Direct placement of composite (white) fillings in the posterior region (molars and premolars) can be a time-consuming and highly technique-sensitive procedure which, in a busy practice, may lead to later problems that would otherwise not occur with the use of conventional amalgam. The use of amalgam allows a less complicated and faster procedure when placing a filling, but especially in recent years aesthetic demands have become increasingly high; in addition, at least in my opinion, there is an unfounded and excessive fear of the toxicity of amalgam components.
In principle, a composite filling can be similar in durability and longevity to almost indestructible amalgam, provided that the dentist devotes considerably more time to its placement than to an amalgam filling. When placing a composite filling in the posterior region, predictable results can only be achieved by incremental application and curing of the material, thereby reducing the effect of polymerization shrinkage on the quality of the marginal seal. The technique is demanding and complex, because any layer that is not placed in the prescribed manner can cause failure. In recent years, composites have gradually been developed that are intended to reduce the problems described above considerably, as manufacturers claim that satisfactory results can be achieved despite a rapid and simple procedure for placing the composite into the cavity (similar to amalgam).
The technique of applying material in layers up to 4 mm thick is called the “bulk” technique and is substantially faster and simpler than conventional incremental layering. Materials (Tetric EvoCeram) are said to outperform other composites in this respect, as their lower polymerization stress should consequently result in lower permeability of the cured material and a better marginal seal. This means a lower likelihood of tooth sensitivity after filling placement and a lower likelihood of secondary caries. Materials intended for the bulk technique have a somewhat modified composition compared with other composites. They contain various glass fillers and two particle sizes: glass particles, ytterbium fluoride, mixed oxides and pre-polymerized particles whose refractive index is matched to the monomer mixture, thereby reducing the degree of shrinkage. The materials also contain a reactive polymerization accelerator so that a four-millimetre-thick layer polymerizes uniformly even in areas that are not directly exposed to blue light. For now, the materials are available in three basic shades, which is in principle entirely satisfactory for fillings in the posterior region, where filling thickness is problematic from the standpoint of curing.
