Table 1. Open in new tab Characteristics...

Study

Design; country; setting

Patients (M/F)

Age*

Matching

Malocclusion characteristics

Breathing/airways characteristics

Extraction

Appliance; anchorage

CBCT voxel size

Chen 2018 [49]

rNRS; Uni; CHN

EX: 25 (10/15)
NEX: 25 (10/15)

EX: 12.2 (NR)
NEX: 12.4 (NR)

Dental Cl. I; no-mild crowding; ANB 0-4°; average angle/growth type; 1s-SN > 110°; 1i-ML > 99°

No snoring/obstructive sleep apnea/adenoid-/tonsillectomy; normal BMI

4 × 1^st PMs

FA; headgear

Feizi 2021 [51]

rNRS; Pract; USA

EX: 9 (4/5)
NEX: 18 (8/10)

EX: 19.2 (11.0–46.0)
NEX: 13.1 (11.0–17.0)

Dental Class II (≥ 1/2 cusp); no agenesis (excluding M2/M3); no craniofacial anomaly

4x PMs

0.3 mm

Guo 2022 [53]

rNRS; Uni; CHN

EX: 120 (0/120)
NEX: 40 (0/40)

EX: 25.1 (20.0–25.0)
NEX: 26.4 (20.0–25.0)

Age; skeletal type

Skeletal Class I-II/1 (ANB > 0°, SN-ML > 28°); no Cl. II/2; mild-moderate crowding

BMI < 27 kg/m²; no breathing disorder

4 × 1^st PMs

FA; MX anterior retraction
≥3 mm

0.3 mm

Joy 2020 [50]

rNRS; Uni; USA

EX: 41 (20/21)
NEX: 42 (22/20)

EX: 26.1 (18.0-NR)
NEX: 26.0 (18.0-NR)

Age; sex

Cl. I-III; any crowding

2x MX or 4x PMs

FA/AL;

0.3 mm

Leslie 2014 [47]

rNRS; Uni; USA

EX: 64 (23/41)
NEX: 90 (42/48)

EX/NEX: NR (NR-18.0)

4x PMs

0.4 mm

Mladenovic 2024_coll [54, 55]

rNRS; Pract; AUS

EX: 54 (18/36)
NEX: 59 (24/35)

EX/NEX: 15.0 (NR)

Crowding

Skeletal Cl. I-II; any crowding; no craniofacial deformities

2x MX or 4 × 2^nd PMs

0.3 mm

Mostanghi 2021 [52]

rNRS; Pract; USA

EX: 20 (7/13)
NEX: 20 (5/15)

EX: 24.9 (18.5–38.3)
NEX: 26.2 (16.0–42.6)

Age; sex; treatment duration

Crowding or bimaxillary dentoalveolar protrusion; no impactions

No reported obstructive sleep apnea

2x MX or 4x PMs

0.3 mm

Pliska 2016 [48]

rNRS; Uni; USA

EX: 26 (8/18)
NEX: 48 (17/31)

EX: 27.4 (18.0-NR)
NEX: 31.9 (18.0-NR)

Cl. I-II (ANB ≥ 0°); no agenesis

≥2x PMs

Shannon 2012 [45]

rNRS; Pract; USA

EX: 27 (11/16)
NEX: 61 (30/31)

EX: 13.5 (9.0–22.0)
NEX: 13.2 (10.0–22.0)

No agenesis; no craniofacial anomaly

4x PMs

Stefanovic 2023 [46]

rNRS; Uni; USA

EX: 31 (15/16)
NEX: 31 (15/16)

EX: 13.0 (NR)
NEX: 12.9 (NR)

Age; sex

Cl. I-III

No breathing disorder

4 × 1^st PMs

0.38 mm

Valiathan 2010 [44]

rNRS; Uni; USA

EX: 20 (10/10)
NEX: 20 (10/10)

EX: 13.6 (11.3–15.6)
NEX: 13.7 (11.3–15.6)

Age,
gender, height, ethnicity, weight, BMI, and
skeletal features, and oropharynx volume

Cl. I; no craniofacial deformities

No pharyngeal
pathology and/or nasal obstruction, snoring, obstructive sleep apnea, adenoid- or tonsillectomy.

