Avaliação mecânica da estabilidade de pilares cone Morse com diferentes características de fabricação: estudo in vitro

Abstract

The aim of this study was to compare quantitatively and qualitatively the retention and adaptation of four types of commercially available implantabutment connections and their different characteristics. A total of 40 Morse taper implants (CM) were used (20 Titamax CM EX 4.0 mm x 11 mm Neodent and 20 Strong SW Morse 4.5 x 10 mm SIN), with 40 abutments installed on the implants, with 10 abutments Neodent solid (NS), 10 SIN (SS) solid abutments, 10 neodent bolt (NP) abutments and 10 SIN screw bolts (SP). The implants were embedded in polystyrene resin (Aerojet) using a standardized device and the prosthetic abutments were installed with manufacturer recommended torques. The tightening and loosening torques of each abutment were evaluated in two moments: Initial moment (I): the torque was applied and after 3 minutes the release was performed; Final torque (F): Tightening and loosening torque after mechanical cycling. Four groups (n = 10) were formed: NSI (Neodent initial solid) and NSF (Neodent final solid) - (32 Ncm of tightening torque at both moments), NPI (Neodent initial passer) and NPF (Neodent final passer) - (tightening torque of 15 Ncm at both times), SSI (SIN initial solid) and SSF (final solid SIN); SPI (SIN initial through) and SPF (SIN final through) - (20 Ncm of tightening torque at both times). Tightening and loosening torques were performed using the MK Control torque wrench coupled to the Lynx acquisition system. Prior to the mechanical cycling, 40 nickel-chromium crowns were made, which were cemented to the corresponding columns using provisional cement based on calcium hydroxide composition. Then the samples were submitted to a mechanical cycling test, with a dynamic load of 50 N, frequency of 2 Hz and 37°C, totaling 1,200,000 masticatory cycles (5 years of mastication). The samples were positioned in a 30º angle on the cycling machine platform, as recommended by standard ISO 14801. After the mechanical cycling, the screws were loosened. Before and after the mechanical cycling test, precision micro-computed tomography (micro-CT) of the abutments were performed at 3 different points of the implant-abutment interface (n=3). Scanning electron microscopy (SEM) images of the abutment screws (n=4) of the 4 groups were performed, before the initial tightening torque and after final loosening, to evaluate the morphology of the threads. Statistical analysis was performed for the evaluation of tightening and loosening in the two moments using the paired T test within each group. For the linear measurements of the three areas selected in the micro-ct images, statistical analysis was performed by the paired T-test within each group, comparing the measurements of each region before and after cycling. A significance level of α = 0.05 was used. SEM images were analyzed qualitatively. After mechanical cycling, there were statistically significant differences for all groups for all methods evaluated. It was concluded that all implant-pillar joints, after mechanical cycling, presented significant percentages of loosening.