Seven Worst Violations of Smile Design
Achieve better esthetics by understanding common mistakes
Students and practitioners of esthetic dentistry study smile design principles to quantify and demonstrate potential esthetic changes to patients and dental team members, including laboratory technicians. These principles encompass facial esthetics, labiodental dynamics, gingival and dental architecture, and phonetics.1-3 To best educate patients and their colleagues alike, many lecturers do a fantastic job of illustrating smile design principles using examples of the ideal, and/or what falls within an ideal range, based on individual patient anatomical and physiologic characteristics.
Although this type of instruction is beneficial, it is equally helpful to recognize the worst violations of these principles. Instructive approaches incorporating proper evaluation and management of deviations from smile design principles are essential. This article examines the seven worst smile design principle violations and how to appropriately evaluate and restore them to ideal form.
1. A Crooked Smile
A smile that appears crooked on the face is immediately obvious to laypersons and dentists,4,5 similar to noticing a crooked wall-hanging. When smiles are restored, often little attention is paid to the inter-incisal line, resulting in a smile that appears tipped in the face (Figure 1 and Figure 2). Straightening the smile requires a pretreatment plan work-up that facilitates evaluation of facial esthetic principles. Among the aspects to be evaluated are horizontal and vertical facial parameters, including the commissural and inter-pupillary lines. A vertical line drawn through the middle of the face should focus attention to the glabellar area, tip of the nose, and middle of the chin. It is also important to ensure that inter-incisal contact areas between the central incisors are perpendicular to the horizon.6
Beginning with facial esthetics when treatment planning a smile may be overlooked if the scope of evaluation quickly becomes narrowed by analyzing only models of teeth on work benches.7,8 Instead, beginning with excellent pretreatment photography enables thorough facial esthetic analysis. Be aware of the patient’s natural horizontal head position when examining facial planes, and choose a horizontal reference line that represents the horizontal plane to be the basis for designing the smile. This is usually the true horizontal plane, which can be influenced by facial asymmetries commonly found among individuals. Perceiving the face as a whole, rather than focusing on one or two references to the horizon, is helpful. The restorative horizontal plane then can be ideally shared with the laboratory technician involved with mounting and waxing the case via a face-bow or digital smile design method (Figure 3 and Figure 4).9
2. The Reverse Smile
A radiating smile requires symmetry among incisal edges of maxillary anterior teeth that follow the lower lip border (ie, labiodental dynamic principle).10 Formed from the incisal edges, this shape creates a convex line blending into the posterior teeth. Posterior teeth would typically follow an occlusal plane or Campers Plane from the nose to the ear tragus. Curvature depends on patient gender, age, lower lip shape, and smile preferences.11,12 Straighter smile curves typically favor a more masculine or older smile characteristic, while more convex curves are characteristic of youth and femininity. A reverse smile or concave curve creates an unesthetic incisal line or an “unhappy”-looking smile (Figure 5).13
Ensuring a “happy”-looking smile involves analyzing tooth lengths and their relationship with lip dynamics. A reference point for incisal edge position is important for determining whether to shorten the canines or lengthen the incisors to correct a concave smile. Although the literature provides guidance for choosing canine incisal edge position from a patient’s lip position at rest, typically just at the lip border, central incisor tooth display varies greatly among patients depending on lip length and shape, tooth length, and lip mobility.6,8,10
Final incisal edge position is communicated to the laboratory before waxing when correcting concave smile lines by analyzing images of the smile and identifying length changes using digital smile design techniques or direct mock-ups on the patients’ teeth (Figure 6 through Figure 8). A precisely taken face-bow also alerts the technician to a concave smile line when the case is properly mounted on an articulator, but addressing labiodental dynamics also requires photographic images or video communication.9,14
3. The Social Six
Esthetically altering anterior teeth, including color and shape, is difficult without creating contrast with the posterior teeth, which produces a fake-looking smile. The dentolabial dynamic relationship of smile width demonstrates that smiles usually include 10 to 12 maxillary teeth, so restorative corrections also must account for more than just the six anterior teeth (Figure 9 through Figure 11). When taking pretreatment photographs, evaluating front and lateral smile views determines how the patient is viewed from the sides and front.
Another dentolabial dynamics principle (eg, buccal corridor or buccal width) dictates that posterior teeth not leave too much or too little space between the buccal aspects of the teeth and cheek. Too much space creates a narrow-looking smile, and treating only the six anterior teeth usually accentuates a narrow smile. Additionally, an artificial look results from emphasizing only the treated teeth, which detracts from the natural smile progression from anterior to posterior teeth.1 Conversely, restoratively brightening and accentuating the buccal aspects of posterior teeth can overfill this space and produce a denture-like look in the new smile.15
Finding the right balance is key. Examine patient smile photographs to assess whether they present a narrow smile and evaluate the color and contour of existing posterior teeth.16 Also consider the occlusal plane and its relationship to the incisal plane. Provide options to correct esthetic shortcomings in the posterior teeth in the smile. Consider offering case fees to improve the entire smile, rather than itemizing individual restorations, to educate patients about the importance of correcting the whole smile and not just the anterior.
4. Ignoring Central Incisor Proportions
Central incisors are naturally dominant in smiles, and central dominance, like radiating symmetry, is paramount to achieving a beautifully restored smile. The Golden Proportion was traditionally the standard applied when creating ideal smiles, but today artistic smile designers lean toward less regimented and proportion-based designs.
The width-to-height ratio is normally around 80% in unworn central incisors, so efforts must be made to maintain a similar ratio to prevent the centrals from appearing too long and narrow or too wide and fat.2,7,8 When planning esthetic length or width changes, or correcting incisor crowding, narrow teeth can easily result from over-lengthening or -narrowing compared to the actual width. A loss of central dominance results, with the two anterior teeth appearing to have the same width as the laterals, creating an unesthetic and artificial appearance.
If space is limited, ensure central dominance is maintained by narrowing or even slightly rotating the laterals to create room for the centrals (Figure 12 and Figure 13). A good guideline is proportioning the laterals to be about 65% of the central width, and the canines to be 75% of the lateral width. Using lines with constrained proportions in Keynote or PowerPoint overlaid on images of a patient’s teeth—or measuring the tooth widths and heights to determine their percentages—facilitates visualizing these proportions, sharing them with the laboratory during preplanning, and ensuring central dominance.6
5. Over-Contoured Teeth
There are three fundamental categories of tooth forms observed in patients: basically tapering, basically square, or basically ovoid. All teeth exhibit reflective and deflective zones separated by transition line angles. Manipulating these line angles impacts whether teeth appear shorter and fatter, longer and narrower, or more rectangular or curved.
Mesiofacial and distofacial line angles are usually found on facial aspects of teeth close to the contact areas. Moving line angles outward toward contact areas creates wider looking teeth. Moving them toward the center creates narrower looking teeth. Without distinction between deflective and reflective zones, teeth can appear over-contoured (Figure 14 and Figure 15).17,18