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Year : 2014  |  Volume : 5  |  Issue : 2  |  Page : 49-54

Smile analysis in orthodontics

Department of Dentistry, Government Medical College and Hospital, Chandigarh, India

Date of Submission24-Oct-2013
Date of Acceptance20-Feb-2014
Date of Web Publication16-Jul-2014

Correspondence Address:
Sapna Singla
Department of Dentistry, Government Medical College and Hospital, Chandigarh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0976-6944.136836

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In the recent years, esthetics has become the primary consideration for the patients seeking orthodontic treatment. Although ideal occlusion should be the primary functional goal of orthodontics, the esthetic outcome is also critical for patient satisfaction and therefore essential to the overall treatment objectives. Hence, orthodontic treatment must incorporate various esthetic elements of smile to achieve desirable results. The article describes the principles of smile analysis, that should be considered during orthodontic diagnosis and treatment planning.

Keywords: Esthetic components of smile, smile analysis, smile designing

How to cite this article:
Singla S, Lehl G. Smile analysis in orthodontics. Indian J Oral Sci 2014;5:49-54

How to cite this URL:
Singla S, Lehl G. Smile analysis in orthodontics. Indian J Oral Sci [serial online] 2014 [cited 2018 Jan 19];5:49-54. Available from: http://www.indjos.com/text.asp?2014/5/2/49/136836

  Introduction Top

Smile is one of the most important expression contributing to facial attractiveness. An attractive or pleasing smile enhances the acceptance of individual in the society by improving interpersonal relationships. [1] With patients becoming increasingly conscious of a beautiful smile, smile esthetics has become the primary objective of orthodontic treatment. [2] Modern orthodontics deals not only with the traditional dental and skeletal aspects, but also face as first priority. The most important esthetic goal in orthodontics is to achieve a balanced smile, which can be best described as an appropriate positioning of teeth and gingival scaffold within the dynamic display zone. [3] Smile analysis is part of a facial analysis and allows dentists to recognize positive and negative elements in each patient's smile. Depending on the type of malocclusion, facial pattern of the patient and mechanics adopted, orthodontic treatment can prove either beneficial or harmful to smile esthetics. Thus, it is reasonable to regard smile analysis as an important tool for diagnosis and orthodontic treatment planning. The purpose of this article is to discuss various elements of a pleasing smile and discuss their impact on orthodontic diagnosis and treatment planning.

Smile analysis should involve evaluation of certain elements in specific sequence: [4]

  • Dento-facial analysis
  • Dentolabial analysis
  • Dento-gingival analysis
  • Dental analysis.

Dento-facial analysis


The starting point of the esthetic treatment plan is the facial midline. A correctly placed midline contributes to the desirable effect of balance and harmony of the dental composition. One of the goals of the orthodontic treatment is to achieve maxillary and mandibular midlines that are coincident-both with each other and with the facial midline. Coincident midline serves both a functional and an esthetic purpose.

The most practical guide to locate the facial midline is to use two anatomical landmarks as references. The first is a point between the brows known as the nasion. The second is the base of the philtrum, also referred to as the cupid's bow in the center of the upper lip. [5],[6] A line drawn between these landmarks not only locates the position of the facial midline but also determines the direction of the midline. [5] Ideally the maxillary central incisor midline should coincide with the facial midline. However if it is not possible, then the midline between maxillary central incisors should be strictly vertical and parallel to the facial midline. [5],[6],[7],[8],[9] Minor discrepancies between facial and dental midlines are acceptable and in many instances, not noticeable as long as central incisor crown is not significantly canted. Although, it is desirable to have concordant maxillary and mandibular midlines for occlusion purposes but mandibular midline is not a very reliable reference point since in 75% of cases maxillary and mandibular midlines do not coincide. [10],[11] Mismatch between maxillary and mandibular midline does not affect esthetics since mandibular teeth are not usually visible while smiling. [5]

Dento-labial analysis

Maxillary incisor display at rest

The starting point of a smile is the lip line at rest, with an average maxillary incisor display of 1.91 mm in men and nearly twice that amount, 3.40 mm in women. [12] The amount of incisor show at rest is the most important esthetic parameter because decreased incisor display is a characteristic of ageing. This steady decline in maxillary tooth exposure at rest with aging, is accompanied by an increase in mandibular incisor display. [12],[13] Therefore in an adult patient with 3 mm of maxillary incisor display at rest, intrusion should be planned carefully.

