Questions

The purpose was to examine the effectiveness of miniscrew-supported appliances for maxillary molar distalization in Class II malocclusion. The research question of the present systematic review was defined according to the PICO format as:

• P (Population / Patients): Subjects with Class II malocclusion treated by maxillary molar distalization, only humans.

• I (Intervention): Miniscrew appliance in maxillary molar distalization.

• C (Comparison): Subjects not receiving any treatment or treated with other molar distalizing appliance.

• O (Outcome): Molar distalization in mm.

Study Eligibility

Included studies were published in the English language only and investigated the effectiveness of miniscrew-supported appliances for maxillary molar distalization in Class II malocclusion. Papers were excluded at this stage if they were editorial letters, case reports, in vitro, or not investigating the effectiveness of miniscrew-supported appliances for maxillary molar distalization in Class II malocclusion.

Study Identification

Research databases were searched including: Cochrane library (Cochrane review, Trails), Medline (PubMed, Ovid MEDLINE, and EBSCO), Embase (European studies, pharmacological literature, conference abstract), Web of Knowledge (Social science, conference abstract), Scopus (Conference abstracts, scientific web pages), CINAHL (Nursing and allied health), PsycINFO (Psychology and psychiatry), ERIC (Education) using key terms focused on the specific search strategy (Molar distalization, molar distal shift, Class II malocclusion, miniscrew, miniscrew implants, temporary anchorage device [TAD], intraoral extradental anchorage system, mini implants, screw, and orthodont). For gray literature, the following databases were searched: Google scholar, Open Grey, National Library of Medicine, Social science research, For thesis (EThOS, DART-Europe), Institutional repositories (OpenDOAR, Bielefeld Base, Lenus, RIAN, e-publications@RCSI). To supplement the searches, the tables of content of four key orthodontic journals (American Journal of Orthodontics and Dentofacial Orthopedics, The Angle Orthodontist, European Journal of Orthodontics, and Journal of Clinical Orthodontics) were searched for relevant articles. No beginning date was used, and the last date of the search was January 30, 2017. Additional studies were searched in the reference lists of all articles included.

Study Selection

All titles and abstracts were screened independently and in duplicate for inclusion. In the event of disagreement or insufficient information in the abstract, the full text of potential articles was reviewed independently and in duplicate. The interrater agreement for study inclusion, as assessed using an intraclass correlation coefficient, was 0.75. Conflicts were resolved by consensus discussion between the two reviewers. For retrospective studies, risk of bias was evaluated using the Quality Assessment Tool for Quantitative Studies,^29,30 and, for prospective studies, risk of bias was evaluated using the Newcastle–Ottawa Scale.³¹

Data Extraction

Data were extracted independently and in duplicate for all variables and conflicts were resolved by consensus. The methodological quality of the retrospective studies was graded by means of the Quality Assessment Tool for Quantitative Studies developed for the Effective Public Health Practice Project (EPHPP), Canada, as adapted by Thomas et al.^29,30 This tool consists of six criteria: selection bias, study design, confounders, blinding, data collection method, and withdrawals/dropouts. Each criterion was rated as strong, moderate, or weak according to the dictionary of the tool; the overall assessment of the study is determined by assessing these ratings. According to the guidelines for the tool, studies with no weak rating and four strong ratings are classified as “strong;” studies with fewer than four strong ratings and one weak rating are classified as “moderate;” and studies with two or more weak ratings are classified as “weak.” Two reviewers independently performed the assessment of the quality of the included studies. Any discrepancies in quality ratings were resolved by discussion and consensus. The methodological quality of the prospective studies was assessed by means of the Newcastle–Ottawa Scale.^31,32 Using this “star system,” the quality of each included prospective study was assessed using the following criteria: study group selection (it included four items, with a maximum of one star for each item), the comparability (one item with two stars maximum), and outcome and follow-up (three items with a maximum of one star for each item). If the total quality score was 0 to 5, the article was rated as low quality and if the total quality score was 6 to 9, the article was rated as high quality.

Data Synthesis

Two reviewers did data extraction independently for the included studies, and any discrepancies were resolved by discussion and consensus. The following data were extracted from each included study: first author, publication year, study type, study quality, length and diameter of the miniscrew used, screw number, site of placement, duration of treatment, sample size, statistical analysis used, the authors' conclusion, molar distal movement, premolar mesial movement, incisor mesial movement, molar distal tipping, premolar vertical movement, and incisor vertical movement.

Trial Flow

Using the search strategy, 286 articles were identified (Table 1) with an additional 12 identified from the review of references and journal indices. From these, 14 articles were identified for inclusion in the present systematic review (Figure 1).

Table 1 Search Strategy of the Databases

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Study Characteristics and Study Quality

The Newcastle–Ottawa Scale rated seven studies as high quality and three studies as low quality (Table 2). The Quality Assessment Tool for Quantitative Studies rated all the four included retrospective studies as moderate (Table 3). The studies were fairly recent, with the oldest study published in 2004. All of the included studies were published in English. From the 14 studies selected for this review, a self-drilling placement method was used in seven (50%) studies and a self-tapping method in seven (50%) studies (Table 4). The number of miniscrews per subject ranged from one to two. Miniscrews with various brand names were used in the present review, with thread diameters from 1.3 to 2.2 mm and thread lengths from 7.0 to 14.0 mm. The number of study participants ranged from 10 to 57 (total n = 414), with a mean of 29.57. The mean treatment duration varied from 4.6 months to 11.27 months. Distalization force applied/quadrant varied from 200 g to 400 g. In the majority (85.71%) of the studies, the paramedian palate was used to place the miniscrews (Table 5).

