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Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.intl.elsevierhealth.com/journals/jden
Effect of bulk/incremental fill on internal gap formation of bulk-fill composites Alan Furness a,*, Marko Yousef Tadros b, Stephen W. Looney c, Frederick A. Rueggeberg a a
Department of Oral Rehabilitation, College of Dental Medicine, United States College of Dental Medicine, United States c Department of Biostatistics and Epidemiology, Medical College of Georgia, United States b
article info
abstract
Article history:
Objectives: To examine the effects of composite type (bulk-fill/conventional) and placement
Received 23 July 2013
(4-mm bulk/2-mm increments) on internal marginal adaptation of Class I preparations.
Received in revised form
Methods: Cylindrical, Class I, 4-mm 4-mm preparations were made on 50 recently
19 December 2013
extracted human molars and restored using either a bulk-fill (SureFil SDR Flow (SDR), Quixx
Accepted 7 January 2014
(QX), SonicFill (SF), Tetric EvoCeram Bulk (TEC)) or a conventional composite designed for 2-
Available online xxx
mm increments (Filtek Supreme Ultra (FSU)). Restorations were placed in 1 or 2 increments using the manufacturer’s bonding agent and curing light (n = 5). Teeth were sectioned
Keywords:
occluso-gingivally and dye was placed on the internal margin and visually examined by
Bulk-fill
3 observers. Gap-free marginal lengths were analysed within three different regions of the
Composites
sectioned tooth: enamel, mid-dentine, and pulpal floor.
Margin adaptation
Results: Marginal integrity was unaffected by placement method. Bulk-placement demonstrated significantly fewer gap-free margins at the pulpal floor than in enamel, for all materials except SDR. Greater percentages of gap-free margins were found within the middentine than at the pulpal floor for FSU. QX had more gap-free margins in enamel compared with the mid-dentine. Proportion of gap-free margins within enamel and mid-dentine was not significantly different for any incrementally placed product. Excluding FSU, gap-free margins within enamel were significantly greater than at the pulpal floor. Notably, significantly more gap-free margins were found within mid-dentine than at the pulpal floor for SF. Conclusions: No significant differences in gap-free margins were found between placement methods within a given product per location. Except for SDR, percentage of gap-free margins was significantly lower at the pulpal floor interface than at the enamel interface for bulk-fill. Published by Elsevier B.V.
1.
Introduction
Recently, several new restorative materials have been advertised as ‘bulk-fill’ composites. Many clinicians, however, have long adopted an incremental cure philosophy, when placing light-cured composites. In light of recent marketing efforts
promoting ‘‘bulk-fill,’’ light-cured composites, the judicious clinician should question what has changed that now allows composites to be placed in increments exceeding 2-mm thickness. The concept of ‘‘bulk-filling’’ a preparation is not a novel idea,1 and has been evaluated numerous times in the literature.2–5 Historically, several disadvantages of bulk-filling preparations with light-cured composites are recognised: the
* Corresponding author at: College of Dental Medicine, Room GC 4210, Georgia Regents University, 1430 John Wesley Gilbert Drive, Augusta, GA 30912, United States. Tel.: +1 706 721 8321. E-mail address: [email protected] (A. Furness). 0300-5712/$ – see front matter . Published by Elsevier B.V. http://dx.doi.org/10.1016/j.jdent.2014.01.005 Please cite this article in press as: Furness A, et al. Effect of bulk/incremental fill on internal gap formation of bulk-fill composites. Journal of Dentistry (2014), http://dx.doi.org/10.1016/j.jdent.2014.01.005
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inability to adequately cure composite to depths greater than 2 mm,6,7 challenges related to preparation design on the Cfactor,8,9 as well as potential complications due to polymerisation shrinkage and increased gap formation, both internally and at the cavo-surface margins.8,10,11 The clinical implication of marginal gap formation is related to discomfort in conjunction with occlusal forces, which may be attributed to fluid accumulation within the gap and the subsequent fluid movement within the tubules.12,13 One reason for the recommended 2-mm thick incremental composite placement relates to compromised light penetration through this material, which is especially true when using darker shades.6 While the surface of the composite is adequately cured, the material may not polymerise well in depth.14,15 Insufficiently polymerised composite has been shown to be cytotoxic and may pose a negative risk to the longevity of the restoration.16,17 Cavity preparation design affects the internal stresses of light-cured composite restorations.8 The C-factor refers to the ratio of bonded-to-unbonded restoration surfaces, with a direct correlation shown between preparation C-factor and internal polymerisation stress development at the bonded interface.11 Placing and light-curing composite in increments is thought to decrease its total volumetric shrinkage, and to potentially decrease stresses resulting from this shape change.3 Other studies however, challenge this concept.18 If the force of polymerisation shrinkage exceeds the strength of the bonding agent and composite interface, then a marginal gap can form to accommodate this strain.4 In addition, stress fractures in enamel and dentine have been observed and are thought to occur when the interfacial bond strength surpasses the physical properties of adjacent tooth structure.19 Therefore, a variety of restorative techniques have been recommended to reduce polymerisation stress. One such strategy includes the use of liners/bases in the preparation.20 A recent study detected internal marginal debonding events using acoustic emission and correlated shrinkage, modulus, and stress development with the potential for observing such events.21 However, if marginal gaps do develop, they will compromise the long-term durability of the restoration and have the potential to create post-insertion sensitivity, increase the incidence of secondary caries, and encourage marginal staining.11 Marginal gap formation is the end product of a number of clinical factors. Poor placement techniques 18 and the variety of incremental and light curing scenarios may lead to such discrepancies as well as polymerisation shrinkage and the cumulative effects of polymerisation stress.8 Marginal integrity has been evaluated using high magnification,5,9,20 while other studies used penetrating dyes to reveal marginal gaps, both externally and internally.9,22 In addition, the effects of using a variety of curing light types and various light exposure techniques on their potential to generate or minimise marginal gap formation and depth of cure have been studied.6,14,23 The recent introduction of many ‘‘bulk-filled’’ restorative materials has re-ignited the controversy of ‘‘bulk vs incrementally’’ placed composites. While the main interest in marketing this class of products is based on time and thus cost savings, other clinically related aspects are relevant as well.
An ideal bulk-fill composite would be one that could be placed into a preparation having a high C-factor design and still exhibit very little polymerisation shrinkage stress, while maintaining a high degree of cure throughout. As a result, reduced polymerisation stress should minimise internal and external marginal gap formation, compared to conventional incrementally placed composites. The newly developed ‘‘bulk-filled’’ resins claim to offer single increment placement thicknesses ranging from 4 to 6 mm, instead of the conventional 2 mm value commonly used. However, the potential development of internal marginal gap formation exists with bulk placement and the proportion of gaps relative to use of conventional 2-mm increments has yet to be determined. In addition, no studies have correlated use of the manufacturer-specific dentine bonding agent and manufacturer-specific curing light unit, as they relate to the potential for maintenance of internal interfacial margins. If the bulk-fill restorative materials are to provide a true clinical advantage, then they require high depths of cure while simultaneously demonstrating a decrease in internal stress, and subsequently decreased incidence of internal gap formation. Only products demonstrating such superior performance over the use of traditional, incrementally placed composites, should then be considered as viable alternatives. The purpose of this research was to examine the potential for maintenance of gap-free internal interfacial bonds within the enamel, mid-dentine, and pulpal floor areas in controlledsize, Class I preparations made in extracted human molars when restored using a variety of the newly marketed ‘‘bulkfilled’’ products. Restorations were placed in either two, 2-mm thick increments, or as a single, 4-mm thick bulk-fill placement, utilising the respective manufacturer’s total-etch bonding agent and curing light. The experimental control material was a conventional composite recommended for only 2-mm thick increments. Three research hypotheses were tested: (1) for bulk-fill materials, marginal integrity at the enamel and mid-dentine restoration interfaces would not be significantly different with respect to type of fill (incremental or bulk), (2) at the pulpal interface, marginal integrity of the bulk-fill materials would be significantly better using the bulk fill technique than with use of the incremental fill technique, and (3) there would be no significant difference in marginal adaptation of the commercial product designed for incremental placement between bulk and incremental placement, except at the pulpal floor, where it is expected that bulk placement would result in less gap-free interface (more interfacial gaps) than when incremental placement was used.
2.
Materials and methods
2.1.
Tooth preparation
Freshly extracted, intact, non-carious and non-restored, human maxillary and mandibular molars were obtained from the Oral Surgery Department of the College of Dental Medicine at Georgia Regents University College of Dental Medicine. The protocol for use of teeth for this purpose was approved by the
Please cite this article in press as: Furness A, et al. Effect of bulk/incremental fill on internal gap formation of bulk-fill composites. Journal of Dentistry (2014), http://dx.doi.org/10.1016/j.jdent.2014.01.005
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Human Assurance Committee, under approval Number IRBHSD00000128. A controlled removal of enamel on the occlusal surface was performed, which resulted in retention of a central portion of enamel in the centre of the tooth, while dentine was slightly exposed where the cusp tips had been located. This type reduction was necessary to provide for a flat occlusal surface having centrally located enamel, so that the light curing units could be held at a repeatable distance of 2 mm from the occlusal margin when photocuring each tooth. Thus the entire occlusal cavosurface margin was in enamel and was located within the curing light beam area upon the tooth. Following cusp tip removal, a Class I preparation (4.0 mm (0.2 mm) diameter, 4.0 mm (0.2 mm) deep, C-factor = 5.0) was made by hand using copious water irrigation and a high speed handpiece equipped with a flat-ended diamond bur (item number 6837KR, Komet USA, Rock Hill, SC). The dimensions of each preparation were measured using a digital micrometre (model CD-600 B, Mitutoyo Corporation USA, Aurora, IL USA). Preparations in which a pulp exposure was identified were not used in the experiment, because a totally intact preparation margin was required for analysis purposes.
