Effectiveness of Preformed Myofunctional Devices in the Treatment of Malocclusions: A Pilot Study

Abstract

Introduction: Preformed myofunctional appliances are increasingly being studied in orthodontics and are typically used to address oral function anomalies as well as malocclusions and development defects of the jaws. The aim of this study is to evaluate the efficacy of a protocol based on the use of preformed devices and myofunctional therapy for the correction of malocclusions. Materials and Methods: A retrospective study was conducted to evaluate the effectiveness of a preformed myofunctional devices in correcting certain orthodontic problems related to overbite, overjet, and cross-bite. Thirty-six patients in the mixed dentition phase were analyzed along with their clinical records, photos, and scans. Overjet, Overbite, and Crossbite were measured by analyzing the files exported in the Standard Tesselation Language format (Stl) of patients’ arches using Zeiss Inspect^® software (version 2025.1.0.1985). Results: The data analysis reveals a statistically significant improvement in the correction of deep bite, overjet, and crossbite. Specifically, regarding the overbite (OVB), the initial measurement at T0 showed an average of 2.52 mm. The average OVB decreased to 1.73 mm at T1. The overjet had an initial average of 3.59 mm at T0, which decreased to 1.77 mm at T1. In this case as well, the difference between the measurements at T0 and T1 was statistically significant. Finally, the crossbite was evaluated by comparing the difference between mandibular and maxillary intermolar widths at T0 and T1. The average difference decreased from 5.84 mm at T0, to 1.68 mm at T1. Conclusions: Preformed myofunctional appliances represent a valid alternative in interceptive orthodontics for correcting and preventing orthodontic issues, especially of mild severity.

1. Introduction

Knowing the cause of malocclusions is essential since it aids in the design of interceptive therapy. By halting undesirable growth patterns, this method seeks to support the healthy development of the patient’s arches and dentition [1].

Malocclusion is a complex condition that can result from a combination of genetic, environmental, traumatic, anatomical, and functional factors.

Malocclusion is often influenced by patterns of autosomal dominant and polygenic inheritance. Genetic variations can cause abnormalities in the development of the jaw and dental arches [2].

Habits such as thumb-sucking or mouth breathing, as well as nutritional influences, play a significant role in the development of malocclusion [3]. Research has highlighted the impact of mouth breathing in childhood, which can lead to malocclusions like an open bite [4].

Conditions such as cleft lip and palate or hemifacial microsomia cause congenital deformities that affect the development of facial bones and teeth, contributing to malocclusion [5].

Misalignments in muscle function (such as improper use of the tongue, lips, or chewing muscles) or inappropriate chewing patterns can contribute to the development of malocclusions [3].

Malocclusions such as variations in overjet or overbite and the presence of unilateral or bilateral crossbite may result from the continuation of these dysfunctions until the permanent teeth appear [1].

Antero-posterior changes or vertical deviations are indicated by overjet, or sagittal overlap of the incisors, and overbite, or vertical overlap of the incisors. A mismatch in the size of the maxillary bones can result in crossbite, a sign of transverse deviation [6].

In terms of the prevalence of malocclusions in the general population, overjet increased in 20.14% and decreased in 4.56%. In relation to vertical malocclusions, the corresponding prevalence rates for open bite and deep overbite are 4.93% and 21.98%, respectively. Regarding the transverse occlusal discrepancies, 6.2 ± 7.8% of children and adolescents have a non-specified crossbite [7,8].

Europe has the lowest frequency of Class I (60.38%) and the highest prevalence of Class II and posterior crossbite (33.51% and 13.8%, respectively) in the permanent dentition. Regarding the prevalence of increased overjet, reversed overjet, deep bite, and open bite, there are no differences between geographic areas [8].

The goal of myofunctional orofacial therapy is to treat facial and oral muscle dysfunction by reestablishing equilibrium between intrinsic and extrinsic forces [9,10]. A common orthodontic treatment for developing kids to address skeletal abnormalities is the use of functional appliances [7]. Jasper jumper, Bionator, Twin block, and Forsus are functional appliances that are used to treat the same malocclusions. Even though therapy success is dependent on patient compliance, many patients reject these unpleasant functional devices [11].

Preformed functional appliances (PFAs) were first introduced in the 1980s and are now available from various manufacturers under different proprietary names, such as LM-Activator^TM (LM-Instruments Oy, Parainen, Finland), Myobrace^® (Myofunctional Research Co., Helensvale, QLD, Australia), and Occluso-Guide^® (Leone SpA, Florence, Italy). Characterized by a removable frame, these appliances are commonly made of soft elastomeric material and feature shields around the dentition. Unlike conventional functional braces, PFAs are distinguished by their softness, lack of customization, and customary association with myofunctional exercises.

