From Volume 41, Issue 6, July 2014 | Pages 483-489
Patients seek dental treatment to improve oral function as well as their attractiveness. In order to improve smile attractiveness, clinicians need to carry out a comprehensive smile assessment. The aim of this paper is to help clinicians to adopt a systematic approach toward smile assessment by introducing a smile assessment form.
The smile, which is often used to show pleasure and amusement, can be defined as the facial expression that is characterized by upward curving of the corners of the mouth.1 It is the second facial feature, after the eyes, that people tend to look at when evaluating the attractiveness and beauty of others,2 and it is equally important for both genders.3
Generally, there are two types of the smile, the posed and the spontaneous smile.3,4 The posed smile is a voluntary smile that is not elicited or accompanied by emotions; it is unstrained and static in the sense that it can be sustained with fairly reproducible lip animation.4 The reproducibility of the posed smile in natural head position makes it amenable to orthodontic treatment planning.3 The spontaneous smile is an involuntary smile with animated lip elevation induced by joy. It is dynamic in the sense that it bursts forth but is not sustained. It can be said that it expresses authentic human emotion.4
When patients attend for a consultation with various concerns about the smile, it is important that a clinician can assess the smile in an objective manner in order to determine the reason for dissatisfaction. Once a cause of the problem has been established, it is possible to undertake a risk-benefit analysis of the treatment approaches that would be required to address the patient concerns. In many cases, there may be anatomical limitations that do not allow the patient concerns to be addressed and an understanding of smile analysis can help these limitations to be identified and outlined as part of the process of consent.
A clinician should be fully aware that the perception of the need for dental treatment can differ considerably between patients and dentists. Dentists are known to be less tolerant and more critical than patients, who are generally less critical about their own smile aesthetics.5,6 It is important to remember that aesthetic values should be judged by what the patient wants and not by what we want as a clinician. Although all components of the smile analysis may not be relevant to the patient, smile analysis serves as a guiding tool, which can be used effectively by both the dentist, to bring together all options of treatment that can improve the patient's smile, and the patient, to decide what parameters in the smile are important.
Different ethnic groups can differ significantly in their smile perception. For example, dental protrusion is a common feature in Afro-Caribbean patients and is well accepted. However, in Caucasians, it might be perceived as unaesthetic.
Females tend to favour more upper gingival exposure during smiling than males. However, males are less critical than females when evaluating a smile.7 This implies a difference in tolerance level between genders and reflects the importance of considering the individual patient's concerns during smile analysis.
A smile can be assessed clinically whilst examining the patient, on a still photograph or by using a digital video of the smile.3,8 Clinically, not all the measures can be made with ease, moreover, it is also time consuming for the patient and dentist. A still photograph can overcome these difficulties and allows a detailed assessment of the smile. The smile mesh can be used with a still photograph and consists of vertical and horizontal lines placed onto the frontal smile photograph.3 The horizontal lines are on the vermilion borders of the upper and lower lips and on the incisal edge of the upper right central incisor. The vertical lines pass through the distal of the maxillary canines, the inner and outer commissures of the lips and the dental midline (Figure 1). Quantitative measurements can then be taken from these lines.
A dynamic method for smile analysis has been introduced involving the capture of the smile with a standardized digital video technique. A cephalostat is used to position the patient's head in a natural reproducible position. Then the mounted video camera captures five-second long clips. These clips are transferred to a computer and the frame representing the best social smile is selected and analysed manually or using computer software.9 This method has the advantage of capturing the most reproducible spontaneous smile frame for analysis.
In addition to analysing the smile in three planes, sagittal, horizontal and vertical, in static and dynamic positions, age should be considered as a fourth dimension.10 This is significant since patient maturation and growth could play a role in smile attractiveness. A good example is reduced upper incisor show as a result of an increased upper lip length in older individuals.
The smile is a sum of a number of features that contribute to it, either positively or negatively. It can be broken down into three major components:
Each of these components may be further subdivided. To ease the smile assessment and analysis, a form was developed and divided into thirteen distinctive features (Figure 2) as follows.
A recent survey in the United Kingdom showed that people are mainly concerned about the colour of their teeth, where half of the respondents considered themselves to have discoloured teeth.11 A lighter tooth shade is considered preferable since it reflects a youthful appearance.12 Teeth within the arch show some shade variation, where the maxillary tooth shade from the central incisor to the canine tends to darken. Maxillary incisors and premolars are similar in shade. The shade of each of the maxillary anterior teeth should be recorded using a shade guide in natural light conditions.
During a full smile the gingiva is exposed superior to the maxillary teeth. This is described as the smile line and can be assessed as high (>2 mm gingival show), average (1–2 mm gingival show) or low (no gingival show), depending on the degree of gingival display (Figure 2). For an attractive smile, the display of upper central incisors in addition to 1 mm of gingiva is ideal.9 The amount of maxillary gingival display during smiling is dependent on a number of factors, including anterior vertical maxillary height, the muscular capability to raise the upper lip,13 upper lip length and incisor crown height. The smile line should be documented (high, average, low) while the amount of gingival and tooth display should be recorded in mm with the patient at smile and rest positions (Figure 3).
The upper and lower lips act as a frame for the display zone of the smile.8 The teeth and the gingival scaffold lie within this framework. A degree of tooth and gingival display is desirable to produce optimal smile aesthetics; the upper lip length can influence this. For a caucasian adult male, the average upper lip length is 22 mm, while it is 20 mm for an adult female. This is measured from the base of the nose (subnasale) to the lower end of the upper lip (stomodium superioris) when the lip is in the rest position. It is crucial to consider the patient age during smile assessment, since ageing is usually associated with an increased upper lip length, which leads to a lowering of the smile line.14
Three aspects of the gingiva are of great importance in the perception of the aesthetics of a smile: gingival colour, shape and level.15 It should be kept in mind that the smile line height is highly correlated with gingival margin display.16
A pale pink gingival colour reflects healthy gingival tissue, which has an impact on smile aesthetic perception. On the other hand, the redness and swollen appearance of inflamed gingivae could contribute to a less aesthetic smile.
