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This in-vitro study evaluated the mechanical properties in terms of microhardness and degree of conversion of expired versus non-expired resin composite. A total of 120 standardized specimens were prepared for this study using Ceram.x one (E2 Enamel shade) resin composite, of which forty specimens were prepared using valid resin composite (E-0), the other forty specimens were prepared using 6 months-expired resin composite (E-6) and the last forty specimens using 12 months-expired resin composite (E-12). They were light cured using LED curing unit. 20 of each group were subjected to measurement of surface microhardness in Vickers hardness tester. The depth of cure was calculated by obtaining the microhardness ratio through dividing VHN of the bottom surface by VHN of the top surface. The other 20 specimens of each group were tested for the degree of conversion using Fourier transform infrared spectroscopy (FTIR). Data was then recorded, tabulated and statistically analyzed. The highest mean microhardness of the specimen's top was recorded for the group of 12-months expired resin composite (E-12: 83.17 ± 3.14), which was significantly different in relation to the group of 6-months expired resin composite (E-6: 72.17 ± 2.55) and the group of valid resin composite (E-0: 72.06 ± 4.20). Regarding B/T ratio (%), there were no statistical significant difference between the three groups (E-0: 69.3 ± 10.1; E-6: 66.8 ± 3.9; E-12: 67.9 ± 4.9). As for the degree of conversion results there was no statistical significant difference between the three groups (E-0: 1.48 ± 0.14; E-6: 1.68 ± 0.20; E-12: 1.74 ± 0.18). In conclusion, expired resin composite within1 year interval showed optimum and accepted mechanical properties in terms of Degree of conversion and microhardness compared to that of non-expired resin composite.

This in-vitro study aimed to evaluate microtensile bond strength and nanoleackage of dentin surfaces pretreated with different etching materials. Twenty four extracted human intact second molar were selected and debrided to remove remnants of periodontal ligaments. Occlusal surfaces were flattened to expose a flat area of dentin under copious water coolant. One dentin bonding system (Te-Econom Bond) and one dental resin composite restoration (Tetric N-Ceram) were used for the study. The teeth were divided into four groups (6 each) according to the type of etchant material used as follows: group A -citric acid 6%, group B -citric acid 10%, group C -citric acid 20%, and group D-phosphoric acid 37%. The etchants were applied for 15 seconds to the dentin surface. After which teeth were washed, dried, then bonding agent was applied followed by the resin composite restoration. Then a longitudinal sectioning of restored teeth was made to obtain composite-dentin beams of (0.9 x 0.9 mm) in area. Each beam was composed of composite and dentin with adhesive at the interface. The microtensile bond strength (μTBS) was measured and the nanoleakage was observed using SEM. Data was then recorded, tabulated and statistically analyzed. There was no statistical significant difference between the results of the μTBS of groups A, B and D while group C has the lowest microtensile bond strength (19.20± 4.59). For all groups, nanoleackage was more demonstrated at group C and D, while group B show mild nanoleackage and no nanoleackage was observed for group A. It was concluded that low concentrations of citric acid was effective as etchant material compared to phosphoric acid on dentin surface in terms of microtensile bond strength and nanoleakage. (4004)

This in-vitro study evaluated the compressive strength and radiopacity of denovo synthesized calcium silicate cement containing zinc oxide nanoparticles versus commercial materials. A total of 100 specimens were prepared for this study, 25 of them were prepared for each of the 4 materials group: Synthesized Calcium Silicate Cement (SYNT), Nano Zinc Oxide added to the synthesized calcium silicate cement (NANO), Angelus White Mineral Trioxide Aggregate (MTA) and Theracal (THCL). The 25 specimens of each group was then distributed as follows: 10 were tested for compressive strength (MPa) on day 10, 10 were tested for compressive strength (MPa) on day 30; the last 5 specimens were tested for radiopacity. Data was then recorded, tabulated and statistically analyzed. The mean MPa results on day 10 recorded the highest by THCL-10 (55.35 ± 9.82), while the lowest value was recorded for NANO-10 (4.90 ± 1.61). The mean MPa on day 30 recorded by the NANO-30 (52.66 ± 19.30) was the highest, while the lowest value was recorded for SYNT-30 (21.70 ± 2.55). All subgroups on day 10 compared to those on day 30 showed significant statistical difference at p<0.05; Where the mean MPa of SYNT-30 was less than that of SYNT-10, the same was observed for the THCL subgroups. As for the mean MPa of NANO-30 was higher than that NANO-10, the MTA subgroups expressed the same results. On the other hand, the radiopacity results showed that the highest mean radiopacity value was recorded for THCL (9.43 ± 0.60), followed by MTA (9.38 ± 0.63), then NANO (5.06 ± 0.54), while the lowest value was recorded for SYNT (1.26 ± 0.24). In conclusion, the incorporation of zinc oxide nanoparticles in calcium silicate based enhances the physicomechanical properties of the cement expressed in terms of compressive strength and radiopacity in comparison to commercially available materials such as MTA and theracal.

This in-vitro study assessed bond strength and micromorphological features of dentin substrates treated with different etching modes using universal adhesive system. A total of 28 freshly extracted human molars with coronal dentin caries were used for this study. A total of 80 composite microcylinders with prepared dentin surface containing both sound dentin and carious affected dentin were divided into two main groups (40 each) according to the bonding mode used: Self-etch mode in one step single dose, and total-etch mode in two steps. Each group was then subdivided into two subgroups (20 specimens each) according to the type of dentin substrate used: Sound dentin and caries affected dentin. For the Scanning Electron Microscope (SEM) examinations, the teeth were divided into two main groups (8 each) according to the bonding mode used: Self-etch mode in one step single dose, and total-etch mode in two steps. Each group was then subdivided into two subgroups (4 specimens each) according to the type of dentin substrate used: sound dentin and caries affected dentin. The interfacial zone was examined using SEM at magnification 5000 X. Data was then recorded, tabulated and statistically analyzed. For sound dentin using total-etch mode (24.02 ± 1.03 MPa) showed statistically significantly lower µSBS than that using self-etch mode (28.04 ± 1.30 MPa) at p<0.05. For caries affected dentin using total-etch mode (18.46 ± 0.86 MPa) showed statistically significantly higher mean µSBS than that using self-etch mode (16.48 ± 0.84 MPa) at p<0.05. Independent of the etch mode used for bonding, sound dentin showed statistically significantly higher mean µSBS than that of caries affected dentin at p<0.05. These results were confirmed by the examination of the SEM images which revealed increase in number and length of resin tags for the groups showing high µSBS. In conclusion, using self-etch universal adhesives on sound dentin is considered to be material dependent. And using total-etch mode of universal adhesive on caries affected dentin can enhance bond strength. Moreover, the type of substrate and etching strategies may affect the bonding performance and durability of restorations in dentistry.