Although PFAs have been available for several decades, clinical trials comparing their effects with those of more traditional functional devices have only recently been conducted [12]. In the literature, there is still a lack of studies evaluating the effectiveness of orthodontic devices combined with a myofunctional rehabilitation program.

The aim of this study is to explore the treatment outcomes regarding vertical and transversal discrepancies in patients treated with the Myobrace^® system. The null hypothesis is that this system does not produce significant occlusal improvements. This pilot work primarily aimed to observe preliminary trends and generate hypotheses to be tested in future, more rigorous studies.

2. Materials and Methods

2.1. Study Participants

Thirty-six patients with different types of malocclusions from the Dental Clinic “Ospedale di Circolo, Fondazione Macchi” University of Insubria, ASST Sette Laghi in Varese were evaluated in this study. The patients were aged between 5 and 13 years old. All the patients were in mixed dentition. This study is consistent with the ethical committee no. 0111335 of Università degli Studi dell’Insubria, Varese, Como, Italy.

2.2. Study Design

This is a retrospective study. All patients were in mixed dentition with malocclusions that were characterized by transversal, sagittal, or vertical discrepancy.

These patients were analyzed through photos, digital impressions, and medical records. The discrepancy was measured through the analysis of the STL files with the use of the software Zeiss Inspect^® (version 2025.1.0.1985).

The inclusion criteria of the study were

• Presence of diagnosed malocclusion and oral dysfunction;
• Patient in mixed dentition;
• Patient without any previous orthodontic treatment.

The exclusion criteria of the study were

• Absence of compliance;
• Patients under 5y;
• Patients with previous therapy.

Diagnosis of malocclusion was made with clinical examinations, radiographic evaluations, and digital impressions. Breathing exercises and Payne’s test were used to diagnose oral dysfunction.

From the total number of 40 patients with an average age of 10 years old, 4 were excluded from the study due to a lack of compliance. In the analysis of transversal discrepancy, 5 patients without permanent first molars were excluded. The final number of the included patients is 20 (9 females and 11 males) for vertical and sagittal discrepancy, while 31 (17 females and 14 males) for transversal discrepancy (Figure 1). A total of 7 patients (3 females and 4 males) were diagnosed with posterior crossbite and evaluated before and after treatment.

The posterior crossbite or posterior transverse interarch discrepancy (PTID) was evaluated analyzing the difference at T0 and T1 between the distance among tips of the distobuccal cusps of right and left first mandibular molars (Mandibular intermolar width) (Figure 2) and the distance of the fossae of right and left first maxillary molars (Maxillary intermolar width) (Figure 3) [13].

Overjet was evaluated by analyzing the difference at T0 and T1 between the distance between the midpoint of the incisal edge of the upper incisor and the lower incisors on the horizontal plane.

Overbite was evaluated by analyzing the difference at T0 and T1 between the distance between the incisal edges of the lower incisors and the incisal edges of the upper incisors on the vertical plane.

Patients were evaluated through digital impressions and clinical examinations at T0, prior to the initiation of treatment, and at T1, following the completion of therapy. The T1 was evaluated after 2 years of treatment. Digital impressions were made with CS 3600 (^®; Carestream Dental, Atlanta, GA, USA).

The post hoc power of the study was calculated based on one of the main outcomes, which is OVJ. It was considered in the global population in mixed dentition that an increased OVJ is 23.01% (SD: ±7.56) widespread [13]. In the sample considered, 55.5% have an altered overjet. To achieve 80% power with an alpha level set at 0.05, the sample size was calculated to be 15.

2.3. Statistical Analysis

The statistical analysis performed consisted of descriptive analysis, analyzing frequencies and percentages. OVJ, OVB, and transversal discrepancy were tested for normality with the Shapiro–Wilk Test. The paired t-test was used to assess the possible statistical differences between T0 and T1 of OVB. Overjet did not show a normal distribution. The Wilcoxon rank test was used for overjet analysis. Transversal measurements did not have a normal distribution. They were tested with the Kruskal–Wallis test. PTID showed a normal distribution. A t-test for paired samples was used for PTID analysis. The p and alpha values were set at 0.05.

2.4. Device Description

The Myobrace^® (MB) is a removable, silicone-based device with a pre-shaped design that includes a buccal and lingual shield, a tongue tag, and a tongue elevator. The buccal shield helps prevent overactivity of the orbicularis and buccinator muscles, thereby reducing the inward pressure from the vestibular muscles [14]. The tongue tag encourages the tongue tip to position itself correctly on the palatine wrinkles, behind the upper incisors, which helps facilitate proper lip closure and promotes natural nasal breathing. The tongue elevator helps elevate the tongue (Figure 4).

