Introduction

The dentogingival complex may be considered an aesthetic unit of the face, i.e. the dentogingival aesthetic unit, composed of the gingival subunit and the dental subunit.

Anatomy

The teeth occupy approximately one‐fifth of the surface area of the oral cavity in adults. They serve the important functional role of mastication and are essential for proper speech and dentofacial aesthetics. In mammals, the teeth are attached to the supporting alveolar bone by a fibrous connective tissue, termed the periodontal ligament (PDL); the flexibility of the PDL within this structural relationship permits the teeth to withstand the considerable forces of mastication. In humans, the succession of the primary (deciduous) dentition by the larger and more numerous teeth of the secondary (permanent) dentition accommodate the substantial growth of the face and jaws.¹

Anatomically, the teeth consist of a crown and a root; the junction between the two is termed the cervical margin. The term clinical crown refers to the part of the crown visible in the oral cavity. The anatomical crown is covered by enamel, which is a hard, acellular and relatively brittle tissue; it is the most highly mineralized tissue in the human body (96% mineralized). Enamel would be unable to withstand the forces of mastication without fracture was it not for its support from the resilient underlying specialized connective tissue termed dentine. Dentine is a relatively hard (70% mineralized), avascular tissue; it is yellowish‐white, which gives teeth their colour. It is sensitive and more importantly, capable of repair by the laying down of secondary dentine by cells called odontoblasts, which initially form the dentine and subsequently line the periphery of the dental pulp. The dentine encloses the central pulp chamber, which is filled with a soft connective tissue called the pulp.

The oral cavity is lined by oral mucosa (oral mucous membrane), which is comprised of the following:²

• Masticatory mucosa: This covers the gingivae and the hard palate. It is tightly bound down to the underlying bone and the covering epithelium is heavily keratinized.
  
• Specialized mucosa: This covers the dorsum of the tongue and is similar to masticatory mucosa but contains papillae and taste buds.
  
• Lining mucosa: The remaining mucosa of the oral cavity is relatively mobile, i.e. the labial and buccal mucous membrane and the mucosa of the soft palate and pharynx.

The term periodontium (Greek peri‐: around; odontos: tooth) refers to the supporting tissues of the teeth. It is comprised of the following component parts:

• Gingiva: This refers to the part of the masticatory mucosa that covers the alveolar process and surrounds the cervical portion of the teeth. The gingiva is comprised of two parts:
  
  
  
  • Free gingiva (Figure 24.1): Healthy free gingiva is pink in colour and has a firm, smooth consistency. It comprises the buccal, lingual and interdental gingival tissue and the interdental papillae. On the buccal and lingual side of the teeth, the free gingiva extends from the free gingival margin apically towards the free gingival groove (only visible in 30–40% of adults), which is positioned at a level corresponding to the cementoenamel junction (CEJ). The typical scalloped gingival margin contour runs parallel to both the underlying osseous crest and the CEJ. In fully erupted teeth, the free gingival margin is located 0.5–2 mm coronal to the CEJ.² In healthy gingivae, the free gingiva is in close contact with the tooth enamel surface, though it is possible to gently probe the gingival sulcus (or gingival crevice) in the enamel–gingiva interface approximately to the level of the CEJ.

    

    
    
  • Attached gingiva: This extends apically from the free gingival groove or, when such a groove is not present, from a horizontal line level with the CEJ, to the mucogingival junction, where it becomes continuous with the lining alveolar mucosa of the oral cavity. Healthy attached gingiva is pink in colour and may exhibit an ‘orange peel‐like’ stippled appearance in some individuals. It is firmly attached to the alveolar bone and relatively immobile compared to the loosely bound and darker alveolar mucosa.
  
  
• Periodontal ligament: This is the soft, richly vascular and cellular connective tissue that surrounds the roots of the teeth, connecting the root cementum to the alveolar bone of the tooth sockets. The PDL space is about 0.2 mm in width and contains sensory receptors.
  
• Root cementum: This is the specialized calcified tissue (50% mineralized) covering the root surfaces of the teeth.
  
