An Insight into the Frenum

Introduction

Labial frenum is a dynamic and often changeable structure and is subject to variation in shape, size and position during the different stages of growth and development.¹ During growth, it tends to decrease in size and lose clinical importance.² In young children, the frenum is generally wide and thick, and during growth, it becomes thin and small.³ In its composition, it consists of epithelium, collagen fibers, nerve fibers and capillaries, and sometimes few elements of minor salivary glands and isolated stratified muscle fibers. It has a wide and relatively deep origin or base on the inferior surface of the upper lip. It extends to the middle portion of the labial surface of the alveolar process between the maxillary central incisors and here it is attached to the periosteum, the maxillary suture’s connective tissue, and the alveolar process.⁴

Normal vertical development of the alveolar process often accomplishes the displacement of the attachment in an apical direction. The prolonged midline diastema has been linked to a major causal component, namely the inability of the connected frenal fibers to move apically, leaving a residual strip of tissue between the maxillary central incisors. In addition to preventing the space closure between the upper central incisors, it can lead to food impaction. The oral hygiene gets poor due to compromised brushing, resulting in inflammatory destruction of periodontium.⁵

Currently, there is no comprehensive review of the frenum, a tiny fold that plays an important role silently. When its location or morphology is abnormal, it attracts interdisciplinary attention in dentistry. This study represents the first attempt to provide a thorough review of the labial frenum. The review of frenum is covered under the following aspects.

Development of Frenum

The maxillary labial frenum is a fold of tissue that extends into the vestibule and midportion of the upper lip from the maxillary midline region of the gingiva. It is typically triangular in form.⁵ The superior labial frenum appears to be developed from the frontonasal process.⁶

Within the first few months of fetal life, it emerges as a part of oral cavity, along with lips and cheeks.⁷ The tuberculum is a protrusion that develops into the central portion of the inner zone of upper lip as growth and development proceeds. This is also the period when the palatine papilla, another protrusion on the anterior portion of the palate, originates.

The tuberculum and the palatine papilla are connected by a continuous tissue fold known as the ‘tectolabial frenum’. By continuing as a continuous band of tissue from the inner side of the upper lip to the palatine papilla, and across the alveolar ridge in the process, the tectolabial frenum in fetuses resemble the aberrant frenum of postnatal life. The continuous tissue fold is normally severed by the expanding alveolar process, separating it into the palatal and labial halves. The attachment of superior labial frenum is from the lip to alveolar crestal ridge, consisting of labial tissue on the labial side which is equivalent to palatine papilla on the palatal side.⁸

Variation in Size of Frenum

Usually broad in origin, it exhibits a smooth septum that becomes narrower as it advances posteriorly, inserting at the outer aspect of periosteum, intermaxillary suture and midline connective tissue of the alveolar process. The frenum is like any other structure. It has a range of normality in that it varies in bulk from a thick mass to a thin fold of tissue, and in attachment height from near the alveolar crest to apical aspect. These frena differ in terms of tissue mass in addition to attachment and height.¹

Histology of Frenum

In 1935, Noyes et al. conducted a histological study on newborn infants and discovered that the frenum is primarily made up of connective tissue.⁷ A small number of striated muscle fibers which originate from the lip muscle bundles on either side of the midline, pass medially and posteriorly in a diagonal direction without reaching the alveolar process. The loose character of the fibrous connective tissue becomes more regular in arrangement with strands lying in an anteroposterior direction as it nears the alveolar attachment. In the labial section, mucus glands are located on each side of central artery and vein close to the lip muscle bundles. The frenum receives branches from this artery and vein that flow anteroposteriorly, supplying the structure's blood supply. The posterior fibers terminate by ramifying with the alveolar crestal connective tissue and its anterior surface (Table 1).

There is dispute on the histologic morphology of the frenum in terms of whether or not muscle tissue is present.

Tension test

By exerting stress on frenum, the papillary tip movement or blanching effect caused by local ischemia is noted. The aberrant or abnormal frenum can be visually identified. A positive tension test represents abnormal frenum and a negative test represents one frenum.¹³

Frenum as Etiologic Factor

The anatomical presence of labial and buccal frenum are extremely important in maintaining the cheeks and lips in place by its tiny fold of mucosa containing muscle fibers or elastic fibers, collagen fibers is controversial.