2.2.
Tooth restoration
The order of material used for restoration was randomised among all specimens, in order to minimise the effect of operator learning on the variation in test results. The specimens were thermocycled and each tooth to be restored was identified with a specific engraved number on the external portion of its crown segment. Teeth were restored using a variety of contemporary bulk filling composite materials, used in conjunction with the totaletch dentine bonding product as well as light curing unit specific for each manufacturer (Table 1). Total etch dentine bonding systems were used among all products to reduce variability in results that might have occurred if some self-etching systems had been used. Four commercial bulk-fill composite systems were tested and one conventional composite that required 2-mm increments was used as control. Only one of the bulk-fill products (SureFil SDR
Flow) recommended that a capping layer of conventional composite be placed. However, because this study was only interested in evaluating internal margins, and not that of the cavosurface location, no capping agent was used. Other than this exception, all manufacturer instructions were followed for placement and curing of the dentine bonding agent as well as the subsequent resin composite material. For SureFil SDR Flow and Quixx, Prime and Bond NT was used as the bonding agent, Optibond Fl was used for SonicFill, ExciTE F for Tetric EvoCeram, and Adper Scotchbond for Filtek Supreme Ultra. The manufacturers instructions were followed for each bonding agent as well as the recommended curing light and exposure times. When light-curing all restorative agents (bonding resins and composites), the tooth was held upright using wax. A 2mm thick, clear acrylic plate, having a 6-mm diameter hole, was placed over the flattened occlusal tooth surface, and aligned so that the centre of the hole was concentric with the centre of the Class I preparation. The distal end of the light guide was then positioned so that the centre of the tip was coaxial with the centre of the plate hole and restoration. This arrangement allowed for the repeatable distancing of the light curing tip to be 2 mm away from the cavosurface margin, simulating the distance that the cusp tips might have restricted light tip placement (Fig. 1). Following completion of cavity restoration, excess restorative material was removed using a finishing diamond bur, under copious water irrigation (item # 8379.314.021, Komet USA, Rock Hill, SC, USA), to expose the cavosurface margin. The restored teeth were then placed into deionised water at room temperature. Restored teeth were subjected to 1000 cycles, between 5 8C and 55 8C, after which they were darkstored in a aqueous disinfectant solution (Thymol, Item T185100, Fisher Scientific, Fair Lawn, NJ, USA) for at least 24 h in a 37 8C oven (Stabil-Therm Constant Temperature Cabinet, Blue M Electric Company, Blue Island, IL USA).
2.3.
Tooth sectioning and embedment
Pencil lines were made on the crown segment of each restored tooth that aligned the centre of the restoration and the long
Table 1 – Products and devices used throughout testing. Composite type
Manufacturer location
Composite name Lot#
Composite shade
Bonding agent
Curing light
Recommended curing light exposure (time – thickness) Bulk
Bulk-fill
Conventional
Caulk Dentsply Milford, DE
Kerr/Sybron Orange, CA Ivoclar Vivadent Liechnstein 3M ESPE St. Paul, MN
SureFil SDR Flow Lot# 100929 Quixx Lot# 100609 SonicFill Lot#3439122 Tetric EvoCeram BF Lot#RZM013 Filtelk Supreme Ultra Lot #N203124
A2
Prime N Bond NT Lot # 100709
SmartLite IQ2
40 s–4 mm
20 s–2 mm
20 s–4 mm
20 s–2 mm
Demi Plus
20 s–4 mm
20 s–2 mm
Bluephase 20i
10 s–4 mm
10 s–2 mm
S10
40 s–4 mm
20 s–2 mm
Universal A2 Universal
A2B
Optibond FI Lot#3553038 ExciTE F Lot # N75726 Adper Scotchbond Lot# N199766
Increment
Please cite this article in press as: Furness A, et al. Effect of bulk/incremental fill on internal gap formation of bulk-fill composites. Journal of Dentistry (2014), http://dx.doi.org/10.1016/j.jdent.2014.01.005
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its water-storage, and the tooth surface was lightly dried, using laboratory wipes (Kimwipes, Kimtech Science, Kimberly-Clark Global Sales, Inc., Roswell, GA, USA). A small amount of a caries detecting solution (Item #1805, Sable Seek, Ultradent Products, South Jordan, UT, USA) was dispensed into a dappen dish and was traced over the internal margins, using a ball-ended hand instrument (PICH, Hu-Friedy, Chicago, IL,USA). Excess dye was removed by blotting with laboratory wipes.
2.5.
Fig. 1 – Graphical depiction of controlling composite-tolight distance during restoration photocuring.
axis of the tooth. The tooth was then held by the root and the occlusal end was fed into the circulating blade (No. 11-4244, Series 15HC D, Diamond Wafering Blade, Buehler Ltd., Evanston, IL, USA) of a water-cooled cutter (Isomet 11-1180 Low Speed Saw, Buehler Ltd) until the cut passed the DEJ. The root sections were then removed using a high speed handpiece and carbide bur (#556, Brasseler), leaving only the sectioned crown segments. Each flat, cut section was then placed facedown on a flat rubber sheet, and a 1-inch diameter plastic ring (20815110, Plastic Ring Form, Buehler) was positioned overtop, so that the tooth was centred within the ring circumference. A self-curing denture repair material (Ref. #680049/680042, Dentsply International, York, PA, USA) was poured into each ring in order to provide a firm embedding matrix for the tooth specimen. Once the embedding polymer set, specimens were placed in a 100% humidity chamber to prevent dentine desiccation, for no longer than 1 week. The complimentary sectioned halves were stored for subsequent analysis using SEM imaging in a future study. Following storage, specimens were individually retrieved, and the tooth-side of the ring was polished through a sequence of abrasive papers (ending in 1200 grit SiC (item 688, Buehler)) and a 1.0 mm alumina slurry (No 40-6361-006, Buehler) on a polishing cloth (No 40-7212, Microcloth, Buehler). Between the applications of each size abrasive, specimens were ultrasonically cleaned in water for 15 min (Model 2014, Ultrasonic Cleaning System, L&R Manufacturing Co., Kearney, NJ, USA). The specimen code number identifying the restorative material and trial number of each specimen was engraved on the polished embedding medium, after which the specimens were water-stored at 37 8C in the dark until staining and imaging. The effects of tooth embedding, sectioning, and storage using this method are felt to be similar to techniques used in microtensile testing specimen preparation.24 The validity of this sectioning method has also been recently been verified, comparing results of internal gap formation with a non-invasive, micro-CT technique.25
2.4.
Margin staining and image recording
Specimens were randomly selected for marginal staining and image recording. An individual specimen was retrieved from
Image analysis
Immediately following removal of excess dye, images of each specimen were obtained using a digital camera (FinePix HS10, Fujifilm Manufacturing, Greenwood, SC, USA) at 10.3 megapixel resolution. The recorded images were then projected on a large screen and three investigators underwent a calibration session to finalise agreement with respect to recognition of (1) open/closed margins (gap formation), (2) tooth fracture, and (3) void formation. Following examiner calibration, images of treated teeth were projected using image analysis software (ImageJ v1.46r, National Institutes of Health, Bethesda, MD, USA). Using this software, the length of the marginal interface was determined at specific locations along the internal tooth/ restoration interface: (1) the enamel/composite portion, (2) within the mid-dentine (defined as length from the DEJ along the axial wall to the line angle where the pulpal floor started, and (3) along the pulpal floor. Within each of these measured locations, the portion of gap-free marginal length (identified as absence of stain) was measured as a percentage of total interfacial length.
2.6.
Statistical analysis
Data were analysed using repeated measures analysis of variance (ANOVA), with one repeated factor (location) and two grouping factors (restorative material and fill type). The general analysis strategy used was similar to that recommended by Looney and Stanley when there is one repeated factor and one grouping factor.26 The first step in this procedure was to test for any significant interactions among the factors. If no significant interactions were found, the next step was to test the main effects for each factor: that is, the null hypothesis that there were no differences among factor levels, ignoring the effects of the other factors. The third step was to use the Tukey–Kramer method to examine all pair-wise comparisons for each factor that had more than two levels (location and restorative material). Repeated measures analysis was used for any tests involving the location factor. If the three-way interaction proved significant, an appropriate two-way ANOVA for two of the factors was performed separately for each level of the third factor. If the three-way interaction was not significant, but one or more two-way interactions were significant, analyses based on contrasts were performed for each of the factors involved in the significant two-way interactions. The Tukey–Kramer method was used anytime pairwise comparisons were analysed. Unless otherwise specified, two-tailed tests with a significance level of 0.05 were used. A Bonferroni adjustment was used, whenever appropriate, to control the family-wise error rate at
Please cite this article in press as: Furness A, et al. Effect of bulk/incremental fill on internal gap formation of bulk-fill composites. Journal of Dentistry (2014), http://dx.doi.org/10.1016/j.jdent.2014.01.005
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0.05. All statistical analyses were performed using software on a personal computer (SAS v9.3 for Windows, SAS Institute Inc., Cary, NC, 2010).
