Objective: to study the effect of using two cement types, with three different thicknesses, on stress levels and distributions within bone around implant premolar using three-dimensional Finite Element Analysis techniques. Materials & methods: A three 3D Finite Element models were built for this purpose. Threaded titanium dental implant was implemented in simplified geometry for jaw bone. While the crown geometry, was acquired by 3D scanner. Two cement materials (Zinc phosphate, Glass Ionomer), with three values of cement layer thicknesses (20, 40, and 60 mm) were investigated. Twenty-four case studies were reported within this research. Each case was analyzed under vertical and oblique loading at Palatal Cusp Tip and Central Fossa. Results: Linear static stress analysis was performed. The results of the model showed the superiority of 60 mm thickness cement layer over the other two thicknesses. Conclusions: Using thicker cement layer increase its lifetime, in addition to reducing the cortical bone Von Mises stress. While, the effect of cement layer thickness and type on spongy bone, is negligible.

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This study aimed to evaluate the role of gingival thickness on stress distribution of implants-retained mandibular complete overdenture using finite element method. A computer aided design (CAD) software and finite element analysis (FEA) software were utilized to construct three dimensional (3D) models on a personal computer to analyze the proposed problem. The three models had different gingival thicknesses ranged 1, 2, and 3mm. Unilateral masticatory loads of 150 N were applied on overdenture in a vertical direction, parallel to the longitudinal axis of the implant, and 45 o oblique. Loads were directed towards the central fossa in the molar region of the overdenture to form six load cases. Location of maximum Von Mises stress on gingival tissue was found at the model tip close to the load application point where the overdenture and cortical bone squeezed the gingival tissue.

Statement of problem:The clinical success of the ceramic restoration system that is strongly bonded to the tooth structure in order to prevent microleakage, marginal fracture, discoloration, and secondary caries. Which do types of cements and surface treatment considerably influence. Purpose: This study investigated the shear bond strength between three all ceramic systems (CAD-CAM CEREC type, The VM7( VITADURVEST) powder, and IPS Empress II) treated by air abrasion and hydrofluoric acid, then cemented to tooth structure by two types of adhesive resin cements. Material and methods: Ninety freshly extracted human lower third molar teeth were used. Each tooth was free of caries or restorations. Teeth were embedded into autopolymerizing resin limited to their cervical line using dental surveyor. The occlusal third of the molars was grounded using diamond stones under water coolant to make dentin discs with smooth and flat surface. Ceramic discs with 5mm diameter and 3mm thickness of three types of all ceramics and two types of chemically cured resin cements were used.All specimens were randomly divided into three groups of 30 teeth each according to the ceramic used. Each group are divided into three subgroup(n=10). The bonding surfaces of each ceramic discs of each subgroup are treated with one of the following: 9% hydrofluoric acid, Airborne particle abrasion with 50 μm grain sized aluminum oxide particles and Air abraded with 50 μm grain sized aluminum oxide particles and etched in 9% hydrofluoric acid .The ceramic disks were bonded to the flattened molars using one of the two types of the resin cement used in this study. All samples were mounted on a computer controlled materials testing machine with a load cell of 5 KN and their data were recorded using computer software. Results: The results of the present study showed the following mean loads at fracture: the Cerec type (7.56+1.96 N), VM7 (6.21+0.99 N) and Empress II (6.96+1.72 N) .ANOVA and Tukey's post-hoc test showed that the differences between these all ceramics types were statistically nonsignificant (p>0.05). However the CAD-CAM Cerec blocs gave the highest mean of Codex : 21/1704