PMC5446872_01
Patient with crossbite of upper left first permanent molar.
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fig1
Clinical and cephalometric evaluations, in compliance with radiation protection criteria especially for growing individuals, showed no orthodontic or skeletal problems, except for crossbite of first permanent molar on the left side (Figure 1).
A single force applied to the bracket (not through the center of resistance) will cause rotation of the tooth.
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fig2
When a force does not act through Cres of a tooth, the tooth rotates (Figure 2).
Moment (M) produced by a force not acting through Cres.
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fig3
The magnitude of M (Figure 3) is measured as the magnitude of the force (F) multiplied by the perpendicular distance (d) between the line of the force and Cres (M = F*d).
Asymmetric Quad Helix (left) and traditional Quad Helix (right).
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fig4
Details of the single terminal (a) and the terminal introduced together with the wire segment of the same diameter into the Goshgarian tube and welded to the band (b).
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fig5
Moreover, it is necessary to place in the palatal attachment that is welded to the band, together with the insert, a segment of wire of the same diameter of the Quad Helix (0.9 mm), the ends of which protrude outwards from the attachment itself and must be appropriately bent in order to avoid disconnection; this avoids the insert from placing itself obliquely which would reduce control of the direction of the applied force (Figure 5).
Asymmetric Quad Helix: extraoral (a) and intraoral (b) views. When the auxiliary wire segment is applied into the mouth, it must not interfere either with the mucosa or with the band in order to not give rise to undesired positions or stress.
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fig6
A further fundamental precaution consists in bending the terminal part of the insert so that it is sufficiently separated from the crown of the banded tooth, so that with the expression of the expansive action it does not contact with the crown (Figure 6).
Application and activation system of the asymmetric Quad Helix; it can be seen that there is the absence of a torque control allowing the expression of a single force on tooth 2.6.
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fig7
Rapid resolution of crossbite of tooth 2.6.
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fig8