The effect of lip augmentation on incisal display and lip projection

INTRODUCTION

Facial balance is generally determined by morphological relationships of the nose, lips, and chin.¹ Nowadays, people search for various ways to improve their facial beauty in the short and long term.¹ There are cosmetic, surgical, and non-surgical procedures that enhance the facial harmony.² Rhinoplasty, lip lifting, and cheek augmentation are some procedures that can further improve the patient’s overall aesthetics and facial balance.² The lips constitute an essential component of the attractive facial image.³ As the eyes and the nose are hallmarks of the middle third of the face, the lips are considered to be the focal point of the lower facial third.⁴ Lip region is an extremely important area when it comes to facial aesthetic enhancement.⁵ Nowadays, injectable fillers for facial-volume augmentation have been extensively marketed.⁶ Cosmetic lip augmentation aims to improve its dimension in relation to the nose, teeth, chin, and surrounding facial structures by increasing lip’s fullness through enlargement and reshaping of its normal structure.⁷ Volume of 0.4–0.8 cc should be sufficient for each lip. Injection of larger volume may result in pain and dense mass, so staging lip augmentation is important.⁸ The small particles hyaluronic acid (HA) 20 mg/mL with lidocaine 0.3% (SPHAL, Restylane Silk; Galderma Laboratories, Fort Worth, Texas) is the first Food and Drug Administration (FDA) approved (2014) filler formulated with lidocaine that is indicated for sub-mucosal implantation for lip augmentation and dermal implantation for correction of perioral wrinkles in the patients over 21-years-old.⁹ Lately, using dermal fillers in minimally invasive facial esthetic procedures has become increasingly popular. Since the indications and the number of procedures performed increase, the number of complications is also likely to increase. Some of the possible complications, causes, and management of dermal fillers are listed in Table 1.¹⁰

Smiling is one of the most important expressions contributing to facial attractiveness. Patients are becoming highly conscious about their smile esthetics and dental appearance.¹¹ The most important esthetic goal in orthodontics is to achieve a balanced smile. The shape, position, and color of the teeth and gingival tissues are the determinants of the harmony of the smile.¹² The treatment planning for each patient aims to correct one or more hard or soft tissue components responsible for the incisal display.¹³ Gingival tissues showing is also considered by many to be unpleasant and usually requires intervention.¹² The projection, support, and bulk of the upper lip are important to the overall macro-esthetics of the lower facial third, and it influences the smile esthetics. As a result, public demand for lip augmentation procedures has evolved. Multiple operations have been developed; for instance, increasing lip fullness, changing the length of the upper lip, and defining the vermilion border and lip philtrum.⁴

Despite widespread use of dermal fillers, the impact of lip augmentation on incisor display and lip projection has not been rigorously quantified. This study aimed to measure changes in maxillary incisor display (frontal view) and lip projection (profile view) after augmentation with varying filler volumes.

MATERIAL AND METHODS

The study was ethically approved by the Institutional Review Board at King Saud Medical City, Ministry of Health (No. H-01-R-053, September 4, 2019). This clinical experimental trial includes thirty healthy Saudi female adults, whose age ranges between 21 and 30 years. The exclusion criteria include previous facial surgery, lip augmentation, or clinical evidence of orthognathic deformity, craniofacial defects, or scar tissue on the face. Participants were informed about the procedure, its possible benefits, risks, side effects, and the expected duration of the results, and written informed consent was obtained. Convenience sampling was used for this study.

Extraoral photographs were taken for each subject to obtain 2D professional photographic images using a Nikon D5300 camera. Standard exposure parameters were used (1/200, F4.8, ISO-A320) with a fixed distance of 1.5 m using a tripod stand and in front of a light background. In the frontal view, the participants were photographed with the maximum smile, and the profile photograph was taken in natural head position. A millimeter ruler was fixed in all photographs for calibration in the image processing software [Figure 1].

