Polymerization shrinkage stress of composite resins and resin cements – What do we need to know?

Abstract

Polymerization shrinkage stress of resin-based materials have been related to several unwanted clinical consequences, such as enamel crack propagation, cusp deflection, marginal and internal gaps, and decreased bond strength. Despite the absence of strong evidence relating polymerization shrinkage to secondary caries or fracture of posterior teeth, shrinkage stress has been associated with postoperative sensitivity and marginal stain. The latter is often erroneously used as a criterion for replacement of composite restorations. Therefore, an indirect correlation can emerge between shrinkage stress and the longevity of composite restorations or resin-bonded ceramic restorations. The relationship between shrinkage and stress can be best studied in laboratory experiments and a combination of various methodologies. The objective of this review article is to discuss the concept and consequences of polymerization shrinkage and shrinkage stress of composite resins and resin cements. Literature relating to polymerization shrinkage and shrinkage stress generation, research methodologies, and contributing factors are selected and reviewed. Clinical techniques that could reduce shrinkage stress and new developments on low-shrink dental materials are also discussed.

Development and status of resin composite as dental restorative materials

“…Previous studies proved that most of the shrinkage occurs in early hours, and the reported volumetric shrinkage of composites ranged from 2 to 6% at 30 min . The polymerization shrinkage can weaken the bond between the tooth structure and the restoration, which can sometimes lead to gaps at the restoration margins, discoloration, postoperative sensitivity, recurrent caries, fracture of the restorations, and restoration failure …”

“…50 The polymerization shrinkage can weaken the bond between the tooth structure and the restoration, which can sometimes lead to gaps at the restoration margins, discoloration, postoperative sensitivity, recurrent caries, fracture of the restorations, and restoration failure. 51,52 To eliminate or minimize the polymerization shrinkage of composites, many efforts evolving associated with low-shrink monomers, light curing code, fillers, filling techniques in the manipulation of restorative procedures, have been put into developing nonshrinking or ideally improved composite materials. 53 The introduction of various newer monomer systems (such as siloranes) may help overcome the problem of shrinkage stress through a photocationic ringopening reaction.…”

Effect of thiourethane filler surface functionalization on stress, conversion and mechanical properties of restorative dental composites

“…Secondary caries is significantly affected by risk factors associated to the patients [4–6], but the presence of defects at the restoration margins can increase the likelihood of bacterial recolonization and reestablishment of the disease in the region [7–9]. Further, the fact that the composite undergoes polymerization, and consequently shrinkage, confined by the cavity walls leads to the transfer of stresses to the bonded interface, which in turn favor the development of marginal defects [10–12], as well as cracks on the tooth structure [12,13]. Therefore, clinical strategies and material developments have been attempted with the goal of minimizing the deleterious effects associated with polymerization shrinkage of resin-based materials [11,12].…”

“…Further, the fact that the composite undergoes polymerization, and consequently shrinkage, confined by the cavity walls leads to the transfer of stresses to the bonded interface, which in turn favor the development of marginal defects [10–12], as well as cracks on the tooth structure [12,13]. Therefore, clinical strategies and material developments have been attempted with the goal of minimizing the deleterious effects associated with polymerization shrinkage of resin-based materials [11,12]. …”

Microporosity and polymerization contraction as function of depth in dental resin cements by X‐ray computed microtomography

“…Regardless the activation method, an inherent characteristic of resin cements is the polymerization contraction (Soares et al, 2017), a volumetric contraction due to molecular approximation caused by the conversion of van der Waals bonds into covalent bonds during the formation of the polymeric chain (Soares et al, 2017; Versluis & Tantbirojn, 1999). Depending on its magnitude, the polymerization contraction may generate tensions in the tooth–restorative–adhesive interface, leading to cohesive failure of the cement and/or of the dental structure (Braga, Ballester, & Ferracane, 2005; Camps, Déjou, Rémusat, & About, 2000; Davidson & de Gee, 2000; Hashimoto, Ohno, Sano, Kaga, & Oguchi, 2003; Soares et al, 2017; Versluis & Tantbirojn, 1999). The cement has also internal microporosity (Condon & Ferracane, 2002; Malkoç et al, 2015; Milutinović‐Nikolić, Medić, & Vuković, 2007), which may impair its mechanical properties (Fleming & Addison, 2009; Ilie, Kunzelmann, Visvanathan, & Hickel, 2005) and, consequently, the prognosis of the treatment (Fleming & Addison, 2009; Malkoç et al, 2015).…”