A new elastic slot system and V-wire mechanics

Abstract

Objective: To biomechanically test a new elastic slot system and V-wire mechanics.

Materials and methods: Conventional twin and self-ligating brackets and the new elastodynamic bracket were biomechanically tested. The conventional brackets had a rectangular 0.022'' slot and the new elastodynamic bracket had a V-slot, a new slot geometry. Torque measurements were performed with 0.018'' × 0.025'' and 0.019'' × 0.025'' stainless steel (ss) archwires. A nickel-titanium V wire was used for the biomechanical measurements on the elastodynamic bracket. The measurements were done with the aid of a six-component measuring sensor.

Results: The results of the biomechanical testing revealed play in the brackets with rectangular slot geometry. The V slot in the elastodynamic bracket assured that the wire fit perfectly in the slot. Dynamic moments of 5 to 10 Nmm were transmitted without any play. No permanent deformation of the slot occurred in the new elastodynamic bracket because of the elastic slot.

Conclusion: Control of torque for three-dimensional positioning of the teeth in the dental arch with rectangular slot geometry as used in straight-wire therapy is difficult. If torque is bent into the wire, because of the play there is a high risk that either too much, too little, or no moment is transmitted to the teeth. The V-slot archwire/bracket geometry in conjunction with nickel titanium composition has no play and allows a reduction of forces and moments with direct and continuous transmission of torque in the bracket. Because of the elasticity of the bracket, there is an upper limit to the moment possible.

Keywords: Biomechanics; Elastic slot system; Forces; Moments; V-wire mechanics.

Figure 1.

Elastodynamic bracket design. Design of the bracket differs from conventional brackets in its slot geometry of a V slot and V wire. This achieves an accurate fit of the wire in the slot. As a result of the V slot, slot-filling archwires can be used for the first time. The monolithic design of the nickel titanium (NiTi) bracket allows for flexible bracket structures and the transmission of small, well-defined moments.

Figure 2.

Measuring device and coordinate system. The measured data are recorded via the six-axis sensor in all spatial directions and plotted.

Figure 3.

Typical graphs of the torque measurements with 0.018′′ × 0.025′′ ss and conventional twin bracket, passive and active SL bracket in comparison with the elastodynamic bracket with V slot and V wire.

Figure 4.

Typical graphs of the torque measurements with 0.019′′ × 0.025′′ ss, conventional twin bracket (Mini Sprint, Forestadent, Pforzheim, Germany), and passive (BioQuick, Forestadent, Pforzheim, Germany) and active self-ligating brackets (In-Ovation C, DENTSPLY Int., York, Pa) in comparison with the elastodynamic bracket with V slot and V wire.

Figure 5.

Comparison of the moments for palatal and buccal root torque in a conventional twin bracket, passive and active self-ligating (SL) brackets, and 0.018′′ × 0.025′′ and 0.019′′ × 0.025′′ ss archwires vs the elastodynamic bracket with V slot and V wire.

Figure 6.

Slot deformation after application of torque. There are changes to the slot in the conventional twin brackets and SL brackets, particularly after using the 0.019′′ × 0.025′′ ss archwire. In contrast, the elastodynamic bracket does not alter its slot shape.