Stomatolog y

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5.2 Removable Prostheses

Defects of dentition can as well be replaced by removable dentures. These are anchored on remaining teeth or lay on an edentulous area. Advantages compared to fixed bridges include the possibility of cleaning outside the mouth, they are less expensive, abutments need minimum preparation and dentures can be easily repaired. Their disadvantages are low functional performance, the possibility of damage of the remaining teeth and an edentulous area, and long period of acceptance. These removable dentures may be either partial or total.

Partial removable dentures complement for large defects that can not be replaced with a fixed bridge and for shortened dental arches. They consist of the following basic construction elements:

1. Body, the most important part of a removable denture, replaces a missing part of an atrophied alveolar ridge and the teeth. It restores the chewing function, personal visage of a patient and his/her ability of phonation. It consists of a saddle and artificial teeth (made of resin or porcelain). Size of a body is determined by the way of transferring the chewing pressure. Prostheses with the dental transfer of the chewing pressure have their body reduced in size and they are similar to flatly sat inserts of fixed bridges. The chewing pressure is not transmitted to a denture’s bedding. Dento-mucosal dentures with a mixed transfer mode have a saddle-shaped body that is greatly extended. Dentures with mucous mode of the chewing pressure transfer have a body that extends into a palatal or lingual plate. The denture’s body is made of a resin.

2. Anchoring elements serve for fastening a partially removable denture to the rest of teeth. Braces and telescopic devices belong here. Braces are among the most often used anchoring elements. Their arms are usually made of a flexible steel wire (0.7-0.8 mm in diameter) or cast of chromium-cobalt alloys. Retention braces (two-armed) should only hold a prosthesis to the rest of teeth. Its retention arm is made of wire, it is flexible and it is positioned along the vestibular teeth surfaces. The stabilizing arm (rigid) stretches along the oral teeth surface; it is mostly made by casting. Propping braces transfer the chewing pressure to a pillar tooth in such a way, that the brace’s supporting arm rests on an occlusal surface of a braced tooth. Propping braces can be wholly made of an alloy.

Telescopic devices provide for better personal appearance than braces. A principle of retention by telescopic anchoring systems lays in a mutual friction of a pin and a socket that fit into each other. A socket of the telescopic connection is located at the pillar tooth construction. A pin that is a part of removable denture, inserts into a socket (inner insertional connection). Similarly, a telescopic crown’s outer metal casing that is a part of the removable denture’s construction, sets onto an inner metal casing, firmly attached to a pillar tooth.

3. Connecting elements connect individual parts of a prosthesis. Main connecting elements form a sort of frame that holds together parts of the prosthesis’ body. To this frame, other construction elements of a prosthesis are attached by tiny clamps (secondary connecting elements). Main connecting elements are used in the form of bars, reduced plates, and palatal plates at the upper jaw, or in the form of bodies that push against the oral slope of the lower jaw alveolar ridge. Front palatal bar connects the front edge of one or more bars of metal construction that belong to a partially removable denture, at the area of palatal rugae. Side palatal bar is usually an extension of a front palatal bar at the distal part of the upper jaw where teeth are present. A wider rear palatal bar connects distal parts of a metal construction. It goes along the back edge of the hard palate in parallel with its boundary and does not extend into the non-movable part of the soft palate. Construction elements of both halves of the dental arch are connected at the lower jaw by a sublingual bar. It leads beneath the marginal gingiva at the lingual slope of the alveolar ridge.

Reduced plates are positioned at the center of a palate and hold together bodies of symmetrical defects prosthesis at the upper jaw near flat palates. At the lower jaw, a reduced plate lies by its upper edge to tubercula dentalia of the lower front teeth, eventually to a horizontal maximum convexity of distal teeth. Its lower edge is placed above the oral cavity base.

Palatal plates cover the whole palatal bed of a prosthesis, in case of mucous dentures of the upper jaw. Their rear edge runs along the non-movable part of the soft palate. None of the above listed elements should constrict the marginal gingiva of other teeth, to avoid damages to the periodontium.

4. Stabilizing elements prevent prostheses to rotate along their axes and a denture’s body to move away from a prosthetic bed. They also prevent dentures from a swinging movements and abutments from heaving. The basis of a stabilizing element is the stabilizing arm of a brace that runs along the maximum horizontal convexity of a pillar tooth on its oral side. An extended brace with higher stabilizing effect is formed by extension of an arm to adjacent teeth. If an arm of three-armed braces leads from one end of a group of remaining teeth to another in such a manner that arms conjoin, a continuous brace is thus formed.

Total dentures.

Total denture is a replacement with mucous transfer of the chewing pressure. It replaces a general defect of teeth, except the third molars and atrophied parts of an alveolus in the jawbones. Its sole construction element - a body - is made of a resin base that bears artificial teeth. At the upper jaw, the basis is formed by a palatal plate; at the lower jaw it is a saddle. Both parts sit on a prosthetic bed by the largest possible area. Total dentures possess problems of retention and stability. The principle of total dentures’ retention lays in their adhesion to a prosthetic bed, and at a negative barometric pressure (capillary pressure) that occurs when a denture moves away from its prosthetic bed. Retention depends on an environment between a denture and a prosthetic bed, on the state of mucous membranes and the quality of saliva. A prosthesis’ stability depends on artificial teeth positions at the body. A correct teeth position is a subject of many articulation theories, although none of them guaranties stability of a denture during its function. Configuration of jawbones and activity of masseters and mimic musculature are important for good stability and retention of a denture. A patient, to whom a total removable prosthesis was given, has to undergo a regular follow-ups and eventual denture sores have to be eliminated by smoothing a denture. If a denture is not fitted well, these denture sores can evolve into mucous rugae - garnuloma fissuratum. These formations not only worsen retention of a total denture but could also result in a neoplasm by chronic traumatization of the

tissue. Total prostheses can also be made according to impressions taken before teeth extraction. This so called immediate prosthesis is given to a patient right after extractions are finished. Discrepancies between this denture and a prosthetic bed can be fixed by denture padding - rebasing. After complete healing of extraction wounds (takes about six months) a definite prosthesis should be made. Immediate dentures have an advantage of quick accustoming ( a patient gets used to it easily) and also the fact that they slow down an alveolar resorption.

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