journal of dentistry 42 (2014) 746–752
Available online at www.sciencedirect.com
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Effect of water storage on the translucency of silorane-based and dimethacrylate-based composite resins with fibres Nurcan Ozakar Ilday *, Neslihan Celik, Yusuf Ziya Bayindir, Nilgu¨n Seven Department of Restorative Dentistry, Atatu¨rk University, Erzurum, Turkey
article info
abstract
Article history:
Objectives: The purposes of this study were (1) to determine the translucency of silorane and
Received 4 March 2013
dimethacrylate-based composite resins and (2) to evaluate the effect of water storage and
Received in revised form
reinforcement with fibre on the translucency of composite resins.
10 January 2014
Methods: Two light-cured composite resins (A2 shade), Filtek Silorane (silorane-based
Accepted 5 February 2014
composite) and Valux Plus (dimethacrylate-based composite), were used in this study. The first group was used as the control with no reinforcements, the second was reinforced with polyethylene (Ribbond THM) and the third was reinforced with a glass fibre (Everstick
Keywords:
Net) for each composite resin. Colour measurements were measured against white and
Translucency
black backgrounds with a Shadepilot (Degu Dent Gmbh, Hanau, Germany) spectrophotom-
Fibre
eter and recorded under a D65 light source, which reflects daylight. CIELAB parameters of
Composite
each specimen were recorded at baseline and at 24 h, 168 h and 504 h. Translucency of
Water storage
materials was calculated using the translucency parameter (TP) formula. Data were ana-
Silorane
lyzed using repeated measures ANOVA and LSD post hoc tests (a = 0.05). Results: The highest baseline TP value was in the Valux Plus/non-fibre reinforced group (14.06 1) and the lowest in the Filtek Silorane/Ribond THM group (8.98 1.11). Repeated measures ANOVA revealed significant effects from the factors storage time, composite resin, composite resin storage time and fibre time (p = 0.047; p = 0.001; p = 0.013; p = 0.022, respectively). Conclusion: Within the limitations of the study, we concluded that inclusion of polyethylene and glass fibres did not alter the translucency of the different-based composite resins. The longest storage time resulted in the greatest change in translucency values of Filtek Silorane composite resins. Clinical significance: Considering the translucencies of composites with different formulations in the selection of composite resins for aesthetic restorations is important in terms of obtaining optimal aesthetic outcomes. # 2014 Elsevier Ltd. All rights reserved.
* Corresponding author. Tel.: +90 442 2313882; fax: +90 442 2360945. E-mail addresses: [email protected], [email protected] (N. Ozakar Ilday). http://dx.doi.org/10.1016/j.jdent.2014.02.002 0300-5712/# 2014 Elsevier Ltd. All rights reserved.
journal of dentistry 42 (2014) 746–752
1.
Introduction
Tooth-coloured dental resin composites have undergone continuous development during recent decades. The development of modern composite resins has led to remarkable improvements in terms of optical properties, biocompatibility, physical strength, wear resistance and stability in the oral environment.1,2 However two major properties of composite resins that still have to be improved are polymerization shrinkage and stress associated with the chain growth nature of the methacrylate-based free radical polymerization process.3 Polymerization shrinkage causes contraction stresses in the composite resin restoration and internal stress and deformation in the surrounding tooth structure.4,5 Several strategies have been used to reduce stress, including changes in monomer structure or chemistry, changes in filler amount6,7 layering techniques or applying a low elastic modulus liners between the tooth structure and8,9 the incremental placement of composites in order to minimize the internal stress and deformation of the tooth structure.10 In addition to these approaches, controlled polymerization techniques (soft-start polymerization)11 and different placement techniques12 have been recommended in order to reduce stress. A new category of restorative material, siloranes, has been recently introduced in order to overcome the problems related to polymerization shrinkage.3,13,14 This monomer is obtained from the reaction of oxirane and siloxane molecules. The volumetric shrinkage of a silorane-based composite was determined as 0.99 vol.% using the Archimedes method.3 The stress reducing mechanism in this new cationic ring opening hybrid monomer system is achieved by the opening and extension of the oxirane rings during polymerization to compensate volume reduction by monomer packing.3,15 The silorane-based resin composites have low polymerization shrinkage and stress,3 good stability in aqueous environments and insolubility in biological fluid stimulants13,14 compared with conventional dimethacrylate based composites. For aesthetic restorations, perfect colour match between the natural teeth and restoration is a very important requirement. Modern composite resins have different hues and opacities that excellently imitate the chromaticity and translucency of enamel, as well as dentine.16 Translucency is the ability of a layer of coloured substance to allow the appearance of an underlying background to show through.17 The translucency parameter of a material refers to the difference in colour between a uniform thickness of the material over a white background and the same thickness of the material over a black background18 and provides a value corresponding to the common visual perception of translucency.18–20 When the colour of a restoration is combined with proper translucency, the restoration can closely match the surrounding tooth structure.2,21 If the composite resins are too translucent, the colour of the abutment tooth may have a considerable effect on the colour of the final restoration.22 The greater the translucency value, the higher the actual translucency of a material.2,21,23 The translucency of dental resin composites depends on their thickness as well as the scattering and absorption coefficients of the resin, filler
