Introduction
Our aim was to assess the available evidence for the effects of orthodontic treatment with 4 premolar extractions on the skeletal vertical dimension of the face compared with nonextraction treatment.
Methods
Electronic database searches (MEDLINE, EMBASE, Cochrane Oral Health Group’s Trials Register, and CENTRAL) of published and unpublished literature and hand searches of eligible studies were performed, with no language or publication date restrictions. Two authors performed data extraction independently and in duplicate. Risk of bias was assessed.
Results
After application of the eligibility criteria, 14 studies were included in this systematic review. All were retrospective. Risk of bias ranged from moderate to critical. Ten studies investigated patients with various skeletal vertical patterns and classes of malocclusion and found no difference between extraction (Ex) and nonextraction (Nonex) treatment in regard to the vertical dimension. Only 2 studies found statistically significant increases in the nonextraction groups, one in N-Me (Ex: +1.5 mm; Nonex: +5.5 mm; P <0.05) and one in SN-GoGn (Ex: −0.9°; Nonex: +0.8°; P <0.05), but without a concurrent significant change in other vertical measurements such as FMA. Two other studies showed opposite findings regarding N-Me (Ex: +2.3 mm; Nonex: +0.9 mm; P <0.05) and FMA (Ex: +0.3°; Nonex: −2.0°; P <0.05).
Conclusions
Although the quality of evidence ranged from moderate to low, there was considerable agreement among these studies, suggesting that orthodontic treatment with 4 premolar extractions has no specific effect on the skeletal vertical dimension. Thus, an extraction treatment protocol aiming to reduce or control the vertical dimension does not seem to be an evidence-based clinical approach.
Highlights
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Fourteen retrospective controlled studies were included in this systematic review.
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Risk of bias ranged from moderate to critical.
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There is no specific effect of premolar extractions on the vertical dimension.
Extractions for orthodontic purposes have always been a controversial issue in contemporary treatment planning. When linked to the control of the vertical dimension during orthodontic treatment, this may be an additional major disputation. It has been advocated that changes in vertical dimension during growth may also influence the anteroposterior position of the mandible and the establishment of the permanent occlusion.
For many years, posterior tooth extractions have been suggested, especially in long-face patients to control the vertical dimension. It has been recommended that extracting permanent teeth may correct an open bite or reduce the vertical dimension of the face by counterclockwise rotation of the mandible, through the forward movement of the posterior teeth: the wedge-type effect. According to various authors, extractions lead to reduction of the vertical dimension not only in hyperdivergent patients, but also in those with skeletal open bite. On the other hand, other studies reported no distinct effects of extraction treatment on the facial vertical dimension.
Hyperdivergent patients comprise a significant part (22%) of the orthodontic patients treated worldwide. Thus, the selection of an extraction vs a nonextraction treatment protocol in regard to effects in the vertical dimension is a common decision made in every practice. The contradictory findings of previous studies, however, do not allow for evidence-based decision making, leading, in turn, to extremely different strategies applied to patients by various clinicians.
Therefore, the aim of this review was to systematically search the literature to evaluate the effects of 4 premolar extractions compared with nonextraction treatment on the skeletal vertical dimension of the face.
Material and methods
Protocol and registration
The protocol was not registered prior to the study.
Selection criteria applied for the review
Any study design was considered eligible for inclusion in this review, including randomized clinical trials, nonrandomized or quasi-randomized controlled trials, and prospective and retrospective studies with a treated comparison or control group.
Patients of any age having orthodontic treatment with full fixed appliances in the maxilla and mandible were eligible.
Orthodontic therapy with fixed appliances including 4 premolar extractions (1 in each quadrant) were eligible.
For the control or comparison group, we chose orthodontic therapy with fixed appliances, but without tooth extractions.
The outcome was the effects on the vertical dimension of skeletal craniofacial structures, quantitatively assessed on radiographic images.
The follow-ups included before and after orthodontic treatment evaluations.
Exclusion criteria were animal and in-vitro studies, studies involving orthognathic surgery, and case reports or studies reporting outcomes from fewer than 10 patients.
Search strategy for identification of studies
Detailed search strategies were developed and appropriately revised for each data base, considering the differences in controlled vocabulary and syntax rules. The following electronic databases were searched: MEDLINE (via Ovid and PubMed, from 1946 to August 2, 2017; Appendix ), EMBASE (via Ovid), Cochrane Oral Health Group’s Trials Register, and CENTRAL.
