Introduction
The frenum is composed of structures such as the maxillary labial frenum (MLF), mandibular labial frenum, lingual frenum, and buccal frenum. The frenum provides essential connections between oral structures and maintains stability and function. It plays a crucial foundational role in maintaining normal oral functions, supporting the movement and proper positioning of both the lips and the tongue. In pediatric patients, normal development and positioning of the frenum significantly affect oral health[1,2].
The MLF, originating from the inner central region of the superior labial area, establishes its connection with the median alveolar ridge situated on the maxilla[3]. Abnormal development or positioning of the MLF can lead to various oral health issues. For instance, an abnormal attachment to the alveolar crest may affect tooth alignment, leading to midline diastema. In addition, a thick or elongated frenum can restrict upper lip movement, resulting in speech impairment or feeding difficulties. Such issues underscore the need for proper diagnosis and treatment to maintain and improve oral health in pediatric patients[4,5].
The MLF changes continuously from fetal development until full growth is achieved[6]. These changes have led clinicians to question the diagnosis, treatment methods, and timing of abnormal frenum conditions. Although an aberrant frenum may require surgical intervention, there are varying opinions among dental professionals regarding the timing of surgery[7,8].
The interval spanning 1997 to 2012 exhibited remarkable escalations in ankyloglossia diagnoses and frenum procedures, with 834 percent and 866 percent increases, respectively. These significant trends underscore the paramount importance of accurate diagnostic methodologies and the implementation of appropriate therapeutic measures in clinical practice[5,9]. Comprehension of the normal developmental process of the MLF is essential for the accurate diagnosis and appropriate treatment of these anomalies.
The aim of this review is to provide essential information for the diagnosis and treatment of MLF, thereby supporting the preservation and enhancement of oral health in children.
Definition and Anatomy of the Maxillary Labial Frenum
The MLF initiates from the inner central region of the upper lip and terminates at the median alveolar ridge of the maxilla. This anatomical structure creates a linkage between the upper lip and the alveolar bone, establishing a physiological connection between these two components. The MLF’s principal function is to offer stability to both the upper lip and the alveolar mucosa. Furthermore, in infants, this frenum plays a crucial role in maintaining proper lip positioning during feeding activities[1,10].
From an embryological perspective, the MLF emerges as a post-eruptive vestige of the tectolabial bands. During the developmental process, these bands undergo division, resulting in the formation of both the MLF and the palatine papilla. It is composed of alveolar mucosa, reflecting the origin of these embryonic connective structures[4].
The MLF is primarily composed of mucosal folds and connective tissue that attach to key anatomical structures, including the alveolar bone, orbicularis oris muscle, and the attached gingiva. Connective tissue forms a horizontal band that fills the midline gap between the bilateral incisivus labii superioris muscles, reflecting its significant role in the anatomical organization of the upper lip and gingiva[11].
Histologically, collagen fibers and elastic fibers dominate the structural makeup of the frenum, contributing to its mechanical properties and function[12]. Although some studies have reported skeletal muscle fibers in 35% of maxillary labial frenum samples, their presence is inconsistent[13]. Sadeghi et al. found muscle fibers in only one specimen embedded with upper lip muscles, confirming that they are not a major component of the MLF, which mainly consists of connective tissue and mucosa[12]. The findings of Iwanaga et al. suggest that muscle fibers do not significantly contribute to MLF function or influence oral health outcomes. The influence of the frenum on oral structures such as the gingival margin is passive and driven primarily by its connective tissue properties[11].
Changes in Maxillary Labial Frenum Position
The MLF undergoes significant positional and structural alterations during the growth and development of the alveolar ridge and dentition. In infancy, the frenum typically attaches to the alveolar crest or the incisive papilla. During the eruption of permanent central incisors and alveolar bone development, the frenal attachment undergoes apical migration, progressing towards the mucogingival junction. In adulthood, the frenum usually attaches to the mucogingival junction, reflecting normal developmental progression[4].
In infants, a conspicuous frenum insertion at the alveolar crest is frequently observed; however, this attachment generally descends as the alveolus undergoes vertical growth[14]. It is imperative to provide reassurance to parents that the presence of a midline diastema is a common occurrence in the deciduous or early permanent dentition stages and frequently resolves spontaneously with the eruption of the maxillary canines[4].
Studies have shown the frenum’s prominence decreases as individuals age, correlating with the progressive growth and downward movement of the alveolar process[6,15]. The frenum maintains its position during development, but its relative position shifts apically owing to downward expansion of the alveolar bone[14,16]. However, in some cases, normal developmental transitions do not occur, resulting in a persistent infant-like frenum. Such cases can lead to esthetic concerns, speech difficulties, or midline diastema due to the thickened frenum. Taylor indicate that 7% of adolescents aged 12 to 18 years experience a failure of the frenum to migrate, resulting in a persistent midline diastema[17].
