Lianshan Lin

Digital image correlation analysis of the load transfer by implant-supported restorations

This study compared splinted and non-splinted implant-supported prosthesis with and without a distal proximal contact using a digital image correlation method. An epoxy resin model was made with acrylic resin replicas of a mandibular first premolar and second molar and with threaded implants replacing the second premolar and first molar. Splinted and non-splinted metal-ceramic screw-retained crowns were fabricated and loaded with and without the presence of the second molar. A single-camera measuring system was used to record the in-plane deformation on the model surface at a frequency of 1.0Hz under a load from 0 to 250N. The images were then analyzed with specialist software to determine the direct (horizontal) and shear strains along the model. Not splinting the crowns resulted in higher stress transfer to the supporting implants when the second molar replica was absent. The presence of a second molar and an effective interproximal contact contributed to lower stress transfer to the supporting structures even for non-splinted restorations. Shear strains were higher in the region between the molars when the second molar was absent, regardless of splinting. The opposite was found for the region between the implants, which had higher shear strain values when the second molar was present. When an effective distal contact is absent, non-splinted implant-supported restorations introduce higher direct strains to the supporting structures under loading. Shear strains appear to be dependent also on the region within the model, with different regions showing different trends in strain changes in the absence of an effective distal contact.

Validation of finite element models for strain analysis of implant-supported prostheses using digital image correlation

OBJECTIVES A validated numerical model for stress/strain predictions is essential in understanding the biomechanical behavior of implant-supported dental prostheses. The digital image correlation (DIC) method for full-field strain measurement was compared with finite element analysis (FEA) in assessing bone strain induced by implants. METHODS An epoxy resin model simulating the lower arch was made for the experimental test with acrylic resin replicas of the first premolar and second molar and threaded implants replacing the second premolar and first molar. Splinted (G1/G3) and non-splinted (G2/G4) metal-ceramic screw-retained crowns were fabricated and loaded with (G1/G2) or without (G3/G4) the second molar that provided proximal contact. A single-camera, two-dimensional DIC system was used to record deformation of the resin model surface under a load of 250N. Three-dimensional finite element (FE) models were constructed for the physical models using computer-aided design (CAD) software. Surface strains were used for comparison between the two methods, while internal strains at the implant/resin block interface were calculated using FEA. RESULTS Both methods found similar strain distributions over the simulant bone block surface, which indicated possible benefits of having splinted crowns and proximal contact in reducing bone strains. Internal strains predicted by FEA at the implant-resin interface were 8 times higher than those on the surface of the model, and they confirmed the results deduced from the surface strains. FEA gave higher strain values than experiments, probably due to incorrect material properties being used. SIGNIFICANCE DIC is a useful tool for validating FE models used for the biomechanical analysis of dental prosthesis.

A digital image correlation analysis on the influence of crown material in implant-supported prostheses on bone strain distribution

PURPOSE A digital image correlation (DIC) method for full-field surface strain measurement was used to analyze the effect of two veneering materials for implant supported crowns on the strain distribution within the surrounding bone. METHODS An epoxy resin model of a bone block was made by housing acrylic resin replicas of a mandibular first premolar and second molar together with threaded implants replacing the second premolar and first molar. Porcelain-veneered (G1 and G3) and resin-veneered (G2 and G4) screw-retained splinted crowns were fabricated and loaded with (G1 and G2) and without (G3 and G4) the presence of the second molar replica. A 2-dimensional DIC measuring system was used to record surface deformation of the bone block model at a frequency of 1.0 Hz during application of a 250-N load. RESULTS Maximum compressive strains (ɛ(XX), %) were found for the following regions: between molars, G1 (-0.21), G2 (-0.18), G3 (-0.26), and G4 (-0.25); between implants, G1 (-0.19), G2 (-0.13), G3 (-0.19), and G4 (-0.14). The magnitude of strains in the simulated bone block with the resin-veneered crowns was lower than that with porcelain-veneered crowns, irrespective of the presence or absence of the second molar. CONCLUSIONS The softer resin veneer helped to spread the load more evenly amongst the supporting teeth and implants, thus reducing the strains in the simulant bone block. Conversely, using the harder porcelain veneer resulted in the load being concentrated within one or two teeth or implants, thus leading to higher strain values in the bone block.

