Surgical dentures replace large defects of both soft and bone tissues of the oral cavity and the face. Among these are the following types:
Obturators. They serve to close large palatal clefts. Obturators consist of a removable palatal plate that covers a defect and is attached to rest of teeth by regular anchoring elements. Soft palate cleft is covered by a “pelota” plate that is coupled to a palatal plate by a joint.
Resection prosthesis. Replaces defects after resection of jawbones due to neoplasms and supports soft cheek tissues. A palatal plate closes resection cavity and also complements for defects of the dental arch. Edges of a prosthesis can be made of an elastic silicone material.
Epithesis replaces a skeleton and soft parts of the face after large surgeries of neoplasms or after injuries. It is usually combined with resection prostheses. They are made of elastic silicon-based materials. Retention of a prosthesis is improved by an eyeglasses frame with spring wire which press an epithesis against the face. An eye prosthesis is usually a part epithesis.
5.4 Damage of Tissues by Dentures and Its Prevention
Incorrectly made fixed or removable denture may cause many damages to its bearer. It can be mainly damages to abutments periodontium during their functional overloading. Wrongly adhering or unstable total removable dentures may cause decubitus ulcers or chronic inflammatory hyperplasia - granuloma fissuratum - of the prosthesis bed mucosa. Similar etiology exhibits ligamentous transformation of the alveolar ridge which further reduces retention of a prosthesis. Another kind of damage is stomatitis prothetica which occurs mostly on a palate under resin plate of a denture. It is caused by chemical irritation by free resin monomers or it appears as a contact allergy to acrylic compounds. Chronic inflammations of mouth commissures - anguli infectiosi - are a result of low occlusion at patients who wear old, abraded total replacements. Monilial infections of oral mucosa - candidiasis - is also frequent at people wearing total dentures.
Most of the above described damages can be avoided by technically correct prostheses, regular check-ups and proper oral hygiene.
6. Dental Implantology
Transplantation and implantation methods are being used more often in medicine. The same situation is in dentistry. Despite some terminological discrepancies, the term transplantation means transfer of an organ, a tissue that becomes a part of an organism, not only by its configuration and function, but also gets integrated into a recipient organism by its composition and metabolic processes - it maintains its vitality. The term transplantation also means such a transfer of precisely configured material or artificial organ that fully or partially integrates into an organism’s function, it is fully biologically tolerated but it is not vital. During last several decades, such a method - method of implanting - has begun to be more intensely utilized for repairs of a defective, incomplete dentition by means of dental implants. The term dental implant means a construction (part) of various forms or shapes which forms an artificial abutment after being inserted into the upper or lower jaw alveolus. Thus implanted artificial abutments allow for more sophisticated denture to be made in cases where teeth replacement would not otherwise be possible. It enables a person to utilize his/her teeth fully with all its functions - processing food, speech and articulation.
Variety of dental implants have been developed so far, differing in materials used, shapes, forms, ways of implanting them into jawbones and their relation to tissues. As our knowledge increases, periods of greater or smaller utilization or refusal of dental implants at clinical practice alternate.
At present times when high technology is possible and social demands increase, dental implantology is again a hot topic. Many authors have been involved in solving problems related to quite wide area of dental implants. Their opinions and results of their work have been a subject of many discussions and publications. The major problems of both foreign and domestic literature are related to materials, forms and shapes of implants, methods of implanting, availability, including suitable instrumentation, and also a very important question of biological tolerance of dental implants. This question is even more amplified by the specific property of dental implants - they penetrate the oral mucosa and stretch out freely into the oral cavity (open implants). In 1979, the FDI (Federation Dentaire Internationale) dealt with the question of biological tolerance and issued recommended international norms for dental implants materials. In Czech republic, these norms have been respected since 1986.
During last couple of decades, the worldwide field of dental implants has reached such degree of quality, especially due to scientific achievements, that it occupies a firm place at specialized extended dental care.
6.1 Classification of Implants, Properties of Materials, Biocompatibility
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.