: Raman-spectroscopy revealed the presence of residual compressive stresses. FEG-SEM revealed a roughened surface between threads and polished surface at the cervical-collar of the ceramic implant. All samples survived fatigue and were free of complications. Mean bending-moments (±SD) were: Ti-Zr-0: 241 ± 45 N cm, Ti-Zr-25: 303 ± 86 N cm, CI-0: 326 ± 58 N cm, CI-25: 434 ± 71 N cm. Titanium-base and implant-material had significant effects in favor of ASC titanium bases (p = .001) and ceramic-implants (p < .001). Failure analysis after SLF revealed severe fractures in ceramic implants, whereas titanium implants were restricted to plastic deformation. CONCLUSIONS: Ceramic and titanium implants exhibited high reliability after fatigue, with no failures. From a mechanical perspective, titanium bases with ASC can be recommended for both ceramic and titanium implants and are safe for clinical application.

Ultrastructural features of vocal fold nodules and polyps.

Earlier investigation did not show any clear distinctive pathological features that differentiate vocal polyps from vocal nodules. The light microscopic distinctive features between the two lesions point in the direction of a more pronounced epithelial reaction and a more fibrous stromal change in vocal nodules. In the present study, 19 vocal polyps and 11 vocal nodules were subjected to ultrastructural examination aiming at finding distinctive features that may be pathognomic for each of these clinically distinct entities. The study was carried out by EM Philips 400 T. The results demonstrate that nodules showed epithelial changes in the form of gaping of the intercellular junctions and absence of the basal lamina in parts. These changes are less apparent in polyps, whereas the stromal changes are more pronounced and varied. The significance of these results and their interpretation are discussed.