A smile plays an important role in determining a person's initial impression [1], and its assessment has become integral to clinical evaluation owing to how appealing a smile could be among people. Expressions conveyed by the face and smile are the main components of nonverbal communication, and the latter is the cornerstone of facial expressions — it may signify pleasure, sympathy, amusement, approval, or sometimes contempt [1—3].

Tjan et al. [4] identified the following features in an esthetic smile: anterior upper teeth fully exposed, gums invisible, the incisional curvature of the anterior upper teeth parallel to the inner curvature of the lower lip, the six front anterior teeth and premolars exposed, and the midline corresponding to the medial cleft. A smile with an esthetic appearance should be symmetrical and should reveal less than 2 mm of gums when smiling [1, 3].

A gingival smile, gummy smile or high smile line, is defined as the amount of excess gums on the upper jaw exposed — the upper lip shifts 6—8 mm upward at a full smile exposing more than 2 mm of the gingiva and the entirety of the clinical crown. This may have some serious psychological repercussions on the patient, which may sometimes lead them to conceal their smile to avoid "embarrassment" [5, 6].

The various causes of the gummy smile include vertical maxillary excess, anterior dentoalveolar extrusion, delayed passive dental eruption and short or hyperactive upper lip elevator muscles. It could affect 10.5% of the population between the ages of 20 and 30, with a noticeable increase in females at a ratio of 2:1 [7, 8].

One of the most common methods of treating a gingival smile resulting from an overactive lip is lip reposition as a surgical procedure and the injection of type A (Botox) toxin as an injectable inhibitor of muscle action [6, 9].

Research objectives: The aim of this study is to evaluate the effectiveness of both Botox toxin injection as a muscle-shaping aesthetic injection and lip repositioning as an aesthetic surgery in correcting gingival smile caused by hyperactive upper lip, in terms of the amount of gingival coverage, resulting in smile width and better patient satisfaction. It also seeks to determine a solid alternative with a minimum amount of damage done to tissues by virtue of the study’s statistically important results as well as the level of patient aesthetic and functional satisfaction.

Materials and methods

This study is a prospective cohort study. A total of 50 patients with a gummy smile resulting from hyperactivity of the upper lip were examined at the Department of Maxillofacial Surgery at Damascus University, and they were asked to choose between botulinum toxin (Botox) injection and upper lip correction surgery, of whom 24 female patients were included in the study. patients (18—41 years old).

The participants underwent preliminary consultation and cephalometric analysis to determine their eligibility to participate in the study. Precise diagnosis and identification of the cause of gummy smile were essential in choosing the optimal treatment method, and those patients exposing 4 mm or more of gingiva above the central incisors were chosen to participate, as a result, 24 patients were included in the study, 12 of the 24 participants were injected with the toxin (Botox), and the other 12 underwent lip repositioning. Clinical observation and photographic documentation were performed to conduct anthropometric measurements. Photographs were taken pre-treatment and two weeks, two months, and six months after it in order to compare the studied criteria and any changes they may have undergone.

Measurements were taken from the gumline on the midline of both the central incisor and canines to the lower part of the upper lip. The researcher used a standard measuring tape to measure gum exposure at maximum smile. Measurements were taken above each teeth of interest (right canine, right central incisor, left central incisor, left canine) individually during 4 different spontaneous smiles to ensure maximum smiling for each measured area and to get the patient's maximum smile while taking measurements. To induce smiling, funny jokes were told or funny scenes shown.

The researcher personally took photos of all patients included in the research study, and high-resolution Canon EOS 700D (18 megapixels) was used.

The same equipment was used in all sessions throughout the study (before injection and three visits after injection). The sagittal and frontal planes were perpendicular to the horizontal plane. Upper and lower jaws were positioned normally, chin muscles and lips were relaxed, and eyes were open and looking straight ahead without tension or contraction. The distance between the camera and the patient's head was 1.5 meters and illumination and zoom ratios were identical.

Surgical protocol

Disinfection was performed inside and outside the mouth using 2% chlorhexidine solution and 0.12% chlorhexidine lotion for one minute. First, using local anesthesia, the subcutaneous branches of the trigeminal nerve were blocked on both sides in using 2% lidocaine with 1:200,000 epinephrin. To reduce bleeding in the mouth vestibule, local infiltration anesthesia was additionally performed.

Small interrupted marks were placed every 5 mm along the proposed slit line. The lower edge was determined by the gingival mucosal junction of the medial side of the first two upper molars bilaterally. A partial-thickness flap was raised from the mesial line angle of right maxillary first molar to that of left maxillary first molar at the mucogingival junction. A second incision 11—14 mm above the first incision was made in the labial mucosa. The two incisions were joined on both sides and a strip of partial-thickness flap was removed, exposing the underlying connective tissue. The two incisions were then approximated using continuous interlocking sutures.

After the surgery, NSAIDs (ibuprofen 600 mg 3 times daily for two days) and oral antibiotics (amoxicillin 500 mg 3 times daily for seven days) were prescribed. Participants were advised applying cold compresses and sticking to a liquid diet only during the first week after surgery to avoid any mechanical trauma. They were also recommended to use toothbrushes gently and limiting lip movements when smiling or talking for a week after the surgery.

