Smile Design

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© Springer Nature Switzerland AG 2021

P. Jain, M. Gupta (eds.)Digitization in Dentistrydoi.org/10.1007/978-3-030-65169-5_13

13. Digital Smile Design

Suprabha Hooda1   and Geeta Paul1
(1)

Department of Prosthodontics, Inderprastha Dental College, Ghaziabad, India
 
Keywords

Facial and dental componentsDigital shade matchingDigital smile designDental photography

13.1 Introduction

An attractive smile is always a desire of an individual for his or her social well-being and confidence. Aesthetics, being one of the most important pillars of dentistry, has always been a part of the research for better outcomes. Smile analysis and designing have been under focus in dentistry since last decade and necessitates a comprehensive approach to patient care.

Knowledge of interrelationships between dental anatomy and physiology and patient’s soft-tissue treatment limitations [1]. From the first generation when hand drawing on printed photos of the patient was used to communicate and explain the final outcome, it has now progressed into complete digital drawing on DSD software on a computer.

The chapter is divided into three parts for ease of understanding. The first part starts with explaining the analysis of dental and facial components required in a smile design followed by the digital shade matching instruments and its advantages over conventional technique and the various systems available commercially. It then goes on to discuss the requirements for a digital smile design technique (and the different software) which is a tool to design and modify the smile of patients and helps them to visualize it beforehand the final outcome. This section also includes information on photographic views required for smile designing. Various devices are now being used to visualize diagnosis and improve communication and enhance predictability throughout treatment. The chapter concludes with the future advancements in this field.

13.2 Historical Perspective

Smiles have been evidenced as early as 300 BC. In 1938, Dr. Charles Pincus described a technique in which porcelain veneers were retained by a denture adhesive during cinematic filming [2].

Introduction of veneers to the dentistry has resulted in the most aesthetic, least invasive treatment modality as these showed most demanding clinical performance in respect of strength, longevity, conservative nature and biocompatibility. Dr. Christian Coachman has been given credit for presenting smile designing in a digital means and proposed generations for the evolution of smile designing [3]. The first generation consisted of analogue drawings (with a pen) on a printed copy of photographs to visualize the treatment outcome. Digital dentistry was still not introduced, and there was no use of a study model. The second generation benefitted from 2D drawings and visual connection to the analogue model. This made it more accurate and less time-consuming. Although digitization had been introduced, it was still not specific to dentistry. The third generation was the era of the digital analogue connection when the first drawing software specific to digital dentistry was introduced. This linked the 2D smile design to a 3D wax mock-up. However, connection to 3D digital world was still not possible. The fourth generation progressed from 2D to 3D analysis involving facial integration and predetermined dental aesthetic parameters. The fifth generation was the complete 3D workflow followed by the latest sixth generation of the 4D concept by adding motion to the smile design process.

13.3 Principles of Smile Design

To obtain desired aesthetic outcomes, diagnostic data from questionnaires and checklists which are obtained from patients should be transferred adequately to the design of the restorations. The diagnostic data must guide the subsequent treatment phases, integrating all of the patient’s needs, desires and functional and biologic issues into an aesthetic treatment design. Recent advances in technology allow the clinician to measure dynamic lip-tooth relationships and incorporate that information into the orthodontic problem list and biomechanical plan.

The principles of smile design require integration of dento-facial composition and dental composition. The dental facial composition includes the hard and soft tissues of the face (lips and the smile as they relate to the face). The dental composition relates more specifically to the teeth (size, shape and positions) and their relationship to the alveolar bone and gingival tissues. Both the analyses are required for a smile design.

13.4 Facial Composition

There are two basic types of smiles (Fig. 13.1): social smile and enjoyment smile.

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Fig. 13.1

Anterior tooth display in social and enjoyment smiles; note difference in gingival show (Reproduced with permission from Journal of Clinical Orthodontics: Ackerman MB, Ackerman JL. Smile analysis and design in the digital era. J Clin Orthod. 2002;36(4):221–236)

Proper alignment, symmetry and proportion of face are believed to be the basic principles in facial aesthetics. When viewed from the frontal aspect, the basic shape of the face can either be square, square tapering, tapering or ovoid. When viewed from the lateral aspect, facial profile can either be convex, concave or straight. These facial features contribute to deciding the morphology of tooth.

The two facial features significant in a smile design are the inter-pupillary line and the lips [4]. The inter-pupillary line should be perpendicular to the midline of the face and parallel to the occlusal plane while the lips create the boundaries of the smile design.

The upper and lower lips form the border of the display zone of the smile. Within this zone lies the components of the smile i.e. teeth and the gingival scaffold (Fig. 13.2). The soft-tissue components of the display zone include lip thickness, inter-commissure width, inter-labial gap, smile index (width/height), and gingival architecture. Although the commissures of the lips form the lateral borders of the smile, the eye can perceive inner and outer commissures, (Fig. 13.3).

