Optimizing the smile: The interface between teeth and lips

Key points

• The overall facial arc should have a slight convexity, with the projection greatest at the subnasale.

• Women typically prefer a more convex face, which is more feminine, rather than a flatter face, which is typical of increasing masculinity and preferred by men.

• Ideal maxillary central incisor show at rest is 2 to 3 mm in males and 3 to 4 mm in females.

• During smiling, 1 to 2 mm of gingival show is considered ideal, whereas there should be no gingival show at repose. Increasing dental display gives a more youthful appearance to the face, and today, a slight gummy smile is considered more attractive.

• Maxillary gingival exposure decreases with lip lengthening, which occurs with aging.

• The orthodontist and the surgeon have the challenge of planning treatment with regard to which smile pattern achieves the best aesthetic outcome.

• The tolerance for dental midline discrepancies is within 2 mm and for angular deviation less than 5 degrees.

• An occlusal cant four degrees or more is noticeable and considered unaesthetic.

• When the maxillary incisal dental arc does not parallel the contour of the lower lip (when it is flat or inverted) the smile is unattractive.

• The buccal corridor space is determined by the width of the maxillary dental arch. Either too full or too narrow a space creates an unaesthetic smile.

• The creation of a beautiful smile requires the orthodontist, the surgeon, the periodontist, and the cosmetic dentist to work as a unified team to transform the smile.


Of all the features of the face, it is the human smile that greatly influences the dynamic component of aesthetic appearance. In patients with dentofacial skeletal deformities, the analysis and treatment planning are, for the most part, static, and the only component that is typically included is the one-dimensional change in dental display between repose and smiling. The orthodontist and the surgeon have the ability to not only influence the vertical display, but the angulation of the dental arches in three-dimensional space. This chapter focuses on the subtle aspects of the smile as an aesthetic unit that can be influenced by orthodontic and surgical approaches ( Fig. 19.1 ). It is by incorporating these subtle characteristics in treatment planning that distinguishes the aesthetically appealing smile.

Fig. 19.1

The smile itself should be considered an aesthetic subunit. It is the interface between the dentofacial skeleton and the soft tissue envelope of the face that is the most visible.

Anatomy of the smile

A smile is a form of facial expression when coordinated contraction of facial muscles that insert along the oral commissure occur. It is believed it takes activation of about 42 muscles to smile. Depending on which muscles are activated and the degree of activation, an individual can express various types of smiles, ranging from the rehearsed smile of portraiture photographs to the spontaneous smile of amusement.

Three basic smile patterns have been recognized ( Fig. 19.2 ). The “commissure smile” (“Mona Lisa smile”) is seen as an expected form of greeting when individuals meet each other in social situations. The commissures are pulled upward with or without showing the anterior dentition. In the “cuspid smile,” the upper lip itself is elevated, displaying the anterior dentition from canine to canine. Both the above types of smile can be forced and consciously controlled. The third smile, “spontaneous smile,” involves a complex coordination of muscles that not only includes the oral commissure but also extends to involve a wider range of facial expression, including the eyes. This smile can only occur as a genuine emotional response and cannot be rehearsed, except perhaps by professional actors and actresses.

Fig. 19.2

The vertical dynamics of the lip–incisor relationship. When the lips are at rest or repose, the dental display ranges typically from 2 to 4 mm. With function, there are different degrees of incisor exposure during speaking and smiling. This is best captured through videos. Because of the numerous variables that need to be controlled, one of the challenges in the planning of orthodontic treatment combined with orthognathic surgical treatment is achieving consistently optimal smile aesthetics.

The orthodontist and the surgeon have the challenge of planning treatment with regard to which smile pattern would achieve the best aesthetic outcome. Although the ideal planning would be based on the spontaneous, natural smile, it is difficult from a practical standpoint. Thus treatment planning is typically based on the second type, the cuspid smile.