4x PMs

0.38 mm

Study

Design; country; setting

Patients (M/F)

Age*

Matching

Malocclusion characteristics

Breathing/airways characteristics

Extraction

Appliance; anchorage

CBCT voxel size

Chen 2018 [49]

rNRS; Uni; CHN

EX: 25 (10/15)
NEX: 25 (10/15)

EX: 12.2 (NR)
NEX: 12.4 (NR)

Dental Cl. I; no-mild crowding; ANB 0-4°; average angle/growth type; 1s-SN > 110°; 1i-ML > 99°

No snoring/obstructive sleep apnea/adenoid-/tonsillectomy; normal BMI

4 × 1^st PMs

FA; headgear

Feizi 2021 [51]

rNRS; Pract; USA

EX: 9 (4/5)
NEX: 18 (8/10)

EX: 19.2 (11.0–46.0)
NEX: 13.1 (11.0–17.0)

Dental Class II (≥ 1/2 cusp); no agenesis (excluding M2/M3); no craniofacial anomaly

4x PMs

0.3 mm

Guo 2022 [53]

rNRS; Uni; CHN

EX: 120 (0/120)
NEX: 40 (0/40)

EX: 25.1 (20.0–25.0)
NEX: 26.4 (20.0–25.0)

Age; skeletal type

Skeletal Class I-II/1 (ANB > 0°, SN-ML > 28°); no Cl. II/2; mild-moderate crowding

BMI < 27 kg/m²; no breathing disorder

4 × 1^st PMs

FA; MX anterior retraction
≥3 mm

0.3 mm

Joy 2020 [50]

rNRS; Uni; USA

EX: 41 (20/21)
NEX: 42 (22/20)

EX: 26.1 (18.0-NR)
NEX: 26.0 (18.0-NR)

Age; sex

Cl. I-III; any crowding

2x MX or 4x PMs

FA/AL;

0.3 mm

Leslie 2014 [47]

rNRS; Uni; USA

EX: 64 (23/41)
NEX: 90 (42/48)

EX/NEX: NR (NR-18.0)

4x PMs

0.4 mm

Mladenovic 2024_coll [54, 55]

rNRS; Pract; AUS

EX: 54 (18/36)
NEX: 59 (24/35)

EX/NEX: 15.0 (NR)

Crowding

Skeletal Cl. I-II; any crowding; no craniofacial deformities

2x MX or 4 × 2^nd PMs

0.3 mm

Mostanghi 2021 [52]

rNRS; Pract; USA

EX: 20 (7/13)
NEX: 20 (5/15)

EX: 24.9 (18.5–38.3)
NEX: 26.2 (16.0–42.6)

Age; sex; treatment duration

Crowding or bimaxillary dentoalveolar protrusion; no impactions

No reported obstructive sleep apnea

2x MX or 4x PMs

0.3 mm

Pliska 2016 [48]

rNRS; Uni; USA

EX: 26 (8/18)
NEX: 48 (17/31)

EX: 27.4 (18.0-NR)
NEX: 31.9 (18.0-NR)

Cl. I-II (ANB ≥ 0°); no agenesis

≥2x PMs

Shannon 2012 [45]

rNRS; Pract; USA

EX: 27 (11/16)
NEX: 61 (30/31)

EX: 13.5 (9.0–22.0)
NEX: 13.2 (10.0–22.0)

No agenesis; no craniofacial anomaly

4x PMs

Stefanovic 2023 [46]

rNRS; Uni; USA

EX: 31 (15/16)
NEX: 31 (15/16)

EX: 13.0 (NR)
NEX: 12.9 (NR)

Age; sex

Cl. I-III

No breathing disorder

4 × 1^st PMs

0.38 mm

Valiathan 2010 [44]

rNRS; Uni; USA

EX: 20 (10/10)
NEX: 20 (10/10)

EX: 13.6 (11.3–15.6)
NEX: 13.7 (11.3–15.6)

Age,
gender, height, ethnicity, weight, BMI, and
skeletal features, and oropharynx volume

Cl. I; no craniofacial deformities

No pharyngeal
pathology and/or nasal obstruction, snoring, obstructive sleep apnea, adenoid- or tonsillectomy.

4x PMs

0.38 mm

Table 1.

Open in new tab

Characteristics of included studies.

