The Journal of Adhesive Dentistry, 01/2016

Purpose: To investigate the influence of three cavity designs on the marginal seal of large Class II cavities restored with low-shrinkage resin composite limited to the enamel. Materials and Methods: One hundred twenty (120) intact human molars were randomly divided into 12 groups, with three different cavity designs: 1. undermined enamel, 2. box-shaped, and 3. proximal bevel. The teeth were restored with 1. an extra-low shrinkage (ELS) composite free of diluent monomers, 2. microhybrid composite (Herculite XRV), 3. nanohybrid composite (Filtek Supreme XTE), and 4. silorane-based composite (Filtek Silorane). After artificial aging by thermocycling and storage in physiological saline, epoxy resin replicas were prepared. To determine the integrity of the restorations' approximal margins, two methods were sequentially employed: 1. replicas were made of the 120 specimens and examined using SEM, and 2. the same 120 specimens were immersed in AgNO3 solution, and the dye penetration depth was observed with a light microscope. Statistical analysis was performed using the Kruskal-Wallis and the Dunn-Bonferroni tests. Results: After bevel preparation, SEM observations showed that restorations did not exhibit a higher percentage of continuous margin (SEM-analysis; p > 0.05), but more leakage was found than with the other cavity designs (p 0.05). The lowest percentage of continuous margin was observed in ELS restorations (p 0.05). More fractured margins were observed in the undermined enamel cavity design groups (p 0.05). Conclusion: Bevel preparation failed to improve margin quality in large Class II composite restorations and is no longer recommended. However, undermined enamel should be removed to prevent enamel fractures. Keywords: cavity design, enamel margins, low-shrinkage resin composite, bevel, box-shaped cavity, marginal gap, enamel fracture, undermined enamel

Purpose: To evaluate the strength, after artificial aging, of resin-zirconia bonds yielded by methods available in dental practice. Materials and Methods: Standardized test specimens consisting of composite resin cylinders cemented to Y-TZP disks were assigned to 24 groups (n = 20 per group) on the basis of the surface conditioning of the disks and the adhesive used (cement + manufacturer-specific primer). Conditioning methods were: none (control), airborne particle abrasion (50-μm Al2O3 at 0.05, 0.10, or 0.25 MPa), or tribochemical silica coating (Rocatec or CoJet). Panavia 21 + Clearfil Ceramic Primer, Multilink Automix + Monobond Plus, BiFix QM + Ceramic bond, or RelyX Ultimate + Scotchbond Universal were used for cementation. Specimens were stored in water at 37°C either for 3 days or for 150 days in conjunction with 37,500 thermocycles before being submitted to a tensile test (crosshead speed: 1 mm/min). Nonparametric ANOVA and post-hoc tests within the same model were applied to the results (α = 0.05). Results: Conditioning, cement, aging, and all their interactions significantly affected bond strength (p 0.0001). After storage in water for 3 days, bond strengths ranged between 4 and 45 MPa (values were lowest in the BiFix QM groups). After long-term aging, the best results were obtained for silica-coated (Rocatec) zirconia samples cemented with Panavia 21/Clearfil Ceramic Primer; this was the only group for which bond strengths were > 10 MPa. Premature failure of the resin-ceramic bond was usually observed during long-term aging, the only exception being the non-control groups cemented with Panavia. Conclusion: Most bonding strategies failed to create bonds to zirconia with acceptable strength after long-term aging. It might therefore be unwise to rely solely on adhesion for retention of load-bearing Y-TZP restorations. Keywords: long-term adhesion, zirconia ceramic, airborne particle abrasion, tribochemical silica coating, tensile test, bond strength