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Figure 1: Pre-operative photographs: (a) Maximum smile, (b) Profile view.

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The participants received a professional clinical assessment by an experienced consultant dermatologist. The need for lip augmentation was determined, and the standard procedure of injecting a Saudi FDA-approved filler Juvéderm VOLIFT (Allergan, Dublin, Ireland) was performed. The injection included the body area of the lips in the superficial submucosal plane, immediately superficial to the orbicularis oris muscle, using linear threading retrograde injection technique with a 30-gauge needle.

All subjects were re-evaluated in 2 weeks for a follow-up appointment and post-operative photographs were taken. Images were analyzed by a single investigator using specialized image processing software (Fiji, Laboratory for Optical and Computational Instrumentation, University of Wisconsin) to measure the maxillary incisor show and the horizontal lip projection. The maximum smile view was assessed in the pre- and post-injection photographs. The visible vertical length of the gingiva and maxillary right central incisor under the upper lip to the incisal edge was measured and recorded in millimeters [Figure 2]. Horizontal lip projection was measured in millimeters in relation to two reference lines: (1) esthetic ricketts plane (E-Plane) and (2) subnasale vertical line (SnV) [Figure 3].^14,15 To minimize measurement bias, all measurements (250 variables) were performed twice by the same calibrated investigator at a 1-week interval. Intra-examiner reliability was assessed using the intraclass correlation coefficient (ICC), demonstrating excellent agreement (ICC = 0.999). The average of the two measurements was used for analysis.

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Figure 2: Close-up sketch view of the smile The blue line represents the measured vertical length of the visible gingiva and maxillary right central incisor under the upper lip.

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Figure 3: (a) Lip projection in relation to esthetic ricketts plane, (b) Lip projection in relation to the subnasale vertical line.

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All statistical analyses were performed using IBM statistical package for the social sciences statistics for Windows, version 24 (2016, Armonk, NY: IBM Corp). Descriptive statistics were presented as means and standard deviations. Pre- and post-injection comparisons were analyzed using paired-samples t-test for normally distributed variables. Pearson correlation coefficient was used to assess associations between filler volume and outcome changes. Multiple linear regression analysis was performed to evaluate predictors of lip changes after adjusting for filler volume. Statistical significance was set at p < 0.05 (two-tailed), corresponding to a 95% confidence interval.

RESULTS

Out of 30 participants, 25 fulfilled the inclusion criteria and were recruited into the study. Among the excluded, three had a zero millimeter upper incisors exposure upon smiling, one was not aware of an old scar in the lower lip and the last one presented with residual old lip fillers.

The descriptive statistics of the study variables are shown in Table 2. On average, the upper lip extends vertically and covers the upper incisors about 1.11 mm and protrudes more horizontally 1.26–1.35 mm (in relation to E-Plane and SnV, respectively) after the injection of the filler material, while the lower lip protrudes horizontally 1.01–1.44 mm. The amount of change in the lip projection was assessed by comparing the mean values of difference between pre and post-observations of the five outcome variables using paired-samples t-test. The comparison shows highly statistically significant difference in the mean values of all these variables [Table 2].

Correlation analysis reveals that there is a statistically significant positive correlation between the volume of the filler injected in the upper lip and volume of the filler injected in the lower lip (r = 0.628, p = 0.001). Furthermore, the change in the projection of the upper lip in relation to E-Plane is statistically correlated to the change of the lower lip to E-Plane (r = 0.501, p = 0.011). While the lower lip projection to E-Plane was moderately correlated to the amount of the filler material injected (r = 0.433, p = 0.03), the same correlation was not significant for the upper lip (r = 0.386, p = 0.056). Similarly, no significant correlations were observed between the volume of the filler and the vertical upper lip change or the change in the projection of the upper and lower lips to SnV.

