For the mandibular molar tipped mesiolingually, whose proximal undercut cannot be approached by ordinary means, which clasp assembly is indicated?

Correct answer: B. A ring clasp

• A. The I-bar is an infrabulge retainer approached from the gingival direction, used on a distal extension abutment with a mesiobuccal undercut. It does not solve an inaccessible proximal undercut on a tipped molar.
• B. CORRECT. The RING CLASP is a circumferential retainer that encircles nearly the entire tooth from its point of origin, and its specific indication is precisely this — a proximal undercut that cannot be approached by other means. It is used for TIPPED molars: mandibular molars tipped mesiolingually and maxillary molars tipped mesiobuccally. On a mandibular molar it originates on the mesiobuccal surface and terminates in the infrabulge area of the mesiolingual surface. Because such a long arm is inherently flexible, it REQUIRES a supporting strut on the non-retentive side, with or without an auxiliary occlusal rest on the opposite marginal ridge; that auxiliary rest also prevents further movement of the tooth.
• C. The embrasure or double Akers clasp is used on the side of the arch with NO edentulous space, passing through the embrasure between two adjacent posterior teeth.
• D. An Akers clasp needs an accessible undercut on the surface away from the edentulous area. On a tooth tipped in this way that undercut is unreachable, which is the whole premise of the question.

Note: Clasps are classified four ways worth memorising: by COMPOSITION (cast or wrought wire), by CONFIGURATION (circumferential or bar), by FUNCTION (retentive or reciprocal), and by DIRECTION OF APPROACH to the undercut (suprabulge or infrabulge). RPA = mesial Rest, distal Proximal plate, Akers wrought-wire retentive arm — the substitute for RPI when a bar cannot be used because of a shallow vestibule, a severe tissue undercut or lingual tori.