Systematic Review The effectiveness of non-surgical maxillary ...

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Jul 4, 2013 - CONCLUSiONS: SME is effective in expanding maxillary arch, while we cannot ... maxillary expansion techniques can be divided into rapid.
European Journal of Orthodontics 36 (2014) 233–242 doi:10.1093/ejo/cjt044 Advance Access publication 4 July 2013

© The Author 2013. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: [email protected]

Systematic Review The effectiveness of non-surgical maxillary expansion: a meta-analysis Yang Zhou, Hu Long, Niansong Ye, Junjie Xue, Xin Yang, Lina Liao and Wenli Lai Department of Orthodontics, State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan, China Correspondence to: Wenli Lai, Department of Orthodontics, State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, No. 14, Section 3, Ren Min South Road, Chengdu, Sichuan 610041, China. E-mail: [email protected] Summary Objective:  To evaluate and compare the effectiveness of rapid maxillary expansion (RME) and slow maxil-

lary expansion (SME).

Materials and methods:  PubMed,

Introduction Transverse maxillary discrepancy, presented with posterior crossbite and/or crowding, is a common malocclusion among adolescents and adults (Proffit et al., 1998). Pertinent maxillary expansion appliances were devised to expand the constricted maxillae (Haas, 1965). Since their introduction in 1860s (Angell, 1860), they have been gaining more and more popularity in the orthodontic community (Lagravere et  al., 2005b). Based on the amount of expansion rate and force, maxillary expansion techniques can be divided into rapid maxillary expansion (RME) and slow maxillary expansion (SME). Compared with RME, SME is characterized with lower forces with longer treatment durations, rendering it a more physiological approach (Martina et al., 2012). A large body of evidence indicated that both modalities were effective for transverse maxillary discrepancy (Cozzani et  al., 2007; Corbridge et  al., 2011). However, great concerns arouse regarding their relapse (Gurel et al., 2010; Corbridge et al., 2011), especially in those without retention (Huynh et  al.,

2009). Furthermore, controversy still exists for their clinical superiority—comparable results (Martina et al., 2012) or superiority of RME (Akkaya et al., 1998). To date, whether they are effective for transverse maxillary discrepancy and which is superior are still poorly understood. Although pertinent systematic reviews have been published (Lagravere et al., 2005a,b, 2006; Zuccati et al., 2011), definitive conclusions are yet to be reached due to limited number of included studies, no up-to-date evidence, and no meta-analyses. Therefore, we conducted an up-to-date systematic review and meta-analysis to determine and compare the effectiveness of RME and SME for transverse maxillary discrepancy. Materials and methods Registration of meta-analysis The protocol for this meta-analysis (CRD42012003473) was registered in International Prospective Register of Systematic Review (http://www.crd.york.ac.uk/prospero/).

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Embase, Web of Science, CENTRAL, ProQuest Dissertations & Theses, ClinicalTrial.gov, and SIGLE were searched from January 1980 to October 2012 for randomized or nonrandomized controlled trials. The processes of study search, selection, and quality assessment were conducted independently and in duplicate. Original outcome data underwent statistical pooling through Review Manager 5. Results:  Fourteen eligible studies were finally included and two interventions (RME and SME) studied. Four outcomes (maxillary intermolar width, maxillary intercanine width, maxillary interpremolar width, and mandibular intermolar width) during three time periods (expansion, retention, and net change) were statistically pooled. The sensitivity analysis revealed that the results from the meta-analysis were generally robust. Egger’s test and Begg’s test detected no publication bias except for maxillary intercanine width in expansion period for SME versus control. Conclusions:  SME is effective in expanding maxillary arch, while we cannot determine its effectiveness in mandibular arch expansion. RME is effective in expanding both maxillary and mandibular arches. Furthermore, SME is superior to RME in expanding molar region of maxillary arch, while similar with RME in mandibular arch expansion. However, we cannot compare their effectiveness in maxillary anterior region.

