Ethyl-2-(tosylmethyl)acrylate: A promising chain transfer agent for the development of low-shrinkage dental composites

Objective: To evaluate the potential of ethyl-2-(tosylmethyl)acrylate (ASEE) as chain transfer agent for the development of low-shrinkage photopolymerizable dental composites. Methods: Composites containing 10, 20 and 30 mol% of ASEE in their organic matrix were formulated. Camphorquinone (CQ)/ethyl 4-(dimethylamino)benzoate (EDAB) (0.33 wt%/0.60 wt%), CQ/EDAB/Ivocerin (R) (0.33 wt%/0.60 wt%/0.10, 0.25 or 0.50 wt%), CQ/EDAB/SpeedCure 938 (SC-938) (0.33 wt%/0.60 wt%/0.30, 0.50 or 1.00 wt%) and Ivocerin (R) (0.50 wt%) were used as photoinitiator systems. The glass transition temperature (Tg) and the crosslink density were determined by DMTA measurements. The flexural strength/modulus and ambient light working time were assessed according to ISO 4049. The shrinkage force was evaluated using a universal testing machine. The double bond conversion (DBC) was determined by NIR spectroscopy. DBC, flexural strength and modulus were measured after the storage of the specimens in deionized water at 37 degrees C for 24 h. The DBC, flexural strength and modulus data were analyzed by one-way ANOVA with p = 0.05 as significance level. Results: ASEE-based composites containing the classical initiator system CQ/EDAB exhibited low mechanical properties (flexural strength/modulus) and DBC. The screening of various photoinitiator systems showed that composites based on CQ/EDAB/Ivocerin (R) (0.33 wt%/0.60 wt%/0.50 wt%), Ivocerin (R) (0.50 wt%) or CQ/EDAB/ SC-938 (0.33 wt%/0.60 wt%/1.00 wt%) were particularly attractive. Indeed, the use of these photoinitiator systems enabled the formulation of composites containing up to 30 mol% ASEE exhibiting excellent mechanical properties, high DBC, good network homogeneity and low shrinkage force values. Interestingly, the addition of SC-938 did not impair the ambient light working time of the uncured composites, whereas the incorporation of 0.50 wt% Ivocerin (R) resulted in a strong decrease of this value. Significance: The addition of the allyl sulfone ASEE in combination with the initiator system CQ/EDAB/SC-938 (0.33 wt%/ 0.60 wt%/ 1.00 wt%) is a promising strategy to develop low-shrinkage dental composites which exhibit excellent mechanical properties, low shrinkage force, high DBC and suitable ambient light working time.