Chapter 17 When and how to replace missing teeth

Do we need to replace missing teeth?

The loss of any tooth does not automatically mean the need for a prosthetic replacement. Patients should be aware that tooth replacement has a biological and financial cost with a long-term commitment to maintenance. Complications can arise with any restorative intervention and a sound justification for tooth replacement is required. Patients should always be informed of the alternatives, irrespective of cost, for tooth replacement and they should be informed of the potential advantages and disadvantages to each. It is only then that informed consent can be given by the patient.

When to replace missing teeth?

Appearance

Tooth loss can have a devastating effect on a patient’s appearance, self-confidence and motivation. The loss of an upper central incisor is an obvious indication for prosthodontic replacement (Figure 17.1), but the technical challenges of designing the restoration must be taken together with the impact of the ‘smile line’. This assessment should be undertaken when the patient is talking and smiling in a relaxed environment and not from under forced conditions! For some patients the replacement of an upper premolar tooth may be unnecessary, but for those with a wide and high smile line tooth replacement may be justified. Whatever the clinical situation, it is advisable that tooth replacement based on appearance should be led by the patient and not the dentist.

Figure 17.1 A patient with a missing upper left central incisor tooth which poses a major aesthetic problem. The patient also has a high and wide smile line involving both first and second premolar teeth.

Occlusal stability

When a tooth is missing the occlusion can change, with overeruption, tilting or drifting of opposing or adjacent teeth, causing a condition commonly referred to as an unstable occlusion. Consider the 25-year-old patient in Figure 17.2. The loss of the upper first and second premolar and lower first and second molar teeth has led to an unstable occlusion. The failure to replace these missing teeth led to overeruption of the lower second premolar and upper first and second molar teeth into the opposing edentulous spaces. This now complicates prosthodontic replacement as there is inadequate space between the teeth and opposing edentulous ridge.

Figure 17.2 A patient with an unstable occlusion and overeruption of the lower premolar and upper molar teeth. Note the alveolar tissues have accompanied the tooth movement, hence the term dento-alveolar compensation.

The overeruption of teeth into edentulous spaces does not always occur and is impossible to predict. Therefore, if restoration of occlusal stability is the only clinical indication for tooth replacement following an extraction, it is advisable to monitor tooth movement over time. This tooth movement or dento-alveolar compensation can occur quickly in some patients and the tooth movement seen in the patient in Figure 17.2 occurred after 6 months. To avoid such a clinical situation, review appointments should be advised and a suggested timing would be after 3 months in the first instance. Baseline study models taken soon after the extraction may also be useful in confirming any tooth movement.

Function

Mastication

Patients frequently complain of difficulty in eating and trauma to the edentulous ridges following tooth loss. The latter problem can only be addressed with a prosthodontic replacement but the former is subjective and individual to each patient. There is little evidence to confirm that loss of molar teeth is accompanied by a significant loss of masticatory function. To the contrary, there is a large body of evidence to support the concept of the shortened dental arch (SDA) (Kanno & Carlsson, 2006). The posterior teeth are mainly involved in mastication and the SDA was proposed as a treatment option if molar teeth had been extracted. The minimum number of occluding pairs of teeth was the four premolar teeth or two pairs of occluding molar teeth. Today, the SDA is generally accepted as a premolar to premolar occlusion, following the loss of the molar teeth.

Opponents to the concept of the SDA have cited loss of masticatory function, mandibular displacement and problems such as temporomandibular dysfunction (TMD). There is some evidence to suggest that these complications are more likely in younger patients and those with unilateral tooth loss. In addition, some patients have reported difficulty in chewing harder foods though they tend to modify their diet accordingly. The other important factor in assessing the role of the SDA is the challenges associated with the prosthodontic replacement of molar teeth. For many patients replacing molar teeth with implants is prohibitively costly and the alternative of removable prostheses, particularly in the mandible with free-end saddles, means denture-based solutions are often not successful. The strength of evidence strongly supports the concept of adopting the SDA when the molar teeth have been extracted.

Does the SDA lead to increased wear of remaining teeth?

It would seem logical that if patients have missing molar teeth and a lack of ‘posterior support’, there would be increased tooth wear of the remaining teeth as these take the entire functional load. This is a frequent comment and perhaps misconception of many dentists. In those patients with tooth wear the rate generally increases over a lifetime but those without evidence of wear are unlikely to develop wear following the loss of the teeth.

The patient in Figure 17.3 has lost all their posterior teeth and due to the severity of posterior alveolar ridge resorption is unable to wear a successful removable prosthesis. The lower anterior teeth are worn, with cupping of the incisal edges resulting from erosion, though attrition might be a contributing factor to the tooth wear. Whether the tooth wear would have reached the same severity if the posterior teeth were present is unknown.