Copyright © 2013 American Dental Association. All Rights Reserved.Copyright © 2013 American Dental Association. All Rights Reserved.1406 JADA 144(12) http://jada.ada.org December 2013

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G o r d o n J . C h r i s t e n s e n , D D S , M S D , P h D

Nearly two decades ago, a few dental manufac-turers began to provide flowable resins to the

marketplace. They became popular immediately. Subse-quently, almost all manufactur-ers of resin-based composite introduced a flowable resin. Manufacturers and dental retailers inform us that flow-able resins are among the most popular dental restorative materials.

In this column, I will discuss the advantages and limita-tions of flowable resins and the most appropriate locations for their use, as well as suggest some products to substitute for flowable resins. This is a brief, state-of-the-art overview of the flowable resin concept, which still is controversial.

ADVANTAGES OF FLOWABLE RESINS

It is well known that the myri- ad brands of conventional restorative resin-based com-posites vary in viscosity. Most manufacturers go to great effort to make the handling characteristics of their conven-tional resin-based composite restorative materials meet the preferences of the majority of dentists, but significant differ-

ences in viscosity exist among the most popular brands. Some dentists prefer a puttylike con-sistency, which allows them to place some load on the restor-ative material as they fill tooth preparations, whereas others prefer less viscosity. Selection of a composite brand certainly is a matter of personal pref-erence and is based largely on handling characteristics. Dentists are able to judge the adequacy of composites in the mouth only after a significant clinical observation period and after reviewing reliable clinical research.

Flowable resins also vary markedly in viscosity.1-4 Some flow almost like water when placed in tooth preparations, and others are relatively putty- like. However, all brands of flowables are less viscous than are conventional composites.

The characteristics of several categories of dental materials are similar to those of flowable restorative resins. These ma-terials include resin restorative cements, resin orthodontic ce-ments, sealants and resin light-cure dental dam. Some dentists replace these materials with flowables.

Why are flowable composites so popular? I have searched

for the answer to this question from my own clinical observa-tions, the dental literature and continuing education in-structors. The major reason flowables are popular is one significant singular advantage: they flow. In searching the literature, it is difficult to find other reasons.

LIMITATIONS OF FLOWABLE RESINS

Polymerization shrinkage and stress. The polymer-ization shrinkage and stress of some flowable composite brands have been shown to be more than those of conven-tional composites.5 However, these properties are improving as the chemistry of flowables is improved. In some brands (such as SureFil SDR Flow, Dentsply Caulk, Milford, Del., and Heliomolar Flow, Ivoclar Vivadent, Schaan, Liechten-stein), the clinical significance of shrinkage is debatable, but the general opinion is that high stress may relate to cracking of tooth structure.5,6

Wear. Excessive wear of flowables in service has been a challenge in the past.7 How-ever, recently it has been shown that some new brands of flowables now exhibit wear characteristics similar to those of conventional composites.8 In

Why are flowable resin-based composites so popular?

Copyright © 2013 American Dental Association. All Rights Reserved. Copyright © 2013 American Dental Association. All Rights Reserved.Copyright © 2013 American Dental Association. All Rights Reserved.

the past, dentists have been advised to use flowables only in areas in which major wear is not expected. This caution is being challenged by the manufacturers of some of the new flowables, and clinicians should watch for research reports regarding wear char-acteristics of newer flowables. Some flowables are suggested as internal fillers only, because the manufacturers state their wear characteristics have been shown to be less than desirable.

Strength. The strength of some flowables has been shown to be lower than that of conventional composites.7 In recent years, nanofillers and microfillers have been added to most resin-based composites—and the filler content of some newer flowables is comparable with that of conventional res-ins. As a result, some of the new flowables are rivaling conventional composites in strength.6,9 As flowables con-tinue to improve, clinicians are advised to watch for additional improvements in strength.

Depth of cure. Depth of resin cure of most flowables has been shown to be less than acceptable for the now-in-vogue “bulk fill” technique. With a few exceptions, flow-ables have been shown to cure to a depth of only 1 to 3 mil-limeters when either halogen or light-emitting diode curing lights are used.6,10 This limita-tion is not a problem in some of the uses of flowable resins I discuss later.

The limitations of flowables, previously noted, are being overcome to some degree. How- ever, that statement does not apply to all flowables. I advise practitioners to seek com-parative research informa-tion about flowable composite brands before using them in some of the indications being

promoted by manufacturers and clinicians.

MOST APPROPRIATE CLINICAL LOCATIONS FOR FLOWABLE RESINS

The preceding brief overview is not intended to be a com-prehensive research-based brand-name comparison of flowable resin-based com-posites. Much more research and clinical information are available in the literature. The following suggestions are based on my own interpreta-tion of the available published research, intensive basic and clinical research accomplished over many years by scientists and clinical evaluators at CR Foundation, Provo, Utah, and my own observations.

Lining tooth prepara-tions in Classes I to VI. Lining tooth preparations in Classes I to VI, after placing appropriate bonding agents, is among the most viable and common uses of flowables.11 When low-viscosity materials are placed in a tooth prepara-tion, they flow rapidly and eas-ily into the many irregularities of the tooth preparation as well as onto the margins.

Many dentists prefer to use resin-modified glass ionomer, instead of flowable composite, for lining direct composite tooth preparations because it has properties close to those of tooth structure, a chemi-cal bond to the tooth and the ability to release fluoride. (Ex-amples of such materials are Vitrebond Plus, 3M ESPE, St. Paul, Minn., and Fuji Lining LC, GC America, Alsip, Ill.)