Study	Design; country; setting	Patients (M/F)	Age*	Matching	Malocclusion characteristics	Breathing/airways characteristics	Extraction	Appliance; anchorage	CBCT voxel size
Chen 2018 [49]	rNRS; Uni; CHN	EX: 25 (10/15) NEX: 25 (10/15)	EX: 12.2 (NR) NEX: 12.4 (NR)	-	Dental Cl. I; no-mild crowding; ANB 0-4°; average angle/growth type; 1s-SN > 110°; 1i-ML > 99°	No snoring/obstructive sleep apnea/adenoid-/tonsillectomy; normal BMI	4 × 1^st PMs	FA; headgear	NR
Feizi 2021 [51]	rNRS; Pract; USA	EX: 9 (4/5) NEX: 18 (8/10)	EX: 19.2 (11.0–46.0) NEX: 13.1 (11.0–17.0)	-	Dental Class II (≥ 1/2 cusp); no agenesis (excluding M2/M3); no craniofacial anomaly	-	4x PMs	FA	0.3 mm
Guo 2022 [53]	rNRS; Uni; CHN	EX: 120 (0/120) NEX: 40 (0/40)	EX: 25.1 (20.0–25.0) NEX: 26.4 (20.0–25.0)	Age; skeletal type	Skeletal Class I-II/1 (ANB > 0°, SN-ML > 28°); no Cl. II/2; mild-moderate crowding	BMI < 27 kg/m²; no breathing disorder	4 × 1^st PMs	FA; MX anterior retraction ≥3 mm	0.3 mm
Joy 2020 [50]	rNRS; Uni; USA	EX: 41 (20/21) NEX: 42 (22/20)	EX: 26.1 (18.0-NR) NEX: 26.0 (18.0-NR)	Age; sex	Cl. I-III; any crowding	-	2x MX or 4x PMs	FA/AL;	0.3 mm
Leslie 2014 [47]	rNRS; Uni; USA	EX: 64 (23/41) NEX: 90 (42/48)	EX/NEX: NR (NR-18.0)	-	-	-	4x PMs	FA	0.4 mm
Mladenovic 2024_coll [54, 55]	rNRS; Pract; AUS	EX: 54 (18/36) NEX: 59 (24/35)	EX/NEX: 15.0 (NR)	Crowding	Skeletal Cl. I-II; any crowding; no craniofacial deformities	-	2x MX or 4 × 2^nd PMs	FA	0.3 mm
Mostanghi 2021 [52]	rNRS; Pract; USA	EX: 20 (7/13) NEX: 20 (5/15)	EX: 24.9 (18.5–38.3) NEX: 26.2 (16.0–42.6)	Age; sex; treatment duration	Crowding or bimaxillary dentoalveolar protrusion; no impactions	No reported obstructive sleep apnea	2x MX or 4x PMs	FA	0.3 mm
Pliska 2016 [48]	rNRS; Uni; USA	EX: 26 (8/18) NEX: 48 (17/31)	EX: 27.4 (18.0-NR) NEX: 31.9 (18.0-NR)	-	Cl. I-II (ANB ≥ 0°); no agenesis	-	≥2x PMs	FA	NR
Shannon 2012 [45]	rNRS; Pract; USA	EX: 27 (11/16) NEX: 61 (30/31)	EX: 13.5 (9.0–22.0) NEX: 13.2 (10.0–22.0)	-	No agenesis; no craniofacial anomaly	-	4x PMs	FA	NR
Stefanovic 2023 [46]	rNRS; Uni; USA	EX: 31 (15/16) NEX: 31 (15/16)	EX: 13.0 (NR) NEX: 12.9 (NR)	Age; sex	Cl. I-III	No breathing disorder	4 × 1^st PMs	FA	0.38 mm
Valiathan 2010 [44]	rNRS; Uni; USA	EX: 20 (10/10) NEX: 20 (10/10)	EX: 13.6 (11.3–15.6) NEX: 13.7 (11.3–15.6)	Age, gender, height, ethnicity, weight, BMI, and skeletal features, and oropharynx volume	Cl. I; no craniofacial deformities	No pharyngeal pathology and/or nasal obstruction, snoring, obstructive sleep apnea, adenoid- or tonsillectomy.	4x PMs	FA	0.38 mm

