October, 2010

Smile Designing in Orthodontics

Dr B.S Chandrashekar
MDS
Associate Professor
Department of Orthodontics
Krishnadevaraya College of Dental Sciences
Bangalore, Karnataka
India.

Dr Sujit Panda
MDS
Reader in Orthodontics
Department of Orthodontics and Dentofacial Orthopedics
RAMA Dental College, Hospital and Research Centre
Lakhanpur, Kanpur,
India.

Dr Ashok Kumar Jena
MDS, PGDHM
Assistant Professor
Unit of Orthodontics
Oral Health Sciences Centre
PGIMER, Chandigarh
India

Corresponding Author:

Dr Ashok Kumar Jena
Assistant Professor
Unit of Orthodontics
Oral Health Sciences Centre
Post Graduate Institute of Medical Education and Research,
Chandigarh,
India
Email- ashokkjena@yahoo.co.in


Abstract

The subject of the smile is related to communication and facial expression of an individual’s emotion and is of great interest to orthodontists. Most of the patients seek orthodontic care because of esthetic reasons, that is, the desire to look more attractive by improving their smile. Thus an attractive smile should be the goal at the end of orthodontic treatment. The purpose of this article is to give an up to date knowledge on smile and its implications in clinical orthodontics.

Introduction
Smile is one of the most important facial expressions and is essential in expressing friendliness, agreement and appreciation. A beautiful smile radiates health and self-confidence. Many patients with missing, malaligned, discolored and chipped teeth hold their hand over their mouth when they smile or use a closed-lip smile to conceal their unsightly teeth.
Esthetics is derived from a Greek word, which means “perception”.  Esthetic deals with beauty and has two dimensions: objective and subjective1. Objective (admirable) beauty is based on consideration of the object itself, which means that the object possesses properties that make it unmistakably praiseworthy. Subjective (enjoyable) beauty is a quality that is value-laden, relative to the tastes of the person contemplating it1,2.
Smile analysis and smile design have become key elements of orthodontic diagnosis and treatment planning3-5. The purpose of this article is to give an up to date knowledge on smile and its implications in clinical orthodontics.
The smile
Smile is one of the most effective means by which people convey their emotions6. Smile is apparently formed in two stages, the first raising the lip to the nasolabial fold, and the second involving further superior raising of the lip and the fold by three muscle groups4. Nearly everyone, irrespective of age, display the maxillary incisors nicely on maximum smiling, even if only the mandibular incisors are visible during conversation.
When viewed from the frontal aspect, the smile begins at the corners of the mouth extend laterally. The lips may remain at contact except with people having a short upper lip. As smile expands and approaches laughter, the lips separate, the corner of the mouth curve upward and the teeth are exposed to view. Some people show only the maxillary teeth; others the mandibular teeth and some show both. As the angles of the mouth extend and the lips separate, the mesial half of the maxillary first molars and the mandibular second premolars may be exposed. In most people the gingival tissue do not expose while smiling and those with a short upper lip always do, especially when smiling. Those with hypermobile lips or massive alveolar processes may do the same in a broad smile. As the smile approaches a laugh the jaws separate and a dark space develops between the maxillary and mandibular teeth. This space is also known as the negative space7. A well-formed dark space lends attractiveness to the smile and enhances the appearance of the oral region.
In profile view, the first manifestation of a smile is a thinning of the lips and a distal extension of the corners of the mouth. This continues until the opening of the lips exposes teeth. As in the facial view the dark space persists and the tongue may or may not be visible.
Anatomy of the Smile
When an individual looks in the mirror, the smile he or she sees is framed by lip curtain8 or soft tissue drape. The upper and lower lips frame the display zone of the smile of which the teeth and the gingival scaffold are the components. (Figure-1) The soft-tissue determinants of the display zone are lip thickness, intercommissure width, interlabial gap, smile index (width/height) and the gingival architecture.
Artists use the “eye unit” theory to describe the topographic interrelationship of facial features. The distance between the base of the nose and the lower border of the lower lip is one eye unit (length of the individual’s eye). This distance remains unchanged whether at rest or during a smile, because the upper lip is stretched laterally and become shorter9.

