The basic elements of dental occlusion need to be known because of the important role played by the dental structures in supporting and shaping the lower third of the face. The sagittal, vertical, and transversal relationship of the two arches during occlusion, as well as any crowding, loss, or abnormal shape of the teeth should be noted as a matter of routine during the direct facial lower third examination. Figure 8.1 shows the dental cast of a subject with optimal dental occlusion [3, 4].

Figure 8.2 shows the three basic sagittal relationships between the incisors (overjet). In the case of ideal overjet (Fig. 8.2a), the upper incisors are in front of the lower ones with little or no space between them. The increased overjet (Fig. 8.2b) consists of an excessive horizontal distance between the teeth, whereas the reverse overjet (Fig. 8.2c) requires that the lower teeth are in front of the upper ones.

The sagittal relationships between the dental arches can be divided into three main classes. Class I presents the ideal posteroanterior relationship between the two dental arches (Fig. 8.3a). Class II is a too anterior upper dental arch and/or a too posterior lower dental arch (Fig. 8.3b). Class III is a too posterior upper dental arch and/or a too anterior lower dental arch (Fig. 8.3c).

Figure 8.4 shows the three basic vertical relationships between the upper and lower incisors (overbite). In the case of ideal overbite, the upper incisors are in front of the lower ones with a limited overlap between them of 1–2 mm (Fig. 8.4a). The deep bite consists of an excessive overlap between the teeth (Fig. 8.4b), whereas the open bite (Fig. 8.4c) requires the presence of a vertical separation between the teeth.

Assessment of the occlusal transversal relationships considers the presence of a midline deviation between the dental arches, a crossbite between opposite teeth, and/or a cant of the occlusal plane (Fig. 8.5).

One important task of the examiner is to correlate the intraoral findings with the external facial appearance of the subject in order to establish the role of dental occlusion on the facial ­aesthetics. The long-term support effect of particular teeth on the lips and cheeks is also considered. With aging, the soft tissue envelope aesthetic is progressively more dependent on the skeletal support offered by well-aligned and correctly inclined frontal teeth and the surrounding alveolar bone (Fig. 8.6).

The upper frontal teeth need special attention in all patients, even if they are not mentioned in the patient priority list. Their role in overall facial aesthetics is so important that a qualitative and sometimes quantitative analysis can add many details that help in planning treatment. The upper frontal teeth consist of the four incisors, the two canines, and the four premolars; these teeth should occupy the larger part of the smile. The teeth shape, color, alignment, and symmetry must be evaluated, as well as the architecture and color of their gingival margin. Figure 8.7 shows the detail of well-proportioned and aligned upper frontal teeth.

One of the most difficult and at the same time most important aspects to assess is the anteroposterior projection of the upper teeth relative to the facial profile. The orthodontic literature has called this topic “anterior limit of dentition.” Clinically and using photographs, the full facial profile view at rest must be compared with the same during a posed smile. Figure 8.8 shows the assessment of the anterior projection of the upper incisors in three different clinical cases.

Two particular aesthetic problems of the upper incisors are the midline diastema and the black triangle. The midline diastema is represented by a space between the two upper incisors (Fig. 8.9b), whereas the so-called black triangle is a base-up triangular space bounded by an excessive mesial inclination of the two upper first incisors (Fig. 8.9c). In both cases, the observer and the patient usually perceive the dark shadow between the teeth as an aesthetic problem.

The spatial position and inclination of the incisors are discussed further in Sect. 9.6.

The first problem in the assessment of the lips is to obtain a truly relaxed position from the patient. When reviewing a complete set of photographs of a clinical case, it is not unusual to discover that the lip position is not constant but changes from a complete seal, most frequently at the start of the photographic session, to a more relaxed (habitual!) one with the presence of a more or less wide space between the two lips (Fig. 8.10). A partial nasal obstruction should be suspected when the subject has the habit of maintaining a space between the lips and breathing through the mouth.

Figure 8.11 shows a case of lip incompetence with absence of lip seal at rest due to an increased overjet with mandibular hypoplasia. In these cases, maintaining perfect lip closure requires a voluntary contraction that results in the flattening of the lip profile curves.