Two significant regression models were analyzed. The first showed a statistically significant linear relation between the vertical upper lip change and pre-incisal display after adjusting for the volume of upper lip filler. The model with these two variables is statistically significant (F = 3.698, p = 0.014), which means that 25.2% of the change in values of vertical upper lip change was due to these two variables. Out of these two variables, pre-incisal display is the only statistically significant predictor. The regression coefficient of this variable is B = 0.189, p = 0.023, and this indicates that for every 1 unit change in pre-incisal display, the vertical upper lip change values will increase by 0.189 units which is statistically significant.

The second regression model shows that there is a statistically significant linear relation between the upper lip to SnV change and pre-upper lip to SnV distance after adjusting for the volume of upper filler. The model with these two variables is highly statistically significant (F = 9.293, p = 0.001), which means that 45.8% of change in values of the upper lip to SnV change was due to these two variables. Out of these two variables, pre-upper lip to SnV is the only statistically significant predictor. The regression coefficient of this variable is B = −0.298, p = 0.001, and this indicates that for every 1 unit change in pre-upper lip to SnV distance, the upper lip to SnV change values will decrease by 0.289 units which is statistically significant.

DISCUSSION

Facial esthetics and outward appearance are significantly affected by the shape and fullness of the lips; therefore, a comprehensive understanding of the lower facial third, injection site, material, and technique is required for a successful lip augmentation.⁹ A very controlled and predictable result can be obtained by lip augmentation through injecting the filler material in any or all of the anatomic parts of the lip. Therefore, the relationship between lip height and incisor shown as well as patient’s occlusion status, possible maxillary hypoplasia, or mandibular retrusion should be carefully analyzed.⁵ The corrective needs of a patient can vary from subtle refinements in lip fullness, labial projection, or degree of eversion to complete lip recontouring.^3,9 The recruited participants represented ideal candidates for the injection of filler material to enhance lip shape. All the participants were pleased with the results during the follow-up. No serious side effects, such as infection, were reported. Mild bruising and edema were reported and lasted 2 days after the injection. Few patients reported mild pain during the injection procedure.

This study has shown that a significant increase in the horizontal upper and lower lip projection can be seen after the lip augmentation. On average, the lips protruded 1–1.5 mm in relation to E-Plane and SnV line. The average pre-injection horizontal lip position in relation to E-Plane was −3.63 mm for the upper lip and −1.37 mm for the lower lip, with a wide range of −7.34 to 3.16 mm. Previously conducted studies that assessed the soft tissue norms in the Saudi population have reported that females present with an average position of the upper lip of −3.9 ± 1.9 mm and the lower lip −1.5 ± 2.0 mm in relation to the E-Plane.¹⁶ Other studies reported similar values of −3.43 to −4.1 mm and −1.7 to 0.09 mm for the upper and lower lips, respectively.^17,18 A recently published study reported that the average value of the upper lip horizontal position is −3.18 ± 2.27 mm while for the lower lip is −1.45 ± 1.82 mm.¹⁹ These values are generally slightly more protrusive than the Caucasian norms and less than those of the Asians.^17,18 Studies that assessed the esthetic preferences of a panel of American laypeople judges concluded that females prefer fuller lip position (upper −1.65 mm, lower −0.65 mm) than the published norms.^20,21 Furthermore, German dental students thought that the attractive female faces have a closer lip position to E-Plane than non-attractive faces.²² In a local study, Saudi female adults identified a tolerance range of −7.02 to −1.62 mm for an acceptable position of the upper lip to E-Plane.²³ In the current study, the average post-injection upper lip position was −2.37 mm and −0.35 mm for the lower lip. These values are close to the outer limit of female individuals’ preference for the horizontal lip position which leans toward fuller lips, and they are above the normal values of Saudi females’ lip projection. One study recruited twenty-six white models to define the most pleasing horizontal lip position in relation to SnV which were 3.7 ± 1.2 mm for the upper and 1.9 ± 1.4 mm for the lower lip.¹⁵ The average post-injection upper and lower lip position in relation to SnV in this study was above than these published means (4.53 mm, 2.04 mm) which confirms that the outcomes of lip augmentation enhance the lip projection above the norms.

