A premolar typically has two main cusps, a characteristic that leads to its common designation as a "bicuspid" tooth. These two prominent cusps are a buccal (cheek-side) cusp and a palatal (roof of the mouth side) or lingual (tongue-side) cusp, which are separated by a mesiodistal occlusal fissure.
However, the exact number can vary depending on the specific premolar. While two main cusps are standard, some premolars, particularly the mandibular (lower jaw) second premolar, frequently present with three cusps.
Understanding Premolar Cusps
Premolars, also known as bicuspids, are transition teeth located between the canines and molars. They play a crucial role in grinding food, acting as a bridge between the tearing function of canines and the heavy grinding of molars. Their characteristic cusps are essential for this function.
The Two Main Cusps
As their name "bicuspid" suggests, premolars are defined by having two prominent cusps. These are:
- Buccal Cusp: The cusp located on the side of the tooth facing the cheek. This is often the larger and more pronounced cusp, especially in maxillary (upper jaw) premolars.
- Lingual/Palatal Cusp: The cusp located on the side of the tooth facing the tongue (lingual) in the mandible or the palate (palatal) in the maxilla.
These two main cusps are separated by a central groove or fissure running from the mesial (toward the midline) to the distal (away from the midline) aspects of the tooth's chewing surface.
Variations in Cusp Count
While two main cusps are the general rule, dental anatomy exhibits variations, particularly in the mandibular second premolar.
- Maxillary Premolars (Upper Jaw):
- Maxillary First Premolar: Almost always has two distinct cusps: one large buccal and one smaller palatal.
- Maxillary Second Premolar: Typically has two cusps, with the buccal and palatal cusps being more equal in size compared to the first premolar.
- Mandibular Premolars (Lower Jaw):
- Mandibular First Premolar: Characteristically has two cusps: a large buccal cusp and a very small, often non-functional, lingual cusp. While technically two, the lingual cusp is so diminutive that it barely contributes to the chewing surface.
- Mandibular Second Premolar: This tooth is notable for its variability. While it can have two cusps (one buccal, one lingual), it very commonly presents with three cusps: one buccal and two distinct lingual cusps (mesiolingual and distolingual). These three cusps often form a Y-shaped occlusal groove pattern.
Why Do Premolars Have Cusps?
The cusps on premolars are integral to their function in the oral cavity. They facilitate:
- Mastication (Chewing): The raised cusps and depressions (fissures) on the chewing surface help to grip, tear, and grind food effectively.
- Occlusion: The cusps interlock with the opposing teeth in the other arch, ensuring proper alignment and distributing biting forces evenly.
- Tooth Structure: Cusps add strength and resilience to the tooth, helping it withstand the significant pressures of biting and chewing.
Premolar Cusp Summary Table
| Premolar Type | Typical Cusp Count | Description
