Dentists love the handling of self-leveling bulk-fill composites because we do not need to move the tip around, which can introduce voids, and we do not need to use a condenser to reduce voids.

A lot of science has gone in today’s bulk fill composites.

• As manufacturers have advanced the science of composites, they have had to balance the percentage of filler content and the viscosity of the material so it flows and has good handling properties.
• We now see bulk fill composites that are relatively translucent when they are non-polymerized, and when they are polymerized, they become opaquer. To increase the depth of cure, manufacturers came up with new photo initiators that require less light to activate an equal amount of polymerization.

Cap Layers

The percentage of filler content in the bulk fill composite determines whether you must do a traditional high fill cap layer. A traditional high fill, nano composite cap layer (veneer) is going to have superior physical properties, including wear resistance, esthetics, and flexural stress. When a cap layer is optional, my decision is based on whether the restoration is in a visible place, how fussy the patient is about esthetics, and if the patient is at high risk for functional wear.

A cap layer should be only 1-2 mm in thickness because our traditional high fill composites have a depth of cure of 1-2 mm. In my practice, I use a perio probe to measure the depth of the prepared cavity. When I do a class I filling, where the prep cavity does not descend beyond 4 mm, I can make the decision to fill the cavity partially with bulk fill and add a cap layer or to completely fill the cavity with a high fill bulk fill composite like SonicFill or G-aenial BULK Injectable (discussed below).

When I do a class II filling, I often place a bulk fill layer and then a cap layer. If the cavity is 6-8 mm or greater in depth, two increments of bulk fill composite can be used before adding a cap layer.

Bulk Fill Composites I Use

Personally, I prefer radiopaque materials. On radiographs, I want to easily see any voids and be able to distinguish the composite from the dentin, the enamel, and possible decay.

I’ve tried SonicFill™ by Kerr. A special handpiece injects a high filler composite while delivering sonic vibration. This composite has a higher percentage of filler content than the bulk fill “flowable” composites. The high percentage improves the physical properties of the composite, so you do not need to add a cap layer unless esthetics are important. The sonic kinetic energy temporarily lowers the viscosity of the composite so it optimally flows. This filler has a 6 mm depth of cure because it is very translucent.

Most manufacturers have a flowable composite. For these to flow, they have a lower percentage of filler content. The flowable composites self-level and have a 4 mm depth of cure. All manufacturers’ versions of flowable require a cap layer because they have lower physical properties to withstand occlusal wear.

I’ve used both Venus® Bulk Fill by Kulzer and Tetric EvoFlow® by Ivoclar in my practice. Both allow me to easily fill class I and II cavities in increments of up to 4mm. I classically use Tetric EvoFlow for my class II boxes because it is radiopaque and nicely self-levels. There are many versions of advanced bulk fill composites and veneer systems on the market, like the Tetric EvoFlow® and Tetric EvoCeram® that I use.

G-aenial™ BULK Injectable by GC is different because it has a higher percentage of filler content. This injectable bulk filler is radiopaque and can be used without a cap layer. I’ve used this in my practice to do some small class I and some class IV restorations.

There are even “condensable,” bulk fill deposits on the market with high percentage fill materials that do not require a cap layer and are highly durable. If you use these, you will have the challenge of placing more viscous materials and condensing them.

My Bulk Fill Technique

What I like to do is inject flowable material in a central position, for example, in the center of my class II box, and move the tip of the syringe as little as possible. I watch for the flow to reach the buccal, lingual, and axial walls of the cavity prep, and then I slowly lift the tip of the syringe as the occlusal is filling. I strive to not lift the tip prematurely and put it back in, because this introduces “stuck back” porosities. I do not play with the composite with an explorer or condenser because this creates “stuck back” porosities. I wait 10 full seconds to allow the composite to self-level before I begin light cure polymerization.

For years and years, we were trained to not use bulk fill composites. We were well trained to layer composites to improve the success of their longevity. For years, it was smaller layers and angled layers. What was that about? The primary issue we were trying to overcome was the shrinkage of the composite material. Shrinkage stress could destroy adhesion and fracture enamel. Another issue was depth of cure. Traditional composites couldn’t be cured in bulk. Between shrinkage and polymerization, layering became important. We would also layer to ensure we condensed the fill.

In time, scientists and manufacturers looking at this were able to alter the chemistry of the composite to alter the impact of polymerization shrinkage. When bulk fill composites first came on the market, despite what the manufacturers told me, I felt some internal resistance and it took me a while to step into the bulk fill arena. What drove me to take that leap of faith was looking into the science behind bulk fill composites.

The Science

I spoke with different scientists, from different manufacturers, and with independent scientists who created these materials. What I came to understand is that bulk fill composites are an improvement in composite technology.

The manufacturers learned how to direct shrinkage away from the bonded interface. Across the category of bulk fill materials, all these materials have a lower shrinkage stress numbers than the categories of composites that came before them. They do better at maintaining the integrity of the interfaces between the composite and dentin adhesive and the dentin adhesive and the walls of the cavity preparation.

The manufacturers increased translucency to increase the depth of cure. In general, when a manufacturer says they have a bulk fill composite, what they mean is that the depth of cure is somewhere between 4 to 6 mm. I often hear the complaint that bulk fill composites are not as esthetic as traditional composites. Each of us must answer individually for ourselves how exact and perfect we want to make the match of the composite to the surrounding tooth. Manufacturers have attempted to address this and now offer bulk fill composites that become opaquer as they cure.

Multiple Choices

Like everything else in dentistry, there are many choices. There are multiple types of bulk fill composite, even from single manufacturers, with variances in the specific depth of cure they recommend. When evaluating bulk fill composites, consider these questions:

• What is recommended depth of cure for that specific composite?
• Is the composited graded high enough to withstand occlusal loading and wear, or does the manufacturer recommend you use a different composite to create a 1 to 2 mm cap layer (typically, a more traditional nano category of composite)? The silver lining is that this provides an option when esthetics are of high concern.
• Is the composite condensable, requiring you to use condensing instruments, or is the composite more flowable and referred to as self-leveling, because it flows perfectly across to perfectly fill the preparation cavity? Self-leveling composites have a chemistry that allows them to have less initial viscosity and then thicken after they have flowed.
• Among your choices are bulk fill composites that come in small containers to go in composite guns, compules, and syringes. The less viscous, flowable composites come in a syringe that looks like a flowable and you can put a flowable tip on it.

I’ll be back with Part 2 of this blog to present more about bulk fill composites. To leap ahead, you may want to visit the Pankey YouTube channel to view the webinar I presented on this topic in 2020. You can view it here.