There are ways in which to line tooth preparations with thin-viscosity composite other than by using flowable resin. One such method is to place a thin layer (0.5 mm) of conventional-viscosity com-posite into the internal aspect

of a tooth preparation and wait a few seconds to allow the patient’s body heat, which is about 30°F hotter than the room-temperature resin, to reduce the viscosity of the con-ventional resin and let the ma-terial flow into the irregulari-ties of the preparation. This simple procedure also saves significant overhead costs. Flowable resins cost approxi-mately $6 to $48 per cubic centimeter, with an average of about $34 per cc.5 By using the previously described tech-nique, it is easy to save most of that cost and still achieve the same result as with using a flowable.12

In addition, devices that warm and reduce the viscosity of conventional composite are available (such as C-Warmer, Dentazon, Torrance, Calif., and Calset Tri Tray Composite Warmer, AdDent, Danbury, Conn.). These warmers rapidly reduce the viscosity of conven-tional composite and allow the material to flow as well as do flowable composites.

Bulk filling of the inte-rior of large tooth prepa-rations. Bulk filling of the internal aspect of large tooth preparations is being advo-cated as a use for flowables by some clinicians and manufac-turers. Example products that serve this purpose well are SureFil SDR Flow, which light cures to a depth of at least 4 mm, and the dual-cure flow-able HyperFIL (Parkell, Edge-wood, N.Y.).6

Core build-up and post cementation. Using flowables for core build-up and post ce-mentation has been promoted and has shown promise in research, because the flowable characteristic allows optimum adaptation to tooth structure and homogeneity when used in these procedures.13

Use as a preventive resin

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Copyright © 2013 American Dental Association. All Rights Reserved.

restoration. As stated, one of the significant advantages of flowable resins is that they flow well into any location in which they are placed. Most of them have characteristics similar to those of sealants, and some practitioners are using them as sealants or preventive resin restorations. Because the prop-erties of some of the current brands of flowables have been improved significantly over those of previous generations, this is an appropriate use.

Repair of bis-acryl provi-sional restorations. Repair of bis-acryl provisional resto-rations is an excellent use of flowables, because the chem-istry of flowable resin-based composites allows them to bond chemically to these most commonly used provisional restoration materials.

SUMMARYFlowable resin-based compos-ites are starting to improve in comparison with the undesir-able characteristics they had when they were introduced

many years ago. At that time, they were weak and had high rates of shrinkage and wear. Numerous new brands are over- coming these undesirable char-acteristics, and they deserve clinicians’ observation and cau-tious, conservative use. n

Dr. Christensen is the director, Practi-cal Clinical Courses, and a cofounder and the chief executive officer, CR Foundation, Provo, Utah. He also is an adjunct profes-sor, University of Utah, Salt Lake City. He is a diplomate of the American Board of Prosthodontics. Address reprint requests to Dr. Christensen at CR Foundation, 3707 N. Canyon Road, Suite 3D, Provo, Utah 84604.

The views expressed are those of the author and do not necessarily reflect the opinions or official policies of the American Dental Association.

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3. Beun S, Bailly C, Devaux J, Leloup G. Rheological properties of flowable resin composites and pit and fissure sealants. Dent Mater 2008;24(4):548-555.

4. Lee IB, Son HH, Um CM. Rheologic properties of flowable, conventional hybrid, and condensable composite resins. Dent Mater 2003;19(4):298-307.

5. New flowable resins: good, bad or just

hype? Clinicians Report 2013;6(7):1-2.6. Alavarez-Gayosso C, Barcelo-Santana F,

Guerrero-Ibarra J, Saez-Espinola G, Canseco-Martinez MA. Calculation of contraction rates due to shrinkage in light-cured composites. Dent Mater 2004;20(3):228-235.

7. Schultz S, Rosentritt M, Behr M, Handel G. Mechanical properties and three-body wear of dental restoratives and their comparative flowable materials. Quintes-sence Int 2010;41(1):e1-e10.

8. Sumino N, Tsubota K, Takamizawa T, Shiratsuchi K, Miyaszaki M, Latta MA. Comparison of the wear and flexural characteristics of flowable resin composites for posterior lesions. Acta Odontol Scand 2013;71(3-4):820-827.

9. Irie M, Tjandrawinata R, Lihua E, Yamashiro T, Kazuomi S. Flexural per-formance of flowable versus conventional light-cured composite resins in a long-term in vitro study. Dent Mater J 2008;27(2): 300-309.

10. Moore BK, Platt JA, Borges G, Chu TA, Katsilieri I. Depth of cure of dental com-posites: ISO 4049 depth and microhardness of types of materials and shades. Oper Dent 2008;33(4):408-412.

11. Stefanski S, van Dijken JW. Clinical performance of a nanofilled resin composite with and without an intermediary layer of flowable composite: a 2-year evaluation. Clin Oral Investig 2012;16(1):147-153.

12. Knight JS, Fraughn R, Norrington D. Effect of temperature on the flow properties of resin composite. Gen Dent 2006;54(1): 14-16.

13. Monticelli F, Goracci C, Grandini S, Garcia-Godoy F, Ferrari M. Scanning electron microscopic evaluation of fiber post-resin core units built up with different resin composites. Am J Dent 2005;18(1):61-65.

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