The Journal of Adhesive Dentistry, 05/2021

Purpose: To evaluate the 24-month clinical performance of Adhese Universal (ADH) (Ivoclar Vivadent) using two different application modes (etch-and-rinse vs self-etch) when restoring non-carious cervical lesions. Materials and Methods: Twenty-six patients participated in this study. A total of 117 non-carious cervical lesion restorations (N = 117) were assigned to two groups: 1) ADH in the etch-and-rinse mode (n = 59) and 2) ADH in the self-etch mode (n = 58). The same resin composite (Tetric EvoCeram, Ivoclar Vivadent) was used for all restorations. The restorations were evaluated at baseline and at 24 months using the World Dental Federation (FDI) criteria. The results were analyzed statistically using the McNemar test (α = 0.05) and a generalized estimating equation. Results: In self-etch mode, significant differences were found for marginal coloring (p = 0.002), marginal adaptation (p = 0.031), and hypersensitivity (p = 0.031) between baseline and the end of the 24-month period. In the etch-and-rinse mode, significant differences were found for marginal coloring (p = 0.004), fractures/retention (p = 0.002), marginal adaptation (p = 0.002), and hypersensitivity (p = 0.000). Significant differences were also detected between groups at 24 months for fractures/retention (p = 0.001). At 24 months, 10 restorations of the etch-and-rinse group were lost and 2 restorations of the self-etch group were lost. Conclusion: In terms of fractures and retention criteria, this universal adhesive obtained better results when applied in self-etch mode than in etch-and-rinse mode. Keywords: clinical trial, self-etch mode, etch-and-rinse mode, universal adhesive, application modes, non-carious cervical lesions

Purpose: To compare different concepts of direct composite restorations in class-II cavities using bulk-fill composites and a conventional composite with different layer thicknesses in a clinical study over a period of 2 years. Materials and Methods: A low-viscosity (SDR), a high-viscosity bulk-fill (Tetric EvoCeram Bulk Fill) and a conventional nanohybrid composite (Tetric EvoCeram) were randomly assigned and placed in different layer thicknesses up to 4 mm in 160 class-II cavities in 94 patients. Restorations were clinically examined at baseline (n = 160), after 12 (n = 150) and 24 months (n = 148) and evaluated according to eight selected FDI criteria. In case of complete loss of the restoration or irreversible pulpitic symptoms, the restoration was rated as failure; repair was considered as relative failure. Results: The materials investigated showed no significant differences regarding the FDI scores and failure rate during the entire follow-up. After 12 months, 7 failures and after 24 months a total of 8 failures were observed. After 2 years, Tetric EvoCeram Bulk Fill with a 4-mm layer thickness and SDR in combination with Tetric EvoCeram Bulk Fill with a 2-mm layer thickness exhibited a non-significant tendency towards increased hypersensitivity (FDI score 5) as compared to the reference material Tetric EvoCeram with a 2-mm layer thickness (p = 0.051; Kruskal-Wallis test). Conclusion: The clinical stability of bulk-fill materials in layers up to 4 mm is comparable to nanohybrid composites after 2 years. Keywords: bulk-fill, clinical examination, 2-year follow-up, FDI criteria

Purpose: To examine the origins of acrylates and adhesive dentistry up to 1955. Materials and Methods: A search of MEDLINE database and a manual literature search were conducted to find relevant articles. Results: Acrylic acid was discovered in 1843, methacrylic acid in 1865. In 1880, light polymerization of acrylate compounds using glass prisms was introduced. In 1928, polymethyl methacrylate (PMMA) was industrially produced from methyl methacrylate (MMA). In 1930, PMMA moldings that could be adapted under heat and pressure were introduced into dentistry. The process was improved in 1936 by mixing pulverized PMMA and liquid MMA. In 1940, the intraoral polymerization of dental resins using UV light or catalysts was discovered. In the same year, the combined procedure (dual-curing) and addition of inorganic fillers to improve the material properties (precursors of composites) were proposed. Effects on the oxygen inhibition layer and intraoral bonding between several resin portions were also described. In 1942, direct restorations with self-curing resins (combined with a precursory version of cavity sealing) were described. These new resins were marketed in the late 1940s. Intraoral repair of restorations and cementation of crowns and bridges with resins were also described in 1942. In 1949, a glycerophosphoric acid-based sealer was marketed. In the same year, it was discovered that etching of the enamel (with nitric acid) caused an adhesion to thin layers of acrylic-based materials. In 1955, phosphoric acid etching of enamel was shown to improve adhesion. Conclusion: In the first half of the 20th century, important but little or unknown discoveries took place. These discoveries can improve our understanding of how adhesive dentistry evolved. Keywords: history of dental acrylates, history of adhesive dentistry, origins of composites, redox cure, dual cure, photocure, origins of acid etching of enamel, beginnings of acrylic-based cementation of crowns and bridges, beginnings of acrylic-based restorations

