Global Health Nexus, Winter 2004

How Dentists Decide What Constitutes a Beautiful Smile

Over the past two decades, the advent of new aesthetic materials, the embrace of aesthetic dentistry by a generation of aging baby boomers eager to maintain a youthful appearance, and the effective marketing of the concept of “feel good dentistry” or “self-esteem dentistry,” have all combined to put aesthetic dentistry on the fast track, making it the most rapidly growing area in dentistry today.

And just as the ancient quest for a stable definition of beauty has yielded over the years to a more subjective, relativist perspective, so too has the aesthetic dentist’s quest for what constitutes a beautiful smile evolved over time.

Indeed, only a generation ago, dentists specializing in aesthetic restorations tended to be guided by the same “golden proportion” of 1.6:1:0.6 that Sheila Samton cites in the preceding essay. In dentistry, that means that the width of the central incisor is in “golden proportion” to that of the lateral incisor. The width of the lateral incisor to the width of the canine is also in “golden proportion.” According to this mathematical formula, when the dentist is looking directly at a frontal view of the patient, the central incisor should appear to be 1.6x the width of the lateral. As we proceed distally from the same view, the canine should appear to be 0.6x the width of the lateral. The reason this formula has long remained the standard is because although people’s teeth can become shorter with age, the widths do not change.

While some dentists still follow the “golden ratio” formula in working toward their aesthetic objective, it is more common today for dentists to rely on eye coordination, or how they perceive the patient’s mouth and teeth in relation to the rest of the face. This more subjective approach, accepted by the American Dental Association, emphasizes the importance of harmony, balance, phonetic ability, and function. 

When a patient smiles, three types of liplines are possible: high, medium, and low. A high lipline exposes a lot of gingiva above the front teeth. A medium lipline reveals a moderate amount of gingiva. A low lipline doesn’t reveal the gum tissue at all. Under ideal conditions the gingival margin and the lipline should be harmonious; that is, there should be a 1-2 mm. display of gingival tissue.

When evaluating where the maxillary incisal edges should be, dentists analyze the contour of the lower lip when smiling. An imaginary line around the incisal edges of the upper front teeth should follow the superior border of the lower lip. This is called the “smile line.” When the centrals appear shorter than the canines, it is referred to as the “reverse smile line.” This is unfavorable and can be corrected in many cases. 

To ensure that balance is achieved, the dentist identifies the “midline,” or the point at which the two central incisors contact each other. This is easily done by holding a piece of dental floss vertically descending from the forehead to the nose, the philtrum (the concavity beneath the nose), and the chin. The floss should bisect the papilla between the two central incisors, be perpendicular to an imaginary line between the patient’s eyes, and be perpendicular to the occlusal plane.

The incisal edge position determines the patient’s ability to make the “f”, “v”, “s” and “t” sounds as well as the lip support (the way the anterior teeth support the upper lip). Varying these positions and having the patient speak can help determine the ideal position for the incisal edges. Along with lingual contours and tooth position, incisal edge position also determines the patient’s bite, or what dentists call the “guidance pattern.” 

The gingival contour must be closely evaluated. Ideally, the height of the gingival margins of the central incisors should be higher than that of the laterals, but should be even with that of the canines. 

Using an articulator, the dentist then proceeds to create a wax rendition that will act as a guide toward the treatment goal. 

The two central incisors are indicative of age, with flat incisor edges indicating old age. Accordingly, the dentist creates rounded central incisor edges to give a more youthful appearance. Similarly, the lateral incisors are indicative of gender (a lateral incisor that narrows toward the gum line suggests femininity and a less tapered, square shape suggests masculinity). As the dentist considers the canines, which are indicative of personality, a sharper-edged point on a canine will be used to create an aggressive look, while a rounder, softer point will create a more passive appearance. 

Another of the dentist’s objectives is called “tooth reveal,” which means that when a patient smiles, it should be possible to see a lot of teeth. In an aesthetically pleasing smile design, the anterior teeth should be taller than they are wide. The midline is vertical, perpendicular to the ground. As we move distally, the axial inclinations of the teeth are mesially inclined. The “buccal corridor” refers to the way posterior teeth appear to be aligned with the natural curvature of the smile. If the alignment is not perfect, a black space appears in the corridor. Finally, color selection must be customized for each patient to achieve a natural, polychromatic appearance.

The above information was provided by Dr. Denise J. Estafan, Associate Professor and Director of Aesthetics, Department of General Dentistry and Management Science. An article by Dr. Estafan, “A New Dimension in Dental Education: The Preclinical Course in Aesthetics,” appears on page 22.