Influence of resin matrix on the rheology, translucency, and curing potential of experimental flowable composites for bulk-fill applications

• Published in: Dental materials 2021-06, Vol.37 (6), p.1046-1053
• Main Authors: Pereira, Leonardo Duarte Eiras, Couto Neto, Mário Pereira, Pereira, Roberto Guimarães, Schneider, Luis Felipe J.
• Format: Article
• Language: English
• Subjects: Bisphenol A glycidyl methacrylate; Bulk fill; Conversion; Curing; Degree of conversion; Dental cement; Dentistry; Infrared spectroscopy; Light emitting diodes; Mathematical analysis; Monomers; Parameters; Polymer blends; Pseudoplasticity; Resin matrix; Resins; Rheological properties; Rheology; Shear rate; Spectroscopy; Thickness; Triethylene glycol dimethacrylate; Variance analysis; Viscosity
• ISSN: 0109-5641; 1879-0097
• DOI: 10.1016/j.dental.2021.03.003

•Bulkfills is considered the most recent approach by the industry and have impacted the possibilities of clinical use.•Manufacturers have claimed to introduce novel technologies to achieve proper depth of cure.•The current scientific investigation demonstrated that bulkfills can be formulated by proper recombination of monomers traditionally used in the manufacture of conventional resin composites. To propose monomer formulations that show an optimal degree of conversion as a function of depth for bulk-fill applications. Four resin blends were formulated with methacrylate-based monomers: BisGMA + TEGDMA (control); BisEMA + BisGMA + TEGDMA (BisEMA-based); UDMA + BisGMA + TEGDMA (UDMA-based) and BisEMA + UDMA + BisGMA + TEGDMA (BisEMA + UDMA-based). For each material, a photoinitiating system and silanized filler particles were added. The rheological analyses were performed with a rotational rheometer using the cone/plate geometry. CIELab coordinates were assessed over black and white backgrounds using a bench spectrophotometer (SP60, X-Rite) to calculate the translucency parameter (TP) for samples with 0.5, 4, and 6 mm thickness. The degree of CC conversion (DC) was determined by infrared spectroscopy (FTIR/ATR) at 0.05 mm (top), 4, and 6 mm depths (bottom), and the bottom-to-top ratio was considered. A broad spectrum–based LED was used for light activation. Analysis of variance and Tukey’s test (95%) were performed on the results. The materials tested showed pseudoplastic and thixotropic behavior and a predominance of viscous effects over elastics. The control resin yielded the lowest viscosity for the entire shear rate investigated, followed by the BisEMA-based, BisEMA + UDMA-based, and UDMA-based group, which had the highest viscosity. The UDMA-based material showed the lowest TP as a function of thickness. Both the materials’ formulations and depths significantly influenced the DC. The UDMA-based group promoted the highest DC ​​on the top (71 ± 1%) and 4 mm depth (68 ± 1%) but exhibited lower bottom-to-top DC ratio. The BisEMA + UDMA-based material promoted the highest bottom-to-top DC ratio at 4 mm (99%) and 6 mm (97%). The resin matrix interferes in the rheological behavior, translucency parameter, and polymerization capacity as a function of depth. The material formulated with the addition of UDMA and BisEMA demonstrated the highest curing potential as a function of depth and can be useful for bulk-fill applications.