Abrasives & Polishing Agents

1What & why

Polishing is a controlled scratch.

Polishing paste is a controlled scratch. The abrasive particles cut microscopic grooves; as the grooves get finer, the surface reads as "shiny." The skill — and the exam's favorite Domain II topic — is knowing what makes a paste more or less abrasive, and choosing the least abrasive agent that removes the stain.

2The five levers of abrasion

Grit, pressure, speed, dryness, time.

Turn this up…Abrasion goes…

🪨Particle (grit) sizeHow large the abrasive particles are: coarse, medium, fine.

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UPlarger, coarser particles cut deeper — the biggest lever

✊Pressure against the tooth

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UPheavier pressure drives particles deeper (and makes heat)

🏃Speed (RPM)

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UPfaster rotation = more strokes per second = more cutting + heat

DrynessHow little liquid the paste carries.

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UPa drier paste is more abrasive; moisture lubricates the cut

⌛Time on the tooth

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UPseconds, not dwell — longer contact keeps cutting

Try it: move the five leversRate of abrasion

GritFine

PressureLight

SpeedLow

PasteMoist

Time on toothSeconds

Rate of abrasion

3Make it stick

Rate of abrasion: G·P·S·D·T

Grit, Pressure, Speed, Dryness, Time — push any one up and you abrade more. Safe polishing pushes all five down: finest effective grit, light intermittent pressure, low speed, moist paste, brief contact.

4The agents on the tray

Choose the least that works.

The agentWhat it is

Prophy pasteCommercial premixed polishing paste, graded coarse/medium/fine; most contain fluoride and flavoring.

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The everyday choicegrades: coarse · medium · fine — choose the finest that works

Flour of pumiceFinely ground volcanic glass — a mild abrasive.

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Mild abrasivefor stain on enamel; too abrasive for esthetic restorations

Chalk (whiting)Precipitated calcium carbonate — a fine polishing agent.

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Fine polishgentle shine on enamel and metals

💎Tin oxideA very fine powder used to polish metal restorations.

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Metal polishera finishing agent for amalgam and gold

💎Aluminum oxideA very fine abrasive powder — the agent of choice for esthetic restorative materials such as composite, porcelain and veneers.

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Restoration-safethe fine agent used on composite, porcelain and veneers

Top: three identical-looking wells of prophy paste labelled coarse, medium and fine, each with a magnified circle above showing progressively smaller abrasive particles. Bottom: four separate mounds of powder labelled prophy paste, flour of pumice, tin oxide and aluminum oxide with what each is for. — **The paste looks the same — the particles do not.** Coarse, medium and fine are indistinguishable in the well, which is why grit is read off the label rather than judged by eye. Choose the **least abrasive agent that removes the stain**. *The four agents are colour-coded here to tell them apart; the real powders are not these colours.*

5Beat the exam

"Which factor increases the rate of abrasion?"→coarser grit, more pressure, more speed, drier paste, more time — any of the five

"How to make the same paste LESS abrasive?"→add moisture, lighten pressure, slow down, shorten contact

"Which paste for a patient with esthetic restorations?"→the finest (least abrasive) agent that removes the stain

"Why does prophy paste usually contain fluoride?"→to help replace surface fluoride polishing removes — it does NOT replace a fluoride treatment

"Which agent for a composite, veneer or porcelain surface?"→aluminum oxide — never coarse pumice or coarse paste

"Powder abrasive is mixed with…"→a liquid — usually water; the moisture cuts frictional heat

"Two different pastes on one patient?"→a separate cup and angle for each — never carry grit from one to the other

"More than one grit in the same appointment?"→coarsest first, finish with the finest — and use the least that works

6Check yourself

Which change makes a polishing agent MORE abrasive?

Larger particle size. Grit is the biggest abrasion lever. Wetter paste, lighter pressure, and slower speed all push abrasion DOWN.

6Check yourself

The guiding rule for selecting a polishing agent is to use:

The least abrasive agent that removes the stain. Every polish removes a little fluoride-rich outer enamel — so you spend the minimum abrasion needed, and nothing more.

Recap

The whole thing in 5 lines.

✓Polishing is a controlled scratch — finer scratches read as shine.
✓Five abrasion levers: Grit · Pressure · Speed · Dryness · Time — all up = more abrasion.
✓Safe polishing: finest grit, light intermittent pressure, low RPM, moist paste, brief contact.
✓Agents: prophy paste (coarse→fine), pumice, chalk, tin oxide — pick the least that works.
✓Paste fluoride helps compensate for what polishing removes — it is not a fluoride treatment.