Effect of insertion angles and reusing procedure on mini-screws??? mechanical properties
Author(s): Valiollah Aarash, Fatemeh Abdollahi, Reza Ghorbanipour, Mohammad Mehdi Naghibi Sistani and Ali bijani
Retrieving mini-screw reduces treatment cost. However, one notable factor in this issue could be insertion angle. This study evaluates influence of insertion angles (50 and 90) and reusing procedure on mechanical properties of mini-screws. In this in-vitro experimental study mini-screws were inserted with 90 and 50 angles in initial and second application. Mechanical properties were measured by Maximum insertion, removal and fracture torque of all test and control groups. Data were analyzed with T test, Paired T- test and ANOVA. In addition surface morphology of mini-screw after initial insertion with 90 and 50 angles and as-received mini-screw were examined under scanning electron microscope (SEM). Mini-screws with 50 degree insertion angle showed higher insertion and removal torque values in initial application than 90 does (p<0.001). These measures were changed insignificantly between initial and second application for samples which were inserted with 90 degree for both application sections. The difference of maximum fracture torque in retrieved and controlled groups was insignificant as well. Scanning electron microscope showed no gross surface changes in retrieved mini-screws, but surface roughness was observed which were highest in samples with 50 degree insertion angles. Reusing mini-screws with 90 degree insertion angle has no adverse effect on their mechanical properties. In addition the reduction of mechanical properties of retrieved miniscrews which were inserted with fifty degree placement angle for both application sections however is acceptable for clinical setting.