Effect of polymerization mode on bond strengths of resin adhesive/cement systems

Effects of curing mode and moisture on nanoindentation mechanical properties and bonding of a self-adhesive resin cement to pulp chamber floor

OBJECTIVE

This study aimed to investigate the effect of dentin surface moisture and curing mode on microtensile bond strength (MTBS) and nanoindentation characteristics of a self-adhesive resin cement.

METHODS

Forty-four extracted human molars were distributed into four groups according to dentin surface moisture (dry or wet) and curing mode of the resin cement (light or chemical). Clearfil SA Cement (Kuraray Noritake Dental, Japan) was used for cementation of composite cores to the pulp chamber dentin. The specimens were sectioned into beams for MTBS test at the pulpal floor. Nanoindentation hardness and creep of the cement layer were measured under 100 mN load with 30s hold segment. Data were statistically analyzed using two-way ANOVA and Weibull distribution of MTBS (α=0.05).

RESULTS

Moisture, curing mode or their interaction did not significantly affect mean MTBS values that ranged 17.6-22.6 MPa (p>0.05); however, the lowest characteristic strength was found in moist chemically cured group. Hardness ranged 437-512 MPa, and was not affected by the experimental factors (p>0.05). Nanoindentation creep ranged 9.3-10.9% with the chemically cured groups showing the highest values, indicating lower cross-linking and deformation resistance of their polymer network.

SIGNIFICANCE

Additional moisture on dentin surface did not contribute to adhesion of the anhydrous self-adhesive resin cement to dentin. Light-curing, despite attenuation through the composite core, was beneficial and improved nanoindentation creep resistance of the cement. The difference was not, however, reflected in the mean bond strength or hardness values.

Physical properties of dual-cured luting-agents correlated to early no interfacial-gap incidence with composite inlay restorations

OBJECTIVES

The aims of this investigation were to investigate dual-cured luting-agents as to whether their bond strength, dimensional change and flexural modulus influence no interfacial-gap incidence parameters of composite inlay restorations during the early stages. The correlations of interest were between: (a) their shear bond strength to dentin, (b) their dimensional change on setting, (c) their flexural modulus, and (d) no interfacial-gap incidence with indirect restorations.

METHODS

Seven dual-cured luting-agents, one self-adhesive resin cement, six resin cements and one resin-modified glass-ionomer for luting, were investigated with specimen sub-groups (n=10) for each property measured. The principal series of experiments were conducted in dentin cavities with interfacial polishing either immediately (3 min) after setting or after 1-day water-storage. After the finishing procedure, each tooth was sectioned in a buccolingual direction through the center of the restoration, and the presence or absence of interfacial-gaps was measured (and then summed for each cavity) at 14 points (each 0.5mm apart) along the composite inlay restoration interface (n=10 per group; total points measured=140), and was expressed by percentage of measured total points. The shear bond strengths to dentin, setting shrinkage-strain and flexural modulus were measured. To estimate the dimensional change of luting-agents, the maximum marginal gap-width and the opposing-width that occurred with luting-agents in a Teflon mold were measured. Moduli were measured in 3-point bending.

RESULTS

For all composite inlay restorations, polished immediately after setting, an incidence of summed no-gaps of 69-88% was observed. For specimens polished after 1 day, a significantly (p<0.05) decreased number of 91-96% summed no-gaps occurred. After 1-day storage, shear bond strengths to dentin and flexural modulus increased highly significantly (p<0.001) for many materials, whereas dimensional changes in the Teflon mold were non-significantly different (p>0.05). There was a highly significant correlation between no interfacial-gap incidence and shear bond strength (r=0.702, p=0.002, n=16). As the dimensional change (shrinkage) within Teflon molds increased, the no interfacial-gap incidence of dentin/inlay interfaces with 'no-gaps' decreased (r=-0.574, p=0.02, n=16). Flexural moduli significantly correlated with no interfacial-gap incidence in the composite inlay restorations (r=0.695, p=0.003, n=16).

