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Seventeen years of using flowable resin restoratives – a dental practitioner's personal clinical review Markus Th Firla Dental Update 2024 42:3, 707-709.
Authors
Markus ThFirla
DMD (Dr med dent)
General Dental Practitioner, Private and Statutory Insurance Services Practice, Hauptstrasse 55, D-49205 Hasbergen-Gaste, Germany
Seen through the author's eyes on the basis of his practising dentistry for almost three decades, light-activated flowable resin restoratives (FRCs) or, in common clinical dental terminology, flowable composites have gradually gained major importance in restorative dentistry. Inputs to this ongoing trend are coming from continuous improvements in material properties and the favourable handling characteristics experienced with this particular group of restoratives.
Intended to be used in direct adhesive filling procedures, the number and variety of recent generations of flowable composites for lining, restoration of all cavity classes (I–V), core build-ups and, more recently, ‘bulk-fill-restorations’, however, necessitates a profound clinical understanding of the selective use of flowable composites to ensure clinical success and guarantee long-term high quality results.
Clinical Relevance: Today's flowable composites allow for reliable restoration of all kinds of defects. However, both the handling characteristics and the material properties of FRCs must be fully understood before taking advantage of their potentially excellent clinical performance.
Article
Light-cured flowable resin restoratives for direct adhesive restorations, more commonly known as ‘flowable composites’, have grown into a substantial group of products for professional use in dental practices.1 All major manufacturers in the global dental market who market conventional ‘paste-like’ RBC restoratives also offer one or more less viscous ‘runny versions’ of their regular, more viscous, composites, reflecting the market demand for such products2,3 (Figures 1–4).
Figure 1. Recent generation's resin flowable – or more fittingly described as ‘precisely-injectable-in-all-kinds-of-cavities’ – composites (eg Shofu Beautifil Flow Plus 00) with no ‘slump’ and excellent ‘steadiness’, even allowing for creating ‘funny, vertical works of art’ when light-cured at the moment of being extruded from their hollow needle tips.Figure 2. ‘Oldies but goldies!’: pre-measured volumes allowed to flow (placed on a mixing pad turned vertically for 30 seconds) of Tokuyama's flowable composites (from left to right) Palfique Estelite LV High Flow, Medium Flow and Low Flow. Available on the dental market now for more than ten years, they have been among the first flowable resin restoratives to set the benchmark for all other products to come.Figure 3. Sometimes a reason for potential confusion: flowable composites, even coming from the same manufacturer, can be hard to tell apart in terms of their actual characteristics of ‘flow’ and ‘slump’. The names of the products sometimes add to the confusion, eg Estelite Flow Quick High Flow, let alone the fact that a ‘high flow’ composite implements a ‘low viscous’ consistency. (Also see paragraph ‘Flowable does not necessarily mean runny’.)Figure 4. In addition to their (more or less) product-specific flowability, recent generation's low viscosity resin restoratives do offer some certain features, eg Heraeus's Venus (Flow) Bulk Fil designed for expeditiously performed one-thick-layer linings and fillings, Cumdente's Synamel, especially for nano-sized particles reinforced inorganic filler load, and the adhesive-restoration-procedures-short-cutting self-etching Vertise Flow by Kerr.
This phenomenon manifests in one of the most prolific commercial print and online rating media of dental products, the Houston/USA-based REALITY – the information source for esthetic dentistry whose ‘2003 Volume’ included 32 pages focusing on ‘Flowable Composites/Compomers’. The recent ‘2012 Volume’, published in 2013, devotes 83 pages to cover the subject ‘Flowable Composites’. The text now groups flowable composites more specifically into ‘Dual-Cured/Self-Cured’, ‘Light-Cured – Conventional’ and ‘Light-cured – Low Stress’ categories. The final subsection discusses the recently developed, so-called ‘Bulk-Fill’ FRC restoratives.4,5
Even with over 80 pages of REALITY dealing with all sorts of flowable composites, only a fraction of all available FRC restoratives are included in the rating register. This fact reflects the enormous number and diversity of flowable resin restoratives currently available on the dental market. The best way for the dental practitioner to keep track of FRC performance is through an understanding of their mechanical properties, individual product specific handling characteristics, and the clinical reasons for their use. Selecting the most suitable flowable composites for adhesive restorative procedures is crucial in ensuring long-term clinical success and quality performance of those FRC restorations (Figures 5 and 6).
