Myofunctional therapy: a bibliometric study of the most cited 50 articles

Myofunctional therapy can enhance the shape, strength, and function of facial and oral muscles while positively influencing the orofacial growth and development of children. Orofacial myofunctional therapy is considered an adjunctive treatment for obstructive sleep apnoea-hypopnoea syndrome and orthodontic interventions.¹ Supporting this, Achmad et al.² noted that myofunctional therapy is highly effective when combined with orthodontic appliances or myofunctional devices to correct a child’s anterior open bite.

Malocclusions, characterised by abnormal relationships between the upper and lower teeth, arise from hereditary factors, environmental influences, or a combination of both. They are often linked to oral habits such as thumb sucking, pacifier use, tongue thrusting, and mouth breathing.³ Rogers was the first to introduce muscle function therapy for malocclusion correction, and Lischer later coined the term “Myofunctional Therapy” to describe this approach.⁴

Managing a malocclusion requires a holistic approach that extends beyond conventional orthodontic treatment. Myofunctional therapy plays a key role by targeting orofacial muscle function and promoting muscle balance.¹ The therapy aims to identify the underlying causes of a malocclusion and promote proper muscle function and oral posture, thereby enhancing the stability of orthodontic treatment outcomes.² Stallard first suggested that sleeping position could be a reason for the development of a malocclusion.⁵ As pioneers in the field, Truesdell and Truesdell⁶ established the relationship between swallowing anomalies and dysmorphosis.

Although there are numerous publications on myofunctional therapy, there remains a lack of systematic bibliometric analyses exploring citation trends, keyword co-occurrence patterns, and interdisciplinary collaborations within the field. While prior bibliometric studies have been conducted in related areas related to orthodontics and sleep medicine, a dedicated analysis of myofunctional therapy is absent. The gap necessitates an examination of the most influential studies to outline research trends, identify underexplored topics, and assess the evolution of collaboration networks. Highly cited papers often shape future research directions and contribute to clinical advancements.⁷ To achieve this, bibliometrics, defined as the application of statistical methods to analyse a body of literature, in order to reveal the historical development of subject areas and identify trends in authorship, publication, and usage, is an essential tool for evaluating scientific output.⁸

Therefore, the present bibliometric analysis aims to evaluate the scientific impact of myofunctional therapy by analysing the top 50 most-cited papers, and offer a perspective on the influence of the forthcoming studies. It was expected that this information would help researchers identify knowledge gaps and outline trends for future research, thereby potentially contributing to the multidisciplinary management of current cases.

An electronic search was conducted in September, 2024, to identify relevant publications using the Web of Science (WOS) database through Ege University’s electronic library. The search strategy employed was: ((TS = (myofunctional therapy OR dental myofunctional therapy OR myofunctional treatment OR myofunctional appliance)) OR (QMTS = (“myofunctional therapy”)) OR (QMTS = (“myofunctional appliance”)) OR (QMTS = (“orofacial myofunctional therapy”)) OR (QMTS = (“myofunctional appliances”)) OR (QMTS = (“myofunctional treatment”))), without a time span restriction. The search entitled “Myofunctional Therapy” and limited to articles and reviews, yielded a total of 388 publications.

The top 50 most-cited articles were identified and independently sorted by two authors and placed in descending order based on their citation counts. The bibliometric information extracted from the selected articles included the title, citation count, year of publication, authors, academic institution, country of origin, and keywords. Subsequently, the data were double-checked by the two authors (ECF, AÇ) and any discrepancies were resolved by a third author (EE). The data were then exported in a comma-separated values (CSV) format. Studies published in languages other than English and topics unrelated to myofunctional therapy were excluded.

The visualisation of similarities was conducted using VOSviewer software (Version 1.6.20; Centre for Science and Technology Studies, Leiden University, Leiden, The Netherlands) alongside Microsoft Excel (Microsoft Corp., Redmond, WA, USA) to analyse the exported data. The VOSviewer software created visual maps in the form of ‘bubbles’ to represent documents, citation counts, sources, countries and keywords.

