https://orcid.org/0000-0002-0887-9385
Abstract
Orofacial myofunctional disorders (OMDs) are conditions or behaviors that negatively affect oral postures and functions. These behaviors can interfere with normal orofacial growth and development and related functions.
Map the available evidence regarding the effectiveness of Orofacial Myofunctional Therapy (OMT) in treating or managing OMDs associated with specific malocclusion traits or orthognathic surgery outcomes.
An experienced librarian developed a comprehensive search strategy for six databases and gray literature. The reference lists of included studies were reviewed.
Randomized controlled trials and non-randomized studies of intervention were included in which individuals with OMDs were treated with OMT, regardless of the healthcare setting or the professional delivering the treatment.
Two independent reviewers screened the retrieved records in two phases based on predefined eligibility criteria and extracted data. The evidence level was assessed using the Oxford Levels of Evidence.
Twenty-four studies were included (18 primary studies and 6 reviews). Seven studies focused on OMDs associated with malocclusion sagittal characteristics (Class I, II, or III), ten examined open-bite-related OMDs, and seven explored OMDs following orthognathic surgery. Only four studies (22%) were randomized controlled trials (RCTs); most studies lacked proper randomization procedures, did not report allocation concealment, and three of the four RCTs were open-label. Among the six comparisons identified, five were deemed plausible (four with a level of evidence 3 and one with a level of evidence 2). No comparisons were rated at level 1 evidence. As a result, the effectiveness of OMT alone or in combination with orthodontic treatment for the conditions of interest could not be conclusively confirmed. Further well-designed RCTs are needed to confirm or refute this finding and to strengthen the overall evidence base.
Although no high-level evidence currently supports the effectiveness of OMT for managing OMDs associated with malocclusion traits, its potential effectiveness remains plausible. Level 2 evidence suggests that OMT may effectively manage OMDs following orthognathic surgery.
Open Science Framework (DOI 10.17605/OSF.IO/M6HNS).
Introduction
Orofacial myofunctional disorders (OMDs) are conditions or behaviors that negatively affect oral postures and functions. Examples of OMDs include tongue thrust, low tongue posture at rest, lip incompetence, open mouth posture, thumb and finger sucking, and biting habits. These behaviors can interfere with normal orofacial growth and development and related functions [1].
Recent systematic reviews have explored potential links between OMDs and malocclusion traits. One review [2] identified an association between atypical swallowing and anterior open bite but found no connection between biting habits and malocclusions. Another review [3] examined the impact of mouth breathing on facial skeletal development in children. The authors found that children who breathed through their mouths exhibited a backward and downward rotation of the mandible and maxilla, along with a steeper occlusal plane. They also noted a tendency for labial inclination of the upper anterior teeth in these children compared to those who did not breathe through their mouths. Furthermore, another systematic review [4] observed a higher prevalence of Angle’s Class II division 1 malocclusion among children with mouth breathing.
Regarding non-nutritive sucking habits, one systematic review [5] suggested a link between these habits and malocclusion traits, including anterior open bite, posterior crossbite, increased protrusion, and a Class II primary canine relationship. The authors also highlighted the negative impact of habit persistence on the development of malocclusion. Another systematic review [6] reported that pacifier use was associated with anterior open bite and posterior crossbite. However, none of these systematic reviews supported a causal relationship between OMDs and malocclusions, primarily because most included studies were cross-sectional.
Orofacial Myofunctional Therapy (OMT), which involves oral or perioral exercises, is sometimes used as an intervention for OMDs. While OMT has been suggested to improve malocclusion traits [7], doubts persist about its effectiveness, both as a standalone treatment and as an adjunct to orthodontic therapy, in managing OMDs associated with malocclusion traits or outcomes of orthognathic surgery. A previous systematic review [8] on the effectiveness of OMT as an adjunct to orthodontic treatment for individuals with OMDs emphasized the need for high-quality evidence to support its use alongside orthodontic therapy. However, this review was published a decade ago. Furthermore, to our knowledge, no systematic or scoping review has specifically investigated the effectiveness of OMT for OMDs related to orthognathic surgery outcomes.
Therefore, this scoping review aimed to answer the following question: ‘What evidence is available in the current literature regarding the effectiveness of OMT in treating or managing OMDs associated with specific malocclusion traits or outcomes of orthognathic surgery?’
