Which tooth most commonly has only 3 cusps?

Maxillary third molars are highly variable in morphology and are most commonly described as having three cusps (forming a triangular or 'compressed' crown outline): the mesiobuccal, distobuccal, and lingual cusps. This is due to the frequent reduction or absence of the distolingual (Carabelli) cusp seen on maxillary first and second molars. Mandibular third molars typically display 4–5 cusps but are also highly variable. The maxillary 3rd molar's three-cusp triangular form is its most characteristic and commonly tested morphology.