Farid Sabry El-Askary

This article aims to evaluate the effect of load weight, unload time, and storage duration on microtensile bond strength (µTBS) of dual-cure resin cement to CAD/CAM composite. Forty-eight composite blocks (Grandio Blocs, n = 24 shade A1, and n = 24 shade A4) were randomly assigned to eight groups (n = 3 shade A1, and n = 3 shade A4) based on load weight (1, 3, 5, and 15 kg), and unload time (immediately before light curing or 10 minutes during/after light curing). Bonded blocks (n = 3/group) were sectioned into multiple sticks. Half of the sticks (n = 21) were tested after 24 hours, while the remaining 21 were stored in distilled water at 37°C and tested after 6 months. Sticks for film thickness were evaluated using a stereomicroscope (60 × ). However, the sticks for µTBS were pulled in tension at a 0.5-mm/min crosshead speed. Data were analyzed using ANOVA and the Games–Howell post hoc test (α = 0.05). There was no correlation between µTBS and FT (r = 0.035; p = 0.737). For the FT, only “unload time” had a significant effect (p < 0.001). For µTBS, “load weight,” and “unload time” had no significant impact (p = 0.948 and p = 0.948, respectively). However, “storage time” significantly influenced the results (p < 0.001). Adhesive mode was significantly predominant (56.85%). Unload time is a crucial factor controlling the film thickness of the dual-cure resin cement. However, it does not affect the resin cement µTBS to CAD/CAM composite. Excessive seating load should be avoided when positioning CAD/CAM composite restorations, while a controlled short time may assist in preventing restoration rebound.

Objective To correlate µTBS of photo- and dual-polymerized luting resins with film thickness (FT), Vicker's hardness (HV) and ultimate-tensile strength (UTS).Methods Human molars (N = 30) were divided (6-groups) according to: 1: Luting resin: Dual- [Bifix QM, (BF)], or photo-polymerized [GrandioSo Heavy Flow (GHF) and VisCalor Bulk (VB)] and 2: Adhesive mode (Optibond Universal): Etch-and-rinse (ER) or self-etching (SE). CAD/CAM blocks (7x7x4mm³) were air-abraded (50µm Al₂O₃/10s/0.2MPa) and silanated. For ER, dentin was etched (15s), rinsed (30s), and blot-dried. For both modes, adhesive was applied (20s), air-dried (5s) and photo-polymerized (10s). Sticks (1x1mm²) were aged either for 24-hours or for 6-months. Sticks were pulled in tension (1mm/min). Debonded sticks were evaluated for failure mode. For FT, nine-bonded slabs/each cement were evaluated. For UTS, eight-hourglass specimens/each cement were tested. For HV, 5-discs/each cement were evaluated using Vicker’s hardness tester. Data were analysed using ANOVA/Pearson's correlation tests (α = 0.05).Results No correlation between µTBS/HV was revealed (P > 0.05). Positive correlation between µTBS/FT and µTBS/UTS (p < 0.05) were observed. Three-Way ANOVA revealed all experimental factors had significant effect on µTBS (p < 0.05). The VB showed significant lower µTBS (20.8 ± 9.3MPa). The ER mode showed higher µTBS (26.0 ± 10.9MPa), and 24-hours revealed the higher µTBS (27.4 ± 10.0MPa). Mixed failure was the predominate type (42.51%). The VB showed the highest FT (122.2 ± 11.9µm). The GHF revealed higher UTS and HV (112.5 ± 19.7MPa and 91.6 ± 0.4Kgf respectively).Conclusions Photo-polymerized flowable resin can substitute dual-polymerized cement for CAD/CAM composite bonding.Clinical relevance: Photo-polymerized flowable composite can replace the dual-polymerized resin cement one to bond CAD/CAM composite to dentin.

The aim of this study was to evaluate the effect of CAD/CAM composite thickness on micro-tensile bond strength (µTBS), microhardness (HV), and film thickness (FT) of different luting composites. Composite blocks (6.8 mm × 6.8 mm) were divided into 12 groups according to: CAD/CAM thickness and luting composite. For each group, 21 rods (1 mm × 1 mm) were tested in tension at crosshead speed of 1 mm/min. Fracture modes were categorized as adhesive, mixed, and cohesive. Microhardness (n = 5/group) was assessed using microhardness tester. Film thickness (12-rods/group) was evaluated using a stereomicroscope (×40). Data were analyzed using the two-way ANOVA/Tukey’s HSD test (p = 0.05). Parameters “thickness”, “cement”, and “thickness x cement” showed significant difference on µTBS and HV (p < 0.05). At 2 mm, heated x-tra fil composite showed the highest µTBS (45.0 ± 8.5 MPa), while at 4 mm thickness, Grandio Flow revealed the lowest µTBS (33.3 ± 6.3 MPa). Adhesive, mixed, and cohesive failures were reported. The HV of all composites decreased when photo-polymerized through 4 mm thickness (p < 0.05). Regardless of CAD/CAM thickness, photo-polymerized composites can be successfully used for luting CAD/CAM composite.

