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Table 4 Distribution of the root length reduction during orthodontic treatment of the individual teeth (upper and lower incisors, canines, first molars) (each n = 100, overall n = 1600): post-treatment RCR relative to pre-treatment RCR (rRCR), absolute (n) and relative (%) frequencies

From: Apical root resorption during orthodontic treatment with aligners? A retrospective radiometric study

  Tooth
rRCR 16 13 12 11 21 22 23 26 46 43 42 41 31 32 33 36
rRCR < 80 7 12 6 10 7 2 7 8 1 2 1 10 14 5 6 3
7.0 12.0 6.0 10.0 7.0 2.0 7.0 8.0 1.0 2.0 1.0 10.0 14.0 5.0 6.0 3.0
80 ≤ rRCR < 90 11 11 15 11 12 11 16 8 9 9 18 15 12 11 7 14
11.0 11.0 15.0 11.0 12.0 11.0 16.0 8.0 9.0 9.0 18.0 15.0 12.0 11.0 7.0 14.0
90 ≤ rRCR < 100 22 24 28 22 22 29 27 36 38 31 25 27 25 32 24 33
22.0 24.0 28.0 22.0 22.0 29.0 27.0 36.0 38.0 31.0 25.0 27.0 25.0 32.0 24.0 33.0
rRCR ≥ 100 60 53 51 57 59 58 50 48 52 58 56 48 49 52 63 50
60.0 53.0 51.0 57.0 59.0 58.0 50.0 48.0 52.0 58.0 56.0 48.0 49.0 52.0 63.0 50.0
Total (n) 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100