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Although resin-based composites have existed in dentistry for more than 50 years, the category of flowable composite resins is relatively new. In late 1996, the first generation of flowable composite was introduced and had been designed to be less viscous than composite resin, but not as fluid as dental sealant. Bayne and colleagues1 wrote of these early materials, “The success of the early flowable composite products was more a result of marketing than of any special properties beyond flow.”
Composite resins are tooth-colored restoratives that are comprised of organic resin matrices and inorganic fillers consisting of proprietary combinations of silica, quartz, zirconia, and prepolymerized resins. Recently, composite categories have evolved based on resin type and filler size and now include hybrid, nanofill, microfill, packable, and flowable. What defines a flowable composite is low-viscosity material capable of being dispensed into small preparations through needles or cannulas (usually 20-gauge) and low filler content typically 20% to 25% less than nonflowable materials.2,3 Some materials are more flowable (ie, less viscous) than others, and, in general, this is directly related to the filler content and particle-size distribution. When 11 flowable composites were compared using a modified flow test technique, PermaFlo® (Ultradent) and Wave (SDI) were more fluid than FZ250 (3M ESPE). The more fluid materials had lower flexural strengths than the more viscous materials when tested at 24 hours and again at 1 month.4
It is commonly believed that filler content is an important characteristic influencing volumetric shrinkage and wear resistance. Shrinkage of flowable composites is estimated at approximately 3.8% to 6.4% and 1% to 3% higher than nonflowable resins.5 Practitioners have limited the range of application and filling techniques to address these shortcomings. In doing so, flowable composites are currently indicated for purposes such as lining Class II proximal boxes, cavity adaptation, repair of bis-acryl provisional, amalgam repair, and restoration of small nonocclusal-bearing lesions (Table 1).6-8 In addition, by placing the flowable composite material in increments not exceeding 2 mm, the challenge of polymerization stress is believed to be minimized.1,9,10
With more than 50 flowable composites on the US market covering a wide range of physical properties among them, it may be difficult to determine which material is most appropriate for each clinical situation. For that reason, this article examines two controversial subjects in regard to flowable composites. First, will the use of flowable composites to seal the gingival cavosurface in the proximal box of a Class II preparation lead to improved outcomes and less microleakage? Second, do recently introduced bulk-fill flowable composites perform as claimed and reduce shrinkage stress?
Volumetric Shrinkage and Microleakage
Shrinkage of flowable composites, despite material advances, remains a principal challenge to restorative dentists. In a worst-case scenario, shrinkage can compromise the success of the restoration and contribute to a poor marginal seal, microleakage, microfracture, and recurrent caries.11
After the flowable composite is expressed into the cavity preparation and before polymerization, the monomer constituents are held together loosely with minimal potential energy.12 At some point during the polymerization reaction, a gel phase is reached and an elastic modulus is created.13 Elastic modulus refers to the rigidity of a material and its ability to resist deformation. If the flowable resin is placed into a confined space and then shrinks during polymerization, stress will develop. According to Hooke’s law, stress is determined by the stiffness of a material when subject to a given strain.14 In this case, the shrinkage stresses are transferred to the surrounding tooth structure because the elastic modulus of tooth is far greater than the restorative material.15
As a result of shrinkage stresses being transferred to the tooth, deformation of the tooth occurs. This may result in postoperative sensitivity, opening of microfractures, bond failure, microleakage leading to recurrent caries, and deterioration of the restorative margin.12,13,16 Several factors have been identified as influencing the shrinkage stress of a restoration: the size and geometry of the restoration (ie, C-factor, depth and diameter), materials used, and curing protocol.17-19
Incremental filling techniques have been proposed as a means to reduce shrinkage stress of composite restorations. There has been disagreement among authors recently on this issue; Versluis et al13 and Abbas et al20 showed that deformation and cuspal deflection could be minimized when bulk-fill techniques were used. Lee et al21 and Park et al22 demonstrated that incremental filling techniques should be used to mitigate polymerization shrinkage and cuspal deformation. Despite differing conclusions, incremental filling techniques are generally recommended and dentists may choose to restore composite restorations in this manner on the basis of additional factors such as acceptable depth of cure, proper adaptation, and adequate bond formation.13,23
The use of flowable composites as a liner to seal the gingival margin and provide an intermediate stress-absorbing layer under Class II restorations is controversial. Some studies have shown decreased microleakage when flowable composite is used as a liner at the gingival margin,24-34 while others have discouraged the practice.35-41 Some research has concluded that location of the gingival margin either above or below the cemento-enamel junction is the most important factor in determining the best restorative material to use. In these studies, glass-ionomer cement has been suggested because of its adhesion properties and lack of shrinkage over flowable composite to prevent microleakage.42-45 When synthesizing the results of these studies, it appears that the use of flowable composite as a liner in the proximal box is recommended to increase cavity adaptation and reduce microleakage. It is important to note, however, that because of high volumetric shrinkage and the possible resulting stress generated, 1-mm increments were most often used in the studies reviewed.
