Introduction of the Lip Classification of Tubercles: A Novel Approach to Minimally Invasive Aesthetic Lip Treatments

Abstract

Background

Lip enhancement procedures involving dermal fillers are one of the most sought after nonsurgical aesthetic treatments. However, current trends are associated with unnatural results and involve increased risks of complications and compromise to normal function. It appears that lips may be classified according to the presentation of their tubercles and this may be used to guide minimally invasive techniques which aim to preserve individual lip shapes and normal function.

Objectives

To test the reliability of a classification system based on lip tubercle morphology, named the Lip Classification of Tubercles (LCT).

Methods

To test the reliability of the LCT, a total of 214 high-definition photographs of patients’ lips with no previous histories of lip treatments were classified independently by 4 experienced aesthetic practitioners on 2 separate occasions 3 months apart; the second followed a more detailed explanation of the classification.

Results

When inter-rater reliability was calculated for the first attempt, the results were 36% and 43% for upper and lower lips, respectively. The second attempt following an education process resulted in 79% for both lips. When 1 practitioner was considered the standard, the average score for the remaining 3 showed some individual variation but improved significantly from 58% to 85%.

Conclusions

The LCT is a reliable way to classify lip types based on the morphology of tubercles.

Level of Evidence: 3

Lips are a central feature of facial aesthetics as they play an essential role in facial expression, phonation, sensation, mastication, physical attraction, and intimacy.¹ Since early recorded history full lips in females have been associated with youth, beauty, and voluptuousness.² It is no surprise then that lip enhancement is one of the most frequently requested nonsurgical procedures.³ A number of studies have evaluated lip positions and shape based on cephalometric analysis and facial dimensions.^4-7 However, the morphological features of lips vary greatly between individuals according to age, sex, and ethnicity.^8-11 A significant aspect of lip morphology is the lip tubercles—embryological remnants of development which appear as dermal projections in both the upper and lower lips.

To help identify different lip types based on shape (tubercle morphology), a classification system was developed, the embryological Lip Classification of Tubercles (LCT). The LCT describes a pattern of 4 tubercle presentations based on their number, size, and position in the mid-third of the upper and lower lips, denoted the Letters A-D and E-H, respectively, for a total of 16 different morphological types (Figure 1). While the LCT has been used to classify and guide lip enhancements by one of the authors, this has never been formally tested for reliability.

Figure 1.

The Embryological Classification of Tubercles (LCT). Panels A-D show the upper lip pattern and E-H show the lower lip pattern. With respect to the upper lip, (A) Type 1, shown in a 26-year-old female, represents a single large middle tubercle occupying the full mid-third; (B) Type 2, shown in a 35-year-old female, represents a small middle tubercle occupying less than the mid-third; (C) Type 3, shown in a 27-year-old female, has an inverted tubercle; and (D) Type 4, shown in a 53-year-old female, is flat. With respect to the lower lip, (E) Type A, shown in a 33-year-old female, is represented by a central indentation. (F) Type B, shown in a 31-year-old female, has no central indentation and is full but level. (G) Type C, shown in a 30-year-old female, has no central indentation and curves upward with more fullness and Type B. (H) Type D, shown in a 49-year-old female, is flat.

METHODS

A total of n = 214 subjects were randomly selected from a patient population of an aesthetic clinic in North London, England. Written consent was provided, by which the patients agreed to the use and analysis of their data. This study was performed in adherence to the Declaration of Helsinki (1996), and in accordance with regional laws and good clinical practice for studies in human subjects.

Participants were excluded if they had any previous aesthetic treatment (surgical and/or nonsurgical) which could affect the shape of their lips; these would include procedures such as a face lift or previous lower face (including lips) minimally invasive procedures (including Botulinum Toxin Type A injections in the last 6 months or if they ever had dermal fillers). Patient photographs were taken close up—30 cm in front of the patient with focus on the lips using a wide lens 28 mm (aperture f1.80 of an iPhone 8 HD camera). The patient's photographs (frontal view of the face at rest) were used to only identify their lower third from pronasale to menton. All 214 photos were distributed to each of the panel of experts for classification of the presenting lips using the LCT chart (Figure 1). A 10-min description of the classification was first introduced to each panel member. The didactic explanation included lip embryology—how tubercles form in both the upper and lower lips and the different tubercle patterns in the LCT chart including how to identify and classify them by focusing on the mid-third of the (upper and lower) lips. Each panel member was then asked to classify each of the lips in the photographs using the LCT chart. The same task was repeated after 3 months, but this involved a longer 20-min explanation which included testing using 20 specific examples in a more socratic approach.

RESULTS

The n = 214 subjects consisted of 173 females and 41 males (female/male ratio = 4.2:1) with an average age of 39 ± 10.4 years (range: 18-68 years). The majority of patients were Caucasian (n = 151), followed by Indian (n = 26), Black (n = 25), and Asian Chinese (n = 12).

The average follow-up time between the 2 expert measurement sets was 94 days (range: 91-100 days). The data were analyzed separately for the 2-task completion attempts, and reliability scores were calculated for each attempt. This analysis would show whether the initial 10-min presentation was sufficient to ensure accuracy, or whether the more extended 20-min presentation led to a significant and desirable improvement in performance on the part of the experts. In each case, separate measures were calculated for upper and lower lips to check consistency.

Two measures were taken of reliability in the judgments of lip type. It was assumed that since one of the panel of experts was the person responsible for the classification design, his decision could be taken in all cases as the “correct” assignment. The measures therefore calibrated the degree to which the other 3 experts agreed with his decisions.