Numerous reports in the past have shown that an average 30-year-old woman displays about 3.5 mm of maxillary central incisor tooth structure when the lips are at rest. [12],[14],[15] For most patients who are esthetically conscious, 3-4 mm of incisor display at rest should be ideal. [4] Excessive tooth display is judged better at rest than on smile, because lip elevation on smiling is quite variable. If exposure at rest is normal, even if a considerable amount of gingival display occurs on smiling, this should be considered normal for that individual.

Maxillary incisor display on smile

The lip line is the amount of vertical tooth exposure in smiling-in other words, the height of the upper lip relative to the maxillary central incisors. As a general guideline, the lip line is optimal when the upper lip reaches the gingival margin, displaying the total cervico-incisal length of the maxillary central incisors, along with the interproximal gingivae while smiling [Figure 1]. [16],[17] A high lip line exposes all of the clinical crowns plus a contiguous band of gingival tissue, whereas a low lip line displays <75% of the maxillary anterior teeth [Figure 2] and [Figure 3]. [1],[18] Because female lip lines are an average 1.5 mm higher than male lip lines, 1-2 mm of gingival display at maximum smile could be considered normal for females. [1],[19],[20] In a study by Kokich et al., [21] it was demonstrated that dental evaluators and lay people still considered it esthetic if 2 mm of gingiva showed in a full smile. According to Mc Laren and Cao, showing up to 3 mm of gingival in a full smile is still in the "esthetic zone," especially if there is slightly more than 8 mm of lip movement during a smile. [4]
Figure 1: The entire cervicoincisal length of maxillary anterior teeth along with interproximal gingivae. Note the parallel relation of the incisal edges to the inner contour of lower lip during smiling

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Figure 2: High smile with complete display of the entire cervicoincisal length and a contiguous band of gingival tissues

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Figure 3: Low smile with <75% display of the maxillary incisors during smiling

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Ideally the gingival margins of the maxillary canines should be coincident with the upper lip and the lateral incisors should be positioned slightly inferior to the adjacent teeth. But such relationship is age related, as tooth display and gingival display are more in children than adults. The amount of vertical exposure on smiling depends on many other factors such as vertical maxillary height, crown height, and incisor inclination besides upper lip length and lip elevation. [22]

Smile arc

The smile arc is defined as the relationship of the contour of the incisal edges of the maxillary anterior teeth relative to the curvature of lower lip during a social smile. [1],[18],[23],[24],[25],[26] On the basis of this relationship, smile lines are of three types. Consonant smile arc has the curvature of incisal edges of the maxillary anterior teeth parallel to the upper border of the lower lip [Figure 1]. [27] It has been suggested that for consonant smile arc, the centrals should appear slightly longer or, at least, not any shorter than the canines along the incisal plane. [1] Straight smile arc is that in which the incisal edges of the maxillary anterior teeth are in a straight line to the upper border of the lower lip [Figure 4]. Reverse or non-consonant smile arc is the one in which the incisal edges of the maxillary anterior teeth are curved in reverse to the upper border of the lower lip. [23],[24] Reverse smile arc occurs when the centrals are shorter than the canines along the incisal plane which can be due to occlusal malfunction or loss of vertical dimension. [5] Parallel and straight smiles provide better esthetic than reverse smile.
Figure 4: Straight smile arc. Note the flat maxillary incisal edges relative to the curvature of lower lip

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Since the smile arc depends upon occlusal plane inclination and second order crown angulations in the upper anterior teeth, there are some limitations to the achievement of this ideal smile arc on every patient. A reasonable objective is to prevent a flat or reverse smile arc and to obtain some degree of curvature that resembles, one found in the lower lip. [28]

Smile symmetry

An asymmetry in the smile can be due to asymmetric smile curtain or transverse cant of the maxillary occlusal plane. Transverse cant can be due to different amounts of tooth eruption on the right and left sides [Figure 5] or skeletal asymmetry of mandible resulting in compensatory cant of maxilla. In an asymmetric smile curtain, there is a difference in the relative positioning of the corners of the mouth in the vertical plane [Figure 6]. [16],[29] It can be assessed by the parallelism of the commissural and pupillary lines. Although the commissures move up and laterally in smiling, studies have shown a difference in the amount and direction of movement between the right and left sides. [30],[31],[32] A large differential elevation of the upper lip in an asymmetrical smile may be due to a deficiency of muscular tonus on one side of the face. [16] Myofunctional exercises have been recommended to help overcome this deficiency and restore smile symmetry. [16],[33] It is estimated that 8.7% of normal adults have asymmetric smiles. [32] It is poorly documented in static photographic images and is documented best in digital video clips. [3]
Figure 5: Smile asymmetry due to transverse cant of occlusal plane