Thus it is not only the elevation of the lip but also the reciprocal relationship of the exposure of maxillary anterior dentition that plays a significant role in defining the aesthetic anatomy of the smile. The proportions of the anterior dentition and their relationship to the adjacent dental unit defines an ideal, attractive smile.

Analysis of the smile

It is essential to systematically analyze the morphology of the lip as it drapes the dentofacial skeletal from multiple positions: frontal, three-quarter, and profile. Additionally, as the lip is a dynamic component on a static skeletal framework, the standardized imaging sequence includes the lips in contact, in repose, and in smiling. To dynamically capture the position of the lips, a high-speed sequence of still photographs and video is obtained to allow the surgeon and the orthodontist to interpolate the full dynamic range for treatment planning.

Analysis of the smile in the frontal view includes the proportions of the lips as a subunit to the overall proportions of the face, the proportions of the anterior dentition, the symmetry of the lips and the dental arches, the dental midline relationships of the respective dental arches to the facial midline, the dental display at rest and during a dynamic smile, the smile arch, the buccal corridor space, and competence. The three-quarter view best demonstrates the relationship of the curvature of the dentition to the curvature of the lip and the lip strain that can occur with lip incompetence. The profile view best demonstrates the incisor inclination relative to soft tissues.

Optimizing the aesthetic smile

There are innumerable articles in the literature addressing the various aspects of the relationship between the morphology of the lip and the dental arches with regard to ideals based on perception and objective criteria. Rather than a lengthy review, the authors present a practical approach based on their experience and an understanding of a selected review of the literature. Although the review may be biased, it will provide the reader with an approach that can be further refined. The following rules will guide this effort.

Optimizing symmetry

Fundamental to the concept of attractiveness is the left–right or the “mirror image” symmetry of the facial form. However, interestingly, perfect symmetry is not the ideal; it is a slight deviation from symmetry that makes a face and its features attractive. However, the structures considered “midline” structures that define the facial midline must be coincident for attractiveness. For the perioral region, the midlines of the dental arches must be coincident with the facial midline, which is defined by the nasal root, the base of the columella, the philtrum, and its tubercle. Ideally, the maxillary dental midline should be perfectly coincident and parallel to the facial midline, but it is important to know the tolerance because surgical–orthodontic treatment can rarely achieve the ideal consistently because of the limitations and variables beyond the surgeon’s control.

The tolerance for dental midline discrepancies is within 2 mm and for angular deviation less than 5 degrees, based on findings from studies involving both professional orthodontists and lay individuals.

As the facial structures are viewed increasingly more lateral to the midline, asymmetry in the natural population increases. The relationship of the lips to the maxillary–mandibular cant, or roll, increases. This cant can occur as a combination of the asymmetry of the skeletal base and the asymmetry in dental eruption or display in the canine, premolar, and molar regions. Added to the asymmetry in the dental skeletal base is the asymmetry in the morphology of the lips themselves. Achieving an acceptable degree of symmetry requires a combination of orthognathic surgery to level the skeleton and the dentition and that to correct the lip form itself. As the ideal can rarely be achieved, the tolerance for the maxillary cant or tool, based on the lay public, is typically less than two degrees. At four degrees, the cant is noticeable, and most individuals would consider it unacceptable.

Optimizing the smile arc

The smile arc is defined as the relationship of the curvature made by the incisal edges of the upper dentition to the curvature of the lower lip ( Fig. 19.3 ). It is in the three-quarter that the arcs can best be evaluated. The ideal smile arc has these two curves in a close parallel relationship to each other. However, when the maxillary incisal dental arc does not parallel the contour of the lower lip when it is flat or inverted, the smile is unattractive. A key objective of orthodontic treatment is not only coordination of the dental arches but also establishing its appropriate curvature in relationship to the lip contours. When dental bases need to be repositioned surgically, the surgeon can control the “total” maxillary arc line as a single unit as the orthodontist controls the individual components of the maxillary arc to optimize the smile aesthetics.

Apr 1, 2021 | Posted by in Aesthetic plastic surgery | Comments Off on Optimizing the smile: The interface between teeth and lips
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