Evaluation of insertion torque of different orthodontic miniscrews: An in vitro study

*Department of P.O.P, college of dentistry, university of Mosul, Mosul, Iraq. Introduction Conservation of anchorage in totality has been a perennial problem to the traditional orthodontist. Conventional means of supporting anchorage have been used by either intra oral sites or relying on extra oral means. Both of these have their limitations. The extra oral forces very difficult device and some time the patient is not able to wear it. On the other hand, strict reliance on intra oral areas. Among the anchorage devices, micro screw implants have increasingly being used for orthodontic anchorage because of their absolute anchorage, easy placement and removal, and low cost. The small size of the miniscrew implants allows them to be placed into bone between the teeth, insertion is a less traumatic procedure, and they can be loaded soon after placement as there is no osseointegration around the screws but only fibrous integration. However, a notable complication is loosening of the screws even though they consist of a biocompatible titanium alloy. Drill screws are most commonly used for this purpose. A prerequisite for the insertion of screws is the preparation of a pilot hole with a minimum diameter equal to the screws core. Thermal necrosis of bone has also been observed. Another problem frequently encounters during the insertion of a screw after drilling is stripping of the bone threads when working in thin cortical bone. Drill-free screws or self-drilling screws are a recent development. They have a tip like a cork screw and specially formed cutting flute that enables them to be inserted without drilling. This results in less insertion time and more patient compliance. Drill-free screws can provide intensive screw bone contact and inserting them produces little bone debris and less thermal damage. Background and objective: The purpose of this study was to evaluate the torque insertion for drill and non drill techniques of two commercially available miniscrews. Methods: Eighty mini screws (forty Dentos miniscrews/Korea and forty 3M miniscrews/ USA), having the same length and diameter, were divided into two groups for each type. Two techniques, non-drill and drill, were used. In drill techniques, manufacturer recommended drill was used. Two bovine tibias were obtained. The first technique used pre drill hole, which was made in the bone using the recommended bur (1.0 diameter). The mini-screw was placed at 9 mm manually, then the remaining 1 mm was inserted through digital torque meter. The same procedure was repeated but without a pilot hole. Results: 3M miniscerws gave high torque insertion in two techniques. Conclusion: The shape, thread design and tip geometry of miniscerw play an important role in the torque insertion.