Bulk-Fill Flowables
Recent advances in monomer technology have ushered in a new category of bulk-fill flowable composites that are designed to address material shortcomings of earlier products. The new category of bulk-fill flowable composites promotes the effective use of 4-mm increments while decreasing shrinkage stresses generated during polymerization.46,47 In 2009, the first bulk-fill flowable resin, SureFil® SDR® flow (DENTSPLY Caulk), was introduced. Currently, four bulk-fill flowable composites are on the US market: SureFil SDR flow, Filtek™ Bulk Flow (3M ESPE), Venus® Bulk Flow (Heraeus Kulzer), and x-tra base (Voco). A comparison of the four currently available bulk-fill flowables is presented in Table 2.
The information provided by the manufacturer of SureFil SDR flow regarding the chemical composition indicates that the organic resin matrix consists of a patent-registered urethane dimethacrylate with incorporated photoactive groups able to control polymerization kinetics. From DENTSPLY’s website: “Through the use of the ‘Polymerization Modulator’, the resin forms a more relaxed network and provides significantly lower polymerization stress.”48 Ilie and Hickel examined SureFil SDR flow compared with other composites and found that the contraction stress generated by SureFil SDR flow was 1.1 mPa compared with 5.3 mPa and 6.5 mPa of Esthet-X® (DENTSPLY Caulk) and Filtek Supreme Plus Flow (3M ESPE), respectively.49 The authors theorized that the stress-relieving properties of SureFil SDR flow, in part, were the result of a delayed gel phase and slower polymerization allowing for increased flow. Compared with the other composites, SureFil SDR flow showed the lowest result on the Vickers hardness test, which may be due to the fact it has the lowest filler content by volume (44%). For this reason, the SureFil SDR flow directions for use recommend that a 2-mm occlusal cap be placed using a traditional composite restorative such as TPH Spectra™ (DENTSPLY Caulk).50
C-factor (configuration factor) is an estimation of the stresses generated through a given cavity configuration by a ratio of bonded to unbonded surfaces. According to Feilzer et al,51 the higher the C-factor (ie, the higher the number of bonded surfaces), the higher the stress generated (eg, Class I, Class II). Conversely, a cavity with a higher ratio of unbonded surfaces should result in lower shrinkage stress (eg, Class III, Class IV). Findings from two recent studies have also suggested that cavity depth and diameter may impact shrinkage stress and resulting microleakage.18,52 Examining the effect of bulk-fill high C-factor cavities with a low-shrinkage flowable composite (SureFil SDR flow), Van Ende and colleagues showed that 4-mm increments placed in high C-factor preparations (mimicking Class I and Class II preparations) did not compromise bond strength secondary to shrinkage stress.53,54 The authors concluded that if bulk-fill techniques are desired for restoration of high C-factor cavities, the dentist should consider low-stress materials to avoid adhesive de-bonding and microleakage. These conclusions appear to align with the conclusions of Rogendorf et al,55 which said that bulk-fill low-shrinkage flowable resin can be used in an open-sandwich technique without a negative impact on marginal integrity.
Cuspal deflection and deformation were studied in Class II preparations by Moorthy et al.56 The authors compared a conventional resin-based composite with two low-stress bulk-fill flowable composites, SureFil SDR flow and x-tra base (Voco). After restoration, cuspal deflection was measured and found to be reduced by greater than 50% when the flowable resins were used; no significant difference was noted between the flowable resins tested. The authors suggested that bulk filling to within 2 mm of the occlusal cavosurface can reduce operator time because of reduced incremental layers without additional shrinkage stress or loss of marginal quality.
