Annotation
In a removable laminar dentures, one should distinguish the basis of the prosthesis, the retaining elements (clamps) and artificial teeth.
The basis of the partial denture is a plate made of plastic or metal, on which the artificial teeth and fixtures for holding the prosthesis in the mouth (clasps) are fixed. The basis of the prosthesis lies on the alveolar process and the hard palate, with its help the chewing pressure from the artificial teeth is transferred to the mucous membrane of the prosthetic bed. The size of the prosthetic bed is proportional to the inverse relationship to the number of remaining teeth: the fewer teeth left in the jaw, the greater must be the basis. The nature of clamp fixation also affects the magnitude of the basis: with an increase in the number of clamps, the prosthetic base decreases.
The border of the prosthesis in the anterior part of the edentulous alveolar process of the upper and lower jaws on the buccal and labial side passes through the transition fold, bypassing the moving strands of the mucous membrane and bridle. Otherwise, they are damaged by the baseline and bedsores are formed. On the lingual side, both in the region of the missing and in the region of the remaining teeth, the prosthesis should cover the alveolar tubercle. The border of the prosthesis in the anterior part of the edentulous alveolar process of the upper jaw is somewhat modified depending on the severity of the alveolar ridge and the length of the upper lip. With a short lip and a well-developed alveolar process, the front teeth are placed on the inflow. With a long lip and large atrophy of the alveolar process, the front teeth are placed on an artificial gum. In these cases, with a smile, the gum will hide behind the lip.
The edges of the prosthesis end in a transition fold, therefore, preference should be given to a rounded edge with a thickness of at least 2 mm. Thinned edges, gradually merging with the surface of the mucous membrane, are created on the palate and in the distal part of the lower prosthesis from the lingual side.
Types of clasps, and their constituent elements.
Klammer is a part of the orthopedic construction, which allows even in difficult conditions to fix the prosthesis in the oral cavity, using natural teeth as a support. There are clasps holding and supporting-holding. The purpose of the clamps is reduced to the fulfillment of the supporting, stabilizing and fixing function. Under the support function understand the transfer of chewing pressure through the supporting elements of the clasp on the supporting teeth, preventing the prosthesis from settling and tissue overload of the prosthetic bed. The stabilizing function is understood as the prevention of lateral movement, and, finally, by the holding (fixing) function, is meant preventing the prosthesis from sliding off the prosthetic bed. The most advanced types of clasps perform all three functions simultaneously.
The components of the clasp are: the shoulder, the body and the process of the clasp. The clasp's shoulder is its springy part, covering the crown of the tooth. The shoulder should cover the tooth from the labial (cheek) side, located directly behind the line of its greatest convexity, that is, between the equator and the gum. The clasp's shoulder should touch the tooth surface all the way, should spring when the denture is displaced, must be passive, i.e. it should not exert pressure on the male tooth when it is under tension.
The body of the clasper is the fixed part of the clasper, located above the equator of the abutment tooth on its contact surface.
The body of the clasp goes into the process, which is designed to fix the clasp in the prosthesis. It lies along the edentulous alveolar process under artificial teeth.
Evaluation of teeth and indications for the manufacture of artificial crowns for clamp fixing
There are several general requirements for abutment teeth. First, they must be sustainable. When the abnormal mobility of the teeth should be blocked with a number standing for the formation of a sustainable system. The teeth with chronic near-peak inflammatory foci can be used for support only after successful canal filling.
Secondly, the teeth must have a pronounced anatomical shape. For clasping fixation, teeth with a low or conical crown, a bare neck and a sharp violation of the ratio of the length of the clinical crown and the root are unsuitable. These deficiencies are a relative contraindication. After special preparation, such teeth may be included in the number of supports of the clamp system.
Thirdly, it is necessary to take into account the relationship of the abutment tooth with the antagonists. These relationships can be so close that even a small occlusal lining placed in a fissure on the chewing surface will break the closure of the teeth. In such cases, to accommodate the support element, select another tooth or occlusal overlay into an occlusal insert, and apply a crown on the abutment tooth.
The indications for the use of crowns are abnormal tooth forms or the destruction of its caries, the exposure of the cervix, causing the clinical crown to lengthen, hyperesthesia of the enamel, the inclination of the tooth in the direction of the defect, violating the parallelism of the supports. The indications for the support of the supporting teeth with crowns can be extended when using support-holding clamps, and when using only holding clamps, they should be narrowed.
Of great importance in the manufacture of removable laminar dentures is the location of the clasps in a certain order in accordance with the clamp lines. By a clasper line is meant an imaginary line through the abutment teeth. It is the axis around which the rotation of the prosthesis is possible. The klammer line may extend in the transverse (transverse), oblique (diagonal), anteroposterior (sagittal) directions.
The best way to fix a partial denture should be considered bilateral arrangement of clamps. In this case, in the upper jaw, preference should be given to the diagonal direction of the clamp line. In the lower jaw the best fixation is ensured if the clasp line has a transverse direction. The direction of the clasp line is determined by the topography of the defects and the periodontal status of the remaining teeth.
When fixing the clamping system of supporting elements, the load on the supporting teeth becomes greater than when using simple sliding, i.e. holding clamps. Therefore, when prosthetics with arc prostheses, the fastening system should be built on a greater number of supports. Such anchorage is called planar, as opposed to linear, when the prosthesis is held by one clamp.