Figure 1. Display zone of the smile.

Types of smile
Smile can be social (posed) which is not accompanied by emotion, and is voluntary, unstrained and static facial expression; and enjoyment (unposed), which is accompanied by emotion, and is involuntary and often more animated. In orthodontics, we usually evaluate the posed smile on the basis of two factors, the amount of incisor and gingival display and the transverse dimension of smile.
Depending on the direction of elevation and depression of the lips and the predominant muscle groups involved, Rubin10 classified three smile styles into commissure, cuspid and complex types. In commissure smile, the corner of the mouth turn upward due to the pull of the zygomaticus major muscles. This is sometimes called as “the Mona Lisa smile”. Commissure smile is characterized by the action of the zygomaticus major muscles, drawing the outer commissures outward and upward, followed by a gradual elevation of the upper lip. In cuspid smile, the upper lip is elevated uniformly without the corners of the mouth turning upward i.e. the entire lip rises like a window shade. (Figure-2) The cuspid smile is characterized by the action of all the elevators of the upper lip, raising it like a window shade to expose the teeth and gingival scaffold. In complex smile, the upper lip moves superiorly as in the cuspid smile but the lower lip also moves inferiorly in a similar fashion. (Figure-3) The complex smile is characterized by the action of the elevators of the upper lip and the depressors of the lower lip acting simultaneously. Patients with complex smiles tend to display more teeth and gingiva.

Figure 2. The cuspid smile. Note the upper lip is elevated uniformly without the corners of the mouth turning upward. (The entire lip rises like a window shade).

Figure 3. The complex smile. Note the upward movement of upper lip and downward movement of the lower lip.

Tjan et al. classified smile as high smile, average smile and low smile11. When there is complete display of the cervicoincisal length of the maxillary incisors and a contiguous band of gingiva, the smile is called high smile and is found in about 10.57% of general population11. In average smile, there is 75-100% display of the maxillary incisors and is found in about 68.94% of general population11. If there is less than 75% display of the maxillary incisors while smiling, the smile is called low smile and is found in about 20.48% of general population11.

Elements of smile design
There are four elements of smile designing i.e. facial esthetics, gingival esthetics, microesthetics and macroesthetics.

Facial esthetics
Facial and muscular considerations vary from patients to patients and are worthy criteria for smile evaluation. Photographic analysis can determine how the lips and soft tissue frame the smile in different positions of speech, smiling and laughter.
Gingival esthetics
Esthetic conditions related to the gingival health and appearance is an essential component of effective smile design. Inflamed, uneven gingival lines detract from a pleasing smile. Blunted papilla and asymmetric gingival crests become part of the overall esthetic picture.
Microesthetics
Microesthetics involves the elements that make teeth actually look like teeth. The anatomy of natural anterior teeth is specific for each tooth and that tooth’s location in the dental arch. Specific incisal translucency patterns, characterization, lobe development and incisal haloing are the microesthetics components of the smile.
Macroesthetics
Macroesthetics represents the principles that apply when group of individual teeth are considered12. The relationship between a group of teeth and the surrounding soft tissue and the patient’s facial characteristics creates a dynamic and three-dimensional canvas. Macroesthetics attempts to identify and analyze the relationships and ratios between anterior teeth and surrounding tissue landmarks.