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particles, colour pigments and opacifiers.24,25 Since the formulation influences the optical properties of resin composite, silorane composites may exhibit differences in colour and translucency compared with dimethacrylate composites.2 Fibre reinforced composites were recently introduced for dental restorations and highly favourable mechanical properties, and their strength-to-weight ratios are superior to those of most alloys. Compared to metals, they offer many other advantages as well, including ease of repair, non-corrosiveness, translucency and good bonding properties.26 The optical properties of fibres used in order to obtain an aesthetic appearance compatible with that of normal teeth in fibresupported adhesive bridges in anterior teeth are very important. Restorative dental materials absorb water slowly, primarily because of the polar properties of the resin molecules. Water molecules act as plasticizers and facilitate the flow of longchain polymers that can infiltrate and reduce the mechanical properties of the polymer matrix, leading to degradation of the matrix/fibre or matrix/filler interfaces, by swelling and reducing the frictional forces between the polymer chains, a process known as ‘plasticization’.27–29 Although there have been several studies on silorane-based dental resin composites1,2,23,25,30 and fibre reinforced composites,22,31–34 the effects of fibres on the translucency of silorane- and dimethacrylate-based composites under water storage have been little studied. The null hypotheses tested were that (1) the effect of fibre addition of silorane-based resin composite and dimethacrylate-based resin composite would affect the translucency values, and (2) different lengths of water storage would create differences in the translucency of different based composite resins. The aim of this study was therefore to evaluate the effect of polyethylene and glass fibres on the translucency of differently based composite resins at different storage times in water.
2.
Materials and methods
The formations and manufacturers of the materials used are listed in Table 1. Two A2 shade light-cured resin composites, Filtek Silorane (a silorane-based composite) and Valux Plus (a dimethacrylate-based composite), were used. Types of fibres, polyethylene fibres versus glass fibres, were also investigated. Ribbond THM (Ribbond Inc., Seattle, USA) fibres 0.18 mm thick are bondable reinforced fibres consisting of ultra-high strength polyethylene fibres. Ribbond fibres are not impregnated with resin, and must be saturated with an adhesive bonding agent before use. EverStick Net (Stick Tech Ltd., Turku, Finland) fibres are glass fibres impregnated with lightcuring Bis-GMA and PMMA. Thickness of the woven preimpregnated EverStick Net reinforcement fibres was 0.06 mm. The first group was used as a control group with no reinforcements, the second group was reinforced with polyethylene (Ribbond THM) and the third group was reinforced with a glass fibre (EverStick Net) for each composite material. Fibres were cut using special scissors that the manufacturers provide with their products to a width of 2 mm and a length of 6 mm, and were used according to the
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journal of dentistry 42 (2014) 746–752
Table 1 – Materials used in the study. Product
Type
Formulations
3M/ESPE, Seefeld, Germany
Silorane based composite
Valux Plus*
3M Dental St. Paul, MN, USA.
Dimethacrylate-based composite (hybrid)
Ribbond THM*
Ribbond, Inc. Seattle, Washington, USA.
Polyethylene fibre
Everstick Net*
Stick Tech, Turku, Finland
Glass fibre
3,4-Epoxycyclohexylethycyclo polymethylsiloxane, Bis 3,4-epoxycyclohexylethylphenylmethysilane, Quartz, yttrium fluoride (76 wt%) BIS-GMA TEGDMA, Zirconia, silica (85 wt%) Plasma treated woven UHMWP, polyethylene fibre (non-impregnated) E-glass (electric glass, silanated); Bis-GMA and PMMA
Filtek Silorane
Manufacturer *
Lot
Code
N279893
FS
N252230
VP
9551
R
2060606-EN-089
E
Bis-GMA, bisphenol-A diglycidylether methacrylate; TEGDMA, triethyelene glycol dimethacrylate; UHMWP, ultra-high-molecular-weight polyethylene; PMMA, polymethylmethacrylate. * Formulations as given by manufacturers.
manufacturers’ instructions and placed in the centre of composite disc specimens under sufficient pressure and light-cured for 20 s. Resin composite disks (8 mm in diameter, 2 mm high and 2.0 mm thick) were prepared using layering filling techniques and covered with celluloid strips on glass plates. All specimens were fabricated by pressing the materials between two glass plates under pressure to obtain the desired thickness and smoothness (Fig. 1). Eight specimens were prepared for each group. After curing with a light-curing unit (with 8 mm tip) LEDs (Elipar S10, 3M ESPE, St. Paul, USA) for 40 s each from the top and bottom, the strips and glass plates were removed. Light intensity of the light-curing unit was delivered at 800 mW/cm2 and was monitored using a power metre (Hilux Curing Light Metre, Benlioglu Dental Inc., Ankara, Turkey). All specimens were stored at 37 8C in 100% relative humidity for 24 h before measurement and stored in dark boxes in distilled water until colour measurement. Colour was measured in dry conditions based on the CIELAB colour scale relative to the standard illuminant D65 over a white tile (CIE L* = 82.3, a* = 0.1 and b* = 0.6) and a black tile (CIE L* = 3.4, a* = 0.2 and b* = 1.2) using a spectrophotometer (ShadePilot, Degudent; Hanau, Germany, Software V. 2.41) and recorded using 28 observer configuration. The same examiner performed the colour measurements for all specimens.
