Marwa Beleidy

Background: Glass Ionomer Cements (GICs) have limited strength, esthetics, and bioactivity. This study aimed to develop a nanoformulation of Gum Arabic (GA) and incorporate it into a commonly used GIC material to evaluate its effects on the cement’s physical, mechanical, adhesive, optical, and biological properties. Methods: GA was oxidized to introduce active functional groups. The resulting solution was atomized using a nanospray dryer to obtain nano-Gum Arabic (nano-GA) powder. Dynamic light scattering (DLS) analysis confirmed the nanoparticle size distribution. Nano-GA was incorporated into GIC (Medicem; Promedica, Dental Material GmbH, Neumuenster, Germany) at concentrations of 0.5, 1.0, 2.0, 4.0, 8.0, and 16.0 wt%. The effects of nano-GA addition on film thickness, water solubility (Wsol) and sorption (Wsp), diametral tensile strength (DTS), shear bond strength (SBS) to enamel and dentin, translucency parameter (TP), and contrast ratio (CR) were evaluated. Biological assessments were also conducted, including cytotoxicity, genotoxicity, and cell viability analyses. Data were statistically analyzed using one-way ANOVA and post hoc tests at a significance level of p < 0.05. Results: The 8.0 wt% group exhibited the highest film thickness among all tested formulations, while the 2.0 wt% concentration demonstrated the lowest Wsol. Increasing nano-GA content up to 16 wt% reduced Wsp compared to the control ( p < 0.05). No significant differences in DTS were observed among the 0.5, 1.0, and 4.0 wt% groups. Regarding adhesive performance, 2.0 wt% showed superior SBS to enamel, whereas the 1.0 wt% formulation achieved higher SBS to dentin. Optical assessments revealed that the 16.0 wt% group had the highest TP values, while the CR decreased with increasing nano-GA content. Biological evaluation confirmed that nano-GA addition up to 4.0 wt% exhibited no cytotoxic or genotoxic effects; however, cell cycle analysis indicated a slight increase in apoptosis at 4.0 wt%, whereas the G0/G1 phase percentage was highest in the 0 wt% group. Conclusions: Incorporating nano-GA into conventional GIC improved its physical, mechanical, adhesive, optical, and biological properties in a concentration-dependent manner. Optimal performance was achieved at 0.5-2.0 wt% nano-GA, enhancing strength, adhesion, and stability without affecting translucency or biocompatibility. Nano-GA up to 4.0 wt% was biocompatible, while higher concentrations induced cytotoxic effects. Thus, nano-GA is a promising additive for improving GIC performance at optimized concentrations.

To investigate the effect of zirconia endocrown-retained fixed dental prosthesis (FDP) designs on marginal integrity and fracture resistance after thermomechanical aging, compared with full-coverage-retained FDPs. Three extracted mandibular second premolars and second molars were randomly assigned to three abutment designs: full-coverage retainers (A), butt-joint endocrowns (B), and endocrowns with shoulder finish line and ferrule-like extensions (C). All teeth were prepared as abutments for three-unit zirconia FDPs replacing a missing mandibular first molar, and each FDP was duplicated into 12 epoxy resin models. High translucent zirconia FDPs were fabricated using Computer-Aided Design-Computer-Aided Manufacturing (CAD-CAM) and cemented using self-adhesive resin cement. Marginal gaps were measured under a stereomicroscope (× 35) before and after thermomechanical aging (1.2 × 10⁵ cycles, 49 N, 5 – 55℃). Fracture resistance was assessed after aging under compressive loading until failure, and failure mode was recorded. Data were analyzed using one-way ANOVA with post hoc tests (α = 0.05). All groups showed a significant increase in marginal gap after aging (P < .05). Group B had the smallest mean marginal gap before and after aging (P < .001). Group A exhibited the highest fracture resistance, significantly exceeding Groups B and C, with Group B showing the lowest values (P < .001). Failure mode analysis indicated that fractures were confined to the connector regions, mainly the distal connectors, with occlusal extension observed in Groups B and C. Abutment design significantly affected the zirconia endocrown-retained FDPs performance. Marginal gaps increased after thermomechanical aging, but remained within clinically acceptable limits. The butt-joint design demonstrated superior marginal adaptation, while the full-coverage design exhibited the highest fracture resistance, exceeding physiologic posterior masticatory forces.