Effect of Surgical Guide Design and Surgeon's Experience on the Accuracy of Implant Placement

Implant position is a key determinant of esthetic and functional success. Achieving the goal of ideal implant position may be affected by case selection, prosthodontically driven treatment planning, site preparation, surgeons experience and use of a surgical guide. The combined effect of surgical guide design, surgeons experience, and size of the edentulous area on the accuracy of implant placement was evaluated in a simulated clinical setting. Twenty-one volunteers were recruited to participate in the study. They were divided evenly into 3 groups (novice, intermediate, and experienced). Each surgeon placed implants in single and double sites using 4 different surgical guide designs (no guide, tube, channel, and guided) and written instructions describing the ideal implant positions. A definitive typodont was constructed that had 3 implants in prosthetically determined ideal positions of single and double sites. The position and angulation of implants placed by the surgeons in the duplicate typodonts was measured using a computerized coordinate measuring machine and compared to the definitive typodont. The mean absolute positional error for all guides was 0.273, 0.340, 0.197 mm in mesial-distal, buccal-lingual, vertical positions, respectively, with an overall range of 0.00 to 1.81 mm. The mean absolute angle error for all guides was 1.61° and 2.39° in the mesial-distal and buccal-lingual angulations, respectively, with an overall range of 0.01° to 9.7°. Surgical guide design had a statistically significant effect on the accuracy of implant placement regardless of the surgeons experience level. Experienced surgeons had significantly less error in buccal-lingual angulation. The size of the edentulous sites was found to affect both implant angle and position significantly. The magnitude of error in position and angulation caused by surgical guide design, surgeons experience, and site size reported in this study are possibly not large enough to be clinically significant; however, it is likely that errors would be magnified in clinical practice. Future research is recommended to evaluate the effect of surgical guide design in vivo on implant angulation and position error.

A novel dentin bond strength measurement technique using a composite disk in diametral compression

New methods are needed that can predict the clinical failure of dental restorations that primarily rely on dentin bonding. Existing methods have shortcomings, e.g. severe deviation in the actual stress distribution from theory and a large standard deviation in the measured bond strength. We introduce here a novel test specimen by examining an endodontic model for dentin bonding. Specifically, we evaluated the feasibility of using the modified Brazilian disk test to measure the post-dentin interfacial bond strength. Four groups of resin composite disks which contained a slice of dentin with or without an intracanal post in the center were tested under diametral compression until fracture. Advanced nondestructive examination and imaging techniques in the form of acoustic emission (AE) and digital image correlation (DIC) were used innovatively to capture the fracture process in real time. DIC showed strain concentration first appearing at one of the lateral sides of the post-dentin interface. The appearance of the interfacial strain concentration also coincided with the first AE signal detected. Utilizing both the experimental data and finite-element analysis, the bond/tensile strengths were calculated to be: 11.2 MPa (fiber posts), 12.9 MPa (metal posts), 8.9 MPa (direct resin fillings) and 82.6 MPa for dentin. We have thus established the feasibility of using the composite disk in diametral compression to measure the bond strength between intracanal posts and dentin. The new method has the advantages of simpler specimen preparation, no premature failure, more consistent failure mode and smaller variations in the calculated bond strength.

Diametral compression test with composite disk for dentin bond strength measurement – Finite element analysis

OBJECTIVE A novel technique using a composite disk under diametral compression was presented in a previous study for measuring the bond strength between intracanal posts and dentin. This study deals with the stress distribution within the composite disk to allow the bond strength to be calculated accurately. The effects of changing geometrical and material parameters on the post-dentin interfacial stress are also evaluated. METHODS The finite element method with 3D models is used to analyze the stress distribution and to carry out the sensitivity analysis. Progressive post-dentin interfacial debonding is also simulated to better understand the failure process observed in experiments. RESULTS Material mismatch causes stress concentrations at the interfaces. The results are presented as correction factors to be used in conjunction with the analytical solution for a homogeneous disk. Comparison between the stresses at the post-dentin interface and those in dentin confirms that interfacial debonding will take place prior to fracture in the dentin. SIGNIFICANCE The numerical solutions presented here will facilitate the adoption of the composite disk in diametral compression for bond strength measurement.

