Introduction
The aims of this meta-analysis were to quantify and to compare the amounts of distalization and anchorage loss of conventional and skeletal anchorage methods in the correction of Class II malocclusion with intraoral distalizers.
Methods
The literature was searched through 5 electronic databases, and inclusion criteria were applied. Articles that presented pretreatment and posttreatment cephalometric values were preferred. Quality assessments of the studies were performed. The averages and standard deviations of molar and premolar effects were extracted from the studies to perform a meta-analysis.
Results
After applying the inclusion and exclusion criteria, 40 studies were included in the systematic review. After the quality analysis, 2 articles were classified as high quality, 27 as medium quality, and 11 as low quality. For the meta-analysis, 6 studies were included, and they showed average molar distalization amounts of 3.34 mm with conventional anchorage and 5.10 mm with skeletal anchorage. The meta-analysis of premolar movement showed estimates of combined effects of 2.30 mm (mesialization) in studies with conventional anchorage and −4.01 mm (distalization) in studies with skeletal anchorage.
Conclusions
There was scientific evidence that both anchorage systems are effective for distalization; however, with skeletal anchorage, there was no anchorage loss when direct anchorage was used.
For Class II malocclusion, several forms of correction produce different dental and skeletal effects depending on the type of treatment. When the problems of this malocclusion are predominantly skeletal, it is likely to be corrected by functional or mechanical orthopedic appliances. However, to achieve satisfactory results, these protocols usually require patient compliance in using the appliances. Lack of compliance can increase treatment time and create an uneasy relationship between parents, patient, and doctor, thus compromising the final treatment result. When the problems of Class II malocclusions are predominantly dental, these malocclusions can be corrected by extractions in at least 1 dental arch, without extractions by using intermaxillary elastics, or by distalizing the maxillary molars to create a Class I relationship.
For several years, the extraoral appliance was the most widely used distalizing device, but it is no longer esthetically acceptable. Also, it is removable and depends on patient compliance, which can compromise the results. Therefore, as alternatives to compliance-dependent headgear, many intraoral methods to distalize the maxillary molars have been proposed, such as repelling magnets, distal jet appliance, Jones jig appliance, nickel-titanium coil springs, pendulum and pendex appliances, Wilson bimetric distalizing arch system (Rocky Mountain Orthodontics, Denver, Colo), first class appliance (Leone, Firenze, Italy), and others, giving clinicians a wide variety of treatment options.
Intraoral appliances have proven to be effective for maxillary molar distalization independently of patient compliance. However, distalizers generally use the Nance button as anchorage, but it is not enough to neutralize the side effects of anchorage loss, represented by maxillary anterior crowding, maxillary incisor labial inclination increasing the overjet, and tipping of premolars and canines.
To prevent anchorage loss, mini-implants can be used as an efficient skeletal anchorage unit for molar distalization, decreasing the side effects with more predictable results and less treatment time, and consequently creating a new perspective in intraoral distalizer appliances.
Previously, 2 systematic reviews on the use of noncompliance distalizing intramaxillary appliances with conventional anchorage and skeletal anchorage were performed. However, there is still no comparison between the efficiency of these 2 techniques of anchorage.
The aims of this meta-analysis were to quantify and to compare the amounts of molar distalization and anchorage loss of conventional and skeletal anchorage methods in the correction of Class II malocclusion with intraoral distalizers.
Material and methods
This systematic review/meta-analysis was based on the PRISMA guidelines, and the main question was defined with the PICO format ( Table I ). Using the main terms distalizers , distalization appliance , orthodontic distalization , noncompliance appliances , first molar distalization , upper molar distalization , and maxillary molar distalization , an electronic search was conducted from 1970 to September 2010 in the following databases: PubMed, Embase, Web of Science, Scopus, and Cochrane Library ( Table II ).