Upon smiling, the upper lip position is often called lip line which is defined as the inferior border of the upper lip and thereby determines the display of teeth or gingiva at this hard and soft tissue interface.²⁴ On average, the full length of the maxillary anterior teeth and only the interdental papillae show upon smiling.^24-28 A high lip line showed the teeth in full display as well as gingival tissues above the gingival margins by more than 2 mm. A low lip line showed no gingival tissues when smiling.²⁹ It has been reported that 1 mm or greater gingival exposure is a feature predominantly observed in female subjects.³⁰ The participants in the current study presented with a wide range of maxillary incisors exposure (2.69–12.87 mm) with an average display of 7.99 mm. The vast majority of the sample had less display of the gingiva and the maxillary incisors after the lip augmentation with an average value of 1.1 mm vertical enlargement of the upper lip. This result indicates that lip fillers can partially correct excessive gingival display upon smiling that may result from short upper lip or vertical maxillary excess; however, it may also reduce the maxillary teeth display to a very minimal range. Previously conducted studies have shown that incisor coverage increases with age, improving the esthetics of gingival smiles and worsening the esthetics of mean and low smiles, leading to an older appearance.³¹ This aspect should be put into consideration during the pre-operative assessment of lip augmentation procedures, and it should be carefully planned to avoid minimizing the maxillary incisors’ exposure to an unesthetic level after the filler injection.

The professional assessment of the esthetic needs of the participants has dictated the amount of the filler material required for each subject. The amount ranged from as little as 0.05 mL to 1.6 mL in each lip with an average amount of 0.36–0.48 mL. The variations in the injected amount of the filler material contributed to the observed variations in the outcomes of the augmentation procedure [Figure 4]. However, this was only true for the lower lip horizontal which was moderately correlated to the amount of the filler material. This simple correlation was not observed for the upper lip and more complex regression models that consider the pre-injection lip position values and the volume of the lip filler were necessary to partially predict the amount of change after the procedure. These results show that the extent of the enhancement of the upper lip vertically and horizontally is multifactorial, and several variables contribute to the outcome.

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Figure 4: Two examples of lip augmentation outcomes: Minimal changes in one case (a and b: pre-treatment, c and d: post-treatment). Significant changes in another case (e and f: pre-treatment, g and h: post-treatment).

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This study is the first to relate the lip augmentation procedure to the exposure of the maxillary incisors and the horizontal lip projection. It shed light on the average observed changes and it will serve as a baseline for more in-depth analysis of the variables that control the enlargement of the lips for more predictable outcomes. We used standard 2D smiling and profile photographs were taken for the participants to analyze the outcomes. Repose photographs were not considered because of the difficulty in identifying suitable and reliable reference points to measure the vertical changes of the upper lip. Future studies should employ three-dimensional digital stereophotogrammetric imaging systems and 3D superimposition software to analyze the changes in three dimensions.

CONCLUSION

Limitations of this study include a single-arm pre–post design without a control group, a small female-only convenience sample from a single center, and a short 2-week follow-up period. In addition, the use of two-dimensional photographic measurements may introduce calibration error and limit spatial accuracy. All measurements were performed by a single calibrated examiner, which may introduce measurement bias despite demonstrated high intra-examiner reliability. These factors limit the generalizability and measurement precision of the findings.

Despite these limitations, HA lip augmentation reduced maxillary incisor exposure on smiling and increased upper- and lower-lip horizontal projection relative to Esthetic Ricketts Plane (E-Plane) and SnV. The magnitude of change depended primarily on baseline soft-tissue position; lower-lip projection relative to the esthetic plane increased with greater filler volume, whereas upper-lip changes showed no association with filler volume.