Each Myobrace^® device has different features depending on the model and the treatment phase. The system offers five specific programs tailored to the patient’s age and dental development. These programs involve using three to four devices, which are swapped out as treatment progresses. The transverse, sagittal, and vertical inconsistencies in this investigation were treated using:

• K (Kids) Series: For the mixed-dentition stage, around ages 6 to 10. It is particularly effective for treating dental crowding and correcting open or deep bites due to oral dysfunction habits.
• T Series (Teens): For the development of permanent teeth, generally between ages 11 and 15. This device helps encourage the correct development of dental arches and tooth alignment.

The different device sizes are selected based on the size of the arches and teeth. The initial devices are more elastic in order to assist the patient in becoming accustomed to wearing them. If the patient wears the device and does the exercises, they advance to harder devices to support teeth alignment and arch growth. The retainer phase is the final stage.

The combination of Myobrace^® and exercises aims to promote comprehensive oral health and address specific problems related to oral dysfunctions.

2.5. The Myobrace System

Myobrace^® is a preformed myofunctional device prescribed during the developmental stage to promote correct oral habits by including Myobrace^® Activities, exercises to improve breathing, tongue, and cheek position [13]. Myofunctional exercises like MRC Trainer Activities^TM, reduce treatment times and enhance result stability by promoting better facial and dental development.

Following the instructions given by orthodontists, the leading manufacturer of PFAs, the exercises should be performed every day after wearing Myobrace^®. The exercises were explained to the patients, who were evaluated at different clinical appointments.

The Myobrace^® System includes the Farrell Bent Wire System (BWS) when dental arch growth is the treatment objective. The BWS can be paired with any first-stage Myobrace^® appliance. Its targeted design allows for simultaneous myofunctional treatment and arch growth. Each expansion cycle lasts an average of three to four months but can be used again until adequate arch development is achieved. After that, the BWS is removed, and the patient moves on to the Myobrace^® device for the second stage.

3. Results

Thirty-six patients, aged between 5 and 13 years, with various types of malocclusions were enrolled in the study; 16 were male and 20 were female. A different Myobrace^® series was given to the patients according to their diagnosis.

The considered outcomes were overjet, overbite, and transversal discrepancy, which are parameters indicative of intermaxillary relationships in the transverse, sagittal, and vertical planes

Table 1. OVJ and OVB measurements.

	OVJ T0 (mm)	OVJ T1 (mm)	OVB T0 (mm)	OVB T1 (mm)
1.	3.3	1.4	2.5	1.1
2.	4.1	1	1.3	2
3.	4.4	2.8	2.3	−0.7
4.	2.8	1.1	2.9	1.6
5.	5.2	2.1	3.4	2.4
6.	3.6	1.6	1.1	2.2
7.	3.4	2	3.5	2.1
8.	2.3	1.7	3.2	3.3
9.	2.8	2.6	3.7	2.5
10.	9.6	1.6	3.6	0.9
11.	3.1	1.9	1.2	1
12.	4.5	1.5	2	0.9
13.	2.7	1.5	−1	0.3
14.	2.8	1.5	3.1	2.4
15.	2.5	2.2	2.3	3
16.	3.7	1.7	2.7	1.5
17.	3.4	2.6	6.4	4
18.	3.4	0	1.9	0
19.	2.1	1.9	3.7	2.5
20.	2.2	2.8	0.7	1.7

,

Table 2. Maxillary intermolar width measurements.

	Maxillary Intermolar Width T0 (mm)	Maxillary Intermolar Width T1 (mm)
1.	38.2	44.2
2.	44.8	45.6
3.	43.3	45.9
4.	40.9	46.3
5.	43.4	44.3
6.	43.6	45.1
7.	39.1	43.9
8.	48.9	49.4
9.	42.1	43.6
10.	46.6	47.1
11.	47.4	50.6
12.	43.9	44.5
13.	42.4	43.7
14.	45.3	46.5
15.	43.5	48.9
16.	43.7	47
17.	43.8	48.2
18.	49.7	53.5
19.	37.2	44
20.	42	46.4
21.	45.9	47.6
22.	44.8	45.8
23.	45.6	46
24.	40.1	46.9
25.	43.5	46.3
26.	41.9	45.5
27.	45.1	44.9
28.	47.1	47.9
29.	40.5	44.3
30.	49	53.5
31.	45.1	49.2

and

Table 3. PTID measurements.

