In my opinion, Bulkfill never made sense. Polymerization shrinkage is the enemy. So what if composite if has “low shrinkage”? Shrinkage is shrinkage and bacteria which get in the resulting gaps are very small. For assured success, the tooth bond to composite interface must be sealed, no gap. FYI, low shrinkage in composite is usually accompanied by high modulus (not easily stretched), effectively negating any benefit of the reduced shrinkage. The resulting high shrinkage stress tends to break the bond to the tooth, leading to a gap.
Well, there is a major development. That is initiating polymerization at the bond, effectively causing the polymerization shrinkage of the bulk fill to be directed toward the tooth. I have mentioned this before in a Newsletter (it has been in lectures) but now there is independent confirmation from two very highly respected independent sources: University of Washington, Prof. Alizeza Sadr, who uses optical coherence tomography (OCT) and University of Alabama, Prof. Nate Lawson, who uses more conventional techniques.
Here are some of Prof. Sadr's images: Two very popular bulk fills, SDR first, Sonicfill next, then the revolutionary material, Bulk EZ, no gap even in a severe C-factor class I filling.
This video is amazing. “Video D” is Bulk EZ and you can see its shrinkage occurring in slow motion like you have x-ray vision. Just compare it to the other bulk fills and you will better understand the "no gap" that I have been talking about. FYI, due to the configuration of the OCT probe, the video images are upside down. As you can see, “Bulk fills work very well until you turn the curing light on.” That reminds me of what Prof. Junji Tagami said last year at Yosemite: “Bulk fills work well if incrementally placed”.
Of special interest to many of my seminar friends is Clearfil Photo Core. It is not gap free but close and clearly better than the bulk fills other than Bulk EZ. Photo Core is a light cure core material that might not be expected to work but we know that is does. The manufacturer says it will light cure 5 mm depth but that is not correct. In an ISO 4049 test, we measured over 9 mm. No wonder it has been so successful for all these years since I introduced it in 1986.
Further confirming the above results, from Prof. Lawson:
Here is a nice clinical comparison of Bulk EZ and a flowable composite placed in contact with enamel, courtesy of Mike Nelson DDS. Mike placed an occlusal-buccal composite restoration but underfilled the buccal surface inside the matrix. So after removing the matrix, he injected in some light cure flowable to fill the void. After light curing, you can see a big difference. Wow! There is no “white line” adjacent to the Bulk EZ like there is around the flowable. This is great proof of both no gap and stress reduction with bulk EZ.
The reason for the difference is management of polymerization stress leading to enamel microfracture as seen in a microscope :
So how does this all affect the gingival margin on a class II composite? Here is a comparison of Bulk EZ and Sonicfill in a laboratory test. Testing was done by thermal cycling, using a stain for identifying leakage.
The Bulk EZ Instructions for Use give the option to place a layer of normal light curing composite over the Bulk EZ when used in posterior restorations. That recommendation was made since initially it was not known know how well the Bulk EZ would resist wear. Our laboratory testing indicated that it would compare to Herculite for wear. We were wrong, it was way better than Herculite. It stays polished well and the margin integrity can’t be beat. Here is a nice clinical example provided by Mike Nelson DDS.
It is clear that Bulk EZ is a game changer. I very highly recommend this product. All Danville/Zest dealers should have it in stock but I usually recommend Tin Man Dental for their great product knowledge and advice.