Maxillary Labial Frenum in Preschool Children: Variations, Anomalies and Associated Factors

INTRODUCTION

The primary function of the maxillary labial frenum (MLF) is to stabilize the upper lip and keep it in harmony with the growing bones of the maxilla [1]. In newborns, the MLF assists the orbicular muscle in suckling [2, 3, 4]. However, divergences of opinion are found regarding the identification, classification, and clinical significance of the MLF in childhood.

The undersurface of the upper lip is not part of the routine clinical examination in pediatric dentistry. Subsequently, clinicians are unclear about what constitutes a typical or atypical appearance of the MLF. Nor it is known whether the morphology and attachment of this frenum have any functional consequences [1, 4, 5]. Variations in the appearance of the MLF may be either misinterpreted as lesions or associated with clinical problems, both of which suggest premature, although unnecessary, surgical interventions.

Potentially, characteristics of the MLF may exert an influence on sucking movements, including breastfeeding [4, 6]. It has been suggested that the labial frenum can interfere with an infant’s ability to flange the upper lip around the nipple [2, 6]. Moreover, the MLF has been associated with midline diastema and interference with effective toothbrushing, preventing adequate plaque removal [1, 5, 7]. Depending on the morphology and attachment of the MLF, there may be an area of the greater retention of milk or other liquids, which could contribute to the occurrence of early childhood caries on the maxillary incisors [2]. While there is evidence of age-dependent differences in frenal morphology and attachment in the permanent dentition [5, 8], there is little evidence to support such differences in the primary dentition. Only a few epidemiological studies have described morphological types and variations in the attachment of the MLF in preschool children and the majority of these studies have methodological flaws, such as a small sample size. Moreover, no studies have described variations in MLF attachment and morphology during a year by year period or have investigated associations with behavioral and socioeconomic characteristics.

The recognition of variations in the morphology and attachment of the MLF in the first years of life could assist pediatric dentists in the identification of patterns of normality and avoid the occurrence of unnecessary surgical procedures. Moreover, the identification of demographic, socioeconomic, and behavioral characteristics associated with abnormalities in the morphology and attachment of the MLF could suggest new hypotheses for risk factors to be tested in cohort studies. Therefore, the aim of the present study was to describe morphological and attachment variations and anomalies of the MLF and investigate associated factors in preschool children in southern Brazil.

MATERIALS AND METHOD

RESULTS

Among the 1,732 children enrolled at public preschools in the city of Canoas, dental exams were performed on 1,522 (response rate: 88%). The reasons for losses were repeated absences from preschool (n = 98), absence of a statement of informed consent signed by a parent/caregiver (n = 44), impossibility to perform the physical exam on the child (n = 38), and impossibility to contact the parent/caregiver for the interview (n = 30). Among the 1,522 children examined, 209 were excluded from the analysis due to the presence of permanent teeth (n = 197) and a history of orthodontic treatment (n = 12).

The final sample consisted of 1,313 children: 682 boys (52%) and 631 girls (48%). Age ranged from zero to five years (mean: 3.1; SD: 1.4). Table 1 shows that the majority of child had white ethnicity (66.9%) and mother’s education ranged from zero to 16 years (mean: 9.5; SD: 2.7; median: 11). Income was low for most of the families, with almost two thirds living on a monthly income up to two times the Brazilian monthly minimum wage. Most children were/had been breastfed (78.1%), used/had used a pacifier (68.1%), and used/had used a baby bottle (91.8%).

The most frequent morphological patterns of the MLF were simple (63.8%), persistent tectolabial (14.2%), and simple with appendix (11.3%), whereas the most frequent attachment patterns were gingival (51.1%), mucosal (19.6%), and penetrating (15.4%). The morphology and attachment of the MLF were significantly associated (p < 0.001; data not shown in table). Among the 838 children with a simple morphology, attachment was gingival in 560 (68.8%). Among the 187 children with persistent tectolabial morphology, attachment was penetrating in 136 (72.7%).