Figure 5. Horizontally placed material samples of some of the flowable composites liked best by the author: (from left to right) Shofu's Beautifil Opaquer, Beautifil Flow F10, Beautifil Flow F02 and Beautifil Flow Plus F00. Outstanding products suited for all indications in the realm of direct adhesive resin restorations; the latter one with its sister-product F03 (meaning a vertical flow of 3 mm within a 60 seconds time frame) also designated for even stress-bearing occlusal restorations.Figure 6. For those who do not blindly trust all that is said about a resin restorative's light-curing properties: why not execute your own material testing?, eg the author's ‘plug test’ in accordance with Professor Fred Rueggeberg's method. The procedure quantifies the vertical depth of any light-curing composite by polymerizing a given, pre-measured amount of the material in a capsule with a dental curing-light (that also should have been tested) according to the manufacturer's instructions. Tested here: Beautifil Flow Plus F00, shade Vita A1. Result: it is close to being a bulk fill resin restorative.
History and development of flowable resin restoratives
Flowable composites can be traced back to the pioneering product, Revolution, offered on the dental market in 1992 by SDS/Kerr. The name of that first flowable resin restorative was well timed since, at that time, even using paste-like, sculptable composites for adhesive restorations was still a topic of much debate, particularly in regard to using RBCs in stress-bearing posterior locations of the dental arch.6
In their early days, flowable composites represented regular resin restoratives whose ‘dispersed phase’, ie the inorganic filler loading, had been reduced to such an extent that the composite flowed when being extruded out of the syringes' and capsules' tips, respectively. Given that all other constituents were unchanged, manufacturers altered the viscosity and hence the handling and clinical properties of their RBCs by alterations to the type of filler and the load (by weight or volume) of the filler used in the resin matrix. That is why, even today by some, FRC restoratives are believed, to some extent, to be merely ‘runny composites of insufficient quality’ and thus offering inferior clinical performance. However, this view is no longer valid.
Nowadays, with almost a quarter of a century of developments in FRC restoratives, through both clinical and laboratory research, current formulations of some flowable composites are such that these products allow for reliable long-term success with even extensive Class II restorations.
Dispersed phase
The ‘dispersed phase’ of flowable composites has been gradually improved by employing harder, more wear-resistant, more radio-opaque, more sophistically-shaped, and more evenly-loaded fillers. Even nano-sized particles have been included in the latest FRCs. Also, the other ‘distinct parts’ of which any composite is made have been improved significantly in recent years.
Matrix phase
The ‘matrix phase’ is the organic, liquid resin component. It consists of purpose-built resin molecules that, depending on the brand of the flowable composite, polymerize with significantly reduced shrinkage and increase polymerization of the composite's monomers and, in addition, positively influence both the composite's ‘pre-light-cured’ clinical handling characteristics and ‘post-light-cured’ mechanical properties and therefore long-term clinical performance.
Coupling phase and polymerization initiators
Last, but not least, is the ‘coupling phase’. This is when the chemical ingredients that help adhere the resin matrix to the filler particles, as well as the ‘polymerization initiators’, have undergone a continuous process of increasing their efficiency.6,7,8
Looking into the near future, new restorative materials, branded ‘future generation products’, may require both ‘university-based’ and ‘practice-based’ clinical research to document their reliable clinical efficacy.
