Table 3 Characteristics of the included studies

Ferro et al. [15]

Observational, Retrospective cohort

N = 260

Mean age (years): 10.2

N = 135

Anterior mandibular crowding of 2 mm or more

Mandibular lip bumper—the gingival level in the vertical plane, under the action of the perioral muscles

24 h/day

28 months average (range, 7–75 months)

Jacob et al. [19]

Observational, Retrospective cohort

N = 67

Mean age (years): 10.6 ± 1.3

No control

Not specified

Mandibular lip bumper—Each LB was adjusted so that the acrylic shield was 2–3 mm away from the labial surface of lower incisors and 4–5 mm away from the facial surfaces of buccal segments

Not specified

0.8 to 2.9 years

Rubin et al. [17]

Prospective longitudinal study

Mandibular lingual holding arch (N = 85)

Mean age (years): 9.5

N = 100

Mean age (years): 8.8

Mild to moderate crowding in the mandibular dental arch of 2–4.5 mm

Mandibular lingual holding arch (N = 85)

The passive mandibular lingual holding arch was constructed with bands on the mandibular first permanent molars, with a soldered .036-inch stainless steel archwire extending lingually and anteriorly along the arch. Anteriorly, the archwire was fabricated to lie passively just below the cingula of the canines and the incisors

24 h/day

2.1–2.5 years

Sonis and Ackerman [16]

Prospective study

N = 200

Mean age (years): 11.2 (9.9–11.9)

Historic control

A non-extraction treatment approach with E-space preservation utilizing passive lingual holding arches

Passive lingual holding arches

Not specified

Not specified

Arevalo et al. [18]

Retrospective study

N = 126

Mean age (years): 8.78 ± 1.52

N = 132

Mean age (years): 9.49 ± 1.75

Lower lingual holding arch or a bilateral maxillary space maintainer and presence of good quality panoramic and/or periapical radiographs

Lower lingual holding arch

Not specified

Not specified