To this point, bulk-fill flowable composite resins have been discussed; however, more viscous bulk-fill materials also exist on the US market and deserve mention. These materials can be used to restore occlusal surfaces and have a published depth of cure of 4 mm to 6 mm; examples include Alert® (Pentron), Tetric EvoCeram® Bulk Fill (Ivoclar Vivodent), and x-tra fil (Voco). Christensen’s Clinician’s Report from January 2012 observed that a potential negative of bulk-fill composites such as the above-named materials was that they were found to have a frequent occurrence of voids.46 The bulk-fill flowables tested showed voids occurred infrequently or occasionally.
An interesting hybrid between the bulk-fill flowable composites and bulk-fill composites is SonicFill™ (Kerr). The technique involves the use of a proprietary handpiece and composite. Shear stress is applied to the composite via sonic vibration, thereby lowering the viscosity of the material by a claimed 87%. In this way, the material can flow into the cavity preparation up to a depth of 5 mm. The manufacturer claims a more gradual buildup of viscosity once the shear stress is removed, allowing a lessening of contraction stresses and no increase in cuspal deflection. To date, few published studies examine the effects of sonic vibration on composite resin or the long-term effects of SonicFill other than on the manufacturer’s website.57-59
Conclusion
Flowable composites are components used in everyday restorative practice. Research has described their shortcomings with respect to physical properties and applications. When used properly for the right indications, flowable composites can provide clinical advantages. The introduction of bulk-fill materials, as either flowable or more viscous composites, is a desired enhancement to composite technology, and these materials are capable of increasing procedural efficiency without increasing negative outcomes. Based on this article, the following clinical suggestions can be made:
Flowable composite materials are a less-filled, less viscous material that can be syringed into small preparations. Because of high shrinkage and low wear resistance, the choice of applications for early flowables should be limited. Each incremental depth should not exceed 2 mm.
Volumetric shrinkage of composite resins remains a clinical concern and should be carefully considered when choosing materials or restorative techniques.
The utilization of incremental filling techniques is recommended to minimize shrinkage stress during composite resin placement.
The use of flowable composite resin is recommended to seal the gingival margin of the proximal box in Class II preparations. If the gingival margin extends below the cemento-enamel junction, dentists should consider the use of glass-ionomer cement.
Low-stress bulk-fill flowables are capable of being placed in 4-mm increments without increased cuspal deflection or loss of marginal integrity. It is important to note that bulk-fill flowable resins do not provide improvements in marginal quality or cavity adaptation over earlier flowable composites; however, they do not negatively affect it either.60
DISCLOSURE
The authors are DENTSPLY Caulk employees.
References
1. Bayne SC, Thompson JY, Swift EJ, et al. A characterization of first-generation flowable composites. J Am Dent Assoc. 1998;129(5):567-577.
2. Strassler HE. Clinical update: flowable composite resins. Incisal Edge. 2007;1:62-69. http://d3e9u3gw8odyw8.cloudfront.net/flow_comp.pdf. Accessed March 28, 2013.
3. Braga RR, Hilton TJ, Ferracane JL. Contraction stress of flowable composite materials and their efficacy as stress-relieving layers. J Am Dent Assoc. 2003;134(6):721-728.
4. Attar N, Tam LE, McComb D. Flow, strength, stiffness and radiopacity of flowable resin composites. J Can Dent Assoc. 2003;69(8):516-521.
5. Flowable resins, comparison of 33 brands. CRA Newsletter. 2002;26(10):3-4.
6. Margolis FS. Flowable composites: aesthetics for tots and teens. Dent Today. 2011;30(4):132,134,136-137.
7. Brown PL. Flowable composites: the unsung heros of bonding. http://www.drbicuspid.com/index.aspx?sec=sup&sub=rst&pag=dis&ItemID=305410. Accessed March 28, 2013.
8. Bonsor SJ. Contemporary use of flowable resin composite materials. Dent Update. 2008;35(9):600-602,604,606.
9. Bohnenkamp DM, Garcia LT. Repair of bis-acryl provisional restorations using flowable composite resin. J Prosthet Dent. 2004;92(5):500-502.
10. Roberts HW, Charlton DG, Murchison DF. Repair of non-carious amalgam margin defects. Oper Dent. 2001;26(3):273-276.
11. Karthick K, Kailasam S, Geetha Priya PR, et al. Polymerization shrinkage of composites–a review. J Indian Acad Dent Specialists. 2011;2(2):32-36.
12. Malhotra N, Kundabala M, Shashirashmi A. Strategies to overcome polymerization shrinkage–materials and techniques. A review. Dent Update. 2010;37(2):115-118,120-122,124-125.
