The Journal of Adhesive Dentistry, 01/2012

Purpose: To report the short-term clinical outcome of a new minimally invasive prosthetic approach utilizing monolithic lithium-disilicate full crowns bonded to feather-edge tooth preparations. Materials and Methods: 235 teeth, 136 anterior and 99 posterior, requiring a full crown were prepared with a feather-edge finish line providing a minimum space on the vertical walls of 0.3 mm at the margin, 0.5 mm along the axial walls, and an occlusal space of 1 to 1.5 mm to ensure sufficient resistance of the restoration. The dental technician manufactured the monolithic restorations using either CAD-CAM or pressed technology. The restorations were individualized with a staining technique to obtain the necessary esthetic characterization and bonded to the natural abutments using an adhesive cementation procedure. Results: Out of 235 treated elements, only one monolithic restoration in a molar position fractured after 3 years of service. No biological or technical complications were observed. The final esthetic result was optimal. Conclusion: This procedure can be considered a further option for the conservative restorative treatment of single elements where a full crown is required. Keywords: lithium disilicate, monolithic, feather edge, minimally invasive, all-ceramic, adhesion, full crown, preparation design

Purpose: The biodegradation of exposed dentin collagen within the adhesive/dentin (a/d) interface is one of the main reasons for composite restoration failures and seriously affects the durability of dental restorations. In the present study, the objective was to investigate whether the inclusion of the cross-linking reagent (glutaraldehyde, GA) in the adhesive would increase collagen biodegradation resistance within the a/d interface. Materials and Methods: The model adhesive consisted of ~60 % monomers (HEMA/bis-GMA, 45/55 wt/wt) and ~ 40 % ethanol as a solvent. 5% GA was added to the above formulation. After the dentin surfaces were etched for 15 s with 35% phosphoric acid, rinsed with water and blotted dry, adhesives both with and without GA were applied and polymerized by visible light for 20 s. These a/d specimens were immersed in the biodegradation solution (prepared by adding 160 mg collagenase in 1 liter of TESCA buffer solution) for up to 30 days after proceeding with the sectioning/fracture to expose the a/d interfaces. The specimens were analyzed using SEM and micro-Raman spectroscopy. Results: SEM results indicated that for the adhesive without GA, there were many voids and a loss of collagen fibrils in the a/d interface after being challenged by the biodegradation solution. The Raman spectra collected from the interface showed that the amide I of collagen at 1667 cm-1 obviously decreased, indicating a removal of collagen fibrils during the degradation process. For the adhesive containing GA, the collagen fibrils within the interface did not degrade at all, which was also confirmed by the Raman results. Conclusion: The results corroborate the previous findings that by using the current adhesive system and wet bonding, the collagen fibrils in the a/d interface are largely unprotected and easily undergo biodegradation. Directly including cross-linking agents in the adhesive could protect collagen fibrils from degradation in situ within the a/d interface. Keywords: dentin, bonding, collagen cross linking, Raman

Purpose: This study analyzed the influence of 10% sodium ascorbate (SA) on tag formation in bleached enamel. Materials and Methods: Five groups were tested: G1 - control; G2 - bleaching with 10% carbamide peroxide (CP) + restoration; G3 - CP + SA + restoration; G4 - bleaching with 35% hydrogen peroxide (HP) + restoration; and G5 - HP + SA + restoration. The teeth were sectioned and decalcified, and the resin tags were analyzed at 400X magnification using an optical light microscope and Axiovision software. Results: The resin tag lengths in µm for each group were as follows: G1 - 36.1A; G2 - 5.8C; G3 - 14.4B; G4 - 1.7D; G5 - 6.5C. Different letters indicate statistically significant differences. Conclusion: Tooth bleaching with CP or HP impairs the formation of resin tags, and the utilization of sodium ascorbate increases tags length. Keywords: dental enamel, tooth bleaching, peroxides

Purpose: To evaluate the effect of surface hydration state and application method on the microtensile bond strength of one-step self-etching adhesives systems to cut enamel. Materials and Methods: One hundred ninety-five bovine teeth were used. The enamel on the buccal side was flattened with 600-grit SiC paper. For the control group, 15 teeth received Adper Single Bond 2, applied according to manufacturer's recommendations. The other specimens were divided into three groups according to the adhesive system used: Futura Bond M (FM; Voco), Clearfil S3 Bond (CS; Kuraray), and Optibond All in One (OA; Kerr). For each group, two hydration states were tested: D: blown dry with air; W: the excess of water was removed with absorbent paper. Two application methods were tested: P (passive): the adhesive was simply left on the surface; A (active): the adhesive was rubbed with an applicator point. A coat of Grandio composite resin (Voco) was applied on the surface. The teeth were sectioned to obtain enamel-resin sticks (1 x 1 mm), which underwent microtensile bond testing. The data in MPa were submitted to a three-way ANOVA and Tukey's test (α = 5%). Results: The ANOVA showed significant differences for application method and the type of adhesive, but not for hydration state. For the application method, the results of Tukey's test were: P: 31.46 (±7.09)a; A: 34.04 (±7.19)b. For the type of adhesive, the results were: OA: 31.29 (±7.05)a; CS: 32.28 (±7.14)a; FM: 34.68 (±7.17)b; different lower-case letters indicate statistically significant differences. Conclusion: Active application improved the bond strength to cut enamel. The adhesive Futurabond M showed the highest bond strength to cut enamel. Keywords: enamel, microtensile bond strength, self-etching adhesives, resin composite

