Objective: to evaluate the effect of bar and clip attachment systems with different materials on retention forces for two implant supported mandibular over dentures after wear simulation. Materials and methods: An edentulous mandibular model was constructed incorporating 2 parallel implants placed in the canine regions. Attachments were embedded in ametal-reinforced experimental over denture designed to be dislodged from the model by a universaltesting machine. Tensile dislodging force was applied to the overdenture at a cross-head speed of 50 mm/min. Four over dentures were constructed for the attachment systems. The attachments evaluated were metal bar with clip from polyoxymethylene (POM), metal bar with clip from polyetheretherketon (PEEK), (PEEK) bar with (POM) clip and(PEEK) barwith (PEEK) clip. Peak loadto-dislodgement was measured. Retention strength values (N) were recorded initially and after 270, 540, 810 and 1080 cycles of insertion and removal simulating 0, 3, 6, 9 and 12 months of denture using repictively. Repeated measure ANOVA was used to compare between more than two groups for dependent samples while One-way ANOVA was used to compare between more than two groups for independent samples. The significance level was set at P ≤ 0.

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Objective: To study the color stability of some denture teeth materials (acrylic &porcelain) and to evaluate some mechanical properties of these denture teeth materials.Material and methods: Forty samples of both acrylic and porcelain teeth were immersed in three staining solutions and distilled water. Color measurements were performed by using spectrophotometer. Before immersion, the initial color value of each tooth was recorded. Color change values were determined after 1 day, 1 week, 2 weeks, 4weeks and 6 weeks of immersion. Color differences were characterized using the CIE L*a*b* color space. Also water sorption and surface roughness were evaluated. Results:showing significant color changes of the different denture teeth materials upon immersion in tea, coffee, cola, or distilled water. This color change was greater in case of immersion in either tea or coffee solutions. The least color change was obtained from samples immersed in distilled water. The different materials used showed no significant statistical difference in water sorption values. Finally the results showed that, there were significant statistical differences in surface roughness of all tested materials after immersion in any of the tested solutions. Conclusion:The acrylic denture teeth material is much more subjected to discoloration than the porcelain denture teeth material. Water sorption of the tested materials was of close values. Surface roughness of the denture teeth material show significant statistical difference by immersion in staining solutions.