Purpose: This study evaluated dentin bond strength, failure mode, interface morphology, adhesive infiltration into dentin, and marginal adaptation of bulk-fill composites used with different adhesives. Materials and Methods: Third molars received occlusal class I cavities (4 mm x 4 mm x 4 mm) that were bulk-filled with Admira Fusion x-tra (Voco) or SonicFill 2 (Kerr) using four adhesives (Scotchbond Multipurpose, 3M Oral Care; Clearfil SE Bond, Kuraray Noritake; OptiBond All-In-One, Kerr; Futurabond U, Voco). Scotchbond was used with acid-etching, while the remaining adhesives were applied in self-etch mode. Sixty-four teeth were selected for the microtensile bond strength test (n = 8). Failure modes were analyzed with scanning electron microscopy (SEM). Interface morphology and adhesive infiltration (n = 3) were investigated using confocal laser scanning microscopy (CLSM). Marginal adaptation (n = 3) was also evaluated using SEM. Bond strength, failure mode, and adhesive infiltration data were analyzed for distribution and homocedasticity, followed by appropriate statistical analyses (α = 0.05). Results: Regarding bond strength, no differences were found among adhesives for SonicFill; Clearfil showed a significantly lower mean value than did Scotchbond (p ≤ 0.05) for Admira; the two composites did not differ. Adhesive and mixed failures were observed for all groups. Scotchbond led to thicker hybrid layers with deeper adhesive infiltration as opposed to Futurabond. The groups Admira+Futurabond, SonicFill+Clearfil, and SonicFill+Futurabond presented the highest marginal discontinuity. Conclusion: The tested bulk-fill composites did not affect dentin bonding. Scotchbond and Clearfil seem to be reliable for bonding SonicFill 2 to dentin. The performance of Futurabond was questionable, given its poor-quality interface and higher percentages of marginal gaps. Keywords: dentin, composite resin, ultrasonics, dental etching, dental bonding, adhesive

Purpose: To three-dimensionally evaluate the interfacial gap of bulk-fill resin composites applied in deep Class-I restorations with different layering techniques and curing modes. Materials and Methods: Ninety-six (n = 96) samples were prepared with standardized deep Class-I cavities and adhesive procedures. Four materials were tested: SDR (SDR), SonicFill2 (SF), Admira Fusion X-Tra (AFXT), Filtek Supreme XTE (FS). Four subgroups (n = 6) were created according to layering and curing techniques: 2+2mm increments with soft start curing (SG1), 2+2 mm with conventional curing (SG2), a 4-mm increment with soft start curing (SG3), a 4-mm increment with conventional curing (SG4). All samples underwent micro-CT scans; afterwards, voids surrounding the restorations automatically underwent a thresholding procedure (Mimics, Materialise; Geomagic Studio 12, 3D Systems) to analyze the 3D interfacial gap. Statistical analysis was performed using three-way ANOVA with Tukey’s test (significance p < 0.05). Results: Statistically significant differences were reported between materials, layering techniques and their interaction. No statistically significant differences were reported for polymerisation mode. Bulk-fill materials showed average interfacial gap volumes ranging from 0.031 mm³ to 0.200 mm³, while FS showed volumes ranging from 0.416 mm³ to 1200 mm³. Conclusions: All bulk-fill materials performed statistically significantly better than did FS (p < 0.05), with no statistically significant differences between them. Curing mode did not influence interfacial gap volume in any group (p > 0.05), while bulk-filling vs layering influenced the volume of interfacial gaps only in the FS group, which performied better when incrementally applied. Regarding gap localisation, the floor of the cavity was the area with the highest likelihood of gaps in all samples. Keywords: 3D interfacial gap, micro-CT, bulk-fill composites, layering techniques, curing modes

