FE study of bone quality effect on load-carrying ability of dental implants.

Extreme stresses in surrounding bone are among the most important reasons for implant failure. Bone density (quality) is a variable that plays a decisive role in achieving predictable osseointegration and long-term survival of implants. The magnitudes of ultimate occlusal load, which generate ultimate von Mises stress at the critical point of peri-implant area for the spectrum of implants inserted into mandible with four different bone qualities (Lekholm and Zarb classification), were calculated. Geometric models of mandible segment were generated from computed tomography images and analysed with osseointegrated cylindrical implants of various dimensions. Occlusal loads were applied in their natural direction. All materials were assumed to be linearly elastic and isotropic. The investigation suggests that an implant's ultimate occlusal load indicates its load-carrying capacity. As a result, bone loss can be predicted, and viable implants can be selected by comparing the values of their ultimate occlusal load in different clinical conditions.

Importance of diameter-to-length ratio in selecting dental implants: a methodological finite element study.

Implant dimensions greatly influence load transfer characteristics and the lifetime of a dental system. Excessive stresses at peri-implant area may result in bone failure. Finding the critical point at the implant-bone interface and evaluating the influence of implant diameter-to-length ratio on adjacent bone stresses makes it possible to select implant dimensions. For this, different cylindrical implants were numerically analysed using geometrical models generated from computed tomography images of mandible with osseointegrated implants. All materials were assumed to be linearly elastic and isotropic. Masticatory load was applied in its natural direction, oblique to occlusal plane. Maximum von Mises stresses were located around the implant neck at the critical point of its intersection with the plane of loading and were functions of implant diameter-to-length ratio. It was demonstrated that there exists a certain spectrum of diameter-to-length ratios, which will keep maximum bone stresses at a preset level chosen in accordance with patient's bone strength.

Ultimate masticatory force as a criterion in implant selection.

Osseointegrated implants often fail because of excessive masticatory forces that cause extremely large stresses in bone tissue. We hypothesized that a proper dental implant could be selected by comparing the ultimate masticatory forces of a wide range of commercially available implants. We determined ultimate oblique masticatory forces for different cylindrical implants, taking into consideration the biomechanical correlation between implant dimensions and stresses in supporting bone. For this purpose, we used the finite element (FE) method and studied von Mises stresses in implant-bone interface areas to evaluate the influence of implant dimensions on stress concentration and on the value of an implant's ultimate masticatory load. Geometric models of a mandibular segment were generated from computed tomography (CT) images and were analyzed with osseointegrated cylindrical implants. Masticatory forces were applied in their natural direction. All materials were assumed to be linearly elastic and isotropic. Critical point in the peri-implant area of bone was determined. The ultimate value of the masticatory load, which generates ultimate stresses at the critical point, was calculated for each implant. These findings provide correct selection of implant dimensions in clinical cases, because corresponding ultimate values of masticatory force were used as a criterion for assessment of their load-carrying capacity and applicability.

[A method for the luminescence microscopy of the thrombocytes in the diagnosis of hemostatic disorders in patients with cerebral atherosclerosis]. / Metod liuminestsentnoi mikroskopii trombotsitov v diagnostike narushenii gemostaza u bol'nykh tserebral'nym aterosklerozom.

The authors evaluated the diagnostic importance of morphological properties of thrombocytes in patients with cerebral atherosclerosis. The proposed method consists in vital staining of thrombocytes in the blood plasma by means of acridine arrange, their fixation, application of a smear, microscopy in ultraviolet rays with determination of the ratio of thrombocytes of separate classes according to the intensity of luminescence of cellular alpha-granules and presence of aggregates. The method may be used for the prognosis of thrombotic complications in patients with atherosclerotic dyscirculatory encephalopathy and controlling the efficacy of therapy by antiaggregant agents.