For adults, most commonly, dentists use the Universal Numbering system, which labels the farthest-back, top molar on the patient's right side as "1." Numbering moves sequentially around to the opposite top molar, which is 16, moves down to the patient's back bottom molar on the left side, labeled "17," and around the bottom teeth to the patient's back bottom right molar, labeled "32." This does not change for missing teeth. For example, patients without wisdom teeth start at tooth 2, according to dentalcare.com.
For children in the primary dentition phase, those with baby teeth, the labeling system uses letters, not numbers. The system is the same though, labeling the farthest-back, top molar on the child's right side as "A" and moving sequentially through the teeth, arriving back at the bottom-right, farthest-back molar as "T."
The Palmer Notation system is an alternative system that orthodontists often use. It still labels the teeth with numbers for adult teeth and letters for baby teeth. However, it breaks the mouth into four quadrants: the upper-left, upper-right, bottom-left and bottom-right.
Within each quadrant, the Palmer system labels the teeth one through eight, starting with the front incisors, rather than the molars. The system creates special symbols to denote each quadrant. So, in the Universal Numbering system, a patient's top, front right incisor would be labeled as "tooth 8." In the Palmer system, this tooth would be labeled with the symbol for the top-right quadrant and "1."