Why Do Clinicians Mistrust Bulk Fills for Class II’s?

David Clark
January 8, 2019
Fig 1) An extracted molar with a Class II composite resin restoration (left) with a very common appearance viewed at high magnification. There are gaping holes, gaps, and the “margin” is short in some places, long in others but nowhere is it well sealed or well adapted. Swiss cheese from the grocery (right) store looks similar

According to most studies, layering produces voids in more than half of the restorations. 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 (Fig 1). Yet as I interview dentists from around the globe, they have resisted the switch to bulk fill composites, and unaware of the advantages of injection molding with heated flowable and regular composite for Class II restorations.  Often times the careful and quality-oriented clinicians are the ones still layering, condensing, and staying away from Bulk Fills.  This is unfortunate, because layering is inherently prone to multiple flaws that compromise the health and longevity of the restoration.   The purpose of this brief article is to encourage our best and brightest dentists to modernize their posterior composite techniques.


Is Bulk Fill a cheap and lazy substitute for layering?

First of all, I wish we had a better name for not layering.  Bulk fill doesn’t sound very elegant.  Injection molding for monolithic strength sounds better to me, and is how we describe it.  Regardless, we are stuck with the term Bulk Fill for a while.  As I interview dentists and dental school faculty, there are six common and misguided fears that quality clinicians express about Bulk Fill in terms of either the method or the material itself


State of the Nation: Class II Composite Resin Restorations

Objections to bulk fill/reasons that dentists are still layering Were these concerns valid? Why and how today is the day to stop layering*
“I don’t trust the depth of cure claims. And how do I measure 5 millimeters easily?” Yes. The only way to get to 5 mm depth of cure, generally is 3-point curing.  That is compromised when using a metal matrix. And guessing about prep depth is not safe. Use a “Go/No Go (Bioclear) curing depth gauge to be sure of your cure (Figs 2-4), and make sure to use a clear matrix such as the new Biofit Matrix (Fig 5).  Powerful curing lights are readily available.  However, many schools and private practitioners have very outdated, weak curing lights
“Bulk Filling will create shrinkage stress that will cause post-operative sensitivity and marginal leakage.” No. Never were. Most studies 1 show that layering will not mitigate curing stresses.  Bulk fills are a little “less bad” in this regard. Most bulk fill composite resins have novel chemistry that mitigates some of the polymerization shrinkage stress, either chemically expanding during polymerization or with rubbery physical properties (low modulus) The best way to mitigate polymerization stress is to lower C Factor and stop cutting a boxy GV Black or Slot Prep.  Instead learn about the Clark Class II or “Saucer” preparation. Today the ONLY reason to layer is when we are deeper than 5 mm in the interproximal, 4mm in the center of the tooth.
“I like putting a flowable down first because I know it will adapt. Yes and no.  Lower viscosity materials adapt better.  But then you will get voids much of the time between the flowable and the regular (paste) composite as you add that 2nd or 3rd layer.  Filling most of a Class II with flowable is not optimal because of lesser strength. Follow your normal bonding protocol.  Then do injection molding with a thin film of uncured adhesive, followed by heated bulk fill flowable, then chased with injected heated bulk fill (regular paste) composite from a compule  can eliminate voids entirely and provide the ultimate in adaptation. The goal is to have at least 90% of the restoration with regular composite and 10% or less flowable.
“Bulk fills are grainy with poor shine retention and wear resistance. That is why I cover the bulk fill with a capping composite that I trust (non-bulk fill).” Yes and no. Early bulk fills were weak, grainy, or both.  Many still are. The bulk fill flowable and paste you select should have the same shine retention and strength as your favorite anterior composite.  If not, switch brands.
“Bulk Fills are ugly and gray.  I’m not confident in bulk fill’s esthetics”. Yes. In order to get deep depth of cure, all early bulk fills were very translucent. Translucent equals Gray.  Gray equals Ugly. Today 3M Filtek One has solved that problem.  It is gorgeous. A few other brands have gotten less grey looking (Fig 5)
Bulk fills will create more voids No.  Early bulkfills had some problems, but less layering will generally result in less voids The real trick to eliminating voids is Injection Molding with heated (Fig 5) multi-viscosity resins as described elsewhere in the article

Figs 2, 3, 4) The Bioclear Go/No Go probe (patent pending) is shown in a clinical case.  The green zone is 4 mm, a “go” for no layering on the occlusal area where we only achieve 1-point light curing. The additional 1 mm yellow stripe for the interproximal area is a “go” in the interproximal of the saucer-interprox) where 3-point curing is possible. The red zone (deeper than 5 mm), if the cavity would have been deeper, would require a 2-step filling technique to achieve full depth of cure, i.e. 2 layers.  For a guide to 2 step injection molding see the Biofit video on the Dentistry Today website

It's time to move beyond the stereotypes! Monolithic materials are stronger and simpler.

