Arches, quadrants, sextants, three dentitions, and the Universal numbering horseshoe — the coordinate system every other lesson (and every charting question) is built on.
The coordinate system~8 min★ Numbering anchors (#1, #8/9, #16, #17, #32) are free points
1What & why
Arches, quadrants, sextants.
Before you polish anything, you have to name where you are. The mouth divides three ways — 2 arches (maxillary = upper, mandibular = lower), 4 quadrants (each arch split at the midline), and 6 sextants (front and back sections).
The exam uses this vocabulary constantly — in numbering questions, sequence questions, and charting questions. It's the map everything else is drawn on.
2Three dentitions
Primary, mixed, permanent.
The dentitionWhat it is
👶PrimaryThe 20 "baby" teeth, lettered A–T in the Universal system.
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20 teeth · A–Terupt from ~6 months; all 20 in by ~age 3
🧒MixedThe transition years when primary and permanent teeth are both present.
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Both at once · ~ages 6–12primary teeth exfoliate as permanent teeth erupt
🧑PermanentThe 32 adult teeth, numbered 1–32 in the Universal system.
The Universal system (standard in the U.S., and on this exam) starts at the upper right third molar (#1), runs across the upper arch to the upper left third molar (#16), drops down to the lower left third molar (#17), and runs across to the lower right third molar (#32).
Anchors worth memorizing cold: #1 upper right 3rd molar · #8/#9 the two upper central incisors · #16 upper left 3rd molar · #17 lower left 3rd molar · #24/#25 lower central incisors · #32 lower right 3rd molar. Primary teeth use the same path but letters: A (upper right 2nd primary molar) through T (lower right 2nd primary molar).
The whole horseshoe, at a glance. Upper right third molar is #1; the count runs left across the top to #16, drops to #17 on the lower left, and finishes back at the lower right third molar, #32. The bracketed quadrant labels are the same 4 quadrants from the top of this lesson — the numbering just walks around all of them in one continuous loop.
4Make it stick
Clockwise from the patient's upper right.
Face your patient: numbering travels like a horseshoe — upper right → upper left → lower left → lower right. And it's always the patient's right, not yours — the same left/right flip you make when you reach for a tooth.
5Surfaces you polish
The surfaceWhere it faces
👄FacialThe surface facing the lips (labial) or cheeks (buccal).
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Toward lips/cheekslabial on anteriors, buccal on posteriors
👅LingualThe surface facing the tongue (palatal on the upper arch).
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Toward the tonguecalled palatal on maxillary teeth
Occlusal / incisalThe chewing surface (posteriors) or biting edge (anteriors).
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The chewing/biting surfacewhere the bristle brush is allowed to work
ProximalThe surfaces between neighboring teeth: mesial (toward midline) and distal (away).
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Between the teethmesial = toward the midline · distal = away from it
Four of the five, in color. Facial/labial (pink) and buccal (teal) are both the "outward-facing" surface — labial on the front teeth, buccal on the back ones, exactly as the table above says. Lingual (purple) faces the tongue, incisal (yellow) is the biting edge of the front teeth, occlusal (green) is the chewing table of the back ones. Proximal — mesial and distal — sits between teeth and isn't visible face-on, which is why it's not pictured here.
Occlusal / incisalThe chewing surface (posteriors) or biting edge (anteriors).
ProximalThe surfaces between neighboring teeth: mesial (toward midline) and distal (away).