Keyword clusters were analysed using density visualisation techniques. The visual analysis for the number of publications was presented as ‘bubble’ maps, and associations between items were depicted by the distances between bubbles.

The co-occurrence of author keywords was examined by setting a minimum occurrence threshold of four times in the network visualisation. The percentage distribution of documents was calculated by dividing the number of documents by the total number of identified records. Similarly, the average citation score per document was determined by dividing the total number of citations by the number of documents.

Table I presents the top 50 most-cited myofunctional therapy articles published between 1998 and 2022. The most productive year was 2020, as six articles were published during that year. Of the articles, 56% were original research papers and 44% were reviews. The articles were produced by academic institutions from 23 countries, predominantly the United States, Brazil, Italy, Belgium, Germany and the United Kingdom. Spain led in funded studies, contributing 13 articles (26%), followed by the United States with 5 articles (10%).

According to the Web of Science (WoS) categories, the primary research areas represented by more than 10% of the articles were: Dentistry, Oral Surgery and Medicine (23 articles; 46%), Clinical Neurology (10 articles; 20%), Neurosciences (7 articles; 14%), Paediatrics (6 articles; 12%), and Respiratory System (5 articles; 10%).

The articles in WoS-CC received a total of 2483 citations, including 89 self-citations (3%). Citation counts ranged from 24 to 197, with 19 articles receiving at least 50 citations, 6 articles receiving 75 or more, and 2 articles receiving more than 100 citations (Table I).

The most-cited article was “Myofunctional Therapy to Treat Obstructive Sleep Apnea: A Systematic Review and Meta-analysis” (Camacho et al., 2015, Sleep). The oldest article, titled “Effects of a Myofunctional Appliance on Orofacial Muscle Activity and Structures” by Antti Tallgren et al., was published in The Angle Orthodontist in 1998. The most recent article was “Prevalence of Orthodontic Malocclusions in Healthy Children and Adolescents: A Systematic Review” (De Ridder et al., 2022). Most of the articles (34 out of 50) were published between 2015 and 2021 (Figure 1).

Figure 1.

Correlation between the 50 most cited articles (1998–2022) and their citation trends over time.

Authors from 104 institutions contributed to the published articles. Leading institutions include Stanford University (USA) and São Paulo University (Brazil), each contributing 7 articles. Stanford University had the highest citation count (518 citations) and total link strength (32). São Paulo University had the highest average citation count per article (111.5), followed by Stanford University (74). Figure 2 presents the co-occurrence map of the institutions.

Figure 2.

Co-occurrence map of institutions.

Eleven countries published at least two articles on myofunctional therapy. The United States led with 18 articles (958 citations), followed by Brazil (10 articles, 433 citations) and Italy (9 articles, 378 citations) (Table II). Germany (79.8) and Taiwan (77.5) had the highest average citation counts per article. Italy, the United Kingdom and France had the strongest collaboration networks, with link strengths of 11, 10, and 10, respectively. The United States collaborated with Germany, the United Kingdom, Brazil, and Australia.

The three most prolific authors in myofunctional therapy were Guilleminault (7 publications), De Felicio (5 publications), and Marzo (4 publications). Guilleminault’s most-cited work was “Critical Role of Myofascial Reeducation in Pediatric Sleep-Disordered Breathing,” which was published in Sleep Medicine in 2013, with contributions from six authors across four institutions in three countries (France, Taiwan, and the U.S.).

The two journals with the highest number of published myotherapy articles were the European Journal of Orthodontics (4 articles, 325 citations, 8%) and the European Journal of Paediatric Dentistry (4 articles, 136 citations, 8%). Other leading journals included Sleep and Breathing (3 articles; 153 citations; 6%), The Angle Orthodontist (2 articles; 73 citations; 4%), and Cranio-The Journal of Craniomandibular & Sleep Practice (2 articles; 120 citations; 4%) (Figure 3).

Figure 3.

Cluster graph of the most cited journals.

From an initial set of 144 unique author keywords, duplicate entries were consolidated into 125 distinct keywords. Nine keywords appeared more than four times, with “myofunctional therapy” (17 occurrences) being the most frequent. Other frequently used terms included “obstructive sleep apnoea” (8 occurrences) and “sleep disordered breathing” (7 occurrences). Figure 4 illustrates the distribution of the most frequently used keywords and their interrelationships.