• Alveolar bone: This is the bone of the alveolar process of the maxilla and mandible that forms and supports the sockets of the teeth. It is firmly attached to the basal bone of the jaws. It is important to bear in mind that the alveolar process forms in relationship to the teeth; as such, tooth loss results in eventual resorption of the alveolar process. This is particularly evident in edentulous patients whose chin and nose approximate as a result of alveolar bone resorption and subsequent reduction in lower anterior face height.

Clinical evaluation

The position of the maxillary incisor crowns in relation to the face in the evaluation of dentofacial aesthetics has been described (see Chapter 23). The shape and size of the maxillary incisor crowns form the starting point in the clinical evaluation of dentogingival aesthetics.

Tooth shape

The morphology of the maxillary incisor crowns, as observed in frontal view, involves the amalgamation of the three basic geometrical shapes, i.e. the circle, square and triangle, from which any shape may be created. Tooth shape is genetically determined and there is considerable individual variability. The overall shape of the crowns of the maxillary incisor teeth in each individual will fit predominantly into one of the following categories (Figure 24.3):

• Ovoid: combination of circle and square/rectangle.
  
• Rectangular: elongated square.
  
• Triangular.

Tooth morphology is remarkably consistent.⁵ When aberrations in the shape of teeth do occur, most commonly in the maxillary lateral incisor crown, which may be peg‐shaped or diminutive, and the third molars, it is as a result of some effect early in the developmental history of the tooth. In fact, the crown pattern of each tooth is determined during the bell stage of dental development.¹

Theories of ‘ideal’ tooth shape

A number of theories have been proposed regarding maxillary incisor crown morphology:

• Tooth shape–face shape correlation: In 1887, Ivy⁶ proposed the temperamental theory, which suggested that an individual’s personality influenced the morphology of the teeth. Williams^7–9 dismissed the temperamental theory, proposing that the shape of the maxillary central incisor crown was related to the inverted frontal view of the face, the so‐called geometric theory. This theory was also subsequently invalidated, but led to the work of House and Loop.¹⁰
  
• Tooth width–face width correlation: House and Loop¹⁰ described the relationship between the width of the maxillary central incisor crown and the bizygomatic facial width, with a ratio of 1:16. LaVere et al.¹¹ subsequently confirmed this finding. Such a correlation may not be absolutely accurate, but is a useful starting point (Figure 24.4).

  

  

  

  

  
  

  Radia et al.¹² undertook a prospective clinical investigation to determine the relationship between maxillary central incisor proportions and facial height and width in adults. The ‘biometric ratio’ of 1:16 for maxillary central incisor:bizygomatic width was not reconfirmed exactly, but very closely, with a mean ratio of 1:15.6. A ratio of 1:18 was proposed for maxillary central incisor height to total face height (Tr‐Me’) and 1:12 for face height (N’‐Me’).

  
  
• Sex, age and personality (SAP) theory: Frush and Fisher (1955)¹³ suggested a correlation between the sex, age and personality of an individual and the shape of the maxillary incisor and canine teeth; this concept was originally proposed for guidance in tooth selection for denture aesthetics (Figure 24.5).
  
  
  
  • Sex: The feminine facial form tends to display ‘soft’ curvilinear relationships and is devoid of sharp line angles, whereas masculine faces tend to have increased angularity. Accordingly, the shapes of the maxillary incisor crowns in women tend to be ‘softer’, with rounded angles.¹⁴
    
  • Age: Attrition may be defined as tooth surface loss (tooth wear) due to repetitive physiological or parafunctional occlusal contact between the teeth. In younger individuals, the incisal edges of the maxillary incisor teeth are unworn, and may present with mammelons, which usually appear as three small rounded prominences on the incisal edges of the incisor teeth (Figure 24.6). Tooth wear from attrition results in a reduction in incisor crown height, which often accompanies the ageing process. However, the aetiology of tooth wear is multifactorial, and younger individuals may present with excessive attrition. Conversely, older individuals with anterior open bites may still possess mammelons. Elderly individuals are sometimes described as being ‘long in the tooth’. This is partly due to buccolabial gingival recession, which has a multifactorial aetiology, but is correlated with increasing age (Figure 24.7).
    
  • Personality: The concept suggests that individuals with extrovert personalities may be better suited to increased incisor exposure with brighter teeth, as opposed to introverts. This concept is not evidence‐based and remains debatable.