Methods
This scoping review was planned and conducted following the JBI Manual for Evidence Synthesis [9] and reported according to the PRISMA extension for Scoping Reviews (PRISMA-ScR) [10]. The protocol was registered on the Open Science Framework with the DOI 10.17605/OSF.IO/M6HNS. This paper represents the second part of a more extensive scoping review aimed at mapping the literature on the effectiveness of OMT in treating and managing OMDs. Given the impracticality of condensing the comprehensive 80-page grant report into a single peer-reviewed article, the material was divided into two publications. The first focused on orofacial myofunctional disorders (OMDs) related to orofacial soft tissue function and oral habits, as reported previously [11]. This paper, in contrast, addresses OMDs associated with malocclusion and outcomes of orthognathic surgery.
The mnemonic PCC (Population, Concept, and Context) [12] was used to define the eligibility criteria.
Randomized controlled trials and non-randomized studies of intervention were included in which individuals with OMDs (Population) were treated with OMT (Concept), regardless of the healthcare setting or the professional delivering the treatment (Context). Additionally, other evidence synthesis papers were considered for inclusion and used either as supplementary literature or to define the level of evidence. We also included studies where OMT was combined with orthodontic appliances or used as part of a pre- or post-orthognathic surgery protocol.
Excluded studies were those that: (1) involved patients with known physical, neurological, and/or orofacial abnormalities; (2) used OMT to manage obstructive sleep apnea, temporomandibular joint disorders, dysphagia, or for cosmetic purposes; (3) employed orthodontic myofunctional appliances passively without associated exercises; (4) tested OMT in individuals without OMDs (i.e. healthy participants); (5) did not describe the OMT protocol, either in the text or cited literature; (6) made it impossible to isolate OMT’s effects from cointerventions; or (7) were preclinical studies, case reports, or case series with fewer than 10 participants.
An experienced health sciences librarian (JYK) developed a comprehensive literature search strategy using controlled vocabulary related to OMT (e.g. myofunctional therapy, myology) and OMDs (e.g. sucking habits, atypical swallowing) or orofacial structures (e.g. lips, tongue, cheek), along with relevant keywords and synonyms. This search strategy was initially applied to the Ovid Medline database and then adapted for use in five other databases: Ovid Embase, Web of Science Core Collection, Cochrane Library, Scopus, and LILACS, as well as gray literature sources (ProQuest Dissertations & Theses Global and Google Scholar). No language or date limits were applied. The complete search strategies for each database and gray literature source are provided in Supplementary Table 1. JYK conducted the first search on May 16, 2023, and updated it on July 30, 2024. The records retrieved from each database or website were imported into Covidence software (https://www.covidence.org/).
Two independent reviewers (CMS and AAL) evaluated the retrieved records using a two-phase approach. In phase one, they assessed titles and abstracts based on the eligibility criteria. In phase two, they reviewed the full text of the records that met the initial criteria. Prior to each phase, the reviewers conducted a calibration round, evaluating the first ten records. Any discrepancies were resolved through consensus or by consulting a third reviewer (FMS). Additionally, the reference lists of the included studies and evidence maps from the American Speech-Language-Hearing Association (ASHA) website [13] were manually searched.
CMS extracted data (population characteristics, target OMDs, intervention, comparison, and effectiveness of OMT) from the included studies using Covidence software. AAL cross-checked all extracted information, and any discrepancies were resolved through consensus or by consulting a third reviewer (FMS).
The level of evidence was appraised using the Oxford-CEBM Levels of Evidence for intervention questions [14], considering the strongest available evidence on the effectiveness of OMT for each OMD. Evidence was rated as Level 1 if a systematic review of randomized trials or n-of-1 trials was available; Level 2 if randomized trials or observational studies with dramatic effects were available; Level 3 if non-randomized controlled cohorts or follow-up studies were available; Level 4 if only case-series, case-control studies, or historically controlled studies were available; and Level 5 if mechanism-based reasoning studies were available. The level of evidence was further downgraded based on the quality of the evidence [14].
Finally, the evidence for the effectiveness of OMT for each comparison was classified according to the highest level of evidence found: (1) confirmed—if moderate or high certainty Level 1 evidence of effectiveness existed; (2) plausible—if Level 2 or 3 evidence was available; (3) inconclusive—if Level 4 or 5 evidence was available; or (4) inexistent—if no evidence was available for a given comparison.
