Background The aim of the study was to investigate the effect of material and occlusal preparation design on the internal fit and marginal gap of endocrowns made of Polyether ether ketone (PEEK) and lithium disilicate. Methods 32 endocrowns were fabricated on prepared mandibular molars and divided into two groups (n = 16) according to the material. Group L: lithium disilicate and Group P: PEEK. Each group was further subdivided into two subgroups (n = 8) according to the occlusal preparation design: full occlusal coverage (LF and PF) and partial occlusal coverage (LP and PP). Samples were analyzed using microcomputed tomography (µCT) with a voxel size of 6 μm to evaluate internal fit, and an optical microscope was used to evaluate the marginal gap. Data were collected, tabulated, and statistically analyzed. Numerical data were described as mean and standard deviation and compared using the ANOVA test. The level of significance was set at α P ≤ 0.05. Results All groups’ internal fit and marginal gaps values were within the acceptable clinical range. However, the lithium disilicates group recorded statistically significantly higher mean internal gap values than the PEEK groups. Regardless of the material, the difference between the two occlusal designs was not statistically significant in both internal fit and marginal gap records. Conclusion Within the limitations of this study, PEEK endocrown restorations revealed better internal fit and marginal gap than lithium disilicate endocrown restorations. The marginal and internal fit of both lithium disilicate and PEEK endocrown restorations were within the clinically acceptable range. The occlusal preparation design had no influence on the internal fit and marginal gap of the endocrown restoration.

Objectives: This study aimed to evaluate the effect of artificial aging and immersing solutions on the color stability and surface roughness of polyether ether ketone material in relation to surface polishing and glazing.Materials and Methods: a total number of 80 plates were sliced out of reinforced polye ther ether ketone PEEK blanks. The samples were divided into two main groups according to polishing and glazing protocols (n=40) then each group was further divided into four subgroups according to the artificial aging and staining protocols (n=10). Artificial aging was done by aging by exposure to light for 120 min and water spraying for 18 min under artificial daylight (D65 illuminant). For staining, samples were subjected to thermos-cycling in colored solutions (coffee and cola) at different temperatures (50˚C and 5˚C). The average color difference (ΔE) was calculated, profilometer was used to measure the Surface roughness. The Kruskal-Wallis test was used to statistically analyze the data. The significance level was set at P ≤ 0.05. Results:The mean values of the average color difference revealed that artificial aging and staining significantly affected PEEK color stability and surface roughness.Conclusions: artificial aging and staining have a noticeable effect on the surface roughness and color stability of Polyether ether ketone material. Also, the Glazing of Polyether ether ketone has better surface roughness and color stability results.

Purpose:The bond strength between ceramics and tooth structure is affected by the degree of polymerization of resin cement. This study evaluated the effect of two light curing modes on polymerization of light cured resin cement through three lithium silicate-based ceramics (Lithium disilicate-reinforced glass ceramic (E.max CAD), Zirconia reinforced Lithium Silicate (Celtra Duo). And Zirconia reinforced Lithium Silicate (Vita Suprinity) with two shades (A2 and B1) and two ceramic thickness (0.5 and 1mm). Materials and methods:Two hundred forty ceramic samples (n=240) were divided into three main groups (n=80) according to the material. Each group was subdivided into 2 subgroups (n=40) according to ceramic shade (A2 and B1). Each subgroup was subdivided into 2 divisions (n=20) according to thickness (0.5mm and 1mm). Then each division was subdivided into two subdivisions (n=10) according to light curing method (Continuous and pulsating light curing). Samples cemented and scanned using OMNIC 5.1c software connected to the FTIR unit. Results:The results illustrated that there was no statistical significance difference in degree of conversion between the three ceramic materials. A higher degree of conversion was recorded with B1 ceramic shade than A2 shade. Also, there was a significant effect on the degree of conversion (DC%) with different thicknesses of the ceramic materials and there was a higher degree of conversion in the continuous light curing mode than the pulsating mode. Conclusions:Within the limitations of this study, the results indicated that with respect to the ceramic thickness used, the ceramic type did not affect the degree of conversion of light cured resin cement. On the other hand, thicknesses up to 1.0 mm have a significant effect on the polymerization of resin cements. Higher degrees of conversion were shown with lighter ceramic shades. Also, mode of light curing had a pronounced effect on the degree of conversion of resin cements (3638)