| Population | Subjects with Class II malocclusion |
| Intervention | Intraoral distalizers with conventional anchorage |
| Comparison | Intraoral distalizers with skeletal anchorage |
| Outcome | Efficiency in the correction of Class II malocclusion |
| Database | Key words | Limits |
|---|---|---|
| PubMed | Distalizers OR distalization appliance OR orthodontic distalization OR noncompliance appliances OR first molar distalization OR upper molar distalization OR maxillary molar distalization | English language; humans, 1970 to September 2010 |
| Embase | Distalizers OR distalization appliance OR orthodontic distalization OR noncompliance appliances OR first molar distalization OR upper molar distalization OR maxillary molar distalization | Only English; humans, 1970 to September 2010 |
| Web of Science | Distalizers OR distalization appliance OR orthodontic distalization OR noncompliance appliances OR first molar distalization OR upper molar distalization OR maxillary molar distalization | English language; only articles (not reviews, letters, abstracts, meetings, and editorials);1970 to September 2010 |
| Scopus | Distalizers OR distalization appliance OR orthodontic distalization OR noncompliance appliances OR first molar distalization OR upper molar distalization OR maxillary molar distalization | English language; only articles (not reviews, letters, abstracts, meetings, and editorials);1970 to September 2010 |
| Cochrane Library | Distalizers; distalization and appliance; orthodontic and distalization; noncompliance and appliances, first and molar and distalization; upper and molar and distalization; maxillary and molar and distalization |
To identify potential articles, the initial search was performed by title and abstract. Initially, the selected articles were preferred to have the following inclusion criteria: published in English, human clinical trial, regarding the correction of Class II malocclusion with noncompliance molar distalization appliances, no reviews or opinion articles, no annals, and no theses. Duplicate studies were eliminated. The selection process was independently conducted by 2 researchers (R.H.C.G. and M.P.P.), and their results were compared to identify discrepancies.
When the abstract did not provide enough information to make a decision, the article was completely analyzed. Interexaminer conflicts were resolved by discussion of each article to reach a consensus regarding all selection criteria. Furthermore, hand searches of the reference lists of the selected articles were conducted.
At this stage, the previously selected articles were rescreened according to the following additional inclusion criteria: correction of Class II malocclusion with a noncompliance molar distalization appliance without concomitant use of other appliances, description of measurable pretreatment and posttreatment cephalometric variables, measurement of the amount of first or second premolar anchorage loss (mesial movement), minimum of 10 patients in each sample group, no case reports, and growing patients.
The quality of each article was scored by using an adapted version of 3 methods previously used by Fudalej and Antoszewska, Cozza et al, and Chen et al. The following characteristics were evaluated: study design, sample size, sample description, error analysis, and statistical analysis. Each characteristic received a score according to the criteria described in Table III . The quality of each study was categorized as high (7-9 points), medium (4-6 points), or low (0-3 points).
| Study design 3 points: randomized clinical trial 2 points: if randomization process was not well described, or if it was a controlled prospective study 1 point: uncontrolled prospective study 0 point: retrospective study or not mentioned |
| Sample size 1 point: larger than or equal to 15 subjects or prior estimate of sample size 0 point: less than 15 subjects and no prior estimate of sample size |
| Sample description 2 points: description of all 3 items (age, sex, Class II malocclusion severity) 1 point: only 2 items described 0 point: only 1 item described |
| Error analysis 1 point: error analysis value cited 0 point: error analysis value not cited, or error analysis not performed |
| Statistical analysis 2 points: adequate 1 point: partially adequate 0 point: no statistical tests conducted |
The data from the selected articles were divided into 2 groups according to the type of anchorage used: conventional or skeletal. There was no distinction between the different types of distalizers.
A meta-analysis was performed according to a method proposed by Antonarakis and Kiliaridis and Perillo et al. Data from each group (conventional and skeletal anchorage) were individually compared with a control group in which the average was zero. Among untreated subjects, these variables are about zero because of the short time of distalization. The standard deviation is equal to the method error in the corresponding study. In studies that did not mention the method error, the mean error from studies that gave the data was used. Only articles of medium and high quality were included in the meta-analysis. The averages and standard deviations of molar and premolar movements were extracted from the articles and subsequently entered into RevMan software (version 5.0 for Windows; Nordic Cochrane Centre, Copenhagen, Denmark) to perform the meta-analysis.
Heterogeneity was assessed by calculating the I 2 index. If there was evidence of heterogeneity, the random effects model should be used. Forest plots were drawn, mean and confidence interval values were calculated (95% confidence interval), and significance tests were carried out (to calculate P values).