Figure 4.

Bibliometric coupling of the most-used author keywords.

Myofunctional therapy is a treatment modality aimed at correcting anomalies in speech, breathing disorders, and dental and jaw structure by promoting proper function of the oral and facial muscles. These therapies are conducted by professionals from various disciplines, including dentists, physical therapists, speech therapists, and sleep specialists.

Myofunctional therapy is effective in adjusting the occlusion and managing conditions such as sleep-disordered breathing, and speech disorders. Through neuromuscular exercises, myofunctional therapy re-trains and restores the normal function of facial and oral structures. Overall, there is evidence that myofunctional therapy may help treat a malocclusion, speech disorders, tongue thrust, and sleep-disordered breathing, as well as improve masticatory function.^9–11 Bibliometric studies in orthodontics and dentistry have traditionally focused on citation trends across broad topics within their respective fields. However, the present study provides a more specialised analysis by identifying key research trends, institutional contributions, and interdisciplinary collaborations specific to myofunctional therapy. Compared to broader orthodontic bibliometric analyses, it offers a focused perspective on a niche yet rapidly expanding area of research. Unlike previous bibliometric studies, the present work highlights the inherently multidisciplinary nature of myofunctional therapy by demonstrating the interrelationship between healthcare providers. From an orthodontic perspective, the review stresses the importance of evaluating sleep-disordered breathing in all patients undergoing treatment with myofunctional appliances, thereby promoting a more comprehensive and integrative approach to patient care.

As the topic of the present bibliometric study involves multiple disciplines, it allows for the analysis of interdisciplinary interactions, thereby providing a unique perspective that distinguishes the current from traditional bibliometric studies. The present study was conducted using the WoS-CC database and, for the first time, provided an in-depth examination and mapping of the topic of myofunctional therapy, which aimed to offer an overview of its status with respect to countries, authors, institutions, and journals. Therefore, it provides researchers with a perspective that can help identify trends and gaps in the literature. In the bibliometric field, the Web of Science Core Collection (WoS-CC) is considered a prestigious database for assessing scientific quality and impact, as it is specifically designed for citation analysis. Therefore, bibliometric studies frequently select WoS-CC as the primary database due to its robust citation metrics, stringent indexing criteria, and comprehensive impact assessment tools. Other databases, such as Scopus, have limitations, particularly in citation coverage, as it only tracks citations starting from 1996. Additionally, Google Scholar, although widely used, organises results based on relevance or publication date and includes citations from non-peer-reviewed sources such as books and dissertations, which may not provide the same level of rigor. Given these considerations,^12–15 WoS-CC was selected as the primary database used by numerous bibliometric analyses in dentistry. The importance of the citation count lies in its ability to reveal the actual impact of the published articles;^16,17 therefore, the evaluation of the top 50 most-cited studies in a relatively niche field like myofunctional therapy was deemed appropriate. The observed increase in the number of publications and citations after 2015 indicates a growing interest in the topic, which is further supported by the cumulative rise in the number of related publications. This increase may be attributed to a heightened awareness of sleep-disordered breathing and the expanding role of myofunctional therapy as a complementary approach in patient management. The publication of influential systematic reviews and meta-analyses around this period, notably the 2015 study by Camacho et al., likely contributed to the growing visibility of myofunctional therapy in clinical practice and research. Additionally, advances in diagnostic tools and treatment protocols may have fueled increased scholarly attention of the subject. This trend suggests that more research in this area may be expected in the coming years.

Since the present study was based on the most-cited articles, the clustering of the top-cited works between 2015 and 2021 suggests that a substantial number of studies have been conducted and are ongoing in this field. As new research continues to be added to the literature, citation rates will cumulatively increase, thereby providing valuable guidance for future research. However, it appears that a large proportion of these studies consist of reviews. Therefore, future randomised controlled trials and multidisciplinary research could help fill the existing gaps in the literature on this topic.