3.
Results
3.1.
Material and location
The three-way repeated measures ANOVA, testing the effect of restorative material, fill method, and internal interface location on percentage of gap-free interface, indicated a nonsignificant 3-way interaction ( p = 0.755). There was a significant 2-way interaction between restorative material and location ( p = 0.012); no other interactions were significant ( p = 0.116 for fill method by material and p = 0.180 for fill method by interface location). Because of the significant material-by-location interaction, it was not appropriate to test the significance of the main effects for material and location.22 Instead, tests of contrasts comparing the levels of these factors were performed using the appropriate multiple comparison procedure. As a main effect, fill type (bulk or incremental) did not have a significant influence on the extent of gap-free location ( p = 0.288).
3.2.
Fig. 2 – Effect of restorative material and fill method on percent of gap-free interface, regardless of location of internal margin. N = 5 replications per condition horizontal bar = +1 standard deviation vertical bar connects values that are not significantly different.
Fill type and location 3.3.
Because the 2-way interaction between material and location was statistically significant, a two-way ANOVA (A) for fill type (incremental/bulk) by location (enamel/mid-dentine/pulpal floor) was performed separately for each material and a twoway ANOVA (B) for fill type by material was performed separately for each location. In the separate two-way ANOVA’s for each material, ANOVA (A) found no significant differences between fill types for any restorative material, using a Bonferroni-adjusted significance level of 0.05/5 = 0.01 for each material (Fig. 2). However, significant differences were found among tooth locations with the bulk-fill method using Tukey-Kramer pairwise comparisons for repeated measures, with a Bonferroni-adjusted significance level of 0.05/5 = 0.01 for each material (Fig. 3). Comparisons of gap-free margin percentages between locations for each material using the incremental fill technique are seen in Fig. 4. As with the bulk-fill method (Fig. 3), these results are based on Tukey-Kramer pairwise comparisons for repeated measures, with a Bonferroniadjusted significance level of 0.05/5 = 0.01 for each material. A similar approach was used for the separate two-way ANOVA’s for each interface location: ANOVA (B). There were no significant differences in percentage of gap-free margins between fill types for any of the 5 materials, using a Bonferroni-adjusted significance level of 0.05/5 = 0.01. For enamel, differences in gap-free margin extent were found between materials, depending on fill type, using TukeyKramer pair-wise comparisons with a Bonferroni-adjusted significance level of 0.05/2 = 0.025 for each fill type (Fig. 5). Within each of the other two internal marginal locations (mid-dentine and pulpal floor), there were no significant differences in gap-free margin percentages between materials for either fill type (Figs. 6 and 7).
Leakage patterns
The individual photos of imaged sections reveal similarities and differences in gap formation patterns and locations among the various groups. Fig. 8 displays the images of the bulk-fill, flowable consistency product, SureFil SDR Flow. For this material, when placed incrementally, or when placed in bulk, there is a consistent presence of leakage of the dye materials
Fig. 3 – Effect of composite brand and location of internal tooth interface on percentage of gap-free margin when using the bulk-fill insertion method. N = 5 specimens/ group. Horizontal bar = +1 standard deviation. Within a composite brand, groups identified with similar upper case letters are not significantly different.
Please cite this article in press as: Furness A, et al. Effect of bulk/incremental fill on internal gap formation of bulk-fill composites. Journal of Dentistry (2014), http://dx.doi.org/10.1016/j.jdent.2014.01.005
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Fig. 6 – Percentage of intact internal margin within the internal mid-dentine/restoration interface. N = 5 specimens/ condition. Horizontal line = +1 standard deviation. Vertical bar joins groups not significantly different. Fig. 4 – Effect of composite brand and location of internal tooth interface on percentage of gap-free margin when using the incremental insertion method. N = 5 specimens/ group. Horizontal bar = +1 standard deviation within a composite brand, groups identified with similar upper case letters are not significantly different.
into the gap, and then down the tubules and towards the pulp chamber. Such a leakage pattern indicates that the composite material bonded to the underlying dentine adhesive system, and lifted the hybrid layer up and off the dentine when the composite cured, leaving direct access to dentine tubules. The dye penetration patterns for second bulk-fill composite material, but not a flowable type product (Quixx) is seen in Fig. 9. A wide range of dye penetration patterns is seen with this product. For either fill type, the majority of gap formation was seen at the pulpal floor interface, with dye filling tubules
Fig. 5 – Percentage of intact internal margin within the internal enamel/restoration interface. N = 5 specimens/ condition. Horizontal line = +1 standard deviation vertical bar joins groups not significantly different vertical arrows identify significant differences between gap-free percentages of incrementally or bulk-fill placed composites.
and not merely being confined to the interfacial opening, using both incremental as well as the bulk-fill techniques. For an additional bulk-fill composite tested, SonicFill, there was a mixture of leakage patterns seen among specimens for both types of restoration filling technique (Fig. 10). For this material, there was evidence of only very mild dye infiltration, dye infiltration into gaps with no downward tubule entry, as well as dye penetrating into the gap, and traversing opened dentine tubules and travelling directly towards the pulp. The last bulk-fill composite tested, Tetric Evo Ceram Bulk Fill, demonstrated a unique pattern of internal gap dye penetration (Fig. 11). Although this product indicated gap formation at the pulpal floor in most instances (as seen with all other products), the unique feature was that the dye penetration seemed limited to that opening, and dye is not seen penetrating tubules and running towards the pulp chamber. Such a pattern of leakage indicates that the hybrid layer was kept intact during shrinkage of the overlying composite, not allowing the dye to enter and run towards the pulp chamber.
Fig. 7 – Percentage of intact internal margin at the pulpal floor region. N = 5 specimens/condition. Horizontal line = +1 standard deviation, vertical bar joins groups not significantly different
Please cite this article in press as: Furness A, et al. Effect of bulk/incremental fill on internal gap formation of bulk-fill composites. Journal of Dentistry (2014), http://dx.doi.org/10.1016/j.jdent.2014.01.005
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Fig. 8 – Sectioned and stained images of using SureFil SDR Flow in both two, 2-mm thick increments or as a single 4-mm thick increment.
Fig. 9 – Sectioned and stained images of using Quixx in both two, 2-mm thick increments or as a single 4-mm thick increment.
Fig. 10 – Sectioned and stained images of using SonicFill in both two, 2-mm thick increments or as a single 4-mm thick increment. Please cite this article in press as: Furness A, et al. Effect of bulk/incremental fill on internal gap formation of bulk-fill composites. Journal of Dentistry (2014), http://dx.doi.org/10.1016/j.jdent.2014.01.005
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Fig. 11 – Sectioned and stained images of using Tetric Evo Ceram Bulk Fill in both two, 2-mm thick increments or as a single 4-mm thick increment.
Images of the control composite (Filtek Supreme Ultra), which was made to use in increments of 2-mm thickness, are seen in Fig. 12. Interestingly, when used according to manufacturer’s directions of placement and curing in 2-mm thick increments, there was a tendency for not only total gap formation at the pulpal floor, but also evidence of dye penetration into opened tubules at that interface, implying separation of the hybrid layer at that location, and exposure of open tubules. However, when placed in one, 4-mm thick bulk increment, although there is still consistent evidence of gap formation at the pulpal floor, there is much less appearance of dye flowing into open tubules at that interface.
4.
