Gordon J. Christensen, DDS, MSD, PhD
In this monthly feature, Dr. Gordon Christensen addresses the most frequently asked questions from Dental Economics® readers. If you would like to submit a question to Dr. Christensen, please send an email to [email protected].
Are “bulk-fill” composite restorations working?
Q
I’m seeing many companies advertising so-called bulk-fill composite materials. The idea sounds like a good one, but I’m concerned about several aspects of this concept. Is there more shrinkage when the entire restoration is cured at one time? Will my curing light reach the depth of the box form? Are contact areas adequate when the major quantity of resin is placed at one time? These are a few of the questions that I have about the concept. Am I too concerned?
A
Your questions are critical to the success of resin-based composite restorations, and there are state-of-the-art answers to them. However, these restorations need to be observed over a long period of time for final conclusions.
I will provide my response to you in the following order:
- History of the bulk-fill concept
- The capability of curing composite deeply with current lights
- Capability of current curing lights to cure deeply
- The most predictable resin placement and curing technique
- My opinions relative to bulk-filling of restorations
History
Bulk-filling composite is not a new idea. This concept has been promoted for many years. Filling tooth preparations all at once instead of by increments makes sense, since it may save time and make the procedure easier. But is it adequate, the same as, or better than placing and curing resin in increments?
Some of the products that are now being promoted as bulk-fill resins were placed on the market many years ago. Some of them were not promoted as bulk-fill when they were introduced, but they are now being represented as such. They have been reintroduced as “new” products. Other products are, in fact, new to the market. The bulk-fill concept has come and gone a few times in the last several decades.
The capability of curing composite deeply with current lights
Our research group, Clinicians Report (previously called CRA), has studied most of the current brands of resin-based composite relative to their ability to be cured deeply with commonly used curing lights. Some of the resins are capable of curing deeply and others are not, even with optimum conditions and potent lights.
Assuming an optimum curing light emits about 1,000 milliwatts per centimeter squared, let’s look at the commonly observed depth of cure of a typical A2 color resin. A2 color resin is by far the most used color in the U.S.
When such a curing light is used on a typical popular restorative resin, such as 3M ESPE Filtek Supreme Ultra or Kerr Herculite Ultra for typical curing times, these resins cure about 2 mm deep on a routine basis. Some resins, such as Dentsply Caulk SureFil SDR, cure up to 4 mm. However, that product should be used primarily as an internal “filler” to be covered with a layer of external fully filled resin.
The capability of current curing lights to cure deeply
The challenge to cure deeply for bulk filling is the most important and problematic challenge at this time. Studies regarding the status of the curing lights used by most general dentists are not impressive. A study of 214 lights in Toronto showed that the typical curing lights tested delivered about 512mW/cm2, and about 12% of the lights tested delivered less than 300mW/cm2.
I see several challenges with light curing:
• Many dentists have old or worn out lights that do not deliver optimum light energy. I highly recommend that practitioners who haven’t recently upgraded their current lights look into upgrading soon. Current examples as tested and proven by Clinicians Report are Bluephase from Ivoclar Vivadent, Fusion 3.0 from DentLight, Paradigm LED curing light from 3M ESPE, and VALO Cordless from Ultradent. (Figs. 1-4) There are many others, so get a new light!
• Most light guides that dentists use have resin debris on them that redirects the light and compromises the energy delivered to the restoration. Clean the tip of your light guide by chipping the debris off the light guide with a sharp scalpel and polishing the surface with progressively finer composite finishing disks. Debride and polish your light guide.
• Many light guides will not allow curing some clinical situations at an angle perpendicular to the surface of the resin. Some of the newer lights have light guides that emit the light from the curing device at up to 90 degrees from the source of the light. Get a new light!
• Clinicians Report studies showed that fast curing lights (three- to five-second cure) do not penetrate as deeply as slow curing lights. This finding does not depreciate the value of fast curing lights, since they significantly decrease the time to place composite resin and, therefore, save considerable money. Many curing lights used by practicing dentists are NOT capable of curing deeply.