Facial appearance

The facial appearance can firstly be assessed for facial asymmetries and skeletal relationship. With the patient’s teeth in contact, the lower face height should be assessed in proportion to the total face height, especially in patients complaining of missing teeth and tooth wear. Loss of teeth and occlusal stops could result in an overclosed appearance but a reduction in lower face height is unusual in patients with tooth wear. This is because of dento-alveolar development or compensation which counterbalances the loss in coronal tooth tissue height. In fact it has been suggested that dento-alveolar development takes place in the absence of tooth wear and some researchers have shown an increase in face height with age. This is the mechanism which leads to overeruption of teeth when taken out of occlusion – for example, by loss of an opposing tooth (Figure 6.4).

Figure 6.4 Loss of the lower left first and second molar teeth and upper left first and second premolar teeth has allowed overeruption of the opposing teeth. This now complicates their replacement as there is reduced height above the edentulous ridges.

Temporomandibular joints (TMJ)

The patient should be asked to open and close their mouth. The extent to which they can open should be measured between the incisal edges of the upper and lower incisor teeth. At maximum opening this should be more than 35 mm for women and 40 mm for men. Any limitation to opening should be recorded. Any deviation of the mandible on opening and closing from a normal vertical straight line should be observed and described. Gentle pressure over the head of the condyle should be applied when the patient opens and closes. This should be repeated with a finger in the external auditory meatus. Any tenderness, clicking or crepitus (grating sensation) should be noted and when they occur in the opening–closing cycle.

Intercuspal position (ICP)

Intercuspal position can be defined as the position of the jaws when the maxillary and mandibular teeth are in maximum intercuspation. This has also been referred to as centric occlusion. Patients usually close from a rest position immediately into this position due to a conditioned path of closure. It is important to establish whether the occlusion in ICP is stable; that is, an occlusion where there is no possibility of tooth movement, namely overeruption, drifting or tilting of teeth (Figure 6.5). If teeth are extracted or lost due to other causes, or if they lose their contour (a carious lesion cavitating, tooth fracture, tooth wear), occlusal contacts and interdental contacts, teeth can move, often complicating any subsequent restorative work (Figures 6.4 and 6.6).

Figure 6.5 Patient with a stable intercuspal position (ICP): all interdental and occlusal contacts are intact preventing any tooth movement.

Figure 6.6 Patient with a heavily restored dentition. Repeated loss of the restoration in the lower left first premolar tooth has allowed overeruption of the upper left canine.

(Courtesy of Suzanne Blacker)

When teeth overerupt in the absence of periodontal disease, the alveolar process remodels and the gingival margin moves with the tooth (see Figure 5.3, Chapter 5). This dento-alveolar compensation can happen quickly in some patients and is a reason why temporary crowns should be placed following tooth preparation for crowns or bridges; the occlusal and proximal reduction will result in an unstable occlusion and if no temporary is placed, overeruption and drifting of teeth could occur. This would result in a prosthesis that does not seat fully and appear to be occluding prematurely or appear ‘high’ in ICP.

Centric relation, terminal hinge axis position and retruded contact position (RCP)

Centric relation describes the jaw relationship between the maxilla and mandible when the mandible is in a retruded position. Differing definitions of centric relation have focused on slightly different positions of the condyle in the glenoid fossa and some on the relationship of the head of the condyle to the interarticular disc. These are rather academic arguments as clinically the position of the condyle cannot be visualized or confirmed without complex equipment. A more pragmatic and practical definition was proposed by Christensen in 2004 which conforms to most dentists’ clinical practice. He described centric relation as the ‘most comfortable posterior location of the mandible when it is bilaterally manipulated gently backward and upward into a retrusive position’. When this is done the mandible opens and closes on an arc of curvature around an imaginary axis drawn through the centre of the head of both condyles; this imaginary axis is termed the terminal hinge axis (Figure 6.7). Measured in the incisor region the arc of opening around the terminal hinge axis position takes place for about 20 mm before the condyles start to translate down onto the articular eminence (Figure 6.8). When the mandible closes in the terminal hinge axis position the first tooth contact is called the retruded contact position (RCP). The terminal hinge axis position is said to be the most reproducible jaw relationship; however, small variations from day to />