Comparative effect of the Myobrace appliance versus traditional functional appliances in treating a class II malocclusion: a systematic review and meta-analysis

Introduction

A Class II malocclusion is characterised by a convex facial profile resulting from maxillary protrusion, mandibular retrusion, or a combination of both.¹ A Class II malocclusion affects approximately one third of the population² and influences an individual’s quality of life, oral-facial function^3,4 as well as affecting psychological wellbeing due to its impact on facial appearance.^3–5

Growth modification with functional appliances such as the Twin Block and Activator is often applied in the treatment of Class II growing patients.^6–8 However, these appliances have disadvantages, which include discomfort, speech difficulty, psychological embarrassment, and reduced aesthetics. These factors sometimes compromise a patient’s compliance.

Since the 1990s, the Myobrace range of functional appliances has been established,⁹ and has spread from Australia to more than 100 countries around the world.¹⁰ The appliance often needs to be worn overnight and for one to two hours during the day.¹¹ Although controversial, the advantages of the Myobrace appliance is the promotion of mandibular growth compared with conventional functional appliances. It has been reported that the Myobrace appliance has a similar effect in promoting jaw growth compared with traditional functional appliances.¹² However, a contrary study has reported that the Myobrace appliance is not as effective as traditional functional appliances.¹³ A recent systematic review compared the effect of Myobrace and the Twin Block on class II malocclusions in children, but the inclusion and exclusion criteria were ambiguous, and only five heterogeneous studies were identified which precluded a quantitative synthesis.¹⁴

Therefore, the aim of the present systematic review was to compare the treatment effect of the Myobrace appliance and traditional functional appliances in the treatment of Class II malocclusions.

Material and methods

This systematic review and meta-analysis adhered to the guidelines set forth by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement.¹⁵

Results

Study characteristics

A total of 48 full-text articles were assessed for relevance. After applying the inclusion and exclusion criteria, 35 studies were excluded, and 13 trials (n = 674 participants) were included in the qualitative analysis^{12,13,19–29} (Figure 1 and Appendix II). An ongoing study was identified on ClinicalTrials.gov; however, attempts to obtain data from the corresponding author were unsuccessful at the time of writing this review.

Figure 1.

Of the participants, 348 wore Myobrace appliances, 196 participants wore conventional functional appliances, and 130 did not use any appliance (Table I). Of the included studies, nine^{12,19–23,26,27,29} were RCTs and four studies^13,24,25,28 were NRS. Eight studies compared the Myobrace appliance with the Twin-block; three studies compared Myobrace and the Activator; and two studies evaluated Myobrace’s other treatment outcomes.

Table I.

