الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 182 |  |  |
| | | from | 182 | | |
Abstract
Summary
The aim of the current study was to synthesize an experimental poly urea-formaldehyde (PUF) microcapsule containing a healing agent of triethylene glycol dimethacrylate (TEGDMA) and N, N dihydroxyethyl-p-toluidine (DHEPT). Such self-healing microcapsules were silanized with γ-methacryloxypropyl trimethoxy silane (MPS) to investigate its effect on the flexural strength and flexural modulus, the fracture toughness, self-healing efficiency, biaxial flexural strength before and after mechanical aging by a chewing simulator, cytotoxicity as well as the color change after different storage intervals.
The specimens were categorized into seven groups as follows: the (0%) serves as the control group with no microcapsules. The six other groups are categorized as non-silanized PUF groups (3 groups: 5%, 7.5% and 10%) coded as (5M, 7.5M and 10M) and silanized PUF groups (3 groups: 5%, 7.5% and 10%) coded as (5S, 7.5S and 10S).
The flexural strength and modulus were tested by a universal testing machine adopting the 3-point loading configuration. The fracture toughness (KIC) testing was employed by a universal testing machine utilizing the single-edge notch beam (SENB) specimen configuration. The self-healing efficiency was measured through (KIC) recovery, which was done by healing the originally fractured (KIC) specimens for 24 hours, followed by refracturing through the same testing setup. Regarding the biaxial strength, the disc-shaped specimens were prepared; half of the specimens were fractured in the universal testing machine, while the other half were fractured after exposure to 500.000 chewing simulation cycles inside a chewing simulator. Cytotoxicity testing was performed by preparing a resin extract in several dilutions (32-fold, 64-fold and 128-fold), which were placed on a fibroblast culture medium, and the cellular viability was evaluated using a microplate reader. Color change of the experimental groups was investigated using a spectrophotometer after different storage intervals (24 hours, 3 months, 6 months and 9 months).
Regarding the flexural strength results, none of the experimental groups containing silanized microcapsules at different weight fractions showed a statistically significant reduction in flexural strength as compared to the control group with no microcapsules. All the experimental groups containing the non-silanized microcapsules at different weight fractions were significantly lower than the control group. Results of flexural strength modulus revealed non-significant differences among all experimental conditions.
The virgin-fracture toughness (KIC-virgin) results revealed no significant difference among all experimental groups. The self-healing efficiency results showed that the silanized groups experienced a self-healing efficiency ranging from 49-77% recovery in (KIC-virgin) which was higher significantly than their non-silanized counterparts that had 38-69% recovery in (KIC-virgin).
The biaxial flexural strength results before aging showed non-significant differences in all the silanized groups compared to the control group. On the other hand, all non-silanized groups were significantly lower than the control group. Following mechanical aging by the chewing simulator, biaxial flexural strength recorded a significant reduction in the control, 5M, 7.5M, and 5S groups.
The cytotoxicity testing results showed that all groups with different dilutions had a significantly higher cell viability % compared to the negative control. Regarding the dilution effect on the cytotoxicity results, the 128-fold cell viability was recorded to be significantly higher than the 32-fold cell viability.
Regarding the color measurements, results of color change ΔE00 of all experimental groups after 24 hours of storage as compared to the control group showed that the 10S group showed the higher color change, followed by 7.5S and 10M, followed by 7.5M and 5S while the significant lower ΔE00 was recorded in 5M. When comparing the ΔE00 after different time intervals as compared to the 24-hour results, the highest significant ΔE00 was recorded after a 9-month storage time, followed by the 6-month storage time, while the lowest significant ΔE00 were recorded for the 3-month storage time.