Table 1 Summary of the data from included studies
Author, year. Study design Country | n (M/F) Mean age (SD) follow-up | Mandibular incisor crowding diagnosis Secondary evaluations Statistical analysis | Results | Conclusions | |||||
|---|---|---|---|---|---|---|---|---|---|
Mandibular incisor crowding in the mixed dentition (M/SD) | Mandibular incisor crowding in the permanent dentition (M/SD) | Mandibular incisor crowding change in the transition of dentition (M/SD) | |||||||
Sinclair and Little [19] Retrospective cohort study USA | 65 (33/32) 9.06 years 4 years | Little index Intra- and inter-arch measurements Pearson's correlation and t-test | 2.22 (1.23) mm | 2.00 (1.17) mm | -0.17 (1.75) mm | Although the average amount of mandibular incisor crowding reduction is only 0.17 mm, the data variability is large | |||
Sampson and Richards [18] Prospective cohort study Australia | 47 (26/21) 8.91 (1.05) years 4 years | Leighton's method PM/M position t test, Pearson's correlation and multiple regression | G1 | G2 | G1 | G2 | G1 | G2 | Children with lower initial crowding (0.4 mm) may present a worsening of 0.6 mm ± 0.2 mm |
0.4 ± 0.4 mm | 1 ± 0.45 mm | 1 ± 0.45 mm | 0.7 ± 0.35 mm | 0.6 ± 0.2 mm | -0.3 ± 0.2 mm | ||||
Hagberg [15] Prospective cohort study Sweden | 24(14/10) 7 years (N.R) 6 years | Difference between incisor width and available space between deciduous canines Canine eruption Wilcoxon, Pearson and Spearman correlations | Male | Female | Male | Female | Male | Female | Mandibular incisor crowding tends to decrease in both sexes in the transition from mixed to permanent dentition after the eruption of permanent canines |
1.49 mm (N.R) | 1.49 mm (N.R) | 0.40 mm (N.R) | 0.65 mm (N.R) | − 1.09 mm (N.R) | − 0.84 mm (N.R) | ||||
Arslan et al. [17] Retrospective cohort study Turkey | 65 (29/36) 9.54 (1.42) 5 years | Little index Intra/inter arch mx and md t test | 1.31 (0.78) | 1.11 (0.86) | − 0.19 (0.69) | Mandibular incisor crowding shows little self-correction in the dentition transition, related to leeway space and facial growth | |||
Barros, et al. [16] Retrospective cohort study Brazil | 42 (22/20) 8.66 (0.83) 4.58 (1.10) Years | Difference between incisor width and space between deciduous canines Cephalometric and intra-arch md measurements Wilcoxon, t test and multiple regression | G1 (≤ 2 mm) 0.73 (0.58) | G2 (≥ 2 mm) 3.96 (1.86) | G1 (≤ 2 mm) 0.61 (1.94) | G2 (≥ 2 mm) 1.46 (2.28) | G1 (≤ 2 mm) − 0.12 (1.89) | G2 (≥ 2 mm) − 2.50 (2.12) | The reduction in mandibular incisor crowding is related to the amount of initial crowding, leeway space, incisor protrusion, and increased maxillary arch width |