Finite element analysis (FEA) has been used extensively to predict the biomechanical performance of various dental implant designs as well as the effect of clinical factors on implant success. By understanding the basic theory, method, application, and limitations of FEA in implant dentistry, the clinician will be better equipped to interpret results of FEA studies and extrapolate these results to clinical situations. This article reviews the current status of FEA applications in implant dentistry and discusses findings from FEA studies in relation to the bone-implant interface, the implant-prosthesis connection, and multiple-implant prostheses.

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Application of finite element analysis in implant dentistry: A review of the literature

Calcium phosphate (CaP) bioceramics are widely used in the field of bone regeneration, both in orthopedics and in dentistry, due to their good biocompatibility, osseointegration and osteoconduction. The aim of this article is to review the history, structure, properties and clinical applications of these materials, whether they are in the form of bone cements, paste, scaffolds, or coatings. Major analytical techniques for characterization of CaPs, in vitro and in vivo tests, and the requirements of the US Food and Drug Administration (FDA) and international standards from CaP coatings on orthopedic and dental endosseous implants, are also summarized, along with the possible effect of sterilization on these materials. CaP coating technologies are summarized, with a focus on electrochemical processes. Theories on the formation of transient precursor phases in biomineralization, the dissolution and reprecipitation as bone of CaPs are discussed. A wide variety of CaPs are presented, from the individual phases to nano-CaP, biphasic and triphasic CaP formulations, composite CaP coatings and cements, functionally graded materials (FGMs), and antibacterial CaPs. We conclude by foreseeing the future of CaPs.

Calcium Phosphate Bioceramics: A Review of Their History, Structure, Properties, Coating Technologies and Biomedical Applications.

With an ageing population, war, and sports related injuries there is an ever-expanding requirement for hard tissue replacement such as bone. Engineered artificial scaffold biomaterials with appropriate mechanical properties, surface chemistry and surface topography are in a great demand for enhancing cell attachment, cell growth and tissue formation at such defect sites. Most of these engineering techniques are aimed at mimicking the natural organization of the bone tissues and thereby create a conducive environment for bone regeneration. As the interaction between the cells and tissues with biomaterials at the tissue–implant interface is a surface phenomenon, surface properties play a major role in determining both the biological response to implants and the material response to the physiological condition. Hence surface engineering of biomaterials is aimed at modifying the material and biological responses through changes in surface properties while still maintaining the bulk mechanical properties of the implant. Therefore, there has been a great thrust towards development of Ca–P-based surface coatings on various metallic and nonmetallic substrates for load bearing implant applications such as hip joint prosthesis, knee joint prosthesis and dental implants. Typical coating methodologies like ion beam assisted deposition, plasma spray deposition, pulsed laser physical vapor deposition, magnetron sputtering, sol–gel derived coatings, electrodeposition, micro-arc oxidation and laser deposition are extensively studied at laboratory scale. In the present article, attempts are made to give an overview of the basic principles behind the coating techniques as well as advantageous features such as bioactivity and biocompatibility associated with these coatings. A strong emphasis will be given on laser-induced textured and bioactive coatings obtained by the author's research group [A. Kurella, N.B. Dahotre, Journal of Biomedical Applications 20 (2005) 5–50; A. Kurella, N.B. Dahotre, Acta Biomaterialia 2 (2006) 677–688; A. Kurella, N.B. Dahotre, Journal of Minerals, Metals and Materials Society (JOM) 58 (2006) 64–66; A. Kurella, N.B. Dahotre, Journal of Materials Science: Materials in Medicine 17 (2006) 565–572; P.G. Engleman, A. Kurella, A. Samant, C.A. Blue, N.B. Dahotre, Journal of Minerals, Metals and Materials Society (JOM) 57 (2005) 46–50; R. Singh, A. Kurella, N.B. Dahotre, Journal of Biomaterials Applications 21 (2006) 46–72; S.R. Paital, N.B. Dahotre, Biomedical Materials 2 (2007) 274–281; S.R. Paital, N.B. Dahotre, 2009, Acta Biomaterialia, doi:10.1016/j.actbio.2009.03.004 ; R. Singh, N.B. Dahotre, Journal of Materials Science: Materials in Medicine 18 (2007) 725–751.]. Since cells are sensitive to topographical features ranging from mesoscale to nanoscale, formation of these features by both pulsed and continuous wave Nd:YAG laser system will be highlighted. This can also be regarded as advancement towards third generation biomaterials which are bioinert, bioactive and which once implanted will stimulate cell adhesion, proliferation and growth at the interface. Further, an overview of various bio-implants and bio-devices and materials used for these kinds of devices, performance factors such as mechanical and corrosion behavior and surface science associated with these materials are also explained. As the present article is aimed at describing the multidisciplinary nature of this exciting field it also provides a common platform to understand this subject in a simple way for students, researchers, teachers and engineers in the fields ranging from medicine, dentistry, biology, materials science, biomedicine, biomechanics to physics.

