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Creating successful posterior restorations

Efficient cavity filling procedure using bulk-fill composites
Michael J. Koczarski, DDS, Woodinville, WA/USA 

Ensuring that posterior restorations avoid polymerization shrinkage and microleakage by utilizing modern bulk-fill composites reduces the risk for secondary caries and failed restorations.

Replacing a failing posterior restoration can be challenging for clinicians. The treatment requires them to recreate a restoration that offers not only a tight marginal seal and appropriate functionality but also esthetic anatomical contours. Using a conventional incremental layering technique may lead to an inadequate marginal seal and air entrapments between the composite layers due to polymerization shrinkage stress. The risk for secondary caries rises. Here, bulk-fill composites offer a unique alternative. They require minimal preparation, enable an efficient cavity filling procedure and can be sculpted for anatomical contours due to their stable consistency. By creating what is known as a hybrid layer and by utilizing an adequate bulk-fill composite, clinicians can achieve posterior restorations with excellent esthetics, anatomical contours and minimal risk.

Creating a hybrid layer

After the removal of caries, an adhesive should be applied and a hybrid layer created to ensure appropriate adhesion between the dentin, enamel and bulk-fill composite. By utilizing a 30 – 40 % phosphoric acid solution, clinicians can etch the enamel and condition the dentin simultaneously. The resulting retentive pattern on the tooth surface is ideal for the micro-mechanical retention of the filling [1]. The total-etch technique dissolves the smear layer and demineralizes the dentin surface, ensuring optimal adhesion [2, 3]. However, conditioning the dentin can occasionally lead to hypersensitivities. To avoid this complication – which affects between 5 – 7 % of all adults [4] – Telio® CS Desensitizer is recommended. This product reduces dentin hypersensitivity and postoperative sensitivity. By combining two essential components (polyethylene glycol dimethacrylate, glutaraldehyde), it prevents further interaction with the materials used in the treatment. 

 Fig. 1: Recurrent marginal caries on tooth 37 and distal radiographic caries on tooth 36 

 Fig. 1: Recurrent marginal caries on tooth 37 and distal radiographic caries on tooth 36 

A fluoride-releasing bonding agent (ExciTE® F) then provides the adequate adhesion between the tooth structure and composite material. ExciTE F creates a transition between the hydrophilic and hydrophobic tooth structure and bonds to the composite. With hydrolytically stable monomers, the bonding agent comprises less solvent content than other adhesives, facilitating thorough polymerization of the adhesive resin layer. ExciTE F offers convenient delivery with the VivaPen®. It releases fluoride to reduce dentinal fluid movement and postoperative sensitivity. Studies have demonstrated that using this total-etch technique is clinically successful [5, 6].

Fig. 2: The defective amalgam restorations and gross decay were removed first. 

Fig. 2: The defective amalgam restorations and gross decay were removed first. 

Fig. 3: Then, the outer caries-infected dentin layer was taken off. 

Fig. 3: Then, the outer caries-infected dentin layer was taken off. 

Successful posterior restorations with bulk fill

Modern bulk-fill materials must exhibit a variety of characteristics, including low shrinkage stress, optimal marginal integrity, high strength as well as excellent polishing properties and esthetics. 

Once a hybrid layer is created, the bulk-fill composite (Tetric EvoCeram®) is applied into the cavity. Adhesive direct posterior restorations have the tremendous benefit that they only necessitate removal of decayed tooth structure. 

No matter whether applied in one increment or several, these materials must offer adequate working time to sculpt and complete the restoration. The goal is to achieve a natural-like shape, esthetic colour match and durability. 

Avoiding polymerization shrinkage 

Shrinkage stress may occur as the composite polymerizes. To overcome this problem, the incremental layering technique has been introduced. However, this technique is time consuming and it involves the risk that air may be trapped between the individual layers. By contrast, bulk-fill composites are especially designed to be cured in one increment. They shorten the restoration treatment time and improve the efficiency of the dental practice. Tetric EvoCeram Bulk Fill is a mouldable composite that achieves a complete cure in layers of up to 4 mm [7], eliminating the need for incremental layering in many cases. 

Tetric EvoCeram Bulk Fill is a nanohybrid composite material. Given its small filler particles, the material demonstrates high wear resistance and low surface roughness and is easy to polish to a high gloss. A special filler, known as shrinkage stress reliever, reduces the shrinkage strain generated during polymerization to prevent marginal gaps. 

