Until recently, the incremental layering technique has been considered the gold standard for the application of light curing composites. Conventional composites are normally applied in individual increments of a maximum of no more than 2mm due to their polymerisation properties and limits on curing depth. The individual increments are polymerised separately. Curing times can vary between 10 and 40 seconds, depending on the light performance of the curing light as well as the shade and degree of translucency of the composite. The composite materials that have been available to date cannot be applied in thicker increments because this would prevent them from polymerising sufficiently and their mechanical and biological properties would be weakened as a result of the insufficient cure. Particularly when restoring large posterior cavities, the conventional incremental layering technique can be very time consuming and technique sensitive. For this reason, many dentists have been looking for an alternative to this complex multi-step regimen. They want to use a procedure that is less time consuming and therefore more economical and offers increased reliability and safety. In response to this demand, bulk-fill composites have been developed in recent years. These composites can be applied in increments of 4-5mm and light-cured in short exposure times per increment (10 to 20 seconds) if a curing light capable of emitting an appropriately high light intensity is employed. The result is a more rapid restorative placement technique for posterior cavities.
Bulk-fill composites
As regards their chemical composition, bulk-fill composites are very similar to hybrid composites and therefore do not form a new category of materials. They comprise an organic matrix, consisting of proven monomer systems, and inorganic fillers. Bulk-fill composites are available in two degrees of viscosity. Both of these viscosities require a different application technique:
Low-viscosity, flowable composites
These bulk-fill composites require the application of a final covering layer of conventional posterior hybrid composite to protect the restoration surface because they contain comparatively large filler particles and feature low filler content. This also causes the mechanical properties of flowable bulk-fill composites to be less advantageous, which is reflected in their susceptibility to wear, increased surface roughness and diminished polishing properties. Additionally, the covering layer assists in creating functional occlusal contours, which would be
difficult to achieve with a flowable material.
Regular to high-viscosity variants featuring a stable and mouldable consistency
These bulk-fill composites can be used up to the occlusal surface. They do not require a covering layer and therefore do not require an additional composite material.
For both versions, their maximum layer thickness is restricted to 4-5mm because of the limits on the depth of cure. This means that only the high-viscosity representatives applied in cavity depths that do not exceed their maximum depth of cure can be considered bulk-fill materials in the true meaning of the word. If a defect is deeper than the maximum curing depth or if a flowable variant is used, an additional layer of material will always be required.
In 2011, Ivoclar Vivadent launched the high viscosity composite Tetric EvoCeram® Bulk Fill. In terms of materials
technology, this product is closely related to the hybrid composite TetricEvo Ceram, which has been successfully competing in the market for more than ten years. Tetric EvoCeram Bulk Fill is based on the monomer formulation
and filler technology of Tetric EvoCeram. Based on a dibenzoylgermanium derivative, this innovative initiator system shows a similar absorption spectrum as camphorquinone, which is widely used as an initiator system in polymers.
However, Ivocerin features a higher visible-light absorption rate, allowing for increased quantum efficiency and, by extension, for an enhanced light-curing performance. Consequently, a low quantity of light (photons) is sufficient to trigger an appropriate polymerization reaction and achieve a deep depth of cure of 4mm with short exposure times. The high quantum efficiency of Ivocerin is responsible for this. Due to the careful coordination of the refractive index of the fillers with the refractive index of the polymer matrix, the light initiator produces favourable optical
properties that match those of the natural tooth structure (in particular those of the enamel). This results in a successful aesthetic integration of the restoration. Virtually invisible restorations can be achieved in posterior cavities free of stained dentin by using one of the three shades available (IVA, IVB, and IVW).
Advantages of the bulk-fill placement technique
- Rapid, time saving restorative technique, eliminating the need for a complex layering technique > increased efficiency
- Easier handling
- Fewer increments > no/fewer increment interfaces > fewer problems with interface imperfections (voids, gaps) between individual composite increments and generally less risk of air entrapments
- No need for time consuming shade selection procedures
- Streamlined logistics > fewer materials to store
Case presentation
Following successful endodontic treatment, the patient expressed a wish to have the restoration on his upper first molar replaced. After the patient had been informed about the treatment options and the corresponding costs he decided in favour of a bulk-filled restoration made of the mouldable composite Tetric EvoCeram Bulk Fill.