This study assessed the validity of torsion test, by comparing it with shear test, in evaluating the bonding of resin composite core after different surface treatments to both zirconia and resin composite CAD/CAM blocks. In total, 108-resin composite core cylinders (3 mm × 3 mm) were prepared and stored in distilled water at 37 °C/48 h. The cylinders were subjected to no-treatment, sandblasting, or surface grinding. Cylinders from each treatment group were then bonded with either zirconia or resin composite CAD/CAM blocks using dual-cure resin cement and stored for 24 h. They were subjected to torsion (rotational speed, 0.25 rpm until failure) or shear (crosshead speed, 1.0 mm/min) tests (n = 9 for each core/block combination in each test). All fractured surfaces were observed by scanning electron microscopy, and the maximum principal stress (MPS) was assessed using finite element analysis (FEA). In the torsion test, the sandblasted composite core and resin CAD/CAM block showed significantly lower bond strength than the other groups (p < 0.05), but the shear test results showed no intergroup differences. While 39.89% of the specimens showed cohesion failures in the torsion test, 55.56% showed adhesion failures in the shear test. FEA demonstrated an even distribution of MPS from the outer edge to the center of the cement layer during the torsion test; however, MPS was unevenly concentrated at the bottom edge of the cement layer during the shear test. The torsion test was better than the shear test in bond testing because of the uniform tensile stress distribution and unidirectional displacement at the bond interface.

The aim of this study was to evaluate the effect of surface treatment and storage time on immediate repair bond durability of methacrylate- and ormocer-based bulk fill composites. In total, 265 discs were divided into 32 groups (n = 8/group) according to: (1) Material: X-tra fil and Admira Fusion X-tra; (2) Surface treatment: oxygen inhibition; matrix; Futurabond M+; Silane/Futurabond M+; Admira Bond; Silane/Admira Bond; ceramic repair system; and Silane/Cimara bond; and (3) Storage time: 24 h and 6 months. Each disc received three micro-cylinders from the same material. Specimens were subjected to micro-shear bond strength testing either at 24 h or 6 months. Data were analyzed using ANOVA/Tukey’s test/Student t-test (p = 0.05). All experimental factors had significant effect on bond strength (p < 0.0001). Drop in bond strength was noticed in both materials after six months (p < 0.05), except for Admira Fusion X-tra treated with silane/cimara adhesive (p = 0.860). Both materials showed insignificant values with Admira bond either at 24 h or 6 months (p = 0.275 and p = 0.060, respectively). For other treatments, X-tra fil showed significantly higher values at 24 h and 6 months (p < 0.05). Ceramic repair system can be used to immediately repair both methacrylate- and ormocer-based composites.

This study evaluated the effect of thickness and photo-polymerization distance on flexure strength of two bulk fill resin composites. In total, 96 rectangular-shaped resin composite bars were divided into eight experimental groups (n = 12/group) according to the three experimental factors; Factor 1: Material (X-tra fil and Admira Fusion X-tra), Factor 2: Thickness (2 mm and 4 mm) and Factor 3: photo-polymerization distance (2 mm and 8 mm). The bars were prepared with fixed 2 mm width and 2 mm length but differed in thickness (2 mm or 4 mm). The bars were light cured either at 2 mm or 8 mm distances. Flexure strength test was run at a crosshead speed of 0.5 mm/min. Data were analyzed using 3-Way ANOVA/Student t-test. Methacrylate-based resin composite exhibited significant higher flexure strength (p < 0.001). At 2 mm distance, there was no significant difference between 2 mm and 4 mm thicknesses for X-tra fil and Admira Fusion X-tra (p = 0.726 and p = 0.486, respectively). At 8 mm distance, both materials showed significantly higher flexure strength with 4 mm thickness compared to 2 mm thickness (p ˂ 0.001). Only X-tra fil with 2 mm thickness had no statistically significant difference on the flexure strength at 2 mm and 8 mm distances (p = 0.437). X-tra fil in 2 mm thickness cured at 8 mm distance and Admira Fusion X-tra in 4 mm thickness cured at 2 mm distance revealed the highest reliability. Methacrylate-based resin composite tested in this study had superior flexure strength compared to ormocer-based resin composite, regardless of the increment thickness and photo-polymerization distance.