Unpublished literature was searched on ClinicalTrials.gov , the National Research Register, and Pro-Quest Dissertation Abstracts and Thesis database. We attempted to identify all relevant studies irrespective of language. The reference lists of all eligible studies were hand searched for additional studies.
Selection of studies
Studies were selected independently and in duplicate by 2 authors (G.K., K.D.) who were not blinded to the identity of the authors of the studies, their institutions, or the results of their research. Study selection procedures comprised reading of titles, abstracts, and full texts. After they excluded noneligible studies, the full report of publications considered eligible for inclusion by either author was obtained and assessed independently. Disagreements were resolved by discussion and consultations with other authors (I.D., N.G.). A record of all decisions on study identification was kept.
Data extraction and management
Data extraction was performed independently and in duplicate by the first 2 authors (G.K., K.D.). To record the desired information, customized data collection forms were used. Disagreements were resolved in reevaluations of the original studies by both authors and discussions with the last author until consensus was reached.
Measures of treatment effect
For continuous outcomes, mean differences and standard deviations were used to summarize the data from each study.
Unit of analysis
In all cases, the unit of analysis was the patient.
Missing data
We contacted the authors via e-mail to request information that was missing. In case of no response, only the available data were reported and analyzed. For missing standard deviations, data could be retrieved if t statistics or P values were reported. When P values were reported as P =0.000, we considered them rounded values and made a worst case scenario hypothesis, imputing the value to be 0.0004 instead.
Assessment of heterogeneity
Heterogeneity can be divided into 3 forms: clinical, methodological, and statistical. We assessed clinical heterogeneity by examining the characteristics of the studies, the similarities between the participants, the interventions, and the outcomes as specified in the inclusion criteria. We determined whether the participants had completed their growth as participant-specific components. We also identified the vertical skeletal pattern and the sagittal skeletal and dental patterns as potential population-specific sources of clinical heterogeneity. The potential effect of varying sex distribution between studies was ignored, since a differential effect due to sex was not expected and angular measurements were mainly considered. On the other hand, treatment protocol was considered to add to the total clinical heterogeneity, and the following aspects were underlined: type of anchorage, treatment biomechanics (eg, headgear application), type of teeth extracted, and type of control group. The final component of clinical heterogeneity was outcome measures, since the vertical changes can be measured on a lateral cephalogram in various ways. Methodologic heterogeneity was considered in terms of both study design and conduct, in the latter case, especially in terms of risk of bias. Finally, the tool we used to assess risk of bias provided a summary measure that also accounted for heterogeneity assessment.
Assessment of reporting bias
Reporting biases arise when the reporting of research findings is affected by the nature or direction of the findings themselves. We attempted to minimize potential reporting biases, including publication bias, multiple (duplicate reports) publication bias, and language bias in this review by conducting an accurate and sensitive search of many sources with no language restriction. We also searched for ongoing trials.
Quality assessment
The quality assessments of the included studies were conducted using the ROBINS-I tool. Two authors (G.K., K.D.) assessed the studies individually and then compared their findings. Disagreements were resolved by discussion with the last author (N.G.).
Results
Description of studies
The flow diagram of study selection is shown in the Figure . A total of 927 studies were initially identified in the electronic search. After title and abstract screening, 34 studies were retrieved to be examined in more detail. Twenty studies were subsequently excluded for the reasons stated in the flow chart. Consequently, 14 articles were included in this review.
All included studies were retrospective and investigated the effects of 4 premolar extractions. In 11 studies, 4 first premolars were extracted; in another study, 2 maxillary first and 2 mandibular first or second premolars were extracted. In 2 studies, the exact premolar extraction pattern was not specified. An overview of the main characteristics of the studies is presented in Table I .
