Prevalence of variations in morphology and attachment of maxillary labial frenum in various skeletal patterns - A cross-sectional study.

BACKGROUND: Maxillary labial frenum is a dynamic structure with a diverse morphology. Although an abnormal labial frenum is associated with syndromic and nonsyndromic conditions, it is often been neglected during the routine intraoral examination. The significance of various types of frenum (normal to abnormal), based on the attachment site and morphology in different skeletal patterns, has not been studied yet.
MATERIALS AND METHODS: A cross-sectional study was conducted in a clinical setting on 150 participants (50 each in Class I, Class II, and Class III skeletal pattern) within the age group of 13-30 years. Frenum was examined by direct visual method and intraoral photographs were taken for all the participants.
RESULTS: Chi-square and Fisher's exact tests were used. No gender-wise differences were found among the various frenum typologies. Mucosal type was the most prevalent in Class I and II and gingival type in Class III. Simple frenum was the common type in all the three groups. However, abnormal frenum categories based on its location and morphology were more in class III and found to be statistically significant. Papillary and papillary penetrating types are significantly associated with skeletal class III pattern and midline diastema (P < 0.05).
CONCLUSION: The prevalence of papillary and papillary penetrating types of frenum are significantly more in Class III skeletal pattern. A labial frenum that is attached close to the gingival margin could be an etiological factor in midline diastema, mucogingival problems, and affect the growth of the alveolar process. Hence, an early diagnosis of abnormal frenum prevents the emergence of periodontal as well as orthodontic problems.

INTRODUCTION

The maxillary labial frenum, also called as frenulum labii superioris, is a mucous membrane fold that connects the upper lip to the alveolar mucosa, gingiva, and the underlying periosteum.[1] Histologically, it is made of loose connective tissue fibers, abundance of elastic fibers, and mucous glands in the subcutaneous tissue on either side of the central artery and vein.[2] Few striated muscle fibers also arise from the muscle bundles of the lip on either side of the midline.[345] It is a dynamic structure with much of physiological importance [6] and exhibits a diverse array of variations. The primary function of the labial frenum is to support or provide stability to the upper lip and to keep the lip in harmony with the growing bones of the maxilla. Thus, it contributes to the regulation of the facial growth.[67891011] A frenum that is attached too close to the gingival margin can cause diastema, gingival recession, bone loss due to the muscle pull, poor lip mobility, especially during smiling and speaking.[8910111213]

The maxillary labial frenum has fibrous tissue running in an anteroposterior direction and merges with the submucosal fibers of the upper lip.[1314] It also encloses the septopremaxillary ligament [6] serves as a means of transmitting the septal growth force to the premaxilla. It also encompasses few striated fibers of the nasolabial muscles.[1516] Delaire had explained anatomic and neurophysiologic correlations existing between the labial frenum, septopremaxillary ligament, and interincisal suture which are important determinants of vertical and anteroposterior relationship of mandible and nasomaxillary complex. He further stated that inadequate muscular reconstruction and mutilation of the labial frenum could result in growth abnormalities.[17]

Based on its attachment site, Mirko et al.[18] has classified into four types [Figure 1] and Sewerin [19] has classified into eight different types based on its variations in the morphology [Figure 2]. There is a scarcity of literature which documents the variations in the diverse morphology of the maxillary labial frenum.[2021] Newer morphological variants are also reported in the literature.[20]

Figure 1

Frenum types based on attachment site. (a) Mucosal frenal attachment; (b) Gingival frenal attachment; (c) Papillary frenal attachment; (d) Papillary penetrating frenal attachment

Figure 2

Frenum types based on morphology. (a) Simple frenum; (b) Simple frenum with appendix. (c) Simple frenum with nodule; (d) Frenum with nichae; (e) Bifid frenum; (f) Double frenum with appendix; (g) Persistent tectolabial band; (h) Trifid frenum; (i) Trifid frenum with nodule

