Factors Involved in the Development of Polymerization Shrinkage Stress in Resin-Composites: A Systematic Review

Department of Dental Materials, School of Dentistry, University of São Paulo, Av. Prof. Lineu Prestes, 2227, São Paulo, SP 05508-900, Brazil.
Dental Materials (Impact Factor: 3.77). 11/2005; 21(10):962-70. DOI: 10.1016/j.dental.2005.04.018
Source: PubMed


Polymerization shrinkage stress of resin-composite materials may have a negative impact on the clinical performance of bonded restorations. The purpose of this systematic review is to discuss the primary factors involved with polymerization shrinkage stress development.
According to the current literature, polymerization stress of resin composites is determined by their volumetric shrinkage, viscoelastic behavior and by restrictions imposed to polymerization shrinkage. Therefore, the material's composition, its degree of conversion and reaction kinetics become aspects of interest, together with the confinement and compliance of the cavity preparation.
Information provided in this review was based on original scientific research published in Dental, Chemistry and Biomaterials journals. Textbooks on Chemistry and Dental Materials were also referenced for basic concepts.
Shrinkage stress development must be considered a multi-factorial phenomenon. Therefore, accessing the specific contribution of volumetric shrinkage, viscoelastic behavior, reaction kinetics and local conditions on stress magnitude seems impractical. Some of the restorative techniques aiming at stress reduction have limited applicability, because their efficiency varies depending upon the materials employed. Due to an intense research activity over the years, the understanding of this matter has increased remarkably, leading to the development of new restorative techniques and materials that may help minimize this problem.