| Author Year Study design |
Main objective | Extraction group (Ex) | Nonextraction group (Nonex) | Malocclusion/Skeletal vertical pattern (pretreatment) | Duration of treatment (mean ± SD) |
Outcome of interest | Magnification correction method | ||
|---|---|---|---|---|---|---|---|---|---|
| Intervention Sample size, age (mean ± SD), sex |
Treatment details | Intervention Sample size, age (mean ± SD), sex |
Treatment details | ||||||
| Basciftci and Usumez (2003) Retrospective |
Changes in craniofacial structures of Class I and Class II patients | Four premolar (NA) extractions Class I n = 22 (13 F, 9 M) age, 14.5 ± 2.0 y Class II, 1 n = 20 (13 F, 7 M) age, 17.4 ± 3.6 y |
NA | Nonextraction treatment Class I n = 25 (15 F, 10 M) age, 13.6 ± 1.8 y Class II, 1 n = 20 (12 F, 8 M) age, 12.7 ± 1.0 y |
NA | Dental Class I and Class II, 1 Hyperdivergent Class I SN-GoGn: Ex: 36.9° ± 5.8° Nonex: 35.3° ± 6.4° Class II, 1 SN-GoGn: Ex: 39.3° ± 5.7° Nonex: 34.7° ± 5.4° |
Class I Ex: 1.9 ± 0.3 y Nonex: 1.6 ± 0.4 y Class II, 1 Ex: 2.0 ± 0.5 y Nonex: 1.9 ± 0.4 y |
(1) Sn-GoGn (°) | NA |
| Bravo et al (1997) Retrospective |
Changes in facial profile of Class II patients | Four first premolar or two maxillary first and two mandibular second premolar extractions n = 16 F age, 13.5 ± 1.8 y |
NA | Nonextraction treatment n = 15 F age, 12.9 ± 0.7 y |
NA | Dental Class II Normodivergent FMA Ex: 26.5° ± 2.5° Nonex: 25.5° ± 3.8° |
Ex: 2.7 ± 0.3 y Nonex: 2.6 ± 0.8 y |
(1) FMA (°) | Machine magnification factor |
| Gkantidis et al (2011) Retrospective |
Changes in vertical dimension of Class II, 1 hyperdivergent patients | Four first premolar extractions n = 29 (16 F, 13 M) age, 11.8 ± 0.9 y |
“Non-extrusive” mechanics: Nance and Goshgarian arches, no Class II elastics, no low-pull headgear or bite plates |
Nonextraction treatment n = 28 (14 F, 14 M) age, 11.0 ± 1.0 y |
“Extrusive” mechanics: low-pull headgear in all patients, anterior bite planes, Class II elastics or posterior crossbite elastics when needed | Dental Class II, 1 Hyperdivergent SN-GoGn: Ex: 38.4° ± 3.8° Nonex: 39.1° ± 3.8° |
Ex: 3.2 ± 0.6 y Nonex: 2.4 ± 0.8 y |
(1) SN-GoGn (°) (2) FH-MP (°) (3) ANS-Me (mm) (4) LFH/TFH (ratio) |
Reference ruler |
| Hayasaki et al (2005) Retrospective |
Changes in craniofacial structures of Class I and Class II patients | Four first premolar extractions Class I: n = 15 (9 F, 6 M) age, 12.3 y Class II: n = 14 (7 F, 7 M) age, 12.3 y |
Headgear, lip bumper when needed No skeletal anchorage |
Nonextraction treatment Class I: n = 15 (8 F, 7 M) age, 11.9 y Class II: n = 15 (7 F, 8 M) age, 12.1 y |
Headgear, lip bumper when needed No skeletal anchorage |
Dental Class I and II, 1 Normodivergent SN-GoGn Class I Ex: 32.3° ± 5.1° Nonex: 31.4° ± 5.3° Class II, 1 Ex: 31.2° ± 6.1° Nonex: 31.9° ± 3.1° |
Class I: Ex: 2.4 y Nonex: 2.0 y Class II: Ex: 2.9 y Nonex: 2.6 y |
(1) SN-GoGn (°) (2) Me-PP (mm) (3) N-Me (mm) (4) ANS-Me (mm) |
Machine magnification factor |
| Hosseinzadeh-Nik et al (2016) Retrospective |
Changes in the mandible of Class I patients | Four first premolar extractions n = 18 F age, 16.4 ± 0.4 y |
Straight wire appliances (0.022 in, MBT) |
Nonextraction treatment n = 18 F age, 16.4 ± 0.4 y |
Straight wire appliances (0.022 in, MBT) |
Class I Ex: with bimaxillary protrusion Nonex: without bimaxillary protrusion |
24 ± 6 months | (1) Pog-SN7 (mm) (2) B-SN7 (mm) |
Machine magnification factor |
| Katsaros et al (1996) Retrospective |
Changes in the soft tissue profile of patients with enlarged overjet | Four premolar extractions n = 33 F age, 13.0 (12.0-15.0) y |
NA | Nonextraction treatment n = 29 F age, 12.1 (12.0-16.0) y |
NA | Overjet ≥ 6 mm Hyperdivergent SN-GoMe Ex: 38.6° ± 6.9° Nonex: 36.3° ± 4.8° |
Ex: 3.7 (1.1-5.9) y Nonex: 3.1 (1.3-5.5) y |
(1) SN-GoMe (°) (2) PP-GoMe (°) |
NA |
