Although each person shares with the rest of the population many characteristics, there are enough differences to make each human being a unique individual. Such limitless variation in the size, shape, and relationship of the dental, skeletal, and soft tissue facial structures are important in providing each individual with their identity (Bishara et al. 2001).

Dorland’s Medical Dictionary defines symmetry as “the similar arrangement in form and relationships of parts around a common axis or on each side of a plane of the body” (Dorland’s Illustrated Medical Dictionary 2000).

The absence of symmetry is asymmetry and is frequently experienced by man in their facial features, both structurally and functionally.

The term symmetry is generally used in two different contexts:

• The first meaning is a precise and well‐defined concept of balance or “patterned self‐similarity” that can be demonstrated or proved according to the rules of a formal system, namely geometry, physics, or otherwise.
• The second meaning is an imprecise sense of harmonious or esthetically pleasing proportionality and balance reflecting beauty or perfection. As such, symmetry was demonstrated within art by Leonardo Da Vinci in his Vitruvian Man in 1492 (Figure 1.1) (Baudouin and Tiberghien 2004).

Asymmetry has, on the other hand, been part of the features characterizing the unpleasant and the unharmonious (Edler 2001; Rhodes et al. 2001).

Whereas symmetry in art is used to express harmony, beauty, and peace, asymmetrical layouts are generally more dynamic, and by intentionally ignoring balance, the designer can generate tension, express movement, or convey a mood such as anger, excitement, joy, or casual amusement (Komoro et al. 2009).

Facial asymmetry, being a common phenomenon, was probably first observed by the artists of early Greek statuary who recorded what they had found in nature – normal facial asymmetry (Lundstrom 1961).

A perfect facial symmetry is extremely rare and practically all normal faces exhibit a degree of asymmetry (Figure 1.2). As in art, where the side has an importance in the interpretation of a movement displayed on a painting, the two sides of the face may express feelings (Schirillo 2000).

The left side of the face is considered more emotionally expressive and more often connotes more negative emotions than the right side. Also interestingly, artists tend to expose more of their models left cheek than their right. This is significant, in that artists also portray more females than males with their left cheek exposed. These psychological findings lead to explanations for the esthetic leftward bias in portraiture (Schirillo 2000; Powell and Schirillo 2009).

The studies of asymmetry of the craniofacial region can be divided into two categories. One is focusing on facial asymmetry in various populations and its impact on perception of the individual’s attractiveness and health. The second category is dealing with the influence of asymmetry on treatment of patients receiving orthodontic treatment or craniofacial surgery.

Studies of various populations belong to the first category, and facial symmetry has been associated with health, physical attractiveness, and beauty of a person. It is also hypothesized as a factor in interpersonal attraction, and relevant research indicates that bilateral symmetry is an important indicator of freedom from disease and worthiness for mating (Edler 2001).