Results
After the electronic database search, 947 studies were retrieved from PubMed, 138 from Embase, 151 from Web of Science, and 185 from Scopus. No studies were identified from the Cochrane Library ( Fig 1 ). After application of the initial inclusion and exclusion criteria and elimination of studies indexed in more than 1 database, 178 were retrieved. The full texts were accessed, and all articles with adult patients (age, ≥18 years), sample size less than 10 in at least 1 group, no evaluation of anchorage loss through premolar mesial movement and of lateral cephalometric radiographs taken immediately after molar distalization, and measurements of only dental casts were excluded. Therefore, 40 studies fulfilling all inclusion and exclusion criteria were included in this systematic review ( Fig 1 ).
From the remaining articles, we independently extracted the following data: author names, year of publication, anchorage method, type of distalizing appliances, sample size, mean age of groups, distalizer treatment time, and amounts of molar and premolar distalization and tipping.
Molar distalization with conventional anchorage was evaluated in 36 studies, and with skeletal anchorage in 6. Two studies evaluated both types of anchorage and were therefore subdivided and separately inserted in the table. The summarized data of the 40 articles included in the review are shown in Table IV .
| Number | Study | Appliance | Anchorage | n | Average age (y) | Distalization treatment time (mo) | Molar distalization (mm) | Molar tipping (°) | Premolar movement (mm) | Premolar tipping (°) |
|---|---|---|---|---|---|---|---|---|---|---|
| Conventional anchorage | ||||||||||
| 1 | Papadopoulos et al, 2010 | First class | Nance button | 15 | 9.2 | 4.3 | −4 | −8.56 | 1.86 | 1.85 |
| 2 | Acar et al, 2010 | Pendulum | Nance button | 15 | 15.0 | 3 | −4.53 | −5.13 | 0.27 | 2.2 |
| 3 | Haq et al, 2010 | Distal jet | Nance button | 30 | 12.8 | 7.11 | −2.93 | −3.41 | 0.95 | 7.33 |
| 4 | Patel et al, 2009 | Jones jig | Nance button | 20 | 13.2 | 10.92 | −3.12 | −9.54 | 2.55 | 9.29 |
| 5 | Patel et al, 2009 | Pendulum | Nance button | 20 | 13.9 | 14.16 | −3.51 | −10 | 2.23 | 2.37 |
| 6 | Polat-Ozsoy et al, 2008 | Pendulum | Nance button | 17 | 13.6 | 5.1 | −2.7 | −5.3 | 2.3 | 3.8 |
| 7 | Schütze et al, 2007 | Pendulum | Nance button | 15 | 12.6 | 8.46 | −3.83 | −6.45 | 1.18 | −1.94 |
| 8 | Önçağ et al, 2007 | Pendulum | Nance button | 15 | – | 7.25 | −5.03 | −6 | 2.16 | 2.98 |
| 9 | Angelieri et al, 2006 | Pendulum | Nance button | 22 | 14.5 | 5.85 | −2 | −9.4 | 3.6 | 6.6 |
| 10 | Fuziy et al, 2006 | Pendulum | Nance button | 31 | 14.6 | 5.87 | −4.6 | −18.5 | 2.65 | 2.5 |
| 11 | Mavropoulos et al, 2006 | Keles slider | Nance button | 20 | 13.1 | 4.37 | −3.1 | −4 | 3.2 | 6.1 |
| 12 | Sayinsu et al, 2006 | Keles slider | Nance button | 17 | 13.5 | – | −2.85 | −2.56 | 2 | 2.21 |