Study	Design; country; setting	Patients (M/F)	Age*	Matching	Malocclusion characteristics	Breathing/airways characteristics	Extraction	Appliance; anchorage	CBCT voxel size
Chen 2018 [49]	rNRS; Uni; CHN	EX: 25 (10/15) NEX: 25 (10/15)	EX: 12.2 (NR) NEX: 12.4 (NR)	-	Dental Cl. I; no-mild crowding; ANB 0-4°; average angle/growth type; 1s-SN > 110°; 1i-ML > 99°	No snoring/obstructive sleep apnea/adenoid-/tonsillectomy; normal BMI	4 × 1^st PMs	FA; headgear	NR
Feizi 2021 [51]	rNRS; Pract; USA	EX: 9 (4/5) NEX: 18 (8/10)	EX: 19.2 (11.0–46.0) NEX: 13.1 (11.0–17.0)	-	Dental Class II (≥ 1/2 cusp); no agenesis (excluding M2/M3); no craniofacial anomaly	-	4x PMs	FA	0.3 mm
Guo 2022 [53]	rNRS; Uni; CHN	EX: 120 (0/120) NEX: 40 (0/40)	EX: 25.1 (20.0–25.0) NEX: 26.4 (20.0–25.0)	Age; skeletal type	Skeletal Class I-II/1 (ANB > 0°, SN-ML > 28°); no Cl. II/2; mild-moderate crowding	BMI < 27 kg/m²; no breathing disorder	4 × 1^st PMs	FA; MX anterior retraction ≥3 mm	0.3 mm
Joy 2020 [50]	rNRS; Uni; USA	EX: 41 (20/21) NEX: 42 (22/20)	EX: 26.1 (18.0-NR) NEX: 26.0 (18.0-NR)	Age; sex	Cl. I-III; any crowding	-	2x MX or 4x PMs	FA/AL;	0.3 mm
Leslie 2014 [47]	rNRS; Uni; USA	EX: 64 (23/41) NEX: 90 (42/48)	EX/NEX: NR (NR-18.0)	-	-	-	4x PMs	FA	0.4 mm
Mladenovic 2024_coll [54, 55]	rNRS; Pract; AUS	EX: 54 (18/36) NEX: 59 (24/35)	EX/NEX: 15.0 (NR)	Crowding	Skeletal Cl. I-II; any crowding; no craniofacial deformities	-	2x MX or 4 × 2^nd PMs	FA	0.3 mm
Mostanghi 2021 [52]	rNRS; Pract; USA	EX: 20 (7/13) NEX: 20 (5/15)	EX: 24.9 (18.5–38.3) NEX: 26.2 (16.0–42.6)	Age; sex; treatment duration	Crowding or bimaxillary dentoalveolar protrusion; no impactions	No reported obstructive sleep apnea	2x MX or 4x PMs	FA	0.3 mm
Pliska 2016 [48]	rNRS; Uni; USA	EX: 26 (8/18) NEX: 48 (17/31)	EX: 27.4 (18.0-NR) NEX: 31.9 (18.0-NR)	-	Cl. I-II (ANB ≥ 0°); no agenesis	-	≥2x PMs	FA	NR
Shannon 2012 [45]	rNRS; Pract; USA	EX: 27 (11/16) NEX: 61 (30/31)	EX: 13.5 (9.0–22.0) NEX: 13.2 (10.0–22.0)	-	No agenesis; no craniofacial anomaly	-	4x PMs	FA	NR
Stefanovic 2023 [46]	rNRS; Uni; USA	EX: 31 (15/16) NEX: 31 (15/16)	EX: 13.0 (NR) NEX: 12.9 (NR)	Age; sex	Cl. I-III	No breathing disorder	4 × 1^st PMs	FA	0.38 mm
Valiathan 2010 [44]	rNRS; Uni; USA	EX: 20 (10/10) NEX: 20 (10/10)	EX: 13.6 (11.3–15.6) NEX: 13.7 (11.3–15.6)	Age, gender, height, ethnicity, weight, BMI, and skeletal features, and oropharynx volume	Cl. I; no craniofacial deformities	No pharyngeal pathology and/or nasal obstruction, snoring, obstructive sleep apnea, adenoid- or tonsillectomy.	4x PMs	FA	0.38 mm

AL, aligner; BMI, body mass index; CBCT, cone-bean computerized tomography; Cl., Angle’s Class; coll, collated multiple reports; CVM, cervical vertebrae maturation; EX, extraction group; FA, fixed appliance; M2/M3, 2^nd/3^rd molar; MX, maxillary; NEX, non-extraction group; NR, not reported; PM, premolar; Pract, private practice; rNRS, retrospective non-randomized study.

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