Purpose: Using the microshear bond strength (µSBS) test, this study investigated the bond strength between a hybrid ceramic and the extrinsic characterization layer after different ceramic surface treatments. Materials and Methods: Hybrid ceramic blocks (Vita Enamic, Vita Zahnfabrik) were sectioned and randomly divided into 4 groups (N = 120) according to the surface treatment and aging (n = 15): P: polishing; E: acid etching with HF; A: aluminum oxide blasting; S: self-etching ceramic primer. The specimens were silanized, then cylinders of light-curing characterization material (Vita Enamic Stain, 1.6 mm diameter x 2 mm height) were fabricated, followed by glazing. The specimens were subsequently immersed in distilled water for 24 h and subjected to the µSBS test using a universal testing machine (load cell 0.5 mm/min, 50 kgf) or tested after thermocycling for 10,000 cycles in water (5ºC–55ºC). After treatment, the specimen surfaces were analyzed using SEM, with failure types defined as adhesive, predominantly adhesive, or cohesive. The data were analyzed by two-way ANOVA followed by Tukey’s test (p < 0.05). Results: The most frequent failure type was predominantly adhesive between ceramic and the characterization layer. There were statistically significant differences between the surface treatments (p < 0.05). Thermocycling did not lead to statistically signifcant different results (p > 0.05). For groups P and A, a sharp decrease in SBS was observed. Conclusion: The absence of surface treatment drastically reduced the microshear bond strength between the ceramic and the characterization layer. Conditioning with 5% hydrofluoric acid for 60 s is the most suitable treatment for adhesion of the characterization layer to hybrid ceramic. Keywords: bond strength, ceramic, hybrid ceramic

Purpose: To evaluate the effects of airborne-particle abrasion and MDP (methacryloyloxydecyl dihydrogen phosphate)-based primer treatment on the strength of resin bonds to highly translucent zirconia. Materials and Methods: Eight groups (n = 20 per group) of specimens were prepared with airborne-particle abrasion treatments (0.1-, 0.3-, or 0.6-MPa pressure) or not (untreated control) and MDP-based primer (treated) or not (untreated). Shear bond strength (SBS) tests were performed on the composite-to-ceramic bonded specimens either with or without thermocycling. After airborne-particle abrasion, the surface topography was evaluated by white light interferometry, and a phase analysis was conducted with x-ray diffraction (XRD). Surface roughness (Ra), surface energy (SE), and SBS measurements were statistically analyzed using either Tukey’s HSD or the Kruskal-Wallis test, based on applicability. Lastly, the failure mode was observed by optical microscope and scanning electron microscope. Results: Airborne-particle abrasion resulted in significantly larger Ra (p < 0.05), especially with higher treatment pressures. Treatment with MDP-based primer caused significantly higher SE and SBS than airborne-particle abrasion alone (p < 0.05), both with and without aging. Conclusion: MDP-based primer can enhance the bond strength and reduce hydrolytic aging of the bonded interface for highly translucent zirconia, exceeding the effects of airborne-particle abrasion. It is recommended that MDP-based primer treatment be applied with a composite cement containing adhesive phosphate monomer. Keywords: highly translucent zirconia, airborne-particle abrasion, MDP-based primer, shear bond strength, surface treatments

