Ceramic-ceramic processes
Introduction :
Ceramic-ceramic systems and processes have continued to evolve and are gradually replacing ceramic-metal restorations.
Currently these systems ensure long-term mechanical resistance, biocompatibility and a
1. Definition
The term ceramic comes from “keramos” , a Greek word meaning clay.
A ceramic is an inorganic, non-metallic, generally fragile material, with a generally two-phase mineralogical structure (amorphous glass and crystallized minerals), composed of oxides (99%), carbides, borides, and whose shaping and consolidation require a heat treatment called sintering.
2. Advantages of ceramic-ceramic systems
2.1. Biocompatibility:
The ceramics used in prosthetic dentistry are bio-inert materials (inertia, chemical, electrical, thermal).
Their chemical structure gives them great stability and therefore good biocompatibility. They are much more stable than metals and resins and do not exhibit degradation by corrosion. “The chemical inertia of ceramic materials makes it possible to minimize reactions of the host organism”). Thermal inertia makes it possible to isolate the pulp-dentin complex and assembly materials from temperature variations. The excellence of the surface conditions results in low adhesion of dental plaque.
Marginal adaptation is precise.
2.2. Physicochemical properties:
- Mechanical resistance in compression: the resistance is comparable to that of enamel but with a thickness greater than 1.5mm.
- Ceramics are characterized by their fragility, that is to say that they will fracture under stress with very low deformation at break.
2.3. Optical properties:
Translucency
The translucent or opaque character of a ceramic is directly linked to the microstructure and in particular to the quantity of amorphous vitreous matrix. Opacity is the ratio of the reflected light intensity to the reflected and transmitted light intensity.
The larger the vitreous matrix in volume, the fewer crystals there will be, the more translucent and aesthetic the ceramic will be. Polycrystalline ceramics made of alumina or zirconia are opaque or semi-opaque due to the absence of a vitreous phase.
3. Classifications of ceramics
There are 4 classifications of ceramic materials:
– According to their melting temperature (the oldest).
– According to their microstructure (presence of vitreous and/or crystalline phases).
– According to their chemical nature (mineralogical composition).
– According to their method of production (manufacturing process).
Ceramic-ceramic processes
3.1. According to their melting temperature:
| Type of ceramic | Melting temperature | Indication |
| High fusion | 1289 to 1390 °C | Artificial teeth removable prostheses |
| Medium fusion | 1090 to 1260 °C | Jacket baked on platinum |
| Low fusion | 870 to 1065 °C | Enameling ceramic-metal crown |
| Very low fusion | 660 to 780 °C | Titanium and gold enameling |
3.2. According to their microstructure:
There are two types of ceramics depending on the number of phases they contain: they are called homogeneous (one phase) or heterogeneous (two phases).
⮚ Homogeneous ceramics (single-phase)
Ceramics consist of only one phase, either vitreous or crystalline.
The interest of these ceramics is either to have excellent optical behavior if there is only one glassy phase, or to have excellent mechanical behavior if there is
only one crystalline phase exists.
⮚ Heterogeneous (two-phase) ceramics
Ceramic is made up of two phases, vitreous and crystalline. The glass will give translucency to the prosthetic piece. The crystals will oppose the propagation of cracks present in the glass.
The optical quality will be proportional to the quantity of vitreous phase and the mechanical quality inversely proportional to it.
3.3. According to the mineralogical structure:
Most ceramics have a two-phase microstructure, meaning they consist of a glassy phase and a crystalline phase.
The crystalline phase represents a more or less important proportion within the ceramic, it is made up of crystals of the same or different nature.
We traditionally distinguish 5 categories of ceramics:
- Feldspathic ceramics (traditional or reinforced).
- Reinforced glass ceramics (with leucite or lithium disilicate).
- Polycrystalline ceramics (based on pure alumina or zirconia).
- Pure aluminous ceramics.
- Zirconia ceramics without glassy phase.
- In Ceram® ceramics (special glass ceramics). We distinguish:
- In Ceram Spinell ®
- In Ceram Alumina®
- In Ceram Zirconia®
- Hydrothermal ceramics (known as low fusion).
3.4. according to the method of preparation:
Regardless of the mineralogical structure or not, the prosthetic part can be shaped using 4 main processes:
– Classic cooking on a refractory coating;
– Hot pressing and injection;
– Sintering with infiltration of a vitreous matrix;
– Machining.
4. Ceramic-ceramic crowns
4.1. Definition:
It is a crown that is entirely made of cosmetic materials (ceramic infrastructure + cosmetic material).
4.2. Indications:
– Pulped or depulped tooth;
– Dysplasia;
– Tooth staining;
– Fractures of the cuspal angles.