	PTID T0 (mm)	PTID T1 (mm)
1.	4.72	−0.6
2.	5.8	1.7
3.	7.9	2.7
4.	7.5	3.7
5.	4.6	0
6.	6.5	3.9
7.	3.9	0.4

.

The mean OVB at T0 was 2.52 mm (SD: ±1.51), while at T1 the mean was 1.73 mm (SD: ±1.14). There was a statistically significant difference, p < 0.05.

At T0, a mean OVJ of 3.59 mm (SD: ±1.63) was reported, while at T1, a mean of 1.77 mm (SD: ±0.66) was reported. There was a statistically significant difference, p < 0.05.

The cross bite was evaluated by analyzing the difference at T0 and T1 between the Mandibular intermolar width and the Maxillary intermolar width. The mean at T0 was 5.84 mm (SD: ±1.52); the mean at T1 was 1.68 mm (SD: ±1.81). There was a statistically significant difference, p < 0.05.

To analyze the level of transversal expansion, the distance between the fossae of the upper sixth molars at T0 and T1 was considered. At T0, the mean was 43.81 mm (SD: ±3.03), while at T1, it was 46.66 mm (SD: ±2.56). There was a statistically significant difference, p < 0.05 (

Table 4. Pre- and post-treatment measurements.

	N	Minimum (mm)	Maximum (mm)	Average (mm)	SD (mm)	Sign.
OVJ (T0)	20	2.10	9.60	3.5950	1.63143	p = 0.000
OVJ (T1)	20	0.00	2.80	1.7750	0.66797
OVB (T0)	20	−1.00	6.40	2.5250	1.51167	p = 0.008
OVB (T1)	20	−0.70	4.00	1.7350	1.14858
Maxillary Intermolar Width (T0)	31	37.2000	49.7000	43.8193	3.0395	p = 0.000
Maxillary Intermolar Width (T1)	31	43.6	53.5	46.665	2.5691
PTID T0	7	3.90	7.90	5.8457	1.52708	p = 0.000
PTID T1	7	−0.60	3.90	1.6857	1.81239

).

4. Discussion

Orthodontic treatments performed with preformed myofunctional appliances in children could lead to a significant improvement in specific clinical signs of malocclusion, such as overjet, overbite, crowding, and molar relationship, compared to controls [15,16,17]. In addition, a reduction in the asymmetric pattern of palatal growth was reported in most subjects compared to the control groups.

One of the key advantages of elastodontic devices is that they are removable, making them easier for patients to maintain oral hygiene. This can improve patient compliance compared to fixed appliances.

In the early mixed dentition stage, elastodontic devices can help guide the eruption of permanent teeth, ensuring proper alignment and correct occlusion. This can potentially reduce the need for more intensive treatment in the future.

According to the results of our study, it is possible to affirm that the Myobrace^® System could be a therapeutic option.

In particular, the different devices (K and T series) resolved and improved three parameters: OVJ, OVB, and transversal discrepancy.

Elastodontic devices can help achieve partial or complete correction of Class II malocclusion when used in growing patients with mixed dentition and mild to moderate sagittal discrepancies. Like other functional orthodontic treatments, elastodontic devices work by stimulating muscle activity, which triggers skeletal and occlusal changes [18,19].

In this study, the improvement of the OVJ was from 3.59 mm (SD: ±1.63) at T0 to 1.77 mm (SD: ±0.66) at T1. While OVB improved from 2.52 mm (SD: ±1.51) to 1.73 mm (SD: ±1.14). These changes can be related to different reasons, such as the advancement of the mandible with an anterior repositioning, but also a vestibular inclination of the lower incisors caused by the elastodontic device. The elastodontic device, although the material is elastic and not as stiff as the other conventional functional device, can determine an edge-to-edge position of the incisors [20]. Elastodontic devices rehabilitate oral muscle function, which can positively influence jaw growth. The Myobrace^® system, which has vestibular and lingual shields, equilibrates jaw growth by reducing the effects of dysfunctional lips, unbalanced muscle strength, and negative pressure determined by oral habits like thumb sucking. With the Myobrace^® system, there is a correction of the position of the tongue, which can determine improper dental occlusion. Indeed, the MB system has a tongue tag that can help lead patients to achieve a correct posture of the tongue. According to the literature, one of the most important keys to resolving or ameliorating occlusion is to achieve proper swallowing. In this way, MB activities can be very helpful, alone or with a speech therapy aimed at myofunctional rehabilitation, to predispose a correct oral pattern in swallowing and respiration, determining a higher stability of treatment results.

