Composite onlays – Cavity preparation, surface treatment and cementation

Indirect composite restorations in posterior teeth provide great advantages as this kind of restoration enhance quality, durability and aesthetics. In the late ’90s and early 2000s there was the manic trend of replacing amalgams with “aesthetic” restorations. Now, a decade later, we are experiencing how these materials are failing, mainly because the wrong techniques were used.


The patient came with two old ceramic inlay restorations, which showed marginal leakage, aesthetic failure (probably since day 1) and fractures that jeopardize the tooth integrity.


After isolating the field with the rubber dam, a wedge was inserted interproximally, one of the most important steps during cavity preparation. The wedge separates teeth, compresses the papilla and pushes the rubber dam below to the cavity margin.


Ceramic inlays were removed with diamond burs and abundant water irrigation. Note how the floor of the cavity is still mixed with excess composite cement, which was not perfectly bonded to the old ceramic restoration.


The cavity floor was cleaned with round carbide burs on a low speed hand-piece and water. Note how some areas were missed. Some materials really blend with dentine and become invisible when wet by irrigation.


For the final stage of the decay removal, a caries detector was applied for 10 seconds and washed away. With low speed carbide bur, and no water, the remaining caries and old cavity base material were removed. Note how the wedge was slightly touched and the rubber dam is interfering in the margin area.


Residual walls that measured less than 2 mm were removed. At his stage, a 5% chlorhexidine aqueuous solution is placed in the sound dentin for 5 minutes. A sectional matrix was carefully placed to ensure the complete visibility of the margin, at the same time chlorhexidine keeps working.


The bonding procedure is carried out and an opaque dentin base is placed for many purposes; first, to make the cavity more even, second, to eliminate retentions, third, to give the cavity the proper thickness, and fourth, to make the margin accessible.


After matrix removal, the preparation was finished and polished. Then the rubber dam was removed and an impression was taken.


One week later, restorations are ready to be cemented and the case can be finished. Isolation was performed and the composite base was sandblasted with 50 micron aluminum oxide particles. After sandblasting, 5% chlorhexidine was placed for 5 minutes.


The restorations are tried in one more time, with the rubber dam on, to make sure that isolation doesn’t interfere with cementation.


This image is intended to highlight the importance of composite conditioning. Sandblasting is the most effective surface treatment for bonding to polymerized composite surfaces. After the second try in, the restorations are sandblasted and thoroughly cleaned with alcohol to eliminate all residual particles.


Selective enamel etching was done for 15 seconds – after having covered the whole cavity enamel contour – and dentin was etched with a self-etching primer. The composite base was already treated by sandblasting to enhance micro-retention.


The same bonding procedures were carried out at the same time on the restorations. A primer is applied to the restorations and to the composite build-up for one minute and then completely air dried. Several studies support this action positively due to the dramatic increase of wettability.


The bonding agent is placed on the restoration and on the build-up, and then carefully blown to become as thin as possible, and polymerized for a full minute. If the bonding agent is dense, it is not advisable to cure it.


The bonding agent is placed on the restoration and on the build-up, and then carefully blown to become as thin as possible, and polymerized for a full minute. If the bonding agent is dense, it is not advisable to cure it.


The restoration is then placed into the cavity and firmly pushed with a big rounded plugger (LM Arte Condensa); excess material will start slowly, but constantly, flowing out of the cavity.


Most of the excess material is immediately to be removed with the Fissura instrument (LM Arte).


Inter-proximal excess is easily removed thanks to the smart proximal box margin design.


A common mistake is to polymerize at this stage. Instead, this is the time when applying pressure again makes excess composite flow out again.


After pushing continuously for 30 seconds even the last part of the excess material will flow out of the cavity. At this stage a brush is useful to remove the little bit of composite cement from the restoration-tooth interface.


After all excess material is removed, the restoration is ready for polymerization. Important note: Cementation must be done with low light conditions to prevent cement from being cured early and creating undesirable thickness underneath.


Initial polymerization is done under mild pressure with an instrument.


Another polymerization cycle is carried out under glycerin to completely isolate from oxygen that might inhibit curing of the outer layer. High power light is applied for 5 minutes.


With a rubber abrasive tip most of the excess is trimmed. With a goat hair brush and polishing paste, the final gloss is achieved.


The restorations after polishing show a highly glossy look.


Once the rubber dam is removed, occlusion is checked. Interferences are removed with a multi blade bur. Usually, with this kind of bur, the surface gloss is not damaged.


The case just finished shows a good integration and gloss. Necessary check-ups will be done.


Even though composite might seem as a cheaper choice, its real advantage is it is repairable, which makes it, sometimes, the best option.


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