Injection stages of type A toxin (Botox)

Injection sites were determined in three places on each side through muscular activity (smiling) and probing extent of shrinkage to ensure accurate muscle position before injection, given that there might occur minor site anatomical variations with no local anesthesia performed.

Surface facial markings used for locating injection sites according to Suber et al. [10], they are as follows: 2 mm lateral incisor pterygoid at the level of the nasal passage, followed by a first 2 mm lateral injection on the same horizontal plane and a last 2 mm below and between the first and second positions. The resulting injection positions take the shape of an inverted triangle. Moreover, the bone marker was the forefront of the upper jaw attached to the muscles covering it: levator labii superioris, the deep nasal wing, and the small adrenal muscle [10].

The amount of botulinum toxin used in each target muscle ranged from 4 to 6 units. A 100-unit bottle of dried botulinum toxin A was dissolved by adding 2 ml of saline serum sodium chloride under sterile conditions so that the extension ratio was 1:2 as each gradient on the syringe indicated 1 unit of diluted Botox prepared for injection. After identifying the three injection sites and without performing local anesthesia, the area was wiped with cotton moistened with alcohol for cleansing, and then 4 units were vertically injected into each of the three muscles on each side. The dose given to each patient in this study was based on previously published literature [11, 12], that provided for a range of 4 to 6 units per side, in addition to what was required by patient measurements.

Research Variables

First, Amount of gingival coverage and width of the resulting smile. Two groups of measurements were used to proceed with determining gingival exposure as the distance between the lower edge of the upper lip and the upper edge of the central incisor. The distance was measured both at the central incisor and the canine from left and right. The statistical study was performed by taking the average measurement for both left and right central incisors, which we would call “average gingival exposure above the central incisors.” Average measurement was calculated from both the right canine and the left canine, which similarly would be called “average gingival exposure above the canines.” The mean of the four calculations was calculated (width of the resulting smile) for four periods: before treatment, after two weeks, after two months, and after six months.

Second, Patient smile satisfaction: Patient satisfaction with the result was assessed on a scale of (1 to 5) where five indicated most satisfied and one the least, where participants were asked about the level of their satisfaction two weeks, two months and 6 months after the procedure.

Statistical analysis

The Mann- Whitney Test was used for comparison between Experimental and Control group. In order to conduct inter-group comparisons over different periods, a Wilcoxon test was used because group members were fewer than 30. The statistical program SPSS version 20.0 (SPSS Inc., Chicago, IL, USA) was used for data analysis. The results were considered significant if p≤0.05.

Results

The study included 24 patients in two groups. The Control group (A) (n=12, the group treated with surgical method), the Experimental group (B) (n=12, the group injected with type A botulinum toxin (Botox)).

Table 1 shows Mathematical averages (mm) of Experimental and Control groups according to different measurements.

Table 1. Results of different measurements (mm) in Experimental and Control groups

Table 2 shows Pairwise comparison of measurements (mm) between the study groups using Mann- Whitney Test.

Table 2. Pairwise comparison of measurements between the study groups using Mann—Whitney Test

Note. * — significant difference at p=0.05.

Table 3 shows the mean values for the patients of the Control group (A) at different periods in which measurements were taken.

Table 3. The mean values for the patients of the Control group (A) at different periods in which measurements were taken

Table 4 shows inter-group (A) comparisons over different periods.

Table 4. Intra-group (A) comparisons over different periods

Note. * — significant difference at p=0.05.

Table 5 shows the mean values for the patients of the Experimental group (B) at different periods in which measurements were taken.

Table 5. The mean values for the patients of the Experimental group (B) at different periods in which measurements were taken

Table 6 shows inter-group (B) comparisons over different periods.

Table 6. Intra-group (B) comparisons over different periods

Note. * — significant difference at p=0.05.

Table 7 shows the results of patient satisfaction.

Table 7. The results of patient satisfaction

Fig. 1. A case of experimental group.

a — before the injection; b — after two weeks.

Fig. 2. A case of control group.

Discussion of gingival exposure and smile width variables

As for pretreatment, there was no difference between the two averages of the Control and Experimental groups, and, therefore, any decrease in the distance would be precisely due to the method of treatment, and this was found with both measurements (above incisor and canine and smile width).

However, after two weeks of treatment, the two averages of above incisor and canine and smile width were somewhat similar because type A toxin (Botox) injection is maximally optimal, whereas surgery would have produced the expected required outcome.

Two months post-treatment, differences were observed between the averages of above incisor and canine and smile width. Table 1 demonstrates that the shortest distance in all cases was in the Experimental group treated with type A toxin (Botox) injection. This result indicates that, for the short-term (2 months), injection with type A toxin (Botox) produced better outcomes than treatment with surgery, which gives priority to the former since some surgical interventions may not produce similar results over such a short period.

