Abstract
Dental bulk-fill restorations with resin-composites (RBC) are increasing in popularity, but doubts concerning insufficient curing in depth still disconcert clinicians. An alternative might be offered by modern dual-cured RBCs, which additionally provide bioactive properties. This study assessed the impact of additional light-curing on polymerization kinetics, the degree of conversion (DC) and mechanical properties of a novel, dual-cured RBC with alkaline fillers. Since the bioactivity of a material often implies a release of compounds, the mechanical stability in simulated clinical environments was also evaluated. Polymerization kinetics and DC were assessed at 2- and 4-mm specimen depths in real-time up to one hour (n = 6). Incident and transmitted irradiance and radiant exposure were recorded at 2- and 4-mm depths. Micro-mechanical profiles (n = 6) were assessed in 100-µm steps along 6-mm deep specimens at 24 h post-polymerization. Flexural strength and modulus (n = 10) were determined up to three months of immersion in neutral (6.8) and acidic (4) pH conditions. DC variation in time was best described by a sigmoidal function (R2 > 0.98), revealing a retarded (3.4 ± 0.4 min) initiation in C=C double bond conversion in self-cured versus dual-cured specimens. The setting reaction kinetic was identical at 2- and 4-mm depths for the self-cure mode. For the dual-cure mode, polymerization initiated at 2-mm depth instantly with light-irradiation, while being retarded (0.8 min) at 4-mm depth. The material behaves similarly, irrespective of curing mode or depth, later than 11 min after mixing. Flexural strength and modulus was comparable to regular RBCs and maintained up to three months in both neutral and acidic conditions. Additional light-curing initially accelerates the polymerization kinetic and might help shorten the restauration procedure by hardening the material on demand, however with no effect on the final properties.
Highlights
The demand for a faster and simplified restorative procedure led to the development of bulk-fillRBCs that are able to be cured in increments up to 4 or 5 mm thickness [1,2]
Apart from a new photo-initiator implemented in one material [4], the identified mechanisms to enhance the depth of cure in light-cured bulk-fill RBCs are the reduction of the filler–matrix interface by enlarging the filler size [5] and the decrease in the amount of pigments
This feature is accounted to the pre-reacted glass-ionomer (PRG) fillers [8], made of a fluoroaluminosilicate glass that has been reacted with a polyalkenoic acid in the presence of water
Summary
The demand for a faster and simplified restorative procedure led to the development of bulk-fillRBCs that are able to be cured in increments up to 4 or 5 mm thickness [1,2]. Within the light-cured bulk-fill RBCs, only giomers [6] are recognized as releasing ions such as F− , Na+ , Sr2+ , Al3+ , BO3 3− , SiO3 2− [7] able to assure a mineralizing and cariostatic potential. This feature is accounted to the pre-reacted glass-ionomer (PRG) fillers [8], made of a fluoroaluminosilicate glass that has been reacted with a polyalkenoic acid in the presence of water
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