Calcium phosphate coatings for bio-implant applications: Materials, performance factors, and methodologies

Calcium phosphate coatings on magnesium alloys for biomedical applications: a review.

Since dental implants must withstand relatively large forces and moments in function, a better understanding of in vivo bone response to loading would aid implant design. The following topics are essential in this problem. (1) Theoretical models and experimental data are available for understanding implant loading as an aid to case planning. (2) At least for several months after surgery, bone healing in gaps between implant and bone as well as in pre-existing damaged bone will determine interface structure and properties. The ongoing healing creates a complicated environment. (3) Recent studies reveal that an interfacial cement line exists between the implant surface and bone for titanium and hydroxyapatite (HA). Since cement lines in normal bone have been identified as weak interfaces, a cement line at a bone-biomaterial interface may also be a weak point. Indeed, data on interfacial shear and tensile "bond" strengths are consistent with this idea. (4) Excessive interfacial micromotion early after implantation interferes with local bone healing and predisposes to a fibrous tissue interface instead of osseointegration. (5) Large strains can damage bone. For implants that have healed in situ for several months before being loaded, data support the hypothesis that interfacial overload occurs if the strains are excessive in interfacial bone. While bone "adaptation" to loading is a long-standing concept in bone physiology, researchers may sometimes be too willing to accept this paradigm as an exclusive explanation of in vivo tissue responses during experiments, while overlooking confounding variables, alternative (non-mechanical) explanations, and the possibility that different types of bone (e.g., woven bone, Haversian bone, plexiform bone) may have different sensitivities to loading under healing vs. quiescent conditions.

In vivo bone response to biomechanical loading at the bone/dental-implant interface.

Average marginal bone resorption of about 1 mm after the first year of functional loading, which is followed by an annual loss of approximately 0.1 mm, has been reported in stable implants. However, finite element analyses on bone stress around implants have been limited to analysing the bone stress in the absence of any bone resorption. Thus, a three-dimensional finite element analysis was performed to compare the bone stresses in a non-resorption model with those in four models with bone resorption of two depths (1.3 and 2.6 mm) and types (horizontal resorption and angular defects). Axial and bucco-lingual forces were separately applied to the center of the superstructure and the maximum equivalent stress was calculated. The main tendencies of bone stress (highest stress concentration around implant neck, higher stresses under bucco-lingual than axial load, as well as in the cortical than cancellous bone) were the same in the non-resorption and resorption models. Bone stress distributions were similar in the non-resorption and horizontal resorption models, but differed from those in the angular defect models. Moreover, the changes of the bone stress values with resorption depth differed for the two resorption types. Thus, in FEA, accurate simulation of the marginal bone shape in the implant neck region is advisable.

Influence of marginal bone resorption on stress around an implant--a three-dimensional finite element analysis.

A 3-dimensional finite element analysis was conducted to assess stress distribution in bone, implant, and abutment when gold alloy, porcelain, or resin (acrylic or composite) was used for a 3-unit prosthesis. A unit force was applied axially and then buccolingually to the center of the pontic. For gold and porcelain, similar maximum equivalent stress was found in each part of the models. In almost all cases, stress in the model with the resin prostheses was similar to or higher than that in the models with the other 2 prosthesis materials. The highest increase in stress with the resins was found in the implant-abutment unit under axial load. The protective role of resin for the implant-bone interface could not be demonstrated under the conditions of this analysis.