The two averages differ on all measurements in the comparison of 6 months post-treatment. Table 1 shows that the distance was shorter in the surgery group, but the difference was almost negligible. This is while noting that the patients were fully aware that relapse would occur 6 months after Botox injection and that re-injection would be necessary. This result does not give priority to treatment with surgery, as the difference in its favor after 6 months was not large enough to make it preferable. Moreover, comparison of the results of treatment with surgery 2 weeks and 2 and 6 months later shows that surgery had a relapse likelihood of more than 80%.

Gingival coverage by type A botulinum toxin injection was bigger than that produced with surgery during follow-ups. That is because, unlike with surgery, muscles became inhibited with type A toxin (Botox) injection. In respect of surgery, muscle response was strong, and the upper lip was shifted back to its preoperative position, which may explain the high percentage of surgical relapses after 6 months.

The results of our study were similar to those reached by Polo M. [9, 11], in which 2.5 units of type A botulinum toxin were injected in the levator labii superioris, the nasal wing, and the small left and right adrenal muscle to achieve neuromuscular correction of excess gingival exposure caused by a hyperactive upper lip. The results were more effective and more statistically significant than the initial smile assessment (P<00001). Although it had a non-lasting effect, the mean average of reduced gingival exposure was 5.2 mm, and despite gradual increase in gingival exposure from week two through week twenty-four, average exposure by the end of the period did not regress to where it was at the very beginning [9, 11].

The findings of Suber et al. [10] are worth mentioning. 5 units of type A botulinum toxin were injected in 3 sites bilaterally. Average gingival exposures before injection on incisors and canines were 4.89 mm and 4.25 mm, respectively. Consequently, a noticeable decline in gingival exposure occurred following injection to an average of 0.75 mm for incisors and an average of 0.74 mm for canines, an improvement of 85% and 83%, respectively. This suggests that there always exists an improvement likelihood in respect of gingival exposure when three sites representing the bases of muscles responsible for raising the upper lip have been injected [10].

Our findings concur with Silva et al. [13] that surgery (lip repositioning) achieved a visible reduction in gingival coverage, but between the third and sixth months postoperatively, gingival exposure began to appear [13].

Our findings are in agreement with those of Mazzuco & Hexsel [5]: there was a reduction in gingival exposure on the long run following several injections with type A botulinum toxin. One explanation for this is that the prolonged muscle inhibition following several injections could eventually result in partial muscle atrophy and, consequently, continuous decline in contraction ability long after the effect of the toxin has diminished [5].

We reached the same results obtained by Rosenbaltt and Simo [6] in respect of gaining a 4 mm postoperative reduction in gingival coverage.

However, our findings depart from Sucupira & Abramovitz [14], who injected only one site distal to the nostrils, targeting the levator labii superioris and the nasal wing, with an improvement rate of 84% [14].

Discussion of patient satisfaction

It could be noted the highest satisfaction level is for treatment with injecting type A toxin (Botox) after two months, even though the extent of satisfaction declined six months afterward. The same result was found for treatment with surgery. However, across the three comparisons, it could be noted that satisfaction with treatment with type A botulinum toxin (Botox) was higher than that of treatment with surgery.

Responses to both the satisfaction questionnaire and direct questions by patients treated with type A toxin (Botox) injection reveal that their smile appeared more appealing one week after the procedure. When the patients were asked about when they felt a certain change had occurred when smiling, responses ranged from one to five days on average (seventh day). As for expression of satisfaction with treatment, patients evaluated their awareness of the enhanced smile aesthetic at an average of 4.5 out of 5, which is quite high for satisfaction levels. As for their desire to repeat the treatment a second time, nine patients answered “yes,” two “maybe” and one “no.” Responding to a question whether they would recommend others with the same condition to undergo injection, eleven patients said “yes,” while one “maybe”.

In respect of the patients who underwent surgical treatment (lip repositioning), the responses on their special questionnaire demonstrate that they felt that their smile appeared more appealing during the first and second day postoperatively. When the patients were asked about when they felt a certain change had occurred when smiling, responses ranged from one to seven days (3.5 days on average). The expression of satisfaction with the treatment was 3.5 out of 5. As for their desire to repeat the treatment, four patients said they would, two they might and six they would not. Responding to a question whether they would recommend others with the same condition to undergo injection of botulinum toxin of type A, three patients said “yes,” while nine “maybe”.

Patients complained that they could not laugh or smile during the first two weeks after the procedure and attributed this to a lip disability they could not identify. After two months, however, they were able to adapt to the new condition and learn to cope with their new smile.

None of the reported results indicated cases of upper lip drooping or lengthening; lower lip protrusion; asymmetry of lips; drooling; or difficulty smiling, speaking or eating after undergoing either surgery or injection.

Conclusion

Correction of gingival smile resulting from hyperactive upper lip by injection of botulinum toxin of type A (Botox) resulted in better results than those of the surgical procedure of lip repositioning in terms of the amount of gingival coverage and patient satisfaction, especially taking into account the risks that may be involved in surgery.

Participation of authors:

Concept and design of the study — Harfoush Munir

Data collection and processing — Makkeiah Mohammad Osama

Text writing — All authors

Editing — All authors

The authors declare no conflict of interests.