Australian Dental Journal
The official journal of the Australian Dental Association
Australian Dental Journal 2015; 60: 490–496 doi: 10.1111/adj.12265
Reducing composite restoration polymerization shrinkage stress through resin modiﬁed glass-ionomer based adhesives SJ Naoum,* PR Mutzelburg,* TG Shumack,* DJG Thode,* FE Martin,* AE Ellakwa* *Faculty of Dentistry, The University of Sydney, New South Wales.
ABSTRACT Background: The aim of this study was to determine whether employing resin modified glass-ionomer based adhesives can reduce polymerization contraction stress generated at the interface of restorative composite adhesive systems. Methods: Five resin based adhesives (G Bond, Optibond-All-in-One, Optibond-Solo, Optibond-XTR and ScotchbondUniversal) and two resin modified glass-ionomer based adhesives (Riva Bond-LC, Fuji Bond-LC) were analysed. Each adhesive was applied to bond restorative composite Filtek-Z250 to opposing acrylic rods secured within a universal testing machine. Stress developed at the interface of each adhesive-restorative composite system (n = 5) was calculated at 5-minute intervals over 6 hours. Results: The resin based adhesive-restorative composite systems (RBA-RCS) demonstrated similar interface stress profiles over 6 hours; initial rapid contraction stress development (0–300 seconds) followed by continued contraction stress development ≤0.02MPa/s (300 seconds – 6 hours). The interface stress profile of the resin modified glass-ionomer based adhesive-restorative composite systems (RMGIBA-RCS) differed substantially to the RBA-RCS in several ways. Firstly, during 0–300 seconds the rate of contraction stress development at the interface of the RMGIBA-RCS was significantly (p < 0.05) lower than at the interface of the RBA-RCS. Secondly, at 300 seconds and 6 hours the interface contraction stress magnitude of the RMGIBA-RCS was significantly (p < 0.05) lower than the stress of all assessed RBA-RCS. Thirdly, from 300 seconds to 6 hours both the magnitude and rate of interface stress of the RMGIBA-RCS continued to decline over the 6 hours from the 300 seconds peak. Conclusions: The use of resin modified glass-ionomer based adhesives can significantly reduce the magnitude and rate of polymerization contraction stress developed at the interface of adhesive-restorative composite systems. Keywords: Dentine bonding, polymerization shrinkage, resin composite, resin modified glass-ionomer, Riva Bond LC. Abbreviations and acronyms: RBA-RCS = resin based adhesive-restorative composite systems; RMGIBA-RCS = resin modified glassionomer based adhesive-restorative composite systems. (Accepted for publication 26 November 2014.)
INTRODUCTION Cuspal fracture and recurrent caries continue to be identifiable causes of failure of resin composite restorations.1–4 During curing of a direct resin composite restoration, stress develops at the restoration-tooth interface due to polymerization contraction of both the resin composite restorative material and the adhesive agent.5–7 In scenarios when polymerization contraction stress does not disrupt resin-tooth adhesion generated by bonding procedures, enamel microfractures frequently manifest which can later result in cuspal fracture.8–10 Conversely, in circumstances when polymerization contraction stress does disrupt resin-tooth adhesion, marginal gap formation and restoration microleakage occurs which can result in recurrent caries.10,11 These detrimental effects resulting from 490
restorative composite and adhesive polymerization contraction impact tooth and restoration longevity, and have led numerous dental manufacturers to develop new restorative composite materials with lower volumes of polymerization contraction.12,13 Additionally, the detrimental effects of composite polymerization contraction have provided the impetus for researchers to investigate clinical techniques which minimize the development of polymerization contraction stress during cavity restoration.14,15 By contrast, however, there has been little focus into lowering the stress generated at the margins of a resin composite restoration through modification of bonding adhesives.16,17 Traditionally, adhesive systems used for bonding resin composite restorations to tooth structure have employed resin based materials containing a low © 2015 Australian Dental Association
