Which mandibular premolar is most likely to have three cusps?

The mandibular second premolar is most likely to have three cusps due to its anatomical variations. Typically, the second premolar has two common forms: the two-cusp type, which is similar to the first premolar with one buccal and one lingual cusp, and the three-cusp type. In the three-cusp variation, the second premolar features an additional cusp on the lingual side, which is a distinguishing characteristic. This additional cusp, often referred to as a distolingual cusp, can provide an increased functional surface area for chewing and contribute to the tooth's overall occlusal complexity.

In contrast, the first mandibular premolar generally has a simpler structure with only two cusps and is not known to develop an additional cusp variant like the second premolar. The maxillary premolars, although important in dental anatomy, are not relevant to this specific question regarding the mandibular premolars, as they differ in buccal and lingual cusp anatomy. As such, when assessing the likelihood of a mandibular premolar having three cusps, the second premolar stands out as the most likely candidate.