الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
”Statement of problem: Rehabilitation of endodontically treated premolar teeth through endocrown approach remains a controversial topic in reconstructive dentistry. To date and despite the increased popularity of endocrowns, there is no clear consensus in the literature considering their effectiveness to restore endodontically treated premolar teeth with extensive loss of tooth structure. Aim of the study : To assess the biomechanical and clinical behaviors of severely-destructed endodontically treated maxillary first premolar teeth restored with a novel endocrown system compared to the conventional one. Materials and methods: For In-vitro testing: twenty sound human maxillary first premolars with homogenous morphology were selected, endodontically treated, and divided into two equal groups (n = 10) according to the system used for endocrown fabrication ; group (C) : conventional monolithic IPS e.max CAD endocrowns, and group (P): novel bi-layered endocrowns with PEKKTON ivory coping veneered with cemented IPS e.max CAD. All cemented specimens were exposed to artificial aging protocol simulating one year of clinical service. All surviving specimens were subjected to fracture resistance testing followed by qualitative analysis using Stereomicroscopy and Scanning Electron Microscopy. For Finite Element Analysis, two models representing both endocrown systems were generated: model (C) for the conventional and model (P) for the novel. A static occlusal compressive load was axially and centrally applied. Modified von Mises and maximum principal stress values on the remaining tooth structure, cement lines and restorative materials were evaluated. Weibull function was incorporated to calculate the long-term failure probability. Clinically, twenty eligible patients were selected and divided into two equal groups (n = 10); group (C) receiving the conventional endocrowns and group (P) receiving the novel. All endocrowns were evaluated based on Modified FDI criteria at baseline, 3, 6, 12 and 18 months. Resulted data were statistically analyzed at p-value ≤ 0.05. Results: A significantly higher load-to-failure was recorded for novel group (P) (1831.37 ± 240.69 N) compared to the conventional group (C) (1433.47 ± 174.39 N). A statistically significant difference was observed between tested groups considering the failure mode (p = 0.036), with more favorable fractures detected with novel group (P). Regarding stresses occurred in the remaining tooth structure (enamel and dentin), model (P) transmitted less stresses than model (C). The individual enamel of model (C) showed about 5% and 40% risk of failure at normal and maximum occlusal load values, respectively, while for model (P), it had no failure risk at both values. For dentin, model (C) showed about 13% failure risk at the normal masticatory force, while model (P) showed only 2%. At clenching value, model (C) dentin showed about 44% failure risk, while only 9% was resulted for model (P). Clinically, FDI scores 4 and 5 were not observed throughout the study period for all evaluated criteria. No endocrown required repair or replacement, resulting in 100% survival rate for both studied groups. Conclusions: Compared to the conventional endocrown system, the studied novel system improved the biomechanical behavior (failure behavior and stress distribution) of the tooth/restoration complex in the restored endodontically treated maxillary first premolar teeth. Clinically after 18 months, both systems presented comparable clinical behavior with acceptable final esthetic, functional, and biological outcomes. ”