Resin modiﬁed glass-ionomer based adhesives volume of filler particles (10–40 wt%).17,18 A result of using a resin based adhesive containing a low filler volume is the propensity for these adhesives to undergo substantial volumetric contraction during polymerization (4–9%). As a result, utilization of a resin based adhesive for restorative composite adhesion in cavity restoration increases the stress developed at the interface of a restorative composite-adhesive system (rather than acting to ‘offset’ contraction undergone by the restorative material).19 In this context it is therefore notable that the ability of manufacturers to reduce the polymerization contraction of resin based adhesives is limited due to the relationship between resin filler volume and adhesive viscosity. Although increasing adhesive filler content is a mechanism for reducing polymerization contraction of resin based adhesives,20 this results in increased viscosity, potentially reducing adhesive infiltration into etched dentine and enamel.21,22 However, while this limitation presents an issue for manufacturers and practitioners alike, it has also resulted in reinvigorating interest in the development of resin modified glass-ionomer based adhesives for the bonding of resin composite restorations. In contrast to the restorative resin composites, restorative glass-ionomers undergo hygroscopic expansion following initial contraction during setting in the oral cavity.23 Consequently, should a resin modified glass-ionomer based adhesive be used for the bonding of direct restorative composite restorations, the level of stress generated at the tooth-restoration interface has the potential to be reduced in comparison to when traditional resin based adhesives are used.24,25 However, only limited analysis of the behavior of resin modified glass-ionomer based adhesives and the level of stress generated at the margins of restorative composite glassionomer adhesive systems has been undertaken.26 The aim of the present in vitro study was to record and evaluate the polymerization shrinkage stress developed at the interface of seven adhesiverestorative composite systems, using five resin based adhesives and two resin modified glass-ionomer based adhesives, in real-time over 6 hours. The null hypothesis was: the rate and magnitude of stress developed at the interface of the resin modified glass-ionomer based adhesive-restorative composite systems (RMGIBA-RCS) was not different to the rate and magnitude of stress developed at the interface of the resin based adhesive-restorative composite systems (RBA-RCS).
in this study (Table 1). Five resin based dentine adhesives: Scotchbond Universal (3M ESPE, St Paul, MN, USA); G Bond (GC Co., Tokyo, Japan); Optibond All-in-One (Kerr, Orange, CA, USA); Optibond Solo Plus (Kerr, Orange, CA, USA); Optibond XTR (Kerr, Orange, CA, USA); and two resin modified glassionomer based dentine adhesives: Riva Bond LC (SDI, Melbourne, VIC, Australia); Fuji Bond LC (GC Co, Tokyo, Japan) were analysed. The method used to measure interface stress in the present study permitted real-time contraction stress to be quantified. The apparatus used for evaluating the polymerization contraction stress is depicted in Fig. 1. Five restorative composite-adhesive specimens of each adhesive were prepared in the following manner and the stress at the adhesive interface was measured over 6 hours. Acrylic rods of 20 mm length and 5 mm diameter were used as a bonding substrate for the adhesives. The bonding surfaces of each rod were polished using 1500 grit silicon carbide paper, prior to being ‘sandblasted’ using aluminum oxide (50 lm) to simulate an etched tooth surface. Following preparation of the bonding surface, each rod was inserted 4 mm into the opposing ‘chuck style’ torsion grips of a universal testing machine (Instron 5942, Norwood, MA, USA). The lower chuck was mounted on a fixed platform and the upper chuck was connected to a load cell. A plastic annulus shaped reservoir with an outer diameter of 12 mm was slipped over the lower rod to hold distilled water in order to simulate the oral environment during testing. With the acrylic rods secured in the universal testing machine, adhesive was applied to the bonding
MATERIALS AND METHODS Polymerization shrinkage stress assessment The polymerization shrinkage stress profiles of seven adhesive composite-restorative systems were recorded © 2015 Australian Dental Association
Fig. 1 Apparatus used to evaluate the polymerization contraction stress of each specimen. (A) acrylic rod; (B) reservoir surrounding composite; (C) extensometer; and (D) chuck. 491
SJ Naoum et al. Table 1. Details of adhesive agents assessed in the present study Adhesive agents