The prevalence of morphological and attachment abnormalities of the MLF was 21.6% and 25.4%, respectively. Figures 1 and 2 respectively illustrate the variation in MLF attachment and morphological anomalies. An accentuated reduction in the prevalence of both outcomes was found in children up to four years of age. The penetrating type accounted for the majority of attachment abnormalities and the tectolabial type accounted for the majority of morphological abnormalities. Table 2 shows significant associations between demographic characteristics and both morphological and attachment aspects of the MLF. The prevalence of both morphological (p = 0.001) and attachment abnormalities (p < 0.001) was higher in girls than boys. Moreover, the prevalence of morphological and attachment alterations decreased with age (p < 0.001) and white children exhibited more attachment abnormalities than nonwhite preschool children (p = 0.004). No significant differences were found with regards to socioeconomic variables. The prevalence of morphological and attachment abnormalities of the MLF was significantly higher in children who were not breastfed (p = 0.010 and 0.006, respectively) and those who used a pacifier (p = 0.022 and p < 0.001, respectively).

Figure 1. MLF attachment abnormalities according to age.

Figure 2. MLF morphological abnormalities according to age.

Table 3 displays the results of the crude and adjusted regression analyses regarding abnormalities in the morphology of the MLF. After the adjustment for confounders, the prevalence of morphology abnormalities was 34% higher in the female sex (PR = 1.34; 95% CI: 1.10 to 1.64). The prevalence of this outcome diminished 64% in children between two to three years of age (PR = 0.36; 95% CI: 0.29 to 0.44) and 76% in those between four to five years of age (PR = 0.24; 95% CI: 0.19 to 0.31) compared to children less than two years of age. The associations with breastfeeding and pacifier use lost their significance after the adjustment for confounding variables.

Table 4 displays the results of the crude and adjusted regression analyses regarding abnormalities in the attachment of the MLF. The female sex was 39% more likely to have attachment abnormalities than the male sex (PR = 1.39; 95% CI: 1.17 to 1.65). The prevalence of this outcome diminished 58% in children between two to three years of age (PR = 0.42; 95% CI: 0.36 to 0.50) and 81% in those between four to five years of age (PR = 0.19; 95% CI: 0.14 to 0.24) compared to children less than two years of age. Moreover, the prevalence of MLF attachment abnormalities was significantly higher in children with white ethnicity (PR = 1.33; 95% CI: 1.09 to 1.63) and those who used a pacifier (PR = 1.38; 95% CI: 1.09 to 1.73). The association with breastfeeding lost its significance after the adjustment for confounding variables.

DISCUSSION

This study provides – for the first time – evidence of strong age-dependent differences in the morphology and attachment of the maxillary labial frenum in the primary dentition. Although three-quarters of the children exhibited anomalies in the morphology and attachment of the MLF in the first year of life, the prevalence diminished to less than 15% at five years of age. Persistent tectolabial frenum and penetrating frenum were the most frequent abnormalities. The frequency of MLF morphological and attachment anomalies was greater among girls, whereas no differences were found among socioeconomic strata. Moreover, attachment anomalies were more frequent among children in the white ethnic group and those who used a pacifier.

The most common MLF morphology was the simple frenum, which was found in more than three-quarters of the children in the present study. Similar frequencies have been reported in other communities [5, 11, 12, 13]. Frenum with a nodule and appendix are also considered normal, as these are considered developmental remnants with no pathological potential and do not require any investigation or treatment procedures [5]. Persistent tectolabial frenum accounted for 14.2% of the morphological abnormalities in the present study. The prevalence of this abnormality ranges widely in previous studies from 1.7% to 24.6% [8, 11]. Other types of frenal abnormalities, such as frenum with a niche, double frenum, the bifid type, or the combination of two or more variations, are rarely found, affecting less than 1% of the population [12].

Regarding MLF attachment, over half of the children exhibited gingival attachment and one-quarter exhibited papillary or penetrating variations. Previous studies report incidences of about 45%, 25%, 15%, and 10% for gingival, mucosal, papillary, and penetrating attachment, respectively [8, 14, 15]. MLF attachment is highly associated with a number of syndromes, such as Ehlers–Danlos syndrome, infantile hypertrophic pyloric stenosis, holoprosencephaly, Ellis–van Creveld syndrome, and orofacial-digital syndrome. Each syndrome has relatively specific frenal abnormalities, such as multiple, hyperplastic, hypoplastic, or the absence of a frenum [1, 5].

Morphological characteristics do not influence the attachment of the MLF in the permanent dentition, except for the persistent tectolabial presentation, for such attachment is always penetrating (i.e., inserting into the papillae) [8, 13]. The results of the present study provide evidence – for the first time – of this hypothesis in the primary dentition, that the simple frenum is mainly inserted in the gingiva, while the persistent tectolabial type is penetrated the incisive papilla.