Discussion
The first research hypothesis proposed that the marginal integrity at the enamel and mid-dentine areas of the restoration would not be significantly different, regardless
of whether the material was placed in bulk or incrementally filled. The research findings validated this hypothesis, as there was no significant difference in percentage of gap-free interface with respect to placement technique (incrementally or bulk), without respect to specific material or interface location. Even within a particular brand of composite, there was no significant difference in terms of bulk or incremental placement (Fig. 2), as it relates to the total margin integrity. It is interesting to note, however, that statistical differences were found between the percentages of gap-free interfaces related to the margin location. Of materials tested in bulk placement, all had a significantly higher degree of gap-free interfaces within the enamel portion compared to pulpal margins, with the exception of SureFil SDR Flow (Fig. 3). For this material, there was no statistical difference found between the marginal integrity at the enamel, mid-dentine, or pulpal margins. This same relationship however, was not observed when SureFil SDR Flow was placed incrementally (Fig. 4). Incremental placement of SureFil SDR Flow resulted in a similar marginal
Fig. 12 – Sectioned and stained images of the control composite (Filtek Supreme Ultra) in both two, 2-mm thick increments or as a single 4-mm thick increment. Please cite this article in press as: Furness A, et al. Effect of bulk/incremental fill on internal gap formation of bulk-fill composites. Journal of Dentistry (2014), http://dx.doi.org/10.1016/j.jdent.2014.01.005
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appearance as observed in other materials tested, with the enamel margins having significantly better gap-free marginal interfaces than those at the pulpal floor. The second research hypothesis proposed that, at the pulpal interface, marginal integrity of the bulk-fill materials would be significantly better using the bulk-fill technique than when restorations were placed in two separate, 2-mm thick increments. This hypothesis was disproven, however. Fig. 7 shows that there was no significant differences in percentage of gap-free margin among the materials at the pulpal margin. In no case was the percentage of a gap-free margin at the pulpal interface above 30% of its length. As with other interfaces, the method of composite placement did not have a significant impact on the percentage of gap-free margin occurrence, but the percentage values were quite low at this interface location: incremental fill averaged 18% of gap-free margin length (max 27%, min 8%), and bulk-fill averaged 9% (max 16%, min 6%). The last research hypothesis proposed that, other than at the pulpal floor, no statistical difference in gap-free margin percentages would be found between placement techniques for the control composite: the material designed for use only with incremental placement. This concept was only partially validated. When the control material was placed and polymerised in a single, 4-mm thick increment, there was no significant difference in the percentage of gap-free margin length between enamel and dentine interfaces, yet the proportion observed at the pulpal floor was significantly lower than at the other two locations (Fig. 3). When using this material as intended (in two separate, 2-mm thick increments), no significant differences were found in the percentage of gap-free margins among all three bonding interfaces (Fig. 4). However, what is interesting to note are the differences in gap-free margin proportions at the same tooth locations between fill types for this material. When using the recommended incremental method, the incidence of gap-free margins at both the enamel and dentine interfaces appeared to be much lower than when using this material in bulk (Figs. 3 and 4). However, no significant difference in marginal integrity was noted at the pulpal floor between delivery techniques: both methods provided gap-free margins of only 10% or less of the total interface length. These differences seem to indicate that, when placed and polymerised in bulk, shrinkage stresses at the enamel and dentine interfaces were less, resulting possibly from the ability of unpolymerised composite deep in the restoration to deform and ‘‘feed’’ the resulting stress development from the strain of composite curing at shallower depths. In contrast, much higher stress development must have occurred in the second 2-mm thick increment, as evidenced by the lower percentages of gap-free marginal interfaces in enamel and dentine. The lower intact margin extent using the incremental layering technique may arise from the absence of a deep reservoir of uncured composite from which to relieve polymerisation stresses of the upper composite segment. Other studies have demonstrated that the degree of cure for Filtek Supreme Ultra decreases significantly after 2-mm depth, validating the possibility of a bolus of deformable composite from which strain of the uppermost material can draw.14,15 It is interesting to note that, for the enamel and mid-dentine interfaces of the bulk-fill materials in
9
general, a smaller difference is noted between bulk or incremental fill, as compared with the control, incrementalfill product (Figs. 3 and 4). However, the trend seems to be that, although the marginal integrity at the pulpal floor is very poor, use of the bulk-fill products in an incremental mode does tend to be slightly better than when these products are placed in a 4-mm increment. This difference may be due to the enhanced translucency and enhanced photochemistry that many bulkfill products have utilised in order to be able to polymerise to deeper depths than the incremental-only products.27 This study shows that use of the new bulk-fill products does not universally eliminate the potential for internal marginal gap formation, as might be hoped. Indeed, overall, there was no significant difference in internal marginal integrity with respect to placement technique only. Still, using either the conventional, incremental-only composite, or a 4-mm bulk fill of composite specifically designed for this application, marginal gap formation at the pulpal floor was very prominent. The clinical implications of this finding may be that, although composite may be curing to enhanced depths, the potential for developing any post-insertion sensitivity that is related to gap formation at the pulpal floor, and the resulting hydraulic movement of fluids that will occupy this space upon occlusal loading, is still present. The correlation between the potential for gap formation and postinsertion sensitivity has long been known.28 Indeed, clinical methods to reduce polymerisation stresses are still under study, in hopes of providing longer-lasting direct, aesthetic restorations.29 An interesting outcome of the present study was the starkly different behaviour of dye penetration into the bonded interface among some products. In particular, although there was notable pulpal floor gap formation when placing Teric Evo Ceram Bulk Fill, using either placement technique, none of the sectioned specimens demonstrated evidence of dye rushing through open tubules, towards the pulp. However, most all other products demonstrated this event. While in some of the specimens, the die pooled within the gap, yet in others, it penetrated the tubules. This observation may be attributed to where the gap occurred along in the interface. If the gap occurred between the composite and the hybrid layer, a localised pooling of the dye may be expected, because the tubules remain sealed. However, if the gap occurred between the hybrid layer and underlying dentine, dye penetration into the tubules would be expected. The implications of these different types of gaps need to be studied further in conjunction with their potential clinical significance. The potential for clinical success may thus also lie within the integrity of the composite/bonding agent/dentine interface to withstand shrinkage stresses. Only with long-term clinical studies can any such differences in clinical performance and patient comfort be addressed. The limitations of the current study deal with the fact that not all commercial bulk-fill materials were included. Indeed, even at the time of writing this report, new bulk-fill products have been introduced on the market, and remain untested. In addition, only five replications were made of each test condition. With a greater sample size, more statistical discrimination among the main test factors of placement method, marginal interface location, and product could have been identified. However, it is felt that the product selection
Please cite this article in press as: Furness A, et al. Effect of bulk/incremental fill on internal gap formation of bulk-fill composites. Journal of Dentistry (2014), http://dx.doi.org/10.1016/j.jdent.2014.01.005
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and sample size provide a very good initial overview of this new composite classification and placement technique. In addition, it is also recognised that the curing lights used were specific for each material and that degree of cure and subsequent marginal gap formation may have been influenced by this selection. Further studies are needed to elucidate the relationship between the curing light type and degree of cure. It is also recognised that each bonding agent used, although specific for each material, may have influenced the marginal gap and this relationship between the bonding agent and the ‘bulk-fill’ composite needs to be studied further. However, it must be noted that manufacturers design these restorative components as integrated systems, yet often studied in isolation. For example, bulk-filled systems may have different types of photointiators and thus require curing lights that adequately activate them. To avoid this complication and to test these products as they are offered, it was decided to study the products as integrated systems.
5.
Conclusions
Within the limitations of this study it can be concluded that (1) Use of a bulk-fill restorative material compared to a conventional composite resulted in a similar proportion of gap-free, internal marginal interface in the mid-dentine and enamel areas. (2) The proportion of gap-free margin at the pulpal interface was lower than at the enamel or mid-dentine interfaces, regardless of type of material used or fill type, with the exception of one bulk fill material used in a single 4-mm increment (SureFil SDR Flow) and for the control: incrementally cured composite placed in two separate, 2-mm thick increments (Filtek Supreme Ultra). (3) The percentage of gap-free internal margins of the control composite was less at the enamel and mid-dentine portions when used as directed (in two, 2-mm thick increments), than when the same material was used in a single 4-mm thick increment, although this difference was not statistically significant.