Number of components
1 Step combined etchant, primer, adhesive
Optibond Solo Plus
2 Step combined primer, adhesive
1 Step combined etchant, primer, adhesive
2 Step combined etchant, primer.
1 Step combined etchant, primer, adhesive
Fuji Bond LC
Riva Bond LC
surfaces of the rods according to the manufacturers’ instructions. All samples were prepared with one layer of adhesive. In addition, a second group of Riva Bond LC specimens were prepared in which two layers of adhesive were applied to each acrylic rod. The first layer was conventionally light-cured immediately following application and the second layer was applied but left uncured. Light irradiation took place at the time of restorative composite curing. For all specimens following adhesive placement, a resin composite (Filtek Z250; Lot: N349802; 3M ESPE, St Paul, MN, USA) was placed immediately on the fixed lower rod. The upper rod was then lowered to a datum point of 1 mm from the lower rod. Extruded composite was trimmed to the diameter of the acrylic rod to create a composite cylinder of volume 19.63 mm3. An extensometer (Instron 2630, Norwood, MA, USA, Instron load Cell 500 N), accurate to 10 nm was placed bridging the two acrylic rods to monitor the distance between the rods during composite and adhesive curing. Following curing, as inter-rod contraction forces were generated during polymerization of the composite and adhesive, feedback was provided to the load cell so that an equal and opposite force was applied to the upper rod in order to maintain the 1 mm distance between the rods. The force needed to maintain the position of the upper rod over the 6 hours of analysis was recorded using the Instron software at 20 intervals per second. The force recorded equalled the sum of polymerization contraction forces exerted by the composite and the adhesive over the 6 hours. Adhesive-restorative composite system polymerization contraction stress was calcu492
Composition Acetone, ethyl alcohol, water methacrylate ester, GDPM, sodium hexafluorosilicate 15% barium glass filler, nano-silica ethyl alcohol (20–25%) dimethacrylate resin sodium hexafluorosilicate Bis-GMA, HEMA water 15% barium glass filler, nano-silica acetone, ethyl alcohol, water GDPM, sodium hexafluorosilicate Acetone, water 4-META, UDMA, TEGDMA Polyacrylic acid, HEMA, UDMA, camphorquinone, fluoroaluminosilicate glass powder Polyacrylic acid, tartaric acid, HEMA, dimethacrylate cross-linker, acidic monomer, fluoroaluminosilicate glass powder
lated according to the following equation: Stress (Pa) ¼
Force ðNÞ Area ðm2 Þ
A period of 80 seconds was allowed to elapse before the system was exposed to light irradiation enabling stabilization of the recording system. A visible light-curing unit (Radii Plus, SDI, Melbourne, VIC, Australia) of wavelength 440–480 nm and intensity 1500 mW/cm2 was used to cure each specimen for 30 seconds from a perpendicular distance of 5 mm. Actual irradiance at 5 mm was measured at >650 mW/cm2, as measured with a MARCâ resin calibrator (Bluelight Analytics Inc., Halifax, Canada). Room temperature distilled water was then added to the annulus shaped reservoir covering each specimen and refilled every hour over the 6-hour analysis. Statistical analysis Statistical analysis of results was undertaken to determine significant differences in the magnitude of cumulative interface contraction stress at various time points and the rate of polymerization contraction stress development of the seven adhesive agents. Findings were assessed using one-way analysis of variance (ANOVA) followed by Tukey testing. The level of significance was set at p = 0.05. RESULTS The real-time polymerization shrinkage stress measured at the interface of each adhesive-restorative © 2015 Australian Dental Association
Resin modiﬁed glass-ionomer based adhesives composite system over 21 600 seconds (6 hours) is depicted in Fig. 2. The five RBA-CS shared a similar polymerization shrinkage stress profile over the 6-hour analysis period. At the completion of the first 220 seconds of analysis (80–300 seconds; 0–80 seconds baseline establishment), each RBA-CS had developed stress at the bonded interface in the range of 2.89 MPa (Optibond XTR) to 3.49 MPa (Scotchbond Universal). This represents 71% (Scotchbond Universal) to 102% (Optibond XTR) of the total interface stress developed after 6 hours of analysis. For all five RBA-CS stress continued to develop from 300 seconds to 21 600 seconds, however at a much lower rate than during the first 220 seconds of analysis. Although the stress levels generated at the interface of each