| Kirschneck et al (2015) Retrospective |
Changes in vertical dimension | Four first premolar extractions n = 25 F age, 10.8 ± 1.2 y |
Headgear and Class II/III elastics | Nonextraction treatment n = 25 F age, 11.1 ± 1.3 y |
Headgear, Class II/III elastics | Dental Classes I, II, and III All patterns SN-GoGn Ex: 35.1° ± 5.1° Nonex: 34.2° ± 4.8° |
2.8 (2.3-4.8) y | (1) SN-GoGn (°) (2) PP-GoGn (°) |
Reference ruler |
| Kocadereli (1999) Retrospective |
Changes in vertical dimension of Class I patients | Four first premolar extractions n = 40 (23 F, 17 M) age, 12.8 ± 2.4 y |
No extraoral appliances Minimal posterior protraction expected due to initial crowding |
Nonextraction treatment n = 40 (24 F, 16 M) age, 12.3 ± 2.2 y |
No extraoral appliances | Dental Class I Hyperdivergent (tendency) SN-GoGn Ex: 36.9° ± 5.5° Nonex: 34.7° ± 6.4° |
NA | (1) SN-GoGn (°) (2) FMA (°) (3) N-Me (mm) (4) ANS-Me (mm) |
NA (same radiographic unit) |
| Kumari and Fida (2010) Retrospective |
Changes in vertical dimension of Class I patients | Four first premolar extractions n = 40 age, 15.4 ± 1.2 y |
No functional appliances | Nonextraction treatment n = 41 age, 15.8 ± 1.5 y |
No functional appliances | Skeletal Class I Hyperdivergent (tendency) FMA Ex: 27.8° ± 6.1° Nonex: 26.3° ± 6.0° |
NA | (1) FMA (°) (2) N-Me (mm) (3) N-ANS/ANS-Me (ratio) |
NA |
| Luppanapornlap and Johnston (1993) Retrospective |
Changes in vertical dimension of Class II patients | Four first premolar extractions n = 33 (18 F, 15 M) age, NA |
NA | Non-extraction treatment n = 29 (18 F, 11 M) age, NA |
NA | Class II Normodivergent (Ex) and hypodivergent (Nonex) FMA Ex: 24.7° Nonex: 18.9° |
NA | (1) FMA (°) (2) N-Me (mm) (3) ANS-Me (mm) |
NA |
| Paquette et al (1992) Retrospective |
Changes in vertical dimension of Class II patients | Four first premolar extractions n = 33 (20 F, 13 M) age, 12.5 y |
NA | Nonextraction treatment n = 30 (11 F, 19 M) age, 12.6 y |
NA | Dental Class II, 1 Normodivergent Ex: 22.9° Nonex: 24.9° |
Ex: 1.8 y Nonex: 1.6 y |
(1) FMA (°) (2) N-Me (mm) (3) ANS-Me (mm) |
NA |
| Porto et al (2012) Retrospective |
Changes in vertical dimension of hyperdivergent patients | Four first premolar extractions n = 23 (14 F, 9 M) age, 12.3 ± 1.0 y |
Lip bumper, intermaxillary elastics, and high-pull headgear for anchorage in all patients |
Nonextraction treatment n = 23 (12 F, 11 M) age, 12.4 ± 1.1 y |
Lip bumper, intermaxillary elastics, and high-pull headgear for anchorage in all patients |
Dental Class II, 1 Hyperdivergent SN-GoGn Ex: 40.0° ± 3.6° Nonex: 38.0° ± 3.1° |
Ex: 2.5 ± 0.7 y Nonex: 2.2 ± 0.4 y |
(1) SN-GoGn (°) (2) FMA (°) (3) N-S-Gn (°) |
NA |
| Sivakumar and Valiathan (2008) Retrospective |
Changes in vertical dimension of Class I patients | Four first premolar extractions n = 31 (26 F, 5 M) age, 17.2 ± 3.9 y |
NA | Nonextraction treatment n = 29 (18 F, 11 M) age, 18.5 ± 3.6 y |
NA | Dental Class I Normodivergent SN-GoGn: 32° ± 1° |
Ex: 1.5 y Nonex: 2.9 y |
(1) GoMe-FH (°) (2) N-Me (mm) (3) ANS-Me (mm) |
Machine magnification factor |
| Staggers (1994) Retrospective |
Changes in vertical dimension of Class I patients | Four first premolar extractions n = 38 age, 14.4 y |
NA | Nonextraction treatment n = 45 Age, 12.8 y |
NA | Dental Class I | NA | (1) MP-HP (°) (2) N-Me (mm) (3) N-ANS/ANS-Me (ratio) |
NA |
Quality assessment
By definition of the tool that we used, no study received the grade of “low” with regard to confounding, because confounding was expected with our topic and was not fully controlled in any case. Most studies were deemed problematic due to the lack of information about the treatment mechanics used to close the extraction spaces. A judgment between “serious” and “critical” overall risk of bias was made for studies that did not provide information for at least 1 bias domain.
