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MM 34"

MM 34"

Fig. 8.12 This shows the force vectors involved in the use of Class II elastics. In low angle Class II cases all four vectors are helpful. (The vertical component in the upper incisor region is balanced by curve of Spee in the upper archwire, and hence does not contribute to unwanted bite deepening). In high angle Class II cases upper molar extrusion should be avoided. In such cases short Class II elastics can be considered.

Fig. 8.11 This shows the force vectors involved in the use of Class III elastics. In low angle deep bite cases all four vectors are helpful. However, in high angle Class III cases with an open bite tendency, upper molar extrusion is contra-indicated. This can be counteracted with a palatal bar (Fig. 5.29, p. 107).

Fig. 8.12 This shows the force vectors involved in the use of Class II elastics. In low angle Class II cases all four vectors are helpful. (The vertical component in the upper incisor region is balanced by curve of Spee in the upper archwire, and hence does not contribute to unwanted bite deepening). In high angle Class II cases upper molar extrusion should be avoided. In such cases short Class II elastics can be considered.

H 33

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