The insertion of all-ceramic restorations always raises questions. Basically the topic is complex. Numerous factors influence the type of attachment in the patient's mouth. Anja Liebermann (research associate at LMU Munich), Bogna Stawarczyk (scientific head of the materials science department, LMU Munich) and Annett Kieschnick (specialist journalist) address fundamental questions.
problematically
The variety of ceramic material classes opened up a wide range of flexibility for the production of all-ceramic restorations. Feldspar, lithium disilicate, oxide ceramics, various zirconium oxides, hybrid ceramics… the product range is wide. The treatment team selects the optimal ceramic material based on the indication and should also know the criteria for the type of attachment.
How should all-ceramics be classified in terms of attachment?
Dental ceramics can be divided into glass ceramics (feldspar, leucite and lithium (di)silicate ceramics), glass-infiltrated ceramics (In-Ceram Alumina, In-Ceram Zirconia) and oxide ceramics (aluminum oxide and zirconium oxide). The prerequisite for traditional cementation (cementing) is a retentive design of the preparation and a restorative material with a flexural strength of more than 350 MPa. Glass ceramics based on feldspar (approx. 60 to 80 MPa) or leucite (approx. 90 to 120 MPa) have a lower flexural strength and must be attached adhesively. On the other hand, lithium (di)silicate, glass-infiltrated ceramics and oxide ceramics can theoretically be cemented.
So does the bending strength make the decision-making process easier?
In any case! It is imperative to adhesively bond ceramics with lower strength values (below 350 MPa).
When does an all-ceramic restoration definitely have to be cemented?
There is no all-ceramic restoration that necessarily needs to be cemented. Theoretically and practically, all all-ceramic restorations can be cemented adhesively. Cementing is only done because of the user-friendliness during attachment.
When is adhesive technology mandatory?
If the tooth preparation is less than 4 mm from the stump height and is prepared relatively conically (6° to 15° convergence angle), the restoration should be cemented adhesively. It is also recommended that adhesive bonding be preferred for zirconium oxide bridges. In addition, all ceramics below 350 MPa must be adhesively bonded.
Cemented or adhesive – what are the advantages and disadvantages?
Traditional cementation using acid-based cements (e.g. zinc phosphate or glass ionomer cement) requires an excellent fit of the restoration. Since the adhesion takes place in the form of cementing, the framework surface should have mechanical retention (e.g. through surface roughening, corundum blasting/etching). Cementing is cost-effective and user-friendly. But: Cements are usually opaque. It should be noted that the esthetics of translucent restorations can be negatively affected by conventional cementation. Pre-treatment of the tooth structure is usually not necessary.
Glass-ceramic anterior crowns
Preparation of the inner surface of the crown for adhesive integration
With adhesive bonding, the remaining hard tooth structure is stabilized by bonding. No mechanical retentions are required, so defect-oriented (minimally invasive) preparation can be carried out. The connection is force-fitting. As a result, the adhesive attachment is also more “forgiving” in terms of fit. Although user-friendliness and moisture tolerance are reduced, the mechanical and optical properties improve. Adhesive luting materials allow a certain translucency. They can be purchased in different tooth colors and are partly responsible for the coloring. The pretreatment of hard tooth structure and restoration plays a crucial role.
How should the tooth be pretreated for adhesive integration?
The hydrophilic structure of dentin requires pretreatment of the collagen mesh with etching and application of dentin adhesives. Buonocore laid the foundation for adhesive dentistry in 1955 with the acid etching technique. Since then, there have been several generations of systems for pre-treating the hard tooth structure. The basis of everything is the etching of the collagen network and the enamel.
The aim of etching is to enlarge the surface. In addition, the smear layer should be acted upon. “Etch-and-rinse” systems completely remove the smear layer using 37% phosphoric acid. “Self-etch” systems have acidic monomers. These do not completely remove the smear layer, but rather make it permeable or incorporate it into the hybrid layer. The etching is followed by the infiltration of the collagen mesh with hydrophobic bonding. With self-adhesive luting material, dentin pretreatment is not necessary. However, pretreatment by selective enamel etching with 37% phosphoric acid can increase adhesion.
How should zirconium oxide surfaces be prepared for insertion?
Zirconia has poor wettability. Therefore, the surface should not only be cleaned, but also modified. This is done by silicating (Rocatec, 3M; Cojet, 3M) or by gentle corundum blasting (≤ 50 µm, 1 bar, distance between jet nozzle and restoration approx. 10 mm). Plasma pretreatment can also have a positive effect on the surface tension of zirconium oxide.
When choosing the fastening system, the following combinations are recommended:
- luting composites with MDP-containing monomers (Panavia 21, Panavia F2.0, both Kuraray Noritake);
- Self-adhesive luting composites (e.g. RelyX Unicem, 3M, Panavia SA Cement, Kuraray Noritake, SmartCem 2, Dentsply);
- Luting composites in combination with an MDP primer or with acid phosphate, phosphorus group adhesive systems (e.g. Multilink Automix with Monobond Plus, Ivoclar Vivadent, Panavia V5 with Ceramic Primer Plus, Kuraray Noritake);
- Many universal adhesives (e.g. Scotchbond Universal, 3M) contain acidic monomers (e.g. MDP) and can therefore be used for the adhesive luting of zirconium oxide restorations.
Can a zirconium oxide be the 3. generation be used adhesively?
Yes. The mechanical and chemical adhesion of the luting composites to the zirconium oxide is the same regardless of the generation.
How should glass-ceramic surfaces be prepared for insertion?
Glass ceramics must be etched with hydrofluoric acid (5 to 9,5%) before attaching. This creates a retentive surface. The higher the luting composite is filled, the more overall stability of the restoration is achieved, e.g. B. with veneers. For a long-term bond, pre-treating the glass ceramic restoration with a ceramic primer is recommended.
Authors: Bogna Stawarczyk, Anja Liebermann, Annett Kieschnick