Cement Selection for Provisional Restorations -- Part I
Avishai Sadan, DMD
The selection of a cement for a provisional restoration may appear to be a relatively trivial issue. When the proper cement has not been selected, however, complications including leakage, subsequent carious lesions, loss of the provisional restoration, and movement of adjacent abutments or teeth may occur. Consideration should therefore be given to the type of the provisional restoration (eg, partial coverage, full-coverage single unit, fixed or removable partial denture), as well as the nature of the restorative foundation of the abutment tooth/teeth (eg, immediate or cast post/core, amalgam, or composite buildup). The estimated provisionalization period and patient caries index should also be assessed.
Cement Selection for Various Restorations
Several partial- or full-coverage restorations--particularly onlays or short and tapered full-coverage preparations--possess minimal mechanical retention, making the retention of the restoration a challenge. In the author's experience, two types of cements are adequate for partial-coverage restorations with minimal mechanical retention: polycarboxylate cement, and temporary resin cement. In addition to mechanical retention, polycarboxylate cements will form a weak chemical adhesion to the tooth surface. Upon removal of the provisional restoration, this cost-effective cement remains retained to the tooth while the inner aspect of the provisional restoration is relatively free of cement. Removal of the cement can easily be achieved using an ultrasonic instrument or by microetching the tooth.
Provisional resin cements may provide another viable alternative. While these materials combine favorable handling properties (eg, easy mixing, cleaning, and clinical efficacy), their relatively high cost makes them a secondary alternative.
Single or multiple full-coverage units with proper retention form that require long-term provisionalization should be seated with a permanent cement. For example, a zinc phosphate cement will not bond to the tooth and therefore removal of residue is minimal. A microetcher can be used to clean the intaglio surface of the provisional restoration. For short-term temporization, provisional cements can be used. In cases that will be finalized with resin cement, many clinicians avoid using eugenol-based provisional cements due to the potential decrease in bond strength of the permanent cement to the tooth. This issue, however, remains controversial.
The decision to use a eugenol-based temporary cement should be based on the potential need to reline the provisional restoration. If the clinician is required to refine the preparations and subsequently reline the existing provisional restoration, the use of eugenol-based temporary cement may inhibit the setting of some of the acrylic-based provisional materials. The use of noneugenol provisional cements is recommended for short periods, and the margins of the provisional restorations must intimately fit the preparation. Open margins will result in rapid washout of the cement and the possible development of carious lesions.
Polycarboxylate cements can be used for partial-coverage restorations or short and tapered preparations. The use of zinc phosphate cement is advantageous in long-term temporization of single or multiple units, and noneugenol provisional cements are indicated for short-term temporization and for cases that will require relining of the provisional restoration in subsequent appointments.
*Dean, Ostrow School of Dentistry, University of Southern California, Los Angeles, CA.