references
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conventionally layered resin composite. Journal of Dentistry 2011;39:643–7. Lazarchik DA, Hammond BD, Sikes CL, Looney SW, Rueggeberg FA. Hardness comparison of bulk-filled/ transtooth and incremental-filled/occlusally irradiated composite resins. Journal of Prosthetic Dentistry 2007;98:129–40. Czasch P, Ilie N. In vitro comparison of mechanical properties and degree of cure of bulk fill composites. Clinical Oral Investigations 2012;1:227–35. Ferracane JL. Developing a more complete understanding of stresses produced in dental composites during polymerization. Dental Materials 2005;21:36–42. Taha NA, Palamara JE, Messer HH. Cuspal deflection, strain and microleakage of endodontically treated premolar teeth restored with direct resin composites. Journal of Dentistry 2009;37:724–30. Van Ende A, Mine A, De Munck J, Poitevin A, Van Meerbeek B. Bonding of low-shrinking composites in high C-factor cavities. Journal of Dentistry 2012;40:295–303. Davidson CL, Feilzer AJ. Polymerization shrinkage and polymerization shrinkage stress in polymer-based restoratives. Journal of Dentistry 1997;25:435–40. Tay FR, Pashley DH. Water treeing – a potential mechanism for degradation of dentin adhesives. American Journal of Dentistry 2003;16:6–12. Opdam NJ, Roeters FJ, Feilzer AJ, Verdonschot EH. Marginal integrity and postoperative sensitivity in Class 2 resin composite restorations in vivo. Journal of Dentistry 1998;26:555–62. Campodonico CE, Tantbirojn D, Olin PS, Versluis A. Cuspal deflection and depth of cure in resin-based composite restorations filled by using bulk, incremental and transtooth-illumination techniques. Journal of the American Dental Association 2011;142:1176–82. Flury S, Hayoz S, Peutzfeldt A, Husler J, Lussi A. Depth of cure of resin composites: is the ISO 4049 method suitable for bulk fill materials? Dental Materials 2012;28:521–8. Emmler J, Seiss M, Kreppel H, Reichl FX, Hickel R, Kehe K. Cytotoxicity of the dental composite component TEGDMA and selected metabolic by-products in human pulmonary cells. Dental Materials 2008;24:1670–5. Carvalho AA, Moreira Fdo C, Fonseca RB, Soares CJ, Franco EB, Souza JB, et al. Effect of light sources and curing mode techniques on sorption, solubility and biaxial flexural strength of a composite resin,. Journal of Applied Oral Science 2012;20:246–52. Versluis A, Douglas WH, Cross M, Sakaguchi RL. Does an incremental filling technique reduce polymerization shrinkage stresses? Journal of Dental Research 1996;75:871–8. Haak R, Wicht MJ, Noack MJ. Marginal and internal adaptation of extended class I restorations lined with flowable composites. Journal of Dentistry 2003;31:231–9. Ratih DN, Palamara JE, Messer HH. Minimizing dentinal fluid flow associated with gap formation. Journal of Dental Research 2006;85:1027–31. Cho NY, Ferracane JL, Lee IB. Acoustic emission analysis of tooth-composite interfacial debonding. Journal of Dental Research 2013;92:76–81. Ciucchi B, Bouillaguet S, Delaloye M, Holz J. Volume of the internal gap formed under composite restorations in vitro. Journal of Dentistry 1997;25:305–12. dos Santos GO, dos Santos ME, Sampaio EM, Dias KR, da Silva EM. Influence of C-factor and light-curing mode on gap formation in resin composite restorations. Operative Dentistry 2009;34:544–50. Pashley DH, Carvalho RM, Sano H, Nakajima M, Yoshiyama M, Shono Y, et al. The microtensile bond test: a review. Journal of Adhesive Dentistry 1999;1:299–309. Park S, Kim H. Measurement of the internal adaptation of resin composites using micro-CT and its correlation with
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polymerization shrinkage. Operative Dentistry 2013. [Epub ahead of print]. 26. Looney SW, Stanley WB. Repeated measures analysis for two or more groups: review and update. American Statistician 1989;43:220–5. 27. Lassila LV, Nagas E, Vallittu PK, Garoushi S. Translucency of flowable bulk-filling composites of various thicknesses. Chinese Journal of Dental Research 2012;15:31–5.
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28. Opdam NJ, Feilzer AJ, Roeters JJ, Smale I. Class I occlusal composite resin restorations: in vivo post-operative sensitivity, wall adaptation, and microleakage. American Journal of Dentistry 1998;11:229–34. 29. Malhotra N, Kundabala M, Shashirashmi A. Strategies to overcome polymerization shrinkage-materials and techniques. A review. Dental Update 2010;37. p. 115–118, 20– 22, 24–25.
Please cite this article in press as: Furness A, et al. Effect of bulk/incremental fill on internal gap formation of bulk-fill composites. Journal of Dentistry (2014), http://dx.doi.org/10.1016/j.jdent.2014.01.005
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.intl.elsevierhealth.com/journals/jden
Effect of bulk/incremental fill on internal gap formation of bulk-fill composites Alan Furness a,*, Marko Yousef Tadros b, Stephen W. Looney c, Frederick A. Rueggeberg a a
Department of Oral Rehabilitation, College of Dental Medicine, United States College of Dental Medicine, United States c Department of Biostatistics and Epidemiology, Medical College of Georgia, United States b
article info
abstract
Article history:
Objectives: To examine the effects of composite type (bulk-fill/conventional) and placement
Received 23 July 2013
(4-mm bulk/2-mm increments) on internal marginal adaptation of Class I preparations.
Received in revised form
Methods: Cylindrical, Class I, 4-mm 4-mm preparations were made on 50 recently
19 December 2013
extracted human molars and restored using either a bulk-fill (SureFil SDR Flow (SDR), Quixx
Accepted 7 January 2014
(QX), SonicFill (SF), Tetric EvoCeram Bulk (TEC)) or a conventional composite designed for 2-
Available online xxx
mm increments (Filtek Supreme Ultra (FSU)). Restorations were placed in 1 or 2 increments using the manufacturer’s bonding agent and curing light (n = 5). Teeth were sectioned
Keywords:
occluso-gingivally and dye was placed on the internal margin and visually examined by
Bulk-fill
3 observers. Gap-free marginal lengths were analysed within three different regions of the
Composites
sectioned tooth: enamel, mid-dentine, and pulpal floor.
Margin adaptation
Results: Marginal integrity was unaffected by placement method. Bulk-placement demonstrated significantly fewer gap-free margins at the pulpal floor than in enamel, for all materials except SDR. Greater percentages of gap-free margins were found within the middentine than at the pulpal floor for FSU. QX had more gap-free margins in enamel compared with the mid-dentine. Proportion of gap-free margins within enamel and mid-dentine was not significantly different for any incrementally placed product. Excluding FSU, gap-free margins within enamel were significantly greater than at the pulpal floor. Notably, significantly more gap-free margins were found within mid-dentine than at the pulpal floor for SF. Conclusions: No significant differences in gap-free margins were found between placement methods within a given product per location. Except for SDR, percentage of gap-free margins was significantly lower at the pulpal floor interface than at the enamel interface for bulk-fill. Published by Elsevier B.V.
1.
Introduction
Recently, several new restorative materials have been advertised as ‘bulk-fill’ composites. Many clinicians, however, have long adopted an incremental cure philosophy, when placing light-cured composites. In light of recent marketing efforts
promoting ‘‘bulk-fill,’’ light-cured composites, the judicious clinician should question what has changed that now allows composites to be placed in increments exceeding 2-mm thickness. The concept of ‘‘bulk-filling’’ a preparation is not a novel idea,1 and has been evaluated numerous times in the literature.2–5 Historically, several disadvantages of bulk-filling preparations with light-cured composites are recognised: the
* Corresponding author at: College of Dental Medicine, Room GC 4210, Georgia Regents University, 1430 John Wesley Gilbert Drive, Augusta, GA 30912, United States. Tel.: +1 706 721 8321. E-mail address: [email protected] (A. Furness). 0300-5712/$ – see front matter . Published by Elsevier B.V. http://dx.doi.org/10.1016/j.jdent.2014.01.005 Please cite this article in press as: Furness A, et al. Effect of bulk/incremental fill on internal gap formation of bulk-fill composites. Journal of Dentistry (2014), http://dx.doi.org/10.1016/j.jdent.2014.01.005
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inability to adequately cure composite to depths greater than 2 mm,6,7 challenges related to preparation design on the Cfactor,8,9 as well as potential complications due to polymerisation shrinkage and increased gap formation, both internally and at the cavo-surface margins.8,10,11 The clinical implication of marginal gap formation is related to discomfort in conjunction with occlusal forces, which may be attributed to fluid accumulation within the gap and the subsequent fluid movement within the tubules.12,13 One reason for the recommended 2-mm thick incremental composite placement relates to compromised light penetration through this material, which is especially true when using darker shades.6 While the surface of the composite is adequately cured, the material may not polymerise well in depth.14,15 Insufficiently polymerised composite has been shown to be cytotoxic and may pose a negative risk to the longevity of the restoration.16,17 Cavity preparation design affects the internal stresses of light-cured composite restorations.8 The C-factor refers to the ratio of bonded-to-unbonded restoration surfaces, with a direct correlation shown between preparation C-factor and internal polymerisation stress development at the bonded interface.11 Placing and light-curing composite in increments is thought to decrease its total volumetric shrinkage, and to potentially decrease stresses resulting from this shape change.3 Other studies however, challenge this concept.18 If the force of polymerisation shrinkage exceeds the strength of the bonding agent and composite interface, then a marginal gap can form to accommodate this strain.4 In addition, stress fractures in enamel and dentine have been observed and are thought to occur when the interfacial bond strength surpasses the physical properties of adjacent tooth structure.19 Therefore, a variety of restorative techniques have been recommended to reduce polymerisation stress. One such strategy includes the use of liners/bases in the preparation.20 A recent study detected internal marginal debonding events using acoustic emission and correlated shrinkage, modulus, and stress development with the potential for observing such events.21 However, if marginal gaps do develop, they will compromise the long-term durability of the restoration and have the potential to create post-insertion sensitivity, increase the incidence of secondary caries, and encourage marginal staining.11 Marginal gap formation is the end product of a number of clinical factors. Poor placement techniques 18 and the variety of incremental and light curing scenarios may lead to such discrepancies as well as polymerisation shrinkage and the cumulative effects of polymerisation stress.8 Marginal integrity has been evaluated using high magnification,5,9,20 while other studies used penetrating dyes to reveal marginal gaps, both externally and internally.9,22 In addition, the effects of using a variety of curing light types and various light exposure techniques on their potential to generate or minimise marginal gap formation and depth of cure have been studied.6,14,23 The recent introduction of many ‘‘bulk-filled’’ restorative materials has re-ignited the controversy of ‘‘bulk vs incrementally’’ placed composites. While the main interest in marketing this class of products is based on time and thus cost savings, other clinically related aspects are relevant as well.