234 Inclusion criteria for included studies Studies that evaluated the outcomes of RME and SME or that compared them were included. Both randomized controlled trial (RCT) and non-RCT were eligible. Participants would be otherwise healthy adults or children who had certain degree of transverse discrepancy and required maxillary expansion. However, participants with orofacial anomalies, dental pathologies, and medical conditions would be excluded. Moreover, interventions would be RME, SME, or both. Search methods PubMed, Embase, Web of Science, CENTRAL, ProQuest Dissertations & Theses, ClinicalTrial.gov, and SIGLE were electronically searched from January 1980 to October 2012 with no language restriction. Specifically, the search strategy for PubMed is presented in Supplementary Table 1. Two review authors conducted the electronic search independently and in duplicate. Disagreements were solved by discussion. Data extraction and analysis

Primary and secondary outcomes. Primary outcomes include the changes of maxillary intermolar widths and maxillary intercanine widths. Secondary outcomes were the changes of maxillary interpremolar widths and mandibular intermolar widths. Data analysis. Original outcome data, if possible, were subjected to statistical pooling by Review Manager 5 (The Cochrane IMS). Mean difference (MD) was used for statistical pooling for continuous data. Heterogeneity across studies was assessed through the I2 statistic, with a value greater than 50 per cent being considered substantial heterogeneity. Egger’s test (Egger et al., 1997) and Begg’s test (Begg and Mazumdar, 1994) were used to assess publication bias through Stata 12.1. Furthermore, sensitivity analysis was conducted to assess the robustness of meta-analysis. The independent quality of included studies was assessed by two reviewer authors according to Cochrane Collaboration’s Tool for assessing risk of bias (Higgins and Altman, 2008). The main items included sequence generation, allocation concealment, blinding, incomplete outcome data, selective outcome reporting, and other risks of bias. Any disagreement was discussed and a third reviewer consulted when necessary. Results The search strategy yielded 2931 studies and finally we included 14 studies in this systematic review (2 RCTs and

12 controlled clinical trials). Sample sizes in individual studies ranged from 24 to 153, with a total being 1048; ages ranged from 6.6 to 32.7  years old. Two studies exhibited high quality, nine studies displayed medium quality, and three studies showed low quality. The process of literature searching is displayed in Figure 1. Moreover, the characteristics and quality assessment of the included studies are presented in Table 1 and Supplementary Table 2, respectively. Description of outcomes All outcomes (the changes of maxillary intermolar, intercanine, and interpremolar widths, and the changes of mandibular intermolar width) were reported in the included studies. Different measurement landmarks and treatment strategies were employed in included studies (Supplementary Table 3). For each outcome, three parameters were studied, i.e. expansion (the changes between before treatment and immediately after treatment), retention (the changes in the retention periods), and net change (the overall change between after retention and before treatment). Description of interventions In this systematic review, two interventions were adopted: RME and SME. For RME, the rate of expansion generally varies in growing children from approximately 0.2 mm (1 turn) to 0.5 mm (2 turns), or more per day over a period of 1–3 weeks, and has an approximate 100 N across the midpalatal suture (Bell, 1982), e.g. Haas and Hyrax. In contrast, SME is defined as 1 turn (0.25 mm of expansion) every second day for a Haas or Hyrax appliance, or 1 molar widths activation for a quad-helix, with a force of 5–20 N (Hicks, 1978). Effects of interventions SME versus control Maxillary intermolar width.  Five studies investigated this outcome (Erdinc et al., 1999; Petren and Bondemark, 2008; Godoy et al., 2011; Petren et al., 2011; Shundo et al., 2012). A  statistical pooling for retention was unavailable due to lack of the data in four studies (Erdinc et al., 1999; Petren and Bondemark, 2008; Petren et  al., 2011; Shundo et  al., 2012). Thus, meta-analysis was only performed for expansion and net change, it revealed that the pooled MD was 4.45 mm [95 per cent confidence interval (CI)  =  (3.31, 5.58)] and 2.49 mm [95 per cent CI = (0.56, 4.42)], respectively (Figure 2). Maxillary intercanine width. Four studies investigated this outcome (Erdinc et al., 1999; Petren and Bondemark, 2008; Godoy et  al., 2011; Petren et  al., 2011). Likewise, only expansion and net change were available for statistical pooling and the results showed that the pooled MD was 2.58 mm [95 per cent CI = (1.25, 3.91)] and 2.27 mm [95 per cent CI  =  (1.43, 3.10)], respectively (Supplementary Figure 1).

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Data extraction. The following data were extracted independently and in duplicate by two review authors: study design, participant information, appliance, activation frequency, treatment duration, and retention duration.

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THE EFFECTIVENESS OF NON-SURGICAL MAXILLARY EXPANSION

Figure 1  PRISMA flow diagram for studies retrieved through the searching and selection processes.

