Paste dries. Cement sets.

A paste is made by mixing a substance with a solvent and when the solvent evaporates the paste dries.

Cements are made of two different substances that combine chemically to form a third substance.

The more accurate term is cement.

In fact the cement that we use is very similar to that which has been used for decades to cement gutta percha in a canal.

There are two issues with the use of a cement.

• Is it toxic?
• Does it dissolve from out of the canal?

The answer to the first is negative. The cement is plain vanilla ZOE which has been used in dentistry and is generally accepted as non-toxic.

The answer to the second is more complex in that we must distinguish between solvency and absorbancy.

ZOE is soluble in saliva as we well know from the use of ZOE as temporary fillings but it does not dissolve from the root canal unless the coronal seal is broken. This is true whether it is used as a sealing AND filling material or whether it is used to cement a gutta percha point into the canal.

The question of absorbability is more counter intuitive.

For a substance to be absorbed macrophages must get at it.

Since macrophages cannot stray very far from the capillary that delivers and oxygenates it, cement can only absorb as far into the canal as the capillary bed can grow, which is not very far.

In fact, if macrophages COULD get up into the canal from the apex, we wouldn't have to do root canals at all.

The body would simply remove the necrotic tissue as it does from around a sliver or other foreign material.

So the short answer is that no, the cement neither dissolves nor absorbs from the root canal.

The only cement that can be absorbed is that which exceeds the bounds of the canal system and can be reached by macrophages. Thus cement will only absorb to the apex and no further.

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