Annotation
Set the model in the position of the CO (central occlusion) in several ways. When the first model is installed in the position of the central location on the signs of closure, characteristic of each type of bite. This can be done if the model has many teeth, and they allow you to accurately make models in the desired position. In those cases when it is impossible to make models in the CO position due to the small number of teeth or their inconvenient location, they preliminarily determine the CO in the oral cavity using the bite roller. The first method is used for small defects (1 - 2 teeth). The second method is more reliable and gives better results. When bridges prosthetic defects of the lateral parts of the dentition, when the distal support is represented by only one tooth (with bilateral defects, especially), bite rollers should be used.
In case of a one-sided defect, the doctor can manufacture the roller itself. Heat the wax plate and make a roller out of it, equal in length to the defect. The height of the roller exceeds the height of the abutment teeth by 1 - 2 mm. The heated roller is introduced into the defect with a small effort so that at its ends prints of the contact surfaces of the abutment teeth and the tops of the alveolar process are formed. It is cooled and checked in the mouth. It should increase the height of the bite by 1 - 2 mm. Then a warm spatula warms the surface of the roller facing the antagonists, inserts it into the defect and asks the patient to close the teeth. If the patient has closed his teeth in anterior or lateral occlusion, the procedure should be repeated until the closure is correct. As a result, imprints of antagonists remain on the occlusal surface of the roller. Roller impose on the model and prints antagonists make up the model in the correct position.
With bilateral defects included, bite rollers are better to prepare a dental technician. For this purpose, on a model powdered with talcum powder, a preheated wax plate is compressed. Excess of it, going beyond the boundaries of the hard palate and transitional fold, is cut off. The wax base is strengthened with wire so that it does not deform during subsequent manipulations. After that, rolls are made from a heated wax plate and are applied to a wax base in the area of the defect, attaching them with melted wax. The roller should have a width of 1.5 - 2 cm and be higher than the occlusal surface of the teeth bordering on the defect by no more than 1 - 2 mm. Then determine the CO, as described above.
The relative height of the physiological dormancy of the masticatory muscles and lower jaw.
Outside chewing and talking, the tooth rows are usually open, since the lower jaw is lowered and there is a gap of between 1 and 6 mm between the front teeth. When the jaw sags, the muscles are somewhat stretched, which reflects the irritation of the proprioceptors. Irritation of proprioceptors entails a tonic contraction of the muscles, which keeps the jaw in the specified position. At this time, various groups of fibers alternately contract in the masticatory muscles, which ensures them peace and at the same time allows them to be ready for a new contraction. The resting position of the lower jaw is a kind of protective innate reflex. It is the source and the end for all its movements.
Clinical guidelines for the selection and production of artificial teeth
There are several types of artificial teeth. The teeth of type 1 are characterized by parallel lines of contact surfaces over half their length, starting from the cutting edge. The teeth of the second type have sharply converging lines on the contact surfaces, so that when they are positioned, they can intersect at the top of the tooth. The teeth of type 3 are distinguished by a biconvex line on the distal surface. Currently, there are transitional forms. A certain relationship has been established between the shape of the teeth and the type of face.
There are three types of faces: square, conical, oval. The contours of the face are determined by the inclination of that part of the cheeks, which is located between the zygomatic bone and the angle of the jaw. If the lines of the cheeks are parallel, then the face is square. If the lines of the cheeks are significantly narrowed downwards, then the face is oblong (conical). Finally, in cases where the lines of the cheeks are downwards, the face is called oval. Between the described strict types there are transitional, so-called soft forms, more often observed in women. Type 1 teeth harmonize with square faces and their varieties. For conical faces, teeth of 2 types are more convenient, in which the contact surfaces have a direction opposite to the lines of the face. Three types of teeth harmonize with the oval shape.