RME versus control Maxillary intermolar width. Six studies investigated this outcome (Handelman et al., 2000; McNamara et al., 2003; Isik et al., 2005; Geran et al., 2006; O’Grady et al., 2006; Phatouros and Goonewardene, 2008). The expansion outcome was a significant increase in the maxillary intermolar width [pooled MD = 4.09 mm, 95 per cent CI = (3.43, 4.76)], followed by a non-significant relapse [pooled MD = −0.40 mm, 95 per cent CI = (−1.00, 0.19)]. Moreover, the pooled MD of net change was 3.58 mm (95 per cent CI = 3.17–3.98; Figure 3). Maxillary intercanine width. Six studies investigated this outcome (Handelman et al., 2000; McNamara et al., 2003; Isik et al., 2005; Geran et al., 2006; O’Grady et al., 2006; Phatouros and Goonewardene, 2008). The expansion outcome was a significant increase in the maxillary intercanine width [pooled MD  =  2.7 mm, 95 per cent CI = (2.15, 3.27)], followed by a non-significant relapse [pooled MD  =  −0.41 mm, 95 per cent CI  =  (−1.22, 0.40)]. Furthermore, the pooled MD of net change was 2.64 mm (95 per cent CI  =  2.20–3.08; Supplementary Figure 3).

Maxillary interpremolar width. Six studies investigated this outcome (Handelman et al., 2000; McNamara et al., 2003; Isik et al., 2005; Geran et al., 2006; O’Grady et al., 2006; Phatouros and Goonewardene, 2008). Similarly, the expansion outcome was a significant increase in the maxillary interpremolar width [pooled MD  =  3.86 mm, 95 per cent CI = (3.10, 4.62)], followed by a non-significant relapse [MD = −0.16 mm, 95 per cent CI = (−0.71, 0.39)]. Moreover, the pooled MD of net change was 3.52 mm [95 per cent CI = (2.68, 4.37)] (Supplementary Figure 4). Mandibular intermolar width. Five studies investigated this outcome (Handelman et  al., 2000; McNamara et  al., 2003; Isik et al., 2005; Geran et al., 2006; O’Grady et al., 2006). The expansion outcome was a significant increase in the mandibular intermolar width [pooled MD = 1.19 mm, 95 per cent CI  =  (0.89, 1.49)], followed by a significant increase in retention period [pooled MD = 0.65 mm, 95 per cent CI = (0.38, 0.92)]. The net change was also a highly significant increase [pooled MD  =  2.02 mm, 95 per cent CI = (1.58, 2.45)] (Supplementary Figure 5). RME versus SME Maxillary intermolar width. Three studies examined this outcome (Ladner and Muhl, 1995; Sandikcioglu and Hazar, 1997; Akkaya et  al., 1998). Retention data were unavailable in Sandikcioglu and Hazar (1997), but we imputed them by using an algorithm through a correlation coefficient (r  =  0.94; Abrams et  al., 2005), which were also done for the outcomes below. Non-significant results were found in expansion [pooled MD = −0.23 mm, 95 per cent CI  =  (−1.24, 0.79)] and relapse [MD  =  −0.02 mm, 95 per cent CI = (−0.13, 0.10)]. However, the pooled net

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Maxillary premolar width. Unfortunately, none of the included studies investigated this outcome. Mandibular intermolar width. Five studies investigated this outcome (Erdinc et al., 1999; Petren and Bondemark, 2008; Godoy et al., 2011; Petren et al., 2011; Shundo et al., 2012). Similarly, meta-analysis was only performed for expansion and net change. The pooled MD was 0.49 mm [95 per cent CI = (−0.10, 1.07)] and 0.06 mm [95 per cent CI = (−1.16, 1.27)] for expansion and net change, respectively (Supplementary Figure 2).

CCT

RCT

CCT

CCT

RCT

CCT

CCT

Erdinc et al. (1999)

Petren and Bondemark (2008)

Petren et al. (2011)

Shundo et al. (2012)

Godoy et al. (2011)

Handelman et al. (2000)

Isik et al. (2005)

CCT

CCT

Akkaya et al. (1998)

Ladner and Muhl (1995)

NA, not applicable.