Background: Limited research evaluates how the type of implant-abutment connection and the material of the abutment together affect the biomechanical behavior of load transfer within both the implant components and the surrounding bone under axial and oblique loading conditions. This 3-dimensional (3D) finite element analysis (FEA) study aimed to provide biomechanical insights to assist clinicians in choosing optimal connection designs and abutment materials, enhancing implant longevity and clinical outcomes. Methods: Two internal implant-abutment connections were modeled in 3D: model (S), which is a star-shaped tube-in-tube design, and model (H), which is a Morse taper combined with an internal hex, both intended to support a mandibular first molar crown and its associated bone geometry. Four abutment materials (Titanium grade V/Ti, Co-Cr, soft-milled Co-Cr–Mo/Co-Cr-S, and zirconia/Zr) were examined using both connection designs. Each crown was subjected to two loading protocols: (1) 200 N vertically was applied at six occlusal points, and (2) 100 N obliquely (at 45º) was applied to three occlusal points on the buccal bevel of the buccal cusp. FEA was performed to analyze the maximum and minimum principal stresses and strains on the peri-implant bone, as well as the von Mises stresses on the implants, abutments, screws, and crowns. Results: Principal stresses and strains were predominantly concentrated in the crestal cortical bone. Under axial loading, stress values were similar across connection types. The highest stress was observed in the H (Zr) model (15.683 MPa) and the lowest in S (Ti) (14.265 MPa). Oblique loading caused higher compressive stresses, peaking at 99.06 MPa in the H (Co-Cr) model. In cancellous bone, stresses were lower, ranging from 0.12888 MPa for H (Ti) to 0.21535 MPa for S (Zr). The highest cortical strain was observed in S (Co-Cr) under oblique loading conditions, measuring 6700 με. Conversely, all models exhibited reduced cancellous elastic strain values, with the maximum strain recorded at 1200.0 με in the S (Co-Cr) axially and 980.0 με in the S (Co-Cr) obliquely. The von Mises stress was localized at the implant and abutment necks, with peak implant stress attaining 135.0 MPa in the S (Co-Cr) model under oblique loading. Titanium abutments demonstrated the lowest stress values consistently across various loading conditions. All models exhibited minimal directional screw deformation (3.897 µm axial; 1.257 µm oblique), demonstrating mechanical stability. Conclusions: Star-shaped tube-in-tube and hybrid Morse taper with internal hex connections showed similar stress patterns, with values below the titanium alloy's yield strength and safe bone stress levels. Oblique loading, however, produced cortical strains above the safe limit. Zirconia, Co-Cr, and soft-milled Co-Cr–Mo abutments had moderate stress distribution, while titanium showed the most favorable profile. Both connections caused minimal screw deformation, suggesting low loosening risk.

Background: To evaluate the graphene-reinforced PMMA wear resistance and surface roughness compared to PMMA after accelerated artificial aging. Methods: Twenty molar-shaped crowns were fabricated ( n = 10): graphene-reinforced PMMA (G) and PMMA (P), and an intraoral scanner digitized them. After thermomechanical aging, equivalent to 6 months of clinical service, the same scanner rescanned each crown. 3D analysis software calculated the wear loss volume of tested crowns. Twenty virtual discs were designed and milled from the two tested materials ( n = 10). The discs were subjected to thermocycling, equivalent to 6 months of clinical service. Before and after thermocycling, a non-contact optical profilometer quantified the surface topography of all discs for assessment of surface roughness (Ra). Data were analyzed using ANOVA, Student’s t, and Bonferroni’s post-hoc tests ( P ≤ 0.05). Results: Both 2D and 3D analysis approaches showed no statistically significant difference in surface wear between the P and G groups ( P -value = 0.053, Effect size = 1.268; P -value = 0.649, Effect size = 0.271), respectively. Surface roughness did not differ statistically between the two materials independent of thermocycling ( P -value = 0.172, Effect size = 0.150). Mean Ra decreased significantly after thermocycling in both groups regardless of material type ( P -value = 0.035, Effect size = 0.320). For PMMA, the mean Ra did not change significantly after thermocycling. While mean Ra decreased significantly following the thermocycling of graphene-reinforced PMMA. Conclusions: Both conventional PMMA and graphene-reinforced PMMA exhibited comparable performance in terms of surface wear resistance and surface roughness, regardless of artificial aging.