The evaluation of the distribution of different types of MLF morphology revealed that simple labial frenum increased significantly with age, whereas persistent tectolabial frenum decreased significantly with age. Only one previous study has suggested this variation in the morphology of the MLF in preschool children [11]. Regarding the attachment of the MLF, the results show that the level of attachment also tends to move apically with age. Thus, younger children exhibited more papillary and penetrating types of attachment, whereas the gingival and mucosal types of attachment were more common in older children. A previous study had suggested that the prevalence of the papillary penetrating type is lower in children older than three years of age compared to those up to three years of age [16]. However, this is the first study to describe this variation year by year in the primary dentition. The lower prevalence of abnormalities in the older children is compatible with findings reported for the permanent dentition [3, 8]. The frenum tends to migrate gingivally after the age of 5 years as the alveolar bone grows vertically with the eruption of the anterior maxillary teeth and the vertical growth of the face.

There is little evidence to support gender or ethnic differences in the MLF. The higher prevalence of morphological and attachment abnormalities in girls found in the present study differs from results reported in the literature for both the primary and permanent dentitions [5, 8, 16, 17, 18]. The greater likelihood of MLF attachment abnormalities in preschool children with white ethnicity has not previously been reported. Further studies are needed to establish possible associations between characteristics of the MLF in the primary and permanent dentition and both sex and ethnicity.

The finding that abnormal MLF attachment was 38% more likely in children who used/had used a pacifier cannot be compared to data from other studies because this is the first study to investigate this factor. Nonnutritive sucking habits are recognized as having an influence on oral myofunctional characteristics, such as the resting position of the lips and tongue, shape of the hard palate, and swallowing pattern [19, 20]. Moreover, the use of a pacifier is strongly associated with malocclusion in the primary dentition [21, 22]. It is therefore plausible that this habit – depending on its intensity, frequency, and duration – can alter the positioning of the MLF due to its influence on the development of the maxilla and upper lip.

Normal suckling begins with the flanging of the lips to create a seal around the areolar tissue of the breast [2]. Thus, anomalies in the attachment of the frenum could potentially limit the mobility and function of the upper lip, resulting in breastfeeding difficulties [2, 6]. However, no association was found between MLF morphological or attachment anomalies and breastfeeding. This result lends support to data from a recent cohort study that found no associations between MLF morphology/attachment and comfort with breastfeeding, pain scores, or latching [23]. Moreover, a recent systematic review concluded that, to date, there is no evidence of the benefit of releasing the labial frenum to improve breastfeeding [24].

The clinical implications of the present study need to be discussed. The MLF has been mistakenly associated with several clinical problems, particularly the pathogenicity of midline diastema. However, diastema between the maxillary central incisors is a relatively common finding at the beginning of the primary and permanent dentitions. The findings of the present investigation showed that the tectolabial morphology and papillary/penetrating attachment of the MLF – considered the main candidates for surgical interventions–are highly prevalent in very young children [8, 13]. This situation increases the possibility of misdiagnosis in the first years of life and may result in unnecessary interventions on the frenum. Moreover, tissue nodules and appendices are remnants that have no pathological potential and do not warrant biopsy. Hence, lack of knowledge regarding the various types of frenal morphology has resulted in unnecessary biopsies. Dentists should correlate the age of the child with the type of frenal attachment and morphological variations during clinical examinations to avoid misdiagnosis and unnecessary treatment. In rare cases, the MLF is exceptionally hypertrophic and can become traumatized and painful in the primary dentition phase.

This study has strengths that should be pointed out. First, the use of an internationally recognized diagnostic classification system strengthened by the ability to identify the outcomes. Secondly, although the cross-sectional design has inherent limitations that preclude the establishment of a temporal relationship between exposure factors and outcome, it is nonetheless effective at identifying associated factors that could be addressed in future longitudinal studies. Thirdly, the sample size was reasonably large, which enabled a reasonable degree of precision in the prevalence rates and effect measures.

CONCLUSIONS

The frequency of morphological and attachment anomalies of the maxillary labial frenum diminish considerably with the increase in age in early childhood. Moreover, there is no socioeconomic gradient in the distribution of such anomalies. The spontaneous reduction in morphological and attachment anomalies of the maxillary labial frenum and the lack of an association with breastfeeding suggest that dentists should be very cautious prior to opting for corrective surgical procedures, especially in the first years of life.