To evaluate the influence of different adhesion strategies and curing modes of a universal adhesive on shear bond strength (SBS) of a dual-cured core build-up resin composite to bovine dentin. In total, 60 bovine anterior permanent teeth were randomly divided into 6 groups (n = 10/group) according to; 1: Adhesion strategy, 3 groups (self-etching, etch-and-rinse/wet and etch-and-rinse/dry) and 2: Curing mode, 2 groups (light-curing and dual-curing). Subsequent to root and incisal half removal of each tooth, labial enamel was wet ground over #180 SiC papers, and exposed dentin surface was wet ground over #600 SiC paper for 60 s to create a standardized smear layer. Universal adhesive was applied according to its manufacturer instructions and each tooth was then restored with one dual-cured composite cylinder (2mm×2mm). Shear bond strength was run at a crosshead speed of 0.5 mm/min, and failure modes were categorized into: 1- Adhesive, 2- Mixed and 3- Cohesive failures. Statistical analysis was performed using Two-Way ANOVA/Tukey HSD test. The results showed that factor ‘adhesion strategy’ had no statistically significant effect on SBS (p = 0.525). However, factors ‘curing mode’ and ‘adhesion strategy x curing mode’ showed statistically significant effect on SBS (p = 0.020 and p = 0.002 respectively). Mixed failure represented 55%, followed by adhesive failure (43.3%) and the cohesive failure represented 1.7%. It seemed better to apply the universal adhesive used in this study in etch-and-rinse strategy rather than self-etching one, especially when the adhesive was used in light-curing mode. The use of the DC activator seemed to be unnecessary.

This study evaluated the repair microshear bond strength (μSBS) of water stored CAD/CAM resin composite under eight different surface treatments using a silane-containing universal adhesive in etch-and-rinse and self-etching modes. In total, 48 CAD/CAM resin composite slices were prepared from Lava Ultimate CAD/CAM blocks and stored in water for 6 months. The slices were assigned into 8 main groups, according to surface treatments (no treatment, no-treatment/silane, surface grinding, surface grinding/silane, sandblasting, sandblasting/silane, silica coating and silica coating/silane). Each main group was divided according to the universal adhesive application mode (either the etch-and-rinse mode or the self-etch mode). Each slice received 6 resin composite micro-cylinders (0.8 × 1 mm). Micro-shear bond strength was run at 0.5 mm/min crosshead speed until failure. Treated surfaces were examined using SEM. Bond strength data were statistically analyzed using Two-Way ANOVA/Tukey HSD post hoc test. Only ‘surface treatment’ significantly affected the repair μSBS (p ˂ 0.001). Parameters ‘Adhesive application mode’ and ‘surface treatment × adhesive mode’ showed no significant effect on μSBS (p = 0.458 and p = 0.286 respectively). Regardless of the adhesive application mode, silica coating showed the highest μSBS (21.6 ± 6.8 MPa), while sandblasting/silane showed the lowest μSBS (13.0 ± 6.1 MPa). Regardless of adhesive application mode, the use of silica coating to treat the water-stored CAD/CAM resin composite surfaces is crucial to improve the repair bond strength.

This study evaluated ascending order of light attenuation distance (0, 2, 4, 8 mm) and specimen dimensions (2 × 2 × 10, 2 × 2 × 12, 2 × 2 × 15 mm³) differing from requirements of ISO 4049 (2 × 2 × 25 mm³) on the flexural strength of nano-hybrid resin composite. Specimens (N = 160) were prepared accordingly and randomly assigned into groups for the factors studied. Specimens were photo-polymerized from increased distances through 1, 2, 3 and 5 overlapping cycles depending on the specimen length after which they were subjected to three-point bending test (0.5 mm/min). Data were statistically analysed using one-way, two-way ANOVA and Tukey’s HSD post hoc tests (α = 0.05). Two-parameter Weibull modulus, scale (m) and shape (₀) were calculated. Both light attenuation distance (p < 0.001) and specimen dimensions (p < 0.001) significantly affected the results. Regardless of the specimen dimensions, 0.2 mm polymerization distance resulted in significantly higher mean flexural strength compared to 4 and 8 mm. Polymerization distance did not significantly affect the mean flexural strength of specimens prepared according to ISO norms (p > 0.05). Weibull distribution presented the highest shape (m) for 10–8 mm (24.65), 12–4 mm (14.54), 15–2 mm (12.32), 25–2 mm (17.56), length–light distance combinations. Specimen dimensions prepared in accordance with ISO 4049 do not allow for comparison of the effect of light attenuation distance on the flexural strength of resin composite tested.