The Journal of Adhesive Dentistry, 05/2010

This articles concerns itself with the testing of adhesion between direct restoratives and dental hard tissue, ie, enamel and dentin. The aim is to survey available methods for adhesion testing and influential parameters affecting experimental outcome. The testing of adhesion to indirect restorative materials, eg, ceramics and metals, is beyond the scope of this article and shall be discussed elsewhere. The longevity and success of modern dental restorations very often relies on potent dental adhesives to provide durable bonds between the dental hard substance and the restorative composite. To predict the clinical outcome of such restorative treatment, a large variety of in vitro laboratory tests and clinical in vivo experiments have been devised, analyzed, and published. The purpose of this review is to provide a current overview of bond strength testing methods and their applicability to the characterization of dental adhesives. Regardless of the method employed, subtle variations in sample preparation may already severely impact test results, usually necessitating at least co-testing of a well-known internal reference to allow conclusive interpretation. This article attempts to list and discuss the most influential parameters, such as substrate nature, age, health status, storage, clinically relevant pre-treatment, and sample preparation. Special attention is devoted to the last aspect, as numerous publications have stressed the tremendous influence of preparatory parameters on the validity and scope of obtained data. Added to the large variety of such factors, an equally large diversity of load-applying procedures exists to actually quantify adhesion between composites and dental hard substance. This article summarizes the basics of macro and micro approaches to shear and tensile bond strength testing, as well as push- and pull-out tests. The strengths and weaknesses inherent to each method and influential test parameters are reviewed and methods for accelerated sample aging and simulation of clinical conditions presented. Alternatively to shear or tensile bond strength tests, fracture toughness is introduced together with its application to dental adhesives and an overview of its physical background. Keywords: dentin, enamel, adhesion, in vitro test, shear bond strength, tensile bond strength, marginal adaptation, fracture toughness

Purpose: To determine whether the adverse interaction between a two-step/acidic etch-and-rinse adhesive (One-Step Plus [OS], Bisco) and chemically cured resin luting cement [Variolink II, Ivoclar Vivadent] can improve adhesive coupling by reducing the dentin permeability with an oxalate desensitizer (BisBlock, Bisco). Materials and Methods: After exposing dentin on the occlusal surfaces of human third molars, bonding was performed on either oxalate treated (BB) or nontreated (NB) demineralized dentin. A resin luting cement was placed in the format of a crown following the light-curing mode (only with the base syringe [LC]) or the chemically curing mode (mixture of base and catalyst syringes [CC]). The activation of the LC or CC cements was either immediately [IM], meaning soon after the placement of LC and the initial set of CC cement (5 min), or after a delay of 20 min [DP] for both modes of polymerization. Five teeth were assigned to each experimental condition. Teeth were sectioned to obtain sticks with a cross-sectional area of 0.95 mm2, which were tested using the microtensile bond strength test soon after the specified periods of polymerization. The bond strength values of each adhesive were analyzed by three-way repeated measures ANOVA and Tukey's tests (α = 0.05). Fractographic analysis of the specimens was performed using SEM. Results: The delayed polymerization (for both LC and CC cements) produced low bond strength values compared to IM activation. When the BB was employed, the bond strength values of the CC cement was approximately doubled, while the BB did not affect the bond strength of the LC cement. Bond strength values of LC cements were higher than CC. The use of BB significantly improved the bond strength of CC cement only. The morphological observations confirmed the bond strength results. A myriad of voids could be detected in the luting cement side when BB was not applied, except for the immediately light-cured group. Conclusion: The use of an oxalate desensitizer (BisBlock) reduced the incompatibility between a two-step etch-andrinse adhesive and chemically cured resin cements and light-cured systems in the delayed polymerization mode. Keywords: etch-and-rinse adhesive, chemically cured, delayed polymerization, resin luting cement, oxalate desensitizer, microtensile bond strength

