Annotation
Porcelain crowns have several advantages compared with other types of artificial crowns:
1. natural and stable color
2. does not swell and does not dissolve in the mouth
3. not permeable to microorganisms
4. does not cause allergic reactions
5. it does not form a dental plaque
6. heat insulator
7. indifferent material
8. resistance to wear
Negative points:
1. fragile
2. low load stability
3. may erase antagonists
Indications for the use of porcelain crowns:
1. partial defects of the coronal part of the tooth (TOSFI = 0,6-0,8 )
2. discoloration of the crown
3. abnormal tooth shape
4. position anomalies (diastemas, tremes)
5. systemic damage to teeth (color, shape, size)
Contraindications:
1. reduction of reserve periodontal forces of abutment teeth and antagonists
2. localized vertical abrasion with deep blocking bite
3. lack of sufficient space for the crown
4. deep bite
5. children under 16 years old have teeth with live pulp.
Principles of tooth preparation:
The optimal thickness of the porcelain crown is 1.2-1.5 mm. Tooth preparation is carried out intermittently, without pressure and vibration.
The first stage is the separation of contact surfaces and the creation of a preliminary step on the mesial and distal sides. During the removal of tissues from the contact surfaces with a diamond disc, a preliminary step is formed to a depth of 1 mm, not reaching the edge of the gum 0.5 mm. At the same time, these surfaces taper in the direction of the cutting edge. The angle of convergence of the walls should be between 7-9 °.
The second stage is the shortening of the crown of the tooth and the creation of a gap between the teeth being prepared and the antagonists within 1.5-2 mm. At the same time, the crown part of the front teeth is shortened on average by the thickness of the future crown. The occlusal surface of the posterior teeth is imitated in such a way as to preserve the anatomical relief with a rounded transition to the vertical walls of the tooth stump.
The third stage is the creation of a preliminary ledge and grinding of the palatal surface of the tooth. Diamond head of the reverse cone form a groove, some 0.8 mm from the tooth neck. From the groove to the right and left of the cylindrical diamond bur remove tissue of the tooth to the dental tubercle.
The fourth stage is the preparation of the vestibular surface. Over the entire surface, a vertical groove is created with a depth of 0.8 mm, not reaching the gum 0.5 mm. From the groove, trying not to go too deep, they sand the vestibular surface to a depth of 1.2 -! 5 mm.
The fifth stage is the rounding of corners, the alignment of the surface of the stump, the final formation of the ledge with the end face bur.