Comparison of the effects of mini-implant and traditional anchorage on patients with maxillary dentoalveolar protrusion

Yanhua Xu; Jiye Xie

doi:10.2319/051016-375.1

Editorial Type:

Article Category: Research Article

Online Publication Date: 29 Sept 2016

Comparison of the effects of mini-implant and traditional anchorage on patients with maxillary dentoalveolar protrusion

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Page Range: 320 – 327

DOI: 10.2319/051016-375.1

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ABSTRACT

Objective: To compare the treatment effects of mini-implants as anchor units with conventional methods of anchorage reinforcement in maxillary dentoalveolar protrusion patients in terms of skeletal, dental, and soft tissue changes.

Materials and Methods: We searched the databases of the Cochrane Library, PubMed, OVIDSP, CBM, VIP, WanFang Data, and CNKI covering December 1966 to March 2016 for randomized controlled trials (RCTs) and clinical controlled trials that compared the treatment effects of mini-implants with conventional anchorage reinforcement in maxillary dentoalveolar protrusion patients. Literature filtering, data extraction, and methodological quality evaluation were finished independently by two researchers and disagreements were solved by discussion. Meta-analysis was performed when possible; otherwise descriptive assessment was done.

Results: Through a predefined search strategy, we finally included 14 eligible studies. Eight outcomes were evaluated in this study: maxillary incisor retraction, maxillary molar movement, U1-SN, SNA, SN-MP, UL-E Plane, NLA and G-Sn-Pg.

Conclusions: Mini-implant anchorage was more effective in retracting the anterior teeth, produced less anchorage loss, and had a greater effect on SN-MP for the high-angle patients than did traditional anchorage. Both mini-implants and traditional anchorage underwent decreases in on U1-SN and SNA. More qualified RCTs are required to make reliable recommendations about the anchorage capacity of mini-implant and traditional anchorage in patients with maxillary dentoalveolar protrusion, especially on the UL-E plane, NLA, and G-Sn-Pg.

Keywords: Systematic review; Implant; Traditional anchorage; Protrusion

INTRODUCTION

Anchorage control in treating severe maxillary dentoalveolar protrusion patients is a difficult problem.¹ Treatment of this malocclusion often includes extraction of maxillary (or bimaxillary) first or second premolars and maximum anchorage.² To reinforce anchorage, various auxiliaries can be used, including a Nance holding arch, headgear, transpalatal arch,³ and others. However, all these methods have inherent disadvantages, such as complicated designs, need for exceptional patient cooperation, and elaborate wire bending.⁴ Thus, some anchorage loss or mesial movement of the maxillary molars is usually observed.

In recent years, the mini-implant has gained enormous popularity in the orthodontic community.⁵Mini-implant is used herein as a generic term for all temporary bone-anchored devices. It can provide stable bony anchorage and overcome problems of anchorage loss during extraction space closure, which usually occurs with traditional methods of anchorage preparation.⁶ However, there is little accurate scientific evidence pertaining to the superiority of the mini-implant anchorage system over traditional anchorage technique in patients with maxillary dentoalveolar protrusion, with the few published studies demonstrating conflicting results. Upadhyay¹ found intrusion and distalization of maxillary molars using mini-implants as anchorage in patients with dentoalveolar protrusion. However, Lai et al.⁷ found that mini-implant anchorage afforded greater anterior tooth retraction and less maxillary molar mesialization than did the headgear.

In clinical practice, orthodontists' concern is which anchorage type—traditional anchorage or the implant—would be more effective.⁸ The aim of this review is to compare the treatment effects with mini-implants in maxillary dental protrusion patients with conventional methods of anchorage reinforcement in terms of dentoskeletal and soft-tissue changes.

MATERIALS AND METHODS

Search Strategy

An electronic literature search was carried out using PubMed, OVIDSP, the Cochrane Library, CBM, VIP, WanFang Data, and CNKI. Terms used in the search included mini-implant, orthodontic anchorage, and protrusion. In order to improve the search, the Related Articles tool was used in the PubMed search.

Inclusion Criteria

Studies were selected if they satisfied all the following inclusion criteria:

Publication date from December 1966 to March 2016,
Original studies based on humans,
Randomized controlled trials (RCTs) or clinical controlled trials (CCTs); prospective or retrospective controlled studies,
Age of patients over 14 years,
Studies conducted on patients with maxillary or bimaxillary dental protrusion, patients whose orthodontic treatment called for extraction of maxillary or bimaxillary premolars, and maximum anchorage during anterior segment retraction,
The experimental group and control group used mini-implants and conventional anchorage as anchorage reinforcement,
Mini-implants were screwed into the buccal alveolar bone between the maxillary second premolars and first molars,
Lateral cephalometric analysis that assessed dental and skeletal movements.

Exclusion Criteria

Trials evaluating only the effects of implant or conventional anchorage,
Studies exploring measurement methods,
Studies concerning other anchorage situations, such as molar distalization,
Case reports, reviews, or letters.

Data Extraction and Quality Analysis

Data were extracted and recorded independently by two reviewers, and in duplicate using a customized data collection form, on the following items: author and year of publication, study design, number, gender, type of malocclusion, anchorage devices, and reported outcomes.

