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Background and aims. Expansion of maxillary sinus towards the alveolar crest due to tooth loss or horizontal‒vertical resorption of the alveolar bone decreases the available bone for the placement of dental implants in the posterior maxilla. The method suggested for placing implants with a standard length is the use of sinus lift surgery with autogenous bone graft or bone substitute materials. The aim of the present research, with split-mouth design, was radiographic comparison of the density and height of the posterior of maxillary bone after open sinus lift procedure with and without PRF. Materials and methods. In this split-mouth clinical trial, 14 patients were evaluated, with complete or partial bilateral edentulism of the upper jaw. In each case, for the sinus lift surgery of the test side, PRF was used, while in the sinus lift surgery of the other side of the same patient no graft materials were used. After six months and before the second surgery, CBCT was used to evaluate bone density and height. Results. All the 41 implants were osseointegrated and were clinically stable. The bone height was 1.42 mm higher in the PRF group than the group without PRF, which was statistically significant. The mean density of the bone formed around the dental implants in the PRF group was 52.85 units higher than that of the group without PRF, which was statistically significant. Conclusion. Using PRF in sinus lift surgery might enhance the quantity and quality of bone formation.

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BACKGROUND Laminate veneers have been introduced as a successful and reliable technique for treating malformed, yellow, or chipped teeth. However, mechanically speaking, their success is questionable. The main reason for the failure of laminate veneer treatments is their fracture. The present study aims at improving the mechanical features of laminate veneers by investigating the factors affecting the success of this treatment through a finite element analysis (FEA). MATERIALS AND METHODS For assessing the distribution in the laminate veneer of maxillary central incisor under different clinical conditions, first a healthy natural maxillary central incisor was prepared, and it was scanned by a 3D Scanner. Then, Window finish line design was defined virtually in the software; feathered incisal edge and overlapped incisal edge were defined virtually. The scanned tooth was modelled in SOLIDWORKS 2015, and it was then entered into ABAQUS FEA which is an analytical software. Finally, the maximum stress tolerated in each of these conditions as well as the stress level distribution were recorded and described in different points of laminate veneers. RESULTS The present results showed that in comparison with other preparation designs, Window preparation design creates more tension in the teeth. Moreover, according to the findings obtained from the finite element analysis, overlapped incisal edge preparation creates the most tension in porcelain. In all kinds of preparations, the amount of tension imposed on the cement was significantly less than the tension imposed on teeth and porcelain. CONCLUSION It can be concluded that, the preparation, cement thickness, and the angle of the forces applied will significantly change the maximum internal tension of teeth, porcelain, and the related cement.

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