Of the 14 retrospective studies, 5 were assessed as moderate, 5 as serious, and 3 as critical risk of bias. Finally, 1 study was assessed as serious for the Class I group and critical for the Class II group.
Disagreements were all between studies with serious and critical risks of bias. An overview of the risk of bias assessment is given in Table II .
| Study | Confounding | Selection bias | Bias in measurement classification of interventions | Bias due to deviations from intended interventions | Bias due to missing data | Bias in measurement of outcomes | Bias in selection of reported result | Overall |
|---|---|---|---|---|---|---|---|---|
| Basciftci and Usumez (2003) |
Class I: moderate |
Moderate | Moderate (extracted premolars not defined) |
No information (NA treatment details) |
Low | Moderate (not blinded assessor) |
Moderate | Serious |
| Class II: critical (difference in age and SN-GoGn pretreatment) |
Moderate | Moderate (extracted premolars not defined) |
No information (NA treatment details) | Low | Moderate (not blinded assessor) |
Moderate | Critical | |
| Bravo et al (1997) |
Moderate | Moderate | Moderate (2 extraction patterns were used) |
No information (NA treatment details) | Low | Moderate (not blinded assessor) |
Moderate | Serious |
| Gkantidis et al (2011) |
Moderate | Low | Low | Low | Low | Moderate (not blinded assessor) |
Low | Moderate |
| Hayasaki et al (2005) |
Moderate | Moderate | Low | Low | Low | Moderate (not blinded assessor) |
Low | Moderate |
| Hosseinzadeh-Nik et al (2016) |
Moderate | Moderate | Low | No information (NA treatment details) |
Low | Moderate (not blinded assessor) |
Moderate | Serious |
| Katsaros et al (1996) |
Moderate | Moderate | Moderate (extracted premolars not defined) |
No information (NA treatment details) | Low | Moderate (not blinded assessor) |
Low | Serious |
| Kirschneck et al (2015) |
Moderate | Low | Low | Moderate (treatment details partially provided) | Low | Low | Low | Moderate |
| Kocadereli (1999) |
Moderate | Moderate | Low | Moderate (treatment details partially provided) |
Low | Moderate (not blinded assessor) |
Low | Moderate |
| Kumari and Fida (2010) |
Serious (unknown treatment time and sex distribution) |
Moderate | Low | Moderate (treatment details partially provided) |
Low | Serious (no method error, not blinded assessor) |
Serious (only posttreatment values compared) |
Serious |
| Luppanapornlap and Johnston (1993) |
Critical (different group baseline characteristics) |
Low | Low | No information (NA treatment details) | Low | Moderate (not blinded assessor) |
Low | Critical |
| Paquette et al (1992) |
Moderate | Low | Low | No information (NA treatment details) | Low | Moderate (not blinded assessor) |
Low | Serious |
| Porto et al (2012) |
Moderate | Moderate | Low | Low | Low | Moderate (not blinded assessor) |
Low | Moderate |
| Sivakumar and Valiathan (2008) |
Critical (differences in treatment time and sex distribution) |
Moderate | Low | No information (NA treatment details) | Low | Moderate (not blinded assessor) |
Low | Critical |
| Staggers (1994) |
No Information (baseline table missing, unknown sex distribution) |
Moderate | Low | No information (NA treatment details) | Low | Serious (NA method error, not blinded assessor) |
Low | Critical |
Qualitative synthesis of included studies
Clinical heterogeneity was high; for this reason, no quantitative synthesis was possible. The diversity between growth stages, skeletal patterns, extraction patterns, controls ( Table I ), and outcomes ( Table III ) did not lead to studies with comparable outcome measures. Most studies included growing patients, but 3 studies included mainly nongrowing participants. No study reported the results separately. Other studies did not report on the vertical skeletal patterns of their samples. Different biomechanical strategies were used between studies; in certain studies, this information was incomplete.