In order to simplify and speed up the restorative process still further, manufacturers have most recently developed ‘multi-feature’, resin-based restorative products. Examples include products such as Constic by DMG or Vertise Flow by Kerr, defined as ‘self-etching’ and ‘self-adhesive’ FRCs. In addition, TheraCal LC by Bisco, a flowable resin-based restorative meant to act therapeutically in the cavity, is designated as a pulp-capping agent on the basis of its MTA-(Mineral Trioxide Aggregate)-fillers.
Two of the most acknowledged European advocates of a joint perspective of ‘university-based‘ and ‘practice-based’ dental evidence are Trevor Burke, who is Professor of Primary Dental Care at the University of Birmingham, School of Dentistry, and Professor Claus-Peter Ernst. Professor Burke needs no introduction to readers of Dental Update. Professor Ernst teaches restorative dentistry at the dental school of Johannes-Gutenberg-University in Mainz, Germany, in addition to running his independent private dental office for restorative dentistry in the same city.9,10
As a general practitioner without any direct and constant university affiliation, all the author's following personal statements on his long-term use of flowable composites presented in this text are to be seen in accordance with the above-mentioned dental colleagues, as well as in the light of their particular support of ‘practice-based’ dental evidence meeting ‘university-based’ dental evidence in order to benefit the continuously developing rationale of direct adhesive resin restorations, be they done with flowable resin restoratives (FRCs) only, or used in combination with more viscous paste-like resin-based composites (RBCs).
‘Flowable’ does not necessarily mean ‘runny’
The days when ‘flowable’ meant, without exception, ‘runny’ concerning resin restoratives designated for direct adhesive filling procedures are long gone. Even in those early days, it was already clear to any general dental practitioner using these particular composites that ‘runny’ is not exactly the equivalent to the physical and material-science terms of ‘flowable’, while the term ‘viscous’ was meant to reflect the ‘paste-like’ and ‘putty-like’ texture of any dental substance better.
In order to have an improved terminology for everyday clinical processes of using FRC restoratives, the following practical terms are suggested.11,12,13,14
Extrudability
This is the manner by which a flowable resin restorative leaves the opening of the hollow needle in the act of being extruded. Given that all technical and physical parameters are the same, it can be observed that flowable composites that obviously have the same runniness in (identically-shaped) cavities form different evenly-shaped bodies of material when being (identically) extruded. This has to do with the physical laws of ‘viscosity’ and ‘rheology’ which consider the behaviour of substances when they are made to flow.
Flow
This may be defined as the restorative's real capability of flowing into cavities and consequently filling all nooks and crannies, and undercuts. In accordance with REALITY's findings, it can be pointed out by the author that different shades of the same product can have different flow characteristics. In addition, rarely, it can even happen that different lots of the same product show (however slightly) different flow rates.
‘Slurriness’
This relates to the composite's ‘ease of delivery’ when the restorative is being navigated or delivered into the areas to be filled. Some flowables appear to be more ‘sticky’ to both their hollow needle tip and cavity walls and cavity floors than other products, causing the restorative to be more ‘hauled’ or ‘dragged’ through the cavity than smoothly being placed gradually.
Steadiness
This is the ability of FRCs to have any extruded portion maintaining or keeping its shape during the application process before light-curing or polymerization.
Slump
This is closely related to flow and steadiness. ‘Slump’ relates to the quantity and quality of a flowable resin composite restoration's retention of its full contour when flowing out of the cavity while the restorative is still not light-cured (Figures 7–10).
