The human mouth contains a variety of teeth, each uniquely shaped for a specific role in the process of eating. Teeth in the front, like the incisors and canines, are designed for cutting and tearing, while molars in the back are built for heavy grinding. Situated between these two functional extremes, the premolar tooth serves as a crucial transitional element in the dental arch. This intermediate position gives premolars a mixed anatomy and function, allowing them to share in the tearing process and initiate the powerful crushing that follows.
Defining the Premolar Tooth
Premolar teeth are permanent teeth located directly behind the canines and immediately in front of the molars. Humans generally possess eight premolars in total, with two located in each of the four quadrants of the mouth.
In each quadrant, the tooth closest to the midline is designated as the first premolar, followed by the second premolar. This consistent positioning places them perfectly to receive food that has been initially torn by the canines.
Distinctive Anatomy and Structure
The structure of the premolar tooth is a blend of the canine’s sharp point and the molar’s broad surface. Their most distinguishing feature is the occlusal, or biting, surface, which typically features at least two main elevations, or cusps. This characteristic is the reason for the common name bicuspid.
The cusps are typically separated by a central groove and are not as pronounced or numerous as the four or five cusps found on a molar. While most premolars have two cusps, the mandibular (lower) second premolar frequently exhibits three distinct cusps. The shape is generally wider than a canine but narrower than a molar, providing a surface that is effective for both grasping and crushing.
Most premolars are anchored in the jawbone by a single root. A notable exception is the maxillary (upper) first premolar, which often has two roots, though a single root is also possible.
Role in Mastication
The primary function of the premolars is to act as a transitional tool in the process of mastication. They take food from the canines and begin the process of breaking it down before it moves further back.
Premolars participate in tearing and gripping food, a function inherited from the adjacent canines. Their broader occlusal surface and cusps enable the initial crushing and grinding of food particles. They reduce the size of the food pieces, preparing them for the final grinding performed by the molars.
Premolars also play a role in maintaining the correct vertical dimension of the face. By supporting the height of the bite, they help ensure the upper and lower jaws meet correctly when closed. Their robust positioning helps stabilize the dental arch during the forces generated by chewing.
Development and Replacement
Premolars are part of the permanent set of teeth and are not present in a child’s initial primary dentition. Calcification for the second premolars often begins between the ages of two and three years. These teeth typically begin to erupt into the mouth later in childhood, usually between the ages of 10 and 12.
The permanent premolars replace the primary molars, which are the largest teeth in a child’s mouth. This is a unique distinction, as permanent molars do not replace any primary teeth. The primary molars are shed, and the developing premolars move into their place to form the adult dental arch.
The eruption of the premolars establishes the full complement of adult teeth necessary for a diverse diet. They solidify the bridge between the anterior teeth, used for biting and incising, and the posterior teeth, solely dedicated to the final stages of grinding.