Gummy smile: proposal of a clinical decision-making algorithm

1.1 Anatomy and Dynamics of the Smile

The human smile is the result of the coordinated activation of the mimetic muscles-cutaneous muscles originating from the second branchial arch and innervated by the facial nerve. These muscles insert into the skin and, upon contraction, generate facial expressions, including smiling. [5]

The perioral musculature involved in smiling can be divided into three functional groups: Group I (Oral commissure muscles): act on the corners of the mouth and include the buccinator, orbicularis oris, levator and depressor anguli oris, risorius, and zygomaticus major; Group II (Upper lip elevators): raise the upper lip and include the levator labii superioris, levator labii superioris alaeque nasi, and zygomaticus minor; and Group III (Lower lip and chin muscles): depress the lower lip and include the depressor labii inferioris, mentalis, and platysma. [6]

Through the synergistic action of these three groups, the smile develops in two main phases: 1) Initial elevation of the upper lip, exposing the maxillary incisors and 2) Full elevation of the lips, involving coordinated action of the levator labii superioris, zygomaticus major, and buccinator muscles — often accompanied by eye squeezing (partial eyelid closure), which enhances the expressive quality of the smile. [23]

An aesthetically pleasing smile depends on harmony among several components:

• The incisal edge of the anterior teeth and the curvature of the lower lip;
• The lip line (amount of tooth visible);
• The buccal corridor, smile arc, and curvature of the upper lip;
• Smile symmetry with respect to the interpupillary line;
• The occlusal plane, dental esthetics (tooth shape, color, alignment), and gingival appearance (color, contour, and health of gingival tissues).

Different perspectives have been proposed in the literature to analyze the morphology and dynamics of the smile, both from an aesthetic and a functional standpoint.

In particular, the smile can be divided into two main types: the Social Smile (or posed smile), which is voluntary, reproducible, and characterized by moderate muscular contraction that partially exposes the dental elements and, in some cases, a minimal portion of the gingival architecture; and the Spontaneous Smile (or enjoyment smile), which occurs involuntarily in response to intense emotional stimuli, such as laughter or pleasurable moments, and is associated with maximum activation of the mimetic musculature, resulting in full exposure of the teeth and gingiva.

Another classification, proposed by Tjan, is based on the vertical extent of dentogingival exposure during smiling. According to this model, a High Smile is identified when exposure reaches 100% of the incisal surface along with visible gingiva; a Medium Smile is defined when visibility ranges between 75% and 100%, generally limited to the visible part of the upper incisors and the interdental papillae; and finally, a Low Smile is observed when exposure is below 75%, resulting in a more contained display even during full muscle contraction.

Rubin, in turn, described three smile styles based on the direction of lip movement and the distribution of muscular tension. The Mona Lisa Smile, also known as the commissure smile, is characterized by elevation of the mouth corners produced by the zygomaticus major muscle, conferring an arched shape to the upper lip, similar to the Cupid’s bow. The Canine Smile, by contrast, presents a uniform elevation of the upper lip without significant involvement of the oral commissures. The third style, referred to as Full Denture Smile or complex smile, corresponds to the contemporary concept of Gummy Smile. In this case, the upper lip rises markedly while the midface appears particularly active during smiling.

1.2 Definition of Gummy Smile and Incidence

Gummy Smile, or gingival smile, is an aesthetic condition characterized by excessive exposure of the maxillary gingival tissue during smiling. In a smile that is considered aesthetically harmonious, gingival display should not exceed 1–2 mm above the cervical margin of the maxillary central incisors. When this threshold is exceeded, the gingival tissue becomes the dominant element in the visual composition of the smile, surpassing the teeth and lips, and often leads to aesthetic dissatisfaction and psychosocial discomfort, even in the absence of any organic pathology. Gummy Smile may result from multiple causes, including eruptive alterations (altered passive eruption), vertical maxillary excess, upper lip hypermobility, short upper lip, gingival hyperplasia, or dentoalveolar extrusion. The etiology is frequently multifactorial, making an in-depth diagnostic process essential for the planning of an effective and personalized treatment strategy.

