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Three languages, one arch
Clinics, labs, and textbooks do not agree on a numbering system. FDI (ISO) is two digits: quadrant then position, 1–8 from the midline. Universal (US) is 1–32 starting at the maxillary right third molar. Palmer uses a quadrant bracket plus 1–8. A D1 who only knows one system will mis-order a crown by the second week of clinic.
FDI quadrants
1 = maxillary right, 2 = maxillary left, 3 = mandibular left, 4 = mandibular right. Permanent dentition. (Primary uses 5–8.) Tooth 16 is the maxillary right first molar. Tooth 36 is the mandibular left first molar. The second digit is always the position from the midline.
Universal trap
Universal 1 is a third molar. FDI 11 is a central incisor. If a lab ticket says “#14” in the United States it is the maxillary left first premolar (FDI 24). Read the system on the ticket before you design.