Archwire seating forces produced by different ligation methods and their effect on frictional resistance

The aims of this study were to determine the mean tensile force of four different elastomeric modules, the archwire seating force of different ligation methods, and its effect on frictional resistance. To determine the mean tensile force, each elastomeric module (purple, grey, Alastik, and SuperSlick) was extended by 5 mm using two hooks attached to a load cell using a Nene M3000 testing machine. To assess the median archwire seating force, a maxillary premolar bracket (3M Unitek) was welded to a sheet of stainless steel (SS) and glued to a Perspex block. The bracket base was removed and the cut continued into the Perspex below. A length of test wire was taken and bent to form a "U" shape, with the middle portion 20 mm in length. The free ends of the wire were secured to the load cell of the Nene testing machine. Two wire sizes were tested, 0.017 x 0.025 and 0.019 x 0.025 inch SS. The load cell was activated and the force with which the wire was displaced into the slot by the ligation method was measured. Four types of elastomeric module were tested together with a pre-formed 0.09 inch SS ligature. The experimental method used to determine the mean frictional force of each module and wire size was carried out using a method described previously. Statistically significant differences existed in the mean tensile forces and median archwire seating forces between the elastomeric modules. Grey modules with either size wire produced the lowest median archwire seating force, whereas SS ligatures produced the highest forces. SS ligatures with either wire produced the lowest mean frictional forces, whereas grey modules produced significantly higher mean frictional force (P < 0.01). The force with which the wire was seated into the bracket did not seem to be related to the subsequent amount of mean frictional force produced.