Bulk-Fill Polymerization Shrinkage is the Enemy!

Raymond L. Bertolotti, DDS, PhD, examines the latest developments on how to overcome polymerization shrinkage issues.

>> This is a preview of the upcoming webinar by Dr. Bertolotti on May 24, 2023. Register here. <<

By Raymond L. Bertolotti DDS, PhD

In my opinion, bulkfill composite never made sense.

The composite is not white amalgam. In all composites, polymerization shrinkage is the enemy. So what about composite that has "low shrinkage"? Shrinkage is shrinkage, and bacteria which get in the resulting gaps are very small. Typical gaps are way larger than bacteria. For assured success, the tooth bond to the composite interface must be sealed with no gap. Low shrinkage in the composite is usually accompanied by high modulus, 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 or white line (fractured enamel) when on enamel.

To overcome polymerization shrinkage issues, there is a major development. That is initiating polymerization at the bond, effectively causing the polymerization shrinkage of the bulkfill to be directed toward the tooth. The result is no gap between the composite filling and the tooth. Naturally, you might ask how this is possible after all these years. To make a long story very short, Dr. Sean Chen's genius devised a new polymerization chemistry to initiate a cascade of polymerization beginning at the bonding agent, which then progresses into the composite, effectively pulling the composite toward the bond.

There is independent confirmation of the concept from two highly respected researchers: Prof. Alireza Sadr at the University of Washington, who uses optical coherence tomography (OCT), and Prof. Nathan Lawson at the University of Alabama, who uses more conventional microscopic techniques.

Here are some of Prof. Sadr's images: Two very popular bulkfills, SDR is shown first, Sonicfill next, then the revolutionary material, Bulk EZ. In this severe C-factor, Class I filling, you can easily see the gap on the pulpal floor in the first two, but the Bulk EZ shows no gap. Say goodbye to post-op bite pressure sensitivity and "recurrent" caries at the gingival margin. Also, you will see remarkably stain-free margins and the absence of white lines (See more below).

Surefill SDR

Surefill SDR



Bulk EZ

Bulk EZ

These images are screenshots taken from a video which you can view: http://depts.washington.edu/b4t/jdr-appendix/

This video is amazing. Video D is Bulk EZ, and you can see, in slow motion, shrinkage occurring to form a gap. Just compare the shrinkage of these bulkfills, and you will better understand the lack of gap formation in Bulk EZ. (Due to the configuration of the OCT probe, the video images are upside down.) As you can see, bulkfills work very well until you turn the curing light on. Exception, Bulk EZ.

This discussion reminds me of what Prof. Junji Tagami said to me last year, "bulkfills work well when incrementally placed."

Of special interest is Clearfil Photo Core in Prof. Sadr's video. It is not gap-free but close and clearly better than the bulkfills other than Bulk EZ. Clearfil Photo Core is a light cure core material that might not be expected to work well, but in personal clinical experience, it does. The manufacturer says it will light cure 5 mm depth, but that is incorrect. In an ISO 4049 test, we measured over 9 mm. No wonder it has been so successful for all these years since we began using it in 1986.

Further confirming the above results from Prof. Lawson at the University of Alabama:

UofA Study

Note: Bulk EZ was the only material that had no microleakage at the cervical margin. The other bulkfill product tested is 3M Filtek BF.

example 1

Here is an excellent clinical comparison of Bulk EZ and a flowable composite placed in contact with the enamel, courtesy of Mike Nelson, DDS. Mike placed an occlusal-buccal composite restoration but underfilled the buccal surface inside the matrix. After removing the matrix, he injected some light curing flowable to fill the void. After light curing, you can see a big margin 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, as evidenced by the lack of a white line with Bulk EZ.

Example 2

In a microscope, the white line at the flowable composite to enamel junction is easily seen. It is a zone of microfracture of the enamel caused by polymerization stress. With Bulk EZ, there is no white line due to lower polymerization stress, insufficient to fracture the enamel.

So how does this all affect the critical gingival margin on a Class II composite? Here is a comparison of Bulk EZ and Sonicfill in our laboratory test. Testing was done by thermal cycling in water, using a stain to mark leakage.

Example 3


The leakage that we can easily see after thermal cycling is quite remarkable. The gingival margin was on phosphoric acid-etched enamel. Kerr's instructions say that any bonding agent can be used with Sonicfill, so we used Optibond Solo Plus, Kerr's best seller.

Example 4

Bulk EZ

The result for Bulk EZ is remarkably different. No leakage is evident. Danville's instructions say that any methacrylate bonding agent may be used. We used Danville's Prelude One, and it worked very well.

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 it was not known how well the Bulk EZ would resist wear initially. Without an added composite layer, it stays polished well, and the marginal integrity (not easily tested in the lab) can't be beaten. Clinical experience has shown that small fillings need not be covered, but larger ones, especially those replacing cusps, should be covered.

Here is a nice clinical result provided by Mike Nelson, DDS.

Example 5

It is clear that Bulk EZ is a game changer. I very highly recommend this product.

Professor Ray Bertolotti is a world-renowned Expert in adhesive dentistry and annually presents at many International Conferences. He will co-host a free webinar with DOCS Education on Bulkfills on May 24, 2023.

To register, click here.

DOCS Members and Trial members are eligible for 1.5 CE for attending the live event. 

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