Pediatric sleep apnea, a subtype of sleep-disordered breathing (SDB), is a prevalent condition with potential implications for a child's health and development [4]. It is important to note that other pathologies, such as sleep bruxism, temporomandibular disorders, and dental caries, can also be associated with sleep disorders [25]. Emerging research suggests that a short lingual frenulum may contribute to the onset of obstructive sleep apnea syndrome (OSAS) in children, highlighting the multifaceted nature of its etiology [8, 11, 17,18,19,20]. Ankyloglossia, characterized by a restrictive lingual frenulum, has been associated with breastfeeding difficulties, including challenges such as poor latching, inability to maintain latch, poor weight gain, irritability during feeding, and maternal pain [9].

Recent data from the United States reveal a noteworthy 110.4% increase in reported diagnoses of ankyloglossia in newborns from 2012 to 2016, as indicated by Wei EX et al.'s comprehensive review of various databases [25]. Meanwhile, the prevalence of OSA in children has been reported to range from 1 to 5% [26].

Given the high prevalence of ankyloglossia and OSAS, both of which carry potential long-term health consequences for children, this review aims to systematically evaluate the evidence surrounding the relationship between ankyloglossia and OSAS. Contrary to the null hypothesis, our analysis of various orofacial variables revealed significant associations with short frenulum and high arch palate, while other analyzed variables did not exhibit statistically significant effects.

The variables under scrutiny in this systematic review fall into two distinct categories: clinical and diagnostic. In the realm of obstructive sleep apnea syndrome (OSAS) diagnosis, polysomnography (PSG) stands as the gold standard. However, this method is known for its expense, limited accessibility, and potential stress for children. Cohen-Levy et al. and Guilleminault et al. advocate a judicious approach, suggesting that PSG should be reserved for children identified as at risk through questionnaires [11, 20].

Cohen-Levy J et al. specifically employed the Hierarchic Severity Clinical Scale (HSCS) to evaluate sleep-disordered breathing (SDB) symptoms. Participants reporting chronic snoring (HSCS > 0) or scoring positive for suspected OSA (HSCS > 2.72), in the absence of craniofacial syndrome, underwent a sleep apnea test. In contrast, other authors, such as those using the Pediatric Sleep Questionnaire (PSQ), diagnosed OSA without recourse to a sleep apnea test and, consequently, without the involvement of medical staff. The current guidelines from the Working Group of the European Respiratory Society endorse the PSQ as a screening tool for detecting OSA risk in children [2, 27]. Notably, the PSQ boasts the highest specificity among all available questionnaires for children, minimizing the occurrence of false positive results. Authors of the PSQ recommend that eight or more "YES" answers in the questionnaire qualify a child for inclusion in the OSAS risk group [21].

In the evaluation of sleep-disordered breathing (SDB) and obstructive sleep apnea syndrome (OSAS), Villa M et al. and Cohen-Levy J et al. utilized the Sleep Clinical Record (SCR), a comprehensive clinical tool designed to identify children at high risk for SDB. The SCR calculates a total score, considering various factors, including abnormalities in the nose, oropharynx, dental and craniofacial occlusion, the Brouillette OSAS score [28], and the presence of symptoms related to inattention and hyperactivity. A total SCR score of 6.5 is deemed positive, indicating a high risk of OSAS defined by an obstructive apnea–hypopnea index (AHI) > 1 episode/h [11, 29].

Regarding the diagnosis of ankyloglossia, the Quick Tongue-Tie Assessment Tool was predominantly employed across studies. This tool measures the inter-incisive distance with the tongue in a low-placed position and the tip of the tongue against the palate. It calculates the percentage difference between measurements, considering normal if the difference is < 50%. Additionally, the tool measures the distance from the insertion of the frenulum at the base of the tongue to the tip of the tongue [8, 17, 19, 20].

Two distinct measurement methods were identified in the literature. The Kotlow method, utilized by Villa M et al., Brozek-Madry et al., Burska Z et al., and Yuen H et al., measures the "free tongue," defined as the length from the insertion of the lingual frenum into the base of the tongue to the tip of the tongue. A normal frenulum length is considered > 16 mm [8, 17,18,19]. In contrast, the Ruffoli method measures the length of the frenulum itself, classifying a normal frenulum length in children aged ≥ 6 years as > 20 mm, with a mild problem at 16–19 mm [10]. Guilleminault et al. [20] considered > 16 mm as a cut-off point for a normal free-tongue length for children aged ≥ 3 years [23].

Tongue characteristics play a crucial role in assessing the risk of obstructive sleep apnea (OSA). Some studies, such as those by Guilleminault C (2016) and Yoon A (2017), conducted a systematic examination using maneuvers defined by myofunctional therapists. This evaluation included assessing the placement of the tongue at rest, the capability of performing maneuvers like touching the nose and chin with the tip of the tongue, creating a "cigar tongue" while protruding the tongue, touching the median raphe with the tip of the tongue with a wide-open mouth, and observing upper jaw closure during the maneuver. Additionally, the ability to pronounce certain letters and vowels was considered.

Yuen H et al. defined tongue mobility as Mpal/Mmax, representing the maximal distance between incisors when the tongue tip touched the palatal papilla and during full mouth opening, respectively, obtained using a digital caliper [30]. Low tongue mobility was defined as mobility less than 60% [11, 19]. Interestingly, trials such as the one by Fioravanti M (2021) demonstrated that diode laser lingual frenectomy therapy can improve the severity of OSAS in pediatric patients [31]. Similarly, lingual frenuloplasty with myofunctional therapy, as indicated by Zaghi S et al. (2019), is deemed safe and potentially effective. These findings underscore the importance of an early diagnosis and treatment of ankyloglossia, coupled with myofunctional therapy, in pediatric subjects experiencing sleep apnea problems. Such interventions showcase the potential for targeted therapeutic approaches to mitigate OSA severity and improve overall outcomes in affected children [32].