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Figure 6: Asymmetric smile due to differential elevation of the corners of lips

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Buccal corridor

Buccal corridor refers to dark space (negative space) visible during smile formation between the corners of the mouth and the buccal surfaces of the maxillary teeth and is measured from the mesial line angle of the maxillary first premolar to the interior portion of the commissure of lips. It is represented by a ratio of the intercommissure width divided by the distance from the first premolar to first premolar. [34] Its appearance is influenced by the following factors: [10]

  • The width of the smile and the maxillary arch
  • The tone of the facial muscles
  • The positioning of the labial surface of the upper premolars
  • The prominence of the canines particularly at the distal facial line angle and
  • Any discrepancy between the value of the premolars and the six anterior teeth
  • Anteroposterior position of maxilla.

Buccal corridor is directly influenced by arch form. [35] The ideal arch is broad and conforms to a U shape and is more likely to fill the buccal corridors than narrow and constricted arch [Figure 7] and [Figure 8]. This negative space should be kept to a minimum as it is unattractive, but at the same the buccal corridor should not be completely eliminated because a hint of negative space imparts to the smile a suggestion of depth. [10] In addition, buccal corridors are heavily influenced by the anteroposterior position of the maxilla relative to the lip drape. Moving the maxilla forward will reduce the negative space because a wider portion of the arch will come forward to fill the intercommissure space. [23],[27] Hulsey examined the influence of buccal corridors on the smile attractiveness and concluded that variation in buccal corridors seemed have no significance. [16] Hulsey considered only six anterior teeth for measuring the buccal corridors. Since buccal corridors as defined by Frush and Fisher [24] are the distance from the posterior teeth to the corners of the lips, thus a smile typically includes not only the six anterior teeth but also the first and sometimes second premolars. Fullness of the smile is one of the important feature that determines smile attractiveness. The effect of buccal corridor on smile esthetics has been studied extensively in the recent years. Moore et al. [36] recommended that having minimal buccal corridors is a preferred esthetic feature in both men and women, and large buccal corridors should be included in the problem list during orthodontic diagnosis and treatment planning. Numerous reports suggest that buccal corridor has an effect on the esthetic evaluation of smiles. [37],[38],[39]
Figure 7: Fuller smile with minimal buccal corridor (too less negative space)

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Figure 8: Excessive buccal corridor

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Dento-gingival analysis

Gingival health

The lips frame the teeth and gingiva and further gingiva acts as the frame for the teeth; thus, the final esthetic outcome is greatly affected by the gingival health. It is of utmost importance that the gingival tissues are in a complete state of health prior to the initiation of any treatment. [40] Healthy gingiva is usually pale pink in color or consistent with the healthy color of individual race variations, stippled, firm and it should exhibit a matte surface. [10]

Height, shape and contour of the gingiva

Establishing the correct gingival levels for each individual tooth is the key in the creation of pleasing and harmonious smile. The gingival margins of the central incisors should be at the same level or slightly incisal to that of the canines, while the gingival margins of the lateral incisors should be towards incisal when compared to central incisors and canines. The gingival margin of the lateral incisor is 0.5-2.0 mm below that of the central incisors. [10] The least desirable gingival placement over the laterals is for it to be apical to that of the centrals and or the canines. [35] The discrepancies in the levels of gingival margin may be caused by attrition of the incisal edges, ankylosis due to trauma in a growing patient, severe crowding, or delayed migration of the gingival tissue. [22] The gingival margins can be leveled by orthodontic intrusion or extrusion or by periodontal surgery, depending on the lip line, the crown heights, and the gingival levels of the adjacent teeth. [41]

Gingival shape implies the curvature of the gingiva at the margin of the tooth. For ideal appearance, the gingival shape of the maxillary lateral incisors should be a symmetrical half-oval or half circle. The gingival shape of maxillary centrals and canines should be more elliptical. The gingival zenith (the most apical point of the gingival tissue) is located distal to the long axis of the maxillary centrals and canines, while the gingival zenith of the maxillary lateral incisor coincides with its long axis. [42],[43]

