Why Clinicians Mistrust Bulk Fills for Class II Restorations

Dr. David Clark


According to most studies, layering produces voids in more than half of restorations placed. Layered and “condensed” composite yields a final restoration that looks a lot like sliced Swiss cheese when the tooth is extracted and examined under a microscope from a side view (Figure 1). Yet, as I interview colleagues from around the globe, dentists have resisted the switch to bulk-fill composites and remain unaware of the advantages of injection molding with heated flowable and regular composites for Class II restorations. Oftentimes, the careful and quality-oriented clinicians are the ones still layering, condensing, and staying away from bulk-fill materials. This is unfortunate because layering is inherently prone to multiple flaws that compromise the health and longevity of a restoration.

The purpose of this brief article is to encourage our best and brightest dentists to modernize their posterior composite techniques.

Figure 1. An extracted molar with a Class II composite resin restoration (left) with a very common appearance is shown at high magnification. There are gaping holes and gaps, and the “margin” is short in some places and long in others, but is it not well-sealed or well-adapted anywhere. Swiss cheese from the grocery store (right) looks similar.

Bulk-Fill Technique: A Cheaper and Lazy Substitute for Layering Composites?
First of all, I wish we had a better name for this technique. “Bulk fill” simply does not sound very elegant. Injection molding for monolithic strength sounds better to me, and that is how we describe it at the Bioclear Learning Center. Regardless, it looks like we may be stuck with the term “bulk fill” for a while yet. As I interview dentists and dental school faculty members, there are 6 common and misguided fears that quality clinicians express about composite resin bulk-filled restorations, in terms of either the technique or the material used (see Table 1). It’s time to move beyond the stereotypes! Monolithic materials are stronger and simpler.

Injection Molding Procedure and Modern Cavity Prep: In Enamel We Trust
1. The Infinity-Edge Tooth-Restoration Interface (IE/TRI):

Out with the old: the concept of flashing. Studies have shown that Class II composites do not work well with the notion of a clean margin. With hand manipulation, you will either be short of or past the margin about 70% of the time.1 The problem is that, in a traditional prep and filling method, the surplus is an “accident”—uncontrolled, unpolymerized composite, floating on a sea of biofilm blood and trapped soft tissue.

In with the new: the infinity edge (IE). After anesthesia and rubber dam placement, Bioclear Dual Color Disclosing Solution is applied to the entire tooth and the Bioclear Blaster is used to remove biofilm. This reduces staining and allows a much better bond on the IE. The IE serves to blend-in and camouflage the margins of the composite. With the Bioclear Method, the IE/TRI is the restoration’s greatest asset.

Figures 2 to 4. The Bioclear Go/No Go probe (patent pending) is shown in a clinical case. The green zone is 4.0 mm, a “Go” for no layering on the occlusal area, where we can only achieve 1-point light curing. The additional 1.0-mm yellow stripe for the interproximal area is a “Go” in the interproximal of the saucer-interprox, where 3-point curing is possible. In the red zone (deeper than 5.0 mm), if the cavity shown here would have been deeper, it would require a 2-step filling technique to achieve full depth of cure (ie, 2 layers). (For a guide to 2-step injection molding, see the Biofit videos on dentistrytoday.com.)

2. Pre-wedging: This step provides multiple benefits to the operator.

Out with the old: traditional wedges. Most traditional wedges fight the papilla, and the wedge (or the tissue) is often sitting inside the cavity prep, leading to both a void in the material at the margin and a concave emergence profile.

In with the new: pre-wedging and the diamond wedge. This wedge system works with, instead of against, the papilla and aggressively separates the tissue from the tooth while forming a small trench into which the Biofit Matrix can slide.

3. Cavity preparation: The Venn diagram in Figure 6 demonstrates the importance of aligning all the components of the Modern Class II. Cutting a modern cavity preparation is one of the 4 codependent features of the Modern Class II.