13. Versluis A, Douglas WH, Cross M, Sakaquchi RL. Does an incremental filling technique reduce polymerization shrinkage stresses? J Dent Res. 1996;75(3):871-878.
14. Xavier JC, de Melo Monteiro GQ, Resende Montes MAJ. Polymerization shrinkage and flexural modulus of flowable dental composites. Materials Res. 2010;13(3):381-384.
15. Craig RG. Selected properties of dental composites. J Dent Res. 1979;58(5):1544-1550.
16. Jensen ME, Chan DCN. Polymerization shrinkage and microleakage. In: Vanherle G, Smith DC, eds. Posterior Composite Resin Dental Restorative Materials. Utrecht, The Netherlands: Peter Szulc Publishing Co; 1985:243-262.
17. Deliperi S, Bardwell DN, Papathanasiou A. Effect of different polymerization methods on composite microleakage. Am J Dent. 2003;16(special issue):73A-76A.
18. Braga RR, Boaro LC, Kuroe T, et al. Influence of cavity dimensions and their derivatives (volume and ‘C’ factor) on shrinkage stress development and microleakage of composite restorations. Dent Mater. 2006;22(9):818-823.
19. Pires-de-Souza Fde C, Drubi Filho B, Casemiro LA, et al. Polymerization shrinkage stress of composites photoactivated by different light sources. Braz Dent J. 2009;20(4):319-324.
20. Abbas G, Fleming GJ, Harrington E, et al. Cuspal movement and microleakage in premolar teeth restored with a packable composite cured in bulk or in increments. J Dent. 2003;31(6):437–444.
21. Lee MR, Cho BH, Son HH, et al. Influence of cavity dimension and restoration methods on the cusp deflection of premolars in composite restoration. Dent Mater. 2007;23:288–295.
22. Park J, Chang J, Ferracane J, Lee IB. How should composite be layered to reduce shrinkage stress: incremental or bulk filling? Dent Mater. 2008;24(11):1501-1505.
23. Schneider LF, Cavalcante LM, Silikas N. Shrinkage stresses generated during resin-composite applications: a review. J Dent Biomech. 2010;Epub 2009 Sep 30.
24. Payne JH. The marginal seal of Class II restorations: flowable composite resin compared to injectable glass ionomer. J Clin Pediatr Dent. 1999;23(2):123-130.
25. M R, Sajjan GS, B N K, Mittal N. Effect of different placement techniques on marginal microleakage of deep class-II cavities restored with two composite resin formulations. J Conserv Dent. 2010;13(1):9-15.
26. Fabianelli A, Sgarra A, Goracci C, et al. Microleakage in class II restorations: open vs closed centripetal build-up technique. Oper Dent. 2010;35(3):308-313.
27. Sadeghi M, Lynch CD. The effect of flowable materials on the microleakage of Class II composite restorations that extend apical to the cemento-enamel junction. Oper Dent. 2009;34(3):306-311.
28. Olmez A, Oztas N, Bodur H. The effect of flowable resin composite on microleakage and internal voids in class II composite restorations. Oper Dent. 2004;29(6):713-719.
29. Attar N, Turgut MD, Güngör HC. The effect of flowable resin composites as gingival increments on the microleakage of posterior resin composites. Oper Dent. 2004;29(2):162-167.
30. Fabianelli A, Goracci C, Ferrari M. Sealing ability of packable resin composites in class II restorations. J Adhes Dent. 2003;5(3):217-223.
31. Peris AR, Duarte S Jr, de Andrade MF. Evaluation of marginal microleakage in class II cavities: effect of microhybrid, flowable, and compactable resins. Quintessence Int. 2003;34(2):93-98.
32. Neme AM, Maxson BB, Pink FE, Aksu MN. Microleakage of Class II packable resin composites lined with flowables: an in vitro study. Oper Dent. 2002;27(6):600-605.
33. Tung FF, Hsieh WW, Estafan D. In vitro microleakage study of a condensable and flowable composite resin. Gen Dent. 2000;48(6):711-715.
34. Leevailoj C, Cochran MA, Matis BA, et al. Microleakage of posterior packable resin composites with and without flowable liners. Oper Dent. 2001;26(3):302-307.
35. Malmström HS, Schlueter M, Roach T, Moss ME. Effect of thickness of flowable resins on marginal leakage in class II composite restorations. Oper Dent. 2002;27(4):373-380.
