To study the precise stress distribution of the apical foramen area of endodontic endosseous implant, and improve the prosthetics of endodontic endosseous implant. After analysis of the two-dimensional endodontic endosseous implants model with finite element method, left right areas beside the apical foramen were selected as infinite domains to calculate. D-N iterative method was used to connect the finite and infinite domains. Under 45 o axial right oblique loading, the center of the tooth rotational movement descended downward to the implant outside the apical foramen of root. The stress concentration occurred in both infinite domains of the apical foramen. The infinite domain at the right side was tension stress concentration but the other side was compression stress concentration. Two stress concentration points were just at the central points, which were intersections between implant and dentin. In the implant and dentin section, the stress reduced in all directions from these two stress concentration points, but in the ligament, the results were contrary. The movement of the rotational center of restoration is helpful to the tooth stabilization and carrying capacity after restoration. In the implant area the diameter of implant at the apical foramen of root shall not be reduced to protect root in clinical work It is very important to preserve the tissue of ligament for endodontic endosseous implants.
Porcelain-fused-to-metal (PFM) is playing a very important role in prosthetics dentistry. The bond strengths in metal-ceramic system have been focused on, since the method of PFM was used to prosthetics. In this paper, the thermal residual stress effects on metal-ceramic bond were considered during cooling of porcelain-fused-to-metal restoration to analysis the metal-ceramic bond stresses. The ISO crack initiation test specimen (three-point flexure bond test) was simulated by finite element method. The analysis was implemented in two steps. In the first step, the porcelain was assumed as viscoelastic material (720℃-550℃), while in the second step the porcelain was as elastic body (550℃-25℃). The results show that the compressive stress caused by difference of thermal expansion coefficients of two materials during cooling occurs in the ceramic. The shear stress induced by mechanical load is offset by thermal shear stress. The mechanical tensile stress and the thermal compressive stress normal to interface are concentrated at the end of the bond interface, but the tensile stress is much higher. It is clear that the thermal residual stresses are very important to metal-ceramic restorations, and it is greatly affected by the viscoelastic behavior of porcelain. This also indicates a higher probability of failure produced by the tensile stress rather than by shear stress.
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