The first measure calculated the percentage of subjects for which the 3 experts all obtained the same, correct assignment. A high score on this measure would suggest that the method had good reliability, with the effect of individual differences between expert judgments being negligible. Since there is a possibility for judgments to be correct purely by chance, a correction was applied (Cohen's kappa) to allow for this. It should be noted that the same calculation would be carried out without the assumption that 1 expert was “correct,” giving the identical result, but in this case, the result can be conventionally interpreted as a measure of inter-rater reliability.

Analysis of First Data Set

Analysis of the data from the first task completion trial gave figures of 36.4% for the upper lip and 43.0% for the lower lip evaluations. Since these figures were well below acceptable levels, a second set of reliability measures was calculated comparing each of the 3 experts with the “correct” judgment. This time, again applying Cohen's kappa, the results were 52%, 47.7%, and 59.5% for the upper lip, and 62%, 49.5%, and 78.2% for the lower lip, across the 3 experts. These showed some apparent difference between lips, but the profile of scores across the 3 experts was similar.

Averaging across upper and lower lips gave scores of 57%, 48.6%, and 68.8%. Since the standard deviation for the difference between 2 percentage scores in this case is around 3.3% (normal approximation to the binomial distribution for 428 trials), the 3 experts differed substantially in the accuracy of their judgments. The average corrected score over the 3 experts was 58.2%.

Analysis of Second Data Set

The second analysis was performed for the task that was completed after the second training session. The data showed that all 3 experts agreed with one another and with the correct classification on 78.6% of occasions, the scores for upper and lower lips being identical. When the performance of individual experts was analyzed, averaged across upper and lower lips, the scores were 79.4%, 84.7%, and 90.3% respectively, with an average of 84.8%. The raw scores in the absence of a guessing correction averaged 88.9%. Although the scoring profiles of the experts showed some variation across the 3, the differences did not achieve statistical significance. The improvement from 58.2% to 84.8% between the first and second trials (26.6%) was highly statistically significant.

DISCUSSION

The LCT was developed by the first author of this study 5 years ago after recognizing that lip morphology may be characterized by the presentation of tubercles. The minimally invasive technique he invented termed the Nonsurgical Lip Tubercle Technique (NLTT) focuses on the enhancement of tubercles to preserve individual lip shapes along with normal lip function (Figure 2). In addition to playing a central role in lip morphology, it is likely that tubercles facilitate complex movements of the mouth by gathering extra surface area in much the same way as the philtral columns.^12-15

Figure 2.

The lips of a 28-year-old female patient shown (A, C) before and (B, D) after lips using the Nonsurgical Lip Tubercle Technique (NLTT). A total of 0.3 mL hyaluronic acid (HA) filler was used for this patient's lips (Type 1A).

The LCT was developed earlier on to classify the morphology of lip types based on an understanding of embryology. Lip development begins at gestational week 4 with the appearance of the frontonasal prominence and the maxillary and mandibular prominences. A series of steps involving extension and fusion of the prominences leads to formation of the external face, including the lips. While the basic steps are common to all humans, the degree and extent of fusion of the prominences determine the appearance of the tubercles and their different presentations represented in the LCT. For the upper lip, a median tubercle is absent in a cleft lip when the medial nasal prominence and maxillary prominence fail to fuse. As part of normal development varying degrees of fusion may appear as partial (an inverted median tubercle in the mid-third), more complete (a small upper tubercle in the mid-third), or complete (a large central tubercle occupying the mid-third). In the lower lip, fusion of the mandibular processes may be partial with a central indentation, more fused with no central indentation, or completely fused with a mid-third central prominence.

With age and thinning of all the anatomical layers of the lips, the tubercles themselves may appear flattened in the upper lip and/or the lower lip. When the lips are flattened, the goal of lip enhancement may be for a greater dry vermillion exposure which may be achieved most safely and effectively with the use of a cannula; the aim of treatment would not be to create tubercles where there are none, but to work with an understanding and respect of the presenting anatomy. When the patient does present with tubercles (the majority of cases), the LCT helps to classify the lip type and can act as a guide to enhance the presenting shape in keeping with the individual's lip type while maintaining normal lip function.

To our knowledge, the LCT is the first lip classification of its kind based solely on the morphological presentation of tubercles. It provides an easy to learn classification system which is both reliable and practical for aesthetic practitioners who want to adopt procedures to enhance lips by focusing on the lip tubercles in order to maintain individual lip types and normal lip function. The results based on a large sample of 214 provided good statistical power; the testing involving 4 examiners on 2 separate occasions spaced 3 months apart showed a highly significant improvement in reliability on the second test following a 20-min training session. Therefore, it is imperative that the practitioner undergoes the appropriate training before adopting the LCT. While our test sample was large and included a wide range of ages, different ethnicities and genders, most of the participants were young Caucasian females. Greater representations for age, ethnicity, and gender would have been desirable to improve reliability. A larger number of examiners with more training and testing could have further optimized the inter- and intrarater scores. Other limitations are that the scale itself does not take into account the different presentations of philtrums (such as length) which are an integral part of the upper lip, or indeed the actual vermillion border which has variable presentations. While the authors agree upon the natural aesthetic outcome of the NLTT, future studies utilizing the LCT classification in treating patients with the NLTT will be evaluated.

CONCLUSIONS

Not withstanding these limitations, the LCT provides a simple, reliable, and practical way for aesthetic practitioners to assess vermillion lip shapes and can act as a guide to enhance them in keeping with normal anatomy and physiology.

Disclosures

The authors declared no potential conflicts of interest with respect to the research, authorship, and publication of this article.

Funding

The authors received no financial support for the research, authorship, and publication of this article, including payment of the article processing charge.