Macroesthetic elements of smile

Midline
In smile design, the starting point of the esthetic treatment plan is the facial midline13. The midline is the most important focal spot in an esthetic smile7. The patient readily recognizes an off-centered midline. A properly placed midline in conjunction with a long solid interproximal contact relationship between the two central incisors produces a desirable effect of “cohesiveness” 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 functional14 and an esthetic purpose7,15-17.  A properly placed midline contributes to the desirable effect of balance and harmony of the dental composition. In cases when it is not possible to match the midline, the midline between the central incisors should be parallel to the facial midline15,18,19. While alignment of the maxillary and mandibular dental midlines is desirable in orthodontics, the mandibular midline becomes a lesser issue in esthetics16. The narrowness and uniform sizes of mandibular incisors make visualization of their middle point more difficult, particularly when seen in relationship to lips and other soft tissue landmarks.
Incisal embrasures
The pattern of silhouetting created by the edges and separations between the maxillary anterior teeth against the darker background of the mouth helps define a good-looking smile. These spaces between the edges of the teeth are known as embrasure spaces. The size and volume of the incisal embrasures between teeth increase as the dentition progress away from the midline20. (Figure-4) In other words, the incisal embrasure space between the lateral incisor and the central incisor should be larger than the incisal embrasure between the central incisors. The embrasure between the canine and lateral incisor should be larger than the embrasure between the lateral incisor and central incisors.

Figure 4. Incisal embrasures. Note the size and volume of the incisal embrasures between teeth increase as the dentition progress away from the midline.

Connectors
The places in which the anterior teeth appear to touch have been referred to as the connector space. 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. An esthetic relationship exists between the anterior teeth that are referred to as the 50-40-30 rule21. This rule defines 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. (Figure-5) The optimum connector zone between a maxillary canine and a lateral incisor when seen in lateral view should be approximate 30% of the length of the central incisor.

Figure 5. Connectors. Note ideal connector zone between central incisors is about 50% of the length of central incisor, between central and lateral incisors is about 40% of the length of central incisor and between lateral incisor and canine is about 30% of the length of central incisor. An esthetic relationship exists between the anterior teeth that are referred to as the 50-40-30 rule.

Symmetry
Any concept of esthetics must consider symmetry22. Symmetry is an essential component in the perception of dental esthetics22. Although perfect bilateral symmetry seldom exists in living organisms23, it is one of the important factors in defining the attractiveness of a smile6. There are two kinds of symmetry, horizontal or running symmetry and radiating or bilateral symmetry.” Horizontal symmetry occurs when the design shows similar elements from left to right in a regular sequence. This type of symmetry is psychologically predictable and comfortable but tends to be monotonous7. The dentition approaches horizontal symmetry when all the teeth have the same shape; that is when they look like central incisors. Radiating symmetry results when the design extends from a central point and the left and right sides are mirror images. Elongating the central incisors and narrowing the lateral incisors exaggerates the effect of radiating symmetry. Teeth are seldom symmetrical, although patients think they are. There must be some asymmetry if teeth are to be natural; however, this does not mean they are esthetically pleasing to the patient.
Axial inclination of teeth
Each combination of tooth inclinations in a smile is unique. The long axis of, or direction of the anterior teeth in, an esthetic smile also follows a progression as the teeth move away from the midline. When the maxillary anterior teeth tip medially, the overall esthetic impact remains in harmonious relationship with the framing of the lower lip7. As in many macroesthetic rules of progression, the medial tipping of the axial inclinations increases as one moves further from the midline.
Tooth shape and harmony
Human teeth can be classified into three principal shapes i.e. rectangular, triangular and ovoid24. Williams claimed that the most pleasing appearance is one in which the outline form of the individual’s face turned upside down and the outline form of the individual’s maxillary central incisor are identical24. However, it was found that the outline forms of the face and the maxillary central incisor coincide in only a small percentage of cases, and it has never been proved that this occurrence results in an ideal esthetic appearance25. The only major addition to Williams’s concept of esthetics was the attempt by Frush and Fisher26 to harmonize the teeth with patient’s age, personality and sex (SPA factors).
Teeth displayed in a smile
In most individuals teeth are displayed till the second premolar in a smile27. Tjan, Miller and The found that the six maxillary anterior teeth and the first or second premolars are displayed during smile28.


Teeth reveal

Tooth reveal means the amount of tooth structure or gingiva that is displayed in various lip positions. Even the most beautiful anterior tooth will have little esthetic value for the patient if the amount of reveal is unflattering to the face.
Upper lip position
The position of the upper lip can be divided into three categories. A high smile, reveals the total cervicoincisal length of the maxillary anterior teeth and a continuous band of gingival. An average smile reveals 75% to 100% of the maxillary anterior teeth and interproximal gingival only. A low smile displays less than 75% of the anterior teeth. The average smile is most common smile.

