A patient presents with a fractured lingual cusp on a mandibular premolar. What is the MOST important initial assessment before determining the treatment plan?

Before initiating any treatment for a fractured cusp, the most critical first assessment is restorability — determining whether sufficient tooth structure remains to support a restoration and whether the fracture extends below the alveolar bone level (which would render the tooth unrestorable/requiring extraction). Restorability drives the entire treatment plan: if the tooth is restorable, further testing (pulp vitality, percussion, periodontal probing) guides the type of restoration needed. If the tooth cannot be restored, no further testing changes the need for extraction. Pulp vitality and percussion guide whether endodontic treatment is needed, but only if the tooth is first determined to be restorable.