European Journal of Molecular & Clinical Medicine

Objective: To measure the maximum force that mini-implants can withstand placed at four different angulations and to check their deflection from the intended path of insertion at the angle with highest pull out strength. Material and Method: The study was done using 60 self-drilling mini-implants of the 1.5mm x 8mm size made from titanium alloy which were divided into four groups of fifteen implants each. The mini implants were inserted into bovine rib segments at angles of 30°, 45°, 60° and 90° at 1kg.cm torque using a long handle driver by a single operator. The insertion angle was measured at the intersection of 2 lines: the longitudinal axis of the mini-implant and another line tangential to the buccal surface. For each test, the maximum force before the failure point was recorded as the primary stability. The implants angulated at the highest pull out strength value were then radiographically assessed to check their angular deflection at the point of insertion. Angular deflection was assessed using a line drawn through long axes of the implant and a true vertical line through the head of implant at point of insertion. Results: Mini-implants loaded along their long axes at 90° showed the greatest stability and resistance to failure. The maximum resistant forces of mini screws are much higher than the forces routinely used for orthodontic purposes. They undergo a mean deflection of 1.8⁰ at the point of entry from the intended angle of insertion. If  the  available  space  between  two  adjacent  roots  is  small,  due  to  this  anatomical limitation a more oblique direction of insertion factoring the additional deflection should be considered to minimize the risk of root contact. Conclusion: Mini-implants placed at 90° resist better force than other 3 angles which were 60°,45°, and 30° and exhibits highest resistance to traction forces before being removed from bone which increases success rate of the mini screws by giving better primary stability. They get deflected from the intended angulation due to the resistance offered by the cortical bone