4.3. Contraindications:
– Tooth with unstabilized apical or periapical reaction;
– Periodontolysis;
– Significant fracture due to caries;
– Large pulp chamber;
– Reduced VL or VP diameter;
– Tight occlusion;
– Stump too short.
4.4. General principles of preparation:
- Type of limits:
A cervical limit in the form of a shoulder with a rounded internal angle will be made all around the preparation.
The shoulder increases fracture resistance while the rounded internal angle allows better reproduction of the profile by the ceramic and makes it easier to adapt the slip.
A wide leave preparation is also possible.
Ceramic-ceramic processes
Shoulder with rounded internal angle
- Limit Level:
A juxta or supragingival limit will be created which will allow:
– Respect periodontal integrity;
– Visually check the accuracy of the limit;
– Facilitate the imprint and the creation of temporary copies;
– Easily clean the dento-prosthetic joint.
- Discount value:
A tissue reduction, imperatively homothetic, must both provide sufficient thickness for the ceramic and at the same time be concerned with tissue economy by preserving pulp vitality.
– vestibular tissue reduction varies from 1.2 to 1.5mm;
– proximally a reduction of 1mm;
– at the occlusal and incisal level: reduction is 1.5mm to 2mm;
– at the palatal level: the reduction varies from 1 to 1.2mm.
– take care to round off sharp corners (avoid stress concentration);
A more pronounced taper of 10° to 14° (to facilitate shaping in the laboratory).
Once the preparation of the stump is complete, the impression of the arches is taken with a synthetic elastomer.
We will then proceed to the choice of shade which is done in daylight using a shade guide.
Recording of intermaxillary relationships, the reference position being the PIM
Placement of a temporary crown during the laboratory time which will allow the patient to regain a certain aesthetic and masticatory comfort.
5. The facets
5.1. Definition:
Porcelain veneer is defined as a bonded partial veneer crown. It can be made of composite or ceramic.
5.2. Indications:
- Improved aesthetics
– Changing an annoying color;
– Dyschromia resulting from fluorosis or tetracycline;
– Extensive composite fillings – aesthetically insufficient;
– Superficial defects of the enamel.
- Corrections of dental morphology
– Dysplasia of the anterior teeth;
– Hypoplasia of the anterior teeth;
– Dental fracture;
– Lengthening of clinical crowns;
– Diastema.
- Correction of the position or alignment of teeth
In the case of slight malpositions and when the patient refuses any orthodontic treatment.
- Functional fixes
– Palatal veneers for the reconstruction of incisor-canine guiding occlusal faces;
– Protection or replacement of lost dental tissue:
°Erosions, abrasions;
°Restoration of loss of substance following caries.
5.3. Contraindications:
– Insufficient quantity (< 50% of the vestibular face);
– Circular carious lesions in the transition zone towards the gum;
– Inability to adequately mask marked dyschromia of hard dental tissues;
– Very wide spaces between the teeth, need for significant lengthening of the dental crown ;
– Patients with marked parafunctions (bruxism, grinding);
– Minor defects (avoid overtreatment);
– Patients with insufficient oral hygiene.
5.4. Advantages:
- On the aesthetic level: better control of color and its three components: hue, saturation, brightness.
- On the periodontal level: the biocompatibility of the ceramic allows it a good marginal seal. Its excellent surface condition allows easy control of dental plaque.
- Longevity: the use of ceramic makes the veneers resistant to biological and chemical attacks.
- Bonded veneers are able to restore tooth rigidity (Reeh et Coll 1994).
5.5. Disadvantages:
– Risk of ceramic fracture;
– Long and delicate collage to implement.
5.6. Preparations for ceramic veneers:
- The first step in preparation is to place depth markers (grooves) on the vestibular surface of the tooth.
- Several shapes of burs are available and offer different depth options to meet clinical situations: between 0.4 mm for veneers made of feldspathic ceramic and 0.8 mm maximum for veneers with framework made on supports in case of dyschromia.
Conclusion
The improvement of ceramic-ceramic processes as well as bonding materials has opened a new area in aesthetic dentistry.
Practitioners are increasingly responding to the aesthetic requirements of their patients.
Ceramic-ceramic processes
Wisdom teeth may need to be extracted if they are too small.
Sealing the grooves protects children’s molars from cavities.
Bad breath can be linked to dental or gum problems.
Bad breath can be linked to dental or gum problems.
Dental veneers improve the appearance of stained or damaged teeth.
Regular scaling prevents the build-up of plaque.
Sensitive teeth can be treated with specific toothpastes.
Early consultation helps detect dental problems in time.