The gingival shape of the mandibular incisors and the maxillary lateral incisors should be symmetrically half oval or half circular (Figure 4). The maxillary centrals and canines should exhibit a gingival shape that is more elliptical.17
Symmetrical gingival display is a significant factor in a satisfactory smile appearance. Asymmetry in gingival display can be judged negatively and may be correlated with personality.3 The criteria for ideal gingival level are described as follows:18
Black triangles (Figure 5) are triangular black spaces that form gingival to the contact area and have a significant aesthetic impact. Risk factors for formation include recession, poor root angulations and triangular-shaped crowns.19 Often, a multidisciplinary team approach is required for their management.
Based on shape, incisors can be generally classified as square, triangular or round. Round incisors were found to be more aesthetic, especially in female smiles.20
The embrasures are the triangular spaces incisal to the contacts and ideally they should get larger as the teeth progress posteriorly (Figure 4). With ageing, and toothwear, the embrasure spaces reduce in size.
The ideal length to width proportion of the maxillary central incisor is approximately 10:8; on average, the upper central incisor length should be 10.4–11.2 mm with a width of 8.4–9.3 mm.15 Once the size of the central incisors has been established, the ‘golden proportion’ can be used to determine the appropriate relevant size of the lateral incisors and canines. The ‘golden proportion’ has been suggested as a method to assess the proportions of anterior maxillary teeth in frontal view. According to it, the width of the lateral incisor should be 62% of the width of the maxillary central incisor. The main problem with the ‘golden proportion’ is that it is not dominant within the population. Another suggested method to determine the ideal tooth proportion is the golden percentage, where the width of each tooth is as follows: canine 10%, lateral incisor 15% and central incisor 25% of the total width of the anterior segment. The golden percentage was found to be suitable in defining the proportionality of maxillary anterior teeth if the percentage is adjusted to take into account the ethnicity of the population.21 Recent research would suggest that there might not be one ideal aesthetic standard to suit all patients, which highlights the importance of seeking the views of individual patients.
The smile arc (Figure 6) is the relationship between two imaginary lines, one representing the lower lip curvature and one connecting the incisal edges of the maxillary anterior teeth and premolar tips in a posed smile.22 This relationship can be either parallel (consonant), increased, reversed or straight. An ideal smile arc has a parallel relationship between the maxillary incisal edges and the lower lip curvature. Smiles with flatter arcs are said to be less attractive.7,22 The smile arc may be flattened during treatment (especially orthodontics) in a number of ways,7 such as changes in incisor vertical position, unfavourable maxillary growth patterns (counter clockwise rotation of the maxilla) and habits such as digit-sucking, which cause upper incisor intrusion.
Patients relate their maxillary midline to the upper lip. They consider dental midline discrepancies a factor in reducing smile attractiveness; discrepancies of 2 mm or more have 56% chance of being noticeable by laypeople.23 Therefore, the upper dental centre line should be assessed in relation to the facial midline and its direction and position should be recorded.
The buccal corridor is defined as the space between the facial surfaces of the posterior teeth and the corners of the lips. It is calculated as follows:22
The smaller the ratio (the smaller the buccal corridor) the more aesthetic is the smile.24 Orthodontic treatment has been claimed to reduce buccal corridors, where patients treated with rapid maxillary expansion showed less buccal corridor than untreated groups.25
Asymmetry in the face and dentition is a naturally occurring phenomenon. Dental asymmetry can be treated by surgery, prosthodontics, periodontics or orthodontics. Facial asymmetries may be addressed surgically to some extent after growth has stopped. Smile asymmetry can be seen as a result of contra-lateral unevenness in crown length, crown width, papilla height, the smile line,5 and the lip thickness. Any asymmetry should be identified and quantified (in millimetres). Interestingly, although asymmetry can impair smile attractiveness, some asymmetry is acceptable to most individuals.
Smiles that display first molar to first molar are usually rated the most attractive.26 This is followed by smiles displaying premolar to premolar. The least attractive smiles are the ones that display only canine to canine.
Tooth display is related to arch form; with more tooth display expected with oval and square than tapered arch forms. The maxillary arch should be assessed from an occlusal view of the patient's study models to determine arch form.
In order to demonstrate the use of the smile assessment form developed, the authors captured and analysed the smile in Figure 7. Figure 8 shows a completed smile form, based on the smile in Figure 7.
Smile reconstruction or improvement starts with diagnosis and understanding the important features of the smile will aid the clinician in identifying what factors may be contributing to the patient's concerns. Table 1 summarizes some possible treatment approaches based on the identified problem.
| Problem | Possible Treatment |
|---|---|
|
Shade of teeth
|
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Smile line and upper lip:
|
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| Decreased vertical gingival and tooth show |
|
|
Gingival tissue
|
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| Asymmetric level and shape |
|
| Black triangles |
|
| Tooth form and proportion |
|
|
Smile arc
|
|
|
Buccal corridors, tooth display and arch form
|
|
Smile analysis is an important procedure prior to smile reconstruction. The use of a smile assessment form helps to provide a systematic method of smile analysis and communication between clinicians. It's crucial to consider the patient age, ethnic background and gender while carrying out smile analysis, and to remember that there is no one ideal formula for all faces and that our decision should be guided by the patient concerns and a careful risk-benefit analysis.