| Author Year Study design |
Intervention | Results Mean ± SD of T1-T0 difference |
Effect on vertical dimension |
|---|---|---|---|
| Basciftci and Usumez (2003) Retrospective |
Class I 4 premolar Ex (NA) vs Nonex Class II, 1 4 premolar Ex (NA) vs Nonex |
Class I SN-GoGn (°), Ex: −1.0 ± 3.2; Nonex: −0.4 ± 2.3; P = 0.460 Class II, 1 SN-GoGn (°), Ex: +0.2 ± 2.5; Nonex: +0.8 ± 2.0; P = 0.425 |
There is no difference between extraction and nonextraction treatment, in both dental Class I and Class II, 1 hyperdivergent patients. |
| Bravo et al (1997) Retrospective |
4 first premolar or 2 maxillary first and 2 mandibular second premolar Ex vs Nonex | FMA (°), Ex: −0.6 ± 1.7; Nonex: −0.4 ± 1.4; P = 0.724 | There is no difference between extraction and nonextraction treatment in dental Class II normodivergent patients. |
| Gkantidis et al (2011) Retrospective |
4 first premolar Ex vs Nonex | SN-GoGn (°), Ex: −0.1 ± 2.5; Nonex: +0.1 ± 1.7; P = 0.616 FH-MP (°), Ex: −0.2 ± 2.5; Nonex: +0.1 ± 2.4; P = 0.709 ANS-Me (mm), Ex: +4.0 ± 4.5′ Nonex: +3.3 ± 3.1; P = 0.643 LFH/TFH, Ex: +0.1 ± 0.9; Nonex: +0.2 ± 1.5; P = 0.822 |
There is no difference between extraction and nonextraction treatment in dental Class II, 1 hyperdivergent patients. |
| Hayasaki et al (2005) Retrospective |
Class I 4 first premolar Ex vs Nonex Class II, 1 4 first premolar Ex vs Nonex |
Class I SN-GoGn (°), Ex: −0.8 ± 2.0; Nonex: +0.8 ± 2.6; P = 0.071 Me-PP (mm), Ex: +2.8 ± 2.6; Nonex: +3.5 ± 2.7; P = 0.456 N-Me (mm), Ex: +4.5 ± 3.8, Nonex: +6.0 ± 4.4; P = 0.341 ANS-Me (mm), Ex: +2.4 ± 2.4; Nonex: +3.3 ± 2.8; P = 0.385 Class II SN-GoGn (°), Ex: −1.1 ± 2.5; Nonex: −0.4 ± 2.1; P = 0.446 Me-PP (mm),Ex: +2.6 ± 2.3; Nonex: +3.5 ± 2.1; P = 0.263 N-Me (mm), Ex: +4.6 ± 2.9; Nonex: +5.7 ± 4.3; P = 0.445 ANS-Me (mm), Ex: +2.3 ± 2.3; Nonex: +3.3 ± 2.0; P = 0.217 |
There is no difference between extraction and nonextraction treatment in dental Class I and Class II, 1 normodivergent patients. |
| Hosseinzadeh-Nik et al (2016) Retrospective |
4 first premolar Ex vs Nonex | Pog-SN7 (mm), Ex: −0.4 ± 9.8; Nonex: −1.0 ± 6.9; P = 0.833 B-SN7 (mm), Ex: +2.0 ± 8.3; Nonex: −0.4 ± 6.5; P = 0.341 |
There is no difference between extraction and nonextraction treatment in dental Class I bimaxillary protrusion patients. |
| Katsaros et al (1996) Retrospective |
4 premolar Ex (NA) vs Nonex | SN-GoMe (°), Ex: −0.8 ± 2.7; Nonex: −0.3 ± 2.2; P = 0.431 PP-GoME (°), Ex: −1.2 ± 2.9; Nonex: −1.1 ± 3.0; P = 0.894 |
There is no difference between extraction and nonextraction treatment in dental Class II, 1 hyperdivergent patients. |
| Kirschneck et al (2015) Retrospective |
4 first premolar Ex vs Nonex | SN-GoGn (°), Ex: −0.9 ± 2.3; Nonex: −1.1 ± 2.5; P = 0.770 PP-GoGn (°), Ex: −1.2 ± 2.7; Nonex: −0.9 ± 2.4; P = 0.680 |
There is no difference between extraction and nonextraction treatment in hyperdivergent patients of varying malocclusion. |
| Kocadereli (1999) Retrospective |