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Fig. 13.2

Smile components (Reproduced with permission from Journal of Clinical Orthodontics: Ackerman MB, Ackerman JL. Smile analysis and design in the digital era. J Clin Orthod. 2002;36(4):221–236)

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Fig. 13.3

Anatomy of commissures (Reproduced with permission from Journal of Clinical Orthodontics: Ackerman MB, Ackerman JL. Smile analysis and design in the digital era. J Clin Orthod. 2002;36(4):221–236)

The face can be divided into horizontal and vertical dimensions. The horizontal dimensional aspect (width of the face) should be the width of five ‘eyes’ and the distance between the eyebrow and chin should be equal to the width of the face (Fig. 13.4).

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Fig. 13.4

Horizontal dimension of the face (Courtesy Dr. Mohan)

The vertical aspect (facial height) is divided into three equal parts from the forehead to the eyebrow line, namely from the eyebrow line to the base of the nose and from the base of the nose to the base of the chin. The full face is divided into two parts with the eyes being the midline while the lower part of the face (from the base of the nose to the chin) is divided into the upper lip and the lower lip with the chin (Fig. 13.5).

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Fig. 13.5

Vertical dimensions of the face (Courtesy Dr. Mohan)

13.5 Dental Composition

I. Tooth Components
  1. (a)

    Dental midline.

     
  2. (b)

    Incisal length.

     
  3. (c)

    Tooth dimensions.

     
  4. (d)

    Axial inclination.

     
  5. (e)

    Zenith Points.

     
  6. (f)

    Incisal embrasures.

     
  7. (g)

    Interproximal contact area and interproximal contact points.

     
  8. (h)

    Sex, personality and age.

     
II. Soft Tissue Components
  1. (a)

    Gingival health.

     
  2. (b)

    Gingival level.

     
  3. (c)

    Smile line.

     
  4. (d)

    Interdental embrasure.

     

13.6 Tooth Components

13.6.1 Dental Midline

The midline, the vertical contact interface between maxillary central incisors, is evaluated by its location and alignment. Ideally, it should be perpendicular to the incisal plane and parallel to the long axis of the face. It should drop straight down from the papilla.

However, some minor discrepancies between facial and dental midlines (up to 4 mm) may either be sometimes not noticed or considered acceptable [5, 6]. Studies have suggested that 75% of maxillary midline do not coincide with the mandibular midline. Maxillary midline is considered as a reference point than mandibular midline as mandibular incisors either do not show or show minimal in smile position.

Midline should be:

  1. (a)

    Parallel to the long axis of the face.

     
  2. (b)

    Perpendicular to the incisal plane.

     
  3. (c)

    Over the papilla.

     

13.6.2 Incisal Length

Maxillary incisal edge position is the most important determinant in smile creation because once set, it serves as a reference point to decide the proper tooth proportion and gingival levels. This is related to labial and lingual contours of the tooth, anterior guidance and lip support which are vital in achieving both aesthetics and function. Patient’s input, phonetics and the amount of tooth display help us to locate this position. Phonetics is evaluated by asking the patient to pronounce alphabets like M, E, F, V and S in an erect sitting or standing position. In young individuals, incisal tooth display is more, approximately 3.5 mm, with decreases with age.

13.6.3 Tooth Dimensions

Correct dental proportion is related to facial morphology and is essential in creating an aesthetically 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 proportions of the centrals must be aesthetically and mathematically correct.

Tooth proportion is related to facial morphology with central incisors playing the dominant role in a smile. Hence, the proportions of central incisors must be both mathematically correct and aesthetically pleasing. The width to length ratio of the centrals should be approximately 4:5 (0.8–1.0); a range for their width of 75–80% of their length is most acceptable.

The lateral incisors and canines have their form and placement depending on the shape, size and location of the central incisors. The shape and location of the centrals influence the appearance and placement of the laterals and canines. Various guidelines for establishing correct proportions are [4].

  1. 1.

    Golden proportion (Lombardi)—This principle states that the width of each anterior tooth is 60% of the width of the adjacent tooth (the mathematical ratio being 1.6:1:0.6) (Fig. 13.6). Its applicability in clinical practice is limited due to differing arch forms, lip and facial proportions [7].

     
  2. 2.

    Recurring aesthetic dental proportions (RED) (Ward)—According to this, as we move posteriorly from the midline, the width proportion should remain constant from the facial aspect (Fig. 13.7).

     
  3. 3.

    M proportions (Methot)—is a comparison of the tooth width with the facial width.

     
  4. 4.

    Chu’s aesthetic gauges—is in support of the RED concept and refutes the golden proportion.

     
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Fig. 13.6

Golden proportion based on apparent width from the frontal view (Courtesy Dr. Mohan)

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Fig. 13.7

Recurring aesthetic dental proportion (Courtesy Dr. Mohan)

The author recommends using these as a guide rather than a rigid mathematical formula. Another important aspect to consider is the buccal corridor. This refers to the dark space (negative space) visible during smile formation between the corners of the mouth and the buccal surfaces of the maxillary teeth (Fig. 13.8). This space should be kept to a minimum during the smile design process and is minimized by restoring the premolars. However, it should not be completely eliminated because a hint of negative space imparts to the smile a suggestion of depth.

