Effectiveness of Myofunctional Therapy in Ankyloglossia: A Systematic Review

Ankyloglossia is a pathology of the tongue in which the frenulum appears anchored to the floor of the mouth. The treatment of choice for this pathology is frenectomy, but myofunctional therapy is emerging in recent years as a complement to surgical intervention. This systematic review aims to synthesize the scientific evidence and assess its quality regarding the use of myofunctional therapy in ankyloglossia. The Cochrane Central Register of Controlled Trials, Physiotherapy Evidence Database, Pubmed, Web of Science and Scopus were searched. Study quality was determined using the PEDro scale, STROBE statement and single-case experimental design scale. Eleven studies were selected. Based on the studies included in this review, surgery is more effective than myofunctional therapy, although better results are achieved if both are combined. Improvements have been found in maternal pain, weight gain of babies, duration of breastfeeding, tongue mobility, strength and endurance, sleep apnea, mouth breathing and snoring, quality of life, clenching teeth, myofascial tension, pain after surgery and speech sound production. These findings must be taken with caution because of the small number of articles and their quality. Future clinical trials using larger sample sizes and with higher methodological quality are needed.


Introduction
The term ankyloglossia comes from the Greek word meaning "tongue-tie". It is a congenital anomaly in which the lingual frenulum restricts the mobility of the tongue [1]. It is most common in newborns, being more frequent in males because of its X-linked genetic characteristics [2] caused by mutations in the TBX22 gene [3].
Its prevalence ranges from 0.1 to 12%. Regarding the current frequency of diagnosis of ankyloglossia compared to 20 years before, there has been an increase probably related to concerns about its impact on breastfeeding [4]. The World Health Organisation (WHO) recommends that babies should be breastfed for the first six months and continue until two years of age, along with food intake [5].
Its main consequence is difficulty in breastfeeding because of ineffective tongue movements that lead to poor nipple attachment and sucking, causing pain and cracks and hindering milk extraction, affecting the mother and the infant's development [4].
Other disorders in adults have also been linked to ankyloglossia, such as solid fee-ding problems, choking, nausea, feeding frustration, tongue thrusting, speech difficulties and airway obstruction [6].
Patients presenting with this pathology are often offered a frenectomy, a surgical intervention that removes the frenulum [7], which sometimes presents postoperative complications such as infections, tongue biting and bleeding [8]. There are different surgical procedures such as frenotomy, frenulectomy, frenuloplasty, miofrenuloplasty, Z-plasty and V-Y plasty [9]. Most commonly, a simple frenotomy with scissors or a laser frenectomy is performed [10].
Scientific literature supports early frenotomy in severe cases of ankyloglossia, but debate continues about treatment of mild and moderate degrees of tongue-tie resulting in extensive variations in clinical practice [11].
Physiotherapy has been used both preoperatively and postoperatively to improve the prognosis. Techniques used have included speech exercises, oral cavity morphology awareness and myofunctional therapy (MFT) involving stretching, exercises, extrabuccal and intrabuccal massages [12]. MFT can lead to the release of tongue-tie through intraoral and extraoral stimulation without the need for surgery [8].
This paper aims to provide an updated perspective on MFT research in ankyloglossia and to analyze its efficacy, as an adjunct or not to frenectomy, in improving patients with ankyloglossia.

Materials and Methods
The PRISMA (preferred reporting items for systematic reviews and meta-analyses) [13] guidelines were followed to perform this systematic review (Appendix A). The search protocol was registered in the PROSPERO database of prospectively registered systematic reviews (CRD42022333529).

Search Strategy
The literature search was performed between May and June 2022 in the following electronic databases: PubMed, Cochrane Central Register of Controlled Trials (CEN-TRAL), Scopus, PEDro (Physiotherapy Evidence Database) and Web of Science (WOS). The following descriptor terms combined with Boolean operators were employed: ("ankyloglossia" OR "tongue tie" OR "lingual frenum" OR "lingual frenulum" OR "short lingual frenulum") AND ("myofunctional therapy" OR "tongue orofacial exercises" OR "functional therapy protocol" OR "functional therapy" OR "oral myofunctional" OR "orofacial myofunctional" OR "myofunctional" OR "myofunctional training" OR "orofacial myo-logy" OR "orofacial myofunctional therapy" OR "therapy" OR "physiotherapy". No date and language filters were applied. Table 1 shows the different search combinations.

