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Table 1 Frequency of 10 treatment protocols in all evaluated intervals (proportion test)

From: Frequency evaluation of different extraction protocols in orthodontic treatment during 35 years

Interval Protocol Total
0 1 2 3 4 5 6 7 8 9 N %
Non-extraction Four first premolar extractions Two maxillary first and two mandibular second premolar extractions Two maxillary premolar extractions Four second premolar extractions Asymmetric extractions - three premolars or only one premolar Incisor or canine extractions First or second molar extractions Atypical extractions Agenesis or previously missing permanent teeth
N % N % N % N % N % N % N % N % N % N %
1 15 A 57 A 11 ABC 6 BC 1 BC 1 ABC 0 0 0 0 2 1.90 12 11.43 105 3.08
(1973 to 1977) 14.29 54.29 10.48 5.71 0.95 0.95
2 28 AB 84 A 5 CD 5 AB 2 BC 1 AB 0 0 0 0 2 1.37 19 13.01 146 4.28
(1978 to 1982) 19.18 57.53 3.42 3.42 1.37 0.68
3 91 B 90 B 40 A 34 BC 11 CD 4 A 1 0.32 3 0.96 14 4.46 26 8.28 314 9.20
(1983 to 1987) 28.98 28.66 12.74 10.83 3.50 1.27
4 273 CD 170 B 34 BC 62 BC 7 BC 13 A 2 0.30 7 1.05 23 3.45 75 11.26 666 19.51
(1988 to 1992) 40.99 25.53 5.11 9.31 1.05 1.95
5 491 C 281 B 63 BC 137 CD 13 BC 61 BC 6 0.48 10 0.79 61 4.83 139 11.01 1262 36.98
(1993 to 1997) 38.91 22.27 4.99 10.8 1.03 4.83
6 290 DE 95 C 25 BCD 67 CD 2 AB 44 C 1 0.16 6 0.98 19 3.10 63 10.29 612 17.93
(1998 to 2002) 47.39 15.52 4.08 10.95 0.33 7.19
7 168 E 23 D 4 D 23 BC 6 BC 21 C 0 0 2 0.65 10 3.25 51 16.56 308 9.02
(2003 to 2007) 54.55 7.47 1.30 7.47 1.95 6.82
Total 1,356 39.73 800 23.43 182 5.3 334 9.78 42 1.23 145 4.24 10 0.29 28 0.82 131 3.83 385 11.28 3,413 100
χ 113.305 222.758 52.847 13.668 19.443 41.901 3.440 2.897 8.640 12.522  
P 0.0000* 0.0000* 0.0000* 0.0335* 0.0034* 0.0000* 0.7518 0.8215 0.1948 0.0512  
  1. Different letters represent statistically significant differences in same protocol. *Statistically significant at P < 0.05.