Interoperability of Materials Database Systems in Support of Nuclear Energy Development and Potential Applications for Fuel Cell Material Selection

Materials database interoperability has been of great interest in recent years for information exchange in support of research and development (R&D). In response to data and knowledge sharing needs of the GenIV International Forum (GIF) for global collaboration in nuclear energy R&D, the European Commission JRC Institute for Energy and Transport (JRC-IET) and the Oak Ridge National Laboratory (ORNL) have established a materials database interoperability project that develops techniques for automated materials data exchange between systems hosted at the two institutes MatDB Online at JRC IET and the Gen IV Materials Handbook at ORNL, respectively. The work to enable automated exchange of data between the two systems leverages the XML data import and export functionalities of both systems in combination with recently developed standards for engineering materials data. The preliminary results of data communication between the two systems have demonstrated the feasibility and efficiency of materials database interoperability, which constructs an interoperation framework that can be seamlessly integrated into the high-throughput First Principles material databases and thus advance the discovery of novel materials in fuel cell applications.

Materials Databases Infrastructure Constructed by First Principles Calculations: A Review

First principles calculations, especially calculations based on the high-throughput density functional theory (DFT), have been widely accepted as the major approach in atom scale materials design. First principles calculations performed in a high-performance computing environment have been used to generate hundreds of thousands of crystal and compound records. The exponential growth of computational materials is one of the main drivers to develop an advanced materials database systems to ensure efficient data storage, management, query, presentation, and manipulation. This review covered the most cutting edge materials database systems in materials design and in important applications, such as fuel cells. By comparing the advantages and drawbacks of these high-throughput first principles materials database systems, an optimized computational framework was suggested to meet the specific needs of fuel cell applications. Further development of high-throughput DFT materials databases, which in essence accelerates materials innovation, was also discussed.

Characterization of Material Properties Using an Inverse Method

A simple finite-element-based inverse method has been devised with the aim of characterizing the properties of isotropic but heterogeneous materials under load. The method has been implemented into the commercial finite element code ABAQUS via its User Material (UMAT) Subroutine to facilitate the process of material characterization. Verification of the method has been carried out using simulated examples and the results showed rapid convergence of the method with good accuracy. The method has also been applied successfully to actual mechanical testing of graphite which has a porous microstructure and hence inhomogeneous distribution of material properties.

Fracture Toughness of Nuclear Graphite NBG-18

Objective: Graphite components in a Very High Temperature Reactor (VHTR) may fracture under the actions of external and internal (irradiation-induced) stresses. Measurement of the fracture properties of graphite is therefore essential in the design and structural integrity assessment of VHTR cores. This study aimed to evaluate the fracture toughness and its associated statistical characteristics of nuclear graphite NBG-18, for which there had been very little data. The effect of specimen size on its fracture toughness was also studied.Materials and methods: Three-point-bending tests were conducted with a MTS machine (858 Mini Bionix II, MTS, US) on single-edge-notched beams (SENB) of NBG-18 to measure its fracture toughness. Three different specimen sizes were considered: (I) 200mm (Support Span S) × 50mm (Width W) × 25mm (Thickness T), (II) 100mm (S) × 20mm (W) × 10mm (T), and (III) 40mm (S) × 10mm (W) × 5mm (T). A notch was machined into each specimen to give a crack length-to-width (a/w) ratio of 0.4 using a 0.3mm-thick diamond blade. The acoustic emission (AE) technique was applied to monitor the damage evolution process during loading.Results: The mean and standard deviation (in brackets) of the critical stress intensity factor KIC (MPa·m1/2) for each group were: (I) 1.69 (0.04), (II) 1.36 (0.05), and (III) 1.33 (0.06). Specimen size was found to significantly influence the fracture toughness results: the smaller the specimen, the lower the mean fracture toughness and the larger the variation.Conclusions: The fracture toughness of NBG-18 appears to reduce with the specimen size. The lower fracture toughness of the smaller specimens could be attributed to a finite process zone ahead of the crack tip.Copyright