Selection Criteria
The PICOS (population, intervention, comparison, outcomes and study design) model [14] was used to establish the inclusion criteria: (1) population: individuals of any age with ankyloglossia; (2) intervention: MFT, used as an adjunct to surgery or as a treatment; (3) comparison: absence of treatment, surgery or other therapies used; (4) outcome: any physical variable susceptible to improvement after MFT; (5) study design: controlled clinical trials, observational studies and case studies. Articles in which participants were people with disorders of the tongue, the origin of which was not ankyloglossia, were excluded.

Study Selection Process and Data Extraction
The papers were independently reviewed and selected by two of the researchers The information was extracted from each study related to authors, date of publication, type of study, number and gender of the sample, interventions, outcome measures, measurement instrument and results obtained.

Assessment of Methodological Quality
The PEDro scale was used to assess the methodological quality of the randomized clinical trials included in the review. It consists of 11 items related to the domains of selection, performance, detection, reporting and attribution bases [15]. A study with a score of 6 or more is considered as a level of evidence 1 (6-8 would be good, 9-10 would be excellent), and a study with a score of 5 or less is considered level of evidence 2 (4-5 would be acceptable, <4 would be poor) [16].
To assess the methodological quality of the observational studies, the STROBE statement was used: it contains a total of 22 items that evaluate elements such as article title, abstract, introduction, methods, results, discussion sections and other information [17].
For the evaluation of the case studies was used the single-case experimental design scale (SCED) with 11 items. Scoring ranges from 0 to 10, with higher scores suggesting higher methodological quality [18].

Risk of Bias of Randomised Clinical Trials
The Cochrane collaboration tool [19] and the Review Manager 5.3 software (The Cochrane Collaboration, London, UK), which includes a description and rating of each item in relation to the bias table, were used to assess the risk of bias of randomized clinical trials. After assessing the risk of bias of each study, they were classified as low risk, high risk and unclear risk. The following types of bias were assessed: selection bias, performance bias, detection bias, attrition bias, reporting bias and other bias.

Selection of Studies
A total of 652 potentially relevant articles were retrieved after the selection process. The entire selection process in the different phases is detailed in a PRISMA flow chart ( Figure 1).
The exercises were performed once or twice daily [21] or three times a day [8,12,22]. Exercise repetitions were variable among the studies that specified them: 3-5 min bursts [21], eight exercises, each one 15 times [12] or two sequences of 15 repetitions [8].
MFT continued for 1 year or longer to prevent relapse of dysfunctional oral motor habits, to promote exclusive nasal breathing and to ensure long-term habituation of ideal resting oral posture.
Almost half of the studies did not specify the protocol used for MFT. In the studies in which it was explained, the treatment lasted 20 min twice a week [22] or 30 min [8,12,24,25]. In one of the articles [23], the myofunctional protocol incorporated bodywork, cranial therapy and/or myofascial therapy depending on the circumstance.
Treatment lasted about 4 weeks in most of the articles [8,[21][22][23][24][25]. The longest total duration of intervention was achieved by Zagui et al. [23] (1 month of preoperative and 2 months postoperative MFT). There was another study in which TFM started before surgical treatment, but in this case it was one week earlier [8].
The variables studied were related to tongue mobility including the ankyloglossia grade evaluated by Kotlow, or the quick tongue-tie assessment tool [27], or tongue range of motion [12,20,26,27]. The strength and endurance of the tongue was also measured with the Iowa oral performance instrument (IOPIpro). In terms of functionality, it was evaluated with the assessment tool for lingual frenulum function, the Bristol tongue assessment tool and the degrees of lingual function [27] or by maximum interincisal opening with the tip of the tongue in contact with the maxillary incisor papillae (MOTTIP) [12,27] or maximum interincisal opening of the mouth (MIO) [12,26] or maximum opening mouth (MAB) [27], the lingual protrusion measured with orofacial myology [27].
The main characteristics of the studies are shown in Table 2.