Figure 5. A mural of some of the essential components of the modern Class II restoration, as taught at the Bioclear Learning Centers and dental schools that we support. This includes the Bioclear dual-color disclosing solution, Bioclear Blaster, Heat Sync Heater, Biofit Matrix, Twin Ring Separator, Diamond Wedges, Scotchbond Universal Adhesive (3M), and Filtek Bulk Fill Flowable Restorative (3M) and the new Filtek One Bulk Fill Restorative (3M) regular paste composite.

Out with the old: the GV Black-style preps (still being taught at most dental schools) and slot preps. These prep designs are essentially for amalgam. These boxy preps, with definitive margins, are the inverse of what we need to create leak-proof restorations.

In with the new: The pre-wedge is removed, and the interproximal area is sanded with the Lightning Strip. The cavity preparation area is then re-blasted to clean 360° around the tooth, and the clear Biofit Matrix is placed.

4. Management of the matrix to optimize the contact area:

Out with the old: burnishing.

In with the new: Simply expand and appose the Biofit matrix with the micro-pliers in the Biofit kit. (Traditional cotton pliers can also be used.)

5. Etch, rinse, and dry:

Out with the old: The use of a dental operating microscope (Global Surgical) (Figure 7) has taught us that selective etching of only the enamel is logistically improbable and, in fact, practically impossible. In my opinion, self-etching alone is probably not the best technique available; separate etching with 37% phosphoric acid and then rinsing with water is still the gold standard and is an incredibly important step in these new enamel-driven prep designs. Using a total-etch technique, the etchant gel is left on the enamel for about 20 seconds and on the dentin for 10 seconds, then rinsed and dried with oil-free air.

Figure 6. These Venn diagrams demonstrate the stark difference between GV Black preps that are filled with either amalgam or composite (bottom left) and the Clark Class II (upper right).

6. Apply bond correctly to the dentin: I use Scotchbond Universal Adhesive (3M) because it allows for a one-step, one-coat application. For buildups when enamel is not present, it can be used as a straight-up self-etching adhesive, thus skipping the rinse-etch step. The adhesive is massaged into the dentin for a full 20 seconds, lightly air-dried, and then light-cured. (Note: Most clinicians are not giving this critical technique step enough time to do it precisely.)

7. Injection molding: The adhesive is reapplied as a wetting agent, then air-dried. Do not light cure. A small amount of Filtek Bulk Fill Flowable Restorative (3M) is then injected into the adhesive film acting as a surfactant and all along the edges. Again, do not light cure. Filtek One Bulk Fill Restorative (3M) is then injected so that the material marries the flowable and, together, fills in all the nooks and crannies. The Filtek One Bulk Fill material makes up at least 90% of the restoration, creating a strong and smooth restoration, while the lesser resins (adhesive and flowable) are displaced out the top.

Figure 7. Utilizing the Global Surgical A-Series Dental Operating Microscope. The creation of high-quality adhesive resin restorations requires the use of advanced magnification. Loupes are great, but
microscopes are a natural progression for precision.

8. Cure, then sculpt: Three-point curing from the occlusal, buccal, and lingual directions is crucial for achieving true 5.0-mm depth of cure in the interproximal. This 3-point curing protocol for bulk fills is aided significantly by using a clear matrix to allow the lateral transmission of light. The composite in the injection zone is then rapidly sculpted with a coarse finishing disc (Sof-Lex XT [3M]), a centerpiece tool in the Bioclear Method that is my go-to disc.

9. Two-step polish: A dual coarseness pre-polish (Bioclear Magic Mix Pre-Polish) is applied for the satin finish, followed by a diamond-impregnated high-shine cup (Jazz Polisher [SS White Burs]). The resultant brilliant shine is what I fondly refer to as the “rock-star polish.”

10. Evaluate: The final step is to evaluate the occlusion. Remember that the composite will absorb water and “grow,” so leave the occlusion a little light. The result of this procedure is an aesthetic and natural-looking composite resin restoration.