Classification of the Maxillary Labial Frenum
The MLF can be classified based on its insertion site and clinical characteristics, which helps to assess its impact on oral structures and determine whether surgical intervention is necessary. The most widely recognized classification systems are Kotlow’s classification (Table 1) and Placek’s classification (Table 2)[18,19]. A classification system was devised by Kotlow to categorize the frenum, employing a four-grade scale that takes into account its visual characteristics and the location where it attaches to the gingival tissue (Fig. 1). The severity of the grade exhibits a positive correlation with the incidence of breastfeeding difficulties, as postulated by Kotlow[18].
Research conducted on adult populations has demonstrated a preponderance of mucosal (M)-type frenum attachments. Specifically, this anatomical configuration was identified in approximately 50% of the 465 adults examined in these epidemiological investigations[19]. Mtype frenum is relatively rare in infants, with less than 6% of children having a frenum inserted above the mucogingival junction[14,20]. In infants, the highest prevalence is observed with the papillary penetrating phenotype[15]. Most newborns (83%) had a frenum attached to the gingival margins (grade 2, Kotlow classification)[21]. The variability in frenum attachment highlights the importance of individualized assessments when evaluating the need for surgical intervention.
Kotlow’s classification has gained attention for breastfeeding assessment, but its interrater reliability is reported to be low, particularly in newborns, with only 8% agreement for grade 2 - 3. The Stanford classification was developed to address some of these challenges by simplifying Kotlow’s classification into three types and combining grades 2 and 3 into Type 2. This approach improved the interrater reliability to 38% but still posed challenges for accurate classification[21]. Clinical examination of the MLF in infants is challenging because of a lack of cooperation, and relying solely on classification systems for maxillary frenectomy may lead to complications. Therefore, careful consideration is essential when deciding whether to proceed with the surgery.
Clinical Issues Related to the Maxillary Labial Frenum
Forward traction of the superior labium may result in blanching of the incisive papilla, potentially indicative of an abnormal frenum. This blanching suggests that the frenum is causing tension, which can contribute to midline diastema[22]. Furthermore, frenectomy may be necessary if the frenum is abnormally wide or extends beyond the alveolar crest to the palatal area. From a histological perspective, the frenum exhibits a composition predominantly featuring mucosal and connective tissues, with a notable presence of elastic fibers interspersed throughout its structure. Current evidence suggests that the persistence of midline diastema is primarily attributed to the prominent elastic component, rather than excessive muscular traction[3]. In cases where a midline diastema persists following the eruption of the permanent lateral incisors and canines, surgical removal of the frenum may be indicated[10].
The presence of a hyperplastic MLF and midline diastema is thought to be responsible for food impaction, plaque retention, and difficulty in performing adequate oral hygiene, resulting in gingival and periodontal inflammation[23]. In such cases, frenectomy is often indicated.
1. Oral Hygiene and Gingival Health
Hyperplastic MLF can interfere with normal oral hygiene, leading to plaque retention, food impaction, and gingival inflammation. Attachment of the frenum can limit lip movement, making brushing challenging and contributing to periodontal issues. In severe cases, it may also exert pressure on the gingiva, leading to gingival margin recession. This condition can have long-term consequences on dental health if left untreated[23].
2. Dental Caries
Hyperplastic MLF has been linked to an increased risk of labial caries in the maxillary anterior teeth. While a direct causal association between hyperplastic maxillary frenum and labial caries remains unestablished, proactive guidance for patients exhibiting restrictive tissues may encompass enhanced oral hygiene practices. Such measures could include post-feeding vestibular cleansing to mitigate potential risks associated with this anatomical variation[24].
3. Midline Diastema
Midline diastema, or spacing between the central incisors, is one of the most common reasons for evaluating the MLF. An aberrant frenum attachment that crosses the alveolus and inserts into the incisive papilla can contribute to the persistence of diastema. Before surgical intervention, other etiological factors of diastema, such as supernumerary teeth, arch length discrepancies, and oral habits, should be ruled out[4]. A significant number of diastemas in children spontaneously close once the permanent canines erupt; therefore, early surgical intervention is generally not recommended.
The ideal timing for performing frenectomy to address maxillary midline diastema has been a topic of debate among clinicians, with differing opinions on whether the procedure should be performed early or delayed until orthodontic treatment.
Traditionally, some experts advocate performing frenectomy before orthodontic closure of the diastema. This approach aims to prevent the frenum from interfering with tooth movement, thereby facilitating a smoother orthodontic alignment. If orthodontic treatment is anticipated, it may be beneficial to perform frenectomy before the canines erupt to allow for effective orthodontic tooth movement and to prevent future relapse[4].