Fig. 1 – Schematic illustration of specimen preparation.
Colour was measured using the CIELAB35 colour notation system: L* (lightness, ranging from 0 to 100 with higher numbers being brighter), a* (green–red coordinate), b* (blue– yellow coordinate). CIELAB parameters (L*, a* and b*) of each specimen were recorded at baseline and at 24 h, 168 h and 504 h. The sequence was repeated three times for each specimen, and the median of those three readings was used for analysis. Translucency of materials was calculated using the translucency parameter (TP) formula.18 TP = [(LW* LB*)2 + (aW* aB*)2 + (bW* bB*)2]1/2, where the subscript ‘‘W’’ refers to CIELAB values for each specimen on the white backing, and the subscript ‘‘B’’ refers to the values for specimens on the black backing. Data were entered using Microsoft Office Excel 2007 for Windows (Microsoft Corporation, Redmond, USA). All statistical analyses were performed using a standard statistical software package (SPSS 16.00, Chicago, USA). Comparisons of the mean TP values were performed using repeated measures ANOVA. Statistical significance was set at a = 0.05.
3.
Results
Means and standard deviations of TP values for the groups stored in distilled water are presented in Table 2. The highest baseline TP value was in the VP non-fibre reinforced group (14.06 1.17) and the lowest in the FS-R group (8.98 1.11). Specimens from FS composite resin were generally more opaque than those from VP composite resin. Repeated measures ANOVA analysis revealed that TP values were significantly affected by storage time ( p = 0.047) and composite ( p = 0.001), but not significantly affected by fibres ( p = 0.097). There were significant interactions between storage time composite resin and storage time fibre, but no significant interaction between composite resin fibre and storage time fibre composite resin ( p = 0.013; p = 0.022; p = 0.652; p = 0.815, respectively) (Table 3). FS translucency behaved differently to that of VP. ( p < 0.05) FS composite resin exhibited lower TP values than did VP (Table 4 and Fig. 3).
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journal of dentistry 42 (2014) 746–752
Table 2 – Means W standard deviations of translucency parameter (TP) values for the groups stored in distilled water (n = 8). Fibre
Time Baseline
24 h
168 h
504 h
FS
Non fibre reinforced R E
9.97 0.44 8.98 1.11 9.90 0.48
10.01 0.51 10.06 0.78 9.83 0.52
10.17 0.35 9.72 1.51 9.72 0.63
10.37 0.66 10.83 1.37 10.79 0.77
VP
Non fibre reinforced R E
14.06 1.17 12.70 1.07 13.46 0.77
13.54 0.85 13.66 0.69 13.10 0.43
13.41 1.49 13.46 0.42 13.04 0.33
13.40 1.08 13.04 0.53 13.491 0.73
Table 3 – The results of repeated measures ANOVA. DF
Effect
Mean square
F
p
Test of within subjects effect Storage time Storage time composite resin Storage time fibre Storage time fibre composite resin
3 3 6 6
2.080 2.840 1.971 0.374
2.722 3.717 2.580 0.490
0.047 0.013 0.022 0.815
Tests of between-subjects effects Composite Fibre Composite resin fibre
1 2 2
533.630 1.592 0.278
827.793 2.470 0.432
0.001 0.097 0.652
Table 4 – Changes in means W standard deviations TP values of composite resins depending on the time (with Bonferroni correction). Composite resin FS VP
Baseline
24 h a
9.62 0.18 13.41 0.18 a
168 h a
504 h a
9.97 0.13 13.43 0.13 a
9.87 0.19 13.30 0.19 a
10.66 0.18 b 13.31 0.18 a
Means followed by different lowercase letters in the rows differ statistically at the 5% level.
A statistically significant time-dependent change in translucency values was observed in the groups with added R fibre ( p < 0.05), while no change was observed in the control groups and the groups with added E fibre. (Table 5 and Fig. 2). TP values of FS rose by the end of 504 h ( p < 0.05).
Fig. 2 – TP values in fibre groups at each time interval.
4.
Discussion
This study analyzed the effect of polyethylene and glass fibres on the translucency of both of silorane- and dimethacrylatebased composite resins at different storage times in water. Dimethacrylate-based adhesively bonded dental composites and silorane-based dental composites are frequently
Fig. 3 – TP values in composite resins at each time interval.