4 first premolar Ex vs Nonex | SN-GoGn (°), Ex: +0.1 ± 3.5; Nonex: +0.3 ± 2.8; P = 0.790 FMA (°), Ex: −0.4 ± 3.2; Nonex: +0.1 ± 3.0; P = 0.412 N-Me (mm), Ex: +4.7 ± 5.0; Nonex: +6.0 ± 5.1; P = 0.234 ANS-Me (mm), Ex: +2.9 ± 3.2; Nonex: +3.8 ± 3.7; P = 0.292 |
There is no difference between extraction and nonextraction treatment in dental Class I hyperdivergent patients. |
| Kumari and Fida (2010) Retrospective |
4 first premolar Ex vs Nonex |
FMA (°), Ex: −0.2; Nonex: +0.6; P >0.050 N-Me (mm), Ex: +1.5; Nonex: +5.5; P <0.05 ∗ N-ANS/ANS-Me, Ex: 0.0, Nonex: +1.1; P >0.050 |
There is a statistically significant increase in N-Me distance (4 mm) in the nonextraction compared with extraction treatment in skeletal Class I hyperdivergent patients; no difference was detected in FMA angle and N-ANS/ANS-Me ratio. |
| Luppanapornlap and Johnston (1993) Retrospective |
4 first premolar Ex vs Nonex | FMA (°), Ex: −0.2, Nonex: +0.7; P >0.050 N-Me (mm), Ex: +5.4; Nonex: +5.0; P >0.050 ANS-Me (mm), Ex: +2.7, Nonex: +3.4; P >0.050 |
There is no difference between extraction and nonextraction treatment in dental Class II, 1 patients. |
| Paquette et al (1992) Retrospective |
4 first premolar Ex vs Nonex | FMA (°), Ex: +0.3; Nonex: −2.0; P <0.010 ∗ N-Me (mm), Ex: +5.4; Nonex: +7.0; P >0.050 ANS-Me (mm), Ex: +3.0, Nonex: +3.9; P >0.050 |
There is a statistically significant, but clinically questionable decrease in FMA angle (2.3°) in the nonextraction compared to extraction treatment in dental Class II, 1 normodivergent patients; no difference was detected in N-Me or ANS-Me distance. |
| Porto et al (2012) Retrospective |
4 first premolar Ex vs Nonex | SN-GoGn (°), Ex: −0.9 ± 2.4; Nonex: +0.8 ± 2.3; P = 0.020 ∗ FMA (°), Ex: −0.3 ± 3.1; Nonex: +0.7 ± 2.5; P = 0.240 |
There is a statistically significant, but clinically questionable increase in SN-GoGn angle (1.7°) in nonextraction compared with extraction treatment in dental Class II, 1 hyperdivergent patients; no difference was detected in FMA angle. |
| Sivakumar and Valiathan (2008) Retrospective |
4 first premolar Ex vs Nonex | FMA (°), Ex: +0.5 ± 1.7; Nonex: +0.1 ± 2.0; P = 0.985 N-Me (mm), Ex: +2.3 ± 3.0; Nonex: +0.9 ± 2.1; P = 0.033 ∗ ANS-Me (mm), Ex: +1.3 ± 1.3; Nonex: +0.6 ± 1.8; P = 0.080 |
There is a statistically significant, but clinically questionable increase in N-Me distance (1.4 mm) in the extraction compared with nonextraction treatment in dental Class I normodivergent patients; no difference was detected in FMA angle and ANS-Me distance. |
| Staggers (1994) Retrospective |
4 first premolar Ex vs Nonex | MP-HP (°), Ex: +0.1 ± 2.5; Nonex: +0.1 ± 2.0; P = 0.950 N-Me (mm), Ex: +5.4 ± 4.7; Nonex: +5.1 ± 3.6; P = 0.740 N-ANS/ANS-Me, Ex: −1.4 ± 3.8; Nonex: −2.7 ± 3.2; P = 0.090 |
There is no difference between extraction and nonextraction groups in dental Class I patients. |
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