Annotation
Requirements for cast construction (inspection on models):
1. The absence of pores, holes on the outer surface.
2. The accuracy of fitting to the plaster cult.
3. Attitude to antagonists and nearby teeth, based on the thickness of the future lining (from 0.5 to 2 mm).
4. The thickness of the cast construction is 0.3-0.5 mm.
The cap that meets the requirements is disinfected and checked on the abutment tooth in the mouth.
Very rarely, the molded cap immediately, without pre-fitting, is superimposed precisely on the prepared tooth. This is due to many reasons. Most often it is a combination of small errors in the preparation of the tooth and the manufacture of the cap. To fit a molded cap, put a damp copy paper under the cap (with a coloring layer to its inner surface) and impose on the tooth. Having received the imprints of the inner surface, the areas that prevent imposition, grind diamond heads. The manipulation is repeated until the molded cap is precisely positioned in place. After that, check the accuracy of the fit of the cap to the cervical part of the tooth. The degree of dissociation of the cap with the antagonist teeth and the amount of space for the facing layer is assessed last. If there is a supercontact, it is detected with a copy paper or occludogram and eliminated by grinding.
The specificity of metal-ceramic prosthetics requires the need to check the design in the oral cavity after the second firing.
A working model with a metal-ceramic crown is transferred to the clinic for examination in the oral cavity. Evaluation of the quality of manufacturing of the crown begins with an inspection of it on the model:
1. Anatomical shape.
2. Interdental contacts.
3. Contact with antagonists
4. Fit the edge of the crown to the gum section of the tooth.
Disinfected crown impose on the abutment tooth in the mouth. After checking the metal cap to prevent the imposition of the crown can:
1. Excess ceramic mass on approximal surfaces.
2. Excess ceramic mass on the edge of the cap adjacent to the ledge of the stump.
Items that interfere with overlapping are detected with carbon paper and removed by grinding. After that, carefully check the occlusal contacts with the central, anterior and lateral occlusions. After that, the conformity with the anatomical form is checked, if necessary, the ceramics (or plastics) layer is ground, or the required amount is applied using a laboratory method. Special attention is paid to color matching. In difficult cases, apply dyes. After appropriate correction, the crown is coated with icing. Glazing is aimed at giving the ceramic coating a shine characteristic of natural teeth enamel.
Clinical and laboratory stages of manufacturing a combined crown
Clinical stage
1. preparation of teeth.
2. removal of the worker (double) and auxiliary repeaters.
Laboratory stage
3. Manufacturing collapsible model.
4. manufacture of plastic cap.
5. modeling wax cast cap.
5. Replacing wax on metal (casting).
6. fitting the molded cap on the model.
Clinical stage
7. fitting a molded cap in the mouth.
8. selection of color facing material
Laboratory stage
10. coating cast cap facing mass.
Clinical stage
11. fitting the combined design in the oral cavity.
12. color correction.
Laboratory stage
13. color correction.
14. glazing.
Clinical stage
15. the imposition and fixation of the combined design.
The algorithm for choosing colors in dentistry. Based on the above features and mechanisms of color perception by a human visual analyzer to recreate the optimal optical and morphological properties of the tooth in the preparation of various restorations, the following rules for choosing the color of aesthetic dentures were proposed.
1. It is best to determine the color in daylight in the first polo ¬
the fault of the day, with light clouds, at a distance of 1 m from the window facing north. When determining the color should always avoid direct sunlight. In artificial light, the color of the tooth should be determined with a light source with a color temperature of 5500K. Too much light from the operating lamps “washes out the color” and the tooth seems too light. If the light is too weak, the tooth appears gray. It is also necessary to exclude the phenomenon of metamerism, making an assessment of color with natural, and then refinement with artificial light.
2. The objectivity of determining shades of color is seriously affected by such a characteristic as the contrast of sensations. That is, a change in perception may occur depending on a prior or accompanying background. In dentistry, gray is considered to be the reference background with a reflectivity of 18%. There are special gray cards with a clipping in the center; gray background is used due to the fact that it does not create a sharp contrast and practically does not form a trace reaction. These cards are called Pensler Shild, they allow you to match and compare natural teeth with reference ones. Besides this, the general environment should be the most neutral. There should not be motley curtains in the room, motley objects behind the window, there should not be lipstick on the lips of the patient and bright clothes. Bright clothes should be covered with a napkin of light gray tones, rather than green or blue, which are widespread in practice. The clothing of medical personnel, the color of the walls and furniture should be neutral (white). It is important to remember that the full-blooded complexion of the patient may emphasize the greenish hues of the teeth, while the pale, with a yellowish tinge, enhances the red component. Remember that the color of the gums will also affect the choice of color. With dark gums, we tend to choose a lighter color, and with a light gum - on the contrary, on the principle of contrast.
3. It is necessary to consider the environment: in the working
The room should not have loud sounds, flashes of light, dust, temperature discomfort, since all of this affects the effectiveness of aesthetic perception.
4. The sensitivity threshold of the analyzer depends not only on the intensity of the stimulus and its nature, but also on the duration of exposure. To make the right choice you should use “quick looks” (2-5 seconds). To relieve fatigue of the visual analyzer, it is necessary to look at a neutral background for a while and then continue choosing the color.
5. The presence of a “subjective” in perception requires participation in
color of at least three observers. The choice of color for the restoration of teeth with veneers, metal-ceramic or all-ceramic crowns should be made by the orthopedic dentist together with the dental technician, with the obligatory participation of the patient himself. The objectivity of the result is enhanced if photographing the test tooth with a standard.
6. The choice of color must be made before the preparation is carried out and applied to the cofferdam. Being isolated from saliva, the tooth becomes lighter and less transparent. It is recommended to use a trial application of the material before applying the cofferdam.
7. The color of the dentin must be determined by the cervical or middle third of the canine. When chipped to dentin, the color is selected directly to the dentin of the tooth.
8. The color of the enamel must be determined by the cutting edge of the tooth being restored.
9. With the complete destruction of the cutting edge determine the color of a symmetric tooth.
All of these parameters help the dentist to achieve better results when performing aesthetic work.