The Injection Molding Procedure & Modern Cavity Prep: In Enamel We Trust

Fig 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 Bioclear dual color disclosing solution, the Bioclear Blaster, Heat Sync Heater, Biofit matrix, Twin Ring Separator, Diamond Wedges, Scotch Bond Universal, Filtek Bulk Fill Flowable, and the new Filtek One Bulk Fill (regular paste) composite
  • The Infinity Edge Tooth Restoration Interface or TRI. Out with the Old Concept of Flashing:  Studies have shown that Class II composites don’t work well with the notion of a clean margin.  With hand manipulation, you will either be short or long of the margin about 70% of the time 2.  The problem is, 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.  After anesthesia and rubber dam placement, Bioclear Dual Color Disclosing solution is applied to the entire tooth and the Bioclear blaster was used to remove biofilm. This reduces stain and allows a much better bond on the infinity edge. The infinity edge blends and camouflages the margins of the composite.  With the Bioclear Method the Infinity Edge TRI is the restoration’s greatest asset.
  • Pre-wedging: This step provides multiple benefits to the operator. Out with the Old: Traditional wedges fight the papilla and often the wedge or the tissue is sitting inside the cavity prep leading to both a void in the material at the margin and concave emergence profile.  With pre-wedging and the Diamond Wedge, the wedge works with instead of against the papilla and aggressively separates the tissue from the tooth, forming a small trench for the Biofit Matrix to slide into.
  • 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 co-dependent features of the Modern Class II. Out with the Old: Classic GV Black Preps (still taught at most dental schools) and slot preps are essentially amalgam preps.  These boxy preps with definitive margins 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 was then re-blasted to clean 360 degrees around the tooth and the clear Biofit matrix is placed.
  • Management of the matrix to optimize the contact area: Out with the Old…Burnishing. Simply expand and appose the Biofit matrix with the micro-pliers in the Biofit kit or traditional cotton pliers.
  • Etch, rinse and dry: Out with the old. Use of a dental operating microscope (Global Surgical) (Fig 7) has taught us that selective etching of just the enamel is logistically improbable and practically impossible. Self-etching alone isn’t smart because rinse etching (etching with 37% phosphoric acid) is still the gold standard, and incredibly important in these new enamel driven preparations.  Using a total etch technique, the etch was left on the enamel for about 20 seconds and on the dentin for 10 seconds, after wards rinse and dry.
  • Apply bond correctly to the dentin. I use 3M™ Scotchbond™ Universal Adhesive because it allows for one-step, one coat application. For buildups where the enamel is gone, I can use it as a straight-up self-etching adhesive and skip the rinse-etch step. The adhesive was massaged into the dentin for a full 20 seconds, lightly air dried and then light cured.  Most clinicians are not giving this critical step enough time.
  • Injection molding: The adhesive was reapplied as a wetting agent, then air dried – do not light cure. A small amount of 3M™ Filtek™ Bulk Fill Flowable Restorative was then injected into the adhesive film acting as a surfactant and all along the edges, and again, do not light cure. Filtek One Bulk Fill Restorative was 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, which creates a strong and smooth restoration, and the lesser resins (adhesive and flowable) are displaced out the top.
  • Cure, then Sculpt: Three-point curing from occlusal, buccal, and lingual is crucial for achieving true 5 mm depth of cure in the interproximal. This new curing protocol for bulk fills, that of 3-point curing, is aided significantly using a clear matrix to allow lateral light transmission. The composite in the injection zone was then rapidly sculpted with the 3M™ Sof-Lex™ XT course disc, a centerpiece tool in the Bioclear method, and my go-to disc.
  • 2 Step Polish: Bioclear Magic Mix dual coarseness is applied for the satin finish then followed with a diamond impregnated high shine cup. (Jazz Polisher SS White) The resultant brilliant shine is revered as the “Rock Star Polish”.
  • 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 a natural looking and esthetically pleasing composite resin restoration.


Case Study: Deep margin Acquisition, Selective Caries Removal, Cuspal overlay with Infinity Edge Tooth Restoration Interface (TRI)

In figures 8 through 18 the modern Clark Class II procedure is demonstrated.  We are currently doing a retrospective study on these non-retentive cavity preparations and will show a very high survival rate.


What about Bioactive materials? Are they the next big thing?

I was at the pet store the other day and spied the new doggie treats that are emblazoned with the “Bioactive” advantage 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 resulting in toth fracturing and poor contacts that lead to periodontal inflammation, food impaction, recurrent decay.    To quote my partner Dr. Jihyon Kim at the Bioclear Learning Center, “A Class II restoration is treatment of disease specific to the contact area.  Shouldn’t an ideal contact be job one?”  And yet nearly all Class II restorations have less than ideal contacts.  To make things worse, the contact is too far to the occlusal, leading to sharp marginal ridges that are prone to fracturing.  The cavity prep taught in nearly every dental school minimizes enamel rod engagement and maximizes dentin tubule involvement. Many have wide open margins.   These preps are designed for amalgam, and when filled with composite they are, essentially, engineered to fail.  Can Bioactives placed in traditional manner bail out a cavity prep from 1890 with butt joints leading to open margins, high C-Factor, and stress risers leading to tooth fracturing?  That would be nice.  But let’s not hold our breath.  For most preparations we can maximize enamel rod integration with infinity edge margins and create TRI’s that are incredibly robust. Bioactivity could be a nice bonus, some day.  Maybe.  But on Monday Morning I need something I know will work.  Good engineering and modern methods are a surer bet.



1) Does Incremental Filling Technique Reduce Polymerization Shrinkage Stresses?

Versluis A, et.al., J Dent Res March 1996; 75(3): 871-878


2) A radiographic and scanning electron microscopic study of approximal margins of Class II resin composite restorations placed in vivo. Opdam NJ, Roeters FJ, Feilzer AJ, Smale I.

J Dent. 1998 May;26(4):319-27.