Purpose: Achieving optimal moisture inside the root canal is a challenge during bonding of fiberglass posts. This study evaluated the effect of different moisture patterns on the push-out bond strength (PBS) and nanoleakage (NL) of fiber posts bonded to the root canal of two simplified etch-and-rinse adhesives. Materials and Methods: The roots of 72 human premolars were endodontically prepared and divided into 6 groups according to the combination of the main factors: adhesive (Ambar and Adper Single Bond 2) and moisture (dry, wet, and overwet). The posts were cemented and after 1 week, the roots were cross sectioned into 6 disks. Two disks each were obtained from the cervical, middle, and apical thirds, and the PBS test was carried out (0.5 mm/min; n = 8). The NL was evaluated by scanning electron microscopy after the immersion of specimens in 50% silver nitrate (n = 4). The failure pattern was examined on all debonded specimens. Data were analyzed by three-way repeated measures ANOVA and Tukey's test (5%). Results: For both adhesives, higher PBS values and lower NL were observed in the wet groups, and lower PBS and higher NL in the dry group. In general, the overwet condition showed intermediate results. Conclusions: The root dentin walls should be left slightly moist before performing fiber post cementation procedures. Keywords: dentin moisture, bond strength, fiber posts, resin cements, root dentin

Purpose: To evaluate the effect of an acid containing 2% chlorhexidine (Ac/CHX) or a 2% CHX aqueous solution (Aq/CHX) on the immediate and 5-year bonding properties of resin/dentin interfaces produced by two adhesives. The presence of CHX in these interfaces was also evaluated under micro-Raman spectroscopy. Materials and Methods: Forty-two molars were ground to expose a flat dentin surface. In the control group, the surfaces were etched with conventional phosphoric acid, and Prime&Bond NT (PB) and Adper Single Bond 2 (SB) were applied. In Ac/CHX, an acid containing 2% CHX was applied after adhesive application. In the Aq/CHX group, an aqueous solution of 2% CHX was applied for 60 s after etching. After placing the restoration, specimens were prepared and tested using the microtensile bond strength test (μTBS, 0.5 mm/min) immediately or after 5 years. For nanoleakage (NL), specimens at each period were immersed in silver nitrate solution and examined by EDX-SEM. In addition, specimens at each period underwent examination for CHX using micro-Raman spectroscopy. Data were submitted to appropriate statistical analysis (a = 0.05). Results: After 5 years, NL was more pronounced in the control than in the Ac/CHX or Aq/CHX (p 0.001). Significant reductions in the μTBS were observed for all groups; however, they were more pronounced for the control (p 0.001). CHX was still present in the hybrid layers Ac/CHX or Aq/CHX groups after 5 years. Conclusion: The use of a 2% chlorhexidine-containing acid or the application of an aqueous CHX primer may increase the long-term stability of resin/dentin interfaces. Keywords: adhesive systems, chlorhexidine, water sorption, nanoleakage, microtensile bond strength, longevity

Purpose: To evaluate the color masking effect of infiltration treatment of artificial white spot lesions (AWSL) using a dedicated resin in comparison to different adhesive systems. Materials and Methods: Enamel/dentin specimens were obtained from bovine incisors and baseline color was assessed using a reflectance spectrophotometer, according to the CIE L*a*b* system. AWSL were produced using a buffered acid solution and a new color evaluation was performed. The specimens were divided into 8 groups: control: artificial saliva changed daily for 7 days; IC: infiltrating resin Icon; EC: EquiaCoat; FU: Futurabond U; SBU: Single Bond U; SBMP: Scotchbond MP; OB: OptibondFL; BF: Bioforty. After the treatments, the color was evaluated again and the values for the parameters ΔL (change in lightness), Δa (change in chroma), Δb (change in hue), and ΔE (general color difference) were calculated in relation to baseline. Data were analyzed by one-way ANOVA and Tukey's tests. Results: After treatment, ANOVA showed significant differences for all parameters (p = 0.001). Tukey's test showed the greatest lightness reduction (ΔL) for the IC group, followed by EC, FU, and SBU. The SBMP, OB, and BF groups were similar to the control. For Δb values, all groups showed differences in relation to the control, with no differences between them. In relation to ΔE, all groups showed differences in relation to the control (ΔE = 5.24), with no significant differences between them. ΔE values after application of all resinous materials were lower than the threshold of 3.7, indicating effective color masking. Conclusions: The Icon infiltrant produced a greater lightness reduction of white lesions (ΔL). For general color difference (ΔE), all the resinous materials tested were able to color mask artificial AWSL. Keywords: tooth color, caries infiltration, white spot lesion, minimally invasive dentistry, esthetic dentistry