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journal of dentistry 42 (2014) 746–752
Table 5 – Changes in means W standard deviations TP values of fibres depending on the time (with Bonferroni correction). Fibre Non fibre reinforced R E
Baseline
24 h a
12.02 0.22 10.84 0.22 a 11.68 0.22 a
168 h a
11.77 0.16 11.86 0.16 ab 11.46 0.16 a
504 h a
11.79 023 11.59 0.23 ab 11.38 0.23 a
11.89 0.22 a 11.93 0.22 b 12.14 0.22 a
Means followed by different lowercase letters in the rows differ statistically at the 5% level.
used in dental practice to meet patients’ requirements for aesthetic and tooth-coloured restorations. However, despite their popularity, these materials are far from ideal in terms of meeting mechanical requirements. For this purpose, short fibres and networked fibres have been used to reinforce resin composites, resulting in modest increases in composite strength.26,32 The optical properties of composite resins play an important role in matching the shade of an aesthetic restoration to the natural appearance of the adjacent teeth.36 Translucency can be evaluated by both visual observation and digital devices, which use colour-matching procedures. However, this second approach is an objective method and more precise than visual assessment, making it the preferred method for research purposes.18,21,37 There are currently several electronic shade-matching instruments available for clinical use. These devices can be classified as spectrophotometers, colorimeters, digital colour analyzers, or combinations of these.38 The Shadepilot is one of the measuring devices for this purpose. It works through a digital camera linked to an LED spectrophotometer. The device can provide impressive translucency data calculated from the reflected light spectrum. The first null hypothesis, that the effect of fibre addition of silorane-based resin composite and dimethacrylate based resin composite would affect TP values, was rejected. The addition of Ribbond THM and EverStick Net fibre caused no significant differences in TP values for any of the restorative materials ( p > 0.05) (Table 3). A previous study showed demonstrated no significant differences in total colour change between the control and fibre reinforced groups for both anterior and posterior composite resins.36 TP values exhibit correlation with colour parameters. A change in colour parameters can affect TP values.39 The lack of change in TP values in our study supports the findings from that previous study. Our scan of the literature revealed no studies comparing the translucencies of composite resins with fibre reinforcement. The effect of the use of different fibres under restorations on TP values now needs to be examined with more detailed studies. FS translucency behaved differently to that of VP. FS exhibited lower TP values than did VP ( p < 0.05). This difference was expected, based on their different matrix compositions, and may be attributed to the fact that the commercial silorane-based composite resin tested (Filtek Silorane) is marketed for posterior use. These findings are consistent with those of Perez et al.,2 who reported that silorane-based composite resins exhibited lower TP values than dimethacrylate-based composite resins both before and after polymerization. Composite resin materials used in restorations consist of a continuous organic matrix phase such as a bisphenol A glycidyl methacrylate (BisGMA) or
urethane dimethacrylate (UDMA) diluted with triethyleneglycol dimethacrylate (TEGDMA) or hydroxyethylmethacrylate (HEMA) and silorane, reinforced with a dispersed inorganic filler phase such as barium or zinc glasses, quartz, zirconia, silica or hydroxyapatite. Recently, Azzopardi40 and Perez2 showed that the organic matrix and the filler particles can influence the translucency of experimental dental resin composites and suggested that there is a linear correlation between translucency and quantity of organic resin matrix. Lee24 stated that there was an inverse correlation between translucency and filler content; as the amount of filler increased, translucency decreased. In addition, translucency of a restorative material depends on absorption and scattering.19,41,42 In dental resin composites, absorption is produced by the organic matrix (monomer matrix reactivity), while scattering is due to refractive index mismatch between the organic matrix and the filler particles. Therefore, the greater opacity and the differences in translucency between the siloranebased and dimethacrylate-based dental resin composites may originate from higher absorption of the cationic ring opening monomers in the silorane organic matrix, and also from the refractive index mismatch between the silorane organic matrix and the filler particles, which can result in more pronounced scattering.2,24,41 Many studies have shown that long-term water storage or accelerated ageing lead to colour and translucency changes in composite resins.13,14,23,30,36 The second null hypothesis was that differences in water storage would lead to changes in TP values for differently based composite resins. This hypothesis was partially corroborated. TP values measured at 24 h, 168 h and 504 h were similar for VP ( p > 0.05). However TP values of FS rose by the end of 504 h ( p < 0.05) (Table 4). These findings were similar to those of a previous study which found that silorane-based composites (P90) became more translucent than methacrylate-based composites over time in water.23 Changes in translucency during water ageing might be attributed to the composition of the different composite materials. Composite resins allow water to penetrate the matrix or filler-matrix interface due to the presence of hydrophilic monomers.43 Long-term in vitro research is required for further investigations regarding changes in TP values after storage in water. Ideal aesthetic restorative materials should have similar properties of light reflection, scattering, fluorescence, opalescence and translucency as those of natural teeth. In order to achieve a successful colour match between silorane and dimethacrylate-based composite resins and the tooth, care needs to be taken over the translucency properties of composite resins. Further studies are now needed to establish full understanding of translucency in silorane-based and dimethacrylate-based composite resins.
journal of dentistry 42 (2014) 746–752
5.
Conclusion
The results of this study suggest that translucency may not be affected by the inclusion of fibre in composite resins. Siloranebased composite resins exhibits different translucency values compared to dimethacrylate based composite resins. This means that the dental clinicians can be recommended for use in depth layers and as a posterior restorative system. VP was more stable than FS when stored in water.
Conflict of interest None declared.