An ideal bulk-fill composite would be one that could be placed into a preparation having a high C-factor design and still exhibit very little polymerisation shrinkage stress, while maintaining a high degree of cure throughout. As a result, reduced polymerisation stress should minimise internal and external marginal gap formation, compared to conventional incrementally placed composites. The newly developed ‘‘bulk-filled’’ resins claim to offer single increment placement thicknesses ranging from 4 to 6 mm, instead of the conventional 2 mm value commonly used. However, the potential development of internal marginal gap formation exists with bulk placement and the proportion of gaps relative to use of conventional 2-mm increments has yet to be determined. In addition, no studies have correlated use of the manufacturer-specific dentine bonding agent and manufacturer-specific curing light unit, as they relate to the potential for maintenance of internal interfacial margins. If the bulk-fill restorative materials are to provide a true clinical advantage, then they require high depths of cure while simultaneously demonstrating a decrease in internal stress, and subsequently decreased incidence of internal gap formation. Only products demonstrating such superior performance over the use of traditional, incrementally placed composites, should then be considered as viable alternatives. The purpose of this research was to examine the potential for maintenance of gap-free internal interfacial bonds within the enamel, mid-dentine, and pulpal floor areas in controlledsize, Class I preparations made in extracted human molars when restored using a variety of the newly marketed ‘‘bulkfilled’’ products. Restorations were placed in either two, 2-mm thick increments, or as a single, 4-mm thick bulk-fill placement, utilising the respective manufacturer’s total-etch bonding agent and curing light. The experimental control material was a conventional composite recommended for only 2-mm thick increments. Three research hypotheses were tested: (1) for bulk-fill materials, marginal integrity at the enamel and mid-dentine restoration interfaces would not be significantly different with respect to type of fill (incremental or bulk), (2) at the pulpal interface, marginal integrity of the bulk-fill materials would be significantly better using the bulk fill technique than with use of the incremental fill technique, and (3) there would be no significant difference in marginal adaptation of the commercial product designed for incremental placement between bulk and incremental placement, except at the pulpal floor, where it is expected that bulk placement would result in less gap-free interface (more interfacial gaps) than when incremental placement was used.
2.
Materials and methods
2.1.
Tooth preparation
Freshly extracted, intact, non-carious and non-restored, human maxillary and mandibular molars were obtained from the Oral Surgery Department of the College of Dental Medicine at Georgia Regents University College of Dental Medicine. The protocol for use of teeth for this purpose was approved by the
Please cite this article in press as: Furness A, et al. Effect of bulk/incremental fill on internal gap formation of bulk-fill composites. Journal of Dentistry (2014), http://dx.doi.org/10.1016/j.jdent.2014.01.005
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Human Assurance Committee, under approval Number IRBHSD00000128. A controlled removal of enamel on the occlusal surface was performed, which resulted in retention of a central portion of enamel in the centre of the tooth, while dentine was slightly exposed where the cusp tips had been located. This type reduction was necessary to provide for a flat occlusal surface having centrally located enamel, so that the light curing units could be held at a repeatable distance of 2 mm from the occlusal margin when photocuring each tooth. Thus the entire occlusal cavosurface margin was in enamel and was located within the curing light beam area upon the tooth. Following cusp tip removal, a Class I preparation (4.0 mm (0.2 mm) diameter, 4.0 mm (0.2 mm) deep, C-factor = 5.0) was made by hand using copious water irrigation and a high speed handpiece equipped with a flat-ended diamond bur (item number 6837KR, Komet USA, Rock Hill, SC). The dimensions of each preparation were measured using a digital micrometre (model CD-600 B, Mitutoyo Corporation USA, Aurora, IL USA). Preparations in which a pulp exposure was identified were not used in the experiment, because a totally intact preparation margin was required for analysis purposes.
2.2.
Tooth restoration
The order of material used for restoration was randomised among all specimens, in order to minimise the effect of operator learning on the variation in test results. The specimens were thermocycled and each tooth to be restored was identified with a specific engraved number on the external portion of its crown segment. Teeth were restored using a variety of contemporary bulk filling composite materials, used in conjunction with the totaletch dentine bonding product as well as light curing unit specific for each manufacturer (Table 1). Total etch dentine bonding systems were used among all products to reduce variability in results that might have occurred if some self-etching systems had been used. Four commercial bulk-fill composite systems were tested and one conventional composite that required 2-mm increments was used as control. Only one of the bulk-fill products (SureFil SDR
Flow) recommended that a capping layer of conventional composite be placed. However, because this study was only interested in evaluating internal margins, and not that of the cavosurface location, no capping agent was used. Other than this exception, all manufacturer instructions were followed for placement and curing of the dentine bonding agent as well as the subsequent resin composite material. For SureFil SDR Flow and Quixx, Prime and Bond NT was used as the bonding agent, Optibond Fl was used for SonicFill, ExciTE F for Tetric EvoCeram, and Adper Scotchbond for Filtek Supreme Ultra. The manufacturers instructions were followed for each bonding agent as well as the recommended curing light and exposure times. When light-curing all restorative agents (bonding resins and composites), the tooth was held upright using wax. A 2mm thick, clear acrylic plate, having a 6-mm diameter hole, was placed over the flattened occlusal tooth surface, and aligned so that the centre of the hole was concentric with the centre of the Class I preparation. The distal end of the light guide was then positioned so that the centre of the tip was coaxial with the centre of the plate hole and restoration. This arrangement allowed for the repeatable distancing of the light curing tip to be 2 mm away from the cavosurface margin, simulating the distance that the cusp tips might have restricted light tip placement (Fig. 1). Following completion of cavity restoration, excess restorative material was removed using a finishing diamond bur, under copious water irrigation (item # 8379.314.021, Komet USA, Rock Hill, SC, USA), to expose the cavosurface margin. The restored teeth were then placed into deionised water at room temperature. Restored teeth were subjected to 1000 cycles, between 5 8C and 55 8C, after which they were darkstored in a aqueous disinfectant solution (Thymol, Item T185100, Fisher Scientific, Fair Lawn, NJ, USA) for at least 24 h in a 37 8C oven (Stabil-Therm Constant Temperature Cabinet, Blue M Electric Company, Blue Island, IL USA).
2.3.
Tooth sectioning and embedment
Pencil lines were made on the crown segment of each restored tooth that aligned the centre of the restoration and the long
Table 1 – Products and devices used throughout testing. Composite type
Manufacturer location
Composite name Lot#
Composite shade
Bonding agent
Curing light
Recommended curing light exposure (time – thickness) Bulk
Bulk-fill
Conventional
Caulk Dentsply Milford, DE
Kerr/Sybron Orange, CA Ivoclar Vivadent Liechnstein 3M ESPE St. Paul, MN
SureFil SDR Flow Lot# 100929 Quixx Lot# 100609 SonicFill Lot#3439122 Tetric EvoCeram BF Lot#RZM013 Filtelk Supreme Ultra Lot #N203124
A2
Prime N Bond NT Lot # 100709
SmartLite IQ2
40 s–4 mm
20 s–2 mm
20 s–4 mm
20 s–2 mm
Demi Plus
20 s–4 mm
20 s–2 mm
Bluephase 20i
10 s–4 mm
10 s–2 mm
S10
40 s–4 mm
20 s–2 mm
Universal A2 Universal
A2B
Optibond FI Lot#3553038 ExciTE F Lot # N75726 Adper Scotchbond Lot# N199766
Increment
Please cite this article in press as: Furness A, et al. Effect of bulk/incremental fill on internal gap formation of bulk-fill composites. Journal of Dentistry (2014), http://dx.doi.org/10.1016/j.jdent.2014.01.005
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its water-storage, and the tooth surface was lightly dried, using laboratory wipes (Kimwipes, Kimtech Science, Kimberly-Clark Global Sales, Inc., Roswell, GA, USA). A small amount of a caries detecting solution (Item #1805, Sable Seek, Ultradent Products, South Jordan, UT, USA) was dispensed into a dappen dish and was traced over the internal margins, using a ball-ended hand instrument (PICH, Hu-Friedy, Chicago, IL,USA). Excess dye was removed by blotting with laboratory wipes.
2.5.
Fig. 1 – Graphical depiction of controlling composite-tolight distance during restoration photocuring.
axis of the tooth. The tooth was then held by the root and the occlusal end was fed into the circulating blade (No. 11-4244, Series 15HC D, Diamond Wafering Blade, Buehler Ltd., Evanston, IL, USA) of a water-cooled cutter (Isomet 11-1180 Low Speed Saw, Buehler Ltd) until the cut passed the DEJ. The root sections were then removed using a high speed handpiece and carbide bur (#556, Brasseler), leaving only the sectioned crown segments. Each flat, cut section was then placed facedown on a flat rubber sheet, and a 1-inch diameter plastic ring (20815110, Plastic Ring Form, Buehler) was positioned overtop, so that the tooth was centred within the ring circumference. A self-curing denture repair material (Ref. #680049/680042, Dentsply International, York, PA, USA) was poured into each ring in order to provide a firm embedding matrix for the tooth specimen. Once the embedding polymer set, specimens were placed in a 100% humidity chamber to prevent dentine desiccation, for no longer than 1 week. The complimentary sectioned halves were stored for subsequent analysis using SEM imaging in a future study. Following storage, specimens were individually retrieved, and the tooth-side of the ring was polished through a sequence of abrasive papers (ending in 1200 grit SiC (item 688, Buehler)) and a 1.0 mm alumina slurry (No 40-6361-006, Buehler) on a polishing cloth (No 40-7212, Microcloth, Buehler). Between the applications of each size abrasive, specimens were ultrasonically cleaned in water for 15 min (Model 2014, Ultrasonic Cleaning System, L&R Manufacturing Co., Kearney, NJ, USA). The specimen code number identifying the restorative material and trial number of each specimen was engraved on the polished embedding medium, after which the specimens were water-stored at 37 8C in the dark until staining and imaging. The effects of tooth embedding, sectioning, and storage using this method are felt to be similar to techniques used in microtensile testing specimen preparation.24 The validity of this sectioning method has also been recently been verified, comparing results of internal gap formation with a non-invasive, micro-CT technique.25
2.4.
