Effect of root canal preparation, type of endodontic post and mechanical cycling on root fracture strength

Objective: To evaluate the impact of the type of root canal preparation, intraradicular post and mechanical cycling on the fracture strength of roots. Material and Methods: Eighty human single rooted teeth were divided into 8 groups according to the instruments used for root canal preparation (manual or rotary instruments), the type of intraradicular post (fiber posts-FRC and cast post and core-CPC) and the use of mechanical cycling (MC) as follows: Manual and FRC; Manual, FRC and MC; Manual and CPC; Manual, CPC and MC; Rotary and FRC; Rotary, FRC and MC; Rotary and CPC; Rotary, CPC and MC. The filling was performed by lateral compactation. All root canals were prepared for a post with a 10 mm length, using the custom # 2 bur of the glass fiber post system. For mechanical cycling, the protocol was applied as follows: an angle of incidence of 45 degrees, 37 degrees C, 88 N, 4 Hz, 2 million pulses. All groups were submitted to fracture strength test in a 45 degrees device with 1 mm/min cross-head speed until failure occurred. Results: The 3-way ANOVA showed that the root canal preparation strategy (p<0.03) and post type (p<0.0001) affected the fracture strength results, while mechanical cycling (p=0.29) did not. Conclusion: The root canal preparation strategy only influenced the root fracture strength when restoring with a fiber post and mechanical cycling, so it does not seem to be an important factor in this scenario

PROPRIETES OPTIQUES DES NITRURES ET CARBONITRURES DE TITANE - SELECTIVITE SPECTRALE

On présente des résultats préliminaires sur l'évolution des propriétés optiques des nitrures et des carbonitrures de titane avec leur composition. On montre que les résultats obtenus sont conformes à un modèle de leur structure électronique qui permet d'orienter les recherches vers la synthèse de matériaux plus sélectifs.We present preliminary results on the optical properties of nitrides and carbonitrides of various compositions. The data is analysed in terms of a model of their electronic structure, which permits the definition of more selective materials

Use of fish otoliths as a temporal biomarker of field uranium exposure

This study aimed to determine uranium (U) pollution over time using otoliths as a marker of fish U contamination. Experiments were performed in field contamination (~20 μg L−1: encaged fish: 15d, 50d and collected wild fish) and in laboratory exposure conditions (20 and 250 μg L−1, 20d). We reported the U seasonal concentrations in field waterborne exposed roach fish (Rutilus rutilus), in organs and otoliths. Otoliths were analyzed by ICPMS and LA-ICP SF MS of the entire growth zone. Concentrations were measured on transects from nucleus to the edge of otoliths to characterize environmental variations of metal accumulation. Results showed a spatial and temporal variation of U contamination in water (from 51 to 9.4 μg L−1 at the surface of the water column), a high and seasonal accumulation in fish organs, mainly the digestive tract (from 1000 to 30,000 ng g−1, fw), the gills (from 1600 to 3200 ng g−1, fw) and the muscle (from 144 to 1054 ng g−1, fw). U was detected throughout the otolith and accumulation varied over the season from 70 to 350 ng g−1, close to the values measured (310 ng g−1) after high exposure levels in laboratory conditions. U in otoliths of encaged fish showed rapid and high U accumulation from 20 to 150 ng g−1. The U accumulation signal was mainly detected on the edge of the otolith, showing two U accumulation peaks, probably correlated to fish age, i.e. 2 years old. Surprisingly, elemental U and Zn signatures followed the same pattern therefore using the same uptake pathways. Laboratory, caging and field experiments indicated that otoliths were able to quickly accumulate U on the surface even for low levels and to store high levels of U. This study is an encouraging first step in using otoliths as a marker of U exposure