A quality evaluation of the methodological soundness of RCT articles was performed according to the standards described in the Cochrane Handbook for Systematic Reviews of Interventions (version 5.1.0).⁹ Meanwhile, a quality score was calculated by a modified version of the method described by Jadad.¹⁰ Otherwise, a methodological quality assessment of the methodological soundness and quality score of CCT articles was performed according to the standards described in the Cochrane Handbook.⁹ The methods and results sections of each article were read and scored by two independent, blind readers. The evaluators discussed their findings, and when disagreement occurred, it was resolved through further discussion and rereading.

Data Analysis

In this systematic review, evaluation of anchorage effects mainly includes eight aspects, as follows:

maxillary incisor retraction,
maxillary molar movement,
axial inclination of the maxillary central incisor to the SN plane (U1-SN),
angle between the SN plane and the NA plane (SNA),
inclination of the mandibular plane to the cranial base (SN-MP),
upper lip to E-plane (UL-E pane, mm),
nasolabial angle (NLA),
facial convexity (G-Sn-Pg).

Original outcome data, if possible, underwent statistical pooling through fixed or random effects models by using Review Manager 5.3. Statistical analysis was assessed by a statistician, especially regarding the choice between fixed and random-effect models.¹¹

RESULTS

Description of Studies

Finally, we selected 14 studies,^1,4,12–23 including 8 RCTs^1,12–18 and 6 CCTs.^4,19–23 Summary details of included studies are given in Table 1. Flow of the selection process is demonstrated in Figure 1.

Figure 1. Flow chart summarizing literature search.
Citation: The Angle Orthodontist 87, 2; 10.2319/051016-375.1

Methodological Quality of Included Studies

Of the 14 included studies, the 8 RCTs^1,12–18 were of high quality, and the 6 CCTs^4,19–23 were grade B (quality score, 6–9). The methodological quality for RCT and CCT trials are presented in Tables 2 and 3, respectively.

Effects of Interventions

The cephalometric variables investigated in this review are shown in Table 4.

Skeletal Effects

SNA

Eleven articles^1,12,15–23 reported the SNA. A forest plot is demonstrated in Figure 2, showing that there was no significant difference between the mini-implant and the traditional anchorage technique (P = .71) and that the weighted mean difference (WMD) 95% confidence interval (95% CI) was −0.03° (−0.19°, 0.13°).

Figure 2. Meta-analysis of SNA.
Citation: The Angle Orthodontist 87, 2; 10.2319/051016-375.1

SN-MP

Six studies^{1,16,17,20–22} investigated this outcome. Because of existing heterogeneity, a random-effect model was adopted. As presented in Figure 3, the WMD (95% CI) between the two groups was −1.12° (−2.21°, −0.03°), with a significant difference (P = .04).

Dental Effects

Maxillary incisor retraction

Thirteen articles^1,4,13–23 were categorized into this study. The forest plot is shown in Figure 4. The WMD (95% CI) was −1.50 mm (−1.84 mm, −1.17 mm), with a significant difference between the two groups (P < .00001).

Maxillary molar movement

Thirteen articles^{1,4,12–17,19–23} were categorized into this study. A meta-analysis was done (Figure 5). Because of existing heterogeneity (I² = 80%), a random-effect model was adopted. The WMD (95% CI) between the mini-implant and traditional anchorage was −2.01 mm (−2.45 mm, −1.58 mm), and there was a significant difference between the two groups (P < .00001).

U1-SN

Twelve articles^{1,4,12–14,16–22} reported U1-SN. A forest plot is demonstrated in Figure 6. Results of the meta-analysis show significant heterogeneity among these 12 trials (I² = 76%), so a random-effect model was adopted. As shown in Figure 6, the WMD (95% CI) was 0.61° (−0.84°, 2.05°), and results from the two groups showed no statistical significance (P = .41).

Soft Tissue Effects

UL-E plane (mm)

Five articles^{1,16,17,19,23} were categorized into this study. A meta-analysis was done; the forest plot is shown in Figure 7. It indicates that there was a significant difference between the mini-implant and the traditional anchorage technique on the UL-E plane (P = .001); the WMD (95% CI) was −0.73 mm (−1.17 mm, 0.28 mm).

Figure 7. Meta-analysis of UL-E plane.
Citation: The Angle Orthodontist 87, 2; 10.2319/051016-375.1

NLA. Four articles^1,16,17,23 reported the nasolabial angle. A forest plot is demonstrated in Figure 8. Heterogeneity was detected, so a random-effect model was adopted. The meta-analysis indicates that there was a significant difference between the mini-implant and traditional anchorage technique (P = .003); the WMD (95% CI) was 3.52° (1.17°, 5.87°).

Figure 8. Meta-analysis of NLA.
Citation: The Angle Orthodontist 87, 2; 10.2319/051016-375.1

G-Sn-Pg

Three articles^1,17,23 were categorized into this study. The meta-analysis is shown in Figure 9. The result was that the WMD (95% CI) between the two groups was −0.77° (−1.55°, −0.02°), and there was no statistical significance (P = .06).

DISCUSSION

Skeletal Effects of Intervention

SNA

Results showed that both groups underwent decreases in SNA. This indicates that point A moved back during retraction of the maxillary incisor. Moreover, the meta-analysis showed that there was no significant difference. Therefore, both anchorage methods produced significant basal bone changes.