Scientific article

The effect of ultra-fast photopolymerisation of experimental composites on shrinkage stress, network formation and pulpal temperature rise

Published inDental materials, vol. 30, no. 11, p. 1280-1289
Publication date2014-11
First online date2014-09-24

Objectives: to complement our previous work by testing the null hypotheses that with short curing times and high DC, TPO-based resin composites would exhibit (1) higher polymerization stresses and consequently display (2) higher temperature rise and (3) higher flexural modulus, flexural strength and hardness, compared to a conventional CQ-based experimental composite.

Methods: Two experimental resin composites using either Lucirin-TPO or camphorquinone/DMAEMA as photoinitiators were prepared. Light curing was carried out using spectral outputs adapted to the absorption properties of each initiator. Different irradiation protocols were selected (0.5, 1, 3, 9 s at 500, 1000 and 2000 mW/cm(2) for Lucirin-TPO based composites and 20 or 40 s at 1000 mW/cm2 for Lucirin-TPO and camphorquinone-based composites). Degree of conversion (DC) was measured in real time by means of FT-NIR spectroscopy. Pulpal temperature rise (ΔT) was studied in a tooth model. Polymerization stress was monitored using the Bioman instrument. For cured specimens, flexural modulus and flexural strength were determined using a three point bending platform and Vickers hardness was determined with a microhardness indentor on samples prior to and after 24 h incubation in 75/25 ethanol/H2O. Premolars were restored with both materials and microleakage at the teeth/composite interfaces following restoration was assessed.

Results: Lucirin-TPO-based composites irradiated at radiant exposures of 3 J/cm(2) and more exhibited significantly higher DCs, associated with increased flexural moduli and hardness compared to CQ-based composites. For an ultra-short irradiation time of 1 s at 1000 mW/cm(2), TPO-composites displayed similar polymerization stresses compared to CQ-controls with yet a 25% increase for flexural modulus and 40% increase for hardness measured after EtOH/H2O sorption. Higher stress rates were however observed in all curing protocols compared to CQ-composites. Microleakage was similar between TPO and CQ-composites irradiated at 1000 mW/cm(2) for 3 and 20 s respectively, while a significant increase was observed for TPO-composites irradiated for 1 s. ΔT measured through a 0.6 mm thick dentin layer were all below 5.5°C; TPO-composites exhibited similar or lower values compared to controls.

Significance: The use of Lucirin-TPO in resin composites along with appropriate curing conditions may allow for a major reduction of irradiation time while improving mechanical properties. The amount of stress observed during polymerization in TPO-based composites can be similar to those using CQ and the cohesion at the restoration-tooth interface was not affected by short curing times. Contrary to other studies, we found that the temperatures increases measured during polymerization were all well below the 5.5°C threshold for the pulp.

  • Dental composite
  • Experimental
  • Irradiance
  • Irradiation parameters
  • MAPO
  • Microleakage
  • Polymerization kinetics
  • Polymerization stress
  • Temperature rise
  • Tooth model
  • Composite Resins
  • Dental Leakage
  • Dental Pulp
  • Photochemical Processes
  • Polymerization
  • Temperature
Affiliation Not a UNIGE publication
Citation (ISO format)
RANDOLPH, Luc D et al. The effect of ultra-fast photopolymerisation of experimental composites on shrinkage stress, network formation and pulpal temperature rise. In: Dental materials, 2014, vol. 30, n° 11, p. 1280–1289. doi: 10.1016/j.dental.2014.09.001
Main files (1)
Article (Published version)
ISSN of the journal0109-5641

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