Sandikcioglu and Hazar CCT (1997)

CCT

O’Grady et al. (2006)

McNamara et al. (2003)CCT

Phatouros and CCT Goonewardene (2008) Geran et al. (2006) CCT

Design

SME (n = 30, mean age: 11.9 years) SRME (n = 10, mean age: 6.6 years) SME (n = 10, mean age: 8.6 years) RME (n = 10, mean age: 8.9 years)

SME (n = 12, mean age: 12.3 years) RME (n = 30, mean age: 11.7 years)

Quad-helix (n = 14, 9.7 ± 1.4 years) Expansion plate (n = 13, 9.3 ± 1.1 years) Control (n = 10, 9.4 ± 1.3 years) Quad-helix (n = 15, 9.1 ± 1.0 years) Expansion plate (n = 15, 8.7 ± 0.8 years) Composite onlay (n = 15, 8.3 ± 0.7 years) Control (n = 15, 8.8 ± 0.7 years) Quad-helix (n = 20, 9.0 ± 1.2 years) Expansion plate (n = 15, 8.5 ± 1.0 years) Control (n = 20, 8.8 ± 0.5 years) Quad-helix (n = 50, mean age: 9.5 years) Control (n = 50, mean age: 9.3 years) Quad-helix (n = 33, 8.0 ± 0.8 years) Control (n = 33, 8.1 ± 0.8 years) Child RME (n = 47, 9.5 ± 1.3 years) Adult RME (n = 47, 29.9 ± 8.0 years) Adult control (n = 52, 32.7 ± 7.4 years) Expansion (n = 15, 14.0 ± 2.9 years) Non-extraction (n = 42, 14.2 ± 2.8 years) Extraction (n = 27, 13.6 ± 2.6 years) RME (n = 43, mean age: 9.1 years) Control (n = 7, mean age: 9.3 years) RME (n = 51, mean age: 8.8 years) Control (n = 26, mean age: 8.8 years) RME (n = 112, 12.2 ± 1.3 years) Control (n = 41, 11.5 ± 1.0 years) RME only (n = 27, 8.5 ± 1.3 years) RME + Schwarz (n = 23, 9.1 ± 0.9 years) Control (n = 16, 8.0 ± 0.8 years) RME (n = 12, mean age: 12.0 years)

Sample 7.2 months 4.8 ± 3.5 months

1.5 years SME (15 months) Control (17 months) 4.2 ± 2.1 months 12 weeks

SME versus control (quad-helix: once a month) SME versus control (quad-helix: every 6 weeks)

SME versus control (quad-helix: every 6 weeks) SME versus control (quad-helix: once a month)

RME versus control (Hass: once a day)

SRME (removable plates, 1/2 day); SME (quad-helix, 1/2 week); RME (Hyrax, 2/day)

RME versus SME

RME versus SME RME (rapid palatal expander); SME (quad-helix)

RME versus SME RME (Hyrax, 2/day); SME (Minne-expander, 1/week)

RME versus control (Acrylic splints, 1/day)

SME: 3–4 months RME: 3 months

SME: 21 ± 8 months SRME: 7 months SME: 2 months RME:19.2 days

RME: 33 ± 13 months SME: 5 months SRME:5.5 months

3 months

5 months

RME: 3 months

SME:1.0–5.1 6 months

RME:0.7–1.6 months

Until a buccal crossbite was approached 21 days (until the screw reached 10.5 mm) Until buccal crossbite was approached

65 days

5 months

9 weeks

RME versus control (Hyrax: 2/day for the first 3 days and 1/day for the next 7 days) RME versus control (bonded crylic splints, 1/day) RME versus control (Hass: 2/day)

13 weeks

NA

Adult RME: >3 months; child RME: 3–6 months NA

6 months

NA

6 months

6 months

NA

Retention duration

RME versus control

SME versus control (quad-helix: once a month)

Treatment duration

Appliances and activation frequency

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Study

Table 1  Characteristics of the included studies. RME, rapid maxillary expansion; SME, slow maxillary expansion; SRME, semi-rapid maxillary expansion; RCT, randomized controlled trial; CCT, controlled clinical trial.

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THE EFFECTIVENESS OF NON-SURGICAL MAXILLARY EXPANSION

Figure 2  Forest plot of pooled mean difference of maxillary intermolar width for slow maxillary expansion versus control.