A thick, wide maxillary labial frenum attached close to the gingival margin is often considered as a contributing factor for midline diastema [1222232425] and delayed growth of premaxilla.[252627] It is considered normal during the early developmental stage.[111328] The attachment of the frenum thins out and relocates to a more apical position as the alveolar process enlarges and maxillary anterior teeth erupt.[922242529] Thus, the papillary and papillary penetrating type are said to be pathogenic if it exists beyond the mixed dentition.[13] The mucosal and gingival types of frenal attachment are more common in permanent dentition.[132230] Midline diastema is the most common esthetic problem, and its prevalence ranges from 1.6% to 25.4%.[22] The aim of the study is to assess the most prevalent type of maxillary labial frenum based on its attachment site and morphology in Class I, Class II, Class III skeletal participants and its association with midline diastema.

MATERIALS AND METHODS

A cross-sectional study was conducted in 150 adults consisting of both males and females with an age ranging from 13 to 30 years who were undergoing orthodontic treatment in our institution. The study protocol was approved by the Institutional Ethics Committee and a written informed consent was obtained from the study participants. The participants who had any congenital/developmental defects, trauma/injuries in the premaxillary region, history of prior orthognathic/frenal surgeries, and under any medication known to affect the gingiva were excluded from the study.

Demographic details such as age and gender were recorded. The study participants were categorized into Class I, Class II, and Class III skeletal pattern (50 individuals in each of the three groups) based on the cephalometric variables. ANB, Wits Appraisal, and Beta angle were used to assess the skeletal pattern [313233] using the standardized digital lateral cephalogram which is then digitized using Dolphin software system [Figure 3]. These mean values of the variables are shown in Table 1.

Figure 3

Cephalometric landmarks, angular, and linear measurements used in the study. (a) ANB (°) – The relative position of jaws to each other. Uses the skeletal landmarks point A, point B, and Nasion (N); Wits Appraisal (mm) – Measures the degree of anteroposterior jaw dysplasia on a lateral cephalometric head film. The points of contact of the perpendiculars onto the occlusal plane from the point A and point B are used. (b) Beta angle (°) – The type of skeletal dysplasia in the sagittal dimension. Uses three skeletal landmarks such as point A, point B, and the apparent axis of the condyle

Table 1

Mean values of cephalometric variables

Clinical examination of the frenum was conducted in the dental chair under adequate light by a single examiner. Attachment site of the frenum and its morphology were examined under direct visual method, by upward distension of the upper lip following which intraoral photographs were taken for all the study participants. The midline diastema is recorded when the space between the maxillary central incisors are more than 1 mm.

The reliability of the measurements was determined on 20 randomly selected adults who were examined at intervals of 14 days. Testing for the method error of all measurements was done with Dahlberg's formula [√∑d2/2n] where d is the difference between two measurements pair and n is the number of subjects.

RESULTS

Data were analyzed using IBM SPSS Statistics Base 24.0, SPSS South Asia Private Limited, Bangalore, India. Chi-square and Fisher's exact tests were performed to evaluate the difference in the prevalence of frenum typology in three groups and also to compare the association between the type of frenum and midline diastema. P < 0.05 was considered to be statistically significant.

The mean age of the individuals and gender distribution in Class I, Class II, and Class III skeletal pattern are shown in Table 2. No statistical significant difference was observed in males and females for different types of frenum based on the attachment site and morphology [Tables 3a and b].

Table 2

Mean age and gender distribution in each group

Table 3a

Gender and attachment site

Table 3b

Gender and morphology

Table 4 shows the overall comparison of maxillary labial frenum attachment site in all three groups. Out of 150 study participants, mucosal type (42%) was most prevalent followed by gingival (34%), papillary (20%), and papillary penetrating type (4%). There is a statistical significant difference between the proportion of the mucosal type which is the most prevalent in Class I (60%) and Class II (54%) than Class III (12%). The cumulative percentage of papillary and papillary penetrating type of attachment is more in Class III (44%) which is statistically significant (P = 0.001) than that of the other two groups.