Dysfunctional swallowing and a low lingual resting posture favor a contracted palate [21,22], which in this sample was improved by using the MB system. Crossbite patients improved, and it was evaluated by analyzing the relationship between the jaws. In particular, the difference between the Mandibular intermolar width and the Maxillary intermolar width [23]. The improvement in the transverse measurement could be attributed to the physiological growth of the palate; this hypothesis cannot be excluded due to the absence of a control group in the current study. Since no internal control group was included, reference values for the fossa-to-fossa distance of the upper first molars were obtained from previous scientific studies conducted on healthy pediatric populations [24]. These data were used as a preliminary comparative parameter to assess the extent of the changes observed in our sample after the combined treatment. According to values reported in the literature, the average increase in the distance between the upper first molars during the period between ages 10 and 12 is less than one millimeter. In our study, however, we observed an average increase of 2.8 mm. However, this physiological growth does not apply to the correction of the crossbite, and the PTID calculated at T1 was 1.68 mm (SD: ±1.81), which is smaller than the size of one cusp. This suggests a possible total absence of crossbite. The significant difference implies that the transverse alterations in our sample may be mostly due to the combined therapeutic intervention’s effects rather than being the exclusive product of natural development.

Nasal breathing is crucial for proper facial development in the first years of life, as it stimulates the growth of the facial bones and the nasal and occipital joints. On the contrary, oral breathing can impair this process and lead to alterations in jaw positioning and facial growth. Clockwise rotation of the jaw and increased lower facial height are among the main changes caused by prolonged oral breathing; this breathing pattern can also alter facial structure, with an increase in anterior facial height and a decrease in posterior facial height.

Our study achieved a correct breathing pattern by using specific exercises from the Myobrace Activities, aimed at stimulating nasal breathing. In addition, the use of devices with specially designed holes supports the patient in the transition from oral to nasal breathing, helping to correct breathing patterns gradually. These approaches can be highly effective in improving respiratory function and preventing problems related to facial deformities or sleep-breathing disorders, such as OSA [25].

Preformed devices are designed to achieve a combined effect that includes guiding teeth positioning, training muscle function, and providing comprehensive early intervention. They have been proven to be effective in treating Class II mixed dentition patients with harmful oral habits, such as dysfunctional swallowing and altered lip strength. Research indicates that the most appropriate time for this treatment is during the mixed dentition phase [26]. Therefore, these devices are effective for interceptive orthodontics in growing patients, especially when the patient’s functional patterns are not conducive to harmonious maxillary base growth [27].

Considering the results of our study and those from other articles, there are intriguing insights into the effectiveness of elastodontic devices compared to traditional functional appliances [11,18,28,29,30,31]. Multiple systematic reviews support our study’s findings, showing that EAs are effective in reducing overjet (OVJ), overbite (OVB), and transversal alteration. According to recent literature, when compared to conventional functional appliances, EAs exhibit lower efficacy in achieving dental, skeletal, and soft tissue changes, despite being more cost-effective [18,20].

Nevertheless, it is important to consider treatment not only with the Myobrace^® device, but also with Myobrace^® Activities. This set of exercises allows correct growth patterns to be achieved. The balance of muscle forces promotes the achievement of better orthodontic parameters and greater stability of outcome.

In summary, the MB system can be a very useful device in cases of mild to moderate malocclusion, as it changes the negative growth pattern into a physiological one. However, the MB system allows the combination of myofunctional and interceptive therapy with the use of fixed orthodontic systems. This can enhance its effectiveness in more complex cases. The MB system can find interesting applications as an approach to intercept the causes of malocclusion and as a guide for the correct phase of tooth eruption.

Limits of the Study

This study has several limitations. Firstly, one notable limitation is the small sample size, which is primarily attributed to participant attrition and the challenge of identifying patients who exhibit sufficient adherence to the protocol instructions. Additionally, the follow-up period is restricted to two years, which may limit the long-term applicability of the findings. Furthermore, as a retrospective analysis, the study is susceptible to inherent biases, including potential selection bias. The most significant limitation, however, is the lack of a control group, which restricts the ability to draw definitive conclusions regarding causality.

5. Conclusions

The results of the study suggest that the use of the Myobrace^® system leads to an improvement in overbite, overjet, and transverse dimensions in patients with oral dysfunctions in mixed dentition. The benefits may be related to the interception of the causes of malocclusion and the restoration of muscular equilibrium due to myofunctional treatment. Controlled longitudinal studies on a larger sample of patients are needed to confirm the obtained results and evaluate any other benefits over a longer period, investigating more specifically and with validated tools the improvements in oral function and the stability of the treatment.