Considering the clinical variables in pediatric SDB, the literature consistently describes a male predominance and younger age at surgery in pediatric SDB, possibly attributed to a less mature craniofacial skeleton and sexual dimorphism or android pattern of fat distribution in older adolescents. However, the present meta-analysis on the "gender" variable did not reveal significant differences between genders. This outcome might be explained by the fact that OSA becomes more pronounced in males after puberty [33].

As regards “short frenulum” variable, the meta-analysis results demonstrated an association between a shortened lingual frenulum and SDB. Specifically, ankyloglossia appear in OSA patients 3.05 times more than in non-OSA patients. Ankyloglossia limits the upward movement of the tongue, thus preventing the formation of lip seal during swallowing, leading to tongue thrusting. Abnormal bone growth stimulation, an absence of nasal breathing (due to anatomical and muscle tone dysfunction) with secondary development of mouth breathing are responsible for the abnormal oral-facial bone structures supporting the upper airway, thus increasing the risk of UA collapse during sleep [34].

Concerning the variable of a "short frenulum," the outcomes of the meta-analysis revealed a notable correlation between a shortened lingual frenulum and SDB. More specifically, ankyloglossia manifests in patients with OSA at a rate 3.05 times higher than in non-OSA patients. Ankyloglossia restricts the superior movement of the tongue, thereby impeding the establishment of a lip seal during the act of swallowing, consequently inducing tongue thrusting. This phenomenon contributes to abnormal stimulation of bone growth, coupled with an absence of nasal breathing (attributed to anatomical and muscle tone dysfunction), resulting in secondary development of mouth breathing. This, in turn, contributes to the anomalous development of oral-facial bone structures that support the upper airway, thereby elevating the susceptibility to Upper Airway (UA) collapse during the sleep cycle [35].

Furthermore, diminished tongue mobility has been linked to constriction of the maxillary arch [36]. The findings from this meta-analysis underscore a connection between a high-arched palate and SDB. Specifically, the presence of a palate characterized by both height and narrowness correlated with a 12.3-fold increase in the risk of SDB. A narrow maxilla combined with a high-arched palate is associated with heightened nasal airflow resistance and posterior displacement of the tongue [37]. Palatal assessment in pediatric populations is a straightforward procedure that should be an integral component of SDB screening protocols in children.

Evaluation of a high-arched palate was conducted by Burska Z et al., Brozek-Madry E et al., Cohen-Levy J et al., Villa M et al., and Guilleminault C et al., solely utilizing a subjective evaluation method (YES/NO). A high-arched palate was assessed based on its curvature, characterized by an abnormally pronounced curvature angled superiorly along the palatal midline [8, 11, 17, 20].

In concordance with the findings of Bussi M (2021) [38], this review substantiates a noteworthy association between lingual frenulum alteration and Obstructive Sleep Apnea. A notable limitation of this systematic review is the modest sample size across the included studies, with the absence of an adequate sample size justification. These characteristics potentially introduce a bias in extrapolating the results beyond the confines of the study. One plausible explanation for the challenge of attaining larger sample sizes in pediatric OSA studies is the existence of accessibility barriers to PSG examinations, encompassing high costs and increased wait times for public health services. Consequently, there is a limitation in the diagnostic methodology, given that polysomnographic examination stands as the gold standard for detecting sleep apnea, yet not all authors have uniformly employed this diagnostic modality. Notably, many children refused to undergo sleep studies or decline additional tests after an initial failure. It is imperative to establish a standardized diagnostic protocol inclusive of the evaluation of tongue mobility and palate anatomy during pediatric dentistry and orthodontics appointments. Following a positive outcome in this evaluation and other diagnostic tests, a sleep study should be recommended in accordance with the international consensus on sleep apnea in children [38].

OSA in children has been correlated with various comorbidities and disorders, including respiratory complications, obesity, adenotonsillar hypertrophy, and craniofacial and behavioral syndromes. The studies included in this review reported the exclusion or matching of participants based on factors such as obesity, craniofacial syndromes, and adenotonsillar size, with a majority of them affirming the non-influence of these features on their results. Integration of the BMI variable into the meta-analysis was precluded due to the lack of homogeneity in reporting results. Discrepancies in BMI calculation methodologies were observed across articles, wherein some computed BMI as body weight divided by the squared height, while others utilized BMI z-scores, representing deviations from the mean adjusted for age and sex.

It would be intriguing to investigate whether there exists a correlation between surgical treatment of the frenulum and the amelioration of sleep apnea in children. According to the literature, surgery proves to be more effective than myofunctional therapy, in order to enhances tongue mobility, strength, and endurance, alleviates sleep apnea, reduces mouth breathing and snoring, improves quality of life, decreases teeth clenching, addresses myofascial tension, alleviates post-surgery pain, and enhances speech sound production. However, further studies are necessary to confirm this hypothesis [39, 40].

The outcomes of this systematic review and meta-analysis underscore a noteworthy correlation between ankyloglossia and pediatric obstructive sleep apnea, as indicated by a moderate evidence profile according to the GRADE tool. Nevertheless, it is imperative to recognize that the assessment of a short lingual frenulum should not be regarded in isolation. A comprehensive evaluation should extend to encompass additional factors, notably the assessment of tongue mobility and the presence of a high-arched palate. Therefore, future investigations ought to prioritize the examination of obstructive sleep apnea improvement concerning interventions such as frenectomy and myofunctional therapy.