Results
A total of 22 201 records were retrieved, with 12 536 remaining after deduplication. After phase 1 (title and abstract screening), 166 studies were selected for full-text review. Ultimately, 74 studies (77 reports) were included. A manual search added 11 additional studies, bringing the total to 85 included studies (88 reports). Of these, 24 studies focused on the effectiveness of OMT for treating or managing OMDs associated with malocclusion traits or orthognathic surgery outcomes and were included in this publication. Studies addressing OMDs related to the functions of orofacial soft structures and oral habits were included in the previous scoping review report [11]. Two studies [15, 16] addressed both topics and were included in both reports. The inclusion process flowchart is shown in Fig. 1. A list of studies excluded after full-text review, along with reasons for exclusion, is available in Supplementary Table 2.
Flow diagram of literature search and selection criteria (adapted from PRISMA 2020).
Regarding the nationality of the corresponding authors of the 24 included studies, the majority were from the Americas and Europe (n = 8, 33.3% each) (Fig. 2A). Brazil had the highest number of studies (n = 4, 16.7%), followed by Japan (n = 3, 12.5%). The publication years ranged from 1997 [7] to 2024 [17, 18]. Most studies (n = 21, 87.5%) were published from 2010 onwards (Fig. 2B). English was the predominant publication language (n = 21, 87.5%).
Distribution of included studies (n = 24) according to corresponding author’s continent (A) and decade of publication (B).
Regarding study design -- some of which were reclassified by the scoping review authors according to the taxonomy proposed by Reeves et al. [19] (2017), non-randomized controlled trials (non-RCTs) and systematic reviews were the most common (n = 5, 20.8% each), followed by RCTs and before-and-after studies (n = 4, 16.7% each). Studies were classified as randomized controlled trials (RCTs) if randomization was mentioned, regardless of whether the specific process was described. Studies were classified as non-RCTs if randomization was not mentioned or if participants were assigned to groups based on availability or willingness to receive treatment.
The Orofacial Myofunctional Disorders (OMDs) considered in the included studies were those associated with dental malocclusions (Angle’s Class I, II, or III) (n = 7), anterior open bite (n = 10), or residual OMDs following orthognathic surgery (n = 7). Fig. 3 illustrates the distribution of target conditions according to the study design.
Distribution of included studies (n= 24) according to target condition and study design.
The sample size of the 18 primary studies ranged from 8 [15] to 384 [20] participants. A total of 1050 patients were treated, with 625 receiving the intervention of interest (OMT). The target population consisted of children (ages 2–18) in 10 studies (55.6%), adults in 7 studies (38.9%), and both children and adults in one study (Fig. 4A). Most studies (n = 12, 66.7%) included two or more therapeutic arms (Fig. 4B), with four studies incorporating a third arm that included non-orthodontic patients for comparison. The follow-up period ranged from 4 weeks [15] to 72 months [21] (Fig. 4C), with half of the studies (n = 9, 50%) having 6 months or less follow-ups. A positive result for OMT was reported in 16 of the 18 primary studies (88.9%) (Fig. 4D). Most studies (n = 10, 55.6%) were conducted in university settings. Private or public clinics accounted for 16.7% (n = 3) of the studies, while 11.1% (n = 2) were conducted in multiple settings. One study (5.6%) took place in a public school, and the setting was not reported in two studies (11.1%).
Distribution of included primary studies (n = 18) according to: A) Target population (Children vs. Adults or Both); B) Number of study’s arms; C) Period of follow-up; and D) OMT efficacy (Positive vs. Negative or Inconclusive).
Over half of the primary studies did not specify the professional delivering OMT (n = 10, 55.5%). Among those who did provide this information, the most common provider was the speech-language therapist (n = 4, 22.2%), followed by the orofacial myologist (n = 2, 11.1%). In one study [22], OMT was delivered by a general practitioner, and in another [23], both an orthodontist and a speech therapist were involved. Five studies mentioned the use of myofunctional devices in conjunction with OMT. Of these, two studies [22, 24] used preformed myofunctional devices, and three [18, 20, 23] used a removable orthodontic appliance.