Tetric EvoCeram Bulk Fill is a hybrid composite featuring a typical dimethacrylate monomer matrix and inorganic filler particles with a smooth mouldable consistency. The composite can be applied in increments of up to 4mm and each increment can be cured in 10 seconds (intensity of the curing light ≥ 1,000 mW/cm2). Given its mouldable consistency and material properties, this composite enables dentists to restore cavities with a single restorative using the bulk-fill technique. Applying a different material to cover the occlusal surface is unnecessary – a step that is normally needed if a flowable bulk-fill composite is employed. Since Tetric EvoCeram Bulk Fill is available in three universal shades (IVA, IVB, and IVW), the need for a detailed shade selection procedure is eliminated.
After the tooth had been cleansed, the existing composite material was completely removed. Following excavation, the openings of the obturated root canal system were covered with glass ionomer cement and preparation of the cavity was finished with fine diamonds. Next, the operating field was isolated with a rubber dam and a sectional metal matrix band was placed around the cavity. Then, the preparation was conditioned using Adhese Universal in the self-etch technique according to the manufacturer’s instructions. Adhese Universal is an advanced single component adhesive that is compatible with all etching techniques: self-etch and etch techniques based on phosphoric acid (selective enameletch and total-etch & rinse techniques involving the enamel and dentin). Fig 3 shows the direct application of a generous amount of Adhese Universal adhesive onto the enamel and dentin. The
material was gently scrubbed into the tooth surface for at least 20 seconds using the brush cannula of the VivaPen delivery form. Next, the solvent was dispersed with a gentle stream of compressed air until a glossy, immobile adhesive film resulted. Then, the bonding agent was light-cured for 10 seconds using a Bluephase Style curing light. A glossy layer evenly covering the entire cavity surface was now visible.
At the next step, Tetric EvoCeram Bulk Fill in shade IVB was applied to the mesial box until the remaining depth was no more than 4mm in the entire cavity. At the same time, the mesial wall was built up to the height of the marginal ridge. Next, the composite was light-cured for 10 seconds with a Bluephase Style LED curing light. Given the high light intensity of the curing light (1,100 mW/cm2), suitable composites can be reliably polymerised with a short exposure time.
The shortened light probe head facilitates access to posterior cavities and the filling material can be illuminated at an ideal angle to ensure reliable polymerisation. With the subsequent increments of Tetric EvoCeram Bulk Fill, the occlusal morphology of the tooth was reconstructed cusp by cusp. We were able to light-cure the restorative material with a single exposure of 10 seconds due to the large diameter of the Bluephase Style light probe. Following the removal of the metal matrix band, the restoration was checked for any imperfections. Finally, the
rubber dam was removed.
The restoration was carefully finished and the static and dynamic occlusion adjusted.
Subsequently, the restoration was polished to a shiny smooth surface using diamond-impregnated silicone polishers (OptraPol) and Astrobrush silicon carbide brushes. Figure 14 shows the completed direct composite restoration, restoring the original tooth shape with an anatomical and functional occlusal surface, a physiological proximal contact point and a favourable aesthetic appearance. To complete the treatment, a fluoride varnish was applied to the teeth using foam pellets.
Conclusion
The advent of bulk-fill composites featuring a large depth of cure and the subsequent acceptance of these materials among dentists presents another milestone in the continued development of the direct adhesive restorative technique. Direct adhesive procedures in posterior teeth are modernised by the possibility of using these light-curing composites to restore large cavities with fewer increments. The result is a state of the art, straightforward, rapid and economically efficient restorative placement technique for posterior teeth. Given the positive clinical
experience reported for Tetric EvoCeram after 10 years on the market, Tetric EvoCeram Bulk Fill is expected to provide an equally successful long term clinical performance because these two materials are closely related to each other in terms of material technology.
References available on request