Acknowledgement The author would like to thank Prof. Dr. Omer Cevdet Bilgin (University of Atatu¨rk) for his advice on the statistical analysis.
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Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.intl.elsevierhealth.com/journals/jden
Effect of water storage on the translucency of silorane-based and dimethacrylate-based composite resins with fibres Nurcan Ozakar Ilday *, Neslihan Celik, Yusuf Ziya Bayindir, Nilgu¨n Seven Department of Restorative Dentistry, Atatu¨rk University, Erzurum, Turkey
article info
abstract
Article history:
Objectives: The purposes of this study were (1) to determine the translucency of silorane and
Received 4 March 2013
dimethacrylate-based composite resins and (2) to evaluate the effect of water storage and
Received in revised form
reinforcement with fibre on the translucency of composite resins.
10 January 2014
Methods: Two light-cured composite resins (A2 shade), Filtek Silorane (silorane-based
Accepted 5 February 2014
composite) and Valux Plus (dimethacrylate-based composite), were used in this study. The first group was used as the control with no reinforcements, the second was reinforced with polyethylene (Ribbond THM) and the third was reinforced with a glass fibre (Everstick
Keywords:
Net) for each composite resin. Colour measurements were measured against white and
Translucency
black backgrounds with a Shadepilot (Degu Dent Gmbh, Hanau, Germany) spectrophotom-
Fibre
eter and recorded under a D65 light source, which reflects daylight. CIELAB parameters of
Composite
each specimen were recorded at baseline and at 24 h, 168 h and 504 h. Translucency of
Water storage
materials was calculated using the translucency parameter (TP) formula. Data were ana-
Silorane
lyzed using repeated measures ANOVA and LSD post hoc tests (a = 0.05). Results: The highest baseline TP value was in the Valux Plus/non-fibre reinforced group (14.06 1) and the lowest in the Filtek Silorane/Ribond THM group (8.98 1.11). Repeated measures ANOVA revealed significant effects from the factors storage time, composite resin, composite resin storage time and fibre time (p = 0.047; p = 0.001; p = 0.013; p = 0.022, respectively). Conclusion: Within the limitations of the study, we concluded that inclusion of polyethylene and glass fibres did not alter the translucency of the different-based composite resins. The longest storage time resulted in the greatest change in translucency values of Filtek Silorane composite resins. Clinical significance: Considering the translucencies of composites with different formulations in the selection of composite resins for aesthetic restorations is important in terms of obtaining optimal aesthetic outcomes. # 2014 Elsevier Ltd. All rights reserved.
* Corresponding author. Tel.: +90 442 2313882; fax: +90 442 2360945. E-mail addresses: [email protected], [email protected] (N. Ozakar Ilday). http://dx.doi.org/10.1016/j.jdent.2014.02.002 0300-5712/# 2014 Elsevier Ltd. All rights reserved.
journal of dentistry 42 (2014) 746–752
1.
Introduction
Tooth-coloured dental resin composites have undergone continuous development during recent decades. The development of modern composite resins has led to remarkable improvements in terms of optical properties, biocompatibility, physical strength, wear resistance and stability in the oral environment.1,2 However two major properties of composite resins that still have to be improved are polymerization shrinkage and stress associated with the chain growth nature of the methacrylate-based free radical polymerization process.3 Polymerization shrinkage causes contraction stresses in the composite resin restoration and internal stress and deformation in the surrounding tooth structure.4,5 Several strategies have been used to reduce stress, including changes in monomer structure or chemistry, changes in filler amount6,7 layering techniques or applying a low elastic modulus liners between the tooth structure and8,9 the incremental placement of composites in order to minimize the internal stress and deformation of the tooth structure.10 In addition to these approaches, controlled polymerization techniques (soft-start polymerization)11 and different placement techniques12 have been recommended in order to reduce stress. A new category of restorative material, siloranes, has been recently introduced in order to overcome the problems related to polymerization shrinkage.3,13,14 This monomer is obtained from the reaction of oxirane and siloxane molecules. The volumetric shrinkage of a silorane-based composite was determined as 0.99 vol.% using the Archimedes method.3 The stress reducing mechanism in this new cationic ring opening hybrid monomer system is achieved by the opening and extension of the oxirane rings during polymerization to compensate volume reduction by monomer packing.3,15 The silorane-based resin composites have low polymerization shrinkage and stress,3 good stability in aqueous environments and insolubility in biological fluid stimulants13,14 compared with conventional dimethacrylate based composites. For aesthetic restorations, perfect colour match between the natural teeth and restoration is a very important requirement. Modern composite resins have different hues and opacities that excellently imitate the chromaticity and translucency of enamel, as well as dentine.16 Translucency is the ability of a layer of coloured substance to allow the appearance of an underlying background to show through.17 The translucency parameter of a material refers to the difference in colour between a uniform thickness of the material over a white background and the same thickness of the material over a black background18 and provides a value corresponding to the common visual perception of translucency.18–20 When the colour of a restoration is combined with proper translucency, the restoration can closely match the surrounding tooth structure.2,21 If the composite resins are too translucent, the colour of the abutment tooth may have a considerable effect on the colour of the final restoration.22 The greater the translucency value, the higher the actual translucency of a material.2,21,23 The translucency of dental resin composites depends on their thickness as well as the scattering and absorption coefficients of the resin, filler