Working time and esthetics 

The new Ivoclar Vivadent patented light initiator, Ivocerin®, allows Tetric EvoCeram Bulk Fill to cure faster and deeper than other composite materials. Coupled with the shrinkage stress reliever, these two components enable an ideal marginal integrity. A further advantage of the light-initiator, together with a light sensitivity filter, is the unique combination of extended working time with faster curing time. Given its smooth consistency, the composite can be applied and contoured easily with conventional instruments. Tetric EvoCeram Bulk Fill is also designed to match the refractive index of the fillers and monomers to enhance the “chameleon effect”. As a result, the restoration harmoniously integrates with the natural dentition. 

Case study 

A 45-year-old female presented with recurrent caries on tooth 37 and distal radiographic decay on tooth 36 (Fig. 1). A rubber dam was placed to isolate the decayed teeth. First, the decay and failing amalgam fillings were removed. Staining was still visible on the exposed dentin (Fig. 2), from which at the next step the outer caries-infected layer was removed (Fig. 3). The preparations were suitable for direct restorations, as the isthmus widths were in the one-third range of the occlusal table.

Fig. 4 A sectional matrix was placed and then the enamel was etched for 5 seconds (Total Etch).

Fig. 5 The preparation (dentin) was etched for an additional 10 seconds. This yielded 15 seconds of enamel and 10 seconds of dentin etch time. 

Fig. 6: After rinsing, Telio CS Desensitizer was placed for 20 seconds to close dentin tubules and reduce hypersensitivities.

Fig. 7: Application of bonding agent to the prepared surfaces of tooth 36

Fig. 8: The bonding areas were shiny, indicating that an optimal hybrid layer had formed. 

Fig. 9: Tetric EvoCeram Bulk Fill was placed in shade IVA and packed with a ball burnisher.

Fig. 10: The restorations were contoured with the pointed end of aP1 plugger to achieve the desired anatomical contours.

Fig. 11: A flame-shaped diamond was utilized to finish the contours after the matrix band had been removed. 

Fig. 12: Composite restoration at 1-week postoperative: tight marginal seal, anatomical contours and natural shade 

Tetric EvoCeram Bulk Fill was selected for the restorations due to the above-mentioned advantages. The patient is typically assigned to one of three categories to determine the shade: universal shade A (IVA), universal shade B (IVB) or white for deciduous or bright teeth (IVW). A universal shade was chosen for the present case. A sectional matrix was applied around tooth 36 and the total-etch technique was utilized. The etchant (Total Etch) was applied to the enamel margin for 5 seconds, and then additional etchant was applied to etch the remaining preparation for an additional 10 seconds (Figs 4 and 5). This procedure yielded a reaction time of 15 seconds for the enamel and 10 seconds for the dentin. After thorough rinsing, Telio CS Desensitizer was applied to avoid dentin sensitivity after treatment (reaction time: 20 seconds) (Fig. 6). Next, ExciTE F bonding agent was applied and allowed to react for 20 seconds (Fig. 7) and then light-cured for 10 seconds at a light intensity of more than 500 mW/cm2. In the process, the final hybrid layer was created. All bonded areas were shiny and ready for the direct restorative material (Fig. 8). 

Tetric EvoCeram Bulk Fill was evenly distributed in the cavity using a ball burnisher (Fig. 9). Final sculpting occurred with the pointed end of a P1 plugger to achieve the desired anatomical form (Fig. 10). The composite was light-cured for 10 seconds at a light intensity of 1,000 mW/cm2. After removing the sectional matrix band, the restoration demonstrated only little excess to remove and finish. This step occurred with a 40-micron flame shaped diamond to achieve anatomical contours (Fig. 11). The restorations were then polished to a final gloss. The patient was completely satisfied with the final result (Fig. 12).

Conclusion

Direct posterior restorations can be predictably and esthetically achieved by creating a hybrid layer and utilizing an advanced bulk-fill composite. The hybrid layer with a total-etch technique provides an ideal foundation to ensure that a reliable bond forms between the tooth structure and composite. Placement of Tetric EvoCeram Bulk Fill minimizes polymerization shrinkage and shrinkage stress, resulting in a durable restoration with beneficial marginal integrity. The technique described above reduces the likelihood of secondary caries and provides functional and esthetic results.

A literature list is available from the editors on request

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