| 13 | Chiu et al, 2005 | Pendulum | Nance button | 32 | 12.5 | 7 | −6.1 | −10.7 | 1.4 | −1.7 |
| 14 | Chiu et al, 2005 | Distal jet | Nance button | 32 | 12.3 | 10 | −2.8 | −5 | 2.6 | 0.3 |
| 15 | Kinzinger et al, 2005 | Pendulum | Nance button | 10 | 9.9 | 6.22 | −3.93 | −6.35 | 1.05 | 0.7 |
| 16 | Kinzinger et al, 2005 | Pendulum | Nance button | 10 | 11.6 | 4.45 | −3.43 | −5.05 | 1.4 | −0.4 |
| 17 | Kinzinger et al, 2005 | Pendulum | Nance button | 10 | 12.6 | 5.95 | −4.20 | −2.55 | 0.8 | −1.8 |
| 18 | Mavropoulos et al, 2005 | Jones jig | Nance button | 10 | 13.2 | 4.37 | −1.9 | −6.8 | 2.08 | 7.5 |
| 19 | Ferguson et al, 2005 | Distal jet | Enlarged acrylic Nance button | 25 | 12.5 | 7.87 | −3.4 | −3.2 | 1 | 3.1 |
| 20 | Ferguson et al, 2005 | Greenfield | Enlarged acrylic Nance button | 25 | 11.5 | 10.4 | −3.9 | −6.5 | 2.9 | 0.2 |
| 21 | Fortini et al, 2004 | First class | Modified acrylic Nance button | 17 | 13.4 | 2.4 | −4.0 | −4.6 | 1.7 | 2.2 |
| 22 | Papadopoulos et al, 2004 | Jig appliance modified | Modified acrylic Nance button | 14 | 13.4 | 4.12 | −1.4 | −6.8 | 2.6 | 8.1 |
| 23 | Taner et al, 2003 | Pendex | Nance button | 13 | 10.6 | 7.31 | −3.81 | −11.77 | 0.73 | 4.08 |
| 24 | Bolla et al, 2002 | Distal jet | Nance button | 20 | 12.6 | 5 | −3.2 | −3.1 | 1.3 | 2.8 |
| 25 | Paul et al, 2002 | Jones jig | Nance button | 11 | 14.8 | 6 | −1.17 | −4.56 | 0.18 | – |
| 26 | Nishii et al, 2002 | Distal jet | Nance button | 15 | 14.6 | 6.4 | −2.4 | −1.9 | 1.4 | – |
| 27 | Chaqués-Asensi and Kalra, 2001 | Pendulum | Nance button | 26 | 11.2 | 6.5 | −5.3 | −13.06 | 2.21 | 4.84 |
| 28 | Ngantung et al, 2001 | Distal jet | Nance button | 33 | 12.8 | 6.7 | −2.12 | −3.26 | 2.6 | −4.33 |
| 29 | Keles, 2001 | Keles slider | Nance button with an anterior bite plane | 15 | 13.3 | 6.1 | −4.92 | −0.89 | 1.31 | 1.25 |
| 30 | Toroğlu et al, 2001 | Pendulum | Nance button | 14 | 13.1 | 5.7 | −5.9 | −14.9 | 4.8 | 3.9 |
| 31 | Toroğlu et al, 2001 | Pendulum | Nance button | 16 | 12.9 | 5.03 | −4.1 | −13.4 | 6.6 | 5.9 |
| 32 | Bussick and McNamara, 2000 | Pendulum | Nance button | 101 | 12.0 | 7 | −5.7 | −10.6 | 1.8 | 1.5 |
| 33 | Üçem et al, 2000 | 3D-BMDA | Intermaxillary elastic system | 14 | 12.2 | 1.5 | −3.5 | −1.8 | 2.1 | 1.4 |
| 34 | Brickman et al, 2000 | Jones jig | Nance button | 72 | 13.7 | 6.35 | −2.51 | −7.53 | 2 | 4.76 |
| 35 | Haydar and Üner, 2000 | Jones jig | Nance button | 10 | 10.7 | 2.5 | −2.80 | −7.85 | 3.35 | 6.05 |
| 36 | Keles and Sayinsu, 2000 | IBMD | Nance button | 15 | 13.5 | 7.5 | −5.23 | −1.15 | 4.33 | −2.73 |
| 37 | Bondemark, 2000 | Nickel-titanium coil | Nance button | 21 | 14.4 | 6.5 | −2.5 | −2.2 | 1.2 | 2.1 |
| 38 | Bondemark, 2000 | Repelling magnets | Nance button | 21 | 13.9 | 5.8 | −2.6 | −8.8 | 1.8 | 6.7 |
| 39 | Runge et al, 1999 | Jones jig | Nance button | 13 | 14.5 | 6.5 | −2.23 | −4 | 2.23 | 9.47 |
| 40 | Gulati et al, 1998 | Sectional jig assembly | Nance button | 10 | 12-15 | 4 | −2.95 | −3.5 | 1.05 | 2.6 |