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Figure 3  Forest plot of pooled mean difference of maxillary intermolar width for rapid maxillary expansion versus control.

change was significantly larger in SME than in RME [pooled MD = −0.75 mm, 95 per cent CI = (−1.09, −0.40)] (Figure 4). Maxillary intercanine width. Three studies examined this outcome (Ladner and Muhl, 1995; Sandikcioglu and Hazar, 1997; Akkaya et  al., 1998). The meta-analysis revealed no significant differences regarding expansion, retention, and net change between RME and SME (Supplementary Figure 6).

Maxillary interpremolar width. Only two studies investigated this outcome (Sandikcioglu and Hazar, 1997; Akkaya et al., 1998). Similarly, the meta-analysis revealed no significant differences regarding expansion, retention, and net change between RME and SME (Supplementary Figure 7). Mandibular intermolar width. Two studies evaluated this outcome (Ladner and Muhl, 1995; Akkaya et  al.,

238

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1998). However, only expansion data were available for in meta-analysis. The pooled MD was −0.68 mm [95 per cent CI  =  (−2.06, 0.69)], indicating that no significant difference between RME and SME (Supplementary Figure 8).

widths in the retention period for RME versus control (Table 3); maxillary intermolar width in expansion period and maxillary intercanine widths in all the expansion, retention, and net change periods for RME versus SME (Table 4).

Sensitivity analysis or subgroup analysis.

Assessment of publication bias.

The sensitivity analysis showed that unstable results were found in mandibular intermolar width in both expansion and net change periods for SME versus control (Table 2); maxillary intermolar, intercanine, and interpremolar

Neither Egger’s test nor Begg’s test revealed any evidence of publication bias except for maxillary intercanine width in expansion period for SME versus control (Supplementary Table 4).

Table 2  Sensitivity analysis or subgroup analysis for SME versus control. SME, slow maxillary expansion. Outcome

Original estimates

Exclusion of studies*

Exclusion of lowquality studies**

Effect model Fixed

Maxillary intermolar width  Expansion   Net change Maxillary intercanine width  Expansion   Net change Mandibular intermolar width  Expansion   Net change

Random

4.45 (3.31, 5.58) 2.49 (0.56, 4.42)

4.54 (2.81, 6.28) 3.47 (2.58, 4.36)

— 3.47 (2.58, 4.36)

4.30 (3.91, 4.69) 2.52 (1.88, 3.16)

4.45 (3.31, 5.58) 2.49 (0.56, 4.42)

2.58 (1.25, 3.91) 2.27 (1.43, 3.10)

— 2.60 (1.58, 3.62)

— 2.60 (1.58, 3.62)

2.46 (1.99, 2.92) 2.27 (1.43, 3.10)

2.58 (1.25, 3.91) 2.24 (1.29, 3.18)

0.49 (−0.10, 1.07) 0.06 (−1.16, 1.27)

0.68 (−0.07, 1.43) 0.64 (0.08, 1.20)

— 0.64 (0.08, 1.20)

0.28 (0.07, 0.48) 0.24 (−0.22, 0.71)

0.49 (−0.10, 1.07) 0.06 (−1.16, 1.27)

Those highlighted in bold are significantly different from the original estimates. *Exclusion of studies using reference points other than central fossa for molars and those other than cusp tip for canines. **Petren et al. (2011) was of low quality, while others were of medium and high quality.

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Figure 4  Forest plot of pooled mean difference of maxillary intermolar width for rapid maxillary expansion versus slow maxillary expansion.

Original estimates

2.96 (2.14, 3.79) — — 3.94 (3.06, 4.83) — — 1.28 (0.94, 1.63) — —

1.43 (0.14, 2.72) 2.24 (0.92, 3.56) — — — — 3.74 (2.68, 4.79) 3.85 (2.22, 5.68) — — — — 1.33 (0.98, 1.69) 0.84 (0.28, 1.39) — — — —

Exclusion of low-­ quality studies***

3.83 (3.29, 4.37) — —

Exclusion of deciduous teeth study**

3.76 (3.41, 4.10) 4.28 (1.08, 7.48) — — — —

Exclusion of studies*

1.28 (0.94, 1.63) 0.65 (0.38, 0.92) 2.02 (1.58, 2.45)

1.28 (0.94, 1.63) 0.90 (0.29, 1.51) — — — —

1.19 (0.89, 1.49) 0.65 (0.38, 0.92) 2.02 (1.58, 2.45)

