Whether a shortened dental arch needs to be extended depends on the degree of the shortening. Four categories of shortened dental arches can be distinguished: 1. slightly shortened dental arches; 2. moderately shortened dental arches; 3. extremely shortened dental arches; and 4. asymmetrical extremely shortened dental arches. Decision-making on extending a shortened dental arch should be based on oral function and the patient’s perceived impact on oral health-related quality of life. According to this principle, there is no evidence for extending slightly shortened dental arches. Extending moderately shortened dental arches is indicated in exceptional cases, especially for aesthetic reasons. In the case of (asymmetrical) extremely shortened dental arches there are reasons for extension. The extension can be restricted to restoring the arch to the level of a moderately shortened dental arch. With this treatment strategy, it is possible in many cases to conform to the current trend of using fixed partial dentures rather than removable partial dentures.