Upper lip curvature
Upper lip curvature can be of three types. (Figure-6) Upward lip curvature means that the corner of the mouth is higher than the center of the lower border of the upper lip. Straight lip curvature means that the corner of the mouth and the center of the lower border of the upper lip are on a straight line. Downward lip curvature means that the corner of the mouth is lower than the center of the lower border of the upper lip. Latter is less esthetic when compared to the former two.

Figure 6. Different curvatures of upper lip. Note upward lip curvature (A); in which the corner of the mouth is higher than the center of the lower border of the upper lip. Straight lip curvature (B); in which the corner of the mouth and the center of the lower border of the upper lip are on a straight line. Downward lip curvature (C) in which the corner of the mouth is lower than the center of the lower border of the upper lip.

Lower lip position
The relationship between maxillary anterior teeth and lower lip can be of three types. Slightly covered means that the incisal edges of the maxillary anterior teeth are slightly covered by lower lip. Touching means that the incisal edges of the maxillary anterior teeth just touch the lower lip. Not touching means that the incisal edges of the maxillary anterior teeth do not touch the lower lip. Touching and not touching smiles are more esthetic than slightly covered smiles.
Smile line or smile arc
The smile arc or smile lines i.e. the parallelism of the maxillary anterior incisal curve with the lower lip. Smile lines are three types. (Figure-7) Parallel means that the incisal edges of the maxillary anterior teeth are parallel to the upper border of the lower lip. It is also called consonant smile arc. Straight smile line means that the incisal edges of the maxillary anterior teeth are in a straight line with the upper border of the lower lip. Reverse smile line means the incisal edges of the maxillary anterior teeth curved in reverse to the upper border of the lower lip. It is also called nonconsonant smile arc. A so-called reverse smile line results when the tips of the canines or premolars are longer than those of the central incisors. This design condition does not harmonize well with other facial features and also may be associated with occlusal malfunction or loss of vertical dimension. Parallel and straight smiles provide better esthetic than reverse smile.

Figure 7. Different smile lines. A. High smile; Note there is complete display of the cervicoincisal length of the maxillary incisors and a contiguous band of gingiva. B. Average smile; Note there is display of cervicoincisal length of the maxillary anterior teeth with only interproximal gingiva. C. Low smile; Note there is less than 75% display of the maxillary incisors during smile.


Intercommissure line and lower lip framing

When the patient’s mouth is in broad smile position, the clinician can draw an imaginary line through the corners of the mouth. This line is known as intercommissure line. The amount of maxillary tooth reveal below this line interacts with the viewer’s perception of the patient’s age. In a youthful smile, approximately 75-100% of the maxillary teeth would show below this line29. The position of the incisal edges of the anterior teeth as they relate to the lower lip may also have esthetic consequences. When the visual space created between upper and lower lips in full smile is considered, the maxillary anterior teeth should fill between 75-100 of that space to create a youthful look30.
Vestibular space
In a broad smile, the amount of reveal of the maxillary posterior teeth also can become an esthetic consideration. In patients who have narrow arch form and wide lip extension, tooth reveal behind the canines can be in shadow or disappear completely. This condition has been called deficient vestibular reveal31. Deficient vestibular reveal have negative esthetic consequences on smile.


