Final answer:
The primary mandibular first molar has four cusps - two buccal and two lingual. These cusps are used to crush food for swallowing. This tooth is part of the 20 deciduous teeth in primary dentition, replaced later by permanent teeth.
Step-by-step explanation:
Morphology of the Primary Mandibular First Molar
The correct trait for a primary mandibular first molar is B) Four cusps - two buccal and two lingual. These molars are designed to crush food so that it is ready for swallowing. Each molar in the posterior region of the mouth is equipped with multiple cusps for this purpose. More specifically, the primary mandibular first molar usually has two buccal cusps located on the cheek side and two lingual cusps on the tongue side.
In general, the primary dentition, which includes molars, is characterized by the presence of 20 deciduous (baby) teeth. These are replaced by 32 permanent teeth during childhood. Among these permanent teeth, the primary mandibular first molar emerges during the developmental phase and is crucial for proper mastication of solid foods.