Margin staining and image recording
Specimens were randomly selected for marginal staining and image recording. An individual specimen was retrieved from
Image analysis
Immediately following removal of excess dye, images of each specimen were obtained using a digital camera (FinePix HS10, Fujifilm Manufacturing, Greenwood, SC, USA) at 10.3 megapixel resolution. The recorded images were then projected on a large screen and three investigators underwent a calibration session to finalise agreement with respect to recognition of (1) open/closed margins (gap formation), (2) tooth fracture, and (3) void formation. Following examiner calibration, images of treated teeth were projected using image analysis software (ImageJ v1.46r, National Institutes of Health, Bethesda, MD, USA). Using this software, the length of the marginal interface was determined at specific locations along the internal tooth/ restoration interface: (1) the enamel/composite portion, (2) within the mid-dentine (defined as length from the DEJ along the axial wall to the line angle where the pulpal floor started, and (3) along the pulpal floor. Within each of these measured locations, the portion of gap-free marginal length (identified as absence of stain) was measured as a percentage of total interfacial length.
2.6.
Statistical analysis
Data were analysed using repeated measures analysis of variance (ANOVA), with one repeated factor (location) and two grouping factors (restorative material and fill type). The general analysis strategy used was similar to that recommended by Looney and Stanley when there is one repeated factor and one grouping factor.26 The first step in this procedure was to test for any significant interactions among the factors. If no significant interactions were found, the next step was to test the main effects for each factor: that is, the null hypothesis that there were no differences among factor levels, ignoring the effects of the other factors. The third step was to use the Tukey–Kramer method to examine all pair-wise comparisons for each factor that had more than two levels (location and restorative material). Repeated measures analysis was used for any tests involving the location factor. If the three-way interaction proved significant, an appropriate two-way ANOVA for two of the factors was performed separately for each level of the third factor. If the three-way interaction was not significant, but one or more two-way interactions were significant, analyses based on contrasts were performed for each of the factors involved in the significant two-way interactions. The Tukey–Kramer method was used anytime pairwise comparisons were analysed. Unless otherwise specified, two-tailed tests with a significance level of 0.05 were used. A Bonferroni adjustment was used, whenever appropriate, to control the family-wise error rate at
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0.05. All statistical analyses were performed using software on a personal computer (SAS v9.3 for Windows, SAS Institute Inc., Cary, NC, 2010).
3.
Results
3.1.
Material and location
The three-way repeated measures ANOVA, testing the effect of restorative material, fill method, and internal interface location on percentage of gap-free interface, indicated a nonsignificant 3-way interaction ( p = 0.755). There was a significant 2-way interaction between restorative material and location ( p = 0.012); no other interactions were significant ( p = 0.116 for fill method by material and p = 0.180 for fill method by interface location). Because of the significant material-by-location interaction, it was not appropriate to test the significance of the main effects for material and location.22 Instead, tests of contrasts comparing the levels of these factors were performed using the appropriate multiple comparison procedure. As a main effect, fill type (bulk or incremental) did not have a significant influence on the extent of gap-free location ( p = 0.288).
3.2.
Fig. 2 – Effect of restorative material and fill method on percent of gap-free interface, regardless of location of internal margin. N = 5 replications per condition horizontal bar = +1 standard deviation vertical bar connects values that are not significantly different.
Fill type and location 3.3.
Because the 2-way interaction between material and location was statistically significant, a two-way ANOVA (A) for fill type (incremental/bulk) by location (enamel/mid-dentine/pulpal floor) was performed separately for each material and a twoway ANOVA (B) for fill type by material was performed separately for each location. In the separate two-way ANOVA’s for each material, ANOVA (A) found no significant differences between fill types for any restorative material, using a Bonferroni-adjusted significance level of 0.05/5 = 0.01 for each material (Fig. 2). However, significant differences were found among tooth locations with the bulk-fill method using Tukey-Kramer pairwise comparisons for repeated measures, with a Bonferroni-adjusted significance level of 0.05/5 = 0.01 for each material (Fig. 3). Comparisons of gap-free margin percentages between locations for each material using the incremental fill technique are seen in Fig. 4. As with the bulk-fill method (Fig. 3), these results are based on Tukey-Kramer pairwise comparisons for repeated measures, with a Bonferroniadjusted significance level of 0.05/5 = 0.01 for each material. A similar approach was used for the separate two-way ANOVA’s for each interface location: ANOVA (B). There were no significant differences in percentage of gap-free margins between fill types for any of the 5 materials, using a Bonferroni-adjusted significance level of 0.05/5 = 0.01. For enamel, differences in gap-free margin extent were found between materials, depending on fill type, using TukeyKramer pair-wise comparisons with a Bonferroni-adjusted significance level of 0.05/2 = 0.025 for each fill type (Fig. 5). Within each of the other two internal marginal locations (mid-dentine and pulpal floor), there were no significant differences in gap-free margin percentages between materials for either fill type (Figs. 6 and 7).
Leakage patterns
The individual photos of imaged sections reveal similarities and differences in gap formation patterns and locations among the various groups. Fig. 8 displays the images of the bulk-fill, flowable consistency product, SureFil SDR Flow. For this material, when placed incrementally, or when placed in bulk, there is a consistent presence of leakage of the dye materials
Fig. 3 – Effect of composite brand and location of internal tooth interface on percentage of gap-free margin when using the bulk-fill insertion method. N = 5 specimens/ group. Horizontal bar = +1 standard deviation. Within a composite brand, groups identified with similar upper case letters are not significantly different.
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Fig. 6 – Percentage of intact internal margin within the internal mid-dentine/restoration interface. N = 5 specimens/ condition. Horizontal line = +1 standard deviation. Vertical bar joins groups not significantly different. Fig. 4 – Effect of composite brand and location of internal tooth interface on percentage of gap-free margin when using the incremental insertion method. N = 5 specimens/ group. Horizontal bar = +1 standard deviation within a composite brand, groups identified with similar upper case letters are not significantly different.
into the gap, and then down the tubules and towards the pulp chamber. Such a leakage pattern indicates that the composite material bonded to the underlying dentine adhesive system, and lifted the hybrid layer up and off the dentine when the composite cured, leaving direct access to dentine tubules. The dye penetration patterns for second bulk-fill composite material, but not a flowable type product (Quixx) is seen in Fig. 9. A wide range of dye penetration patterns is seen with this product. For either fill type, the majority of gap formation was seen at the pulpal floor interface, with dye filling tubules
Fig. 5 – Percentage of intact internal margin within the internal enamel/restoration interface. N = 5 specimens/ condition. Horizontal line = +1 standard deviation vertical bar joins groups not significantly different vertical arrows identify significant differences between gap-free percentages of incrementally or bulk-fill placed composites.
and not merely being confined to the interfacial opening, using both incremental as well as the bulk-fill techniques. For an additional bulk-fill composite tested, SonicFill, there was a mixture of leakage patterns seen among specimens for both types of restoration filling technique (Fig. 10). For this material, there was evidence of only very mild dye infiltration, dye infiltration into gaps with no downward tubule entry, as well as dye penetrating into the gap, and traversing opened dentine tubules and travelling directly towards the pulp. The last bulk-fill composite tested, Tetric Evo Ceram Bulk Fill, demonstrated a unique pattern of internal gap dye penetration (Fig. 11). Although this product indicated gap formation at the pulpal floor in most instances (as seen with all other products), the unique feature was that the dye penetration seemed limited to that opening, and dye is not seen penetrating tubules and running towards the pulp chamber. Such a pattern of leakage indicates that the hybrid layer was kept intact during shrinkage of the overlying composite, not allowing the dye to enter and run towards the pulp chamber.
Fig. 7 – Percentage of intact internal margin at the pulpal floor region. N = 5 specimens/condition. Horizontal line = +1 standard deviation, vertical bar joins groups not significantly different
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Fig. 8 – Sectioned and stained images of using SureFil SDR Flow in both two, 2-mm thick increments or as a single 4-mm thick increment.
Fig. 9 – Sectioned and stained images of using Quixx in both two, 2-mm thick increments or as a single 4-mm thick increment.