Table 4

Overall comparison of frenum types based on attachment site in three groups

Table 5 shows the overall prevalence of frenum in the three groups based on morphological variations. Simple frenum (45.33%) was the most prevalent in all three groups, followed by bifid frenum (19.33%). Trifid frenum was found to be 8% in the present study. Abnormal frenum morphology categories [persistent tectolabial, bifid, trifid, and double frenum] were more in Class III (50%) than in Class I (25%) and II (24%) which was statistically significant (P = 0.013).

Table 5

Overall comparison of frenum types based on morphology in three groups

Forty-six percent had a frenum which was thick and wide. Wide frenum was more in class III skeletal pattern (70%) than that of class I (32%) and class II (36%) skeletal pattern. There was a statistically significant difference (P = 0.001) in the proportion of wider frenum in three groups [Figure 4].

Figure 4

Wide frenum in Class I, Class II, and Class III skeletal pattern

There is no statistically significant difference in the presence of midline diastema in the three groups [Table 6a]. The association of diastema with normal and abnormal frenum typologies is tabulated in Tables 6b and c. 29.3% of the total study participants had diastema. The papillary and papillary penetrating types of frenum were significantly associated with the diastema (P = 0.007).

Table 6a

Presence of diastema in Class I, Class II, and Class III

Table 6b

Diastema and abnormal frenum categories based on attachment site

Table 6c

Diastema and abnormal frenum categories based on morphology

DISCUSSION

The prevalence of different types of maxillary labial frenum in primary, mixed, and permanent dentition and its significance in gingival recession and periodontal pocket formation in the maxillary anterior teeth and midline diastema had been studied extensively.[5131420292130343536] Since the frenum is in passive relation with the growth of the alveolar process,[13] an attempt is made to study the prevalence of frenum in various skeletal patterns based on the attachment site and the morphology of frenum.

The primary role of the frenum is to provide stability to the upper lip and to maintain a balance between the growing bones.[8] The pull on the septopremaxillary ligament which is enclosed in the frenum induces alveolar basal bone development and translative growth of entire maxilla.[34] Pushing of the nasal septal cartilage is transmitted to the anterior nasal spine by the septopremaxillary ligament and the nasolabial muscles.[15] Henceforth, the displacement of the maxilla downward and forward occurs by the direct thrust of the septal cartilage, biomechanical forces exerted by the forward traction of the nasolabial muscles, and the induction mechanism emanating from the septopremaxillary ligament and maxillary labial frenum resulting in forward traction of premaxilla.[16]

When the frenum is in close proximity to the gingival margin, it limits the movement of these structures, particularly the anterior portion of the maxilla.[526] An adequate zone of attached gingiva is essential for maintaining the gingival health.[3738] Hence, a frenum which is inordinately large and wide with no apparent zone of attached gingiva in the permanent dentition and/or when the interdental papilla shifts when the frenum is extended, is said to be pathogenic.[222339] It interferes with plaque control measures and leads to gingival recession and periodontal pocket.[8918] The frenal attachment is considered normal when it is attached apically away from the gingival margin, usually at the mucogingival junction [5] and does not exert pull on the attached or marginal gingiva (pull syndrome).[1820]

The maxillary labial frenum is a posteruptive remnant of tectolabial bands connecting the tubercle of the upper lip to the palatine papilla.[12] The developing alveolar process causes severance of this band into labial and palatal portion which forms the maxillary labial frenum and the palatine papilla, respectively.[2425] The present study comprises of the only adult population which shows that papillary (20%) and papillary penetrating (4%) types are least common which is concomitant with the previous studies.[5141829353640] However, a study conducted by Christabel SL reported that there were no papillary and papillary penetrating type of frenum in permanent dentition.[13]

Any interference in the relocation of the continuous band of connective tissue of the frenum during the growth of the alveolar process can cause midline diastema and also affects the growth of anterior part of the maxilla. In such cases, frenum retains its primitive state, a sort of maturational arrest.[41] Thus, papillary and papillary penetrating type are said to be pathological in the permanent dentition, and interestingly, those types were more common in Class III (44%) compared to that of Class I (14%) and Class II (14%) skeletal patterns with a high statistical significant difference.