Factors affecting smile

Aging and smile
The effects of aging on the exposure of the maxillary and mandibular central incisors in both resting and smiling positions was investigated by Choi et al.32. They reported that the amount of maxillary incisor exposure gradually decreased with age; this was accompanied by a gradual increase in mandibular incisal exposure in the smiling position. The sagging of the perioral soft tissue is partly due to the natural flattening, stretching, and decreasing elasticity of the skin33.
Tooth extraction and smile
Poor smile esthetics have also become one of the critiques of premolar extraction treatment in the highly politicized and commercialized extraction-nonextraction debate. It has been suggested that extraction of premolars lead to a narrowing of dental arch width and a decreased fullness of the dentition within the mouth during a smile34,35. In addition, this arch width reduction creates unaesthetic black triangles at the corners of the mouth and ‘negative’ spaces lateral to the buccal segments34,35. Despite these important issues, there are only few studies that have evaluated smile esthetics after orthodontic treatment6,36-38. However, none of these studies distinguished between extraction and nonextraction treatment effect on the smile.
Oral condition and smile
Oral conditions such as missing teeth, prostheses and malalignment like crowding and spacing influences smile39. It was reported that missing or malaligned teeth impair the smile39 and restoration of missing teeth improved the esthetic level of smile.
Personality and smile
Kim et al. investigated the correlation between personality factors and the smile, assuming that smile esthetics were closely related to an individual’s physical condition and psychologic state40. They concluded that extroversion and low anxiety were correlated to an attractive smile. Female’s personalities were correlated to attractive smiles but male’s personalities were not. The esthetic levels of female’s smiles were correlated significantly to personality. But for males there were no significant relationship between personality and smile esthetics.


Evaluation of smile

Observation of the smile is a good start; quantification of resting and dynamic lip-tooth relationships is critical to smile visualization and the information gathered from measuring smile characteristics can then be translated into terms meaningful to the treatment plan. Direct measurement permits the clinician to quantify resting and dynamic lip-tooth relationships. Direct measurement also has application in research efforts relative to time-related changes and the repeatability of the social smile. Systematic measurement of resting tooth-lip relationships virtually leads the clinician to a quantified treatment plan. Thus the following are the factors those affects the style of smile.
Philtrum height- It is a distance from subspinale (base of the nose at the midline) to most inferior portion of the upper lip on the vermilion tip beneath the philtrum columns. (Figure-8) In adolescents, philtrum height is often shorter than the commissure height and the difference is compensated by differential lip growth with maturation41-44.

Commissure height- It is measured from a line constructed from the alar bases through subspinale and then fromthe commissures perpendicular to this line. (Figure-8)

Figure 8. Philtrum height, Commissure height and Interlabial gap.

Interlabial gap- It is the distance between upper and lower lips when lip incompetence is present. (Figure-8)
Maxillary incisor show at rest- The amount of incisor show at rest is an important esthetic parameter and decreases with increase in age41. In an adult patient with 3mm of maxillary incisor display at rest should carefully be considered for intrusion, because with aging the incisor display diminishes which is a characteristic of the aging face.
Maxillary incisors show at smile- All part of the maxillary incisors is visible while smiling. The lower the smile index, the less youthful the smile appears. The percentage of incisor display in combination with crown height helps the clinician to decide how much tooth movement is required to improve the smile index.
Clinical crown height- In adults, clinical crown height is normally between 9mm and 12mm, with an average of 10.6mm in male and 9.6mm in female45. The age of the patient is a factor in clinical crown height because of the apical migration of the gingiva in the adolescents.
Gingival display- The amount of gingival display on smile that is acceptable esthetically can vary widely, but the relationship between gingival display and incisor show at rest is important. In general it is better to treat a gummy smile less aggressively, because aging naturally diminishes this characteristics. A gummy smile is often more esthetic than a smile with less tooth display.
Smile arc (Smile line)- Smile arc cannot be measured quantitatively and can only be observed. Hulsey6 found that the smile line ratio appeared to be important in an attractive smile. According to him the most attractive smile displayed a smile line ratio of 1.00:1.25. Tjan et al.11 reported that an average smile exhibits the full length of the maxillary incisor teeth, displays an incisal curve of the maxillary teeth that is parallel to the inner curvature of the lower lip, and displays the six maxillary teeth and the premolars.
In a recent study, Ackerman et al. evaluated the smile arc in both treated and untreated patients in their own practice46. Almost 40% of the treated patients showed a discernible change in the smile arc; flattening of the smile arc occurred in 32% of patients. In the untreated group, 13% had a change in the smile arc, and flattening of the arc occurred in only 5%. They noted no gender differences in the smile characteristics when the treated and untreated groups were compared46.
Smile index- Ackerman and Ackerman developed smile index, to quantify and to visualize the frontal smile. It is determined by dividing the intercommissure width by the interlabial gap during smile46,47. It describes the area framed by the vermilion borders of the lips during the social smile.
Smile should be evaluated in respect to four dimensions i.e. frontal, oblique, sagittal and time, the fourth dimension.
Evaluation of smile in frontal dimension
Lombardi pointed out that detailed esthetic judgments could only be made by viewing patients from the front, in conversation, facial expressions and smiling7. It is impossible to gain adequate information on dentofacial midline, alignment and right-left symmetry of canine and premolar torque unless the patient is observed directly from the front. In frontal dimension, the vertical and transverse characteristics of smile are visualized and quantified. Those factors pertaining to incisor and gingival display are vertical characteristics of smile. The relationship between the incisal edges of the maxillary incisors and the lower lip, and between the gingival margins of the maxillary incisors and the upper lip are other vertical characteristics of smile in frontal dimension.  Arch form, buccal corridor6,7,48 and transverse cant of the maxillary buccal plane are the transverse characteristics of smile in frontal dimension. Therefore, it is fundamentally important that the following esthetic factors should be analyzed by sitting or standing in front of the patient.
Crown lengths of maxillary and mandibular incisors
Lip coverage of the maxillary incisors tends to increase with age, and therefore the percentage of high smiles may be greater among younger age groups37,49 and smaller among older adults50There is also a sex difference in smile type: low smile lines are a predominantly male characteristic, and high smile lines predominantly female11.


