The wrong story on zinc oxide and eugenol:
Recently there have been instances whereas the clinician has been given misinformation as it relates to zinc oxide and eugenol. Specifically Gordon Christensen and more recently Frank Spears have stated that temporary restorations made of zinc oxide and eugenol will not interfere with the polymerization of composite resin restorations subsequently placed. Both sources stated that any residual eugenol associated with the temporary restoration would eventually dissipate.
This statement is not true. First, zinc oxide reacts with eugenol to form zinc eugenolate, which is a chelate compound. This compound crystallizes to give a matrix of long sheath-like crystals that bind together the remaining unreacted zinc oxide (Restorative Dental Materials, University of Michigan, CV Mosby Company). Unreacted eugenol is absorbed by both the zinc eugenolate and the unreacted zinc oxide. The hardened mass therefore consists of a mesh-like matrix of zinc eugenolate crystals binding together particle of zinc oxide and the excess eugenol absorbed by both the zinc eugenolate and zinc oxide.
The point is this: the excess eugenol remains in a free state (unreacted) and will remain in the material indefinitely. Unless all of the residual material is removed prior to placing the dentin-bonding agent, the polymerization process stands to be impeded.
Clinically there are a couple of ways that the problem can be prevented. One way would be to hybridize the preparation before the zinc oxide containing temporary material (IRM) is placed. Obviously, this may not always be a practical approach, depending upon the specific procedure being carried out. The other way to deal with the matter is to sand blast the preparation (Danville Microetcher) immediately after the zinc oxide and eugenol temporary has been removed. The final and third way is to use “no- eugenol based temporaries. Unfortunately most of the eugenol-free temporary agents do not have the same quality of handling as do those that contain eugenol.
Karl Leinfelder
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