To evaluate the effect of different oral media (artificial saliva, carbonated orange juice and coffee) on the surface roughness and color stability of 3D printed temporary material. Methodology: twenty one discs samples were designed using additive manufacturing technique (SLA) were divided into 3 groups and stored in artificial saliva, coffee and carbonated orange juice at 37 ℃. Surface roughness was measured before and after immersion using non-contact USB Digital microscope. Color measurements were made before and after immersions using CIE L*a*b*. Data was analyzed by ANOVA followed by Tukey's pair-wise tests. Results: After two, three and twelve weeks of immersion period there was statistically significant difference between the three tested oral media groups regarding the surface roughness. The highest ΔE values were observed in the coffee (3.58, 4.40 and 10.35 ΔE) followed by Carbonated orange juice mean values (3.29, 3.84 and 7.18 ΔE) while the lowest color changes mean values were for A. Saliva immersed group (1.91, 2.29 and 2.98 ΔE) respectively. Conclusions:1. All different oral media (except A.saliva) used in the present study affected the surface roughness and the color stability of Interim discs constructed using 3-D printing technique. 2. Manufacturing of interim crowns using 3-D printing technique could be used for short-term provisional restoration. 3. This study has shown a strong positive correlation between color change and surface roughness of provisional restorative material.

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This paper proposes a new topology for single-phase photovoltaic PV grid-tied applications. The whole system consists of a two-stage, high-frequency boost inverter cascaded by rectifier-inverter system. A single-phase high-frequency transformer is used to link both stages and provide galvanic isolation between the AC and DC sides. A single-stage high-frequency boost inverter (HFBI), in the first stage, boosts and converts the DC output voltage of the PV array to a high-frequency single-phase square waveform and achieves maximum power point tracking (MPPT). In the second stage, the rectifier-inverter system (RIS) interfaces HFBI to the grid. The proposed topology has many advantages such as increasing the inverter output voltage level, MPPT, high reliability, small size, and light weight. In addition, a proportional integral current control (PI) is used to inject a sinusoidal current into the grid at unity power factor. The proposed topology has been verified analytically using PSIM software and experimentally by using a laboratory prototype.