No statistically significant difference in gender-based comparison was noted in all the three groups based on attachment site and morphology which were consistent with the similar studies in the literature.[1435] However, Sewerin reported higher frequency of variations among males.[19] Few studies also document significant difference among females.[37]

Based on the morphological variation, simple frenum (45.33%) is the most prevalent type reported followed by frenum with nodules (12%) and appendix (6%) which are similar with that of the previous studies reported.[513141920213742] Nodules and appendix found commonly in the simple frenum is a normal variant with no pathological potential, frequently seen with increase in age.[1441] Frenum with nichum and bifid frenum were 2.67%, 19.33%, respectively, in the present study which was concomitant with the results of Sagar et al.[43] However, it was found to be <1% in a study conducted by Kakodkar et al. in permanent dentition.[42] As most of the prior studies were done in children of different age groups, and in diverse population, direct comparison with other study should be done cautiously.

Persistent tectolabial frenum, bifid frenum, double frenum, and wide frenum which are considered abnormal,[540] showed a statistical significant difference among the three groups. The overall prevalence of trifid frenum, a newer variant, was 8% which was only 0.58% by Mohan et al.[20] These variations can be attributed to racial or ethnic differences which are inherent with the frenum morphology.[1014] Wide frenum was found to be 32%, 36%, and 70% in Class I, Class II, and Class III skeletal patterns, respectively, which was highly significant.

The development of abnormal frenum is an important diagnostic feature of several syndromic conditions such as Ehlers–Danlos syndrome, infantile hypertrophic pyloric stenosis, holoprosencephaly, Ellis–van Creveld Syndrome (EVCS), and oro-facial-digital syndrome.[11354445] Two potentially fatal conditions associated with hyperplastic frenum are EVCS and hypoplastic left heart syndrome.[1011] The most striking feature of EVCS is the concave facial profile with midfacial retrusion resulting in a Class III skeletal pattern.[45]

Maxillary midline diastema is one of the most common malocclusion.[22] An aberrant maxillary labial frenum is considered one of the major etiological factor for diastema if other associated dental conditions persist.[2223242546] The fibroelastic band of the frenum crosses the alveolus and inserts into the incisive papilla and hinders the approximation of the maxillary central incisors.

Studies relating the midline diastema with various morphological variations of frenum in different skeletal patterns are scarce. Diastema is significantly associated with papillary and papillary penetrating type of frenum,[223746] whereas no significant association was noted with the variation in the morphology of frenum which was similar to the prior study.[43] However, diastema can also occur even without an abnormal frenum and vice versa.[24] The width of the diastema is inversely correlated with the presence of an abnormal maxillary labial frenum.[4647]

An attractive balanced smile and confident speech are the most valuable assets for the proper psychosocial development of an individual. A frenum that is close to the gingival margin intervenes the pronunciation of certain words as well as a good smile.[10] This study also reveals that the papillary and papillary penetrating types of frenum are commonly noticed in Class III skeletal pattern. Hence, an early diagnosis and prompt treatment of the aberrant frenum will intercept the developing skeletal Class III malocclusion and other mucogingival problems.

The limitation of the study is its smaller sample size. Hence, a similar study with larger samples involving siblings/twins should be conducted to evaluate the genetic and racial variations in the morphology and attachment site of the labial frenum.

CONCLUSION

The prevalence of papillary and papillary penetrating type of frenum are significantly more in Class III skeletal pattern which calls for an interdisciplinary attention. A labial frenum that is attached close to the gingival margin interferes with normal oral hygiene maintenance and mucogingival problems and can affect the growth of the maxillary alveolar process. Thus, the present study attempts to add insight into the importance of prompt early diagnosis of abnormal frenum in preventing the emergence of periodontal as well as orthodontic problems.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.