Introduction
In the field of restorative dentistry, light-curing composite resins have revolutionized esthetic and functional treatments. Dentists and laboratory technicians alike are faced with a wide range of options when choosing these materials. To make informed decisions and achieve optimal clinical results, it is crucial to understand some of the factors that influence the light-curing of composite resins.
Proper selection of a light-curing resin involves considering multiple aspects, including the shade of the resin1, the thickness of the applied layers, the distance between the lamp and the surface, the exposure time and the power of the light used. These elements directly influence the quality of polymerization and thus the durability and esthetics of the final restoration.
Historical evolution
The development of modern composite resins began in 1962 with Dr. Rat L. Bowen2 who introduced BIS-GMA monomer as an organic matrix. This breakthrough laid the foundation for today’s light-curing resins, significantly improving the esthetics and handling of these materials. Over the decades, significant improvements have been made:
- In the 1990s: Emergence of microhybrid resins, with increasingly smaller filler particles, which meant a qualitative leap in terms of esthetics and strength.
- From 2000: Incorporation of nanoparticles, further optimizing material properties and enabling an unprecedented level of performance.
Basic composition of composites
Composite resins consist of several essential components:
- Organic matrix3: Composed of various monomers that form a polymer network. It has a viscous consistency.
- Inorganic matrix4: Filler material including fine particles of silica, borosilicates, aluminosilicates, quartz or zirconium. This component is crucial to the mechanical properties of the material.
- Bonding agent: Facilitates a strong bond between the organic and inorganic matrices, ensuring material cohesion.
- Pigments: Provide colors similar to natural teeth, allowing for esthetic restorations.
- Polymerization inhibitors4: Prevent spontaneous polymerization, improving product shelf life and working time.
Classification of composite resins
Resins are mainly classified according to the size of the inorganic filler particles:
- Macrofiller:
- 10-50 µm particles.
- They were the first resins used.
- Low aesthetics and difficult to polish and shine.
- Microfiller:
- Particles of 0.01-0.05 µm.
- Better esthetics and polishing, but with limited mechanical properties.
- Indicated mainly for the anterior sector.
- Hybrid6:
- 0.6-1 µm particles.
- Balance between mechanical and esthetic propertiess.
- Better finish.
- Can be used in both anterior and posterior sectors.
- Modified hybrids7:
- Combination of macrofiller (50-60%) and microfiller (10-20%).
- Particles of 0.04-1 µm.
- Improve the aesthetic and mechanical properties of the resin.
- Nanohybrids8:
- Particles smaller than 75 nm (some as small as 10 nm).
- Excellent esthetics and strength.
- Allow a better finish and long lasting polish.
- Good mechanical properties for both anterior and posterior use.
Critical factors in light curing
To achieve optimal polymerization, it is essential to consider:
- Distance between the lamp and the resin9: Impacts the intensity of the light received and thus the polymerization efficiency.
- Power of the light source9: Directly influences the polymerization efficiency. It is measured in milliwatts per square millimeter (mW/mm²).
- Resin translucency10: Influences the depth of polymerization, varying between enamel and dentin resins.
- Irradiation time11: Determines the degree of polymerization and directly affects the mechanical and chemical properties of the restoration.
Specific considerations:
- Lamp-resin distance:
- Keep the tip of the lamp a minimum of 0.5 mm above the resin.
- Power may decrease up to 50% at 10 mm distance.
- It directly affects the mechanical and chemical characteristics of the resin.
- It is essential to use visual protection elements to correctly position the lamp.
- Power:
- Strictly follow the manufacturer’s instructions.
- Use radiometers to verify the power of the lamps, since it decreases with the time of use.
- Surface microhardness is closely related to irradiation time and lamp power.
- Translucency:
- Enamel resins are generally more translucent than dentin resins.
- Higher translucency allows better light penetration.
- The incremental technique is recommended with layers of maximum 2 mm.
- Studies show higher microhardness values in light-cured resins by incremental technique versus block technique.
- Irradiation time:
- Critical for mechanical properties such as hardness.
- Incomplete polymerization can result in free monomers that can affect patient tissues.
- Incomplete irradiation time can cause leakage in the marginal zone, potentially leading to secondary caries.
- Lamp-resin distance:
Conclusion
A detailed understanding of these factors is critical to clinical success in the use of light-curing composite resins. Dental professionals should keep up to date on the specific characteristics of the products they use and rigorously follow manufacturers’ recommendations.
It is important to remember that each brand of resin may have variations in its indications for use. Although these variations may seem minor, they are crucial to achieving a successful restoration. Attention to these details will ensure long-lasting, esthetically satisfactory restorations with optimal long-term performance.
Bibliografía
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- Catelan A, de Araújo LSN, da Silveira BCM, Kawano Y, Ambrosano GMB, Marchi GM, et al. Impact of the distance of light curing on the degree of conversion and microhardness of a composite resin. Acta Odontol Scand. 2015;73(4):298–301. https://www.ncbi.nlm.nih.gov/pubmed/25639534.
- Nakfoor B, Yaman P, Dennison J, Herrero A. Effect of a light-emitting diode on composite polymerization shrinkage and hardness. J Esthet Restor Dent. 2005;17(2):110–116; discussion 117. https://www.ncbi.nlm.nih.gov/pubmed/16036127
- Kopperud HM, Johnsen GF, Lamolle S, Kleven IS, Wellendorf H, Haugen HJ. Effect of short LED lamp exposure on wear resistance, residual monomer and degree of conversion for composites. Dent Mater. 2013 Aug;29(8):824-34. doi: 10.1016/j.dental.2013.04.022. Epub 2013 Jun 10.
