Balance between optical and bulk fill features
The application of the incremental technique appeared together with the light-cured composites. This is important for two reasons: for the proper polymerization taking place and for decreasing the shrinkage and shrinkage stress due to the polymerization reaction. The incremental placement is used to help the adequate adaptation in the more sensitive areas (cavity wall, matrix), however, it involved the risk of contaminating the layers on the posterior areas requiring longer treatment period. Packable composites were launched in the late 1990s in order to meet the demands raised by the incremental placement. Besides their higher viscosity, they were capable of being bulk placed, that meant the placement and light-cure of 4-5 mm increments. The photo-initiators begin the polymerization in a proper wavelength of the light. If the light penetration is not sufficient, no reaction will be resulted, and this could lead to under-cured or uncured materials. Several factors like the wavelength, the light intensity, the distance from the light source, as well as the exposure time influences the effectiveness of the light. The monomers, the initiators and the shade/opacity of the material determine the depth of cure of a composite. Still, these materials were described as materials having high shrinkage and polymerization stress.
The latest advancements in the field of materials science have led to appearance of bulk fill composites which correspond to the low polymerization shrinkage stress also seen and experienced in case of the composites used in the multi-layer techniques.
Due to the decrease of the filler particles the volume of the resin matrix also decreases and as a result of this polymerization shrinkage decreases as well. The smaller the fillers are, the better the optical attributes of the material are. However, light scattering and gloss retention depend on the arrangement and distribution of the filler particles within the resin matrix. The most important advantage of these materials is its fast and easy one-step placement. During their use the higher viscosity can be beneficial in case of many operators. The good polish attributes improve the final aspect of the finished restoration. Although, for their aesthetic attributes they are recommended to be used mainly in the posterior area, efforts are made to have them manufactured in the several shades in order not to make big compromises in terms of shade effect.
The 3M Filtek Bulk Fill Posterior material – used in the next restoration – is outstanding in this field.
Img. 1 – Upper left first molar with the old composite filling.
Img. 2 – Initial situation.
Img. 3 – Old filling removed, cavity preparation.
Img. 4 – Photodam isolation, cavity cleaned.
Img. 5 – Final cleaning with Danville Microetcher CD Intraoral Sandblaster (50micron Al2O3).
Img. 6 – Bonded cavity (Kerr Optibond FL).
Img. 7 – Placing of the filling material starts in the deepest portion of the preparation, holding the capsule tip close to the preparation wall. Note: avoid lifting the tip out of dispensed material while dispensing, to reduce voids.
Img. 8 – Proper adaptation of the material to the cavity walls. Mass increment light-cured.
Img. 9 – Cavity filled up. Occlusal morphology restored, some stains were used.
Img. 10 – Close-up of the finished restoration.
Img. 11 – Photodam removed. Final result after finishing and polishing.
Img. 12 – 2 years follow-up untouched (not repolished) restoration. Note the positive optical attributes of the material used. Excellent polish retention observed. Mesio-approximal decay already scheduled for treatment.
Img. 13 – Pre-op and post-op appearance compared.
Img. 14 – Morphology and stain details.
Img. 15 – Morphology and stain details.
The increased volume of the fillers in 3M Filtek Bulk Fill Posterior Restorative material optimized the translucency and the opalescence, and improved both the handling and aesthetic attributes of the product. In case of bulk fill materials the polymerization of thicker layers (up to 4-5 mm) was solved, but it has not served as an advantage of the optical attributes. The 3M successfully managed to keep the balance between the optical and bulk-fill attributes, ensuring this way a scarce compromised aesthetic final result.