Case 1. Direct composite technique
The first case is a 20 years-old woman who presented a devitalized maxillary right second premolar (tooth 1.5) with a large occluso-distal provisional restoration (Figure 1a). During the preliminary steps of the endodontic phase, the cavity was first cleaned and the pulpal tissue was removed. Then, a pre-endodontic composite resin wall was bonded on the distal aspect in order to seal the cavity during the provisional phase. A special care was put in all these preliminary adhesive procedures because the subgingival portion of that resin wall is often left in place for the definitive restoration. Once filled the root canal with gutta-percha and cement, the cavity is cleaned with a diamond bur (Figure 1b). The total loss of substance and cavity configuration are now evaluated. In a correct occlusal context, the width of the remaining walls is generally considered safe when it exceeds 1.0 to 1.5 mm, especially in the cervical part. Also the presence of weakening fissures should be detected. In the specific case of the premolar presented, the presence of a large and sound mesial wall, which protects the tooth from dramatic mesio-distal failures, allows the entire conservation of the vestibular and palatal cusps (Table 1).
A radiographic examination must always confirm the clinical diagnosis (Figure 1c). According to the minimally invasive philosophy, the restoration by a full adhesive approach is the best choice to reinforce the system and to avoid a further loss of substance. As their quality and longevity are not essentially different, the choice of a direct or indirect technique is above all dictated by clinical feasibility. From an esthetic point of view, the possibility to conserve entirely the vestibular wall of a maxillary premolar is a great advantage. In case of pre-existing dentin discolorations, an internal bleaching with a mixture of perborate and hydrogen peroxide can be performed before the definitive restoration (Figure 4). Once the cavity isolated with a rubber-dam and a metallic matrix, adhesive procedures can be effectuated (Table 2). The distal resin composite wall is cleaned and conditioned by use of 27 microns Al2O3 sandblasting. Then, enamel and dentin are both etched with 35-37% orthophosphoric acid 10 and 30 seconds, respectively. The cavity is abundantly rinsed with water and gently dried. Dentin is then wet with an amphiphilic primer solution and well dried. Organic silane application on composite is omitted to avoid contamination of the dentinal hybrid layer. A thin layer of bonding resin is spread into the cavity, excess is removed and the resin is polymerized with a powerful LED device for 20 seconds as close as possible to the surface of the bonding layer. The next step is the application of the resin composite. The goal is to limit the resin polymerization shrinkage. To that purpose, the resin composite is progressively stratified into the cavity by 2-3 mm oblique increments, starting from the interproximal distal wall (Figures 2a-2b).
Each layer is polymerized for 40 seconds with the LED lamp. Then, restoration is finished and polished with silicone points and fine abrasive disks. A final touch of polymerization under glycerin gel avoids any oxygen-inhibition layers. Finally, rubber-dam is removed and occlusion is checked and eventually adjusted (Figure 2c).