Fig. 10 – Sectioned and stained images of using SonicFill in both two, 2-mm thick increments or as a single 4-mm thick increment. Please cite this article in press as: Furness A, et al. Effect of bulk/incremental fill on internal gap formation of bulk-fill composites. Journal of Dentistry (2014), http://dx.doi.org/10.1016/j.jdent.2014.01.005
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Fig. 11 – Sectioned and stained images of using Tetric Evo Ceram Bulk Fill in both two, 2-mm thick increments or as a single 4-mm thick increment.
Images of the control composite (Filtek Supreme Ultra), which was made to use in increments of 2-mm thickness, are seen in Fig. 12. Interestingly, when used according to manufacturer’s directions of placement and curing in 2-mm thick increments, there was a tendency for not only total gap formation at the pulpal floor, but also evidence of dye penetration into opened tubules at that interface, implying separation of the hybrid layer at that location, and exposure of open tubules. However, when placed in one, 4-mm thick bulk increment, although there is still consistent evidence of gap formation at the pulpal floor, there is much less appearance of dye flowing into open tubules at that interface.
4.
Discussion
The first research hypothesis proposed that the marginal integrity at the enamel and mid-dentine areas of the restoration would not be significantly different, regardless
of whether the material was placed in bulk or incrementally filled. The research findings validated this hypothesis, as there was no significant difference in percentage of gap-free interface with respect to placement technique (incrementally or bulk), without respect to specific material or interface location. Even within a particular brand of composite, there was no significant difference in terms of bulk or incremental placement (Fig. 2), as it relates to the total margin integrity. It is interesting to note, however, that statistical differences were found between the percentages of gap-free interfaces related to the margin location. Of materials tested in bulk placement, all had a significantly higher degree of gap-free interfaces within the enamel portion compared to pulpal margins, with the exception of SureFil SDR Flow (Fig. 3). For this material, there was no statistical difference found between the marginal integrity at the enamel, mid-dentine, or pulpal margins. This same relationship however, was not observed when SureFil SDR Flow was placed incrementally (Fig. 4). Incremental placement of SureFil SDR Flow resulted in a similar marginal
Fig. 12 – Sectioned and stained images of the control composite (Filtek Supreme Ultra) in both two, 2-mm thick increments or as a single 4-mm thick increment. Please cite this article in press as: Furness A, et al. Effect of bulk/incremental fill on internal gap formation of bulk-fill composites. Journal of Dentistry (2014), http://dx.doi.org/10.1016/j.jdent.2014.01.005
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appearance as observed in other materials tested, with the enamel margins having significantly better gap-free marginal interfaces than those at the pulpal floor. The second research hypothesis proposed that, at the pulpal interface, marginal integrity of the bulk-fill materials would be significantly better using the bulk-fill technique than when restorations were placed in two separate, 2-mm thick increments. This hypothesis was disproven, however. Fig. 7 shows that there was no significant differences in percentage of gap-free margin among the materials at the pulpal margin. In no case was the percentage of a gap-free margin at the pulpal interface above 30% of its length. As with other interfaces, the method of composite placement did not have a significant impact on the percentage of gap-free margin occurrence, but the percentage values were quite low at this interface location: incremental fill averaged 18% of gap-free margin length (max 27%, min 8%), and bulk-fill averaged 9% (max 16%, min 6%). The last research hypothesis proposed that, other than at the pulpal floor, no statistical difference in gap-free margin percentages would be found between placement techniques for the control composite: the material designed for use only with incremental placement. This concept was only partially validated. When the control material was placed and polymerised in a single, 4-mm thick increment, there was no significant difference in the percentage of gap-free margin length between enamel and dentine interfaces, yet the proportion observed at the pulpal floor was significantly lower than at the other two locations (Fig. 3). When using this material as intended (in two separate, 2-mm thick increments), no significant differences were found in the percentage of gap-free margins among all three bonding interfaces (Fig. 4). However, what is interesting to note are the differences in gap-free margin proportions at the same tooth locations between fill types for this material. When using the recommended incremental method, the incidence of gap-free margins at both the enamel and dentine interfaces appeared to be much lower than when using this material in bulk (Figs. 3 and 4). However, no significant difference in marginal integrity was noted at the pulpal floor between delivery techniques: both methods provided gap-free margins of only 10% or less of the total interface length. These differences seem to indicate that, when placed and polymerised in bulk, shrinkage stresses at the enamel and dentine interfaces were less, resulting possibly from the ability of unpolymerised composite deep in the restoration to deform and ‘‘feed’’ the resulting stress development from the strain of composite curing at shallower depths. In contrast, much higher stress development must have occurred in the second 2-mm thick increment, as evidenced by the lower percentages of gap-free marginal interfaces in enamel and dentine. The lower intact margin extent using the incremental layering technique may arise from the absence of a deep reservoir of uncured composite from which to relieve polymerisation stresses of the upper composite segment. Other studies have demonstrated that the degree of cure for Filtek Supreme Ultra decreases significantly after 2-mm depth, validating the possibility of a bolus of deformable composite from which strain of the uppermost material can draw.14,15 It is interesting to note that, for the enamel and mid-dentine interfaces of the bulk-fill materials in
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general, a smaller difference is noted between bulk or incremental fill, as compared with the control, incrementalfill product (Figs. 3 and 4). However, the trend seems to be that, although the marginal integrity at the pulpal floor is very poor, use of the bulk-fill products in an incremental mode does tend to be slightly better than when these products are placed in a 4-mm increment. This difference may be due to the enhanced translucency and enhanced photochemistry that many bulkfill products have utilised in order to be able to polymerise to deeper depths than the incremental-only products.27 This study shows that use of the new bulk-fill products does not universally eliminate the potential for internal marginal gap formation, as might be hoped. Indeed, overall, there was no significant difference in internal marginal integrity with respect to placement technique only. Still, using either the conventional, incremental-only composite, or a 4-mm bulk fill of composite specifically designed for this application, marginal gap formation at the pulpal floor was very prominent. The clinical implications of this finding may be that, although composite may be curing to enhanced depths, the potential for developing any post-insertion sensitivity that is related to gap formation at the pulpal floor, and the resulting hydraulic movement of fluids that will occupy this space upon occlusal loading, is still present. The correlation between the potential for gap formation and postinsertion sensitivity has long been known.28 Indeed, clinical methods to reduce polymerisation stresses are still under study, in hopes of providing longer-lasting direct, aesthetic restorations.29 An interesting outcome of the present study was the starkly different behaviour of dye penetration into the bonded interface among some products. In particular, although there was notable pulpal floor gap formation when placing Teric Evo Ceram Bulk Fill, using either placement technique, none of the sectioned specimens demonstrated evidence of dye rushing through open tubules, towards the pulp. However, most all other products demonstrated this event. While in some of the specimens, the die pooled within the gap, yet in others, it penetrated the tubules. This observation may be attributed to where the gap occurred along in the interface. If the gap occurred between the composite and the hybrid layer, a localised pooling of the dye may be expected, because the tubules remain sealed. However, if the gap occurred between the hybrid layer and underlying dentine, dye penetration into the tubules would be expected. The implications of these different types of gaps need to be studied further in conjunction with their potential clinical significance. The potential for clinical success may thus also lie within the integrity of the composite/bonding agent/dentine interface to withstand shrinkage stresses. Only with long-term clinical studies can any such differences in clinical performance and patient comfort be addressed. The limitations of the current study deal with the fact that not all commercial bulk-fill materials were included. Indeed, even at the time of writing this report, new bulk-fill products have been introduced on the market, and remain untested. In addition, only five replications were made of each test condition. With a greater sample size, more statistical discrimination among the main test factors of placement method, marginal interface location, and product could have been identified. However, it is felt that the product selection
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and sample size provide a very good initial overview of this new composite classification and placement technique. In addition, it is also recognised that the curing lights used were specific for each material and that degree of cure and subsequent marginal gap formation may have been influenced by this selection. Further studies are needed to elucidate the relationship between the curing light type and degree of cure. It is also recognised that each bonding agent used, although specific for each material, may have influenced the marginal gap and this relationship between the bonding agent and the ‘bulk-fill’ composite needs to be studied further. However, it must be noted that manufacturers design these restorative components as integrated systems, yet often studied in isolation. For example, bulk-filled systems may have different types of photointiators and thus require curing lights that adequately activate them. To avoid this complication and to test these products as they are offered, it was decided to study the products as integrated systems.
5.
Conclusions
Within the limitations of this study it can be concluded that (1) Use of a bulk-fill restorative material compared to a conventional composite resulted in a similar proportion of gap-free, internal marginal interface in the mid-dentine and enamel areas. (2) The proportion of gap-free margin at the pulpal interface was lower than at the enamel or mid-dentine interfaces, regardless of type of material used or fill type, with the exception of one bulk fill material used in a single 4-mm increment (SureFil SDR Flow) and for the control: incrementally cured composite placed in two separate, 2-mm thick increments (Filtek Supreme Ultra). (3) The percentage of gap-free internal margins of the control composite was less at the enamel and mid-dentine portions when used as directed (in two, 2-mm thick increments), than when the same material was used in a single 4-mm thick increment, although this difference was not statistically significant.
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