The contour of the gingiva (i.e. gingival scallop) to the tip of the papilla should be between 4 mm or 5 mm, and the tips of the papillae should have the same radiating symmetry as the incisal edges and the free gingival margins. In an esthetic smile, the volume of the gingiva from the apical aspect of the free gingival margin to the tip of the papilla is about 40-50% of the length of the maxillary anterior tooth and fully fills the gingival embrasure. [43],[44] In situations where this condition does not exist, an open gingival embrasure above the connector results, and these "black triangles" present an unesthetic condition. In these situations, periodontal and orthodontic procedures are the treatments of choice to create the correct gingival architecture. [4]

Dental analysis

Contacts and connectors

The elements of tooth contacts, connectors and embrasure morphology can be of great significance in the appearance of smile.

There is distinction between a connector space and a contact point. The contact points between the anterior teeth are generally smaller areas that can be marked by passing articulating ribbon between the teeth. The connector is a large, broad area that can be defined as the zone in which two adjacent teeth appear to touch. The contact points of maxillary teeth move progressively gingivally from the central incisors to the premolars, so that there is a progressively larger incisal embrasure, whereas connectors decreases in size from the centrals posteriorly. An esthetic relationship exists between the interproximal connectors of anterior teeth that is referred to as the 50-40-30 rule [Figure 9]. [45] According to this rule, the ideal connector zone between maxillary central incisors should be 50% of the length of central incisor and between a maxillary lateral incisor and a central incisor should be 40% of the length of the central incisor. The optimum connector zone between a maxillary canine and a lateral incisor when seen in lateral view should be 30% of the length of the central incisor. [5]
Figure 9: Decrease in size of connectors from centrals posteriorly and progressively larger incisal embrasure from centrals to the posterior teeth

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The incisal embrasures are the triangular spaces incisal to the contact point. Ideally these should display a natural, progressive increase in size or depth from the central to the canine [Figure 9]. [46] This is a function of the anatomy of these teeth and as a result, the contact point moves apically as we proceed from central to canine. The contact points in their apical progression should mimic the smile line. Failure to provide adequate depth and variation to the incisal embrasure will

  • Make the teeth appear too uniform and
  • Make the contact areas too long and impart to the dentition a box like appearance.

The individuality of the incisors will be los t if their incisal embrasures are not properly developed. Also, if the incisal embrasures are too deep, it will tend to make the teeth look unnaturally pointed. As a rule, a tooth distal to incisal corner is more rounded than its mesio incisal corner. [10]

Crown height and width

Since the smile reveals the maxillary anterior teeth, two aspects of proportional relationships are important components of their appearance: The height/width proportions of the individual teeth, and the tooth width in relation to each other.

Crown height combined with percentage of incisor display is the deciding factor in the amount of tooth movement required to improve the smile index. [12] The vertical height of the maxillary central incisors in the adult is normally between 9 and 12 mm, with an average of 10.6 mm in men and 9.6 mm in women. The age of the patient is a factor in crown height because of the rate of apical migration in the adolescent. [16],[47]

The width is a critical part of smile display in that, the proportion of the teeth to each other is an important factor in the smile. The proportions of the centrals must be esthetically and mathematically correct. Most references specify the central incisors to have about an 8:10 width/height ratio. [34],[35] In one of a recent study the optimal width-to-length ratio for the maxillary central zone was found to be between 75% and 85% of the length. [4] Smiles with these values were most often considered "esthetic to highly esthetic."

Relationships of the mesio-distal width

Correct dental proportion is related to facial morphology and is essential in creating an esthetically pleasing smile. Central dominance dictates that the centrals must be the dominant teeth in the smile and they must display pleasing proportions. They are the key to the smile. The shape and location of the centrals influences or determines the appearance and placement of the laterals and canines. For best appearance, the apparent width of the lateral incisor (as one would perceive it from a direct frontal examination) should be 62% of the width of the central incisor, the apparent width of the canine should be 62% of that of the lateral incisor, and the apparent width of the first premolar should be 62% of that of canine. This ratio of recurring 62% proportions appears in a number of other relationships in human anatomy is referred to as the "Golden proportion." [48]

  Conclusion Top

Current trends in orthodontics place greater emphasis on smile esthetics. Although the concept of smile analysis is not new but is often not incorporated in orthodontic treatment planning. It is therefore emphasized that all the above discussed elements of smile analysis should be considered as guidelines and reference points for beginning esthetic evaluation, treatment planning and subsequent treatment.

  References Top

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9]


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