ABSTRACT
Limited cure depth is a drawback of light-activated composites. We hypothesize that curing light transmission and cure depth are influenced by monomer reactivity and filler/resin refractive index mismatch. Light transmission throughout cure was recorded for composites based on strontium (refractive index 1.51) or barium (refractive index 1.53) glass fillers. Fillers were mixed (70 wt%) with 4 bisphenol-A diglycidyl-ether-dimethacrylate (bis-GMA):triethylene glycol dimethacrylate (TEGDMA) formulations with refractive indices ranging from 1.4703 to 1.5370. Following polymerization, cure depth and pre- and post-cure translucency parameters were determined. Transmission changes and cure depths related to monomer reactivity and filler/resin refractive index mismatch with significant interaction. Composites became more opaque or translucent on curing. Optimizing filler/resin refractive index mismatch provides increased curing depth and assists shade-matching.
Subject(s)
Composite Resins/chemistry , Glass/chemistry , Barium/chemistry , Barium/radiation effects , Bisphenol A-Glycidyl Methacrylate/chemistry , Bisphenol A-Glycidyl Methacrylate/radiation effects , Color , Composite Resins/radiation effects , Glass/radiation effects , Humans , Materials Testing , Optics and Photonics , Polyethylene Glycols/chemistry , Polyethylene Glycols/radiation effects , Polymers/chemistry , Polymers/radiation effects , Polymethacrylic Acids/chemistry , Polymethacrylic Acids/radiation effects , Refractometry , Strontium/chemistry , Strontium/radiation effects , Surface Properties , TemperatureABSTRACT
During the radical polymerization of dental composites, the monomers polymerize to form a three-dimensional network containing remaining double bonds and free radicals. At 37 degrees C, these radicals decompose logarithmically with a half-life of 2-5 d. In this study, the half-life of radicals in a light-cured inlay composite was determined at different temperatures, and the influence of different fillers and filler amounts on the stability of these radicals in light-cured experimental composites was investigated. There is a strong logarithmic relationship between the half-life of the radicals and temperature. At a constant temperature, the half-life of radicals depends on the type of filler, the filler fraction, and the filler surface treatment. The stability of radicals determines to a great extend the adhesion of one composite to another, such as the adhesion of a luting cement to an inlay material.
Subject(s)
Composite Resins/chemistry , Free Radicals/chemistry , Adhesiveness , Analysis of Variance , Drug Stability , Half-Life , Light , Silanes/chemistryABSTRACT
Previous studies have shown that lateral condensation of gutta-percha and sealer can provide an adequate apical seal. The purpose of this study was to compare the level of apical dye penetration when different sealers were used. One-hundred twenty-five teeth with single root canals were biomechanically prepared using the step-back technique and irrigation with EDTAC and 1% NaOCl solutions. The teeth were divided into five groups of 25 teeth each. The control group root canals were filled with laterally condensed gutta-percha and no sealer and the other four groups were filled with laterally condensed gutta-percha and either Apexit, Sealapex, Tubli-Seal, or AH26 sealer. After storage in 100% humidity at 37 degrees C for 48 h, the root surfaces were coated with nail varnish (except at the apex) and placed in 2% methylene blue dye solution and centrifuged at 3 x g for 3 min. The roots were sectioned transversely at 1-mm intervals to determine the following mean levels of dye penetrations: Apexit, 1.67 mm; Sealapex, 2.28 mm; Tubli-Seal, 1.95 mm; AH26, 0.82 mm; and gutta-percha alone, 8.37 mm. This study demonstrated that a root canal sealer should be used in conjunction with laterally condensed gutta-percha and that AH26 sealer provides a significantly better apical seal than the other sealers.