Methodological Quality Assessment
The results of the quality assessment of the different studies are shown in Tables 3-5.  Table 3 presents the methodological quality of the clinical trials. Tables 4 and 5 show the methodological quality of the observational studies and the case studies, respectively.   The mean methodological quality of the clinical trials as measured by the PEDro scale was 5.6, that of the case studies as measured by the SCED scale was 3.3, and in the case of the observational studies 71% of the recommendations of the STROBE statement were met.

Risk of Bias of Included Randomised Clinical Trials
Regarding the risk of bias of the randomized clinical trials included in this review, the study conducted by Fioravanti et al. [27] presented the lowest risk of bias, as shown in Figure 2. It should be noted that the risk of bias is low in relation with attrition and reporting bias in all of them ( Figure 3).

Risk of Bias of Included Randomised Clinical Trials
Regarding the risk of bias of the randomized clinical trials included in this review the study conducted by Fioravanti et al. [27] presented the lowest risk of bias, as shown in Figure 2. It should be noted that the risk of bias is low in relation with attrition and reporting bias in all of them ( Figure 3).

Discussion
This systematic review was developed with the aim of finding out the efficacy of MFT in people with ankyloglossia. In view of our results, we can conclude that there is not enough evidence that the MFT is effective on its own because in the articles evaluated it was accompanied by surgery. In addition, the studies were not of good methodological

Discussion
This systematic review was developed with the aim of finding out the efficacy of MFT in people with ankyloglossia. In view of our results, we can conclude that there is not enough evidence that the MFT is effective on its own because in the articles evaluated it was accompanied by surgery. In addition, the studies were not of good methodological quality to draw extrapolatable conclusions. Even so, when both treatments have been combined, the results were positive.
Concerning characteristics of the participants, ankyloglossia has a high prevalence in infants aged 0-6 months, the population studied in 36% of the studies in our review, although the average age range is 8 years in 80% of the articles chosen. It is important to study this pathology at an early age in order not to condition the development of the cranio-mandibular-occlusal complex of the child and to avoid future problems when they reach adulthood [30].
According to the gender, in our review, the number of males is higher. Our results are in agreement with the data obtained in other research [31][32][33]. This may be due to the link of ankyloglossia to the X chromosome with variations in gene expression, in particular in the mutation of the T-box transcription factor gene (TBX22) during palatogenesis [34].
Another important aspect to consider is the heterogeneity in the scales for making the diagnosis of ankyloglossia. It should be unified on a more functional scale, such as the one proposed and validated by Yoon et al., after their analysis of 1052 subjects. It would be a more practical way to establish therapeutic objectives. This scale establishes 4 degrees of ankyloglossia: grade 1: tongue range of motion ratio is >80%, grade 2 50-80%, grade 3 <50% and grade 4 <25% [28].
In reference to the variables studied, a distinction could be made between those relating to babies and those studies in children or adults. Concerning infant studies, the most assessed has been nipple pain, feeding time and weight gain, as in the review by Walsh et al. [35]. Others are mostly found in adults, such as speech difficulties and upper respiratory tract development, as in the study by Jaikumar et al., (2022) in which aspects such as social interactions and academic activities are examined in depth. On the other hand, the variables studied in children and adults are speech difficulties and respiratory disturbances resulting from restricted mobility of the tongue. Nevertheless, social interactions and academic activities have not been studied as they were evaluated in the article of Jaikumar et al. [30].
Concerning the interventions, the option of frenectomy is the most commonly used method for lingual frenulum release in the neonatal and infant population and it is efficient for the improvement of symptoms caused by ankyloglossia [36]. Researchers of a systematic review of Shea et al., reported no serious complications; however, the authors added that the total number of infants studied was small as well as the number of trials which were also of low methodological quality [37]. The most frequently encountered complications have been pain, infections or hemorrhages [38].
Conservative treatment should therefore be taken into account [39], and the work of a multidisciplinary team would be essential [40]. Miranda et al., (2016) commented that MFT could be the only method of treatment in some cases and, in cases where surgery is necessary, it would be an essential part that could complement it. MFT can be given by both speech therapists and physiotherapists. The more functional part, which includes stretching, exercises and intrabuccal and extrabuccal massotherapy, would be given by a physiotherapist, and the area that involves more speech would be developed by a speech therapist [41].
Finally, in clinical settings, although MFT has been done with the surgery in ankyloglossia, there are therapeutic plots where this has been done without the support of surgery and with satisfactory effects: in preterm infants where myofunctional and orofacial therapy resulted in improvements in weight gain [42,43] or in obstructive sleep apnea [44] where decreases in apnea-hypopnea index by approximately 50% in adults and 62% in children with lowest oxygen saturations, snoring, and sleepiness outcomes improve in adults were found. Conversely, there has not been scientific evidence supporting the use of MFT in combination with orthodontic treatment to achieve better results in the correction of dentofacial disorders in orthodontic patients [45].

