Effects of implant diameter, implant-abutment connection type, and bone density on the biomechanical stability of implant components and bone: A finite element analysis study.

STATEMENT OF PROBLEM: Various kinds of implants of different diameters and connection types are used for patients with a range of bone densities and tooth sizes. However, comprehensive studies simultaneously analyzing the biomechanical effects of different diameters, connection types, and bone densities are scarce. PURPOSE: The purpose of this 3-dimensional finite element analysis study was to evaluate the stress and strain distribution on implants, abutments, and surrounding bones depending on different diameters, connection types, and bone densities. MATERIAL AND METHODS: Twelve 3-dimensional models of the implant, restoration, and surrounding bone were simulated in the mandibular first molar region, including 2 bone densities (low, high), 2 implant-abutment connection types (internal tissue level, internal bone level), and 3 implant diameters (3.5 mm, 4.0 mm, and 4.5 mm). The occlusal force was 200 N axially and 100 N obliquely. Statistical analysis was performed using the general linear model univariate procedure with partial eta squared (ηp2) (α=.05). RESULTS: For bone tissue, low-density bone induced a larger maximum and minimum principal strain (in magnitude) than high-density bone (P<.001). As the implant diameter increased, the volume of the cancellous bone in low-density bone at the atrophy region (strain<200 µÎµ) increased (P<.001). For implant and abutment, the internal bone-level connection type was associated with increased peak stress as compared with the tissue-level connection type (P<.001). For all models, the stress distribution on the implant complex was influenced by implant diameter (P<.001): a decrease in implant diameter increased the stress concentration. CONCLUSIONS: The implant connection type had a greater impact on the stress of the implant and abutment than the diameter. A tissue-level connection was more advantageous than a bone-level connection in terms of stress distribution of the implant and abutment. Bone density was the most influential factor on bone strain. The selection of dental implants should be made considering these factors and other important factors including tooth size.

Stress analysis of intervertebral disc during occupational activities.

BACKGROUND AND OBJECTIVE: Manual material handling activities cause large compression of the intervertebral disc of the lumbar spine. Intradiscal pressure (IDP) has generally been employed to predict the risk of low back injury. As an alternative to in vivo measurements, either motion analysis or finite element (FE) analysis has been used to estimate IDP. The purpose of this study is to propose a new biomechanical method that integrates FE analysis with motion analysis, in order to estimate the stresses and deformations of the intervertebral disc of the lumbar spine during occupational activities. METHODS: In the proposed method, motion analysis is performed first by using motion capture data, and the results are employed as input data to FE analysis at specific times of interest during motion. In this method, an in-house interface program is used to scale an initial reference FE model to the subject of experiment, and transformed to the corresponding posture at a specific time during motion. The muscle forces and GRF obtained from motion analysis are applied to FE analysis as boundary and loading conditions. For a total of eighteen occupational activities, the IDP, shear stress, and strain of the L4-L5 segment are estimated. RESULTS: Under each in vivo activity, the predicted IDP was in overall agreement with the available in vivo data. For lifting activities according to lift origin position, the maximum IDP occurred in the far-knee position immediately after lifting. As the lift origin position moved away from the spine, the stresses and strains in the disc increased. CONCLUSIONS: This new proposed method is expected to allow the estimation of the stresses and deformations in the intervertebral disc during various occupational activities.

Biomechanical effects of dental implant diameter, connection type, and bone density on microgap formation and fatigue failure: A finite element analysis.

BACKGROUND AND OBJECTIVE: Understanding fatigue failure and microgap formation in dental implants, abutments, and screws under various clinical circumstances is clinically meaningful. In this study, these aspects were evaluated based on implant diameter, connection type, and bone density. METHODS: Twelve three-dimensional finite element models were constructed by combining two bone densities (low and high), two connection types (bone and tissue levels), and three implant diameters (3.5, 4.0, and 4.5 mm). Each model was composed of cortical and cancellous bone tissues, the nerve canal, and the implant complex. After the screw was preloaded, vertical (100 N) and oblique (200 N) loadings were applied. The relative displacements at the interfaces between implant, abutment, and screw were analyzed. The fatigue lives of the titanium alloy (Ti-6Al-4V) components were calculated through repetitive mastication simulations. Mann-Whitney U and Kruskal-Wallis one-way tests were performed on the 50 highest displacement values of each model. RESULTS: At the implant/abutment interface, large microgaps were observed under oblique loading in the buccal direction. At the abutment/screw interface, microgap formation increased along the implant diameter under vertical loading but decreased under oblique loading (p < 0.001); the largest microgap formation occurred in the lingual direction. In all cases, the bone-level connection induced larger microgap formation than the tissue-level connections. Moreover, only the bone-level connection models showed fatigue failure, and the minimum fatigue life was observed for the implant diameter of 3.5 mm. CONCLUSIONS: Tissue-level implants possess biomechanical advantages compared to bone-level ones. Two-piece implants with diameters below 3.5 mm should be avoided in the posterior mandibular area.

Donor-set-induced coordination sphere and oxidation-state switching in the copper complexes of O2S2X (X = S, O and NH) macrocycles.

Reaction of the O(2)S(2)X-macrocycles (L(1), X = S; L(2), X = NH; and L(3), X = O) with Cu(ClO(4))(2) x 6 H(2)O affords 1:1 (M/L) square-pyramidal Cu(II) complexes when X = S and NH but yields a rare 1:2 sandwich-type tetrahedral Cu(I) complex when X = O; the X-ray structures of all three complexes are reported. Substitution of O for S or NH in the ligand structure thus results in a donor-set-induced II/I oxidation state change of the copper, and this is accompanied by a square-pyramidal to tetrahedral topological change in the solid state. Spectrophotometric titration data (including Job plots) indicate that similar behavior occurs in acetonitrile. In further experiments aimed at investigating the generality of the above redox behavior, it was shown that the 16- and 18-membered analogs of the 17-membered L(3) also induce a similar II/I redox change in acetonitrile. It was demonstrated for L(3) that the above-induced Cu(II/I) change is also maintained when the reaction solvent is changed from acetonitrile to methanol or ethanol.

Supramolecular copper(I) halide complexes of O2S2X (X = S, O and NH) macrocycles exhibiting dinuclear, 1D- and 2D-coordination polymeric structures.

The effect of varying donor X in otherwise structurally similar O(2)S(2)X-macrocycles (L(1): X = S, L(2): X = O and L(3): X = NH) on the corresponding assembly reactions with Cu(I) halides has been demonstrated to yield three supramolecular complexes with different architectures: L(1) resulted in a discrete dimeric complex (1), while L(2) and L(3) gave respectively 1D (2) and 2D (3) coordination polymers; the solid state photoluminescence of 3 is also described.