A hot topic: sealing preparations

April 1, 2000
Iroutinely place Gluma after prepping and impressing crowns just before provisional cementation. This seems to help with sensitivity. There are still some teeth that may have sensitivity and I removed the temp and placed Prime & Bond NT and cured. My thought was that if the film thickness is thin enough to cure prior to cementing all ceramic crowns, then it should be OK with metal ceramic also. I did not have any further problem with sensitivity, but I did not want to continue with a procedure t

Michael Miller, DDS

Iroutinely place Gluma after prepping and impressing crowns just before provisional cementation. This seems to help with sensitivity. There are still some teeth that may have sensitivity and I removed the temp and placed Prime & Bond NT and cured. My thought was that if the film thickness is thin enough to cure prior to cementing all ceramic crowns, then it should be OK with metal ceramic also. I did not have any further problem with sensitivity, but I did not want to continue with a procedure that may not be appropriate. If it is OK, then why do we not seal dentin on all preps after impressing?

The subject of sealing preparations at the preparation appointment is a hot topic. That is why we have researched several aspects of this issue and reported on the results in the desensitizer section of the 2000 edition of REALITY. In short, there are several issues, which need to be addressed.

1. If you seal before the impression, does the sealer affect the setting of the impression material and the accuracy of the impression itself? We have not yet studied this issue and suggest sealing after the impression. Another reason to wait until after the impression is practicality. If your margins are subgingival, you will need to pack cord. Sealing a preparation with cord in place will result in the cord also being covered by the sealer. This will make removing the cord more difficult and may lead to hemorrhaging when the cord is removed, thus interfering with the impression. It may also be more difficult to prevent the sealer from pooling at the margin when cord is in place, since the cord itself may become super-saturated with the sealer.

Additionally, if you fabricate your provisional restoration out of a composite material such as Luxatemp, the sealer may make it more difficult to remove the provisional, even if the preparation is lubricated liberally.

2. Does the sealer affect the ultimate bond strength of the definitive restoration? In other words, if you actually hybridize the dentin at the preparation appointment, will that make it more difficult to bond the definitive restoration? To investigate this issue, we tested the bond strength of OptiBond Solo Plus/Nexus under the following pretreatment conditions:

- Preparation was etched, OptiBond Solo Plus was applied and cured, Temp-Bond Clear was applied, and the specimen was stored in the T/H chamber for seven days. Then Temp-Bond Clear was removed, the preparation was cleaned, etched, and bonded using OptiBond Solo Plus/Nexus. Bond strength of this group = 28.5.

- Preparation was not etched, OptiBond Solo Plus was applied and cured, Temp-Bond Clear was applied, and the specimen was stored in the T/H chamber for seven days. Then Temp-Bond Clear was removed, the preparation was cleaned, etched, and bonded using OptiBond Solo Plus/Nexus. Bond strength of this group = 28.5.

- Preparation was etched, All-Bond DS Primers A&B were mixed, applied, and cured, Temp-Bond Clear was applied, and the specimen was stored in the T/H chamber for seven days. Then Temp-Bond Clear was removed, the preparation was cleaned, etched, and bonded using OptiBond Solo Plus/Nexus. Bond strength of this group = 25.7.

- Control = 34.2

These results suggest that there is a price to pay for sealing your preparations at the preparation appointment. Whether the lowering of the bond strength is clinically significant still needs to be determined. If you are using a more conventional cement and relying on mechanical resistance and retention (as would typically be the case with ceramometal preparations), then this reduction in bond strength should be of no concern. However, if you are depending on the adhesion of the adhesive/resin cement complex to provide most of the retention, then this lowering of ultimate bond strength could cause problems.

3. Does the film thickness of the sealer compromise being able to completely seat your definitive restoration? Most studies (including our own) show metal-free restorations, in general, do not fit their preparations as precisely as metal-based ones.

Therefore, it?s not a certainty that even the thin-film thicknesses of most adhesives will not have an effect on the seating of a metal-based restoration. That is why non-setting sealers such as Gluma have been favored for metal-based restorations.

Nevertheless, with the film thickness of Prime & Bond NT Dual Cure being reported as low as 4 microns, it is highly unlikely it will interfere with seating the restoration, unless it pools in a line angle.

4. Should you etch before sealing a preparation? If your preparations are bloodless and you can isolate the teeth to be sealed with cotton rolls/saliva ejectors (since it is very unlikely you will be using a rubber dam with full-crown preparations), etching will help whatever adhesive you choose to seal the dentin more effectively.

However, if the procedure has traumatized the tissue and it is not possible to keep the preparation completely isolated, then you should definitely not etch. With a product such as Prime & Bond NT, it actually has some self-etching properties anyway.

Therefore, make the best effort you can in cleaning the preparation (Consepsis is a good choice) and then apply the adhesive using the technique described in the dental adhesives section of the 2000 edition of REALITY.

Dr. Miller is the publisher of REALITY and REALITY Now, the information source for esthetic dentistry. He is an international lecturer and a fellow of the American Academy of Cosmetic Dentistry, as well as a founding member. He maintains a private practice in Houston, Texas. For more information on REALITY and to receive a complimentary issue of his monthly update, REALITY Now, call (800) 544-4999 or visit www.reality=esthetics.com.