The incisogingival length of the lingual dovetail in tooth preparation is approximately 25 mm to ensure adequate retention and resistance form. This length allows the dovetail to engage sufficient tooth structure, preventing dislodgment of the restoration during function. A length shorter than 25 mm may compromise the mechanical lock, while a longer length can unnecessarily weaken the tooth. Proper dimensions of the lingual dovetail are critical for the longevity and stability of indirect restorations.

Reference: Principles of Operative Dentistry, 4th Edition.