3.60 (2.66, 4.54) 4.36 (4.09, 4.64) 4.10 (3.38, 4.81) −0.16 (−0.71, 0.39) −0.30 (−0.53, −0.08) −0.16 (−0.71, 0.39) 3.52 (2.68, 4.37) 3.7 (3.40, 4.17) 3.52 (2.68, 4.37)

3.94 (3.06, 4.83) 4.95 (4.46, 5.44) — — — —

1.19 (0.89, 1.49) 0.65 (0.38, 0.92) 2.02 (1.58, 2.45)

2.65 (1.89, 3.41) 2.98 (2.67, 3.28) 2.94 (2.29, 3.59) −0.41 (−1.22, 0.40) −0.46 (−0.67, −0.24) −0.41 (−1.22, 0.40) 2.64 (2.20, 3.08) 2.64 (2.20, 3.08) 2.64 (2.20, 3.08)

2.96 (2.14, 3.79) 3.56 (2.00, 5.13) — — — —

Random

3.64 (3.23, 4.06) 4.03 (3.75, 4.31) 4.09 (3.43, 4.76) −0.40 (−1.00, 0.19) −0.27 (−0.51, −0.03) −0.40 (−1.00, 0.19) 3.58 (3.17, 3.98) 3.58 (3.17, 3.98) 3.50 (2.96, 4.03)

Fixed

Expansion only

Expansion + fixed

Effect model

Treatment

3.83 (3.29, 4.37) 5.16 (3.90, 6.43) — — — —

Exclusion of s tudies on adults****

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Data are presented as mean difference (95% confidence interval); those highlighted in bold are significant different from the original estimates. *Exclusion of studies using reference points other than central fossa for molars and premolars and those other than cusp tip for canines. **Phatouros and Goonewardene (2008), Geran et al. (2006), McNamara et al. (2003), O’Grady et al. (2006). ***Handelman et al. (2000) was of low quality, while others were of medium quality. ****Handelman et al. (2000) examined the comparison between RME and control only in adults.

Maxillary intermolar width  Expansion 4.09 (3.43, 4.76)  Retention −0.40 (−1.00, 0.19)   Net change 3.58 (3.17, 3.98) Maxillary intercanine width  Expansion 2.94 (2.29, 3.59)  Retention −0.41 (−1.22, 0.40)   Net change 2.64 (2.20, 3.08) Maxillary interpremolar width  Expansion 4.10 (3.38, 4.81)  Retention −0.16 (−0.71, 0.39)   Net change 3.52 (2.68, 4.37) Mandibular intermolar width  Expansion 1.19 (0.89, 1.49)  Retention 0.65 (0.38, 0.92)   Net change 2.02 (1.58, 2.45)

Outcome

Table 3  Sensitivity analysis or subgroup analysis for RME versus control. RME, rapid maxillary expansion.

THE EFFECTIVENESS OF NON-SURGICAL MAXILLARY EXPANSION

239

−0.09 (−0.18, −0.00) −1.50 (−2.59, −0.41) −0.08 (−0.17, 0.01)

Discussion In this systematic review, the included 14 studies evaluated four outcomes (maxillary intermolar, intercanine and interpremolar widths, and mandibular intermolar width). All four outcomes were included in the meta-analysis. Most of the included studies were of medium quality. Although significant changes from the original estimates were found for several outcomes in the sensitivity analysis, the results from the meta-analysis were generally robust. Egger’s test and Begg’s test detected no publication bias except for maxillary intercanine width in expansion period for SME versus control. SME versus control

Those highlighted in bold are significantly different from the original estimates. *Exclusion of studies using reference points other than central fossa for molars and premolars and those other than cusp tip for canines. **Exclusion of low-quality studies. For each item, the same study, Ladner and Muhl (1995), was excluded.

−0.68 (−2.06, 0.69)

−0.10 (−0.51, 0.31) 0.06 (−0.09, 0.21) −0.12 (−0.52, 0.27) — — — 1.35 (−2.09, 4.78) −0.09 (−0.60, 0.43) 1.06 (−1.80, 3.92)

−0.08 (−0.17, 0.01)

1.35 (−2.09, 4.78) −0.09 (−0.60, 0.43) 1.06 (−1.80, 3.92)

2.13 (1.75, 2.50) −0.21 (−0.24, −0.08) 1.92 (1.55, 2.29) — — — 0.49 (−3.30, 4.28) 0.66 (−1.24, 2.56) 1.45 (−0.24, 3.14)