Characteristics of the 13 included studies

	Study (Author year)	Country	Study design	Sample size	Age (years)	Myobrace group	Compa rison group	Treatment time	Outcomes
									Dentoalveolar	Skeletal	Soft tissue
1	Ramirez-Yañez 200725	USA	NRS	120	8.3 ± 1.0	T4K® (n=60)	No treatment (n = 60)	6 months	U6-6(mm), U3-3(mm), L6-6(mm), L3-3(mm)	N/A	N/A
2	C̈rgić 201530	Sweden	RCT	97	7-14	Myobrace® (n=57)	Activator (n=40)	12 months	Overjet, Overbite	sagittal relation,	lip seal
3	Sun 201821	China	RCT	20	8-11	Myobrace® (n=10)	Activator (n=10)	6 months	L1-NB(mm), L1-NB(°), U1-NA(mm), U1-NA(°), Co-Pg, Overjet, Overbite	SNA, SNB, ANB	N/A
4	Idris 201922	Syria	RCT	60	10.3 ± 1.4	T4K® (n=30)	Activator (n=30)	12-18 months	Overjet, Overbite, Ls to E, Li to E, U1-SN	SNA, SNB, ANB, N-Me, N-ANS, ANS-Me, MP-FH	N/A
5	Elhamouly 202026	Egypt	RCT	20	9-12	T4K® (n=10)	Twin-Block (n=10)	18-24 months	Overjet, U1-FHP, L1-MP, Is-APog(mm), li-NB(mm), U6-PL.P (mm), L6-MP(mm), mi-PtV(mm), UAP(mm), LAP(mm)	N/A	N/A
6	Hanoun 202023	America	RCT	43	11-14	T4F (n=21)	Twin-Block (n=22)	10-12 months	Overjet, Overbite, Sv_is (mm), Sv_ii (mm), Sv_ii (mm)	SNA, SNB, ANB, Sn-Man(°), MMPA(°)	N/A
7	Ji 202027	China	RCT	25	9.1 ± 1.3	Myobrace® (n=13)	Twin-Block (n=12)	12 months	U1-SN(mm), U1-SN(°), L1-NB(mm), L1-NB(°), L1-MP, Overjet, Overbite	SNA, SNB, ANB, FH-MP, NP-FH	N/A
8	Xie 202019	China	RCT	22	9.7 ± 1.3	Myobrace® (n=11)	Twin-Block (n=11)	12 months	U1-NA mm), U1-NA (°), L1-NB (mm), L1-NB (°), Po-NB (mm),	SNA, SNB, ANB, FMA, FH-MP, Y-axis (°), NP-FH (°), SN-FH (°)	N/A
9	Chen 202128	China	NRS	40	12.43 ± 0.76	Myobrace® (n=20)	Twin-Block (n=20)	6 months	U1-SN, L1-MP	SNA, SNB, ANB, FH-MP, Y axis, NP-FH	CmSnLs( ° ), A’Ls-FH(°), IMsLs-FH(°), IMsLs-FH(°), LiB’Pg’(°), GSnPg’(°)
10	Johnson 202131	UAE	RCT	20	10.40 ± 1.89	Myobrace® (n=10)	Twin-Block (n=10]	9 months	U1-NA (mm), U1-NA (°), L1-NB (mm), L1-NB (°), U1-SN, Overjet, Overbite, U6-6(mm), L6-6(mm)	SNA, SNB, ANB, NA-Pog, PP-MP, Ar-Gn, Go-Ar, Go-Me	N/A
11	Habumugisha 202224	China	NRS	145	7.41 ± 1.21	Myobrace® (n=75)	No treatment (n=70)	12 months	U1-NA (°), L1-NB(°), Overjet, Overbite, U6-6(mm), U3-3(mm), L6-6(mm), L3-3(mm)	SNA, SNB, ANB, FH-MP, SN-GoGn, S-Go	N/A
12	Çoban Büyükbayraktar and Camci (2023)13	Turkey	NRS	36	12.14 ± 1.23	Myobrace® (n=18)	Twin-Block (i=18)	12-16 months	U1-NA (mm), U1-NA (°), L1-NB (mm), L1-NB (°), U1-SN (°), Overjet, Overbite, Pg-NB (mm), FMA (°)	SNA, SNB, ANB, FMA (°), FMIA (°),	Upper lip-E line, Lower lip-E line
13	Madian 202312	Egypt	RCT	26	9 – 12	Myobrace® (n = 13)	Twin-Block (n=13)	16 months	N/A	SNA, SNB, ANB, Wits appraisal, FMA	phaiyngeal airway area

One study²⁹ claimed that there was no significant difference in the effectiveness of the Myobrace appliance and the Activator in correcting overjet, overbite, the sagittal molar relationship, and lip seal in a 6-month study, but the essential data were missing from the article. The corresponding authors were contacted via email to request their original experimental data, however, no response was received by the time of writing the present review. Consequently, this study²⁹ was only included in the qualitative analysis and excluded from the meta-analysis. Therefore, 12 studies were finally included in the meta-analysis, and comprised 577 participants (291 wore the Myobrace appliance; 116 wore a Twin-block; 40 wore an Activator; and 130 patients did not use any orthodontic appliance).

The results were categorised into skeletal measurements and dental measurements, including SNA, SNB, ANB, Ar-Go (mm), Go-Me (mm), overbite (mm), overjet (mm), U1-SN (°), U1-NA (°), U1-NA (mm), L1-MP (°), L1-NB (°), L1-NB (mm), U3-3 (mm), U6-6 (mm), L3-3 (mm), L6-6 (mm). Soft tissue measurements were not pooled due to the lack of results.