RBA-CS differed at various time points over the analysis, there was no significant (p > 0.05) difference in the magnitude of stress developed by each RBA-CS at each time point. The profile of polymerization contraction stress development of the five RBA-CS differed considerably to the profile of stress development of the two RMGIBA-RCS. The shrinkage stress developed at the Riva Bond LC composite system interface increased from 0 MPa at the beginning of the light irradiation to a peak level 1.64 MPa at 300 seconds. This peak stress created by the Riva Bond LC composite system bonded interface was significantly (p < 0.05) less than the stress developed at the interface of all five RBA-CS, both at 300 seconds and at the completion of analysis (21 600 seconds). At 300 seconds, the stress at the bonded interface of the Fuji Bond LC composite system (1.40 MPa) and
the Riva Bond LC (2 layer) composite system (2.17 MPa) was also significantly (p < 0.05) lower in comparison to the stress developed at the interface of the five RBA-RCS at 300 seconds and 21 600 seconds. The Riva Bond LC composite system exhibited a continual decline in interface stress from 300 seconds to 21 600 seconds. The Fuji Bond LC composite system behaved in a similar manner to the Riva Bond LC composite system. The contraction stress for the interface of the Riva Bond LC composite system and the Fuji Bond LC composite system at 21 600 seconds was 16.2% and 26.3% less respectively, than the contraction stress recorded at the Optibond XTR composite interface at 21 600 seconds; the Optibond XTR composite system exhibiting the lowest interface stress of the RBA-RCS at the end of analysis. The Riva Bond LC (2 layer) composite system exhibited a continual decline in interface stress from 300 seconds to approximately 7200 seconds. From 7200 seconds to the completion of the analysis at 21 600 seconds post-irradiation, the Riva Bond LC (2 layer) composite system was observed to undergo expansion. The peak expansion stress developed at the Riva Bond LC (2 layer) composite system bonded interface occurred at 21 600 seconds (6 hours) and was 22% less than the peak contraction stress at the Riva Bond LC (2 layer) composite system interface that was observed at 300 seconds. This peak expansion stress (0.54 MPa) was lower than the contraction stress present at the Optibond XTR composite interface at 300 seconds (by 16.6%) and at 21 600 seconds (by 16.9%).
5 Optibond Solo
Optibond All-in-One Optibond XTR
G-Bond ScotchBond Universal
Riva Bond LC (2 layer) Riva Bond LC
Fuji Bond LC
0.8 0.1 -0.6
-1.3 -2 80
2700 3600 Time (s)
7200 10800 14400 18000 21600
Fig. 2 Polymerization contraction stress developed at the interface of each adhesive-restorative composite system over the 6 hours (21 600 seconds) of analysis. Note: positive values indicate contraction stress. © 2015 Australian Dental Association
SJ Naoum et al. The rate at which bonded interface polymerization contraction stress was developed by each adhesivecomposite system over the 6-hour period of analysis is illustrated in Fig. 3. When considering the rate of bonded interface stress development of the adhesivecomposite systems, two distinct phases can be identified: 80 seconds to 300 seconds and 300 seconds to 21 600 seconds. The peak rate of interface contraction stress development for all systems occurred at the commencement of light irradiation. From then until 300 seconds, the rate at which the RMGIBA-RCS developed interface stress was significantly (p < 0.05) lower than the rate at which stress developed at the interface of the five RBA-RC. At 300 seconds, the Riva Bond LC composite system developed contraction stress at a rate of 0.00007 MPa/s and the Fuji Bond LC composite system developed interface contraction stress at 0.00023 MPA/s; these rates being lower by at least a factor of 10 in comparison to the rate of stress development at the interface of the RBA-RCS. During the period of 300 seconds to 21 600 seconds, the rate of stress development at the Riva Bond LC composite system interface was negative, indicating expansion, peaking at 0.00038 MPa/s at 900 seconds and declining to less than 0.0001 MPa/s by 1800 seconds. The Fuji Bond LC composite system and Riva Bond LC (2 layer) composite system followed a similar pattern between 300 seconds to 21 600 seconds with regards to rate of change of interface stress; the Fuji Bond LC composite system exhibiting a peak contraction of –0.00019 MPa/s (900 seconds) and the Riva Bond LC (2 layer) composite system demonstrating a peak rate of contraction of 0.0013 MPa/s (600 seconds). No statistical difference (p > 0.05) was observed in the rate at which the five RBA-RCS developed contraction stress over the 6 hours of analysis. 0.016