Analysis of the evidence found according to target OMD
Effectiveness of OMT in the treatment of OMDs associated with malocclusion sagittal classification (Class I, II, or III)
Seven studies focused on OMDs associated with malocclusion, including five primary studies [18, 20, 22, 24, 25] and two systematic reviews [8, 26]. Among the primary studies, one had a before-and-after design [25], one was a prospective cohort [24], one a retrospective cohort [20], one a non-RCT [22], and one an RCT [18]. The total number of participants in primary studies was 452, with 261 receiving the intervention of interest. Four studies [18, 20, 22, 24] included patients with Class II division 1 malocclusion, while one study [25] did not specify the type of malocclusion addressed. Two primary studies [22, 24] tested preformed myofunctional orthodontic devices in combination with OMT, while two others [18, 20] tested removable orthodontic appliances, both with and without associated OMT.
The strongest evidence came from a small open-label RCT [18] with randomization conducted by the operator, which tested the effects of combining headgear (HG) with lip exercises (OMT) on lip incompetence in children with Class II division 1 malocclusion. After 6–8 months of treatment, the HG + OMT group showed significantly greater improvements in interlabial gap closure, upper lip length, and upper lip vermilion height compared to the HG-only group.
The next strongest evidence came from a robust retrospective cohort study [20] with blinded outcome assessors, which compared Twin Block (TB) braces for Class II, division 1 malocclusion with and without OMT (n = 384). Although combining TB with OMT resulted in a shorter treatment time (a mean difference of 46 days, which could be considered clinically irrelevant), no differences were found in cephalometric or electromyographic parameters.
One non-RCT [22] tested OMT combined with the Myobrace® preformed removable orthodontic device, comparing it to both no treatment and a group without malocclusion, using electromyography (EMG). After six months, the results showed improved muscle activity (masseter, temporalis, and mentalis) in the OMT + Myobrace® group compared to the untreated group, with no significant differences between the OMT + Myobrace® group and the group without malocclusion. Clinically, improvements were observed in breathing type, lip hypotonia, lip seal, and tongue posture at rest.
In a prospective multicenter, single-arm cohort study [24], a preformed myofunctional device (EF Line®) combined with OMT was tested for 12 months. This study found improvements in tongue position and function, increased tongue/palate contact, enhanced lip tension and function, and better breathing type.
A small before-and-after study [25] tested OMT alone for treating OMDs associated with an unspecified malocclusion. The study reported subjective clinical improvements in breathing type, swallowing, and lip position at rest.
Finally, one systematic review [8] addressed a PICO question similar to the one explored in this subsection. However, of the four studies included, only one [21] met the inclusion criteria for this scoping review and had already been included (it is described in the section addressing the effectiveness of OMT for treating open bite-associated OMDs). Two other studies [27, 28] briefly mentioned the use of OMT but lacked detailed descriptions, and the fourth study [29] used OMT as part of an orthognathic surgery protocol without presenting individualized results. A second systematic review [26] evaluated the use of preformed versus custom-made myofunctional appliances. Of the four studies included, only one [30] used exercises with the preformed appliance. However, it was excluded from this review as it focused in the comparison of two removable orthodontic appliances (preformed versus conventional functional activator), and not in the OMT.. Therefore, the systematic reviews could not be considered to define the evidence level for this subsection.
Level of evidence: The strongest evidence for the comparison ‘OMT vs. no treatment’ was Level 4 (one before-and-after study [25]), therefore considered inconclusive. For the comparison ‘OMT with preformed myofunctional appliance vs. no treatment’, the best evidence was Level 3 (plausible) from one non-RCT [22]. For the comparison ‘OMT associated with orthodontic treatment vs. orthodontic treatment alone’, the best evidence came from a small RCT [18] testing OMT + Headgear, which was downgraded due to critical methodological limitations, and a retrospective cohort [20] testing OMT + Twin Block. The level of evidence for this comparison was considered Level 3, with efficacy deemed plausible.
Table 1 summarizes the evidence on the effectiveness of OMT for treating malocclusion-associated OMDs and the corresponding levels of evidence. Detailed information on the included studies can be found in Supplementary Table 3.
