RESUMEN
PURPOSE: An experimental approach was designed to measure the preload force, the coefficient of friction and the component of the tightening torque that is needed to surmount the thread-friction in an implant-abutment-screw complex that includes a carbon-coated screw. With the determined preload values the coefficient of friction was calculated. METHODS: 25 unused complexes, containing an implant, an abutment and a carbon-coated titanium alloy abutment screw, were tested. A custom load frame with two load cells and associated electronics was used. The threads were not lubricated. All abutment screws were torqued ten times to 25 Ncm. The produced preload values and a force that was proportional to the thread-friction component of the tightening torque were recorded. RESULTS: Mean preload values decreased significantly with the number of repetitions (p < 0.0001) from initially 329.9 N ± 33.3 (range 255.7 to 383.9) to 253.7 N ± 36.8 (range 200.1 to 332.5) for the last tightening procedure. The corresponding change in the calculated coefficient of friction was 0.33 ± 0.04 (range 0.28 to 0.43) to 0.44 ± 0.07 (range 0.32 to 0.56). For the thread-friction no corresponding trend for consecutive tightening repetitions could be noticed. CONCLUSIONS: In the investigated implant-abutment units, repeated use of a coated abutment screw appears to increase the friction of the screw head and thereby decrease the preload. These results indicate that a pre-used coated implant-abutment-screw will fail reaching optimal screw preload.
Asunto(s)
Tornillos Óseos , Carga Inmediata del Implante Dental , Diseño de Implante Dental-Pilar , Fricción , Titanio , Torque , Aleaciones DentalesRESUMEN
BACKGROUND: The working group for aortic surgery and interventional vascular surgery of the German Society for Thoracic and Cardiovascular Surgery (GSTCVS) initiated the web-based German Registry for Acute Aortic Dissection type A (GERAADA). It is the project's aim to collect standardized data from a large pool of patients with acute aortic dissections type A (AADA) to gain a deeper insight and knowledge to improve surgical therapies and perioperative management for these patients in the future. METHODS: In addition to new medical insights, the working group has gained more experience over the last 4 years in how to collect valid and high-quality data. This experience led us to revise the database completely. In this article we describe the new version of GERAADA, providing an overview as well as defining the parameters, and explaining the new features. This overview fulfills a request by the users of GERAADA in the participating centers. RESULTS: Since its inception, 50 cardiac centers in Germany, Austria and Switzerland have provided over 2000 records and the first statistical results have been published. CONCLUSION: GERAADA's new design allows it to stay abreast of changes in medicine and to focus on the essentials necessary for statistically relevant results, while keeping the work load low for the data providers at each cardiac center.