Owais et al. (2010) [16] | Randomized clinical trial | N = 67 | Group 1: 20 Subjects (12 males and 8 females, average age: 10.76 ± 0.75). Group 2: 24 subjects (12 males and 12 females, average age: 10.58 ± 0.54). Control group: 23 subjects (15 males and 8 females), average age: 10.63 ± 0.66). No. of dropouts: 9 | Mild lower anterior crowding (less than 2 mm). | Lower lingual holding arch with 0.9 mm stainless steel wire for group 1 and 1.25 mm stainless steel wire for group 2. | Arch length measured using Boley caliper to the nearest 0.5 mm. | Not reported | Group 1: arch length increased by 0.53 ± 0.73. Group 2: arch length decreased by 0.98 ± 0.28. Control group: arch length increased by 0.16 ± 0.33. |
Fichera et al. (2011) [18] | Case-control study | N = 60 | Cases group: 48 patients, average age: 9 ± 0.8 years. Control group: 18 patients (8 males and 10 females), average age: 9.2 ± 0.6 years. No. of dropouts: 0 | Not reported | Lingual arch with 0.9 mm stainless steel rounded wire. | Arch length measured using brass wire and then calculated by digital calipers and recorded to the nearest 0.02 mm | Not reported | Cases Group: arch length increased by 0.04 mm Control group: arch length decreased by 1.8 mm |
Ciftci et al. (2018) [17] | Controlled clinical trial | N = 34 | Group 1 (unilateral tooth loss): 8 males and 8 females, average age: 8.8 ± 0.9 years. Group 2 (bilateral tooth loss): 10 males and 8 females, average age: 8 ± 0.7 years. No. of dropouts: 0 | Not reported | Lingual arch with 0.9 mm stainless steel wire. | Arch length measured on study casts | Not reported | Group 1: total arch length decreased by 0.4 mm. Group 2: arch length increased by 0.9 mm. |
Nevant et al. (1991) [23] | Retrospective cohort study | N = 40 | Group 1: 20 patients, average age 11 years. No. of dropouts: 8 Group 2: 20 patients, average age 12.1 years. No. of dropouts: 10 | Moderate crowding (4–8 mm) | Lip bumpers with 1.14 mm stainless steel round wire covered with a layer of plastic shrink tubing for group 1, and prefabricated lip bumpers that had a relatively thick shield of acrylic from canine to canine for group2. | Arch length measured on dental casts with electronic dial calipers to the nearest 0.01 mm. | Group 1: 1.4 years. Group 2: 1 year. | Group 1: total arch length increased by 2.7 mm/ year. Group 2: total arch length increased by 7.45 mm/ year. |
Rebellato et al. (1997) [19] | Case-control study | N = 30 | Cases group: 14 patients, average age: 11.5 years). Control group: 16 patients, average age: 11.3 years). No. of dropouts: 0 | Crowding of ≥ 3 mm | Lingual arch with 0.81 mm stainless steel wire, which contacted the cingulae of the lower incisors. | Arch length measured to the nearest 0.02 mm. | Cases group: 10.5 months. Control group: 12.5 months. | Cases group: arch length increased by 0.07 mm. Control group: arch length decreased by 2.54 mm. |
Raucci et al. (2015) [20] | Case-control study | N = 56 | Cases group: 14 males and 22 females, age was ≤ 9 years. Control group: 10 males and 10 females, age was ≤ 9 years. No. of dropouts: 0 | Mild to moderate maxillary crowding | A prefabricated transpalatal arch with 0.9 mm stainless steel wire with a mesially directed loop in the middle | Arch length measured using digital calipers Crowding was measured as tooth-size/total-arch discrepancy | 3 years after the end of treatment with roughly 2 years of passive retention using Hawley retainers in the maxillary arch. | Arch length changes were not significant in both cases and control groups. Cases group: crowding decreased by 4.18 mm. Control group: crowding increased by 1.6 mm. |
Brennan et al. (2000) [24] | Cohort study | N = 107 | Study group: 43 males and 64 females, average age 8.6 years (range: 7 to 11 years). No. of dropouts: 0 | Mandibular incisor crowding | Lingual arch with 0.9 mm stainless steel wire, which contacted the cingulum region of the incisors and soldered to the lingual surfaces of the first molar bands. | Arch length measured using digital calipers to the nearest 0.01 mm. Crowding was identified as tooth size-arch size discrepancy. | Not reported | Arch length decreased by 0.44 mm ± 1.35 mm. Average amount of incisor crowding resolved was 5.0 ± 2.1 mm and it decreased in 105 of the 107 patients. |
De Baets et al. (1995) [25] | Cohort study | N = 39 | Group 1: (9 patients)-well-aligned lower arch with multiple diastemas, revealing an excess of space. Group 2: (16 patients)- well-aligned incisors, with all teeth in contact. Group 3: (12 patients)- considerable remaining crowding, indicating the need for extractions. Group 4: (2 patients)-occlusal interferences preventing proper alignment of the teeth, even though space was available. No. of dropouts: 0 | Crowding only mentioned as “lower incisor crowding”. | Passive lingual arches | Mandibular arch length measured using a dial caliper on plaster casts. | 5 years following retention for only an example of 1 patient. | Group 1: arch length decreased by 1.24 ± 0.74 mm. Group 2: arch length decreased by 0.79 ± 0.97 mm. Group 3: arch length decreased by 0.23 ± 1.28 mm. Group 4: arch length decreased by 1.15 ± 1.63 mm. |
Dugoni et al. (1995) [26] | Retrospective cohort study | N = 25 | Study Group: 13 patients with class I occlusion (5 males and 8 females) and 12 patients with class II occlusion (3 males and 9 females). No. of dropouts: 0 | Mandibular anterior crowding of ≥ 3 mm. | Lingual arch appliance used was a removable, Unitek, Monrovia, Calif with 0.76 mm stainless steel wire and an adjustment loop. | Arch length measured using dial calipers on casts to the nearest 0.01 mm. | 9.5 years with a range of 5 to 22 years. | Arch length increased by 0.33 ± 2.65 mm in the treatment group (T1-T2). |
Miotti (1984) [21] | Case-control study | N = 63 | Cases group: 33 patients (12 males and 21 females), average age of 12.0 years. Control group: 30 patients (11 males and 19 females), average age of 11.8 years. No. of dropouts: 0 | Not reported | Lower lingual arch adapted as a passive space maintainer. | Tracings were made on the lateral radiographs and arch length changes were measured at the CEJ level of the incisors and molars and from the incisal edge to the mesial molar cusp | Not reported | Cases group: arch length decreased by 1.22 ± 1.7 mm at the crown level and 1.6 ± 1.4 mm at the CEJ level. Control group: arch length decreased by 3.0 ± 1.5 mm at the crown level, and 1.9 ± 1.3 mm at the CEJ level. |
Dincer et al. (1996) [22] | Case-control study | N = 20 | Cases group: 10 patients, average age of 9 years and 5 months. Control group: 10 patients, average age of 9 years and 7 months. No. of dropouts: 0 | Not reported | Removable lower space maintainer | Arch length measured on dental casts which were taken before treatment and after eruption of permanent canines. | Not reported | Cases group: arch length decreased by 1.4 mm in intercanine perimeter. Control group: arch length increased by 4 mm in intercanine perimeter. |