Figure 8. Pre- and postoperative bite-wing radiographs demonstrate the value of monolithic composite in a difficult case made easier with modern techniques, instruments, equipment, and materials.
Figures 9 to 11. The cavity preparation is nearly finished on this deep, previously challenging case. The pre-wedge controlled the field and gently separated the tissue away from the deep interproximal area of the tooth. Figure 11 shows the radius bevel mapped in red and the zone of additive material mapped in white. This is the new “extension for prevention” and will extend to the line angle areas. Light doesn’t bend within the gravitational forces of the interproximal, and the use of a metal matrix precludes the ideal restoration of the infinity-edge tooth-restoration interface. Selective caries removal, the new standard of excellence, is demonstrated via carious dentin, stained with caries indicator, retained over the otherwise healthy pulp.

Deep Margin Acquisition, Selective Caries Removal, and Cuspal Overlay Using the IE/TRI

In Figures 8 to 18, the modern Clark Class II protocol is demonstrated. Currently, a retrospective study is being done on these non-retentive cavity preparations, and, in my opinion, it will likely show a high survival rate.

Figure 12. A lateral view of the Calla Lily/partial cuspal overlay preparation with opportunistic access into the incipient decay of the neighboring tooth. This can be quickly restored with a clear matrix and bulk-fill flowable composite before the large restoration is injection molded.
Figures 13 to 16. Multiple views (at low and high magnification) demonstrate the ideal environment to recreate the rounded emergence profiles and embrasures for bulletproof Class II restorations. Crumbly, burnished point contacts have been the norm.
Figures 17 and 18. Occlusal and lateral views of the finished restoration. Once the occlusion is checked, primary anatomy will be carved into the occlusal and polished. Secondary and tertiary anatomy can weaken composite (a brittle material) and has never been linked to improved mastication.

I was at the pet store the other day and spied the new doggie treats that are emblazoned with “bioactive” messaging on the packaging. Is this bioactive thing a fad or is it the future? Well, here is what we do know: Many of the failures of composite come from structural and design flaws of the prep and the filling method that result in tooth fracturing and poor contacts and, in turn, can lead to periodontal inflammation, food impaction, and recurrent decay. To quote my partner Dr. Jihyon Kim at the Bioclear Learning Center, “A Class II restoration is a treatment of disease specific to the contact area. Shouldn’t an ideal contact be job one?” And yet, nearly all Class II restorations being placed have less-than-ideal contacts! To make things worse, the contact is too far to the occlusal, leading to sharp marginal ridges that are more prone to fracturing. The cavity prep taught in nearly every dental school minimizes enamel rod engagement and maximizes dentin tubule involvement and brutally high C-factor. Many restorations have wide-open margins. These preps were historically designed for the use of amalgam and, when filled with composite resin, they are essentially engineered to fail.

So, can bioactive materials placed in a traditional manner bail out a cavity prep from 1890 with butt joints leading to open margins, a high C-factor, and stress risers, leading to tooth fracturing? That would be nice, but, please, let’s not hold our breath. For most preparations, we can maximize enamel rod integration with an IE margin and create a tooth-restoration interface that is incredibly robust. Sure, bioactivity could be a nice bonus and might be a fully proven option at some point in the future. However, on my next day in the office, I need something that I know will work. At present, solid engineering concepts and modern methods are the best bet!

I am pleased to help close the door on the past and to assist the dental profession in moving into the future with improved restorative techniques.


  1. Opdam NJ, Roeters FJ, Feilzer AJ, et al. A radiographic and scanning electron microscopic study of approximal margins of Class II resin composite restorations placed in vivo. J Dent. 1998;26:319-327.
  2. Versluis A, Douglas WH, Cross M, et al. Does an incremental filling technique reduce polymerization shrinkage stresses? J Dent Res. 1996;75:871-878.

Dr. Clark maintains a private practice in Tacoma, Wash, and is the founder of the Academy of Microscope Enhanced Dentistry. He is also a course director at the Newport Coast Oral Facial Institute in Newport Beach, Calif, and he and Dr. Jihyon Kim are co-directors of the Bioclear Learning Center in Tacoma. Dr. Clark’s main areas of interest include the redesigning of restorative preparations and endodontic access preparations. He can be reached at the website bioclearmatrix.com.

Disclosure: Dr. Clark is the owner of Bioclear Matrix Systems.

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