— — —

0.49 (−3.30, 4.28) 0.66 (−1.24, 2.56) 1.45 (−0.24, 3.14)

−0.61 (−0.98, −0.24) −0.02 (−0.13, 0.10) −0.75 (−1.09, −0.40) 0.60 (−0.57, 1.77) — — −0.74 (−1.13, −0.35) −0.02 (−0.13, 0.10) −0.75 (−1.09, −0.40)

Maxillary intermolar width  Expansion −0.23 (−1.24, 0.79)  Retention −0.02 (−0.13, 0.10)   Net change −0.75 (−1.09, −0.40) Maxillary intercanine width  Expansion 0.49 (−3.30, 4.28)  Retention 0.66 (−1.24, 2.56)   Net change 1.45 (−0.24, 3.14) Maxillary interpremolar width  Expansion 1.35 (−2.09, 4.78)  Retention −0.09 (−0.60, 0.43)   Net change 1.06 (−1.80, 3.92) Mandibular intermolar width  Expansion −0.68 (−2.06, 0.69)

— — —

−0.23 (−1.24, 0.79) −0.02 (−0.13, 0.10) −0.75 (−1.09, −0.40)

Fixed Expansion + fixed Expansion only

−0.74 (−1.13, −0.35) — —

Random Effect model Outcome

Original estimates

Exclusion of studies*,**

Treatment

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This meta-analysis indicated that SME could gain a significant increase in the width of maxillary arch although there was relapse to some extent (Figure  2 and Supplementary Figure 1). The pooled MD of mandibular intermolar width for expansion (Supplementary Figure 2) indicated that SME was ineffective in widening mandibular arch. As stated above, the sensitivity analysis showed that results from the meta-analysis were stable except for mandibular intermolar width (Table  2). Although maxillary intercanine width in expansion period suffered from a publication bias, that in net change period did not. Thus, we suggest that SME is effective in expanding maxillary arch. Nevertheless, due to unstable results in mandibular intermolar width, we could not determine the effectiveness of SME on mandibular arch. RME versus control As presented in Figure 3, for maxillary intermolar width, the meta-analysis was indicative of a significant increase in expansion period, a non-significant relapse in the retention period, and a significant increase in net change. Similar results were found for maxillary intercanine width (Supplementary Figure  3), maxillary interpremolar width (Supplementary Figure  4), and mandibular intermolar width (Supplementary Figure  5), except for an increase in mandibular intermolar width in the retention period. Although no direct expanding forces existed in mandibular arches, expanded maxillary molars could exert occlusal forces on mandibular molars that would expand mandibular arches (Gryson, 1977). Moreover, due to the rapid expansion nature of RME and slow adaptation of occlusion, there was a mild increase in mandibular intermolar width in retention period. Although sensitivity analysis revealed that the results of maxillary arch widths (intermolar, intercanine, and interpremolar) were not stable for retention period, those were stable for expansion period and net change (Table  3). Moreover, neither Begg’s nor Egger’s test detected any publication bias. Therefore, we suggest that RME is effective in expanding both maxillary and mandibular arches.

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Table 4  Sensitivity analysis or subgroup analysis for RME versus SME. RME, rapid maxillary expansion; SME, slow maxillary expansion.

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RME versus SME

Conclusions SME is effective in expanding maxillary arch, while we cannot determine its effectiveness in mandibular arch expansion. RME is effective in expanding both maxillary and mandibular arches. Furthermore, SME is superior to RME

