Final answer:
The effective strategy to increase tooth structure available for crown preparation when a tooth has an inadequate ferrule is through elective endodontic treatment and a post core.
Step-by-step explanation:
In order to increase the tooth structure available for crown preparation when a tooth has an inadequate ferrule, an effective strategy is to perform elective endodontic treatment and a post core. Elective endodontic treatment involves removing the damaged or infected pulp from the tooth and filling it with a material that provides support for the crown. A post core is a restoration that reinforces the tooth structure and provides a foundation for the crown.