Axial inclinations of all maxillary and mandibular incisors

The amount of anterior maxillary projection also greatly influences smile characteristics in the frontal view, even in terms of transverse smile dimension. In maxillary retrusion situation the wider portion of the dental arch is positioned more posteriorly relative to the anterior oral commissure. This creates the illusion of greater buccal corridor in the frontal dimension.
Maxillary incisor curve and lower lip
The parallelism of maxillary incisor curve and the lower lip is the “normal” finding in untreated persons, and should be an optimal goal for objective beauty in all kinds of esthetic oral rehabilitations49,50, including orthodontic and orthodontic-prosthetic treatment51. A straight or reverse smile line may contribute to a less attractive facial appearance7,51. In addition, the reverse curve is often associated with marked abrasive wear of the maxillary incisors. A survey by Tjan revealed that 85% of the students had a maxillary incisal curve parallel to the inner contour of the lower lip, 14% showed a straight rather than a curved line and 1% had a reverse smile line11.
Arch form
Arch form plays a pivotal role in the transverse dimension of the smile. Recently much attention has been focused on the use of broad, square arch forms in orthodontic treatment. When the arch form is narrow or collapsed, the smile may also appear narrow and therefore present inadequate transverse smile characteristics. The axial inclination of the posterior teeth has an important role while considering in widening a narrow arch form. Patients with upright posterior teeth are good candidate for arch expansion. Arch expansion reduces the size of buccal corridors and thus improving the transverse smile dimension. The wider the arch forms in the premolar area, the greater the portion of the buccal corridor that is filled. This is because transverse smile dimension is related to the projection of the premolars and molars into the buccal corridor. Arch expansion can result two undesirable side effects. First, the buccal corridor can be obliterated and resulting in a denture like smile. Second, when the anterior sweep of the maxillary arch is broadened, the smile arc may be flattened.
Buccal corridor
The presence or absence of the buccal corridors can be influenced not only by the broadness of the denture as discussed by Frush and Fisher, but also by the antero-posterior position of the maxilla relative to the lip drape52. Hulsey examined the influence of buccal corridors on the smile attractiveness and concluded that variation in buccal corridors seemed have no significance. Hulsey considered only six anterior teeth for measuring the buccal corridors. However, buccal corridors as defined by Frush and Fisher 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. Moore et al. 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. Fullness of the smile is but one feature that determines smile attractiveness53.
Transverse cant of the maxillary occlusal plane
Transverse cant of the maxillary occlusal plane can be due to differential eruption and placement of the anterior teeth or skeletal asymmetry of the mandible resulting in a compensatory cant of the maxilla. Only frontal smile visualization permits the orthodontist to visualize any tooth-related or skeletal asymmetry transversely. Either full face or close-up frontal smile photograph is better indicator of transverse dental asymmetry than the frontal retractor view. With good visualization and documentation of the tooth-lip relationships, orthodontist can make appropriate treatment planning and adaptations in appliance placement. Smile asymmetry may also be due to soft tissue consideration, such as an asymmetric smile curtain. In asymmetric smile curtain, there is a differential elevation of the upper lip during smile, which give the illusion of a transverse cant to the maxilla. This smile characteristic is poorly documented in static photographic images and is best documented in digital video clips.