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Influence of prosthesis material on stress distribution in bone and implant: a 3-dimensional finite element analysis

The present study concerns the surface layered structure of the cast Ti. A commercial Ti was cast into a mold which was made of a phosphate-bonded Al2O3/SiO2 investment. Elemental analyses of the interfacial zone of the casting were made under an electron probe micro-analyzer.The interfacial zone was composed of four layers: the outermost reaction or casting burn layer, the second layer of an O-and Al-stabilized α case, the third layer in which Si, P, O, and C were inhomogeneously concentrated, and the fourth layer which consisted of acicular or plate-like crystals. It was observed that the larger the cast volume and the higher the mold temperature, the thicker became each layer and the coarser became the acicular grains. Probably, the layered structure was formed through decomposition of reducible species in the burnout investment and diffusion of the resulting elements into the casting.

Layered structure of cast titanium surface.

There are many controversies about the long-term prognosis of hydroxyapatite (HA)-coated implants. Failure may be related to compositional and structural changes of the coating occurring during implantation. Two retrieved and two unused HA-coated blade-type implants were examined by stereomicroscopy, secondary electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and electron probe microanalysis. The objective was to investigate the HA morphology, composition, and structure, and to characterize the changes that occurred in the retrieved implant coatings. Retrieved implants presented partial loss of the coating, especially at the apical and mesiodistal edges. Remaining HA was thick and flattened in the cervical and central areas and gradually thinner and rougher towards the apical and mesiodistal edges. Increase of Cl and Mg, decrease of OH, and X-ray diffraction peak broadening were found in the retrieved implant coatings, in comparison with the unused implants. Morphological changes of the retrieved implants seem to depend on stress values in the surrounding bone and on implant mobility. Compositional changes and increased amount of lattice imperfections appeared in the retrieved implant coatings, as a result of ion substitutions in the apatite lattice. However, the present study could not confirm the influence of these changes on implant failure.

Long-term changes of hydroxyapatite-coated dental implants.

Statement of problem Fatigue failure in a removable partial denture framework includes fracture of the occlusal rest at the rest-minor connector angle. Purpose This in vitro study evaluated the fatigue resistance of 0.8-mm–thick occlusal rests cast with Co-Cr and Ag-Pd-Cu-Au alloys. Material and methods The specimen consisted of occlusal rest (0.8 × 2.0 × 10 mm), vertical minor connector (0.9 × 2.0 × 5.0 mm), and denture base connector (1.5 × 5.0 × 25 mm). Twenty-five specimens each were cast with Co-Cr and Ag-Pd-Cu-Au alloys. From each group, 5 specimens were subjected to a load-deflection test conducted to determine the amount of deflection to be used in fatigue test. The fatigue test was performed such that the occlusal rest component was deflected by displacing the denture base component in a tissueward direction. Predetermined denture base displacement values of 0.25 and 0.49 mm for Co-Cr and Ag-Pd-Cu-Au specimens, respectively, were repeated at a rate of 500 cycles/min by use of a displacement-controlled fatigue testing machine, until occlusal rest failure occurred or a preset limit of 2 million cycles was achieved. The survival rates of the occlusal rests were calculated assuming a chewing cycle of 2 × 10 5 per year. Scanning electron microscopy (SEM) photographs were made to examine the fracture surfaces and to identify casting defects. The relationship between fatigue cycles and number of casting defects was determined by Spearman rank correlation analysis ( P Results All 20 Co-Cr specimens outran the preset limit, whereas 18 Ag-Pd-Cu-Au specimens fractured. After 3 years of simulated clinical use, only 50% of the Ag-Pd-Cu-Au occlusal rests survived. Statistical analysis showed that the fatigue cycles and number of casting defects were inversely related ( P Conclusions This study suggests that cast Co-Cr rests are more rigid and fatigue resistant than Ag-Pd-Cu-Au rests. The fatigue resistance of 0.8-mm–thick occlusal rests may be adequate if cast with Co-Cr alloy. An increased number of casting defects may hasten the fatigue failure of occlusal rests.

Osamu Miyakawa

Papers

Influence of marginal bone resorption on stress around an implant--a three-dimensional finite element analysis.

Influence of prosthesis material on stress distribution in bone and implant: a 3-dimensional finite element analysis

Layered structure of cast titanium surface.

Long-term changes of hydroxyapatite-coated dental implants.

Fatigue resistance of cast occlusal rests using Co-Cr and Ag-Pd-Cu-Au alloys.