A dental arch is the curved, horseshoe-shaped structure of the teeth and their supporting bone within the mouth. This arrangement forms the complete set of teeth, known as the dentition. The shape of the arch is functionally important, as it determines how the upper and lower teeth meet when a person chews. A properly aligned dental arch is also a major factor in the clarity of speech and the overall shape and appearance of the lower face.
The Two Dental Arches
There are two dental arches in the human mouth. The upper arch is known as the maxillary arch because it is supported by the maxilla, the bone that forms the upper jaw and is fixed to the skull. The lower arch is referred to as the mandibular arch, as it is anchored in the mandible, or lower jawbone.
A significant difference between the two is that the mandibular arch is mobile, moving at the temporomandibular joints to meet the stationary upper arch. This mobility is what allows the mouth to open and close, powering the grinding and cutting motions required for eating.
When the mouth is closed, the upper arch is typically slightly larger, meaning it naturally overlaps the lower arch both at the front and along the sides. This specific overlapping relationship, known as occlusion, allows the various types of teeth to shear and crush food effectively.
Teeth Count by Arch Adult Dentition
The full adult dentition contains a total of 32 teeth. These teeth are evenly distributed between the two structures, with 16 teeth in the maxillary arch and 16 in the mandibular arch. Each arch is then divided into two quadrants, with eight teeth in the upper right, eight in the upper left, eight in the lower right, and eight in the lower left.
The 16 teeth in each arch are comprised of four distinct types, each serving a specialized purpose during the chewing process:
- Moving from the center of the arch outward, the front four teeth are the incisors, designed for cutting food.
- Next to them are the two canines, which are pointed and used for tearing food.
- Behind the canines are the four premolars, which begin the work of crushing and grinding.
- Finally, at the very back of the arch are the six molars, the largest teeth, which are primarily responsible for the heavy-duty grinding of food before swallowing.
Variations in Arch Structure
Pediatric Dentition
While the two-arch structure remains constant throughout a person’s life, the number of teeth housed within them changes significantly from childhood to adulthood. Children initially develop a primary, or deciduous, set of teeth. This set contains only 20 teeth in total, distributed with 10 teeth in the upper arch and 10 in the lower arch.
The primary dentition lacks premolars, which are only present in the permanent adult teeth. The childhood arches accommodate four incisors, two canines, and four molars, which are later replaced by the permanent teeth, including the new premolars.
Wisdom Teeth
Another common variation in the arch count involves the third molars, widely known as wisdom teeth, which account for the final four teeth in the 32-tooth adult total. Many adults ultimately have only 28 teeth because these third molars are frequently removed due to impaction or misalignment issues. The removal of these teeth alters the final count of teeth within each arch from 16 to 14.