Bonding Indirect Restoration – Do You Need to Polish the Resin Cement Gap?

When bonding indirect restorations, do you need to polish the resin cement gap? The simple answer is yes!

The best seal of an indirect restoration to the tooth is achieved by bonding with composite resin. To achieve a long-term, biologically sound outcome, it is recommended you polish the resin cement gap.

Why is it important to polish the resin cement gap?

Unpolished resin is rough. This roughness allows for biofilm formation, bacterial adherence, and colonization, resulting in gingival inflammation. This is especially true if the preparation finish line is placed subgingival. It has been reported in the literature that the range of cement margin widths range from 20 to 373 microns.

The additional challenge in the removal of excess cement is that most adhesives and resin cements are translucent and colorless, so it is difficult to see if the excess cement has been removed. Using an adhesive and cement that are radiopaque can be beneficial so radiographs can be used to help identify the location of excess material.

Unpolished resin cements are in the roughness range of 1.0 to 1.7 microns. Plaque accumulation is significantly reduced if the surface roughness is less than 0.2 microns. The only way to achieve this is with a 2-step polishing process.

I recommend using composite resin polishing cups. A flexible cup allows the cup to adapt to the convex surfaces of the tooth and restoration, and composite resin polishers will not damage the ceramic material.

Some clinicians recommend ceramic polishers, but the composition and shape of particles used in ceramic polishers is too abrasive for composite resin. Using ceramic polishers will also change the surface of the ceramic restoration, potentially removing any overglaze material or stains that were used to achieve the proper esthetics.

How to polish the resin cement gap — clinical steps

It is best to achieve the desired ceramic surface extra-orally, not after restoration insertion.

The clinical steps that I perform during restoration insertion are:

1. Remove the provisional restoration.
2. Clean the tooth with flour of pumice and a soft/flexible prophy cup at slow speed (2,000-4,000 rpm). It is critical to place the rubber cup into the sulcus, apical to the preparation finish line. Removing the bacterial biofilm here is important.
3. Airborne particle abrasion of the preparation with 27-50 micron aluminum oxide at low pressure (15 to 30 psi), 1 cm from the surface for a few seconds (5 seconds maximum).
4. Place a gingival retraction cord to isolate the tooth.
5. Etch the tooth with 35 percent phosphoric acid for 30 seconds on enamel surfaces and 15 seconds if it is dentin/cementum.
6. Rinse with water for at least 30 seconds.
7. Remove the retraction cord.
8. Apply the adhesive with a scrubbing action. Apply four coats and follow manufacturers recommendations.
9. Air thin and evaporate the solvent.
10. Place the restoration on the tooth. The resin cement must cover 100 percent of the intaglio surface and extend slightly over the margin to the outer aspects of the restoration. Excess cement should be expressed at 100% of the margins.
11. Spot cure for two seconds or clean the excess resin cement with a synthetic hairbrush. Some clinicians floss at this point — I do not, because I am afraid I may dislodge the restoration. If the cement is spot cured, I only push on the excess bead to move it slightly, but do not remove it.
12. Apply glycerin over all margins.
13. Light cure for at least 40 seconds per surface.
14. Remove cured excess resin cement with a #12 surgical blade or small scaler. It is difficult to see the clear adhesive and resin cement. Air dry to help visualize the remaining cement. Alternately, apply alcohol with a microbrush and the resin will be identified.
15. Begin the 2-step polishing of the resin cement which fills the gap between the tooth and restoration. First, use the Universal Composite Polisher – green cup (Brasseler USA). Use speeds ranging between 5,000 - 8,000 rpm. Second, use the Universal Composite Polisher – pink cup (Brasseler, USA), using speeds between 2,000 – 5,000 rpms.

Using these polishers and techniques will result in smooth composite resin cement line with less bacterial adherence and healthier gingival tissue.

Robert Winter, D.D.S., is a member of Spear Resident Faculty.

References:

1. Glauser S, Astasov-Frauenhoffer M, Muller JA, Fischer J, Waltimo T, Rohr N. Bacterial Colonization of Resin Composite Cements: Influence of Material Composition and Surface Roughness. Eur. J. Oral Sci (2017) 125 (4): 294-302.
2. Rohr N, Bertschinger N, Fischer J, Filippi A, Zitzmann NU. Influence of Material Surface Roughness of Resin Composite Cements on Fibroblast Behavior. Oper Dent (2020) 45(5): 528-536.