The most cited 50 articles in WoS-CC received a total of 2483 citations, including 89 self-citations (3%) which is a comparatively low rate. Despite this, potential citation biases should be acknowledged. Moreover, the exclusion of non-English publications may limit the representation of myofunctional therapy research conducted in non-English-published journals. Additionally, the reliance on a citation count as a measure of impact does not necessarily reflect the clinical applicability or methodological quality of a study. These factors should be considered when interpreting the findings

The most cited article was authored by Camacho et al. in 2015 and entitled “Myofunctional Therapy to Treat Obstructive Sleep Apnea: A Systematic Review and Meta-analysis.” This study involved a meta-analysis of patients treated with myofunctional therapy for obstructive sleep apnoea (OSA) in children and adults, and evaluated related parameters such as polysomnography, snoring, and sleepiness. As a systematic review, it also served as a comprehensive reference for numerous later studies. The second most cited article was by Tausche et al., entitled “Prevalence of Malocclusions in the Early Mixed Dentition and Orthodontic Treatment Need,” which used the Index of Orthodontic Treatment Need (IOTN) to assess malocclusion prevalence and identify factors requiring early intervention. The third most cited article was “Critical Role of Myofascial Re-education in Pediatric Sleep-Disordered Breathing,” which evaluated paediatric sleep disorders in relation to adenotonsillectomy, orthodontics and myofunctional therapy.

Consistent with the literature,¹⁸ it was found that socioeconomically developed countries contributed more significantly to scientific research. The top three countries with the highest citation counts were the United States, Italy, and Brazil, all of which are among the world’s top 10 economies based on nominal Gross Domestic Product in 2024.¹⁹ Stanford University and Leuven University appear twice in the list of institutions that have produced more than two articles due to their representation as distinct entities within the same overarching institution. This reflects the internal structure in which different organisations, such as hospitals or research centres, operate under the same institutional umbrella. However, when the data is analysed at the institutional level, the ranking based on the total number of articles remains unchanged, with Stanford University ranked first and Leuven University ranked third. Therefore, the authors chose to evaluate the institutions separately in order to illustrate the interrelationships during the mapping and listing processes.

The association between keywords clearly demonstrates the interaction between various disciplines and underscores the interdisciplinary nature of myofunctional therapy. The most commonly occurring keyword was “myofunctional therapy”, reaffirming its pivotal role in the field. Other frequently appearing terms included “obstructive sleep apnoea and “sleep-disordered breathing”, thereby emphasising the link between myofunctional therapy and respiratory health. Around these central terms, distinct groupings emerge, forming two primary conceptual clusters: one related to sleep disorders, CPAP (Continuous Positive Airway Pressure) treatment, and sleep-disordered breathing, and the other associated with orthodontics, malocclusions, and children. The notable co-occurrence of myofunctional therapy and sleep-disordered breathing indicates a growing clinical and academic interest in its applications beyond conventional orthodontic frameworks, extending into respiratory and sleep medicine. In addition, the frequent linkage of malocclusion and orthodontic treatment reinforces the well-established role of myofunctional therapy in dentofacial development in children and malocclusion correction. These observations offer insights into the expanding interdisciplinary nature of myofunctional therapy, possibly shaping future research trajectories. Given that physicians are often the primary healthcare providers who evaluate children, myofunctional therapy serves as a key resource for early referrals to dentists and orthodontists, thereby ensuring that relevant treatment aspects within their scope are effectively managed. This highlights the significance of cross-disciplinary collaboration and the necessity for stronger cohesion between dentistry, sleep medicine, and associated medical fields in myofunctional therapy.

The present bibliometric analysis evaluated the scientific literature on myofunctional therapy and its interdisciplinary connections. It identified increasing research interest, particularly after 2015, and the contributions of key countries, institutions, and authors. The study highlighted the role of myofunctional therapy in addressing malocclusion, obstructive sleep apnoea, and other orofacial conditions. It also identified gaps that require further research. While review articles are common, more randomised controlled trials and interdisciplinary studies are needed. The findings indicate a growing international collaboration but also reveal limited cross-specialty integration. Future research should focus on strengthening interdisciplinary co-operation to advance evidence-based practices.