Classification of Implants, Properties of Materials, Biocompatibility

By Dr. Vishaal Bhat on Thursday, 6 December, 2007 with 0 comments

Dental implants can be classified according to various points of view. From the clinical point of view, the classification that is based on the relationship between implants and tissues in which an implant is embedded, is the most often used one. The classification is as follows:

1. Closed, i.e. implants that are not in contact with the oral cavity since they are fully covered by an organism’s live tissues, the alveolar bone. Magnets made of a chromium-cobalt alloy and embedded in a tantalum mesh, are an example. A magnet with the opposite polarity is placed inside a removable denture’s body. Magnetic force improves retention of a removable prosthetic denture during its function in situ. Other forms of such implants exist, too. Their use is limited, though.

2. Semi-closed implants, also called endodontic, transdental, transradicular, or root. They have a form of long pins, smooth or threaded, made of metal (tantalum, titanium) or non-metallic (sapphire) materials, that create a firm tooth or pillar for fitting a prosthetic denture, by penetrating the root and crown part of a tooth to the bone. This way is not often used, either. Reasons for it are technical or instrumental rather than a usefulness.

3. Open implants: these implants represent the most often used and the most variable group. Their characteristic is that they pass through a mucosa or muco-periosteum freely inside the oral cavity where they form dental pillars. These implants can be further divided according to their relationship to the alveolar tissue:

a) intramucous implants: these implants are based on the “pin and socket” principle. The socket in this case is a well, artificially made in a bone but coated with epithelium. A denture contains metal or ceramic pin that fits into the socket and helps to retain a removable denture. Although, this mode is not very common and can be used rather for temporary solutions.

b) Subperiosteal tooth implants (synonym juxtaosseal): these implants are formed by metal constructions placed on the surface of conditioned alveolar bone, they are covered by the periosteum and artificial pillars protrude from them through periosteal mucosa into the oral cavity. Implants may be also fixed into the bone by screws. This kind of implants have been in use since Twenties. Various metal materials were used, from fine steel to titanium and its alloys used in these days. These implants are widely used today in cases of atrophied alveoli both in the upper and lower jaws. Limiting factors of their use are requirements for great care during implanting and also relatively high (up to 50%) unsuccessfulness rate followed by quite large damages to the bone.

c) enosseal implants: are the most commonly used and perhaps also the most promising group of dental implants. The method of implanting the enosseal dental implants has became a part of dental care in all developed countries. It is used in many forms in the Czech Republic as well. Basically, implants which may vary in their shapes, are inserted enosseally into the spongy bone, their parts penetrate the cortical bone, periosteum, and mucosa into the oral cavity where they form an artificial pillar. Their variability does not concern only shapes, but also materials, surface finish and ways of surgical implanting of a denture anchors. At present, an emphasis is put on the following requirements for enosseal implants: they have to integrate perfectly into the bone and surrounding tissues, i.e. no interstitial layers of ligaments, granulous tissue or groove between the implant and mucosa that would allow for microorganisms to penetrate deeper into tissues, can occur. Besides biocompatibility, biomechanics of dental implants that is determined by their shape and material they are made of, plays an important role. At present, the most suitable materials appear to be pure titanium or tantalum, titanium and vanadium alloys, hydroxylapatite ceramic, aluminum oxide containing monocrystalline and poly-crystalline ceramic, phosphate-based ceramic, and experimentally also bio-glass and bio-carbon containing ceramic materials. A combination of metal and ceramic implants is used mainly due to the surface finish. Shapes, forms and surface finish of enosseal implants should assure the largest area of contact with a bone, thus making conditions for complete integration of an implant. In concordance with these requirements, including the way of a denture anchoring, tens of enosseal dental implant systems have been developed. Single-phase implants have an endosteal part that verges into a pillar part, as compared to two-phase implants, where the endosteal part is implanted first and the supraconstruction is fixed in the second phase after 3-6 months, when a prosthesis is made, too. The well known brands of dental implants are MTI, Ardent - cylindrical, Impladent, LTI, Precioza, Disal, VNI, Timplant, IMZ, Swiss-made Bonefit, Swedish Branemark, American Cor-vent and tens of others.

Category: Dental Materials Notes



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