Figure 7. Clinical Case 1: various defects of different aetiologies at the cervical buccal region of a lower right first premolar, canine (in the centre of this figure), and lateral incisor. Direct adhesive restorations accomplished with the help of flowable composites will immensely facilitate the restorative process, providing high quality results.Figure 8. The flowable composite, Beautifil Flow Plus F00, shade A2, is ‘injected’ in the (state-of-the-art prepared, conditioned and bonded) cavity. The restoration is being increasingly ‘blown-up’ to the needed size and shape starting from the cavity's floor rather than pressed in increment by increment – no excess material to be reduced, no cervical matrix needed! (Note the mild, transient burn of the marginal gingiva caused by the application of a two-step adhesive bonding system prior to FRC injection.)Figure 9. All three restorations after the final finishing at baseline review. The needed gingival retraction and haemostasis in the sulcus area of the lateral incisor was conducted by applying 3M ESPE's Astringent Retraction Paste. The excellent aesthetic performance of the flowable composite used can clearly be seen.Figure 10. The same restorations after 15 months (please note, in this figure the lower right first premolar is at the centre of the picture!) In the author's opinion, the excellent clinical performance of the composite restorations is also related to the Giomer fillers in Beautifil composites since those fillers consist of glass ionomer particles which are ‘pre-reacted’ on their surfaces, resulting in fluoride release and recharge.
Selective use of flowable composites allows for clinical success
According to a survey conducted in the USA by the Clinical Research Association in 2005, 79% of dentists regularly use flowable composites.15 Prime areas of application then were lining, micro restorations, small Class I and Class II restorations, core build-ups, Class V restorations, primary teeth restorations, patching/repairing fillings, and even adhesive luting.
Another survey, focusing on dentists' preferences of using flowable composites, done by Semman et al in Germany in 2011, states that FRCs are increasingly used to restore posterior teeth in stress-bearing locations.16
This fact can be confirmed in accordance with the author's clinical experiences in his dental office. Currently, some 90% of all direct adhesive resin restorations executed by the author are performed using flowable FRCs. The selective use on the basis of a sensible understanding of the mechanical properties and the handling characteristics, however, are paramount to achieving high quality results.17,18
Restoration process options
Regular FRCs only
Flowable or injectable resin restoratives of all kinds find their way into undercuts, nooks and crannies partly by gravity and partly by navigated application. The efficient restoration of cavities depends on the site-directed choice and application of appropriately viscous, ie ‘runny’ flowable composites. In addition to that, physical material properties have to be taken into account in order to ensure long-term mechanical success of the restoration.19,20,21
Regular FRC and RBCs in combination
A clinically proven and scientifically supported method to achieve high quality direct adhesive resin restorations is the co-ordinated application of FRCs and RBCs. It may involve a protocol based on the application of flowable composite as the first increment with subsequent light-curing in the common procedure of building up the restoration in layers. Alternatively, the protocol may require the first low viscous composite increment to be left without being light-cured until the second RBC increment is placed and packed into the cavity, thus making the still easily adaptable FRC lining the cavity act as a ‘sealing restorative’ by helping to avoid voids and imperfections in the tooth-RBC-interface.
In contrast to the method mentioned above, FRCs can, of course, also be used as a ‘final covering layer’ in the process of packing and adapting the uppermost RBC increment to the cavity walls before light-activated polymerization. In this manner, FRCs contribute to compensate any leakage between the resin restoration and the surrounding cavity margins through polymerization shrinkage (Figures 11–20).