Purpose: To investigate the changes in the dentin bond strengths of universal adhesives during the early phase and evaluate the effect of a double-layer adhesive application on the performance of the dentin bond. Materials and Methods: Three universal adhesives and a two-step self-etch adhesive were employed to ascertain the shear bond strengths (SBS) of specimens to bovine dentin with the use of the etch-and-rinse or self-etch mode. The specimens were further divided into two groups based on adhesive application in a single or a double layer. The bonded specimens were stored in distilled water at 37°C for 5 min or 1, 6, 12, or 24 h prior to SBS measurement and the adhesives’ Knoop hardness number (KHN). Results: All the adhesives showed increased SBS with prolonged storage periods regardless of the adhesive layer (single or double) or etching mode. Most universal adhesives in the double adhesive layer groups showed significantly higher SBS than single adhesive layer groups for the same storage period. All the adhesives also showed increased KHN with increased storage period. Conclusion: The SBS and KHN values of the adhesives increased with increasing storage duration over a 24-h period. Double adhesive layer application mediated increased dentin bond strength in the early phase. Keywords: dentin bond strength, double-layer application, universal adhesive, early bond effectiveness, SEM analysis

Purpose: To evaluate the microtensile bond strength (µTBS) of a one-step self-etch adhesive (1-SEA) to dentin and its interfacial nanomechanical properties after 8 years of water storage. Materials and Methods: Flat coronal dentin surfaces of extracted human third molars were bonded with a 1-SEA (Clearfil S3 Bond Plus, CS3+) and built up with a hybrid resin composite (Clearfil AP-X). After storage in water for 24 h or 8 years, non-trimmed stick-shaped specimens were fabricated from the central part of each bonded tooth and subjected to the µTBS test at a crosshead speed of 1.0 mm/min. Failure modes and the morphology of debonded interfaces were analyzed using a scanning electron microscope (SEM). In addition, the elastic modulus (E) and hardness (H) of the adhesive layer and the resin composite were determined by an instrumented nanoindentation test. The acquired µTBS, E, and H data were statistically analyzed using t-tests to examine the effect of storage time (α = 0.05). Results: The 8-year µTBS was slightly lower than that after 24 h, but the difference was not significant (p = 0.123). The SEM observation of debonded surfaces after 8 years revealed extrusions and lacunas. E and H of the adhesive layer and the resin composite significantly decreased over the 8-year water storage (p < 0.001). Conclusions: Although 8 years of water storage did not decrease the µTBS of CS3+ significantly, the observed failure mode patterns and significantly decreased nanomechanical properties indicated resin degradation of the adhesive and the resin composite. Keywords: bond durability, microtensile bond strength, one-step adhesive, dentin, resin composite, nanohardness, elastic modulus, failure mode

Purpose: To evaluate the effect of composite cement components and thermocycling on the bond strength of monolithic lithium-disilicate (LS2) glass-ceramic implant-supported restorations bonded to titanium (Ti) abutments. Materials and Methods: Eighty LS2 blocks were treated with five types of composite cement and primer, then divided accordingly into groups: M (Multilink hybrid abutment), G (G-CEM LinkAce), GP (G-CEM LinkAce with G-Multi PRIMER), P (Panavia F2.0), and U (RelyX U200). Half of the 16 specimens from each group were subjected to thermocycling (groups T-M, T-G, T-GP, T-P, and T-U). The tensile bond strength (TBS) of all specimens was measured using a pull-off test. The cross section of the LS2 block from which the Ti abutment was removed was examined for mode of failure. Two-way ANOVA and Tukey’s HSD test (significance level = 0.05) were used to determine the effect of composite cement composition and thermocycling on TBS. Results: There was no difference in TBS between the five groups before thermocycling (p = 0.16). However, groups M (p < 0.001) and G (p = 0.014) showed significantly lower TBS than the corresponding thermocycled groups. Groups T-GP, T-P, and T-U did not show significant changes in TBS after thermocycling (p > 0.05). All failures occurred at the interface between the composite cement and Ti abutment and not between the cement and the LS2 block. Conclusion: Thermocycling can reduce the bond strength between the composite cements and Ti abutment. The composite cements containing 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) or methacrylate phosphate ester monomers stabilize bonding. Keywords: bond strength, cements, composite, lithium-disilicate glass-ceramic, thermocycling, titanium abutment