The prevalence of Gummy Smile in the general population varies with age and sex. This condition affects approximately 10% of individuals aged between 20 and 30 years. It is more frequently observed in females, with a reported ratio of 2:1 compared to males. Prevalence decreases with age, primarily due to the physiological descent of the upper lip, which, with aging, tends to progressively cover the incisors and gingival tissues, thereby masking the condition. [1]

1.3 Diagnosis of Gummy Smile

The clinical evaluation of a patient affected by Gummy Smile is based on established diagnostic principles and involves the systematic collection and integration of information obtained through anamnesis and physical examination, conducted under both static and dynamic conditions. The primary objective of the diagnostic process is the accurate identification of the etiology underlying the clinical condition reported by the patient. Only a precise etiological diagnosis allows the therapeutic approach to be correctly directed, guiding the clinician toward the most appropriate treatment option or options. [1]

The diagnostic evaluation of patients with Gummy Smile is structured in multiple phases, aimed at precisely identifying the cause of the condition. Facial analysis represents a fundamental first step. This must be conducted by observing the face in both frontal and sagittal views, dividing it into three thirds: upper (from the trichion to the glabella), middle (from the glabella to the subnasale), and lower (from the subnasale to the menton). An increase in the middle third may suggest the presence of vertical maxillary excess (VME), a hypothesis that requires confirmation through radiographic investigations, in particular via cephalometric analysis. In the latter, the distance between the palatal plane and the cemento-enamel junction of the upper incisors is measured, as this parameter is less influenced by dental wear compared to the incisal edge. [2–3]

The analysis of the upper lip and perioral musculature includes both static and dynamic evaluations. In static assessment, the length of the upper lip is measured, distinguishing between the cutaneous portion (15–16 mm) and the mucosal portion (5–6 mm); lower values are indicative of a short upper lip. In the dynamic evaluation, potential muscle hypermobility is assessed during both natural and forced smiling, by observing the extent of dentogingival exposure, which should not exceed 2–3 mm to remain within aesthetic standards.

This is followed by dental and periodontal analysis. At rest, the three-dimensional position of the incisors is evaluated. Using the phonation of the sound “m”, the muscular resting position is identified, allowing assessment of incisal exposure. An incisal display greater than 4 mm may suggest VME or a short upper lip, while lower values may be indicative of dental wear or altered passive eruption. In this case, a thorough periodontal examination with probing and radiographic imaging is necessary to assess the position of the cementoenamel junction and the amount of excessive gingival tissue.

Finally, it is essential to analyze the layout of the gingival smile, that is, to determine whether the exposure involves only the anterior region or extends to the entire arch. A localized presentation often allows for the use of minimally invasive treatments with satisfactory aesthetic outcomes, whereas a more extensive involvement may require more complex and invasive therapeutic approaches. [3]

1.4 Therapeutic Options

The planning of Gummy Smile treatment is based on the correct interpretation of clinical data collected during diagnostic evaluation. The therapeutic approach must be individualized according to the underlying etiology, which may sometimes be multifactorial, thus requiring the combination of multiple corrective strategies.

The available therapeutic options can be grouped into three main categories:

• Periodontal surgery (gingivectomy or clinical crown lengthening);
• Orthodontic treatment and orthognathic surgery (intrusion or Le Fort I osteotomy);
• Plastic surgery and aesthetic medicine (lip repositioning or botulinum toxin).

1.5 Introduction to the use of the decision-making algorithm

The variety of therapeutic options available can complicate clinical decision-making, especially for less experienced dental practitioners. Currently, there is no structured and shared decision-making model that systematically supports the selection of the most appropriate treatment based on the specific etiology.

Considering this, one of the main objectives of this study is to develop a critical review of the existing literature and, based on the evidence gathered, to propose a clinical decision-making algorithm. This tool is intended to guide the practitioner in both diagnostic evaluation and in selecting the most appropriate treatment for each patient affected by Gummy Smile.

The proposed decision-making diagram is designed to be easily consultable, also thanks to the integration of an explanatory legend and glossary (Figures 1 and 2). The process begins with the identification of Gummy Smile and continues with the determination of the predominant etiological factor. Based on the identified cause, two therapeutic options are suggested, which may both be surgical or may include a non-surgical solution. Additionally, the algorithm includes an important indication: in the presence of multifactorial etiologies, it may be appropriate to adopt a combined therapeutic approach.

It should be noted that the algorithm is presented as a guiding proposal, the application of which must be assessed considering the practitioner’s competence and the clinical needs of the patient. Further studies will be necessary to validate its effectiveness, improve its structure, and possibly adapt it to new clinical scenarios.

2.1 Study Design

The protocol for this systematic review was developed a priori in accordance with the guidelines for registration on the PROSPERO platform, following internal discussions among the team members, and registered with PROSPERO, the International Prospective Register of Systematic Reviews, under the ID CRD420251047332.

The systematic review was conducted in compliance with the Cochrane Handbook for Systematic Reviews of Interventions. The included studies (Observational Studies and RCTs) were identified between October 2024 and May 2025, and the results were reported in accordance with the PRISMA 2020 statement.