Figure 11. Clinical Case 2: one of the domains of flowable composites is their ability to be applied without any pressure as the final layer of a dressing covering the exposed (as can be seen here) or semi-exposed pulp (without any inflammatory symptoms!). Whatever material is placed on top, the exposed pulp, eg calcium hydroxide or MTA, adhesively applied flowable composite will stabilize and protect it.Figure 12. Using, ie applying, flowable composites of various flow characteristics, shades and opacities allows efficient and controlled restoration of cavities post endodontic treatment in cases such as this. Note that three different layers of FRCs have already been placed without any ‘messing up’ of the cavity and leaving troublesome excess.Figure 13. Clinical Case 3: with flowable resin restoratives of no slump, and designed to be used in stress-bearing areas, eg like Beautifil Flow Plus F00 and F03 – the author's first choice – even cuspids in both premolars and molars can be reproduced easily restoring an anatomically correct occlusal plane on the basis of the ‘cone technique’.Figure 14. The completed filling. Almost no excess had to be removed while finishing (contouring and polishing) the occlusal plane. ‘Time is money!’Figure 15. Clinical Case 4: one of those cases occurring in the author's practice. Patient: ‘I need and want to have crowns but cannot afford to have them done’ and, in addition, not very uncommon in Germany, ‘I wish you, doctor, to remove my amalgam fillings as well!’.Figure 16. The affordable and, at that moment, less invasive solution: direct adhesive resin restorations. All the amalgam fillings are removed leaving the cavities exposed to view here.Figure 17. The cavity floors were sealed for demarcation purposes with Beautifil Opaquer (colour Universal Opaque) in case the currently symptom-free, vital premolars and the already endodontically filled molar would possibly need additional treatments before receiving crowns.Figure 18. Direct resin restorations being executed. Note: no rubber dam, however, absolute moisture control is accomplished. The distinct shape and alignment of the teeth to be filled make it a complex situation to cope with. Once again flowable, better to say ‘injectable’, composites hugely facilitate the filling procedures.Figure 19. The completed composite restorations right after completion. The amalgam fillings are removed and the patient is satisfied by that particular kind of minimally invasive treatment with the further benefit of slowing down the ‘tooth countdown’ by postponing the need to do crowns.Figure 20. The Beautifil Flow Plus F00/F03 restorations after 18 months in excellent repair still waiting to change function from ‘crown-substitute-fillings’ to adhesive ‘core build-ups’.
Physically manipulated application of regular RBCs
To make viscous, regular RBCs more flowable in the process of being applied, two different ways of physical manipulation are commonly executed: One method involves pre-heating the RBC before a portion of it is inserted into the cavity; the other is inducing flow by using an ultrasonic device to deliver the composite from capsules into the cavity more easily. The latter method was initiated some 20 years ago by the former ESPE company, then independently inventing and developing products such as Sono-Cem. This material was conceived to compensate for the poor accuracy of fit of the chairside-made inlays/onlays/crowns to the prepared tooth when only CEREC systems of the first generation were available and cementing the milled items with viscous RBC-like materials was the only way to ensure long-term clinical success. Today, the one resin-based restorative intended for all kind of restorations using ultrasonic manipulation in the process of being applied is SonicFil (Kerr, Orange, CA, USA). In the author's view the effective and elaborate SonicFil system needs an expensive applicator and is comparatively costly in terms of the exclusive composite capsules needed to operate the ultrasonic handpiece.
Pre-heating RBCs is an excellent means of reducing the viscosity of regular resin-based restoratives transiently, in order to facilitate both application into cavities and adaptation to cavity walls and floors.22 This technique requires acquiring and maintaining a heating device for composite syringes. According to the experiences of the author, who still implements the method in certain cases, the restoration procedure is only working well as long as the pre-heated composite part is kept at its required temperature, which is not easy to maintain in cases when packing and moulding the placed, pre-heated increment takes a relatively long time.23,24,25,26
And what about flowable Bulk-Fil composites?
In short, flowable Bulk-Fil composites are chemically improved and modified FRCs which, in consequence, allow for rapid and reliable light-curing 4 mm resin restorative layers without causing clinically relevant shrinkage and material insufficiencies.27
One of the first flowable Bulk-Fils, when polymerized in a single 4 mm layer, Dentsply's SDR – an acronym that stands for ‘Smart Dentine Replacement’ – has set the benchmark for all products of that particular group.
It is the author's opinion that resin-based Bulk-Fil restoratives, be they high viscous, paste-like or low viscous, flowable, are among the most successfully marketed products to come into the realm of direct adhesive dentistry.28
Conclusion
It is hoped that this article has enhanced understanding of the many improvements in recent generations of flowable resin composites (FRCs), the different types available, and their many clinical applications.
