Numbering & Mounting · Indigo RHS

1The problem

"The upper back one" isn't good enough.

Charting, referrals, and exams all need one unambiguous name per tooth. In the US, that's the Universal Numbering System — permanent teeth get numbers 1 through 32, primary teeth get letters A through T. One number, one tooth, no confusion.

The catch is direction. A number only helps if you know which way you're looking — and that's where mounting comes in. Tap the chart below to see how the two fit together — there's one for permanent teeth, then one for primary right after it.

2The instrument — permanent

Tap a tooth. Learn its number.

This chart is laid out the way a mounted film series is — you're facing the patient, so their right side is on your left. Tap any tooth for its Universal number and name. The four gold-edged corners — #1, #16, #17, #32 — are the wisdom teeth, and the exam loves them.

Universal numbering chart

Fig. 9.1 · interactive · you are facing the patient

Tap any tooth to see its Universal number and name.

3The instrument — primary

Now do the same for a child's mouth.

Primary (baby) teeth follow the identical clockwise path, but with letters A–T instead of numbers — only 20 teeth, since primary dentition has no premolars and no third molars. Tap any tooth below.

Universal numbering chart — primary teeth

Fig. 9.2 · interactive · you are facing the patient

Tap any tooth to see its Universal letter and name.

4The rule for mounting

Pimple (convex) out — never dimple (concave).

Every film has an embossed identification dot — feel for it and it's either a little pimple (bump, poking out) or a dimple (dent, poking in). Mount it pimple-side toward you — the convex, raised side — never the dimple/concave side. That's the labial method, and it means you're looking at the mouth as if the patient were sitting across from you: their right is on your left, maxillary roots point up, mandibular roots point down.

5The essentials

Everything on one card.

Idea

What to know

Universal · permanent

Numbers 1–32. Start at the patient's upper right (#1), sweep across the top to #16, drop to the lower left (#17), and come back to the lower right (#32) — one big clockwise "C."

The four corners

#1, #16, #17, #32 are the four third molars (wisdom teeth), one at the back of each section. See those four numbers together → the answer is "the third molars."

The four corners, primary

A, J, K, T are the four primary second molars — the back corner of each primary quadrant. Primary dentition has no third molars, so the second molar is as far back as it goes.

Universal · primary

The 20 baby teeth use letters A–T, same C-shaped path. Memory hook: Letters are for the little teeth.

Mixed dentition

A child mid-transition has both at once — letters and numbers on one chart. A letter = a baby tooth; a number = a permanent tooth. They're never interchangeable.

The dot & orientation

Mount pimple (convex) toward you, never dimple (concave) — the labial method — and you view as if facing the patient: their right is on your left, maxillary roots up, mandibular roots down.

6Spot it on the exam

Two flavors — "which tooth?" and "which way is it mounted?"

"teeth #1, #16, #17, #32"→the four third molars (wisdom teeth)

letters "A, J, K, T"→the four primary second molars (no primary third molars exist)

a tooth shown as a letter (A–T)→a primary (baby) tooth

a tooth shown as a number (1–32)→a permanent (adult) tooth

"raised dot toward the viewer" (pimple, not dimple)→labial mounting — facing the patient

"finding on both sides (bilateral)"→usually normal anatomy, not pathology

7Check yourself

A chart lists restorations on teeth #1, #16, #17, and #32. Which teeth are these?

The four third molars. In the Universal System, #1, #16, #17, and #32 sit at the very back corner of each section — the wisdom teeth. See those four numbers together, think "third molars."

7Check yourself

On a pediatric patient's chart, decay is noted on teeth "A," "J," "K," and "T." When locating these on the mounted images, the assistant should look at the:

Four primary second molars. Primary teeth are lettered A–T along the same clockwise path as the permanent numbers — A (upper right) through J (upper left), K (lower left) through T (lower right) always land on the back corner of each quadrant. Since primary dentition has no third molars, the second molar is as far back as it goes — the exact parallel to #1/#16/#17/#32 marking the four permanent third molars.

7Check yourself

A child's chart shows "T," "A," "#3," and "#14." What does this tell you?

"T" and "A" are primary; "#3" and "#14" are permanent. Baby teeth use letters A–T; adult teeth use numbers 1–32. Both at once means mixed dentition — a child with some baby and some adult teeth.

7Check yourself

Using the labial mounting method, the raised (embossed) dot on each image should face:

Toward the viewer (convex). Pimple, not dimple — labial mounting has the raised dot facing out, so you view the films as if facing the patient — the patient's right is on your left.

Recap

The whole thing in 6 lines.

✓One tooth, one name: Universal Numbering System — 1–32 for permanent teeth, A–T for primary.
✓The count runs one big clockwise "C": upper right (#1) → upper left (#16) → lower left (#17) → lower right (#32).
✓#1, #16, #17, #32 are always the four third molars — the wisdom teeth, and an exam favorite.
✓Same idea for baby teeth: A, J, K, T are always the four primary second molars — the back corner of each quadrant (primary dentition has no third molars).
✓A letter always means a baby tooth; a number always means a permanent one. Both together = mixed dentition.
✓Mount pimple (convex) toward you, never dimple (concave) — labial method — and you're viewing as if facing the patient — their right is on your left.