Risk of bias of the studies

A limitation of all RCTs is the impossibility of imposing blinding to either participants or personnel, resulting in an assessment of a high risk of bias. Based on the Cochrane Collaboration’s tool for assessing the risk of bias, the results of assessment for the RCTs are shown in Figure 2. For the NRS’s assessment using the MINORS tool, the results showed that, of the four studies, two were of high quality and two were of medium quality (Table II). Appendix III details the risk of bias assessment reason for all included studies.

Figure 2.

Table II.

Summary of risk bias of Non-Randomized Study (NRS) included in the study based on Methodological Index for Non-Randomized Studies (MINORS) scores (0-8 points: low quality; 9-16 points: medium quality; 17-24 points: high quality)

Assessment criteria	Ramirez-Yañez (2007)25	Chen (2021)28	Habumugisha (2022)24	Çoban Büyükbayraktar and Camcı (2023)13
Clear research objectives	2	2	2	2
Continuity of inclusion of patients	2	2	2	2
Expected data collection	2	2	2	2
Outcome indicators reflect appropriately research purpose	2	2	2	2
Outcome measure objectivity	0	1	2	2
Whether the follow-up time was sufficient	2	2	2	2
The rate of lost to follow-up	0	0	0	2
Whether to estimate the sample size	0	0	1	2
Whether the control group was appropriate	2	2	2	2
Whether the control group is synchronized	0	0	2	0
Intergroup baseline	1	0	2	0
Reliability of data statistics	2	2	2	2
Total	15	15	21	20
Quality level	Medium	Medium	High	High

1 Table 2. Summary risk bias of NRS.

Meta-analysis of Myobrace versus Twin-Block

Statistically significant differences were observed in three out of the five skeletal measurements assessed. The meta-analysis indicated that the pooled mean difference (MD) was SNA (0.36°, 95% CI 0.06–0.66, P = 0.02), Ar-Go (-1.51mm, 95% CI -2.82– -0.15, P = 0.03), and Go-Me (2.19mm, 95% CI 0.37– 4.02, P = 0.02). The results suggest that the Myobrace appliance may be less effective than Twin-Block appliances in inhibiting maxillary growth and promoting mandibular ramus advancement. However, in promoting mandibular body growth, the Myobrace appliance appears to be superior to the Twin-Block appliance (Figure 3–1).

Figure. 3-1.

Statistically significant differences were found in two of the eight dental measurements analysed. The meta-analysis indicated that the pooled mean difference (MD) was overbite (0.83mm, 95% CI 0.10–1.55, P = 0.03), and overjet (1.45mm, 95% CI 0.10–2.79, P = 0.03). These might indicate that the Myobrace appliance is less effective than Twin-Block appliances in reducing overjet and overbite in Class II malocclusion patients (Figure 3–2).

There were no statistically significant differences observed in the other cephalometric parameters (Figure 3–1 and 3–2).

Meta-analysis of Myobrace versus activator

Statistically significant differences were observed in one out of the three skeletal measurements assessed. The meta-analysis indicated that the pooled mean difference (MD) was SNB (-0.86°, 95% CI -1.51– -0.21, P = 0.009). These may indicate that the Myobrace appliance was inferior to Activator appliances in promoting mandibular growth. No statistical difference was found in the other cephalometric parameters (Figure 4).

Figure 4.

Meta-analysis of the Myobrace for transverse expansion

The meta-analysis showed no statistically significant difference between the Myobrace group and the no-treatment control group for the U3-3 (mm) (cuspal distance of the cuspids on both sides of the maxilla), U6-6 (mm) (central fossa distance of the first molar on both sides of the maxilla), L3-3 (mm) (cuspal distance of the cuspids on both sides of the mandible), or L6-6 (mm) (central fossa distance of the first molar on both sides of the mandible). These results suggest that the effect of the Myobrace appliance on increasing the transverse width of the maxillary and mandibular dental arches is weak (Figure 5).

Figure 5.

Discussion

A Class II malocclusion is a prevalent relationship problem in adolescents¹⁹ and a previous study has shown that approximately 32.6% of 700 subjects presented with a Class II malocclusion.² The present systematic review focused on 13 articles involving a total of 674 patients. According to current knowledge, this is the first systematic review to evaluate the comprehensive effectiveness of the Myobrace appliance in the treatment of a Class II malocclusion in comparison with the Twin-Block, Activator and a no-treatment control group.