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Fig. 13.8

(a) Insufficiently developed buccal corridor; (b) properly developed buccal corridor (Courtesy Dr. Mohan)

13.6.4 Axial Inclinations

In this, we compare the central vertical midline to the vertical alignment of maxillary teeth that is visible in the smile line. As we move from central incisor to canine, the progressive increase in the mesial inclination of each subsequent anterior teeth should appear natural i.e. central incisors should be least noticeable, lateral incisors slightly more pronounced and canines the most pronounced. It also refers to the degree of tipping of the tooth.

13.6.5 Zenith Points

This is the most apical position of the cervical tooth margin. It is located distal to the long axis of the maxillary centrals and canines (Fig. 13.9). Location of these points is important in cases of diastema closure and correction of tooth angulation.

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Fig. 13.9

Zenith points and its relation to midline (Courtesy Dr. Mohan)

13.6.6 Incisal Embrasures

The size and depth of incisal embrasures must progress naturally from central incisors to canines. The apical contact point moves apically as we progress towards canines, mimicking the smile line (Fig. 13.10a). If this depth and variation in the embrasures is not achieved, then the dentition may impart to have a box-shaped appearance with teeth appearing too uniform and contact areas too long.

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Fig. 13.10

(a, b, c) (c) ICAs—50:40:30 rule, (b) ICPs—moves apically as we move from central to canine, (a) Incisal embrasure—increase in size and depth from central to canine (Courtesy Dr. Mohan)

13.6.7 Interproximal Contact (ICA) Area and Interproximal Contact Points (ICP)

ICA is the broad zone where two adjacent teeth touch. The zone coronal to ICA is called the spillway spaces or embrasures. The embrasures are important as they make a spillway for the escape of food during chewing and prevent food from being forced through the contact area. The area apical to ICA forms the interproximal spaces. The most incisal aspect of ICA is the interproximal contact point (ICP) [8]. As a general rule, as we go posteriorly, the ICP moves apically (Fig. 13.10b). The increasing ICA helps to create the illusion of longer teeth by wider and also extend apically to eliminate black triangles.

The design of the above zone varies with the form and alignment of teeth. ICA of maxillary teeth helps in defining the pink aesthetics for patients who have a high smile line. Tarnow et al. introduced the ‘mm rule’, which states that when the distance from the contact point to the interproximal osseous crest is 5 mm or less, there would be a complete fill of the gingival embrasures with interdental papilla. The chance of complete fill is progressively reduced by 50% for each millimetre increase above the 5 mm distance (the 50:40:30 rule) (Fig. 13.10c) [9].

13.6.8 Sex, Age and Personality

Differences in the length, shape and positioning of the maxillary teeth allow for different characterization (Table 13.1).

Table 13.1

Characteristics of SPA

Characteristics

Sex

Maxillary incisors

•  Females: Round smooth, soft delicate

•  Males: Cuboidal, hard vigorous

Personality

Maxillary canine

•  Aggressive, hostile angry: Pointed long ‘fangy’ cusp form

•  Passive, soft: Blunt, rounded, short cusp

Age

Maxillary central incisor

•  Youthful teeth: Unworn incisal edge, defined incisal embrasure, low chroma and high value

•  Aged teeth: Shorter; so less smile display, minimal incisal embrasure, high chroma and low value

13.7 Soft Tissue Components

13.7.1 Gingival Health

The gingiva frame symmetry of the smile. The health, colour and texture of the gingival tissues are paramount for long term success and the aesthetic value of the treatment.

The gingival height of contour of both maxillary central incisors should be at the same level, i.e. symmetrical. Cuspids may also have the same gingival level. If all the anterior teeth have the same height of contour, the smile may appear too uniform, thus appear un-aesthetic [10].

The amount of gingiva displayed is another key factor that is noted. A patient can have a gummy smile with teeth either being too short, at normal height or teeth that are too long [11]. When planning the smile makeover, interproximal papillae must have symmetry across the arch and black triangles avoided.

13.7.2 Gingival Level

Establishing the correct gingival levels for each individual tooth plays a vital role in the smile design process. The cervical gingival height (position or level) of the centrals should be symmetrical. The gingival margin of the lateral incisor is 0.5–2.0 mm below that of the central incisors. The least desirable gingival placement over the laterals is for it to be apical to that of the centrals and or the canines and is instead preferred to be located toward the incisal level (Fig. 13.11a). The darkness of the oral cavity should not be visible in the interproximal triangle (black triangle) between the gingiva and the contact area. A healthy and pointed papilla is preferred instead of a blunted tissue form that accomplishes a black triangle [12] (Fig. 13.11b).

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Aug 7, 2022 | Posted by in General Dentistry | Comments Off on Smile Design
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