Purpose: To examine the influence of the oxygen inhibited layer (OIL) on shear bond strength (SBS) to dentin and surface free energy (SFE) characteristics of different adhesive systems. Materials and Methods: Three adhesive systems were used: Scotchbond Multipurpose (SM), Clearfil SE Bond (CS), and Scotchbond Universal (SU). Resin composite was bonded to dentin surfaces to determine SBS with and without OIL of adhesives. The SFE, dispersion force (γSd), polarity force (γSp), and hydrogen bonding force (γSh) of cured adhesives with and without an OIL were measured. Two-way ANOVA and Tukey's honestly significant difference (HSD) test were used for analysis of SBS data, and one-way ANOVA and Tukey's HSD test were used for the SFE and contact angle data. Results: The SBS of SM and CS showed no significant differences between specimens with and without the OIL. However, the SBS of SU with the OIL was significantly higher than without the OIL. The SFE, γSp, and γSh of cured adhesives with an OIL were significantly higher than those of cured adhesives without an OIL. The SFE, γSp, and γSh of SM and CS with an OIL were significantly higher than those of SU with an OIL. Conclusion: The results of this study indicate that the presence of an OIL with a single-step self-etching adhesive promotes higher SBS to dentin, unlike in the other types of adhesive systems. The SFE characteristics of the OIL of dental adhesives differed depending on the type of adhesive system. Keywords: oxygen inhibited layer, bond strength, surface free energy, adhesive system

Purpose: To clinically evaluate the performance of indirect composite resin restorations cemented with conventional and self-adhesive resin cements over a 12-month period. Materials and Methods: Ten patients fulfilled all the inclusion criteria. Twenty-four composite resin restorations were performed using an indirect technique and cemented with a resin cement (RelyX ARC) or a self-adhesive resin cement (RelyX U100). Two independent evaluators analyzed the restorations using modified USPHS criteria after periods of two weeks and 6 and 12 months. Statistical significance between the cements at each timepoint was evaluated with the Wilcoxon test and between timepoints with the Mann-Whitney test, both at a significance level of 5%. Fisher's exact test was used to assess the occurrence of absolute failures. Results: No statistically significant differences were found between the groups at the same timepoint nor between groups at different timepoints. The only significant difference was found for color match for both groups after 12 months. Conclusion: After 12 months, indirect composite resin restorations cemented with self-adhesive resin cement performed similarly to those cemented with conventional resin cement. Keywords: clinical trials, composite resin, resin cements, self-adhesive resin cements

Purpose: To investigate the influence of selective enamel etching on long-term clinical performance of partial ceramic crowns (PCCs) luted with a self-adhesive luting material (RXU: RelyX Unicem). Materials and Methods: At baseline, 34 patients received the intended treatment: two PCCs (Vita Mark II; Cerec 3D) for the restoration of extended lesions with multiple-cusp coverage were placed in a split-mouth design with a self-adhesive luting material, one without (RXU) and one with selective enamel etching (RXU+E). Patients were evaluated clinically (modified USPHS criteria) at baseline and up to 6.5 years (70 to 88 months). The chi-square test was used for statistical analyses (α = 0.05). Clinical survival of all restorations (n = 68) after 6.5 years was evaluated by Kaplan-Meier analysis. Results: After 6.5 years, 18 patients (9 male, 9 female; median age 41, range 25 to 59 years) with 36 RXU and RXU+E restorations were available for clinical assessment (patient recall rate: 53%), with 13 RXU and 14 RXU+E PCCs placed in molars and 5 RXU and 4 RXU+E PCCs in premolars. Clinically, no statistically significant differences between the luting procedures were detected. Both RXU and RXU+E revealed significant changes over time with respect to marginal adaptation (significant deterioration) and marginal discoloration (significant increase). RXU revealed no cases of postoperative hypersensitivity and RXU+E only did so at baseline (n = 5). Kaplan-Meier analysis showed a cumulative survival for RXU of 60% and for RXU+E of 82%, indicating a significantly higher survival rate for RXU+E. Conclusion: Clinically, RXU and RXU+E perform similarly. In PCC restorations with multiple-cusp coverage, lack of retention due to adhesive preparation, and little dentin available for adhesion caused by extensive core buildups or cavity linings, selective enamel etching is recommended. Keywords: partial ceramic crowns, self-adhesive luting materials, selective enamel etching, prospective clinical study