Incisor display at rest and at smile  (Morley ratio)

It is necessary to ascertain whether the patient displays adequate gingival and dental architecture in smile frame. According to Morley and Eubank, if a patient displays less than 75% of the central incisor crowns at smile, tooth display is considered inadequate3. It is generally accepted that the gingival margins of the maxillary incisors should be coincident with upper lip in the social smile. Normally the gingival margins of the maxillary canines should be coincident with the upper lip and the lateral incisors positioned slightly inferior to the adjacent teeth. However such relationship is age related, as tooth display and gingival display are more in children then adults54.


Evaluation of smile in oblique dimension

In orthodontic patients, palatal plane can be canted antero-posteriorly in a number of orientations. In most desirable orientation, the occlusal plane is consonant with the curvature of the lower lip on smile. Deviation from this orientation includes a downward cant of the posterior maxilla, upward cant of the anterior maxilla or variations in both55. Thus it is important to visualize the relationship of occlusal plane to the lower lip during initial patient examination and diagnosis and treatment planning. Whether the posterior maxilla should be impacted or the anterior maxilla should come down depends on the amount of incisor show at rest and on smile and the smile arc relationship.
The visualization of the complete smile arc afforded by the oblique view expands the definition of the smile arc to include posterior teeth. The anatomic contributions to the smile arc are visualized best in the oblique dimension, but the factors influencing it are found in all three dimensions. The following treatment strategies can be used while attempting to alter the smile arc54.

  • Treating the occlusal plane in preadolescents with growth modification appliances can be advantageous.
  • In late adolescent and adult patients, surgical modifications of the maxillary occlusal plane are often indicated.
  • Bracket placement is also crucial to either maintaining or modifying the smile arc.

Conventional straight-wire prescriptions call for a 0.05mm difference in the incisal-edge-to-bracket-slot distance between maxillary central and lateral incisors. However, a distance of 1 to 1.5mm between lateral and central incisor bracket slots and the incisal edges is needed to preserve or create consonant smile arc145. This helps to superiorly position the lateral incisors and preserve the gradual sweep of the smile arc.

  • Cosmetic porcelain laminates or composite bonding can also play a role in enhancing the smile arc.
  • Enamel odontoplasty can be used to conservatively reshape the incisal edges of the maxillary anterior teeth during orthodontic finishing.

Evaluation of smile in sagittal dimension
Overjet and incisor angulation are the two characteristics of smile that are best visualized in the sagittal dimension. In terms of the smile, excessive positive overjet is not as readily perceived in the frontal dimension as it is in the sagittal dimension. For example, in many Class-II and III patterns, the smile is esthetic from front but the problem become obvious when observed from the side, which shows the underlying skeletal pattern and dental compensation. Incisor proclination can also have a dramatic effect on incisor display. Flared maxillary incisors as in Class-II division-1 malocclusion tend to reduce incisor display and uprighted incisors as in Class-II division-2 malocclusion tend to increase incisor display.


Evaluation of smile in relation to time (the fourth dimension)

The effects of age on the smile have already been discussed. However, the growth, maturation and aging of the perioral soft tissues have a pronounced effect on the social smile. Dickens et al.44 studied the changes in philtrum height and commissure height in patients from age 6 yrs to their 40s and relationship to the smile. They demonstrated the lengthening of the philtrum and commissure with increase of age. The rate of philtrum lengthening was greater than that of the commisssures. This explains the flattening of the ‘M’ characteristics of the vermilion border of the upper lip in the youthful lip.


