A dislodged provisional is a major inconvenience to both dentists and patients. This event usually happens in the evening, weekends, or when the dentist or patient is out of town. Therefore, luting a provisional so it does not dislodge prematurely is an important requirement for a provisional cement.
On the other hand, excessive retention is not good either, since you don't want to place undue pressure on the tooth or restoration when it's time to remove it. Thus provisional cements are almost in a no-win position.
They are most commonly used for the period between the preparation and seating of a definitive restoration, but we also need cements for long-term provisionals. For these latter types, a more "permanent" type of cement such as a polycarboxylate may be used.
Besides good retention and stress-free removal, we also need a material that will clean up easily after it sets. In addition, it should be easily removed from inside a provisional restoration just in case you need to recement it, should be easily removed from the tooth preparation, and should not affect the adhesion of the definitive restoration.
These are the typical cements we have used for many years. Most of them are white opaque as a result of the zinc oxide base and may have eugenol to give them the familiar odor we've all come to love or loath. We have also included in this section ionomer-type cements.
Satisfies the need for a cement that doesn't shine through a thin anterior provisional. These products are typically dual-cured, but you should not be tempted to try to clean off the excess until the cement is thoroughly cured. Otherwise, you run the risk of breaking the gasket-like seal these products can form. If this seal is broken, retention can suffer and leakage can be rampant.
While at least one product in this subcategory incorporates an antimicrobial agent in its composition, it is still prudent to apply and then dry a disinfectant such as Consepsis on the prep before seating the provisional. The layer of disinfectant has anecdotally performed well in minimizing leakage and keeping preps from discoloring between the prep and luting appointments.
Because of the resin content in these cements, they can bond with composite buildups. Therefore, it is prudent to apply a very thin layer of lubricant such as KY Jelly over a buildup to prevent this adhesion.
Effect on Bond Strength
We tested all the provisional cements concerning their effect on bond strength. Each cement was mixed and placed on a flat dentin specimen. A glass slide was then placed over the cement to thin it out to a 100µ thickness. This film thickness simulates the clinical situation. After dwelling 24 hours in our temperature/humidity chamber, the cement was removed with a scaler and the dentin was cleaned using Consepsis with its typical syringe tip applying the cleaning pressure or with a pumice slurry, which was applied using a STARbrush in a slowspeed handpiece.
Then, bond strength was tested on these dentin specimens as well as control teeth that were never contaminated by cement. Note that, due to different testing periods, the controls may be different for different cements. That is the reason you should compare the individual bond strengths to the controls, not to those of other cements. The results are listed in the commentary for each product.
CAUTION: Our tests also revealed that using an abrasive such as pumice on a preparation can remove visibly noticeable amounts of dentin. If you aggressively clean dentin margins of a preparation with pumice using a brush such as a STARbrush, you could inadvertently open a margin. Therefore, use judicious pressure when cleaning marginal areas.
While the shade of a provisional cement is not critical, it can certainly affect the appearance of a thin provisional crown, especially if the provisional material is more translucent than opaque. This is especially true of the white or off-white, opaque cements that can shine through a provisional restoration.
Therefore, if you are seating a provisional restoration that is 1.0mm or less in thickness, you may want to select a more translucent, resin-based cement.
Discs of all products in 100µ thicknesses (to simulate the thickness of the cement under a provisional restoration) were measured for relative degrees of translucency/opacity in a spectrophotometer. The scale was 0 - 100, with 0 being totally clear and 100 being totally opaque. Our findings are in each product's commentary.
Extraoral Working Time
If you have an assistant and are using an automix material, you will rarely if ever have to worry about the cement prematurely setting up in the restoration before you fully can seat it, especially if you are only seating 1-2 units.
However, if you are working alone, seating multiple provisionals at one time, and/or using a hand-mixed version, you may find yourself going through the inconvenience of removing a partially seated provisional restoration to try again. Therefore, having adequate working time is very important in saving you from the aforementioned scenario.
Extraoral working time could be especially critical when you are working alone. In this scenario, you (the dentist) would most likely mix and load the provisionals with cement and then place them on the bracket table or cart. You would then redirect your attention to the patient, hoping he or she has not closed in the interim, which would require you to rinse and dry the preparations once again. You then retrieve and seat the provisionals in the patient's mouth, hoping the cement has not prematurely set. Therefore, the time between mixing, loading, and seating the provisionals could be critical.
To test this working time, we used a test restoration and standardized preparation. For the control, we loaded cement into the test restoration (crown) and immediately seated it on the preparation and visually assessed the marginal integrity. We then repeated the test, but instead of seating the restoration immediately after mixing and loading the cement, the crown was allowed to sit on the countertop for a duration consistent with the manufacturer's stated extraoral working time (if the manufacturer gave a range, we tested the shortest and longest times).
Then the crown was seated and the marginal integrity was again assessed. If there was no difference between the control and test specimens, we concluded that the stated working time was accurate. However, if the working time was not correct and a marginal gap was created by the partially set cement, we repeated the test at less working time until the crown could be completely seated. The results can be found in each product's commentary.
Excess Cement Removal Time
We mixed each cement, loaded it quickly into a test restoration, seated it on the aforementioned standardized preparation, and placed it in the T/H chamber. When the cement was set to the point that the excess could be removed cleanly, we recorded the time, which is noted in each product's commentary.