Supplementary material Supplementary material is available at European Journal of Orthodontics online. Funding National Natural Science Foundation of China (81070858, 81100778). References Abrams K R, Gillies C L, Lambert P C 2005 Meta-analysis of heterogeneously reported trials assessing change from baseline. Statistics in Medicine 24: 3823–3844 Akkaya S, Lorenzon S, Ucem T T 1998 Comparison of dental arch and arch perimeter changes between bonded rapid and slow maxillary expansion procedures. European Journal of Orthodontics 20: 255–261 Angell E C 1860 Treatment of irregularities of the permanent or adult teeth. Dental Cosmos 1: 540–544 Begg C B, Mazumdar M 1994 Operating characteristics of a rank correlation test for publication bias. Biometrics 50: 1088–1101 Bell R A 1982 A review of maxillary expansion in relation to rate of expansion and patient’s age. American Journal of Orthodontics and Dentofacial Orthopedics 81: 32–37 Corbridge J K, Campbell P M, Taylor R, Ceen R F, Buschang P H 2011 Transverse dentoalveolar changes after slow maxillary expansion. American Journal of Orthodontics and Dentofacial Orthopedics 140: 317–325 Cozzani M, Guiducci A, Mirenghi S, Mutinelli S, Siciliani G 2007 Arch width changes with a rapid maxillary expansion appliance anchored to the primary teeth. The Angle Orthodontist 77: 296–302 Egger M, Davey Smith G, Schneider M, Minder C 1997 Bias in metaanalysis detected by a simple, graphical test. British Medical Journal 315: 629–634 Erdinc A E, Ugur T, Erbay E 1999 A comparison of different treatment techniques for posterior crossbite in the mixed dentition. American Journal of Orthodontics and Dentofacial Orthopedics 116: 287–300 Geran R G, McNamara J A Jr, Baccetti T, Franchi L, Shapiro L M 2006 A prospective long-term study on the effects of rapid maxillary expansion in the early mixed dentition. American Journal of Orthodontics and Dentofacial Orthopedics 129: 631–640 Godoy F, Godoy-Bezerra J, Rosenblatt A 2011 Treatment of posterior crossbite comparing 2 appliances: a community-based trial. American Journal of Orthodontics and Dentofacial Orthopedics 139: e45–e52 Gryson J A 1977 Changes in mandibular interdental distance concurrent with rapid maxillary expansion. The Angle Orthodontist 47: 186–192 Gurel H G, Memili B, Erkan M, Sukurica Y 2010 Long-term effects of rapid maxillary expansion followed by fixed appliances. The Angle Orthodontist 80: 5–9 Haas A J 1965 The treatment of maxillary deficiency by opening the midpalatal suture. The Angle Orthodontist 35: 200–217 Handelman C S, Wang L, BeGole E A, Haas A J 2000 Nonsurgical rapid maxillary expansion in adults: report on 47 cases using the Haas expander. The Angle Orthodontist 70: 129–144 Hicks E P 1978 Slow maxillary expansion. A clinical study of the skeletal versus dental response to low-magnitude force. American Journal of Orthodontics and Dentofacial Orthopedics 73: 121–141

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The meta-analysis showed that no significant differences between two modalities for maxillary intercanine (Supplementary Figure  6), maxillary interpremolar (Supplementary Figure 7), and mandibular intermolar (Supplementary Figure  8) widths in expansion period, relapse period, or net change. Moreover, no significant differences between two modalities existed in expansion and retention periods for maxillary intermolar width, but, ironically, the net change differed significantly for maxillary intermolar width (Figure 4). We attribute this inconsistence to different treatment strategies in included studies, which may confound the results (expansion only or expansion plus additional fixed orthodontic treatment). Therefore, we performed a subgroup analysis on expansion only and found RME was less effective than SME in expanding maxillary molars in expansion period and net change, with no difference in retention period (Table 4). The sensitivity analysis was indicative of unstable result of maxillary intercanine width in all three periods. Neither Begg’s test nor Egger’s test detected any publication bias. Therefore, we suggest that SME is superior to RME in expanding molar region of maxillary arch, with no differences in effectiveness regarding maxillary interpremolar and mandibular intermolar width. However, we cannot compare their effectiveness in anterior region of maxillary arch. The limitations of this systematic review included limited number of high-quality studies, different treatment strategies (expansion only or expansion plus fixed orthodontic treatment), and different measurement landmarks (central fossa, cervical margin, or mesiobuccal cusp tip). Hence, more studies are expected to produce high-quality evidence with standard measurement method and unified treatment strategy. Moreover, although the pre-post tipping change of maxillary first molar is a very interesting topic, the limited number of studies comparing RME with SME and the inaccuracy of measurement method prevented us from an in-depth analysis. Specifically, these studies measured molar tipping by calculating the changes in angles formed by the intersection of lines passing buccal and palatal tips of left and right molars. We think this measurement is unreliable: palatal expansion may cause molar buccal tipping, which in turn may result in a lower position of palatal tips. These low positioned palatal tips may undergo abrasion during the treatment period, which may cause the measurement based on buccal and palatal tips unreliable. Therefore, further studies based on more reliable methods, e.g. cone-beam computed tomography, are recommended.

in expanding molar region of maxillary arch, while similar with RME in mandibular arch expansion. However, we cannot compare their effectiveness in maxillary anterior region.

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