Current research findings and clinical protocols increasingly favor a more conservative approach. This methodology advocates postponing frenectomy procedures until after the complete eruption of the six maxillary anterior teeth and the subsequent closure of the diastema through orthodontic treatment modalities. A substantial number of dental professionals specializing in pediatric and orthodontic care contend that midline diastemas occurring in primary and mixed dentitions are often considered within normal parameters and arise from multiple factors, with a tendency to resolve naturally as the child undergoes physiological development. A systematic review confirmed that early surgical intervention is not necessary unless diastema persists after orthodontic efforts[9]. Moreover, delaying surgery reduces the risk of orthodontic relapse caused by scarring, which is a potential complication of early frenectomy[25]. If the diastema fails to close with orthodontic treatment, frenectomy may be considered to prevent reopening of the gap.
Opponents of early frenectomy in infancy emphasize that the position and structure of the frenum change dynamically throughout childhood. As children grow older, the frenum tends to become less prominent, reducing the need for early intervention[6]. Furthermore, there is limited evidence supporting a correlation between the appearance of the frenum in infancy and oral health outcomes later in life. These experts caution against preventative frenectomy without clear indications, as it carries the risk of unnecessary surgery with no proven long-term benefits[21].
On the other hand, some studies suggest that early frenectomy during the primary or mixed dentition stages can effectively reduce the width of midline diastema. A recent retrospective cohort study demonstrated that laser frenectomy performed in these stages led to a measurable reduction in diastema width. However, the study acknowledged some limitations, emphasizing the need for long-term follow-up to determine whether early frenectomy can prevent future orthodontic intervention. It remains unclear whether early surgical treatment can consistently eliminate the need for orthodontic closure of persistent diastemas in adolescence, highlighting the need for prospective studies with proper controls[8].
The indication for frenectomy arises when the frenum imposes excessive tension on the gingival tissue, manifesting as papillary blanching upon upper lip elevation, or when a persistent diastema greater than two millimeters is observed in the permanent dentition, given that such interdental gaps seldom resolve spontaneously[7,15]. If diastema remains unresolved in the permanent dentition, treatment must address both the diastema and its underlying etiology to ensure lasting results. The therapeutic approach may incorporate orthodontic interventions, frenectomy, restorative techniques, or a synergistic combination thereof, meticulously tailored to meet the unique clinical requirements of each patient[7].
There is also a divergence in treatment philosophies among dental and healthcare specialists regarding the impact of the frenum on oral function and development. Pediatricians, speech pathologists, lactation consultants, and dental specialists often differ in their recommendations, reflecting varied perspectives on the significance of frenum attachment[6,26]. This diversity in clinical opinions underscores the importance of individualized treatment planning based on both functional needs and developmental outcomes.
In conclusion, the timing of frenectomy should be carefully considered, and the risks and benefits of early versus delayed intervention should be weighed. Although early surgery may prevent interference with orthodontic treatment, it also carries the risk of scarring and relapse. Conversely, a more conservative approach, delaying frenectomy until after orthodontic closure, aligns with evidence suggesting that most diastemas resolve naturally over time. Ultimately, the decision to perform frenectomy must be patient-specific, taking into account the severity of diastema, functional impairments, and aesthetic concerns to ensure optimal outcomes.
4. Breastfeeding Difficulties
The MLF has been characterized as a “lip tie” when it is postulated to compromise breastfeeding efficacy. This problematic anatomical structure is thought to impair the infant’s capacity to properly flange the upper lip around the maternal nipple, thereby hindering the establishment of an effective latch during nursing[18]. Severe instances of restrictive MLF attachment have been linked to feeding challenges in infants, affecting both breastfeeding and bottle-feeding. Empirical evidence suggests that a restrictive MLF can compromise the infant’s ability to create an effective seal on the mother’s breast due to inadequate lip flanging. This impairment may result in suboptimal latching and excessive air ingestion during feeding, potentially contributing to symptoms such as colic or general infant discomfort[27,28]. Moreover, the MLF has been correlated with infant reflux, attributed to the introduction of air caused by an imperfect seal during the feeding process[28,29].
However, Shah et al. argued that the anatomical position of the MLF does not necessarily interfere with breastfeeding. The researchers’ findings indicated no substantial relationship between the degree of maxillary labial frenum restriction and successful breastfeeding outcomes, quality of latch, or maternal comfort levels. They emphasized that functional aspects, such as lip flexibility and mobility, are more relevant than anatomical appearance. Additionally, this study challenges the assumption that upper lip and tongue ties frequently cooccur, suggesting that other factors, such as maternal technique and infant feeding patterns, play a more significant role in breastfeeding outcomes[30].
Conclusion
The maxillary labial frenum plays an essential role in oral stability and development. However, variations in its attachment may lead to functional problems such as midline diastema, breastfeeding difficulties, and poor oral hygiene. Surgical treatment of the maxillary frenum remains controversial, particularly with regard to the timing and indications for frenectomy in pediatric patients. Most cases of prominent MLF resolve with natural growth, and early surgical intervention may be unnecessary. Therefore, careful consideration of the patient’ s age, frenum attachment, and associated symptoms should guide clinical decision making, ensuring that unnecessary surgical procedures are avoided. Future research should focus on improving assessment tools for frenum attachment and evaluating non-surgical management strategies for problematic frenums.
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