| 41 | Byloff and Darendeliler, 1997 | Pendulum | Nance button | 13 | 11.1 | 4.15 | −3.39 | −14.5 | 1.63 | – |
| 42 | Byloff et al, 1997 | Pendulum | Nance button | 20 | 13.1 | 6.81 | −4.14 | −6.07 | 2.22 | – |
| 43 | Ghosh and Nanda, 1996 | Pendulum | Nance button | 41 | 12.4 | 6.2 | −3.37 | −8.36 | 2.55 | 1.29 |
| Skeletal anchorage | ||||||||||
| 1 | Kinzinger et al, 2009 | Distal jet | 2 mini-implants | 10 | 12.1 | 6.7 | −3.92 | −3 | 0.72 | 0.79 |
| 2 | Oberti et al, 2009 | Dual force | 2 mini-implants used in maxillofacial surgery for osteosynthesis + Nance button | 16 | 14.3 | 5 | −5.9 | −5.68 | −4.26 | −5.43 |
| 3 | Polat-Ozsoy et al, 2008 | Pendulum | 1 or 2 mini-implants + Nance button | 22 | 13.6 | 6.8 | −4.8 | −9.1 | −4.1 | −9.9 |
| 4 | Önçağ et al, 2007 | Pendulum | 1 implant | 15 | – | 6.75 | −3.95 | −12.2 | −3.1 | −6.795 |
| 5 | Escobar et al, 2007 | Pendulum | 2 mini-implants + Nance button | 15 | 13.0 | 7.8 | −6.00 | −11.31 | −4.85 | −8.62 |
| 6 | Kircelli et al, 2006 | Pendulum | 1 or 2 mini-implants + Nance button | 10 | 13.5 | 7 | −6.4 | −10.9 | −5.4 | −16.3 |
Quality assessment
After quality analysis, 2 articles were classified as high quality, 27 as medium quality, and 11 as low quality ( Table V ).
| Number | Study | Study design 0-3 | Sample size 0-1 | Selection description 0-2 | Method error analysis 0-1 | Adequacy of statistical analysis 0-1 | Quality Score 0-9 | Judged quality standard |
|---|---|---|---|---|---|---|---|---|
| Conventional anchorage | ||||||||
| 1 | Papadopoulos et al, 2010 | 3 | 1 | 2 | 1 | 2 | 9 | High |
| 2 | Acar et al, 2010 | 1 | 1 | 1 | 1 | 1 | 5 | Medium |
| 3 | Haq et al, 2010 | 0 | 1 | 1 | 1 | 1 | 4 | Medium |
| 4 | Patel et al, 2009 | 2 | 1 | 2 | 1 | 2 | 8 | High |
| 5 | Polat-Ozsoy et al, 2008 ∗ | 0 | 1 | 1 | 1 | 1 | 4 | Medium |
| 6 | Schütze et al, 2007 | 0 | 1 | 1 | 1 | 2 | 5 | Medium |
| 7 | Önçağ et al, 2007 ∗ | 2 | 1 | 0 | 0 | 1 | 4 | Medium |
| 8 | Angelieri et al, 2006 | 1 | 1 | 2 | 1 | 1 | 6 | Medium |
| 9 | Fuziy et al, 2006 | 1 | 1 | 2 | 1 | 1 | 6 | Medium |
| 10 | Mavropoulos et al, 2006 | 1 | 1 | 1 | 1 | 0 | 4 | Medium |
| 11 | Sayinsu et al, 2006 | 1 | 1 | 1 | 1 | 1 | 5 | Medium |
| 12 | Chiu et al, 2005 | 0 | 1 | 1 | 0 | 1 | 3 | Low |
| 13 | Kinzinger et al, 2005 | 1 | 1 | 1 | 1 | 1 | 5 | Medium |
| 14 | Mavropoulos et al, 2005 | 1 | 0 | 1 | 1 | 0 | 3 | Low |
| 15 | Ferguson et al, 2005 | 0 | 1 | 1 | 1 | 1 | 4 | Medium |
| 16 | Fortini et al, 2004 | 1 | 1 | 1 | 1 | 1 | 5 | Medium |
| 17 | Papadopoulos et al, 2004 | 1 | 0 | 2 | 1 | 2 | 6 | Medium |
| 18 | Taner et al, 2003 | 2 | 0 | 1 | 1 | 1 | 5 | Medium |
| 19 | Bolla et al, 2002 | 0 | 1 | 1 | 1 | 1 | 4 | Medium |
| 20 | Paul et al, 2002 | 3 | 1 | 1 | 0 | 1 | 6 | Medium |
| 21 | Nishii et al, 2002 | 1 | 1 | 1 | 1 | 1 | 5 | Medium |
| 22 | Chaqués-Asensi and Kalra, 2001 | 1 | 1 | 1 | 1 | 1 | 5 | Medium |
| 23 | Ngantung et al, 2001 | 0 | 1 | 2 | 1 | 1 | 5 | Medium |