Tooth size

Tooth size is genetically determined. Tooth size does not necessarily correlate well with standing height or stature, i.e. a tall individual may have small teeth. However, men tend to have larger teeth than women, and black individuals tend to have larger teeth than Caucasians.¹⁸ Maxillary incisor crown size may be measured as the mesiodistal width, the inciso‐gingival height and the width‐to‐height ratio. Various authorities have provided data on maxillary incisor crown dimensions in Caucasian individuals, from which are derived the following ‘average’ dimensions:

• Average crown width: 8–9 mm.
  
• Average crown height: 10–11 mm.

Width‐to‐height ratio of maxillary central incisor crown

The average width‐to‐height ratio of the maxillary central incisor crown is 0.75–0.8, i.e. the crown width should be 75–80% of its height (Figure 24.8). A ratio of less than 60% creates a tall narrow crown, whereas a ratio greater than 85% results in a short wide crown appearance. This ratio is more important than the component crown width or height.

Cooper et al.²⁰ undertook an attractiveness research investigation to determine the influence of varying the width‐to‐height ratio of maxillary central incisors on perceived smile aesthetics. They found that an 82% (+/− 4%) width‐to‐height ratio was perceived as the most attractive for normal central incisors, although there was variability in the rater responses. There is a definite trend towards the extremes of very long or very short teeth being less attractive. The very ‘long’ central incisors, and those with tooth wear were perceived as unattractive. The investigators also found significant differences between the aesthetic perceptions of dentists, dental technicians and patients and also lack of agreement within each group, in particular within the patient group. The individual variability in patient response should be considered during treatment planning.

Seventh key and dental occlusion

Tooth size is described as the seventh key to ‘ideal’ dental occlusion, the other six morphological characteristics of an ‘ideal’ occlusion represented as Andrew’s six keys (i.e. Class I molar relationship, correct crown angulation and inclination, no rotations, no spaces and a level curve of Spee) (see Chapter 22). The presence of a tooth size discrepancy will either result in a spaced dentition or a less than ideal dental occlusal relationship.

Tooth size analysis

For ‘ideal’ dental aesthetics, the anterior teeth must be proportional in size as described above. Additionally, for ‘ideal’ dental occlusion, the maxillary and mandibular teeth must have a certain proportionate relationship in terms of size. It will not be possible to achieve an ‘ideal’ occlusion if individual teeth or groups of teeth in the maxillary or mandibular arches are either too large or too small compared to their antagonists in the opposing dental arch. Such a discrepancy is termed tooth size discrepancy.

Evaluation of tooth size is an important part of clinical diagnosis. Tooth size analysis (also termed a Bolton analysis after its development in 1958 by the orthodontist Wayne Bolton) may be undertaken by measuring the mesiodistal widths of either the anterior teeth (canine‐to‐canine) or the entire arch (first molar to first molar, excluding second and third molars).²¹ A table of standard values (Table 24.1; based on Caucasian values) lists the summed tooth width value in the opposing arch that is ideally related to the measured value, i.e. it is used to compare the summed widths of the maxillary to the mandibular anterior teeth (anterior Bolton ratio) or the summed widths of the entire maxillary to the mandibular arch (overall Bolton ratio).²² The difference between the ‘ideal’ value from the standard table and the actual measured dental width in the arch with the excess value provides an estimate in millimetres of the extent of tooth size discrepancy.

It has been demonstrated that a significant number of patients have a tooth size discrepancy of greater than 2 mm, which is clinically significant as it may affect the dental occlusion. Additionally, simple visual estimation has been shown to be inaccurate at determining a tooth size discrepancy.²³

Maxillary anterior 3–3 summed widths (mm)	Mandibular anterior 3–3 summed widths (mm)	Maxillary total 6–6 summed widths (mm)	Mandibular total 6–6 summed widths (mm)
40	30.9	86	78.5
41	31.7	88	80.3
42	32.4	90	82.1
43	33.2	92	84.0
44	34.0	94	85.8
45	34.7	96	87.6
46	35.5	98	89.5
47	36.3	100	91.3
48	37.1	102	93.1
49	37.8	104	95.0
50	38.6	106	96.8
51	39.4	108	98.6
52	40.1	110	100.4
53	40.9
54	41.7
55	42.5