Clinic meets research Vol.3
Cementation is a crucial step in the process of ensuring the retention, marginal seal and durability of indirect restorations. Cementing procedures are either adhesive or non-adhesive. Adhesive cementation involves the use of an agent to promote bonding of the restorative material to the substrate; it is a combination of adhesive chemical bonding and micromechanical interlocking. Non-adhesive cementation involves the use of a luting agent to fill the space between the restoration and the natural tooth and relies solely on micromechanical retention. The clinician must have a good understanding of metal alloys or ceramic type to determinate whether a restoration should be cemented adhesively or non-adhesively. Choosing and applying the appropriate surface treatment and cementation procedure will contribute to long-lasting restorations.
A Blog by Giuseppe Marchetti and Giovanna Orsini
BONDING PROCEDURES IN INDIRECT POSTERIORS
CEMENTATION OF METAL RESTORATIONS
The cementation of metal or metal-ceramic restorations can be performed with conventional cements (zinc phosphate, glass ionomers, resin-modified glass ionomer) or with a chemical polymerization resin cement. In using chemical polymerization composite cements, base-metal alloys can increase adhesive bond to metal and metal-ceramic restorations due to the formation of a oxides layer capable of reacting with cement acid groups (1-2). Silanization of surfaces of silicate metal (Rocatec, 3M ESPE, St. Paul, Minnesota, USA; and Silicoater, Heraeus Kulzer, Hanau, Germany) can further improve the micromechanics interconnection and chemical covalent bonds (3). The adhesion that is reached is a micro-mechanical type and some surface treatment is generally required to increase the adhesive bond. However, the noble alloys offer a lower adhesion capacity compared to other materials, such as vile alloys.
CEMENTATION OF GLASS CERAMICS RESTORATION
This ceramic is highly esthetic, biocompatible and resistant to abrasion and compressive forces. It must be cemented to the prepared tooth adhesively to increase the restoration’s resistance to fracture (4). Non-adhesive cementation is not indicated for feldspathic ceramic (5). The clinician must condition the glass feldspathic ceramics before performing adhesive cementation. The clinician etches the ceramics’ internal surface with a solution of hydrofluoric acid (HF) 5% for approximately two minutes (6), to increase surface area, micromechanical retention and to clean surface for adhesive cementation. Then the surface must be silanized (5-6). Adhesive cementation to enamel or dentine requires the use of an adhesive system, followed by application of a resin cement (7). Adhesive systems can be either self-etching or total etching (8). Resin cements can be cured via light, chemicals or a dual process combining the two. Light-polymerized resins are recommended when the ceramic is thin and fairy translucent (9). Dual-polymerized resin cements are indicated when the ceramic is too thick or too opaque to allow the light transmission (5).
CEMENTATION OF ALUMINUM OXIDE CERAMICS
Adhesives protocols applied with success to the silica-based ceramics cannot be used for the aluminum oxide ceramics, because the etching with HF acid does not appear to increase the retention of resin cements (10). These ceramics can be cemented conventionally rather than adhesively. Long-term adhesion studies recommend blasting (with particles of Al2O3 from 30-50 µm at 2,8-3 atm) to roughen the surface for micromechanics adhesion (11-12). Coating the ceramic with tribochemical silica and air abrading of internal surface, followed by application of 10-methacryloyloxydecyl dihydrogen phosphate before using resin cement (chemical or dual cured resin cement ), improve the bond to this type of ceramic (13-14).
CEMENTATION OF ZIRCONIA CERAMICS
Zirconium oxide ceramics are characterized by the absence of glass in their composition. These ceramics possess high toughness and strength. Polycrystalline ceramics most often are cemented conventionally but can benefit from adhesive cementation. The use of low-pressure air abrasion with aluminum oxide particles or tribochemical silica application followed by application of an adhesion-promoting agent increase the bond-strength of resin cements (chemical or dual cured resin cement ) (15).
It is imperative that the clinician achieve affective isolation to keep the field free of saliva and other contaminants when using adhesive cements (16). Field isolation in not required in the case of zinc-phosphate and glass-ionomer cementation, but it’s necessary the fluid and saliva control.
CEMENTATION OF COMPOSITES
The bond between composite restoration and resin cements is very high and allows to have good levels of adhesion. So we can reach a very good adhesion even with indirect restorations. To have it one of the most effective protocols is that one that provides sandblasting the inner surface of the restoration with aluminum oxide for about 10 seconds , silanization (possibly activation with hot air or in special ovens of the silane ) , drying , then the application of a layer of bonding resin and at the end the luting procedures with a resin material that could be a dual composite cement or composite photo – polymerizable ( generally pre-heated in a special oven ) (17-18).
New rubber dam isolation.
The build up of the endo treated tooth is performed with a fiber post and composite.
Details of the build up of 4.5
Final curing with glycerin gel to inhibit the presence of oxygen.
I.D.S. and build up of 4.6 4.7 are performed and preperationss are done for indirect restorations under rubber dam.
The three restorations on the plaster model.
Details of the composites restorations
Note the presence of the stitches, no troubles in placing the preps 3 mm far from the bone crest.
Details of the new isolation.
Try in of the composite restorations.
The contact areas fit well.
Bonding procedures: Total etching for 15 seconds, rinse for 15 seconds, gently dry.
Apply the primer for 10 seconds(if needed with the exposure of the dentin) and apply the bonding for 20 seconds with a brush, gently dry it and cure fore 20 seconds.
With a preheated composite the restorations are bonded.
Details after the bonding procedures.
Details after rubber dam removal.
One week later, shape and morphology look good and the restorations are well integrated too.
In a different clinical case the same procedures, I.D.S. and build up.
An ultrsasonic tip is used to refine the cavity shape.
A retraction chord is placed to take the impression.
The composite restoration is done indirectly by the laboratory technician.
And its bonded under the dam.
Details of the bonding procedures.
One week after, we have a proper integration.
Sometimes we can perform posteriors in semi direct ways.
After the preps an impression is taken.
A silicon model is done with two different types of silicon.
Details of the two different types of silicone .
A lego base is used.