Evaluation of changes in different force directions of zirconium framework ceramic restorations applied to the implants placed at four different angles in maxilla and mandibula by three-dimensional modeling and finite element analysis.

In order to ensure an ideal stress distribution in dental implants, the forces on implants must be parallel to the long-axis of the implant. Otherwise, depending on over-load, it will be probable to observe resorption in the bone that surrounds the implant. However, it is not always possible to place the forces on implants with the desired angle due to many factors in the mouth including anatomical ones. In some cases in which the occlusal surface is sloping, the forces are decomposed into their vertical and horizontal components and therefore cause over-loading on certain locations other than the long-axis of the implant. Along with the implant material, implant design and osseointegration; prosthetic approaches have also a profound effect particularly on the stress distribution of the implant and the bone surrounding it. In implant-supported fixed prosthetic restorations; many materials such as metal-ceramic, zirconium-ceramic or full ceramic, precious metal alloys, acrylics, fibre-aided resins are used. However, recently, due to its mechanic and aesthetic features, zirconium-ceramic restorations have become more popular. In implant-supported fixed partial denture, while deciding the material and design of framework, one should consider both functional factors and aesthetic expectations of the patient. Moreover, it is also vital to be aware of biomechanical features of the material that will be used in prosthetic dentistry applications. So as to examine biomechanical features of the dental implant and implant-supported restorations and to analyse the angle of implant locations, finite elements stress analysis method (FEM) is quite useful in that it provides a unique three-dimensional opportunity for examining mechanical stress distribution in pre- and post-treatment processes of craniofacial structures. In this in vitro study; two dental implants with the same length (10 mm) but different diameters (3,7 mm, 4,7 mm) are applied into maxilla and mandible with four different angles (vertical, 15°, 30° and 45°). As a result, 16 experimental models are obtained. Then, in the same virtual environment, abutment and zirconium-supported ceramic crowns are placed into all implants. From certain points of zirconium-supported ceramic crowns, steep and oblique forces are separately applied and totally 32 study groups are obtained. As a result of the forces applied, certain stress values have emerged in implants, zirconium frameworks and feldspathic porcelain. Finally, these von Misses stress values are examined by using three-dimensional finite elements stress analysis method (FEM).