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particles, colour pigments and opacifiers.24,25 Since the formulation influences the optical properties of resin composite, silorane composites may exhibit differences in colour and translucency compared with dimethacrylate composites.2 Fibre reinforced composites were recently introduced for dental restorations and highly favourable mechanical properties, and their strength-to-weight ratios are superior to those of most alloys. Compared to metals, they offer many other advantages as well, including ease of repair, non-corrosiveness, translucency and good bonding properties.26 The optical properties of fibres used in order to obtain an aesthetic appearance compatible with that of normal teeth in fibresupported adhesive bridges in anterior teeth are very important. Restorative dental materials absorb water slowly, primarily because of the polar properties of the resin molecules. Water molecules act as plasticizers and facilitate the flow of longchain polymers that can infiltrate and reduce the mechanical properties of the polymer matrix, leading to degradation of the matrix/fibre or matrix/filler interfaces, by swelling and reducing the frictional forces between the polymer chains, a process known as ‘plasticization’.27–29 Although there have been several studies on silorane-based dental resin composites1,2,23,25,30 and fibre reinforced composites,22,31–34 the effects of fibres on the translucency of silorane- and dimethacrylate-based composites under water storage have been little studied. The null hypotheses tested were that (1) the effect of fibre addition of silorane-based resin composite and dimethacrylate-based resin composite would affect the translucency values, and (2) different lengths of water storage would create differences in the translucency of different based composite resins. The aim of this study was therefore to evaluate the effect of polyethylene and glass fibres on the translucency of differently based composite resins at different storage times in water.
2.
Materials and methods
The formations and manufacturers of the materials used are listed in Table 1. Two A2 shade light-cured resin composites, Filtek Silorane (a silorane-based composite) and Valux Plus (a dimethacrylate-based composite), were used. Types of fibres, polyethylene fibres versus glass fibres, were also investigated. Ribbond THM (Ribbond Inc., Seattle, USA) fibres 0.18 mm thick are bondable reinforced fibres consisting of ultra-high strength polyethylene fibres. Ribbond fibres are not impregnated with resin, and must be saturated with an adhesive bonding agent before use. EverStick Net (Stick Tech Ltd., Turku, Finland) fibres are glass fibres impregnated with lightcuring Bis-GMA and PMMA. Thickness of the woven preimpregnated EverStick Net reinforcement fibres was 0.06 mm. The first group was used as a control group with no reinforcements, the second group was reinforced with polyethylene (Ribbond THM) and the third group was reinforced with a glass fibre (EverStick Net) for each composite material. Fibres were cut using special scissors that the manufacturers provide with their products to a width of 2 mm and a length of 6 mm, and were used according to the
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Table 1 – Materials used in the study. Product
Type
Formulations
3M/ESPE, Seefeld, Germany
Silorane based composite
Valux Plus*
3M Dental St. Paul, MN, USA.
Dimethacrylate-based composite (hybrid)
Ribbond THM*
Ribbond, Inc. Seattle, Washington, USA.
Polyethylene fibre
Everstick Net*
Stick Tech, Turku, Finland
Glass fibre
3,4-Epoxycyclohexylethycyclo polymethylsiloxane, Bis 3,4-epoxycyclohexylethylphenylmethysilane, Quartz, yttrium fluoride (76 wt%) BIS-GMA TEGDMA, Zirconia, silica (85 wt%) Plasma treated woven UHMWP, polyethylene fibre (non-impregnated) E-glass (electric glass, silanated); Bis-GMA and PMMA
Filtek Silorane
Manufacturer *
Lot
Code
N279893
FS
N252230
VP
9551
R
2060606-EN-089
E
Bis-GMA, bisphenol-A diglycidylether methacrylate; TEGDMA, triethyelene glycol dimethacrylate; UHMWP, ultra-high-molecular-weight polyethylene; PMMA, polymethylmethacrylate. * Formulations as given by manufacturers.
manufacturers’ instructions and placed in the centre of composite disc specimens under sufficient pressure and light-cured for 20 s. Resin composite disks (8 mm in diameter, 2 mm high and 2.0 mm thick) were prepared using layering filling techniques and covered with celluloid strips on glass plates. All specimens were fabricated by pressing the materials between two glass plates under pressure to obtain the desired thickness and smoothness (Fig. 1). Eight specimens were prepared for each group. After curing with a light-curing unit (with 8 mm tip) LEDs (Elipar S10, 3M ESPE, St. Paul, USA) for 40 s each from the top and bottom, the strips and glass plates were removed. Light intensity of the light-curing unit was delivered at 800 mW/cm2 and was monitored using a power metre (Hilux Curing Light Metre, Benlioglu Dental Inc., Ankara, Turkey). All specimens were stored at 37 8C in 100% relative humidity for 24 h before measurement and stored in dark boxes in distilled water until colour measurement. Colour was measured in dry conditions based on the CIELAB colour scale relative to the standard illuminant D65 over a white tile (CIE L* = 82.3, a* = 0.1 and b* = 0.6) and a black tile (CIE L* = 3.4, a* = 0.2 and b* = 1.2) using a spectrophotometer (ShadePilot, Degudent; Hanau, Germany, Software V. 2.41) and recorded using 28 observer configuration. The same examiner performed the colour measurements for all specimens.
