August 9, 2021
by Robert A. Lowe, DDS, FAGD, FICD, FADI, FACD, FIADE, FASDA, Diplomat, American Board of Aesthetic Dentistry
The typical Class II posterior composite restoration is “placed on blind faith” using techniques and armamentarium designed specifically for amalgam placement. It is extremely difficult to evaluate the quality of composite layering in an interproximal preparation that is between the buccal and lingual line angles and thus, not clinically visible. Unlike amalgam, composite is not “condensable”; using round “amalgam pluggers” to “condense” composite in proximal boxes with geometric line and point angles makes it virtually impossible to ascertain that these areas are properly filled without voids. To make matters worse, these “potential” voids are neither clinically nor radiographically detectable. Left undetected, microleakage and bacterial contamination of voids can lead to early clinical failure. Dental researchers have long sought a technique for flowable composite resins that would eliminate the need for “condensing” and/or “packing” while improving the internal adaptation of the material to the cavity walls.
A Comparison of Composite Resins Techniques:
Incremental Vs Bulk Fill Placement
Traditionally, clinical placement of composite resins has utilized a 2mm increment technique. This approach was recommended to decrease the effects of polymerization shrinkage on the material during light curing, and to assure curing light penetration to the entire resin depth. Some studies advised placing each increment diagonally, engaging only one vertical wall of the preparation at a time, in order to avoid “pulling the cusps together.” Given the many advances in polymer chemistry, photo activation, and curing light technologies that we currently employ, do these “old rules” still apply?
Research comparing incremental vs bulk fill placement of composite resins concluded almost 20 years ago that there is no statistical difference in cuspal deflection (pulling of cusps) or decrease in marginal integrity (marginal gaps or “white lines”). The main clinical issue with bulk placement of composite resins appears to be the depth of polymerization – does the material at the base fully cure when placed in increments larger than 2 mm? Other studies have proposed directional curing at the gingival embrasures from both buccal and lingual, after matrix band removal, to increase the full cure of composite at the gingival margin of the proximal box in a Class II restoration.1-4
Bulk Fill Flowable Composite Resin Technologies
Bulk fill (up to 4 mm) flowable composite resins have been clinically used for several years and are traditionally designated as “dentin replacement”, reducing the number of increments required in posterior composite restorations. The lower viscosity of the flowables (compared to conventional “paste” composites) is claimed5 to increase marginal adaptation in the line and point angles of the cavity, reducing the potential of marginal failure due to microleakage. Until recently, bulk fill flowable composite resins all required the addition of a nanohybrid composite as a “capping (enamel) layer” (1-1.5 mm thick) to withstand posterior occlusal forces and blend aesthetically with surrounding tooth structures. Bulk flowables have also been claimed6 to reduce the polymerization shrinkage stress of overlying composite resins due to their more elastic nature. While neither of these proposed advantages have been validated through research, there is a relatively broad consensus that the use of flowable composites does help to optimize the adaptation of overlying composite to the geometric intricacies of cavity preparations.
A New Evolution in Bulk Fill Flowable Composite Resins
Estelite Bulk Fill Flow (Tokuyama Dental), as a new “class”, changed the way bulk fill flowable composites are placed by eliminating the need for a nanohybrid “capping layer” as the final increment. According to the manufacturer, the spherical nature of the fillers in the material allows for an increase in physical properties and aesthetics, particularly opacity, the major drawback that relegated flowables to dentin replacement. As a result of their uniform geometry, these “supra-nano” filler particles can be closely compacted in the resin matrix to enhance the physical properties (wear resistance, compressive and tensile strength) of the material. Furthermore, they permit more light diffusion and refraction that penetrates into the material. This offers a more predictable cure depth and an increased ability for the material to blend aesthetically with surrounding tooth structures. Estelite Bulk Fill Flow is more translucent at placement, allowing a 4mm depth of cure. During polymerization, the material becomes more opaque to better match the optical properties of the surrounding enamel tooth structure. The spherical supra-nano fillers (200 nanometers), create an extremely smooth surface that can be quickly polished to a very high, long-lasting luster.) Abrasion and surface plucking will not impact the shine and reflectivity for years to come.
Clinical Case Report: Class II Posterior Bulk Fill Flowable Composite
The Class II DO composite in tooth 24 (Fig. 1) had a fractured marginal ridge and required replacement. The remaining composite material and any recurrent decay were removed with a 330-carbide bur (SS White, Lakewood NJ) while the adjacent surface was protected by a Wedge Guard (Ultradent Products, South Jordan UT). (Fig. 2) Once removal of the existing restoration was complete, the quadrant was isolated with Isolite (Isolite Systems, Zyris, Santa Barbara CA) and a Dry Tip (Microbrush International, Grafton WI) to cover Stenson’s (parotid) duct. Next, a Dual Force sectional matrix (Clinical Research Dental, London ON) was placed around the completed cavity preparation. (Fig. 3) The preparation was selectively etched for 15 seconds on the enamel periphery with 37% phosphoric acid and then rinsed with water. The enamel was air-dried.
Tokuyama Universal Bond (Tokuyama Dental America, Encinitas CA) Bond A and Bond B are applied sequentially to the cavity preparation enamel and dentin per manufacturers’ instructions, (Fig. 4) then air thinned. The selected shade (A2) of Estelite Bulk Fill Flowable (Tokuyama Dental) was inserted into the cavity preparation. (Fig. 5) A sable brush (Fig. 6) was used to gently remove any minimal excess and to ensure that the cavity margins were covered. Since a “capping layer” is not required with Estelite Bulk Fill Flowable composite, the cavity preparation was filled to the cavosurface margin and the top of the matrix band interproximally. The importance of a properly fitted anatomic sectional matrix to limit any potential excess restorative material cannot be overemphasized. (Fig. 7) The goal is to have as little rotary finishing and contouring as possible. After light curing the composite per manufacturer’s instructions, the matrix system and isolation were removed, and the finishing process begun.
The occlusal contacts were checked with articulating paper (Fig. 8) and adjusted using a “needle” or “mosquito” type composite diamond finishing bur 8392.016 (Komet USA, Rock Hill SC). (Fig. 9) Finally, the restoration was polished with A.S.A.P. All Surface Access Polishers rubber composite polishing instruments (Clinical Research Dental, London ON). (Figs. 10 & 11) ContacEZ Interproximal Finishing Instruments (ContacEZ, Directa Dental, Newton CT) removed excess resin bonding material and refined the interproximal contours as needed to facilitate flossing. (Fig. 12) A post-operative occlusal view of the completed restoration shows contact, contour, and esthetics. (Fig. 13) Note the extremely high luster and the imperceptible blend of the restorative material into the surrounding tooth structure.
Dentists have been seeking a simplified, less technique sensitive approach to clinical placement of posterior composites. Bulk fill flowable composites offer the benefits of accurate adaptation to the cavity preparation and elimination of incremental placement and condensation. Estelite Bulk Fill Flow (Tokuyama Dental) goes one step further by eliminating the need for an enamel “capping layer”; cavity preparations of up to 4mm depth can be filled entirely with one highly polishable flowable bulk fill increment. This technique offers the clinician a high-quality restorative option for a variety of clinical applications.
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About the Author
Dr. Robert A. Lowe graduated magna cum laude from Loyola University School of Dentistry in 1982. He maintains a private practice in Charlotte, North Carolina, publishes and lectures internationally on aesthetic and restorative dentistry. He is also an Assistant Professor in the Department of Oral Rehabilitation at James B. Edwards College of Dental Medicine – MUSC in Charleston, SC. Dr. Lowe can be reached at 704-450-3321 or at email@example.com