Characteristics of the evidence found on the effectiveness of OMT according to target OMDs and respective levels of evidence.
| Target OMDs | Studies and designs | Comparisons and best evidence founda | Level of evidence and interpretationb |
|---|---|---|---|
Malocclusion (Angle’s Class I, II, and III) associated OMDs
| Before-and-after [25] Prospective cohort (single arm) [24] Retrospective cohort (two arms) [20] Non-RCT [22] RCT [18] Systematic reviewc [8, 26] |
|
|
Anterior open bite associated OMDs
| Before-and-after [15, 16, 31] Retrospective cohort [7, 21] RCT [32] Narrative review [33] Systematic reviewc [17, 34, 35] |
| |
Post-orthognathic surgery associated OMDs
| Retrospective cohort [23] Non-RCT [36–39] RCT [40, 41] |
|
| Target OMDs | Studies and designs | Comparisons and best evidence founda | Level of evidence and interpretationb |
|---|---|---|---|
Malocclusion (Angle’s Class I, II, and III) associated OMDs
| Before-and-after [25] Prospective cohort (single arm) [24] Retrospective cohort (two arms) [20] Non-RCT [22] RCT [18] Systematic reviewc [8, 26] |
|
|
Anterior open bite associated OMDs
| Before-and-after [15, 16, 31] Retrospective cohort [7, 21] RCT [32] Narrative review [33] Systematic reviewc [17, 34, 35] |
| |
Post-orthognathic surgery associated OMDs
| Retrospective cohort [23] Non-RCT [36–39] RCT [40, 41] |
|
Note: descriptive characteristics of included studies for each target OMD are displayed in Supplementary Tables 1 to 3.
aIn bold letters, the favored treatment (P < .05). Comparisons not highlighted indicate no difference between interventions. Inconclusive results were not highlighted, even in the occurrence of statistically significant differences.
bThe best evidence found for each comparison identified. Only studies in which OMT effectiveness could be evaluated individually were considered to determine the level of evidence.
cThese Systematic reviews did not contribute to determining the level of evidence (see the main text for details).
Characteristics of the evidence found on the effectiveness of OMT according to target OMDs and respective levels of evidence.
| Target OMDs | Studies and designs | Comparisons and best evidence founda | Level of evidence and interpretationb |
|---|---|---|---|
Malocclusion (Angle’s Class I, II, and III) associated OMDs
| Before-and-after [25] Prospective cohort (single arm) [24] Retrospective cohort (two arms) [20] Non-RCT [22] RCT [18] Systematic reviewc [8, 26] |
|
|
Anterior open bite associated OMDs
| Before-and-after [15, 16, 31] Retrospective cohort [7, 21] RCT [32] Narrative review [33] Systematic reviewc [17, 34, 35] |
| |
Post-orthognathic surgery associated OMDs
| Retrospective cohort [23] Non-RCT [36–39] RCT [40, 41] |
|
| Target OMDs | Studies and designs | Comparisons and best evidence founda | Level of evidence and interpretationb |
|---|---|---|---|
Malocclusion (Angle’s Class I, II, and III) associated OMDs
| Before-and-after [25] Prospective cohort (single arm) [24] Retrospective cohort (two arms) [20] Non-RCT [22] RCT [18] Systematic reviewc [8, 26] |
|
|
Anterior open bite associated OMDs
| Before-and-after [15, 16, 31] Retrospective cohort [7, 21] RCT [32] Narrative review [33] Systematic reviewc [17, 34, 35] |
| |
Post-orthognathic surgery associated OMDs
| Retrospective cohort [23] Non-RCT [36–39] RCT [40, 41] |
|
Note: descriptive characteristics of included studies for each target OMD are displayed in Supplementary Tables 1 to 3.
aIn bold letters, the favored treatment (P < .05). Comparisons not highlighted indicate no difference between interventions. Inconclusive results were not highlighted, even in the occurrence of statistically significant differences.
bThe best evidence found for each comparison identified. Only studies in which OMT effectiveness could be evaluated individually were considered to determine the level of evidence.
cThese Systematic reviews did not contribute to determining the level of evidence (see the main text for details).
Effectiveness of OMT in the treatment of OMDs associated with open bite
Ten studies addressed open bite-associated OMDs, including six primary studies [7, 15, 16, 21, 31, 32], three systematic reviews [17, 34, 35], and one narrative review [33]. Among the primary studies, three were before-and-after designs [15, 16, 31], two were retrospective cohort studies [7, 21], and one was a randomized controlled trial (RCT) [32]. The total number of participants across primary studies was 189, with 112 receiving the intervention of interest (OMT).
The only RCT [32] identified did not provide details on the randomization process, allocation concealment, or blinding. It compared children with anterior open bite who received OMT to untreated children. The authors reported increased tongue strength, improved tongue position at rest, better swallowing patterns, and open bite closure six months after OMT was completed.
