In vitro comparative study on the mechanical behavior of Zirconia and Polyetheretherketone in applied dental sciences.

OBJECTIVE: Recently, Zirconia and polyaryletherketone (PEEK) have attracted increasing interest as reliable and safe materials in dental applications, mainly because of their good biomechanical characteristics. The aim of this study was to investigate the response to different loads by prosthetic frameworks for supported fixed partial dentures (FPDs), thus simulating osseointegrated implants. MATERIALS AND METHODS: The specimens were divided into two groups (n= 5 each). Group A: FDPs in zirconia-ceramic; Group B: FDPs in PEEK-composite. These 2 groups were subjected to vertical loads so to evaluate structural deformation; then, they have been analyzed by scanning electron microscopy (SEM) at different magnifications. RESULTS: In tested samples, different types of mechanical failures have been observed. In Zirconia-specimens, chipping is the main failure noticed in this study, mostly in distal margins of the structure. Also, peek-specimens show failure and fracture. CONCLUSIONS: Zirconia and PEEK could be considered both good materials, but several investigations are needed to use these materials as an alternative to metals for fixed partial dentures.

Three-point bending test simulation on implant fpds with a bio-faithful model.

AIM OF THE STUDY: It is well known by previous important studies that mandible flexes during different jaw movements. According to this assumption it is very important to know how implant supported fixed partial dentures could restrict mandibular movements and, could lead to excess strain accumulation that could modify the resolution of implant treatment. The aim of our project is to create a bio-faithful model able to recreate mandibular movements, during three point bending test methods of (FIXED -PARTIAL -DENTURES) FPDs, to avoid a not flexible metal base, where models' properties doesn't allow to obtain a bio-faithful simulation during testing phases. MATERIALS AND METHODS: 2 implants (premium Sweden and Martina®) were embedded in mandible resin section to mimic osteointegrated implants in premolar and molar areas, in order to recreate a Kennedy Class II configuration. Our mandible test simulator was creating according to the measurement obtained according to the study of Schwartz-Dabney and Dechow (2002). Sample so created is tested with testing machine (Instron 5566®, UK) adopting the three point bending mechanical tests configuration. DISCUSSION AND CONCLUSION: We can admit that oral cavity is a bio-dynamic system, where different variables incurr, so it's very important that experimental conditions simulate clinical environment. Experimentation should be based on the correlation between the failure mechanisms exhibited for in vitro samples and those observed in fractured clinical prostheses made of the same composition and processing conditions. A bio-faithful model could reduce this wide range between in vitro and in vivo study experimentation.

Sem analysis zirconia-ceramic adhesion interface.

OBJECTIVES: Modern dentistry increasingly tends to use materials aesthetically acceptable and biomimetic. Among these are zirconia and ceramics for several years, a combination that now has becoming synonym of aesthetic; however, what could be the real link between these two materials and especially its nature, remains a controversial topic debated in the literature. The aim of our study was to "underline" the type of bonding that could exist between these materials. MATERIALS AND METHODS: To investigate the nature of this bond we used a SEM microscopy (Zeiss SUPRA 25). Different bilaminar specimens: "white" zirconia Zircodent® and ceramic "Noritake®", after being tested with loading test in bending (three-point-bending) and FEM analysis, were analyzed by SEM. Fragments' analysis in closeness of the fracture's point has allowed us to be able to "see" if at large magnifications between these two materials, and without the use of linear, could exist a lasting bond and the possible type of failure that could incur. RESULTS: From our analysis of the specimens' fragments analyzed after test Equipment, it is difficult to highlight a clear margin and no-adhesion zones between the two materials, although the analysis involving fragments adjacent to the fracture that has taken place at the time of Mechanical test Equipment. CONCLUSIONS: According to our analysis and with all the clarification of the case, we can assume that you can obtain a long and lasting bond between the zirconia and ceramics. Agree to the data present in the literature, we can say that the type of bond varies according to the type of specimens and of course also the type of failure. In samples where the superstructure envelops the ceramic framework Zirconium we are in the presence of a cohesive failure, otherwise in a presence of adhesive failure.

Palatal obturators in patients after maxillectomy.

Prosthodontic management of palatal defects is fundamental to improve patient's life undergoing to a maxillary surgical treatment. A lot of maxillary defects are a direct consequence of surgical treatment of malformations, neoplasms or trauma. The obturators are prosthesis used to close palatal defects after maxillectomy, to restore masticatory function and to improve speech. The primary goals of the obturator prosthesis are to preserve the remaining teeth and tissue and to provide comfort, function, and aesthetics to the patients. Different materials and retention methods are a characteristic of new types of obturators.

Mechanical evaluation and fem analysis of stress in fixed partial dentures zirconium-ceramic.

OBJECTIVE: Over the last several years, the Finite Element Analysis (FEM) has been widely recognized as a reference method in different fields of study, to simulate the distribution of mechanical stress, in order to evaluate the relative distribution of loads of different nature. The aim of this study is to investigate through the FEM analysis the stress distribution in fixed prostheses that have a core in Zirconia and a ceramic veneer supported by implants. MATERIALS AND METHODS: In this work we investigated the mechanical flexural strength of a ceramic material (Noritake(®)) and a of zirconium framework (Zircodent(®)) and the effects of the manufacturing processes of the material commonly performed during the production of fixed prostheses with CAD/CAM technology. Specifically three point bending mechanical tests were performed (three-point-bending) (1-3), using a machine from Test Equipment Instron 5566(®), on two structures in zirconium framework-ceramic (structures supported by two implant abutments with pontic elements 1 and 2). A further in-depth analysis on the mechanical behavior in flexure of the specimens was conducted carrying out FEM studies in order to compare analog and digital data. RESULTS: The analysis of the data obtained showed that the stresses are distributed in a different way according to the intrinsic elasticity of the structure. The analysis of FPD with four elements, the stresses are mainly concentrated on the surface of the load, while, in the FPD of three elements, much more rigid, the stresses are concentrated near the inner margins of the abutments. The concentration of many stresses in this point could be correlated to chipping (4) that is found in the outer edges of the structure, as a direct result of the ceramic brittleness which opposes the resilience of the structure subjected to bending. CONCLUSIONS: The analysis of the UY linear displacement confirms previous data, showing, in a numerical way, that the presence of the ceramic is related to the lowering of the structure. So, the reference values are those of the linear lowering obtained in the Mechanical Test and in our FEM analysis. zirconium framework with four elements 4,227 10(-2)mm.zirconium framework with ceramic structure with four elements 2,266 10(-2) mm.That suggests that the presence of ceramics halves the flexion capabilities of the prosthetic materials.