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Previous issue date: 2016-07-28 === The loosening and/or fracture of abutment screws is a common complication in implant-supported restorations. The torque generates a force of compression between the abutment and implant called preload, which increases when the friction between the surfaces decreases. With this objective, coating materials were developed that work as a dry lubricant. The present study compared titanium screws with titanium screws with a DLC (Diamond- Like Carbon) coating by measuring the preload and removal torque when
submitted to mechanical cycling. The correlation between methods was also evaluated. For this study, 32 implants with external hexagon and 16 screws of each material were used. A cell was developed that enabled monitoring the compression between the abutment and implant with strain gauges during the cycling period. With a significance level of 5%, significant differences were observed between the groups, with the highest preload values (336.06?101.54N) being related to the lowest removal torque (24.03?2.51Ncm)
in the titanium with coating group, while the titanium screws had a preload average of 269.98?91.93N and 26.41?2.94Ncm for the removal torque. We did not observe significant differences regarding loss of preload between cycling periods in both groups. DLC coated titanium screws group presented the highest preload (293.74?94.32N; 219.68?85.16N), with significant differences, and removal torque (19.82?3.47Ncm; 17.93?3.59Ncm) values after cycling, although with no significant differences. The correlation between removal torque and preload was weak for both groups, demonstrating that they evaluate different characteristics. === O afrouxamento e/ou fratura de parafusos para fixa??o de pilares constitui uma complica??o frequente nas reabilita??es implanto-suportadas. O torque de apertamento de parafusos gera uma for?a de compress?o entre pilar e implante denominada pr?-carga, que tem seu valor aumentado quando o atrito entre as superf?cies do parafuso e implante diminui. Com este objetivo foram desenvolvidos materiais de recobrimento que funcionam como lubrificantes. Este trabalho comparou parafusos de tit?nio com parafusos de tit?nio com recobrimento de DLC (Diamond-Like Carbon) atrav?s da medida de pr?-carga e torque de remo??o quando submetidos ? ciclagem mec?nica atrav?s de extensometria. Tamb?m foi avaliada a correla??o entre m?todos. Para este estudo foram utilizados 32 implantes com hex?gono externo e 16 parafusos de cada material. Foi desenvolvida uma c?lula de carga que permitiu o monitoramento da compress?o entre pilar e implante por extensometria durante o per?odo de ciclagem. Com um n?vel de signific?ncia de 5% foram observadas diferen?as significativas entre os grupos, sendo que os maiores valores de pr?carga (336,06?101,54N) estavam relacionados aos menores de torque de remo??o (24,03?2,51Ncm) no grupo de tit?nio com recobrimento de DLC, enquanto os parafusos de tit?nio sem recobrimento apresentaram uma m?dia de pr?-carga de 269,98?91,93N e 26,41?2,94Ncm para o torque de remo??o. N?o foram observadas diferen?as significativas na perda de pr?-carga entre per?odos de ciclagem nos dois grupos. Os parafusos recobertos por DLC apresentaram os maiores valores de pr?-carga p?s-ciclagem (293,74?94,32N; 219,68?85,16N), com diferen?as significativas, assim como os maiores de torque de remo??o p?s-ciclagem (19,82?3,47Ncm; 17,93?3,59Ncm), mas sem diferen?as significativas. A correla??o entre torque de remo??o e pr?-carga foi fraca para ambos os grupos, demonstrando que avaliam caracter?sticas diferentes, n?o podendo ser consideradas correspondentes entre si.
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