A retrospective cohort study [21] emphasized the importance of combining OMT with orthodontic treatment, suggesting that the combination was more effective than orthodontic treatment alone in preventing open bite relapse. It also showed improved habit control, tongue position at rest, and swallowing patterns. Another retrospective cohort study [7] included patients who received OMT before, after, or simultaneously with orthodontic treatment, as well as those who received OMT without orthodontic treatment. This study found improvements in overjet across all groups, regardless of the timing of orthodontic treatment. However, open bite correction was 0.6 mm greater in the groups that received orthodontic treatment after OMT or no orthodontic treatment at all compared to those who received orthodontic treatment before or simultaneously with OMT. Additionally, the study found no significant association between patient age and improvement in tooth position.
Among the before-and-after studies, one [15] tested OMT for tongue reeducation in boys with open bite, focusing on changes in both soft and hard tissues. The authors observed a cephalometric trend toward open bite reduction and further eruption of the upper and lower incisors, although the differences were not statistically significant. They also noted small changes in swallowing patterns, but again, these were not statistically significant. The second study [16] assessed variations in labial force values and open bite following OMT, which included lip massage and tongue training. Lip strength increased, 90.3% of children achieved lip seal, and the open bite (measured in mm) was significantly reduced after 12 months, with a mean reduction of 2.1 mm. The third study [31] evaluated the effectiveness of OMT using electromyography (EMG), comparing a group of children with anterior open bite to a control group without malocclusion. The study found that the muscles involved in chewing exhibited increased strength during maximum voluntary contraction in the intercuspal position, while the perioral muscles involved in lip sealing showed relaxation, suggesting a tendency toward functional normalization following OMT.
Three of the included reviews [33–35] shared a similar goal: to compare the effectiveness of various orthodontic, OMT, or combined therapy interventions in managing anterior open bite. One systematic review [34], despite significant methodological limitations, concluded that the combined approach (OMT + orthodontics) was often overlooked. Another methodologically rigorous systematic review [35] emphasized the lack of high-quality evidence regarding early orthodontic management and myofunctional treatment in the developing dentition. A narrative review with a systematized search [33] suggested that combined therapy was the best approach, though the authors did not include any primary studies testing this combined treatment. As a result, these three reviews were not used to determine the level of evidence for the comparisons in this subsection.
The most recent systematic review [17] focused on management strategies for open-bite relapse. Among the studies included, only two used OMT [21, 32], both of which were already included in this scoping review. Despite differences in study design—one being an RCT [32] and the other a retrospective cohort study [21]—and variations in the interventions tested (OMT + fixed orthodontic appliances vs. fixed orthodontic appliances alone [21], and OMT vs. no OMT [32]), the authors of the systematic review pooled the results in a meta-analysis, comparing them with four other subgroups. The review found that OMT was associated with a lower relative risk of open-bite relapse compared to surgical modalities and both fixed and removable appliances. However, while the authors highlighted a noticeable impact of OMT in reducing relapse risk in the results section, they later stated in the discussion that OMT was the least effective management strategy for open-bite relapse. This inconsistency, along with significant methodological issues, led to the exclusion of this systematic review in determining the level of evidence for this subsection.
Level of evidence: The strongest evidence for comparing ‘OMT vs. no treatment’ came from a small RCT [32], which was downgraded to level 3 due to significant limitations and a short follow-up period. Despite these issues, the efficacy of OMT was considered plausible. For the comparison ‘OMT with orthodontic treatment vs. orthodontic treatment alone’, the strongest evidence came from a retrospective cohort study [21], with the level of evidence rated as 3. This also suggests that the efficacy of OMT in this context is plausible.
Table 1 summarizes the evidence found on the effectiveness of OMT for treating OMDs associated with open bite and the levels of evidence. Supplementary Table 4 provides detailed information on the included studies.
Effectiveness of OMT in the treatment of OMDs associated with orthognathic surgery outcomes
Seven studies addressed residual OMDs post-orthodontic surgery, all of which were primary studies. These included one retrospective cohort study [23], four non-RCTs [36–39], two of which [36, 37] had an additional group of non-malocclusion subjects, and two RCTs [40, 41], both of which also included a third group of non-malocclusion subjects (non-malocclusion group). The total number of participants across primary studies was 238, with 113 receiving the intervention of interest. Notably, only one study [23] used removable orthodontic appliances in combination with the intervention.