SIGNIFICANCE

For three classes of luting-agents during the early stage of setting (<1 day), the shear bond strength to dentin, the dimensional change measured by marginal gaps in Teflon mold and flexural moduli correlated with no interfacial-gap incidence in the composite inlay restoration.

Effects of adhesive systems and luting agents on bonding of fiber posts to root canal dentin

The study evaluated the influence of different luting materials on the microtensile bond strength of glass fiber posts to root canal dentin. Thirty extracted maxillary premolars were endodontically treated, and the roots were prepared for post cementation using the FRC Postec system (Vivadent). Two luting materials (Multilink, Vivadent and Clearfil Photo Core, Kuraray) were used in combination with three adhesive: Multilink Primer (Vivadent), Clearfil Photo Bond, and Clearfil New Bond (Kuraray). A composite build-up was performed around the root to provide adequate gripping during testing. Specimens were cut to obtain beams with the post in the center and with the radicular dentin overlaid by the composite build-up on each side. Microtensile testing was performed with a universal testing machine at a cross-head speed of 0.5 mm/min. The failure mode was classified under a stereomicroscope and four representative beams of each group were selected for SEM analysis. Bond strength data that were analyzed with two-way ANOVA and Student-Newman-Keuls multiple comparisons tests revealed that adhesive systems, luting materials, and the interaction between these two factors significantly influenced the bond strength results (p < 0.01). Multilink applied with its own adhesive system obtained the best results, while the lowest bond strength was achieved with clearfil photo core in combination with multilink primer.

ADHESIVE-COMPOSITE INCOMPATIBILITY, PART II

Apart from some questions related to the repairability of resin composite restorations, dentists have always assumed that methacrylate-based resins are compatible with each other. For example, there is no clinically relevant problem in using a microfilled composite to laminate a Class IV restoration made with a hybrid composite, even if they are not of the same brand or manufacturer. In the context of adhesive systems, we have always believed that resin composites, regardless of their type or composition, bond well to all types of bonding agents. However, unexpected debonding of self-cured, core buildup composites that had been bonded with single-bottle adhesive systems was reported about 5 years ago. Subsequent studies demonstrated that there were, indeed, compatibility problems between simplified adhesive systems and self- or dual-cured resin composites. Apparently, when such combinations are used, reduced bond strengths and subsequent failures at the resin-adhesive interface can occur because of adverse reactions between the acidic resin monomers, an integral part of the simplified adhesive systems, and the chemicals involved in the polymerization mechanism of the self- or dual-cured composites, particularly the basic tertiary amines.

Marginal and flexural integrity of three classes of luting cement, with early finishing and water storage

OBJECTIVES

The aims of this investigation were to clarify the effects of finishing-time and 24 h water-storage on mechanical properties and marginal adaptation to dentin of seven modern luting cements, representing three chemical types.

METHODS

Bistite II, Chemiace II, Compolute, XenoCem, PermaCem, Fuji Cem and Fuji Plus were investigated with specimen sub-groups (N=10) for each property measured. The principal series of experiments was conducted in dentin cavities with interfacial polishing either immediately (3 min) after setting or after 24 h water-storage. After the finishing procedure, the maximum marginal gap width and the opposing width (if any) per cavity were measured microscopically, and summed. Then the overall sum of gap-widths (per group; N=10) was calculated. Marginal gaps were similarly measured in Teflon cavities, together with shear-bond-strengths to dentin and early flexural strengths, moduli and swelling data.

RESULTS

For specimen-sets polished immediately after setting, summed marginal gaps of 23-121 microm were observed, for all luting cements except Compolute. A significantly different (p<0.05) result of either no gap or 6-28 microm summed gap-widths occurred in specimens polished after 24 h. For all materials, their shear-bond-strengths, flexural strength and moduli significantly increased after 24 h storage.

