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The V bend delivers a force system that is highly dependent on its position [2, 3]. Placed exactly in the middle of the interbracket distance, it will always deliver two equal and opposite couples and no forces. This is independent of whether it is placed as a second‐ or a first‐order bend [1–3]. This situation simulates a Burstone geometry VI. The two teeth will be subject to a pure rotation with neither extrusive nor intrusive forces. It is essential that the wire first be checked outside the mouth for total passivity, before the bend is placed midway between the two bracket units [2].

The force system produced by an alpha/beta spring or by a V bend varies during the tooth movement and is defined as ‘fluctuating’ (Figure 3.10a–c). The configuration changes between Burstone geometry VI and geometry IV, which only delivers an extrusive force to the canine. Friction and the resistance to movement of the reactive unit are factors that may influence the force system and the clinical effects. Thus, uprighting a canine by pure rotation is not easy to achieve unless distally uprighting the molar is needed as the reactive force vector. The uprighting of the canine can therefore be very slow compared to the action of a cantilever [2].

Fig. 3.10 (a–c) Changing the position of the V bend will create totally different force systems. To show the influence of the interbracket position of a V bend, the force systems (forces and moments) generated are indicated by arrows. Note how a displacement can alter the distribution and direction of forces and moments completely.

The activation of a statically indeterminate system includes two angles, with two brackets. The measurement of the angular values in the clinic is difficult to assess, and has little significance. The wire activation with respect to the two brackets, however, is important information and may be assessed by other means [2].

The angular activation corresponds to a linear activation, namely the distance between the wire end and one bracket when the wire has been inserted in the other. This can be measured by means of a caliper [2].