Dental composite resin is an increasingly reliable, low-cost and minimally invasive treatment for the restoration of function and aesthetics to both anterior and posterior areas of the mouth. With the phasing down of dental amalgam, composites have become one of the most widely used materials to restore tooth structure lost through trauma, caries or other diseases, and can also be used as cements for crowns and veneers. As restorative bonding materials, composites can successfully replace biological tissue in both appearance and function. At least half of posterior direct restoration placements now rely on composite materials.
Composite resins are often considered the best option for direct restorations when an aesthetic outcome is needed. The human tooth is a polychromatic structure and its colour is a result of the light interaction with enamel, dentin, and pulp. Many modern composite materials can now seamlessly mimic the colour, translucency, fluorescence, opalescence, and gloss of natural teeth.
Resin composite materials can be divided into categories based on their particle size and shape. For example, microfilled composite is made of colloidal silica with a particle size of 0.4µm. This type of composite has high polishability, but has a low mechanical load, making it inadvisable for load-bearing situations. Hybrid filler contains particles of varied sizes. Resins with hybrid filler have reduced thermal expansion and higher mechanical strength. However, a larger volume of diluent monomer controlling viscosity can result in shrinkage. Nanofilled composite is filled with nanocluster units that act as a single unit. It has high mechanical strength, high wear-resistance, and is easily polished.
Microhybrid composites are considered universal materials and may be applied in both anterior and posterior teeth, combining the resistance properties of hybrid composites with the polishing characteristics of microfilled composites. Hybrid, microfilled and nanofilled composites are currently among the most commonly used materials for posterior restorations.The durability of materials used in composites has advanced greatly over the last decade, and the use of resin composite – especially as a posterior restorative material – has markedly increased as a result. Nowadays, survival rates of direct composite resin exceed those of amalgam and they also present less risk of tooth or restoration fracture and cracking.
However, the average composite resin restorative material shrinks approximately two to six per cent, in a process known as polymerisation shrinkage, and this can result in breakdown of the adhesive bonds, leading to restoration failure. The polymerisation shrinkage of composite resins occurs following the conversion of monomer molecules to a polymer structure through the replacement of van der Waals spaces with covalent bonds, leading to a decreased free volume.
Layering techniques were introduced to manage polymerisation stress. Application of composite in 2mm increments can also result in much more natural layering of colour and translucency. Using a composite system which offers a wide range of shades and translucencies, including an opaque shade, will enable clinicians to more accurately mimic the appearance of natural dental structures. Practitioners should use opaque shades to mimic dentine, followed by translucent shades to replicate layers of enamel. In doing so, this will accurately imitate the appearance of neighbouring teeth. However, the process requires skill to ensure aesthetic results, and takes time. There is a risk of air being trapped between layers, which compromises the overall integrity of the restoration.
The snowplough method of application was introduced to relieve shrinkage stress and improve the overall integrity of the restoration, while reducing the risk of the formation of air pockets. In this technique, a small amount of flowable composite is applied and not light-cured. In tests, this method has been found to be effective for posterior restorations in terms of cure and porosity, significantly reducing microleakage. Brilliant EverGlow Flow from Coltene offers low viscosity with high stability – making it extremely versatile to use. Its high-quality characteristics ensure polishability and gloss retention, along with a shade assortment including Duo Shades and three translucency levels.
There is every indication that resin-based composite will continue to evolve as a solution for restoring dental function and aesthetics. Exciting new materials are continuously developing, to offer the means to restore tooth structure and appearance for patients who have experienced damage to teeth due to trauma, caries or other diseases.
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