Limitations and Future Recommendations
Some limitations should be remarked. The results provided by the present review should be taken with caution because of the limited number of controlled trials analyzed. Another limitation was the variability of the samples in the studies and the differences between the registered outcomes, which made it impossible to carry out a meta-analysis to complete the review.
There was a wide disparity in age range in the studies. Some were conducted in infants [22,24,25], in infants or children [6], others in children [8,12,20,26] or young adults [21] or even in people over 65 years of age [23].
Furthermore, the wide range measuring instruments used makes it difficult to compare the results on the studies and, in some of the trials [22,24,25], not only the patients were analyzed but also the maternal pain was the variable studied. With regard to MFT, many of the articles [6,20,27] did not describe the protocol accurately in terms of number of sessions, techniques used and time and frequency of treatment.
Despite an extensive search in six databases, without using date or language restrictions, only 11 articles were found, of which only three were randomized clinical trials and of these only one was of good methodological quality. However, as stated by Baxter et al. [6] (2020), it is difficult to conduct a randomized control group study as mothers of babies with ankyloglossia request surgery and benefit from it. In addition, 100% of the studies had an uncertain risk under other bias. There may be certain factors that could influence the results such as the assessment of certain variables that may be subjective or the different levels of compliance of patients or their relatives when performing the exercises at home.
Finally, a great limitation is that it was not possible to assess MFT without surgery being present because in all the articles frenectomy was performed. In only one article [12] the treatment did not incorporate surgery in the intervention protocol, but it was not specified whether it had been performed before.
Regarding future recommendations, it should be noted that myofunctional therapy could go beyond being an adjunct to surgery.
Frenectomy is an effective surgical treatment in people with ankyloglossia [27], but there will be cases where it is not necessary; however, there are not enough RCTs to draw firm conclusions [46]. It is therefore important that more studies on this pathology are done. A good diagnosis should also be made to differentiate those individuals with ankyloglossia who should go directly to surgery from those who could benefit from conservative treatment such as MFT [47]. Hence, it could be a great tool for individuals with ankyloglossia. Improvement should be measured at different levels according to the variables and age studied. Regarding the age range, it would be useful to have more information on how ankyloglossia develops in adults, as this pathology is associated with babies because of the problems it triggers in the breastfeeding period, but complications in adults have hardly been investigated [48].
In addition, pediatric and women's physiotherapy has been booming in recent years, with the need for this type of therapy emerging as a solution to future problems in both the baby and the mother, not only functional but also social [4].
This systematic review could serve as a reference for future studies with a higher methodological quality that take into account the above-mentioned aspects.

Conclusions
According to the literature consulted in this review, surgery is more effective than myofunctional therapy, although better results are achieved if both are combined. Improvements have been found in babies and their mothers with regard to maternal pain, weight gain of babies and duration of breastfeeding. On the other hand, in children and adults it improves tongue mobility, strength and endurance, sleep apnea, mouth breathing and snoring, quality of life, clenching teeth, myofascial tension, pain after surgery and speech sound production.
These findings must be taken with caution because of the small number of articles and their quality. Future clinical trials using larger sample sizes and with higher methodological quality are needed. Overall, myofunctional therapy is expected to have a positive impact on patients with ankyloglossia.  Specify the methods used to decide whether a study met the inclusion criteria of the review, including how many reviewers screened each record and each report retrieved, whether they worked independently and, if applicable, details of automation tools used in the process.
Pag. 3 Data collection process 9 Specify the methods used to collect data from reports, including how many reviewers collected data from each report, whether they worked independently, any processes for obtaining or confirming data from study investigators and if applicable, details of automation tools used in the process.