Optibond Solo Optibond All-in-One
G-Bond ScotchBond Universal
Riva Bond LC (2 layer)
Riva Bond LC Fuji Bond LC
0.00675 0.0049 0.00305 0.0012
-0.0025 Time (s)
Fig. 3 Rate of polymerization contraction stress development at the interface of each adhesive-restorative composite system over the 6 hours (21 600 seconds) of analysis. Note: positive values indicate contraction stress. 494
The null hypothesis was rejected on the basis of these results. DISCUSSION The present study revealed that employing RMGIBARCS for the bonding of direct resin composite restorations has the potential to significantly alter the profile of polymerization contraction stress developed at the bonded interface, when compared to conventional resin based adhesives. The significantly (p < 0.05) lower maximum stress and lower rate of stress development (p < 0.05) at the interface of the RMGIBA-RCS, in comparison to the five RBA-RCS can be attributed both to the differing composition and the differing setting reactions of resin modified glass-ionomers and resin adhesives. Resin modified glass-ionomers are defined as glass-ionomers that are modified by the addition of a resin monomer which set by both an acid-base reaction and through photo-polymerization.26 In addition, there is a third setting reaction included so that any remaining monomer that has not set photochemically will undergo chemical polymerization. In contrast, resin adhesives contain filler particles, organic solvents, reaction initiators, reaction inhibitors and acrylic monomers; these monomers linking together to create a polymer through addition polymerization.27 As a consequence of these different setting reactions, the degree and rate of volumetric change during setting within resin modified glass-ionomer based materials is less than that in resin adhesives; the distance between particles undergoing an acid-base reaction changing to a limited degree in comparison to changes in the distance between monomers linking through addition polymerization.28,29 The significantly lower rate of stress development at the interface of the RMGIBA-RCS has potential clinical implications. Not only can the magnitude of interface stress affect the integrity of a tooth-restoration bond, but high rates of polymerization contraction stress at a restoration interface can also jeopardize the integrity of tooth-restoration adhesion.15,28,29 High rates of stress development at a bonded interface raise the possibility that when the stress development reaches its peak, the accommodating ability of the adhesive-tooth bond can be exceeded.12,29 The ability for resin modified glass-ionomer adhesives in the present study to reduce the rate of interface contraction stress development for an adhesive-restorative composite system, in comparison to when a resin based adhesive is used, suggests that use of resin modified glass-ionomer based adhesives may reduce the risk of this threshold being reached in vivo. Previously, it has been suggested that should an adhesive be placed in two layers so that the restora© 2015 Australian Dental Association
Resin modiﬁed glass-ionomer based adhesives tive material and the adhesive are cured simultaneously (co-cured), bonded interface stress can be reduced.30 In the present study, the second layer of Riva Bond LC was applied to a previously irradiated layer and was cured simultaneously with the composite restorative material. It has been speculated that since the setting reaction of resin modified glass-ionomer based materials occurs at a slower rate than that of restorative composite setting,31 a ‘co-cured’ layer of glass-ionomer based adhesive has the potential to function as a ‘dimensionally malleable layer’ during restorative composite setting,30 with a capacity to ‘offset’ the contraction of the restorative composite in real-time. However, the results of the present study do not unequivocally support this proposal as the peak stress of the 2 layer ‘co-cured’ Riva Bond LC system exceeded that of the 1 layer Riva Bond LC restorative composite system. Further studies are planned to compare the bonded interface stress profiles of adhesive-restorative composite systems when 1 and 2 layer glass-ionomer adhesive application is used to cavities of different dimensions and c-factor. The reduction in bonded interface stress in all three RMGIBA-RCS after 360 seconds is consistent with previous studies examining hygroscopic expansion of resin