Luc D Randolph1, William M Palin2, David C Watts3, Mathieu Genet4, Jacques Devaux5, Gaetane Leloup6, Julian G Leprince6. 1. Louvain Drug Research Institute, Université catholique de Louvain, Brussels, Belgium; Institute of Condensed Matter and Nanosciences, Bio- and Soft- Matter, Université catholique de Louvain, Louvain-la-Neuve, Belgium; CRIBIO (Center for Research and Engineering on Biomaterials), Brussels, Belgium. Electronic address: lucrandolph@gmail.com. 2. Biomaterials Unit, University of Birmingham, College of Medical and Dental Sciences, School of Dentistry, St Chad's Queensway, Birmingham, B4 6NN, UK. 3. School of Dentistry and Photon Science Institute, University of Manchester, UK. 4. Louvain Drug Research Institute, Université catholique de Louvain, Brussels, Belgium; CRIBIO (Center for Research and Engineering on Biomaterials), Brussels, Belgium. 5. Institute of Condensed Matter and Nanosciences, Bio- and Soft- Matter, Université catholique de Louvain, Louvain-la-Neuve, Belgium; CRIBIO (Center for Research and Engineering on Biomaterials), Brussels, Belgium. 6. Louvain Drug Research Institute, Université catholique de Louvain, Brussels, Belgium; Institute of Condensed Matter and Nanosciences, Bio- and Soft- Matter, Université catholique de Louvain, Louvain-la-Neuve, Belgium; CRIBIO (Center for Research and Engineering on Biomaterials), Brussels, Belgium; School of Dentistry and Stomatology, Université catholique de Louvain, Brussels, Belgium.
Abstract
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.
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.
Authors: Sri Vikram Palagummi; Taeseung Hong; Zhengzhi Wang; Chang Kwon Moon; Martin Y M Chiang Journal: Dent Mater Date: 2019-12-19 Impact factor: 5.304
Authors: Gabriel Felipe Guimarães; Edilmar Marcelino; Ivana Cesarino; Fábio Bossoi Vicente; Carlos Roberto Grandini; Rafael Plana Simões Journal: J Appl Oral Sci Date: 2018-06-18 Impact factor: 2.698