Fig. 1 – Schematic illustration of specimen preparation.
Colour was measured using the CIELAB35 colour notation system: L* (lightness, ranging from 0 to 100 with higher numbers being brighter), a* (green–red coordinate), b* (blue– yellow coordinate). CIELAB parameters (L*, a* and b*) of each specimen were recorded at baseline and at 24 h, 168 h and 504 h. The sequence was repeated three times for each specimen, and the median of those three readings was used for analysis. Translucency of materials was calculated using the translucency parameter (TP) formula.18 TP = [(LW* LB*)2 + (aW* aB*)2 + (bW* bB*)2]1/2, where the subscript ‘‘W’’ refers to CIELAB values for each specimen on the white backing, and the subscript ‘‘B’’ refers to the values for specimens on the black backing. Data were entered using Microsoft Office Excel 2007 for Windows (Microsoft Corporation, Redmond, USA). All statistical analyses were performed using a standard statistical software package (SPSS 16.00, Chicago, USA). Comparisons of the mean TP values were performed using repeated measures ANOVA. Statistical significance was set at a = 0.05.
3.
Results
Means and standard deviations of TP values for the groups stored in distilled water are presented in Table 2. The highest baseline TP value was in the VP non-fibre reinforced group (14.06 1.17) and the lowest in the FS-R group (8.98 1.11). Specimens from FS composite resin were generally more opaque than those from VP composite resin. Repeated measures ANOVA analysis revealed that TP values were significantly affected by storage time ( p = 0.047) and composite ( p = 0.001), but not significantly affected by fibres ( p = 0.097). There were significant interactions between storage time composite resin and storage time fibre, but no significant interaction between composite resin fibre and storage time fibre composite resin ( p = 0.013; p = 0.022; p = 0.652; p = 0.815, respectively) (Table 3). FS translucency behaved differently to that of VP. ( p < 0.05) FS composite resin exhibited lower TP values than did VP (Table 4 and Fig. 3).
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Table 2 – Means W standard deviations of translucency parameter (TP) values for the groups stored in distilled water (n = 8). Fibre
Time Baseline
24 h
168 h
504 h
FS
Non fibre reinforced R E
9.97 0.44 8.98 1.11 9.90 0.48
10.01 0.51 10.06 0.78 9.83 0.52
10.17 0.35 9.72 1.51 9.72 0.63
10.37 0.66 10.83 1.37 10.79 0.77
VP
Non fibre reinforced R E
14.06 1.17 12.70 1.07 13.46 0.77
13.54 0.85 13.66 0.69 13.10 0.43
13.41 1.49 13.46 0.42 13.04 0.33
13.40 1.08 13.04 0.53 13.491 0.73
Table 3 – The results of repeated measures ANOVA. DF
Effect
Mean square
F
p
Test of within subjects effect Storage time Storage time composite resin Storage time fibre Storage time fibre composite resin
3 3 6 6
2.080 2.840 1.971 0.374
2.722 3.717 2.580 0.490
0.047 0.013 0.022 0.815
Tests of between-subjects effects Composite Fibre Composite resin fibre
1 2 2
533.630 1.592 0.278
827.793 2.470 0.432
0.001 0.097 0.652
Table 4 – Changes in means W standard deviations TP values of composite resins depending on the time (with Bonferroni correction). Composite resin FS VP
Baseline
24 h a
9.62 0.18 13.41 0.18 a
168 h a
504 h a
9.97 0.13 13.43 0.13 a
9.87 0.19 13.30 0.19 a
10.66 0.18 b 13.31 0.18 a
Means followed by different lowercase letters in the rows differ statistically at the 5% level.
A statistically significant time-dependent change in translucency values was observed in the groups with added R fibre ( p < 0.05), while no change was observed in the control groups and the groups with added E fibre. (Table 5 and Fig. 2). TP values of FS rose by the end of 504 h ( p < 0.05).
Fig. 2 – TP values in fibre groups at each time interval.
4.
Discussion
This study analyzed the effect of polyethylene and glass fibres on the translucency of both of silorane- and dimethacrylatebased composite resins at different storage times in water. Dimethacrylate-based adhesively bonded dental composites and silorane-based dental composites are frequently
Fig. 3 – TP values in composite resins at each time interval.