2.2 Literature Search Process

The systematic review of the literature was initiated by searching for scientific articles aimed at answering the following research question:

“Can surgical treatment always be considered the most appropriate therapeutic approach for the management of Gummy Smile?” To identify the articles relevant to this research question, two reviewers queried the following databases: PubMed (https://pubmed.ncbi.nlm.nih.gov), Scopus (https://www.elsevier.com/products/scopus), and Cochrane (https://www.cochranelibrary.com). Six possible treatment strategies for Gummy Smile were considered, and for each, a dedicated folder was created to organize the selected articles. The treatments evaluated were:

• - Botulinum toxin injection
• - Gingivectomy or clinical crown lengthening
• - Orthognathic surgery
• - Lip repositioning surgery
• - Orthodontic treatment
• - Multimodal approach

The search process was structured into three distinct phases:

• ○ Phase 1: preliminary search for scientific articles related to the topic of interest;
• ○ Phase 2: selection of articles meeting the predetermined inclusion criteria;
• ○ Phase 3: critical analysis of the collected information.

The preliminary search in the three platforms was conducted by applying the following selection filters:

• Articles published from 2010 to 2025 (the last 15 years)
• Articles classified as: RCTs, Clinical Trials, Case Series

The PubMed search engine was queried using MeSH (Medical Subject Headings). Articles related to the investigated treatments were identified using Boolean operators (“OR” and “AND”), which enabled the combination of terms related to the research question, resulting in the following queries:

• ○ “Gummy smile” OR “excessive gingival display” AND “botulinum toxin”
• ○ “Gummy smile” OR “excessive gingival display” AND “gingivectomy” OR “clinical crown lengthening”
• ○ “Gummy smile” OR “excessive gingival display” AND “lip repositioning”
• ○ “Gummy smile” OR “excessive gingival display” AND “orthognathic surgery”
• ○ “Gummy smile” OR “excessive gingival display” AND “orthodontic treatment”

The Scopus database was queried using the “Search within Article Title, Abstract, Keywords” function, searching for the keywords: “Gummy smile”, “excessive gingival display”, “botulinum toxin”, “gingivectomy”, “clinical crown lengthening”, “lip repositioning”, “orthognathic surgery”, and “orthodontic treatment”, combined using Boolean operators.

To obtain specific results for each treatment modality, the final keyword was replaced each time with one of the different descriptors corresponding to the individual therapeutic techniques.

In the Cochrane database, the advanced search mode was applied, requesting the software to identify publications containing the following keywords: “Gummy smile”, “excessive gingival display”, “botulinum toxin”, “gingivectomy”, “clinical crown lengthening”, “lip repositioning”, “orthognathic surgery”, and “orthodontic treatment”. The terms were combined using Boolean operators, replacing the final keyword in each search to obtain results specific to each therapeutic approach.

At the end of this preliminary search phase, the total number of retrieved articles amounted to 691. A manual duplicate removal process was then conducted, reducing the number of articles admitted to the second phase of the search process to 313.

2.3 Inclusion and Exclusion Criteria

The second phase of the search process involved reading each article with the objective of assessing its compliance with the inclusion criteria defined using the PICO model (Table 1).

2.4 Study Selection and Methodological Quality Assessment

Two reviewers carried out the study selection process, following the outlined research protocol.

The analysis of each study led to the identification of 23 articles eligible for evaluation. The reading of the publications made it possible to define an additional category of studies, labeled “Comparative Studies”, which included those works that explicitly compared the different therapeutic modalities under analysis.

This systematic review was carried out according to the PRISMA 2020 guidelines (Preferred Reporting Items for Systematic Reviews and Meta-Analyses), in order to ensure transparency, reproducibility and methodological rigor in the selection and analysis of studies. (Figure 3)

The assessment of the methodological quality of the included studies was conducted using validated tools recommended by the Cochrane Collaboration, differentiated according to the design of each selected study. Specifically, the RoB 2.0 tool (Risk of Bias version 2) was used for randomized controlled trials (RCTs), and the ROBINS-I tool (Risk Of Bias In Non-randomized Studies - of Interventions) was applied to non-randomized observational studies.

The evaluation was conducted independently by two reviewers. In case of disagreement, discrepancies were resolved with the intervention of a third reviewer. The results of the assessments were graphically presented using visual representations to facilitate immediate consultation. (Figures 4, 5)

Given the types of studies included in this research project, it is important to clarify that although the present review follows a rigorous systematic approach, the clinical and methodological heterogeneity of the selected studies — in terms of design, population, treatment modalities, and measured outcomes — only allowed for a purely descriptive synthesis of the results. Therefore, the findings from the entire cohort of selected studies were subjected to a narrative synthesis.