Purpose: To determine whether or not re-etching of oxalate-treated dentin and enamel increases microshear bond strength (µSBS) and improves hybridization. Materials and Methods: Two single-bottle etch-and-rinse adhesives, SingleBond (3M/ESPE) and OptiBond S (Kerr), were bonded to deep occlusal dentin and enamel after perfusion under 20 mmHg simulated intrapulpal pressure. For each adhesive tested, the experimental groups were: G1: bonding according to manufacturer's instructions (control); G2: application of oxalate desensitizer (D/Sense Crystal, Centrix) to acid-etched substrate followed by 60 s water rinsing prior to bonding; G3: same as G2, but with a further 15-s re-etching with 35% phosphoric acid before bonding. The microshear bond strength (µSBS) to dentin and enamel was tested (n = 15); a scanning electron microscopic (SEM) analysis of surface topography (n = 2), interface (n = 2), and failure mode was also performed. The data were statistically analyzed using ANOVA and Tukey's tests at p = 0.05. Results: In enamel, both adhesives showed no significant difference in µSBS among groups. In dentin, the highest statistically significant µSBS for both adhesives was recorded for G1, followed by G2, with the lowest values in G3. The predominant mode of failure was adhesive. SEM analysis of the topography after oxalate treatment revealed remnants of calcium oxalate crystals that were removed only from enamel surfaces after re-etching. SEM images of the interface revealed inadequate dentin hybridization in G2 and G3 compared to G1. Conclusion: Re-etching after oxalate treatment compromises bonding of single-bottle etch-and-rinse adhesives to dentin and provides no added benefit to enamel bonding. Keywords: oxalate desensitizer, etch-and-rinse adhesives, single-bottle adhesives, acid etch, bond strength, SEM

Purpose: To determine the effect of the polymerization mode of simplified bonding systems and the corresponding core buildup resin composite on the bond strength to dentin. Materials and Methods: Composite core buildups were bonded to flat prepared dentin surfaces of 320 human molars using a two-step etch-and-rinse (Excite, ER) and a two-step self-etching (AdheSE, SE) bonding system. Bonding systems were used both with and without their respective self-curing activators (Excite DSC, ER+SC; AdheSE DC, SE+SC). Six curing protocols for the dual-curing composite (MultiCore Flow) were examined: self-curing for 5 min (a); irradiation with light from each aspect for 10 s (b), 20 s (c), and 40 s (d); and irradiation with light from the occlusal aspect only for 60 s (e) and 120 s (f). Shear bond strengths were measured immediately after curing. Additional measurements were performed after water storage of the specimens for 24 h at 37°C. These specimens had been cured according the curing protocols given in the manufacturer's instructions (groups a and d). Failure modes were analyzed using scanning electron microscopy. Results: Immediate bond strengths were significantly different among the bonding systems (p 0.001): SE > ER > ER+SC > SE+SC. Immediate bond strengths of ER and SE were significantly lower when the composite was self-cured (p 0.05). The use of SC activators reduced the bond strength and promoted adhesive failures to dentin. A severe incompatibility problem was observed between the composite and SE+SC. Conclusion: Dentin bonding of dual-curing composite core buildups in combination with simplified bonding systems is still unsatisfactory, even when SC activators are employed. For adequate bonding to dentin, polymerization of the dual-curing composite should always be light initiated. Keywords: self-curing activator, bonding system, composite core buildup, curing protocol, incompatibility, bonding effectiveness

Purpose: To evaluate the flexural strength of two fixed dental prosthesis (FDP) designs simulating frameworks of adhesive fixed partial prostheses, reinforced or not by glass fiber. Materials and Methods: Forty specimens, made with composite resin, were divided into 4 groups according to the framework design and the presence of fiber reinforcement: A1 - occlusal support; A2: occlusal support + glass fiber; B1: occlusal and proximal supports; B2: occlusal and proximal supports + glass fiber. The specimens were subjected to the three-point bending test, and the data were submitted to two-way ANOVA and Tukey's test (5%). Results: Group A2 (97.9 ± 38 N) was statistically significantly different from all other experimental groups, presenting a significantly lower mean flexural strength. Conclusion: The use of glass fibers did not improve the flexural strength of composite resin, and designs with occlusal and proximal supports presented better results than designs simulating only occlusal support. Keywords: glass fiber, flexural strength, composite resin

