Читать книгу Orthodontic Treatment of Impacted Teeth - Adrian Becker - Страница 49

The force system is acting on the canine and first molar (see Figure 3.1a–d). The cantilever will produce forces and moments in different planes of space. In the sagittal plane (Figure 3.1c), note the stepped bypass created in the otherwise continuous archwire. The vertical plane is shown in Figure 3.1d. Forces and moments are shown 2 dimensional for simplicity’s sake. The plane of space they are acting in is indicated by their colour. A colour code convention table (Table 3.1) is annexed.

Fig. 3.1 (a) Buccal cantilever for extruding a canine. In practice, an eyelet is often to be preferred in the early stages of the canine eruption. (b) The whole arch comprising rectangular wire is used as an anchorage unit. Cantilevers are inserted in the utility tube and tied with a one‐point contact to the displaced tooth. (c) Activation of the spring by tying it to the impacted canine creates an extrusive force on the canine, an intrusive force and a tipping moment on the molar in a crown mesial root distal direction (sagittal plane). The moment in the auxiliary tube is equal to the product of the applied force and the distance between the centre of resistance (CR) of the molar and the point of force application on the canine. If the extrusive force does not pass through the CR of the canine, an additional but small moment will be generated on the canine in the sagittal plane. (d) Activation of the spring by tying it to the impacted canine creates a third‐order couple at the molar, an intrusive force at the molar and an extrusive force at the canine. If the point of force application at the canine is lingual to the CR of the molar, buccal root torque will be generated at the molar tube instead of lingual root torque.