Data items 10a
List and define all outcomes for which data were sought. Specify whether all results that were compatible with each outcome domain in each study were sought (e.g., for all measures, time points, analyses) and, if not, the methods used to decide which results to collect.
Pag. 3 10b List and define all other variables for which data were sought (e.g., participant and intervention characteristics, funding sources).
Describe any assumptions made about any missing or unclear information.
Study risk of bias assessment 11 Specify the methods used to assess risk of bias in the included studies, including details of the tool(s) used, how many reviewers assessed each study and whether they worked independently, and if applicable, details of automation tools used in the process.
Pag. 3 Effect measures 12 Specify for each outcome the effect measure(s) (e.g., risk ratio, mean difference) used in the synthesis or presentation of results.

Synthesis methods 13a
Describe the processes used to decide which studies were eligible for each synthesis (e.g., tabulating the study intervention characteristics and comparing against the planned groups for each synthesis (item #5)).

Pag. 3 13b
Describe any methods required to prepare the data for presentation or synthesis, such as handling of missing summary statistics, or data conversions. 13c Describe any methods used to tabulate or visually display results of individual studies and syntheses. 13d Describe any methods used to synthesize results and provide a rationale for the choice(s). If meta-analysis was performed, describe the model(s), method(s) to identify the presence and extent of statistical heterogeneity, and software package(s) used. 13e Describe any methods used to explore possible causes of heterogeneity among study results (e.g., subgroup analysis, meta-regression). 13f Describe any sensitivity analyses conducted to assess robustness of the synthesized results.

Section and Topic Item # Checklist Item Location Where Item Is Reported
Reporting bias assessment 14 Describe any methods used to assess risk of bias that is due to missing results in a synthesis (arising from reporting biases). Pag. 3 Certainty assessment 15 Describe any methods used to assess certainty (or confidence) in the body of evidence for an outcome. Results

Study selection 16a
Describe the results of the search and selection process, from the number of records identified in the search to the number of studies included in the review, ideally using a flow diagram. Figure 1 16b Cite studies that might appear to meet the inclusion criteria, but which were excluded, and explain why they were excluded.

Study characteristics 17
Cite each included study and present its characteristics. Table 2 Risk of bias in studies 18 Present assessments of risk of bias for each included study. Figures 2 and 3 Results of individual studies 19 For all outcomes, present, for each study: (a) summary statistics for each group (where appropriate) and (b) an effect estimate and its precision (e.g., confidence/credible interval), ideally using structured tables or plots. Table 2 Results of syntheses 20a For each synthesis, briefly summarize the characteristics and risk of bias among contributing studies. Present results of all statistical syntheses conducted. If meta-analysis was done, present for each the summary estimate and its precision (e.g., confidence/credible interval) and measures of statistical heterogeneity. If comparing groups, describe the direction of the effect. 20c Present results of all investigations of possible causes of heterogeneity among study results. 20d Present results of all sensitivity analyses conducted to assess the robustness of the synthesized results.

Reporting biases 21
Present assessments of risk of bias due to missing results (arising from reporting biases) for each synthesis assessed.

Other Information
Registration and protocol 24a Provide registration information for the review, including register name and registration number, or state that the review was not registered.

Pag. 2 24b
Indicate where the review protocol can be accessed, or state that a protocol was not prepared. 24c Describe and explain any amendments to information provided at registration or in the protocol.

Support 25
Describe sources of financial or nonfinancial support for the review, and the role of the funders or sponsors in the review. Report which of the following are publicly available and where they can be found: template data collection forms; data extracted from included studies; data used for all analyses; analytic code; any other materials used in the review.