Myofunctional devices were initially proposed by Robin in 1902 and Anderson in 1908 with the aim of promoting growth in patients with a mandibular deficiency.²² Myofunctional appliances have been used extensively, especially in the treatment of Class II malocclusions.^32,33 Several types of myofunctional appliances commonly used include the Twin-block, Activator appliances, and the Myobrace appliance.^2,22,29,34

Similar to other functional appliances, the Myobrace elongates the fibres of the mandibular protractor muscles.³³ When using the ‘Trainer’ appliance, the muscles remain stretched. During a sleep period (10–12 hr), the diameter of blood vessels is reduced, which hinders adequate blood flow and decreases blood oxygen levels and metabolism. The result is the accumulation of lactic acid leading to muscle fatigue. Upon removal of an appliance, the overextended muscles become hyper-contractible, which causes both forward and backward movement of the mandible.³³ The Myobrace appliance is designed to provide a comprehensive effect, including guidance of tooth development, training of muscle function, and early intervention.^23,35 The appliance is user friendly, easy to remove and to clean plus allows for the correction of dental alignment and habits without the need for fixed appliances.³⁶

Of the included studies, the reported treatment effects often incorporated skeletal and dental measurements. For example, the skeletal measurements usually included SNA, SNB, ANB, Ar-Go (mm), Go-Me (mm), FH-MP (°), NP-FH (°), Y-axis (°).^{12,13,19–24,27,28} The dental measurements usually included overbite (mm), overjet (mm), U1-SN (°), U1-NA (°), U1-NA (mm), L1-MP (°), L1-NB (°), L1-NB (mm), U3-3 (mm), U6-6 (mm), L3-3 (mm), L6-6 (mm).^13,19–28 In relation to soft tissue changes, there were only a few studies which reported changes in the lip seal, Gla-Sub-Pg (°), nasolabial angle (Cl.Sn.SLS), mentolabial angle (Li.Ils.Pog), upper lip-E line, lower lip-E line.^13,28,29 Changes in the pharyngeal airway area were only reported in one study.¹² Based on the current meta-analysis, traditional functional appliances demonstrated a more significant effect than the Myobrace appliance in reducing overbite and overjet, decreasing the SNA angle, and increasing the SNB angle; however, the Myobrace appliance showed a similar effect compared with a conventional functional appliance in reducing the ANB angle. Although quantitative results demonstrated that Twin Block appliances achieved a 1.45 mm greater reduction in overjet and a 0.83 mm greater reduction in overbite compared to the Myobrace appliance, some clinicians contend that these differences may not reach the threshold of clinical significance, particularly considering evidence suggesting that initial differences may not persist long-term.³⁷ A notable advantage of the Myobrace appliance is its lower cost, as it eliminates the need for impressions and laboratory work.³⁰ However, this conclusion is based on a single RCT, which highlights the need for further studies to evaluate its cost effectiveness. The potential cost savings could be particularly appealing to clinicians, especially those in remote areas without laboratory access, and the elimination of impressions may benefit early childhood treatment.

A previous study also showed that the Myobrace appliance and the Twin Block had similar effectiveness in treating a Class II malocclusion.³¹ However, an earlier study reported that conventional functional orthodontic appliances were slightly more effective than the Myobrace appliance in reducing the ANB angle, which decreased by 1.92° in a Twin Block group and 1.34° in a Myobrace group.²³ Both appliances promoted an increase in mandibular body length and contributed to the correction of the Class II malocclusion.²³ In relation to soft tissue changes and the convexity of the facial angle, the Twin Block showed a greater effect than the Myobrace appliance.³⁸ In addition, the Myobrace appliance did not seem to have a significant effect on arch expansion compared to natural growth in the no treatment group.

The Myobrace appliance showed limited efficacy in treating a Class II malocclusion compared with conventional functional appliances like the Twin-Block or Activator, which indicated that these findings are of clinical significance. The modest effect size of the Myobrace appliance suggests that it may be more appropriate for patients with a mild-to-moderate malocclusion or those seeking an economic treatment approach. In contrast, traditional functional appliances may provide better outcomes, particularly for moderate-to-severe Class II cases, due to their ability to deliver more direct and consistent forces to dental and skeletal structures.

