Towards the Optimal Crown-to-Implant Ratio in Dental Implants

2017 ◽  
Author(s):  
T. J. Sego ◽  
Yung-Ting Hsu ◽  
Tien-Min Gabriel Chu ◽  
Andres Tovar
Keyword(s):  
Dental Implants ◽  
Strain Distribution ◽  
Mechanical Stability ◽  
Element Model ◽  
Equivalent Strain ◽  
Skeletal Tissue ◽  
Term Stability ◽  
Long Term Stability ◽  
Clinical Scenarios

Short dental implants are commonly recommended to be implemented with small crown-to-implant (C/I) ratios due to their mechanical stability — decreasing C/I ratios cause less deformation in skeletal tissue under occlusal force. However, the long-term stability of short implants with high C/I ratios remains a controversial issue due to biomechanical complications. This study evaluates the strain distribution and functional implications in an implant-supported crown with various C/I ratios using a high-fidelity, nonlinear finite-element model. Several clinical scenarios are simulated by loading implants with various implant lengths (IL) and crown heights (CH). Strain distribution and maximum equivalent strain are analyzed to evaluate the effects and significance of CH, IL, and the C/I ratio. The study shows underloading for certain implant configurations with high C/I ratio. Increasing IL and decreasing C/I in moderation demonstrates a positive effect in long-term stability.

scholarly journals On the Significance and Predicted Functional Effects of the Crown-to-Implant Ratio: A Finite Element Study of Long-Term Implant Stability Using High-Resolution, Nonlinear Numerical Analysis

2016 ◽  
Author(s):  
T. J. Sego ◽  
Yung-Ting Hsu ◽  
Tien-Min Gabriel Chu ◽  
Andres Tovar
Keyword(s):  
Finite Element ◽  
Functional Response ◽  
Strain Distribution ◽  
Element Model ◽  
Equivalent Strain ◽  
Implant Design ◽  
Interface Surface ◽  
Clinical Scenarios ◽  
Maxillary Molar ◽  
Interface Surface Area

With the rising popularity of short dental implants, the effects of the crown-to-implant (C/I) ratio on stress and strain distributions remain controversial. Previous research disagrees on results of interest and level of necessary technical detail. The present study aimed to evaluate the strain distribution and its functional implications in a single implant-supported crown with various C/I ratios placed in the maxillary molar region. A high-fidelity, nonlinear finite-element model was generated to simulate multiple clinical scenarios by laterally loading a set of single implants with various implant lengths (IL) and crown heights (CH). Strain distribution and maximum equivalent strain (MES) were analyzed to evaluate the effects and significance of the CH, IL and C/I. Predicted functional response to strain at the implant interface was analyzed by interface surface area. Results. Results were evaluated according to the mechanostat hypothesis to predict functional response. Overloading and effects of strain concentrations were more prevalent with increasing C/I. Overloading was predicted for all configurations to varying degrees, and increased with decreasing IL. Fracture in trabecular bone was predicted for at least one C/I and all IL of 10 mm or less. Higher C/I ratios and lower IL increase the risk of overloading and fracture. Increasing C/I augments the functional effects of other implant design factors. Greater C/I ratios may be achieved with implant designs that induce less significant strain concentrations.

scholarly journals The Influence of Operation Pressure on the Long-Term Stability of Salt-Cavern Gas Storage

2014 ◽  
Vol 6 ◽  
pp. 537679 ◽  
Author(s):  
Jianjun Liu ◽  
Qiang Xiao
Keyword(s):  
Internal Pressure ◽  
Element Model ◽  
Gas Storage ◽  
Salt Cavern ◽  
Term Stability ◽  
Long Term Stability ◽  
Rock Creep ◽  
Operation Pressure ◽  
Salt Cavern Gas Storage

The operation pressure of underground salt-cavern gas storage directly affects its stability. Because of seasonal demand and other emergency reasons, the gas storage working pressures always change from high to low or from low to high cyclic variation. In order to analyze the effect of gas storage pressure changing on its long-term stability, considering the salt rock creep, a 3D finite element model was built using the software Abaqus. Moreover, the deformation and analyzed results of the storage under 0 MPa, 4 MPa, 6 MPa, 8 MPa, 10 MPa, and 12 MPa and also circulating changes pressure operation were given in the 10-year creep. It concluded that how working pressures have effect on long-term stability of salt-cavern gas storage. The research results indicated that the long-term creep performance of underground salt cavern gas storage is affected by internal pressure, the smaller the internal pressure creep is, the more obvious the creep and the greater deformation of gas storage are. The greater the internal pressure is, the smaller the deformation of the gas storage is. The low pressure and excessive high pressure must be avoided during the operation of gas storage. These results have an important significance on determining the reasonable pressure of gas storage operation and ensure the long-term stability of gas storage.

Stability of unsupported tunnels in clay

1992 ◽  
Vol 29 (4) ◽  
pp. 609-613 ◽  
Author(s):  
Z. Eisenstein ◽  
L. Samarasekera
Keyword(s):  
Finite Element ◽  
Stress Field ◽  
Limit Equilibrium ◽  
Element Model ◽  
Soil Parameters ◽  
Term Stability ◽  
Long Term Stability ◽  
Shallow Tunnels ◽  
Starting Point

An overall long-term stability of unsupported shallow tunnels in overconsolidated clays which is directly related to the stand-up time is investigated. A new approach that combines finite element methods and the limit equilibrium theory is used to overcome limitations of current design practice. A more realistic initial stress field, unloading due to excavation, and variation of strength and modulus with depth are used. The pore-pressure change is analysed using a finite element model that incorporates an uncoupled consolidation theory. These pore pressures along with the previously obtained stress field are utilized to predict the variation of stability with time for given soil parameters such as strength and coefficient of earth pressure at rest. The results obtained employing a simple mechanism are presented using non-dimensional quantities. These results relate time, stability of the tunnel, and soil strength. The analysis showed that, under certain circumstances, the initial undrained stability may be of no practical value and may only be used as a starting point for more practical long-term stability. This procedure explains the stand-up time phenomenon in tunnels and may also be used in design as a direct tool for its evaluation. Key words : overconsolidated clay, long-term stability, stand-up time, shallow tunnels, finite elements, limit equilibrium.

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