36. Ziskind D, Adell I, Teperovich E, Peretz B. The effect of an intermediate layer of flowable composite resin on microleakage in packable composite restorations. Int J Paediatr Dent. 2005;15(5):349-354.
37. Tredwin CJ, Stokes A, Moles DR. Influence of flowable liner and margin location on microleakage of conventional and packable class II resin composites. Oper Dent. 2005;30(1):32-38.
38. Sensi LG, Marson FC, Monteiro S Jr, et al. Flowable composites as “filled adhesives:” a microleakage study. J Contemp Dent Pract. 2004;5(4):32-41.
39. Jain P, Belcher M. Microleakage of Class II resin-based composite restorations with flowable composite in the proximal box. Am J Dent. 2000;13(5):235-238.
40. Beznos C. Microleakage at the cervical margin of composite Class II cavities with different restorative techniques. Oper Dent. 2001;26(1):60-69.
41. Kwon Y, Ferracane J, Lee IB. Effect of layering methods, composite type, and flowable liner on the polymerization shrinkage stress of light cured composites. Dent Mater. 2012;28(7):801-809.
42. Kasraei S, Azarsina M, Majidi S. In vitro comparison of microleakage of posterior resin composites with and without liner using two-step etch-and-rinse and self-etch dentin adhesive systems. Oper Dent. 2011;36(2):213-221.
43. Hagge MS, Lindemuth JS, Mason JF, Simon JF. Effect of four intermediate layer treatments on microleakage of Class II composite restorations. Gen Dent. 2001;49(5):489-495.
44. Loguercio AD, Bauer JR, Reis A, et al. Microleakage of a packable composite associated with different materials. J Clin Dent. 2002;13(3):111-115.
45. Wibowo G, Stockton L. Microleakage of Class II composite restorations. Am J Dent. 2001;14(3):177-185.
46. Advantages and challenges of bulk-fill resins. Clinician’s Report. 2012;5(1):1-6.
47. SureFil® SDR™ flow Posterior Bulk Fill Flowable Base. Inside Dentistry. 2009;5(9):124.
48. SureFil SDR flow. http://www.surefilsdrflow.com. Accessed March 28, 2013.
49. Ilie N, Hickel R. Investigations on a methacrylate-based flowable composite based on the SDR™ technology. Dent Mater. 2011;27(4):348–355.
50. SureFil SDR flow Directions for Use [product brochure]. Milford, DE: DENTSPLY Caulk; 2012. http://www.surefilsdrflow.com/sites/default/files/SureFil_DFU.pdf. Accessed March 28, 2013.
51. Feilzer AJ, De Gee AJ, Davidson CL. Setting stress in composite resin in relation to configuration of the restoration. J Dent Res. 1987;66(11):1636-1639.
52. Watts DC, Satterthwaite JD. Axial shrinkage-stress depends upon both C-factor and composite mass. Dent Mater. 2008;24(1):1-8.
53. Van Ende A, De Munck J, Van Landuyt KL, et al. Bulk-filling of high C-factor posterior cavities: effect on adhesion to cavity-bottom dentin. Dent Mater. 2013;29(3):269-277.
54. de la Macorra JC, Gomez-Fernandez S. Quantification of the configuration factor in Class I and II cavities and simulated cervical erosions. Eur J Prosthodont Restor Dent. 1996;4(1):29-33.
55. Roggendorf MJ, Krämer N, Appelt A, et al. Marginal quality of flowable 4-mm base vs. conventionally layered resin composite. J Dent. 2011;39(10):643-647.
56. Moorthy A, Hogg CH, Dowling AH, et al. Cuspal deflection and microleakage in premolar teeth restored with bulk-fill flowable resin-based composite base materials. J Dent. 2012;40(6):500-505.
57. Walmsley AD, Lumley PJ. Applying composite luting agent ultrasonically: a successful alternative. J Am Dent Assoc. 1995;126(8):1125-1129.
58. Cuevas S. Sonic activation: new paradigm for composite resins. Dent Today. 2011;30(8):100,102-103.
59. Portfolio of Scientific Research. Kerr Dental. http://www.kerrdental.com/cms-filesystem-action/KerrDental-University-3rdPartyData/sonicFill-psr-2011-10-11.pdf. Accessed March 28, 2013.
60. Walter R. Critical appraisal: bulk-fill flowable composite resins. J Esthet Rest Dent. 2013;25(1):72-76.