• The abnormality of frenum is recognized in its attachment to gingiva and its size. The different attachments beyond the normal mucosal attachment can affect the health of mucogingival junction by its pull effect during muscular movements, resulting in plaque accumulation indirectly leading to gingivitis, localized periodontitis, and in cases where gingiva thickness is less than 1 mm, could result in gingival recession. The effect of pull syndrome is only realized on clinical presentation of above changes.

• Conversely, diastema is caused by the unsightly, thick, abnormally large frenum in the front part of maxillary arch, which is frequently subjected to mechanical damage when brushing. Some writers claim that labial frenum in the maxilla is the intervening factor responsible for midline diastema closure. Studies on children with primary, mixed, or permanent dentitions, however, have not shown a connection between the various forms of frenum and the formation of midline diastema.¹⁴

• The labial frenum in maxilla or its accompanying interdental soft tissue are often cited as the causative factors for recurrence of approximated teeth in prior diastema areas. In addition to functional and aesthetic compromise, as an anatomical entity, frenum is crucial in the expression of different symptoms such as diastema or recession of gingiva.

Classification of Frenum

The analysis of literature indicates that the maxillary labial frenum exhibits various morphologies, each with distinct clinical significance (Tables 2 and 3).

Modified Classification

Frenum per se is not responsible for the presentation of signs, such as spacing between teeth and gingival recession. Its adjacent mucosal relations contribute to the frenum induced consequences. Hence the use of term ‘high frenum’ should be avoided which usually refers to those frenum close to gingival margin producing the consequences such as diastema and gingival recession. The use of terms such as ‘abnormal’ or ‘normal’ is recommended based on its location, size and functional ability, that is presence of positive tension test or pull syndrome or not. On visual examination, frenum can be designated as thin or thick without any dimensional measurements (Table 4).

Association of Frenal Attachments with Various Syndromes (Table 5a)

• Ehlers-Danlos syndrome

• Ellis-van Creveld syndrome

• Holoprosencephaly

• Infantile hypertrophic pyloric stenosis

• Oro-facial-digital syndrome

Abnormal Frenum in Mixed Dentition from Ortho­dontic and Pedodontic Perspective: Diastema and Timing of Frenum Excision

Most tests state that an abnormally large and margin­ally positioned labial frenum would result in persistent maxillary midline diastema. Moreover, there appears to be consensus in the pedodontic and orthodontic litera­ture that, given that most diastemas close on their own when all the anterior teeth erupt, there is little reason to remove any part of an "abnormal" labial frenum, before the eruption of maxillary lateral incisors and canines.

• Taylor described the presence of diastema in maxilla as normal with a 98 percent prevalence among 6-7 year old children, while only 7 percent of 12 to 18 years old retained these diastemas.²⁵

• Dewel has shown that in diastema conditions, early ("preventive") frenectomies without previous orthodontic closure may cause scar development, which may in turn tend to prevent normal mesial migration of the incisors.

• Archer illustrated the traditional frenectomy procedure which involved excision of the whole frenum, the palatine papilla and the interdental papilla, exposing the bone and/or periosteum.¹⁰

• While there is little evidence that a frenectomy performed before orthodontic closure speeds up tooth movement, orthodontists have long opposed early frenectomy, arguing that even without this, the tissue configuration after the diastema closure would be less predictable and the rate at which a frenum can close is still relatively quick. This is in contrast to the opinions of many oral surgeons.

• However, during frenectomy, it is recommended to remove the periosteum beneath the excised portion of the frenum to eliminate the elastic fibers of the frenum that have been known to pierce the periosteum in order to reduce the recurrence of orthodontically closed diastemas. Such elastic fibers have not been demonstrated to adversely affect the increase in attached gingiva following a frenotomy, nor have they been shown to adversely affect the alleviation of relapse in diastema cases.

• Nevertheless, since there is no evidence of elastic tissue involvement with attached gingiva anywhere in the normal human periodontium, it appears cru­cial to remove the elastic fibers impregnating the periosteum beneath the frenum, if the goal of the surgical procedure is to remove the unwanted frenal tissue and establish a normal interdental soft-tissue anatomy.

• There was a considerable, though not total, association between a midline diastema and a clinically "abnormal" appearing maxillary midline frenum prior to treatment. A certain proportion of individuals had either no diastema at all or no diastema at all but an “abnormal” frenum.

Conclusion

The frenum is an unremarkable structure when normal; however, abnormalities draw significant attention and often necessitate excision. It holds importance in various dental specialties, including periodontics, orthodontics, conservative dentistry and prosthodontics.

Conflicts of Interest

Nil