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    • "The first part of the null hypothesis, that composite pre-heating would not affect shrinkage force formation, was rejected: increasing composite temperature prior to photoactivation significantly reduced polymerization-induced shrinkage forces of both the bulk-fill and conventional resin composites under investigation . Shrinkage forces are generated when polymerization contraction is obstructed and the developing polymer network loses its ability to re-arrange, due to mobility restrictions, and thereby to macroscopically and microscopically accommodate the reduction in volume by plastic deformation [14] [15]. Raising the temperature of resin composites reduces system viscosity and improves molecular mobility as a result of higher thermal energy, facilitating polymer chain segmental movement and postponing the onset of vitrification to a later stage of the polymerization process [33] [34]. "
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    ABSTRACT: To investigate the influence of pre-heating of high-viscosity bulk-fill composite materials on their degree of conversion and shrinkage force formation. Four bulk-fill composite materials (Tetric EvoCeram Bulk Fill-TECBF, x-tra fil-XF, QuixFil-QF, SonicFill-SF) and one conventional nano-hybrid resin composite (Tetric EvoCeram-TEC) were used. The test materials were either kept at room temperature or pre-heated to 68 °C by means of a commercial heating device, before being photoactivated with a LED curing unit for 20 s at 1170 mW/cm(2). Shrinkage forces (n = 5) of 1.5-mm-thick specimens were recorded in real-time for 15 min inside a temperature-controlled chamber at 25 °C (simulating intraoral temperature after rubber dam application) with a custom-made stress analyzer. Degree of conversion (n = 5) was determined at the bottom of equally thick (1.5 mm) specimens using Fourier transform infrared spectroscopy. Data were analyzed with Student's t-test, ANOVA and Tukey's HSD post-hoc test (α = 0.05). Composite pre-heating significantly increased the degree of conversion of TECBF, but had no effect on monomer conversion of the other materials investigated. For each of the test materials, pre-heated composite generated significantly lower shrinkage forces than room-temperature composite. At both temperature levels, TECBF created the significantly highest shrinkage forces, and QF caused significantly higher shrinkage forces than both XF and TEC. Both the composite material and the pre-cure temperature affect shrinkage force formation. Pre-heating of bulk-fill and conventional restorative composites prior to photoactivation decreases polymerization-induced shrinkage forces without compromising the degree of conversion. Composite pre-heating significantly reduces shrinkage force formation of high-viscosity bulk-fill and conventional resin composites, while maintaining or increasing the degree of monomer conversion, dependent upon the specific composite material used. Copyright © 2015. Published by Elsevier Ltd.
    Journal of dentistry 07/2015; 43(11). DOI:10.1016/j.jdent.2015.07.014 · 2.75 Impact Factor
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    • "This will result in poor marginal adaptation, postoperative pain, and recurrent caries [30]. It has been claimed for many years that stress generation at tooth/resin composite interfaces and the resulting interfacial deficiencies remain one of the most important reasons for clinical failure [30] [31] [32]. "
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    ABSTRACT: The aim of this randomized controlled study was to evaluate the long term effectiveness of a reduced shrinkage stress resin composite in Class II restorations. The material was compared intra-individually with a microhybrid resin composite. Each of 50 patients with at least one pair of two similar sized Class II cavities participated (22 female, 28 male, mean age 43 years, range 18-64). Each participant received in each pair, in a randomized way, one Class II restoration performed with a reduced shrinkage stress resin composite (InTen-S) and the other restoration with a microhybrid resin composite restoration (Point 4). Both restorations were placed with an etch-and-rinse bonding system and an oblique layering technique. A total of 106 restorations, 33 premolar and 73 molars, were placed. The restorations were evaluated blindly each year using modified USPHS criteria. The overall performance of the experimental restorations was tested after intra-individual comparison using the Friedmańs two-way analysis of variance test. The hypothesis was rejected at the 5% level. At 15 years, 91 restorations were evaluated. The drop out frequency was 15 restorations (5 male, 3 female participants; 2 premolar and 13 molar restorations). Except for 2 participants, who reported slight symptoms during a few weeks after placement, no post-operative sensitivity was observed at the recalls. The overall success rate at 15 years was 77%. Twenty-one non acceptable restorations were observed during the 15 years follow up, 10 InTen-S (21.7%) and 11 Point 4 (24.4%) restorations (p>0.05). Annual failure rates for the resin composites were 1.5% and 1.6%, respectively. The main reasons for failure were secondary caries (8) and resin composite fracture (7). The differences between premolar vs. molar restorations and between restorations in male vs. female participants were not significant. Significant differences were observed between 2-surface vs. 3-surface restorations. During the 15-year follow up, the reduced shrinkage stress resin composite showed a good clinical durability in Class II cavities, but not significantly better than the control microhybrid resin composite. Secondary caries and material fracture were the main reasons of failure. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
    Dental materials: official publication of the Academy of Dental Materials 07/2015; 31(9). DOI:10.1016/j.dental.2015.06.012 · 3.77 Impact Factor
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    • "Flowable RBCs differ from their conventional ( " non-flowable " ) counterparts in that they contain substantially less (as much as 25% by weight) filler than conventional RBC (Labella et al., 1999), and several studies have shown significant differences in the elastic modulus and volumetric shrinkage between materials of these two classes (Braga, Ballester & Ferracane, 2005; Furuse et al., 2008). Although the high volumetric shrinkage that characterizes flowable composite materials may lead to high stress values, it is possible that their low elastic modulus could compensate to some degree for the stress buildup, by helping to maintain the marginal seal and integrity of the restoration (Braga, Ballester & Ferracane, 2005). Although flowable RBCs generally have a lower elastic modulus than their non-flowable counterparts, in some cases the elastic modulus may not be low enough to provide significant stress relief, as has been observed in studies evaluating unfilled resins (Braga, Hilton & Ferracane, 2003). "
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    ABSTRACT: Purpose. This study tested the null hypothesis that different classes of direct restorative dental materials: silorane-based resin, low-shrinkage and conventional (non-flowable and flowable) resin-based composite (RBC) do not differ from each other with regard to polymerization shrinkage, depth of cure or microhardness. Methods. 140 RBC samples were fabricated and tested by one calibrated operator. Polymerization shrinkage was measured using a gas pycnometer both before and immediately after curing with 36 J/cm(2) light energy density. Depth of cure was determined, using a penetrometer and the Knoop microhardness was tested from the top surface to a depth of 5 mm. Results. Considering polymerization shrinkage, the authors found significant differences (p < 0.05) between different materials: non-flowable RBCs showed lower values compared to flowable RBCs, with the silorane-based resin presenting the smallest shrinkage. The low shrinkage flowable composite performed similarly to non-flowable with significant statistical differences compared to the two other flowable RBCs. Regarding to depth of cure, low-shrinkage flowable RBC, were most effective compared to other groups. Microhardness was generally higher for the non-flowable vs. flowable RBCs (p < 0.05). However, the values for low-shrinkage flowable did not differ significantly from those of non-flowable, but were significantly higher than those of the other flowable RBCs. Clinical Significance. RBCs have undergone many modifications as they have evolved and represent the most relevant restorative materials in today's dental practice. This study of low-shrinkage RBCs, conventional RBCs (non-flowable and flowable) and silorane-based composite-by in vitro evaluation of volumetric shrinkage, depth of cure and microhardness-reveals that although filler content is an important determinant of polymerization shrinkage, it is not the only variable that affects properties of materials that were tested in this study.
    PeerJ 06/2015; 3(2):e864. DOI:10.7717/peerj.864 · 2.11 Impact Factor
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