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Fig. 6 | Progress in Orthodontics

Fig. 6

From: The inflection point: a torque reference for lingual bracket positioning on the palatal surface curvature of the maxillary central incisor

Fig. 6

a Increments [P1 + 3] and [P1 + 3.5] has a \( {Torque}_{Value}^{Angle} \) equal to − 60° and − 45°, respectively. The incremental subtraction value between [P1 + 3.5] and [P1 + 3] is + 15°. b, c When a bracket with a 0° third order prescription is placed at [P1 + 3] or [P1 + 3.5], the slot inclination of the bracket will be perpendicular to the tangent at [P1 + 3] or [P1 + 3.5], respectively. The + 15° difference in incremental subtraction value between [P1 + 3.5] and [P1 + 3] is reflected as a 15° difference in the slot inclination. d, e Placement of a full-sized rectangular wire with minimal play in the slot of the bracket in b or in c, will change the initial slot inclination (ISI) to a final slot inclination (FSI) parallel to the archwire plane. The horizontally positioned incisor in d, e is the initial position of the incisor before rectangular wire placement, while the incisor superimposed on it represents its new position after the rectangular wire placement. Cervically shifting the vertical bracket position from [P1 + 3.0] as in b and d to [P1 + 3.5] as in c and e, results in a 15° of decreased crown palatal/root labial incisor movement in e compared to d. The positive incremental subtraction value between [P1 + 3.5] and [P1 + 3] resulted in an extra + 15° of crown labial/root palatal incisor movement in e compared to d

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