Dentistry – Prosthodontics – Dental implant construction
Reexamination Certificate
2000-03-27
2001-02-06
Lucchesi, Nicholas D.. (Department: 3732)
Dentistry
Prosthodontics
Dental implant construction
C623S016110
Reexamination Certificate
active
06183255
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to medical orthopedic and dental implants which are made of titanium materials. More specifically, the present invention relates directly to surface modifications of titanium material implants by either mechanical, chemical, thermal, or any combination thereof in order to promote and improve the bony ingrowth for a better biological fixation in the receiving hard/soft vital tissues. Furthermore, due to the fact that different surface modifications, as described above, form different types of crystalline structure of titanium oxides as a treatment product, the present invention also is directed to crystalline compatibility for successful titanium material implants.
BACKGROUND OF THE INVENTION
One of many universal requirements of implants, wherever they are used in the body, is the ability to form a suitably stable mechanical unit with neighboring hard or soft tissues. A loose (or unstable) implant may function less efficiently or cease functioning completely, or it may induce an excessive tissue response. In either case, it may cause the patient discomfort and pain. In several situations, a loose implant is deemed to have failed and has to be surgically removed.
For a long time, it has been recognized that any type of implant (whether a dental implant or orthopedic implant), should possess a biological compatibility with implant-receiving-surrounding hard and soft vital tissues. Accordingly, the material choice for implants is limited to certain types of materials, including titanium materials such as un-alloyed commercially pure titanium (ASTM Grades 1, 2, 3, 4 and 7) and Ti-based alloy such as Ti-6Al-4V, AISI Type 316L stainless steel, or some ceramic materials such as pure alumina or synthetic compounds having Ca and P ions (including hydroxyapatite or tri-calcium phosphate).
Dental or orthopedic prostheses, particularly surface zones thereof, should respond to the loading transmitting function. The placed implant and receiving tissues form a unique stress-strain field. Between them, there should be an interfacial layer. During the loading, the strain-field continuity should be held, although the stress-field is obviously in a discrete manner due to different values of modulus of elasticity of both implant material and tissues. If the magnitude of the difference in modulus of elasticity between implant and tissue is large, then the interfacial stress, accordingly, will be so large that the placed implant system will face a risky failure situation. Therefore, materials for implants or surface zone of implants should be mechanically compatible to mechanical properties of the receiving tissues, so that the interfacial stress can be minimized. This is the second compatibility and is called mechanical compatibility.
Furthermore, a third compatibility, i.e., morphological compatibility is also important. In a scientific article published by the present inventor (“Fractal Dimension Analysis Of Mandibular Bones: Toward A Morphological Compatibility Of Implants” in
Bio-Medical Materials and Engineering
, 1994, 4:397-407), it was found that surface morphology of successful implants has upper and lower limitations in average roughness (1~50 &mgr;m) and average particle size (10~500 &mgr;m), regardless of the type of implant material (metallic, ceramics, or polymeric materials). If a particle size is smaller than 10 &mgr;m, the surface will be more toxic to fibroblastic cells and have an adverse influence on cells due to their physical presence independent of any chemical toxic effects. If the pore is larger than 500 &mgr;m, the surface does not exhibit sufficient structural integrity because it is too coarse. This third morphological compatibility (which was proposed by the present inventor) is now well accepted in the implantology society.
The attachment of cells onto titanium surfaces is an important consideration in the areas of clinical implant dentistry. A major consideration in designing implants has been to produce surfaces that promote desirable responses in the cells and tissues contacting the implants. Cellular behaviors such as adhesion, morphologic change, functional alteration, and proliferation are greatly affected by surface properties such as hydrophilicity, roughness, charge, free energy, and morphology.
It is well known that the surface chemistry, surface energy, and surface topography govern the biological response to an implant material. The tissue response to a dental implant may involve physical factors such as size, shape, surface topography, and relative interfacial movement, as well as chemical factors associated with the composition and structure.
Biomaterials used in a living organism may come into contact with cells in the related tissue for a long period of time. For this reason, they should naturally be harmless to the organism, and the mechanical properties should be suited to the purpose, as described previously. Furthermore, they should possess biological effect capable of providing favorable circumstances for the properties and functions of the cells at the implant site. For example, materials used in the construction of an artificial heart or heart valve must provide for anti-thrombogenesis, which prevents attachment of the cellular components of blood. By contrast, materials for a dental or bone implant must be suitable for cell attachment, because both the connective and epithelial cells (with which these materials mainly come into contact) are anchorage-dependent and therefore need a cell attachment scaffold for cell division and cell differentiation to be conducted. Therefore, “attachability” of the cells to the material is one of the important parameters in the evaluation of biomaterials.
Surface properties of biomaterials play a critical role in the adhesion process of adjacent cells. Little is known about the optimal surface characteristics of titanium that promote tissue-implant interaction. Cell adhesion to and spreading on a biomaterial are, amongst other factors, dependent on the surface wettability of the biomaterial. Measurement of the wettability of a material, expressed by the contact angle in the presence of the different liquids, might be a predictive index of cytocompatibility. Surface modification of titanium surfaces has been shown to improve bony apposition, tissue adhesion, and migration. With the surface chemistry of titanium altered, different rates of cellular attachment have been observed. However little is known about the biochemical responses of cells to other surface properties, such as oxide thickness, oxide crystal structure, surface topography, or the dynamic surface changes which can occur after implantation.
It has been shown that methods of implant surface preparation can significantly affect the resultant properties of the surface and subsequently the biological responses that occur at the surface. Recent efforts have shown that the success or failure of dental implants can be related not only to the chemical properties of the implant surface but also to the micromorphologic nature of the surface.
Many clinical studies on dental implants have focused on the success of endosseous implants with a variety of surface characteristics. In an attempt to improve the quantity and quality of the bone-implant interface, numerous implant surface modifications have been proposed.
In order to achieve morphological compatibility, titanium implant surfaces need to be modified. They can be treated by additive methods such as the titanium plasma spray procedure to increase surface area. They have also been modified by subtractive methods such as acid pickling, acid etching, sandblasting and other small particle-blasting to change the texture as well as to increase the effective surface area. The development and use of these surface modifications have been based on the theory that improved osseointegration can be achieved by increasing the topography or roughness of the implant surface.
As briefly mentioned above, to modify the surface layer, there are mainly two types of texture
Breiner & Breiner
Lucchesi Nicholas D..
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