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Table 5 – Changes in means W standard deviations TP values of fibres depending on the time (with Bonferroni correction). Fibre Non fibre reinforced R E
Baseline
24 h a
12.02 0.22 10.84 0.22 a 11.68 0.22 a
168 h a
11.77 0.16 11.86 0.16 ab 11.46 0.16 a
504 h a
11.79 023 11.59 0.23 ab 11.38 0.23 a
11.89 0.22 a 11.93 0.22 b 12.14 0.22 a
Means followed by different lowercase letters in the rows differ statistically at the 5% level.
used in dental practice to meet patients’ requirements for aesthetic and tooth-coloured restorations. However, despite their popularity, these materials are far from ideal in terms of meeting mechanical requirements. For this purpose, short fibres and networked fibres have been used to reinforce resin composites, resulting in modest increases in composite strength.26,32 The optical properties of composite resins play an important role in matching the shade of an aesthetic restoration to the natural appearance of the adjacent teeth.36 Translucency can be evaluated by both visual observation and digital devices, which use colour-matching procedures. However, this second approach is an objective method and more precise than visual assessment, making it the preferred method for research purposes.18,21,37 There are currently several electronic shade-matching instruments available for clinical use. These devices can be classified as spectrophotometers, colorimeters, digital colour analyzers, or combinations of these.38 The Shadepilot is one of the measuring devices for this purpose. It works through a digital camera linked to an LED spectrophotometer. The device can provide impressive translucency data calculated from the reflected light spectrum. The first null hypothesis, that the effect of fibre addition of silorane-based resin composite and dimethacrylate based resin composite would affect TP values, was rejected. The addition of Ribbond THM and EverStick Net fibre caused no significant differences in TP values for any of the restorative materials ( p > 0.05) (Table 3). A previous study showed demonstrated no significant differences in total colour change between the control and fibre reinforced groups for both anterior and posterior composite resins.36 TP values exhibit correlation with colour parameters. A change in colour parameters can affect TP values.39 The lack of change in TP values in our study supports the findings from that previous study. Our scan of the literature revealed no studies comparing the translucencies of composite resins with fibre reinforcement. The effect of the use of different fibres under restorations on TP values now needs to be examined with more detailed studies. FS translucency behaved differently to that of VP. FS exhibited lower TP values than did VP ( p < 0.05). This difference was expected, based on their different matrix compositions, and may be attributed to the fact that the commercial silorane-based composite resin tested (Filtek Silorane) is marketed for posterior use. These findings are consistent with those of Perez et al.,2 who reported that silorane-based composite resins exhibited lower TP values than dimethacrylate-based composite resins both before and after polymerization. Composite resin materials used in restorations consist of a continuous organic matrix phase such as a bisphenol A glycidyl methacrylate (BisGMA) or
urethane dimethacrylate (UDMA) diluted with triethyleneglycol dimethacrylate (TEGDMA) or hydroxyethylmethacrylate (HEMA) and silorane, reinforced with a dispersed inorganic filler phase such as barium or zinc glasses, quartz, zirconia, silica or hydroxyapatite. Recently, Azzopardi40 and Perez2 showed that the organic matrix and the filler particles can influence the translucency of experimental dental resin composites and suggested that there is a linear correlation between translucency and quantity of organic resin matrix. Lee24 stated that there was an inverse correlation between translucency and filler content; as the amount of filler increased, translucency decreased. In addition, translucency of a restorative material depends on absorption and scattering.19,41,42 In dental resin composites, absorption is produced by the organic matrix (monomer matrix reactivity), while scattering is due to refractive index mismatch between the organic matrix and the filler particles. Therefore, the greater opacity and the differences in translucency between the siloranebased and dimethacrylate-based dental resin composites may originate from higher absorption of the cationic ring opening monomers in the silorane organic matrix, and also from the refractive index mismatch between the silorane organic matrix and the filler particles, which can result in more pronounced scattering.2,24,41 Many studies have shown that long-term water storage or accelerated ageing lead to colour and translucency changes in composite resins.13,14,23,30,36 The second null hypothesis was that differences in water storage would lead to changes in TP values for differently based composite resins. This hypothesis was partially corroborated. TP values measured at 24 h, 168 h and 504 h were similar for VP ( p > 0.05). However TP values of FS rose by the end of 504 h ( p < 0.05) (Table 4). These findings were similar to those of a previous study which found that silorane-based composites (P90) became more translucent than methacrylate-based composites over time in water.23 Changes in translucency during water ageing might be attributed to the composition of the different composite materials. Composite resins allow water to penetrate the matrix or filler-matrix interface due to the presence of hydrophilic monomers.43 Long-term in vitro research is required for further investigations regarding changes in TP values after storage in water. Ideal aesthetic restorative materials should have similar properties of light reflection, scattering, fluorescence, opalescence and translucency as those of natural teeth. In order to achieve a successful colour match between silorane and dimethacrylate-based composite resins and the tooth, care needs to be taken over the translucency properties of composite resins. Further studies are now needed to establish full understanding of translucency in silorane-based and dimethacrylate-based composite resins.
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5.
Conclusion
The results of this study suggest that translucency may not be affected by the inclusion of fibre in composite resins. Siloranebased composite resins exhibits different translucency values compared to dimethacrylate based composite resins. This means that the dental clinicians can be recommended for use in depth layers and as a posterior restorative system. VP was more stable than FS when stored in water.
Conflict of interest None declared.
Acknowledgement The author would like to thank Prof. Dr. Omer Cevdet Bilgin (University of Atatu¨rk) for his advice on the statistical analysis.
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