Clinical implications


Clinical Implications for High Smile Types

A different treatment philosophy is needed for patients with high lip lines than for those with average or low smile types. Active maxillary incisor intrusion should be the goal in patients with high lip line. Treatment alternatives include various combinations of orthodontic, periodontal, and surgical therapy4,56,57. Intrusion base arches or utility arches may succeed in reducing a gummy smile orthodontically in some cases. Such treatment can produce a remarkable change in facial appearance5. Selective intrusive and restorative techniques can also be used to improve the final esthetic result in patients with fractured or overerupted and abraded incisors57,58. In other instances, gingival display can be eliminated by a simple gingivectomy or surgical crown lengthening with removal of crestal alveolar bone56-58. Such procedures are particularly indicated in cases with altered passive eruption, excessive gingival margins, and short clinical crowns, because they will expose more of the anatomical crowns. Treatment of the most severe gummy smiles may require maxillary superior repositioning surgery (Le Fort I osteotomy), along with reduction of the associated vertical maxillary excess4. This approach does have limitations, however, since the upper lip may be considerably shortened59,60.


Clinical Implications for Low and Average Smile Types

The correction of deep overbite can be accomplished by various combinations of intrusion of the anterior teeth and extrusion of the posterior teeth61. From the esthetic perspective, a serious mistake commonly made in orthodontic practice is “overintrusion” of the maxillary incisors. In most deep overbite cases, this will tend to hide the maxillary anterior teeth behind the upper lip in normal conversation. Such a mistake can go undetected by the orthodontist unless the patient’s tooth display and smile are analyzed from the front. With increasing age and concomitant drooping of the upper lip50, an unesthetic anterior tooth display may worsen. The maxillary incisors should be moved in the vertical direction that improves their relationship to the resting lip position, and the tooth-to-lip position should be monitored constantly throughout treatment. In some deep overbite cases, this may actually mean extrusion rather than intrusion of the maxillary incisors5,38. In most orthodontic patients, except those with marked “gummy” smiles, active intrusion of the maxillary incisors is undesirable. The best treatment strategy in the majority of deep overbite cases is to actively intrude the mandibular incisors, using double tubes on the mandibular first molars and continuous or segmented base arches61 or utility arches62. In a young patient with a short lower face, extrusion of the posterior teeth might correct a deep overbite, but the stability of such correction is uncertain, especially with less than adequate growth during and after treatment61. Another common mistake in orthodontic finishing is to create a straight (or even reverse) maxillary incisal curve relative to the smile line. Parallelism of the incisal curve and the inner contour of the lower lip in smiling may seem difficult to produce. In practice, however, this appearance can readily be achieved if the maxillary central incisors are symmetrically positioned .5-1mm longer than the lateral incisors63. If the lower lip shows a marked curvature in smiling, the distoincisal edges of the maxillary central incisors can be ground slightly without affecting functional occlusion64. It is particularly undesirable to combine maxillary incisor overintrusion with a straight arrangement of these teeth.

Conclusion

There is no universal “ideal” smile. The most important esthetic goal in orthodontics is to achieve a “balanced” smile65, which can best be described as an appropriate positioning of the teeth and gingival scaffold within the dynamic display zone. As mentioned previously, this includes lateral, vertical, and anteroposterior aspects, as well as the cant of the maxillary anterior transverse occlusal plane and the sagittal cant of the maxillary occlusal plane. Smile design and mechanotherapy must be built around this esthetic plane of occlusion, which is often different from the natural plane of occlusion55.  The first consideration in obtaining a consonant smile arc, or preserving an already consonant smile arc, is bracket positioning. Smile design also necessitates changes in overall treatment mechanics.
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Comments One Response

  1. Dr.Vinay.p

    12. Oct, 2010

    very informative article as a soft tisssue consideration during dental camouflage based on lip position.

    Reply to this comment

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