All studies included adult patients who had undergone orthognathic surgery, and all reported positive outcomes when these patients engaged in chewing, swallowing, and tongue position exercises. Three Japanese non-RCTs [36, 37, 39] focused on mastication training using hard chewing gum, which involved simple, easy-to-execute exercises. Two of these studies [36, 37] included a third group without malocclusion for comparison. The results showed that masticatory efficiency, the number and area of occlusal contacts, and occlusal force improved with chewing exercises, although these measures were still lower than the non-malocclusion group [36]. Additionally, muscle activity and jaw movement patterns during chewing improved in the training group when compared to a negative control group [37, 39].
The remaining four studies focused on a more traditional and intensive form of OMT, which involved multiple exercises—both in-office and at home—targeting chewing, swallowing, jaw movement, lip and tongue tone, and position at rest. Two of these were small RCTs [40, 41]. The first RCT [40], part of a doctoral thesis, was carefully designed (the only study to describe allocation concealment) but included a small sample size (n = 11). The study compared an intensive OMT program to a brief orientation focused on chewing patterns and included a third group of non-malocclusion controls. Results showed that OMT significantly improved mobility, chewing, swallowing, and jaw movements compared to the instruction group, with no significant differences from the non-malocclusion group. However, there were no differences between groups in electromyographic (EMG) activity of the masseter and temporalis muscles, both of which were inferior to those in the non-malocclusion group. The second RCT [41], which lacked allocation concealment and blinding, compared traditional intensive OMT to no treatment, also including a third group of non-malocclusion participants. The study found that OMT improved orofacial functions compared to no treatment, although these functions were still worse than those in the non-malocclusion group.
One non-RCT [38] compared intensive OMT to no treatment and reported improvements in all orofacial functions (breathing, chewing, swallowing, and speech) following OMT, although there were no significant differences in oral health-related quality of life between groups. Finally, a single-arm retrospective cohort study [23] noted that 63% of patients who underwent orthognathic surgery required a more intensive OMT approach for facial muscle reeducation, while 17% failed to improve even after intensive OMT. The authors concluded that many patients’ functional habits do not change substantially after orthognathic surgery; rather, they often revert to their original functional patterns. They suggested that only active reeducation could alter these old patterns and establish new functional ones compatible with the new orofacial structural configuration.
Level of evidence: The strongest evidence for the comparison of ‘traditional OMT vs. no treatment’ came from two small RCTs [40, 41], with the level of evidence rated as 2, indicating that the efficacy of OMT is plausible. For the comparison of ‘OMT (mastication exercises with hard chewing gum) vs. no treatment’, the best evidence came from three non-RCTs [36, 37, 39]. The level of evidence was rated as 3, and the efficacy of OMT was considered plausible.
Table 1 summarizes the evidence found on the effectiveness of OMT for the treatment of OMDs associated with open bite after orthognathic surgery and levels of evidence. Supplementary Table 5 provides detailed information on the included studies.
Discussion
This scoping review aimed to map the available evidence on the effectiveness of Orofacial Myofunctional Therapy (OMT) for treating or managing Orofacial Myofunctional Disorders (OMDs) associated with malocclusion traits or outcomes following orthognathic surgery. Of the seven comparisons on the efficacy of OMT for different OMDs linked to dental malocclusion or orthognathic surgery, six were considered plausible, meaning OMT was deemed potentially effective. Five of these comparisons had a level of evidence rating of 3, while one was rated level 2. No comparisons reached level 1 evidence, which is typically derived from systematic reviews (SR).
SRs are considered the highest level of evidence for evidence-based practice and clinical decision-making in healthcare [14]. An SR aims to gather and critically appraise all available evidence that meets pre-specified eligibility criteria to answer a specific clinical question. Methodologically rigorous SRs provide reliable findings using explicit, systematic methods that minimize bias, draw trustworthy conclusions, and inform clinical decisions [42]. The effectiveness of a treatment can only be considered confirmed (level 1 evidence) when SRs show clinically and statistically significant results with moderate to high certainty of evidence.
Although five of the included studies were SRs—two focused on malocclusion traits [8, 26] and three on anterior open bite [17, 34, 35] – none of them presented the same PICO (Population, Intervention, Comparison, Outcome) framework as the comparisons identified in this review. The closest match was the SR by Homem et al. (2014) [8], which sought to determine whether there was scientific evidence supporting the use of OMT as an adjunct to orthodontic treatment in individuals with orofacial disorders. However, the authors concluded that there was insufficient evidence to support the combined use of OMT and orthodontic treatment. As a result, none of the systematic reviews contributed to determining the level of evidence for any of the comparisons identified in this scoping review.