modified glass-ionomer restorative materials.23 It has been reported that due to hygroscopic expansion, restoration of large cavities using resin modified glassionomers can cause cuspal flexure and cuspal stress;25 the magnitude of developed stress being dependent on the volume of resin modified glass-ionomer within the cavity.24 In the present study, the expansion by Riva Bond LC (1 layer) and Fuji Bond LC (1 layer) was insufficient to generate a net expansion of the adhesive-restorative composite system, contraction stress at the interface was observed at all points over the 6 hours. In contrast, the expansion by Riva Bond LC (2 layer) resulted in a net expansion of the adhesivecomposite system after 7400 seconds, this difference was possibly due to the greater resin modified glassionomer volume in the 2 layer system. While the expansion force for the Riva Bond LC system in the present study was lower than that reported for cavities entirely restored with resin modified glassionomer restorative materials, further investigation is required to investigate what effect resin modified glass-ionomer adhesive expansion has on cuspal integrity. In terms of extrapolating results to the clinical environment, the limitations of the present study should be acknowledged. Firstly, the bonding substrate presents a limitation. While using acrylic surfaces has the benefit of mitigating the effect of dentine variation on adhesive bonding, the use of tooth substrate for the bonded surface and in different cavity designs more readily simulates the clinical scenario. © 2015 Australian Dental Association
It is also important to acknowledge the disadvantage of the polymerization stress measurement method employed in the current study. This method presents very low compliance and, consequently, the stress values tend to be higher than those recorded using compliant systems.32 Further research is needed to evaluate these findings using a system compliance that is clinically relevant. The constant contact of water with the bonded interface via the reservoir is in variance with the clinical setting where an adhesive layer would be exposed to fluid from either the patient’s saliva or from within the dentine tubules. Finally, the thickness of the bonding agents was not measured in the current study. Further research is needed to investigate the outcomes using standardized thicknesses of bonding agents. CONCLUSIONS Within the limitations of the present study it can be concluded that resin modified glass-ionomer based dentine adhesives can significantly reduce both the magnitude and rate of contraction stress development at the interface of adhesive-restorative composite systems, in comparison to when conventional resin based adhesives are employed. This finding suggests that the marginal integrity of composite restorations might be improved in situ by using a resin modified glassionomer based adhesive rather than a resin based adhesive. Therefore, the results of the present study indicate the potential for resin modified glass-ionomer based adhesives to improve the longevity of direct composite restorations and should be considered when cavity dimensions and ‘c-factor’ are unfavourable. Further in vivo and in vitro analysis is warranted to confirm this potential. REFERENCES 1. Manhart J, Chen HY, Hamm G, Hickel R. Review of the clinical survival of direct and indirect restorations in posterior teeth of the permanent dentition. Oper Dent 2004;29:481–508. 2. Turkan LS, Aktener O, Ates M. Clinical evaluation of different posterior resin composite materials: a 7-year report. Quintessence Int 2003;34:418–426. 3. Tantbirojn D, Versluis A, Pintado MR, Delong R, Douglas WH. Tooth deformation patterns in molars after composite restoration. Dent Mater 2004;20:535–542. 4. van Dijken JWV, Pallesen U. Four-year clinical evaluation of Class II nano-hybrid resin composite restorations bonded with a one-step self-etch and two-step etch and rinse adhesive. J Dent 2011;39:16–25. 5. Goncßalves F, Pfeifer CS, Ferracane JL, Braga RR. Contraction stress determinants in dimethacrylate composites. J Dent Res 2008;87:367–371. 6. Goncßalves F, Azevedo CLN, Ferracane JL, Braga RR. BisGMA/ TEGDMA ratio and filler content effects on shrinkage stress. Dent Mater 2011;27:520–526. 495
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Address for correspondence: Dr Ayman Ellakwa Faculty of Dentistry The University of Sydney Westmead Centre for Oral Health Level 1, Faculty Office Westmead Hospital Darcy Road Westmead NSW 2145 Email: [email protected]
© 2015 Australian Dental Association