Background: The internal fit of the implant-abutment connection plays a crucial role in implant success. This study aims to assess the impact of various connection designs and materials of customized implant abutments on the gap distance at the implant-abutment interface. Methods: Two internal connection implant systems, star-shaped tube-in-tube and hybrid Morse taper with internal hex anti-rotation feature (n = 24 each, total n = 48) were evaluated. Each group was subdivided into four material groups: zirconia (Zr), titanium (Ti), cobalt-chromium (Co-Cr), and soft-milled cobalt-chromium-molybdenum (Co-Cr-Mo). The internal fit was assessed via micro-computed tomography (µCT). Results: All specimens demonstrated clinically acceptable microgap values (≤ 150 μm). The star-shaped tube-in-tube connection exhibited significantly narrower gaps compared to the hybrid connection. Zr showed the greatest gaps among materials, followed by Ti, Co-Cr, and soft-milled Co-Cr-Mo, which had the smallest gaps. Conclusions: The star-shaped tube-in-tube connection demonstrated superior internal fit to the hybrid connection. Zirconia abutments demonstrated inferior internal adaptability. Dimensional changes during sintering of soft milled materials may have influenced these outcomes and should be considered when interpreting the data. All tested abutments fell within clinically acceptable misfit ranges.

Problem: CAD/CAM PMMA, as a provisional material, needs physical, mechanical, and biological improvements. Purpose: To compare graphene-reinforced PMMA crowns' marginal adaption and fracture resistance to CAD/CAM PMMA crowns under simulated oral conditions. Methods: A typodont mandibular first molar was prepared for an all-ceramic crown. Duplicating it yielded 20 dental epoxy resin dies. A 3D scanning was performed for each die to design 20 crowns. Ten crowns were milled from PMMA blanks (P) and 10 from graphene-reinforced PMMA blanks (G). Next, resin cement luted each crown to its die. Each specimen was digitally imaged for marginal gap assessment. Four equidistant landmarks at each specimen's cervical circumference were measured. A chewing simulator aged tested crowns for 120,000 cycles. The marginal gap evaluation was repeated after aging. Each crown was evaluated for fracture resistance in a universal testing machine that determined fracture load in Newton. All data were statistically analyzed. Results: The tested materials did not differ statistically before or after thermocycling. Group (P) showed no statistically significant difference in mean gap distance after thermocycling, while Group (G) showed a statistically significant rise (P-value = 0.033, Effect size = 0.719). The fracture resistance of the two groups was not significantly different (P-value = 0.839, Effect size = 0.132). Conclusions: The mean marginal gap between PMMA and G-PMMA was clinically acceptable. Neither material fractured beyond posterior maximal masticatory stresses, demonstrating clinical resistance. The clinical uses of graphene-reinforced PMMAs are similar to CAD/CAM PMMAs, considering them effective long-term interim materials rather than permanent restorative alternatives.

Statement of problem: CAD/CAM PMMA needs to improve its color stability as used for long-term provisional restoration.Purpose: To evaluate the nanographene-reinforced PMMA surface roughness after thermocycling and color stainability after immersion in coffee and ginger (two different pH media) to frequently used pre-polymerized PMMA. Methods: Sixty CAD/CAM interim materials discs were divided into two groups (n=30): PMMA (P) and graphene-reinforced PMMA (G). All specimens were polished according to the manufacturer's instructions, followed by artificial accelerated aging. Surface roughness (Ra) was analyzed using a non-contact profilometer. Then, both tested groups were immersed in 3 different pH media (coffee, ginger, and distilled water) (n=10) for 3 and 7 days. The color difference (ΔE) was assessed. All data were statistically analyzed.Results: Thermocycling did not significantly change mean Ra (P-value=0.172, Effect size=0.150) between tested materials. After 3 days of coffee or ginger immersion, group (P) showed a significant decrease in mean ΔE compared to group (G). The two materials were not statistically different after distilled water immersion. After 7 days of coffee immersion, group (P) showed a significant rise in mean ΔE compared to group (G). After ginger immersion, the two materials did not differ significantly. After distilled water immersion, group (P) showed a significant reduction in mean ΔE compared to group (G). However, both materials showed unacceptable color change clinically (ΔE3.3). Conclusion: Nanographene-reinforced PMMA had no significant improvement regarding surface roughness after thermocycling and color stainability after immersion in different pH media compared with frequently used CAD/CAM PMMA.