2.5 Comparative Analysis

At the conclusion of the selection process, the literature review proceeded with a meticulous analysis of each selected article, identifying the information necessary to perform a qualitative comparison among the various treatment modalities for Gummy Smile.

The comparative analysis of the considered therapeutic options was carried out by extracting data related to the following comparison criteria:

1. Clinical indications
2. Execution technique
3. Aesthetic and functional outcomes
4. Duration of results
5. Post-treatment recovery modalities
6. Presence of intraoperative or postoperative complications and risks
7. Patient satisfaction

The data extraction was performed by responding to guiding questions formulated to facilitate the critical reading of the available documents. For the first criterion (clinical indications), the questions guiding the data analysis were:

“In what situation was surgical treatment performed?”

“Under what conditions was a minimally invasive approach sufficient?”

“In which cases was orthodontic treatment carried out?”

Information regarding the execution technique was obtained by answering the following questions:

“What procedures or surgical techniques were performed?”

“Was it necessary to administer anesthetics?”

“What was the duration of the intervention?”

The remaining criteria (aesthetic and functional outcomes, duration of results, post-treatment recovery protocols, presence of intra- or post-operative complications, patient satisfaction) were investigated by asking:

“What were the outcomes of the performed treatment?”

“What was the duration of the results obtained?”

“What adverse events occurred?”

“Were the treated patients satisfied with the treatment?”

The information gathered was summarized in a summary table (Table 2)

3.1 Qualitative Analysis

The comparison between the various treatment modalities for Gummy Smile highlights that the therapeutic choice must be guided by the underlying etiology, which may be muscular, skeletal, dento-gingival, or mixed. The injection of botulinum toxin type A (BTX-A) represents a minimally invasive solution, particularly indicated in cases of hyperactivity of the upper lip elevator muscles. Some studies propose its use even in multifactorial forms, with gingival exposure greater than 2–3 mm. Injections are usually administered at the Yonsei Point or directly into the target muscles (LLS, LLSAN, ZMi, ZM), with an average dosage of 2.5 U per site. The clinical effect becomes evident within two weeks and lasts on average 3–6 months, with high patient satisfaction and a very low incidence of complications.

In cases where Gummy Smile is caused by altered passive eruption, periodontal surgery (gingivectomy or clinical crown lengthening) represents an effective option. Techniques vary from the use of traditional scalpel to laser devices or digitally guided procedures, with stable results at six months and an average healing time of approximately 14 days, in the absence of significant complications. In the presence of severe skeletal components, orthognathic surgery — specifically maxillary osteotomy according to the Le Fort I technique — allows for the definitive correction of the aesthetic defect, with additional benefits on the facial profile. Results remain stable over the long term (up to 10 years), although recovery times are longer and associated with possible complications (paresthesia, pain, functional difficulties), especially with the traditional approach compared to the Surgery First protocol, which has demonstrated higher patient satisfaction.

Upper lip repositioning surgery proves effective in cases sustained by hypermobility, short upper lip, altered passive eruption (APE), or mild-to-moderate vertical maxillary excess (VME). Techniques such as LipStaT^®, laser-assisted variants, or approaches involving myotomy and periosteal sutures enable a significant reduction of gingival exposure, with average clinical stability of 12 months. Healing typically occurs within 10–14 days, and side effects are mild and transient. Finally, orthodontic treatment is indicated in patients with mild to severe VME, hypermobile or short upper lip, often associated with complex malocclusions. The use of fixed appliances, in combination with temporary anchorage devices (TADs), enables vertical control of the occlusal plane, retraction of the upper incisors, and improvement of the facial profile, with long-term stable results. The main complications include root resorption and mini-screw failure, though patient satisfaction is generally high.

Comparative studies included in the review assessed the effectiveness of BTX-A versus surgical interventions (periodontal, orthognathic, or lip repositioning), showing that although all techniques produce a significant reduction in Gummy Smile, the duration of the effects varies considerably. Botulinum toxin yields rapid but transient results; lip repositioning surgery provides greater stability, albeit with a risk of recurrence; orthognathic surgery guarantees long-lasting outcomes but is more invasive; whereas periodontal surgery, when well planned, ensures stability with relatively short recovery times. Lastly, one study compared orthognathic surgery with orthodontic treatment using skeletal anchorage through miniplates, concluding that both approaches are effective, although the orthodontic strategy is less invasive while maintaining high aesthetic and functional efficacy.