Which premolar most commonly presents with three cusps?

The mandibular second premolar is the only premolar that regularly presents with three cusps: one buccal cusp and two lingual cusps (mesiolingual and distolingual). In its three-cusp form (Y-type), it also typically has three grooves and three pits. This three-cusp variant occurs in approximately 30–40% of cases; the two-cusp form is also common. The mandibular first premolar usually has one large buccal cusp and a small, non-functional lingual cusp. Maxillary premolars typically have two cusps (buccal and lingual), though the maxillary first premolar sometimes has a prominent mesial root groove.