Purpose: To test whether or not dentin desensitizing or sealing methods influence the bond strength of universal resin cements. Materials and Methods: The bond strength of two universal resin cements (RelyXUnicem, Self-adhesive Prototype Cement) to human dentin was assessed after different dentin surface treatments (test). A conventional resin cement (Panavia 21) served as control. The influence of the following pretreatment methods was tested and compared to freshly ground dentin: dentin desensitizing by means of glutaraldehyde-containing primers (Gluma Desensitizer, Syntac Primer/Adhesive), or dentin sealing by means of bonding agents (Heliobond, ClearfilSE Bond). Additionally, the influence of provisional cement (Freegenol) was analyzed after its application and subsequent mechanical removal. Bond strength after thermocycling was measured in a shear test (n = 10). Data were analyzed with one-way ANOVA, followed by a post-hoc Tukey test (p 0.05). Results: Both test cements exhibited significantly lower bond strength to freshly ground dentin than the control cement. The desensitization methods did not affect the bond strength of the test cements. Furthermore, the sealing methods significantly increased the bond strength of both test cements as compared to freshly ground dentin. The application and subsequent removal of the provisional cement only had a minor influence on the bond strength of the test cements. The contamination with provisional cement, however, significantly affected the bond strength of the control cement compared to the values achieved on freshly ground dentin. Conclusion: Desensitization or sealing of dentin have a beneficial effect on the bond strength of universal resin cements. The application of a provisional cement prior to adhesive cementation exhibits no significant influence on the bond strength of the universal resin cements. Keywords: resin cements, universal resin cements, shear bond strength, desensitization, dentin sealing

Purpose: The aim of this study was to evaluate dentin sealing ability and microshear bond strength of two different resin cements. Materials and Methods: Resin composite overlays (Estenia C&B) were fabricated and cemented to mid-dentin surfaces with either a self-adhesive resin cement (RelyX Unicem) or a resin cement with a self-etching primer (Panavia F2.0). After 24 h storage in water, the specimens were sectioned, placed into 50% (w/v) ammoniacal silver nitrate solution for 24 h, exposed to photodeveloping solution and observed using FE-SEM and EDS. Percentage distribution of metallic silver particles in the resin cement/dentin interface was calculated using digital image analysis software. In addition, small resin overlay cylinders were also bonded to dentin using either of the resin cements, and their bonding performance was evaluated with the microshear bond strength test. The statistical significance was defined as p = 0.05. Results: No statistically significant difference was detected in the microshear bond strength between RelyX Unicem and Panavia F2.0 (24.9 ± 4.8 and 26.1 ± 5.3 MPa, respectively, p > 0.05). However, a significant difference was detected in silver particle penetration percentage between RelyX Unicem and Panavia F2.0 (7.4 ± 4.6 and 18.7 ± 8.7 MPa, respectively). The Kruskal-Wallis mean ranks for nanoleakage were 6.8 and 14.2, respectively (p 0.05). Conclusion: While the bond strengths of the two materials were comparable, the self-adhesive resin cement may provide better dentin sealing compared to the self-etching primer resin cement. Keywords: nanoleakage, microshear bond strength, resin cement, self-adhesive, self-etching primer

Purpose: To assess under load the biomechanical behavior of the cementing system of feldspathic vs alumina porcelain veneers. Materials and Methods: A 3D model of a maxillary central incisor, the periodontal ligament (PDL) and the alveolar bone was generated. Incisors restored with alumina and feldspathic porcelain veneers were compared to a natural sound tooth. Enamel, cementum, cancellous and cortical bone were considered isotropic elastic materials; conversely, dentin was designated as orthotropic. The nonlinear visco-elatic behavior of the PDL was considered. The adhesive layers were modelled using spring elements. A 50-N load at a 60-degree angle to the tooth's longitudinal axis was applied and validated. Stress concentration in the interfacial volumes of the main models was identified and submodelled in a new environment. Results: Regarding tooth structure, strain concentrations were observed in the root dentin below the CEJ. As to the cement layer, tensile stresses concentrated in the palatal margin of the adhesive complex. Conclusion: Despite the effects on tooth deformation, the rigidity of the veneer did not affect the stress distributions in the cement layer or in the adhesive layers. In both cases, the palatal and cervical margins seemed to be the most stressed areas. Keywords: finite element analysis, veneer, feldspathic ceramic, alumina, prosthodontics