Adhesive posterior restorations allow us to recreate the whole lost dental structure, preserving the remaining healthy tissues as much as possible. Ideally, in most cases, ceramic materials should be chosen for this purpose, but often we have to face financial limitations of patients, and resort to materials such as composite resins to directly restore te tooth. Yet, there are several disadvantages to this approach (mandibular wear resistance, polymerization stress, possible post-operative hypersensitivity, difficulty in creating an adequate emergency profile in cases of great destruction at the cervical level, and difficulty in creating a favourable contact point). To avoid all of this, we can resort to semi-direct restorations, which have the following advantages: ideal control of the anatomy of the occlusal surface, excellent control of the contact point and emergence profile, possible evaluation of the occlusion with the articulation of the models and minor polymerization stresses.
The patient arrived complaining of a broken tooth. By examining the tooth, we can see there was an old and extensive MOD restoration, with a mesial fracture. We can also appreciate the already existing undercuts on the distal adjacent tooth.
After removing the old restoration, the remaining structure showed unsupported axial walls. Also because the tooth was endodontically treated, an overlay restoration was chosen to provide full coverage of the tooth. We also know that, according with Dr. Maciej Zarow’s classification, we are in the presence of a class 0 tooth, which means that we won’t need extra retention besides a build up, because, by being a posterior tooth, we can take advantage of the anatomy of the pulp chamber to increase the adhesion area.
So we decided to first perform a Deep Margin Elevation on the mesial, with a banana matrix mounted in a Tofflemire retainer, following the protocol proposed by Dr. Pascal Magne.
Then we started the tooth conditioning in order to do the build-up restoration.
The build-up is made in order to fill the undercuts that are produced during caries removal, to provide a correct geometry of the cavity (being conservative with the remaining dental structure), and to allow us to control the thickness of our future restoration in order to do a photo-polymerization at the time of adhesion.
After doing the build-up, we started the the tooth preparation doing the reduction of all of the cusps in order to avoid future fractures.
Divergent walls are highlighted in red. In green we did a hollow chamfer of the buccal and palatal margins in order to better mimetize the transition of the restoration and to increase the enamel surface area, and in yellow are highlighted the mesial and distal margins which were prepared with a butt joint preparation and in a deeper position in order to allow the correct contact point.
A one step double paste impression of the preparation was taken.
And of that impression, two cast models were made. To fabricate this semi-direct overlay, we used Vincenzo Musella’s Inverse Layering Technique. The first model will be used for the fabrication of the restoration (because it is always more reliable), and the second one was used to make a wax-up.
Final wax-up. It is important that the wax up is made with articulation, so that we can be sure that the future restoration will have the right function.
Since our goal is that our future restoration reproduce all the detail of the wax up, a transparent silicone key is made with the help of a thermoplastic tray, that is custom made, to allow the correct stability and penetration of the silicone on the waxed model.
This is how we made the transparent silicone key.
In the silicone key, the composite resin is applied and brought onto the first cast model. This first cast model was previously treated with an isolating material (so the composite doesn’t stick to it) and the retentive areas around the preparation were relined with a small amount of wax to remove the future restoration easily.
A bulk fill composite resin was used because in mesial and distal we had a 4mm depth, and we didn’t want to compromise the polymerization of the luting agent in those areas.
Composite must be applied in the restoration area so as to avoid trouble with excess material. In this case it was easy, as we had to reline all the cusps, but in onlays, we must only reline the cusps that are going to be covered.
It’s also important to press the silicone key well, in order for the composite to adapt to the cast model and also reproduce all the detail of the wax up. 20 sec per key surface of polymerization was made.
Brief video on how we apply the composite on the silicone key.
This is the restoration freshly taken out the silicone key.
At this point, the characterisation of the restoration was made with the use of stains. We can use a 08 endodontic file or a blade to apply them, and a really thin brush to blend them. We normally use three stains: yellow for the occlusal surface, brown in the sulcus and white on the cusps, to enhance volume perception. It is very important to not abuse of stains because it would get very ugly and unnatural. Once we finish the stain application, we light cure.
testo sotto immagine
The final polymerization of the restoration was made with glycerin in order to promote the polymerization of the layer inhibited by oxygen.
These are the materials that were used for the adaptation and polishing of the restoration. The disc to adapt the margins, the rubbers to polish, and the brushes and diamond paste to give the final gloss.
Final aspect of the fabricated overlay restoration.
Firstly we did the try in of the restoration without the rubber dam, so that we could be sure that it fit correctly. Once the fitting was checked, we isolated the tooth and tried the restoration again, in order to make sure that the isolation did not interfere with the fitting.
We can now start the adhesive procedure. It was started with the treatment of the restoration, which was firstly sandblasted, making sure that we were not too close to the restoration (the aluminum oxide can produce undercuts on the composite surface and we can loose the fitting of the restoration). After sandblasting, the Veneer ME was used to clean the restoration with orthophosphoric acid, to rinse it with water and dry with air, and to apply the adhesive system.
The normal adhesive procedure was then performed on the tooth, with the sandblasting of the prepared surface, the tooth conditioning with orthophosphoric acid (30 sec on enamel and 15 sec on dentin), the application of the adhesive system, the adhesion with heated composite and the final polymerization of the restoration with glycerin.
Final restoration with the rubber dam still on.
Final restoration without the rubber dam.
Semi-direct restorations are reported in the literature as a good alternative in cases with the need of cusp coverage. These restorations are basically direct resin restorations with the advantage of an extra-oral fabrication. They are considered to be fast, low-cost and a clinically acceptable treatment option. In this article, we presented a case of a first maxillary molar, with the need of a total cusp coverage by the fabrication of a semi-direct restoration based on a functional wax up. We can conclude that using this technique, it is possible to restore teeth with cusp coverage needs in a functional, esthetic and cheap option for the patient.
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