Purpose: To assess whether the polymerization extent of cement is influenced by curing mode of the adhesive and/or by photoactivation of the cement. Materials and Methods: One hundred five root segments were prepared from endodontically treated teeth. After post space preparation, the root segments were randomly divided into 7 groups, based on the cementation procedure to lute RelyX Fiber Posts (3M ESPE): 1. Variolink II (V, Ivoclar Vivadent); 2. V light-cured (LC); 3. Excite LC (ELC, Ivoclar Vivadent)/V; 4. ELC/V LC; 5. ELC-V LC (One Shot); 6. Excite DSC (EDSC)/V; 7. EDSC-V LC (One Shot). Each root segment was submitted to the acetone shake test to remove the unpolymerized resin and then cut longitudinally. On each half, the extent of cure of the cement was measured with image analysis software. Results: The deepest and basically complete polymerization was obtained with EDSC (groups 6 and 7), regardless of whether light curing was performed. The extent of polymerization was most limited when adhesive was not applied (groups 1 and 2), or when ELC was only light cured, while V was allowed to auto-cure (group 3). With the one-shot polymerization of ELC and V (group 5), the extent of polymerization was similar to the procedure involving separate irradiation of adhesive and cement (group 4). The one-shot technique was significantly more effective if EDSC was used (group 6). Conclusion: The use of a self-activating dual-curing adhesive system in combination with a dual-curing cement enables effective luting of FRC posts regardless of the amount of light transmitted through the post. Keywords: fiber post, light transmission, dual-cure cement, dual-curing adhesive

Purpose: Since adhesion of the restorative materials to pre-polymerized or aged resin composites presents a challenge to the clinicians, existing restorations are often removed and remade prior to cementation of fixed dental prostheses (FDPs). This study evaluated bond strength of non-aged and aged resin composite to an indirect resin composite and pressed glass ceramic using two resin cements. Materials and Methods: Disk-shaped specimens (diameter: 3.5, thickness: 3 mm) (N = 160) produced from a microhybrid resin composite (Quadrant Anterior Shine) were randomly divided into eight groups. While half of the specimens were kept dry at 37°C for 24 h, the other half was aged by means of thermocycling (6000 times, 5°C to 55°C). The non-aged and aged resin composites were bonded to a highly filled indirect composite (Estenia) and a pressed glass ceramic (IPS Empress II) using either a photopolymerizing (Variolink Veneer) or a dual-polymerizing (Panavia F2.0) resin cement. While cementation surfaces of both the direct and indirect composite materials were silica coated (30 µm SiO2, CoJet-Sand) and silanized (ESPE-Sil), ceramic surfaces were conditioned with hydrofluoric acid (20 s), neutralized, and silanized prior to cementation. All specimens were cemented under a load of 750 g. Shear force was applied to the adhesive interface in a universal testing machine (1 mm/min). Failure types of the specimens were identified after debonding. Results: Significant effects of aging (p 0.05), restorative material (p 0.05), and cement type (p 0.05) were observed on the bond strength (3-way ANOVA). Interaction terms were also significant (p 0.05) (Tukey's test). After aging, in terms of bond strength, indirect composite and pressed glass ceramic in combination with both cements showed no significant difference (p > 0.05). Both indirect composite (24.3±5.1 MPa) and glass ceramic in combination with Variolink (22±9 MPa) showed the highest results on non-aged composites, but were not significantly different from one another (p > 0.05). On the aged composites, indirect composite and glass ceramic showed no significant difference in bond strength within each material group (p > 0.05), with both Panavia (17.2±6 and 15±5.5 MPa, respectively) and Variolink (19±8, 12.8±5.3 MPa, respectively), but in all groups, glass ceramic-Variolink on aged composite revealed the lowest results (12.8±5.3 MPa). Among all groups, predominantly cohesive failures were observed in the indirect resin composite substrate (79 out of 80) as opposed to the ceramic (18 out of 80) (p 0.05) (Chi square). Conclusion: Regardless of the resin cement type, considering the bond values and the failure types, the adhesion quality of indirect composite cemented to non-aged and aged resin composite was superior with both cements compared to that of pressed glass ceramic. Keywords: aging, cementation, glass ceramic, microhybrid composite, silica coating, surface conditioning