SIGNIFICANCE

The marginal behavior can be interpreted in terms of the contributions of bonding, shrinkage, swelling and compliance of components, along with compositional features of the cements. With these types of cement it is generally inadvisable to polish the interfacial luting surface immediately after cementing. The polishing procedures should be carried out not less than 24 h later. One resin-cement was able to withstand immediate finishing.

Adverse surface interactions between one-bottle light-cured adhesives and chemical-cured composites

OBJECTIVES

This study examined the effect of one-bottle adhesives with different acidities on bonding to chemical-cured and light-cured resin composites.

METHODS

Twenty-four non-carious human third molars were divided into eight groups. A flat dentin surface was created for each tooth. Acid-conditioned dentin surfaces were bonded with Prime&Bond NT (Dentsply), OptiBond SOLO (Kerr), Single Bond (3M) or One-Step (Bisco). Each adhesive group was covered with composite buildups, using either a light-cured (Z100, 3M) or a chemical-cured composite (BisFil 2, Bisco). Specimens were vertically sectioned into 0.9x0.9 mm beams. Microtensile bond strengths were recorded and failure modes were classified using a stereoscopical microscope. Four representative beams from each group were further prepared for SEM examination.

RESULTS

Two-way ANOVA showed that the effect of adhesive types, composite curing modes and their interaction were statistically significant (P<0.001). Multiple comparison tests revealed no statistically significant difference in the bond strength of the four adhesives with the light-cured composite (P>0.05). However, they were significantly lower when used with the chemical-cured composite (P<0.01). A positive correlation was observed between the acidity of adhesives and the bond strengths of the chemical-cured composite. Failure occurred predominantly along the composite-adhesive interface, with microporosities on the adhesive surface and voids within the chemical-cured composite.

SIGNIFICANCE

Air incorporated during mixing of chemical-cured composites only contributed partially to the decreased bond strength observed in simplified-step adhesives. Ultrastructural observations suggested the presence of a surface interaction between the uncured, acidic resin monomers from the oxygen inhibition layer of the adhesive and the initiator components in the chemical-cured composite.

Curing potential of dual-polymerizable resin cements in simulated clinical situations

STATEMENT OF PROBLEM

Little is known about the ability of dual-polymerizable resin cements to polymerize when they are used in various clinical scenarios.

PURPOSE

This study was conducted to determine whether any of 6 commercially available dual-polymerizable resin cements should be classified as an "all-purpose" resin cement.

MATERIAL AND METHODS

. Chemical conversion values (C=C converted to C-C, or the extent of the curing reaction) of 6 commercially available dual-polymerizable resin cements were determined with infrared spectroscopy in 5 clinically relevant scenarios. Scenarios included: using each cement in a dual-polymerizable mode (mixing of 2 pastes); light polymerizing curing through Mylar sheets (dual-Mylar), which served as the control; light polymerizing through 3-mm porcelain (dual-3 mm); and no exposure to light (dual-no light). The single-component light-polymerizable product was also tested as follows: exposed directly through Mylar (light-Mylar) or exposed through 3 mm of porcelain (light-3 mm). Results. For each product, dual-Mylar treatment yielded the highest conversion value of all treatments (control for each product). For all products, dual-3 mm conversion was at least 97% of control and equivalent to control, with the exception of Lute-It!. Dual-no light conversion was less than control treatment but at least 86% of control for all products except for Variolink II (62% of control). For all products in dual-no light mode, except Choice and Variolink II, conversion was at least equal to the light-Mylar values. Only 1 product (Variolink II) did not demonstrate increased conversion values for dual-Mylar compared with light-Mylar treatments. For most other products (Calibra, Insure, and Lute-It!), conversion values for light-3 mm were significantly less than for light-Mylar. Conversion values for Nexus, Choice, and Variolink II were equivalent between light-Mylar and light-3 mm treatments.

CONCLUSION

The choice of a dual-polymerizable cement should be based on its intended use because not all products polymerize adequately in every clinical situation. Although no cement met the stated criteria for an "all-purpose" cement, those tested did produce a range of product-specific results.