Table 2 Risk of Bias Assessment of Included Prospective Studies Using The Newcastle–Ottawa Scale^a

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Table 3 Risk of Bias Assessment of Included Retrospective Studies^a

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Table 4 Descriptive Data of Included Studies^a

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Table 4 Extended

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Table 5 Summary of Dimensions of Miniscrew Used for Distalization, Sample Size, Treatment Duration, Distalization Force Used, Skeletal Anchorage Site, and Analysis Used^a

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Table 5 Extended

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Table 6 shows the results of the included studies. The mean molar distalization values varied from 1.8 mm to 6.4 mm. The largest distalization effects (6.4 mm) were achieved by Kircelli using the miniscrew-supported pendulum appliance. The shortest linear distalization (1.8 mm) measurements were reported by Bechtold et al. with one miniscrew in the interradicular area. The mean distal tipping of molars varied from 1.65° degrees to 11.3°. The highest extent of distal tipping (11.3°) was recorded by Escobar et al. The mean distal movement of premolars and incisors varied from 1.75 mm to 5.4 mm and 0.1 mm to 2.7 mm, respectively (Table 6).

Table 6 Summary of Results of Included Studies (Molar Distal Movement and Distal Tipping; Premolar and Incisor Mesial Movement; and Mesial Tipping, Molar, Premolar, and Incisor Vertical Movement)^a

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Effects on Molar Distalization, Tipping, and Vertical Movement

In the present review, the molars were distalized with a mean value varying from 1.87 mm to 6.4 mm, with the highest (6.4 mm) distalization observed by Kircelli et al.¹⁷ Distal tipping of the molars varied from 1.65° to 11.3°. Distal tipping of the molar was minimal when the distalizing force was applied palatally as the reactive forces were located gingivally, close to the center of resistance of the molar.^24,25 Cozzani et al. compared the distal screw appliance with the MGBM system⁷ and distal jet appliance.⁶ The results showed that distal tipping of the molars was minimal with the distal screw with more bodily movement of the molars. This might possibly be related to the rigidity of the distalizing arms and the point of the force application with respect to the center of resistance of the molar. Vertical movement of the maxillary molar was minimal and the miniscrew-supported appliance caused both maxillary molar intrusion and extrusion. The mean rate of intrusion varied from 0.1 mm to 1.4 mm. This may be due to the fact that dentoalveolar vertical growth was prevented by the rigid bonded appliance or by the intrusive force exerted by the tongue. The studies by Kircelli et al.,¹⁷ Escobar et al.,¹⁹ and Sar et al.,¹⁸ who used a miniscrew-supported pendulum appliance, showed extrusion of the maxillary molars with mean values from 0.1 mm to 2.7 mm.

Single Screw vs Dual Miniscrew Effect on Molar Distalization

In the present review, studies^20,27 which compared single vs dual miniscrews for molar distalization showed greater molar distalization in the dual screw group compared to the single screw group. Polat-Ozsoy et al.²⁰ used one screw in nine subjects and two screws in 12 subjects, and showed overall success was greater in subjects with two screws. This may be attributed to the double magnitude of force from using a dual screw.

Miniscrew in Interradicular Area vs Midpalatine

The paramedian palate is a favored site for miniscrew placement because it has an adequate bone mass which in-turn reduces the risk of damage to anatomic structures such as dental roots, nerves, and blood vessels.²³ In the present review, 11 studies used the paramedian region of the palate to place miniscrews. Appliances with miniscrews placed in the paramedian palate caused distal movement of the molars by more than 5 mm without undesirable side effects on the premolars and incisors. The main limitation with the placement of miniscrews in the anterior part of the palate is that this procedure is complex to place and remove the screws. Extensive molar distal movement is difficult to achieve with interradicular miniscrews because the screws would come in contact with the surrounding root during tooth movement.^21,27

Effects on the Premolars and Incisor/Anchorage Unit

The conventional anchorage setup in noncompliance molar distalization includes the use of acrylic buttons on the palatal mucosa by using the periodontium of anchorage teeth.¹⁰ The disadvantages of this kind of anchorage include, in particular, restrictions to hygiene and contraindications based on certain dentition stages and local situations. Alternative anchorage components for molar distalization appliances include titanium miniscrews of small diameter and orthodontic implants of short length. In comparison to mini implants, miniscrews are less expensive and less invasive.^6,7 Miniscrew anchorage not only causes distal movement of premolars, but also prevents flaring of maxillary incisors, an undesirable side effect of molar distal movement, but could also cause significant distal movement of the incisors. In the present systematic review, eight out of 14 studies showed distalization of premolars and incisors and the mean distal movement of premolars and incisors varied from 1.75 mm to 5.4 mm and 0.1 mm to 2.7 mm, respectively. This may be attributed to the fact that the reactive forces arising from the appliances were directly resisted by an intraosseous screw, the premolars were free from any attachment, and they drifted distally via transseptal fibers during the distalization period.

Limitations

The limitations of the present review were due to heterogeneity across the studies a meta-analysis of the included studies could not be performed. Therefore, no forest plots or funnel plots were constructed. Due to the disparate nature of the studies, only simple descriptive and stratified comparisons were reported.