Additionally, we found no SRs that addressed the effectiveness of OMT for treating OMDs associated with post-orthognathic surgery. Nevertheless, based on the available evidence, it is too early to justify a systematic review (SR) that will change the current conclusions.
In the absence of SRs, randomized controlled trials (RCTs) are considered the next most trusted source of evidence for intervention-related questions [14, 42]. Among the 18 primary studies identified, only four were RCTs—two [18, 32] focused on the effectiveness of OMT for malocclusion traits and two [40, 41] on the efficacy of OMT for post-orthognathic surgery-associated OMDs—addressing three different comparisons. Of these, only one comparison was classified as plausible, with a level of evidence 2: intensive OMT versus no treatment for post-orthognathic surgery-associated OMDs. This evidence came from two RCTs: one [40] with a more rigorous design and a longer follow-up (12 months), and another [41] with methodological limitations (no allocation concealment, no blinding) and a shorter follow-up (6 months). While their methods were not identical—one study [40], compared traditional intensive OMT sessions versus two sessions focusing on the perception of the stomatognathic system and mastication patterns, and the other [41] had a no-treatment control group—their findings were comparable. Both studies also included a third group of non-malocclusion participants. The results suggested that orofacial functions were normalized by the end of the evaluation period, with muscle activity in the OMT group falling between the non-OMT and non-malocclusion groups. However, the study [40] with the most rigorous design and strongest results also had the smallest sample size, while the other study’s results [41] were less pronounced. Needless to say, reliable and replicable results are essential to establish the effectiveness of an intervention [43]—clinicians need confidence that the chosen intervention consistently delivers clinically meaningful results compared to other interventions or no treatment, ideally in a cost-effective manner.
Only one RCT [32] tested the effectiveness of OMT for treating anterior open bite-associated OMDs. Due to critical methodological limitations—such as the lack of description of the randomization process, no allocation concealment, and no blinding—the level of evidence for this comparison was downgraded to 3, although its plausibility was still considered. Among OMDs associated with anterior open bite, atypical swallowing (with tongue thrust) is the most common, although a low rest position is also frequently observed. The study’s findings suggested improvements in swallowing patterns, tongue position, and incisor contact by the end of the evaluation period.
One RCT [18] addressed OMDs associated with Class II, division 1 malocclusion, comparing OMT combined with activator high-pull headgear to headgear alone. Like the other RCT, this study had several methodological issues, including the lack of blinding and randomization carried out by the operator. Although the authors reported improvements in interlabial gap closure, upper lip length, and upper lip vermilion height in the test group, these results should be interpreted with caution, leading to a downgrade in the level of evidence to 3 (still plausible).
Since OMT increases the overall cost of orthodontic treatment and impacts families’ routines, more robust evidence is needed to justify its use for treating or managing malocclusion traits. In contrast, the benefits of OMT in post-orthognathic surgery are more evident. However, well-designed, methodologically sound RCTs are crucial to confirm these findings and elevate the level of evidence for the comparisons identified. Since level 1 (confirmed) evidence is unavailable, individual case evaluation and professional discretion are recommended to determine whether OMT should be combined with orthodontic treatment.
Furthermore, the effectiveness of orofacial myofunctional therapy may be influenced by key features of the intervention, including the prior training and expertise of the administering professional, as well as the type and intensity of the therapy delivered. These characteristics were not examined within the scope of this review and may constitute a valuable avenue for future research.
Conclusion
Although high-level evidence is currently lacking (with only Level 3 evidence available) regarding the effectiveness of OMT for managing OMDs associated with malocclusion traits, its efficacy remains plausible. Level 2 evidence suggests that OMT may be effective in managing OMDs associated with post-orthognathic surgery. However, further well-designed RCTs are needed to confirm or refute these findings and strengthen the overall evidence.
Conflict of interest
The authors declare no conflict of interest.
Funding
This scoping review was supported by the Federation of Dental Hygiene Regulators of Canada (FDHRC) —Grant number RES0063426 FDHRC SROMT.
Data Availability
Online supplementary tables present additional detailed primary data.
