Such an explanation can be related to the setting reaction of zinc phosphate cements.

Zinc phosphate is formed from zinc phosphate cement and used in dentistry.

During the machining procedure all the surfaces to which the zinc phosphate cement would be attached were finished to roughness values around 6.3 μm.

Of the placed 87 crowns, 79 had been cemented with zinc phosphate cement and the remaining 8 crowns with glass ionomer.

Zinc phosphate cement is used for cementation of inlays, crowns, bridges, and orthodontic appliances and occasionally as a temporary restoration.

He recommended that the prepared cavity be coated with zinc phosphate cement just prior to filling with amalgam, in order to improve the seal and retention.

A major component of zinc phosphate cement produced by this reaction is hopeite, Zn(PO) 4HO.

In addition, removal of set phosphate cement excess was perceived as being easier to do with zinc phosphate cement than with resin cements.

There is also a possibility that corrosion of the steel dies and release of iron ions from the dies affected the setting reaction of the zinc phosphate cement.

A zinc phosphate cement (Phosphate Cement, Heraeus Kulzer, Dormagen, Germany) was mixed on a room tempered glass plate.

Having justified the use of zinc phosphate cement in a clinical study, it is also important to emphasize that such an evaluation should consider retention and solubility of the luting agent too.

Several years earlier McLean [ 12 ] had showed that after seven years of clinical service, only 2.1% of anterior aluminous core crowns cemented with zinc phosphate cement failed.

However, based on Burke et al.'s [ 5 ] review, which supported the use of resin cements, one can question the rational of even considering using zinc phosphate cement as a luting agent in a clinical study.

Our results suggest that a clinical evaluation of Denzir crowns cemented with zinc phosphate cement are likely to perform as well as Procera crowns cemented with zinc phosphate cement.

Because of the above considerations, the objectives of this study was to determine in vitro whether Denzir copings cemented with zinc phosphate cement to metal dies could provide as good retention strength as Procera crowns cemented to similar metal dies.

Second, the simplicity of using zinc phosphate cements, their ease of removal from marginal regions after setting, and the ease with which a zinc phosphate cemented crown can be removed if remake is needed, are beneficial clinical advantages that cannot be neglected.

Conclusions Denzir copings, cemented with zinc phosphate cement to steel dies, perform at least as well as Procera copings cemented with the same zinc phosphate after storage in water and artificial saliva for one year when tested in vitro.

Because of the published success rate of Procera after 10 years in clinical service [ 13 ] , our in vitro results suggest that Denzir copings, sandblasted or not, and cemented with zinc phosphate cement are likely to perform equally well as Procera crowns, at least regarding retention.