Purpose: To evaluate Well-Root ST and Expoxidin Duo sealers’ contact angle, dentinal tubule penetration, and their impact on fiber post-bond strength.Materials and Methods: Fifty-eight maxillary central incisor teeth were collected and decoronated. Ten teeth were longitudinally split into 20 segments and treated with bioceramic (Well-Root ST) and epoxy resin-based (Epoxidin Duo) sealers (n=10 per group) to evaluate the contact angle. Forty-eight teeth were divided into two groups (n=24) based on the same sealers used for obturation. Both obturated teeth groups were subdivided into two subgroups based on the evaluating test; 14 specimens were assessed for dentinal tubule penetration using a scanning electron microscope (SEM), and 10 specimens were restored with fiber posts and cross-sectioned to evaluate the push-out bond strength using a universal testing machine. Failure mode was determined for pushed-out slices under a SEM. Independent t-test was used to compare two different groups. One-Way ANOVA and Tukey's Post Hoc tests were used for multiple comparisons. P < 0.05 was the significance level.Results: Epoxidin Duo group showed a significantly higher contact angle (56.78 ± 0.68o) than Well-Root ST group (53.25 ± 0.25o). Well-Root ST group showed significantly higher dentinal tubule penetration (10.40 ± 1.05 µm) than Epoxidin Duo group (7.61 ± 1.08 µm). Both groups showed a non-significant push-out bond strength difference.Conclusions: Bioceramic sealer showed higher wettability and dentinal tubule penetration than epoxy resin-based sealer. However, both sealers affected the fiber post-bond strength at various regions throughout the root canal length without influencing the total bond strength.

Purpose: Due to a lack of data on their wear behavior, the study aimed to analyze the two-body wear rate of two different composite veneered computer-aided design/computer-aided manufacturing (CAD/CAM) polyetheretherketone (PEEK) posterior crowns after wear simulation using 3D surface deviation. Materials and Methods: Twenty duplicated epoxy resin models of prepared mandibular first molar to receive an all-ceramic crown were fabricated. Twenty CAD/CAM PEEK substructures were manufactured and divided according to the veneering technique into two groups (n=10); group (H): CAD/CAM High Impact Polymer Composite (HIPC) veneered PEEK substructures, and group (C): Conventional Crea.lign composite veneered PEEK substructures (control). The specimens underwent thermal and mechanical loading (49N, 5/55◦C; 120,000 chewing cycles) as antagonized by steatite ceramic balls. 3D surface deviation analysis using a 3D dental scanner and Geomagic Design X software was applied before and after chewing simulation to determine the volumetric wear loss (mm3). Data were statistically analyzed with the Mann-Whitney U test to compare the two groups. The significance level was set at p≤0.05. Results: H group (-0.0398 [-0.0913- -0.0042] mm3) showed statistically significant lower median volumetric wear loss than C group (0.1195 [0.0233-0.233] mm3) (P-value=0.050, Effect size=2.928). Conclusions: HIPC veneered PEEK crowns showed lower volumetric wear loss than Crea.lign veneered PEEK crowns

Purpose: To verify whether 3D surface deviation analysis software can detect the surface changes of composite veneered polyetheretherketone posterior crowns following wear simulation compared to optical digital profilometry.Materials and methods: Twenty dental crowns, fabricated from CAD‐CAM polyetheretherketone (PEEK) and veneered with high impact polymer composite (HIPC), were subjected to wear test (50N, 5/55°C; 120,000 chewing cycles). Optical digital profilometry and 3D surface deviation using Geomagic design X software was used before and after the wear test to measure volumetric wear loss (mm³). The data were statistically analyzed with Wilcoxon signed‐rank test to compare the two methodologies. The significance level was set at p ≤ 0.05.Results: There was no statistically significant difference between the two assessment methods (p‐value = 0.075, Effect size = 0.854). Regarding the optical digital profilometry analysis, HIPC veneered PEEK crowns showed 0.01686 (0.018‐0.02155) mm³ as a median volumetric wear loss value. While the crowns analyzed by 3D surface deviation showed –0.0398 (–0.0913 to –0.0042) mm³ as a median volumetric loss value (p‐value = 0.075, Effect size = 0.854). In addition, there was no statistically significant correlation between wear measurements by optical digital profilometry and 3D surface deviation analyses (ρ = –0.177, p‐value = 0.685).Conclusions: There was no significant difference or correlation between optical digital profilometry and 3D surface deviation analyses for volumetric wear loss of veneered PEEK crowns.