Purpose: To evaluate the cohesive strength between composite and different light-curing characterizing materials (LCCM), which were prepared using the intrinsic technique. Materials and Methods: One hundred composite specimens were made by using a prefabricated Teflon device, and a layer of LCCM was applied at the interface. The specimens were divided into 5 groups (n = 20): group 1 (control), no LCCM was used; group 2: application of White Kolor Plus Pigment (Kerr) LCCM; group 3: White Tetric Color Pigment (Ivoclar/Vivadent) LCCM; group 4: Brown Kolor Plus Pigment (Kerr) LCCM; group 5: Black Tetric Color Pigment (Ivoclar/Vivadent) LCCM. All materials were used according to the manufacturers' instructions. Specimens were submitted to a tensile test in a universal testing machine (EMIC DL-200MF) to evaluate the cohesive strength at the composite interface. Data were subjected to one-way ANOVA and Tukey's test (α = 5%). Results: ANOVA showed a p-value = 0.0001, indicating that there were significant differences among the groups. The mean values in MPa (± standard deviation) obtained for the groups were: G1: 28.5 (±2.74)a; G2: 23.5 (±2.47)b; G3: 20.3 (±2.49)b; G4: 10.5 (±2.40)c; G5: 9.66 (±3.06)c. The groups with the same letters presented no significant differences. The control group presented statistically significantly higher cohesive strengths when compared to the other groups. The groups in which Brown Kolor Plus Pigment and Black Tetric Color Pigment LCCM were used showed significantly lower cohesive strengths when compared to the groups in which White Kolor Plus Pigment and White Tetric Color Pigment LCMM were used. Conclusion: The use of LCCM produced with the intrinsic technique reduced the cohesive strength of composite. Keywords: composite, cohesive strength, light-curing characterizing materials

Purpose: Zirconia-based ceramics offer strong restorations in dentistry, but the adhesive bond strength of resin cements to such ceramics is not optimal. This study evaluated the bond strength of silane/adhesive/resin cement and zirconia primer/resin cement combinations on non-glazed and glazed zirconia surfaces before and after aging. Materials and Methods: Disk-shaped zirconia ceramic specimens (diameter: 8 mm; thickness: 2 mm) (N = 80, n = 10 per group) were randomly divided into 2 groups. While half of the specimens received one coat of glaze and were later finished by grinding, the other half was only ground using 1200-grit silicone carbide abrasives under water. The glazed specimens were then conditioned with 9.5% HF acid gel for 60 s, rinsed with water for 90 s, and neutralized. The glazed and non-glazed specimens were further divided into two groups. Two resin cements, namely, Variolink II and Multilink Automix were adhered onto the zirconia surfaces with their corresponding adhesive systems. In the Variolink II group, zirconia surfaces were silanized (Monobond-S), and adhesive resin (Heliobond) was applied and photopolymerized. In the Multilink Automix group, one coat of Metal/Zirconia Primer was applied with a microbrush, left to react for 180 s, and dried using oil-free air. Half of the specimens in each cement group were subjected to 5000 thermocycles (5°C to 55°C) and the other half was kept in the dark for 24 h at 37°C prior to testing. Specimens were mounted in the jig of the universal testing machine, and force was applied to the ceramic/cement interface until failure occurred (1 mm/min). After evaluating all debonded specimens under SEM, the failure types were defined as either "adhesive" with no cement left on the zirconia (score 0) or "mixed" with less than half of the cement left on the surface with no cohesive failure of the substrate (score 1). Data were analyzed using three-way ANOVA and Dunnett-T3 post-hoc tests. Results: Application of a glaze layer significantly improved the bond strength in the silane/adhesive/Variolink II group (p 0.05), but no significant effect was found in the zirconia primer/Multilink Automix group (p > 0.05) (three-way ANOVA). Interaction terms were also significant (p 0.05) (Dunnett-T3). Thermocycling did not decrease the results significantly in any of the groups (p > 0.05). Failure analysis revealed exclusively adhesive failures (score 0: 40 out of 40) in the non-glazed groups, but predominantly mixed failures (score 1: 34 out of 40) in the glazed groups. Conclusion: The silane (Monobond S)/adhesive (Heliobond)/Variolink II resin cement combination benefitted from glazing the zirconia surface, but the zirconia primer/Multilink Automix resin cement combination alone also provided sufficient bond strength to zirconia. Keywords: adhesion, adhesive cement, glaze, surface conditioning, zirconia, zirconia primer

Dental erosion is increasing, and only recently are clinicians starting to acknowledge the problem. A prospective clinical trial investigating which therapeutic approach must be undertaken to treat erosion and when is under way at the University of Geneva (Geneva Erosion Study). All patients affected by dental erosion who present with signs of dentin exposure are immediately treated using only adhesive techniques. In this article, the full-mouth adhesive rehabilitation of one of these patients affected by severe dental erosion (ACE class IV) is illustrated. By the end of the therapy, a very pleasing esthetic outcome had been achieved (esthetic success), all of the patient's teeth maintained their vitality, and the amount of tooth structure sacrificed to complete the adhesive full-mouth rehabilitation was negligible (biological success). Keywords: dental erosion, palatal veneers, full-mouth adhesive rehabilitation