Compared with traditional functional appliances, the Myobrace appliance eliminates the need for impressions and subsequent laboratory work.³² It is small, comfortable, and enables children to adapt more quickly.³⁹ Moreover, it costs less than conventional functional appliances.⁴⁰

Patient compliance is critical for the success of functional treatment, and maintaining motivation throughout a treatment period is essential. Poor compliance can lead to delayed or less effective treatment outcomes, and may incur slower occlusal progress or failure to achieve intended corrections.³⁹ An inconsistent use of the Myobrace appliance may impair its ability to promote dental and skeletal changes, including correcting a Class II malocclusion and improving jaw alignment.²⁶ This can result in longer treatment durations, more frequent clinical visits, and potentially the need for additional interventions, thereby increasing overall treatment costs. With proper patient co-operation, functional treatments (such as Myobrace) can also help reduce the risk of future relapse.²⁹

Patient compliance with the Myobrace appliance is an important consideration, as it is generally associated with high dropout rates and poor adherence.^22,23 For example, a large Swedish RCT reported a 70% unsuccessful treatment rate in the Myobrace group.³⁷ The looseness of the appliance, which creates a gap between teeth and the appliance particularly during sleep, may contribute to the high failure rate. Moreover, the Myobrace appliance can interfere with speech and daily activities, causing inconvenience and requiring significant adjustment, which delays treatment and hinders its effectiveness.²²

It is also noteworthy that in some studies, patients who did not adhere to the prescribed wearing protocol were excluded from analysis, and only those who followed the established wearing protocol were included. This approach fails to accurately represent the real clinical setting, as some patients may be unable to consistently and fully adhere to their treatment regimen in their daily lives. Consequently, the results of the study may be subject to selection bias and fail to accurately reflect the treatment outcomes of a typical patient. Such selective exclusion may result in an overestimation of the treatment effect, thereby limiting the external validity and clinical applicability of the study findings.

It is important to note that the majority of current studies on the Myobrace appliance lack sufficient follow-up, with only two studies reviewed for six months to one year.^12,28 However, the two studies did not report dental and skeletal changes after follow-up. A limitation of short-term follow-up is that it may not allow for a comprehensive evaluation of long-term stability and changes in treatment effects. During childhood and adolescence, oral and facial structures undergo significant growth.^41,42 A follow-up period of only 6 to 12 months may fail to capture the full impact of ongoing growth on a treated occlusion. For example, mandibular growth may continue post-treatment, potentially altering corrected overjet and overbite. While the Myobrace appliance aims to guide muscle function and skeletal development, the long-term effects of its intervention on craniofacial growth remain unclear.

Patient compliance was reported in only a limited number of Myobrace studies.^22,26,37 Many studies did not document the number of operators nor their experience levels, which may be potential sources of bias. Additionally, selection bias was likely in participant recruitment and inclusion criteria. The variability in selection processes across studies potentially led to unrepresentative samples and affected the generalisability of the results. Although stringent inclusion criteria were applied to mitigate this, inherent biases in the original studies remain.

The present review has several limitations. The small number of included studies warrants caution in interpreting the results. Some studies were retrospective, and relied on pre-existing data, which may introduce selection bias. The lack of random subject allocation and blinding of participants and staff further increases the risk of performance bias. Additionally, the scarcity of studies assessing long-term outcomes, particularly post-retention results, significantly limits the ability to comprehensively evaluate the stability of Myobrace treatment.

Future research should examine how patient factors such as age, compliance, and malocclusion severity influence treatment outcome stability, soft tissue changes, psychological outcomes, patient satisfaction, anxiety, and self-esteem. High-quality, well-designed clinical trials are crucial for developing definitive clinical recommendations for Myobrace appliances.

Conclusions

Moderate evidence suggests that the Myobrace appliance and traditional functional appliances are effective in correcting a Class II malocclusion, but the Twin-Block appliance is more effective than the Myobrace appliance in inhibiting maxillary growth and reducing overjet and overbite, while the Activator better promotes mandibular growth. The Myobrace appliance offers a cost-effective, less invasive treatment option but may not be suitable for all cases, particularly a severe Class II malocclusion. In contrast, traditional appliances like the Twin-Block and Activator may provide superior dental and skeletal outcomes.