When 400 dentists were surveyed on which composite improvements they most wished for in proprietary research for 3M, one of the top asks was for a composite that could be bulk filled.
It's easy to see why. Dentists like bulk filling because it's speedier, easier and less technique-sensitive than standard filling. With bulk filling, dentists can place and cure 5 millimeters or less of composites.
In contrast, with incremental or standard filling, dentists can place and cure less than 2 millimeters of universal composite and then must repeat that process until the prep is filled. Bulk filling also has another advantage: Dentists can make restorations with fewer voids.
Fortunately, many of those surveyed now have a chance to work with a composite that can be bulk filled. Considerable innovation in this space has taken place since the survey was conducted in 2012, as seen with 3M's Filtek™ One.
That said, many myths and misunderstandings still persist. Here's a look at eight common myths about bulk fillings and the realities behind them.
Reality: High polymerization stress can lead to the composite pulling away from the tooth. And, if the bond between the composite and tooth is strong, the shrinkage the composite undergoes can be exerted as a force or stress against the tooth itself. This can result in cracking of the enamel and postoperative sensitivity.
However, these situations are preventable using 3M's stress-relieving system. It relies on a molecule called AUDMA, which has two methacrylates at each end. It shrinks less per unit volume because the shrinkage that the methacrylates undergo comes from the methacrylate bond itself.
Another innovation in this space is additional fragmentation. A molecule like this, which has methacrylates at each end, has a chemical structure that lets it relieve the stress that builds up in the network as it cures. It polymerizes into the network and the vinyl group in the center. When the vinyl group is attacked by a free radical during the blitz of free radicals that happens during light polymerization, it breaks in half.
Reality: Depth of cure depends on exposure time. The longer the light is on, the deeper it will cure. But, depth of cure also depends on the optical properties of the composite, such as how much light absorber there is. When Dr. Gerry Kugel from Tufts University examined a variety of bulk fills, he discovered you can either have a high depth of cure or an aesthetic composite. Which brings us to the next myth...
Reality: When 3M first measured 20 or so universal composites and figured out what band their opacities or contrast ratios would typically fall in, they saw that at an opacity of 30, it's fairly easy to read through that composite. However, once you get up to and above 60, the print shown beneath this 1-millimeter-thick composite becomes really hard to read. Thanks to smart contrast ratio technology, 3M has been able to increase the opacity and put it nicely within the band of contrast ratios that other universal composites have.
Reality: When 180 dentists in Germany, Italy and UK gave feedback, 90% were satisfied or very satisfied with the ease of use. In addition, 80% of them liked the sculpting, 87% thought the material stayed in place, 72% said it adapted easily or very easily and 78% said they were satisfied or very satisfied with the ability to establish proximal contacts. In addition, 92% liked the overall handling of the material. When the organization, The Dental Advisor, reviewed this, they also came to similar conclusions. They came up with a four-and-a-half star or a four-and-a-half plus sign out of five rating for this material and included things like ease of dispensing, ease of placing and ease of sculpting in their clinical evaluation.
Reality: Technology makes it unnecessary to do that. Let's talk a little bit about the filler system. In 3M's nano filler system, they use Filtek™ Supreme Ultra, consisting of silica/zirconia clusters, and individual silica or zirconia nanoparticles. Because Filtek One gets used in the posterior so much, 3M also added ytterbium trifluoride to increase its radiopacity.
How can putting nanoparticles into a composite make it more abrasion resistant? Since resin essentially is a type of plastic, it's not very abrasion resistant — it's the filler that's abrasion resistant. Whereas with Filtek One, everywhere you go on that surface, you don't have to go very far before you hit a little rock; a nanoparticle. That's the basis for how 3M gets good wear resistance and good polish retention out of these composites.
They've also been able to keep its flexural strength really high. Fracture toughness is a measure of how well the composite can resist the growth of a crack. Fracture is one of the leading killers of composite restorations. 3M kept Filtek One's fracture toughness, again, nicely high relative to comparison products.
Let's also look at compressive strength. Once again, Filtek One is about the same as the other materials 3M compared it to. Key mechanical properties are comparable or higher to competitive universal composites.
Reality: Some people ask if you can place all that composite and still not get voids. 3M designed this material to have a softer handling to it and the ability to flow through a capsule that provides shear when it's being placed. That shear thins the material. And as it shears more, the material thins even more.
3M conducted a fairly large marginal adaptation study as well. In Chicago, they asked 79 clinicians to place composites in teeth within the four different quadrants, into 5-millimeter-deep cavities. They were Class II MO preparations in typodonts at 37 degrees Celsius.
The clinicians then cured those composites and 3M brought them back up to St. Paul. They were examined by evaluators who didn't get to know what composite was being placed. The evaluators saw some examples of good adaptation. They saw some examples of poor proximal box adaptation. And then they saw some examples of poor proximal box and poor inter-layer adaptation.
When filling with Filtek One up to 5 millimeters deep, 30% of those restorations placed had marginal defects, whereas with a leading bulk fill that can be filled 5 millimeters, about 68% had defects. And, with a bulk fill that needed to be layered, it had, again, about the same number of defects. Placing universals incrementally enabled users to have a somewhat smaller number of defects, but still more than you would ideally like to have.
Why are defects occurring when having to place increments? That comes from each new increment needing to have good adaptation to the increment previously placed. And that can just, quite frankly, be somewhat difficult.
Reality: Dr. Richard Price tested this for 3M for Filtek One and four different bulk fills. He found that in terms of average roughness, where lower numbers are better, or in terms of the mean amount of gloss measured — with higher gloss being better — Filtek One performed the best.
This comes back to 3M's nano story, where when they make something with a nano composite, they've taken very small particles and made them into clusters. These particles can wear away a little bit at a time as opposed to the larger particles in nano and microhybrids, which wear away in big chunks.
Reality: In an in vivo study conducted in Brazil, almost 300 restorations were placed, and three different categories of filling were done. First, bulk filling from Filtek One was supplied in capsules. Second, bulk filling from the predecessor product, Filtek™ Bulk Fill Posterior, came in syringes. And then finally, incremental filling was achieved using Filtek Supreme Ultra. The time to place the restoration was measured from the end of the drilling to initial finishing, and the clinicians didn't know that they were being timed. In addition, the cavities were of varying sizes, to be as ethical in the study as possible.
The result? Using time per unit volume as a basis for the study, Filtek One was determined to be 57% faster when delivered from a capsule as compared to 3M's incremental filling procedure — debunking the idea that bulk fill composites don't really save clinicians time.
Bulk filling has advanced considerably in the past decade, and now there are composites that can be bulk filled. If you've been worried about shrinkage, difficult handling, wear and tear and other concerns, it could be time to give these products a second look.
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