Dental professionals rely on a precise system to identify each tooth quickly and accurately. Since the human mouth contains multiple teeth that look similar, dentists use a standardized cataloging method rather than generic descriptions. Assigning a unique identifier to every tooth removes ambiguity, ensuring that treatment is focused on the correct location. This systematic approach is essential for consistent record-keeping and effective communication in dentistry.
Understanding the Universal Numbering System
The Universal Numbering System (UNS) is the method most commonly used in the United States to identify permanent teeth. This notation assigns a distinct number, from 1 to 32, to each adult tooth. The sequence begins in the upper right quadrant of the mouth with the maxillary right third molar, designated as tooth number 1.
The count proceeds sequentially across the upper arch, ending with the upper left third molar (number 16). The numbering then drops to the lower jaw, starting with the lower left third molar (number 17). The sequence continues across the lower arch toward the patient’s right side, concluding with the lower right third molar, which is tooth number 32.
This standardized, continuous numbering method provides a clear, universally recognized map of the permanent dentition. The system ensures that a tooth’s number conveys its exact location and type, simplifying treatment planning and data exchange.
Identifying Tooth 18
The specific tooth designated as number 18 in this system is the lower left second molar. Located in the mandibular arch, this tooth is the second one from the back on the left side of the mouth. It sits immediately in front of the lower left third molar (tooth number 17) and behind the lower left first molar (tooth number 19).
Tooth 18 is a permanent tooth often referred to as the 12-year molar due to its typical eruption time in early adolescence. Its position places it in the third quadrant of the mouth, the lower left section. This specific molar is one of four second molars in the mouth, along with numbers 3, 15, and 31.
Role and Common Issues of the Second Molar
The second molar plays a significant role in the mechanical process of digestion, primarily serving as a powerful grinding surface during mastication. These teeth are characterized by their broad, cusped surfaces, which are adapted to crush and break down food. The position of the second molar is also important for maintaining the alignment of the dental arch and absorbing the heavy bite forces generated by the jaw muscles.
The posterior location of tooth 18 makes it vulnerable to dental health issues. Its position deep in the mouth makes it difficult for a toothbrush and floss to reach the surfaces effectively, leading to inadequate cleaning. This difficulty allows plaque and food debris to accumulate, significantly increasing the risk of dental decay (caries).
Decay and Wisdom Teeth
A specific concern for the lower second molar is distal caries, which is decay on the back surface of the tooth. This issue is frequently linked to the adjacent third molar (tooth 17), or wisdom tooth. If the wisdom tooth is impacted or partially erupted at an angle, it creates a trap for bacteria and food debris. This can cause severe decay on the second molar that is often difficult to detect without radiographs.
The second molar is also susceptible to periodontal disease due to these same access challenges. Poor hygiene can lead to inflammation, gum bleeding, and eventual bone loss supporting the tooth. In severe cases, an impacted wisdom tooth can exert physical pressure causing root resorption, where the wisdom tooth slowly dissolves the root structure of the second molar.
Structural Risks
Given its high exposure to bite force, the second molar is prone to micro-fractures, cracks, and chips, especially in individuals who grind or clench their teeth (bruxism). Loss of this tooth can overload the remaining front teeth, leading to excessive wear and potential issues with the temporomandibular joint. Proper care, including meticulous cleaning and regular professional check-ups, is necessary to maintain the integrity of this tooth.