| 24 | Keles, 2001 | 0 | 1 | 1 | 0 | 1 | 3 | Low |
| 25 | Toroğlu et al, 2001 | 1 | 1 | 1 | 0 | 1 | 4 | Medium |
| 26 | Bussick and McNamara, 2000 | 0 | 1 | 1 | 0 | 1 | 3 | Low |
| 27 | Üçem et al, 2000 | 1 | 0 | 2 | 1 | 1 | 5 | Medium |
| 28 | Brickman et al, 2000 | 1 | 1 | 1 | 0 | 1 | 4 | Medium |
| 29 | Haydar and Üner, 2000 | 2 | 0 | 0 | 0 | 0 | 2 | Low |
| 30 | Keles and Sayinsu, 2000 | 1 | 1 | 1 | 0 | 0 | 3 | Low |
| 31 | Bondemark, 2000 | 0 | 1 | 1 | 1 | 1 | 4 | Medium |
| 32 | Runge et al, 1999 | 0 | 0 | 1 | 0 | 1 | 2 | Low |
| 33 | Gulati et al, 1998 | 1 | 0 | 0 | 1 | 1 | 3 | Low |
| 34 | Byloff and Darendeliler, 1997 | 1 | 0 | 1 | 0 | 1 | 3 | Low |
| 35 | Byloff et al, 1997 | 1 | 1 | 1 | 0 | 1 | 4 | Medium |
| 36 | Ghosh and Nanda, 1996 | 0 | 1 | 1 | 1 | 1 | 4 | Medium |
| Skeletal anchorage | ||||||||
| 1 | Kinzinger et al, 2009 | 1 | 0 | 1 | 0 | 1 | 3 | Low |
| 2 | Oberti et al, 2009 | 1 | 1 | 1 | 0 | 1 | 4 | Medium |
| 3 | Polat-Ozsoy et al, 2008 ∗ | 0 | 1 | 1 | 1 | 1 | 4 | Medium |
| 4 | Önçağ et al, 2007 ∗ | 2 | 1 | 0 | 0 | 1 | 4 | Medium |
| 5 | Escobar et al, 2007 | 1 | 1 | 1 | 0 | 1 | 4 | Medium |
| 6 | Kircelli et al, 2006 | 1 | 0 | 1 | 0 | 1 | 3 | Low |
∗ Both studies compared the effects of the Pendulum on both anchorage types (conventional and skeletal).
Among the high-quality articles, only that by Papadopoulos et al received a full score. These authors evaluated the treatment effects of the first class appliance in patients with Class II malocclusion in the mixed dentition. The study was a randomized clinical trial with a sample of 15 treated children (mean age, 9.2 years). Another 11 subjects served as the control group (mean age, 9.7 years). The first class appliance was placed on the 2 maxillary first molars and the second deciduous molars or the second premolars. A modified Nance butterfly-shaped button was used as anchorage. The mean molar distal movement was 4 mm with distal tipping of 8.56° in 4.01 months. The mean premolar or first deciduous molar mesial movement was 1.86 mm (31.84% of anchorage loss) with 1.85° of tipping. The control group showed distal molar movement of 0.04 mm in the same period.
The other study classified as high quality compared the dentoalveolar changes of Class II patients treated with the Jones jig and the pendulum appliances. Forty Class II malocclusion patients were divided into 2 groups of 20. Group 1 (11 boys, 9 girls), with a mean pretreatment age of 13.17 years, was treated with the Jones jig appliance for 0.91 years, and group 2 comprised 20 patients (8 boys, 12 girls) with a mean pretreatment age of 13.98 years, treated with the pendulum appliance for 1.18 years. The maxillary second premolars showed greater mesial tipping and extrusion in the Jones jig group, indicating more anchorage loss during molar distalization with this appliance. The amounts and the monthly rates of molar distalization were similar in both groups.
