The wisdom teeth, scientifically known as the third molars, are the final set of teeth to develop and erupt in the human mouth. They typically emerge much later than other permanent teeth, usually between the ages of 17 and 25. Because they are the last to arrive, their eruption can sometimes be problematic, often due to a lack of available space in the jaw.
Dentistry requires a precise method for identifying each of the 32 permanent teeth. To achieve this standardization, dentists utilize various charting methods, with the Universal Numbering System being the most widely accepted method in the United States. This system assigns a unique number to every tooth.
The Universal Numbering System
The Universal Numbering System (UNS) identifies the wisdom teeth using four specific numbers: 1, 16, 17, and 32. These numbers represent the four wisdom teeth positioned at the very back of the dental arches. The system begins its count with the upper right third molar, assigning it the number 1.
The count continues sequentially across the upper jaw to the far left side, where the upper left third molar is designated as number 16. The numbering then drops down to the lower jaw, starting with the lower left third molar, which is labeled as number 17. Finally, the sequence continues across the lower arch, concluding with the lower right third molar, which is assigned the number 32.
Understanding Dental Quadrants
The structure of the Universal Numbering System is based on the mouth’s division into four dental quadrants: upper right, upper left, lower left, and lower right. Each quadrant in the adult permanent dentition contains eight teeth, starting from the central incisor at the front and extending back to the third molar.
The numbering sequence follows a clockwise path when viewed from the perspective of the dentist looking into the patient’s mouth. It begins in the upper right quadrant with tooth number 1 and proceeds through number 8, which is the upper right central incisor. The sequence continues into the upper left quadrant, running from number 9 (upper left central incisor) to number 16 (upper left third molar).
After completing the upper arch, the numbering transitions to the lower left quadrant, starting with number 17 and moving to 24. The final numbers, 25 through 32, are assigned to the teeth in the lower right quadrant.
Reasons for Removal
The decision to remove wisdom teeth often stems from clinical issues related to their late eruption and position in the mouth. A common problem is impaction, which occurs when the tooth is blocked by the jawbone or adjacent teeth and cannot fully emerge through the gum line. Impaction can lead to localized pain and swelling in the back of the jaw.
Infection and Decay
When only partially erupted, the area around the wisdom tooth is susceptible to inflammation and recurrent infections, a condition termed pericoronitis. These issues can cause food and debris to become trapped, increasing the risk of tooth decay in the wisdom tooth itself or damage to the neighboring second molar. A fluid-filled sac, or cyst, can sometimes develop around an impacted tooth, which can potentially damage the surrounding bone structure.