According to each criterion for quality analysis, the following results were obtained.
Study design: only 2 studies were randomized clinical trials with the randomization process described in detail.
Sample size: the authors of 30 studies performed sample-size calculation or had sample sizes larger than or equal to 15 patients.
Selection description: 7 studies mentioned the severity of the malocclusions. One article did not mention the mean age, and 2 articles did not mention the sex of the sample.
Error analysis: the authors of 24 studies performed and described the method error results. Some studies stated that the error of the method was performed but did not present the results.
Statistical analyses: the authors of 4 studies performed only a descriptive analysis.
Maxillary molar distalization appliances with conventional anchorage
Treatment effects of distalizers with conventional anchorage were analyzed in 43 groups assessed in 36 studies ( Table IV ).
Fourteen distalizers were used: first class, pendulum, distal jet, Jones jig, dual force, Keles slider, greenfield, jig appliance modified, pendex, 3-dimensional bimetric maxillary distalizing arch (3D-BMDA), intraoral bodily molar distalizer (IBMD), nickel-titanium coil, magnets, and sectional jig assembly. The pendulum appliance was the most used (22 articles), followed by the distal jet (7 articles) and the Jones jig (6 articles). The most used anchorage reinforcement appliance was the Nance button and its variations ( Table IV ).
The included studies evaluated patients during the growth period, and the mean initial chronologic age ranged from 9.2 to 15 years. Treatment times were 1.50 to 14.16 months.
Molars demonstrated distal movements from 1.17 to 6.10 mm with conventional anchorage. The pendulum appliance showed the greatest distalization in 7 months. The least distalization was obtained with the Jones jig in 6 months. The greatest molar distal tipping was 18.5°, and the least was 0.89°.
Anchorage loss could be identified in the studies with conventional anchorage through premolar movement, which showed positive values indicating mesial movement. These values ranged from 0.27 mm in 3 months to 6.6 mm in 5 months with the pendulum appliance. The greatest premolar mesial tipping was 9.47° observed in the study of Runge et al.
Maxillary molar distalization appliances with skeletal anchorage
In 6 studies, the treatment effects of distalizers with skeletal anchorage were analyzed. Four studies used the pendulum appliance to distalize the maxillary molars, one used the distal jet, and the other used the dual force. One or 2 implants or mini-implants were used in the paramedian region of the midpalatal suture as anchorage. The screw was connected to an acrylic plate except in the studies of Kinzinger et al and Önçağ et al ( Table IV ).
The mean initial chronologic age ranged from 12.1 to 14.3 years. One study did not report the mean initial age. Treatment time ranged from 5.0 to 7.8 months.
The mean molar distal movement ranged from 3.9 to 6.4 mm, and the mean molar distal tipping ranged from 3.0° to 12.2°. The greatest distalization was obtained with the pendulum and the smallest with the distal jet.
Studies with mini-implant anchorage showed negative values for premolar movement (−3.1 to −5.4 mm) indicating distal movement of these teeth and no anchorage loss. Only the study of Kinzinger et al showed mesial movement (0.72 mm) and mesial tipping (0.79°) of premolars, indicating anchorage loss even when associated with mini-implants.
No article with skeletal anchorage was classified as high quality, 4 were classified as medium quality, and 2 had low quality ( Table V ).
Meta-analysis
After we assessed the quality of the 36 studies with conventional anchorage included in the systematic review, 34 were rejected because of low or medium quality. Thus, the meta-analysis was conducted with 2 high-quality studies with no heterogeneity (I 2 = 0%). However, in the group with skeletal anchorage, no study had high quality, and 2 articles with low quality were excluded. The meta-analysis was conducted with 4 studies of medium quality, with heterogeneity of I 2 of 82% in the analysis of molar distalization, and of I 2 of 69% in the analysis of premolars.
One study with more than 1 group was subdivided according to the number of groups and separately included in the meta-analysis. Therefore, 3 items were analyzed with conventional anchorage and 4 items with skeletal anchorage.
The meta-analysis of molar distal movement had estimated combined effects of 3.34 mm in studies with conventional anchorage and 5.10 mm in studies with skeletal anchorage ( Figs 2 and 3 ).
