Abstract
ObjectiveDetermine the degree of conversion (DC) and in vitro pulpal temperature (PT) rise of low-viscosity (LV) and high-viscosity (HV) conventional resin-based composites (RBC), bulk-fill and short-fibre reinforced composites (SFRC). MethodsThe occlusal surface of a mandibular molar was removed to obtain dentine thickness of 2 mm above the roof of the pulp chamber. LV and HV conventional (2 mm), bulk-fill RBCs (2–4 mm) and SFRCs (2–4 mm) were applied in a mold (6 mm inner diameter) placed on the occlusal surface. PT changes during the photo-polymerization were recorded with a thermocouple positioned in the pulp chamber. The DC at the top and bottom of the samples was measured with micro-Raman spectroscopy. ANOVA and Tukey’s post-hoc test, multivariate analysis and partial eta-squared statistics were used to analyze the data (p < 0.05). ResultsThe PT changes ranged between 5.5–11.2 °C. All LV and 4 mm RBCs exhibited higher temperature changes. Higher DC were measured at the top (63–76%) of the samples as compared to the bottom (52–72.6%) in the 2 mm HV conventional and bulk-fill RBCs and in each 4 mm LV and HV materials. The SFRCs showed higher temperature changes and DC% as compared to the other investigated RBCs. The temperature and DC were influenced by the composition of the material followed by the thickness. SignificanceExothermic temperature rise and DC are mainly material dependent. Higher DC values are associated with a significant increase in PT. LV RBCs, 4 mm bulk-fills and SFRCs exhibited higher PTs. Bulk-fills and SFRCs applied in 4 mm showed lower DCs at the bottom.
Highlights
Setting reaction of photo-polymerizable resin-based composite restorative materials (RBC) is induced by light curing units (LCU) at different irradiance levels and exposure durations
Our results showed that the radiant exposure of the LCU delivered through the 2 and 4 mm deep empty mold with 6 mm orifice diameter was decreased by 42% and 63%, respectively, with an exposure duration of 20 s
The degree of conversion (DC) values at the bottom surfaces of the 4 mm thick samples failed to reach the values measured on the top, the short-fibre reinforced composites (SFRC) resin-based composites (RBC) reached or exceeded the results found at the bottom of the 2 mm thick conventional highly viscous RBCs cured for 20 s and even 40 s
Summary
Setting reaction of photo-polymerizable resin-based composite restorative materials (RBC) is induced by light curing units (LCU) at different irradiance levels and exposure durations. The amount of light energy transmitted to the RBC restoration is influenced by several factors, such as exposure duration, power density of the LCU, the accordance between the spectral absorption range of the photoinitiators and spectral emission profile of the curing unit, distance between the light guide tip and the restoration, composition, shade, opacity and thickness of the RBC material [1,3,4,5,6]. An improved DC can be achieved by using a high-irradiance curing unit and/or by lengthening the exposure duration [13], this processes involves thermal reactions, which represent a potential hazard for the dental pulp tissue [14,15]. Even though the real value of the potentially harmful critical temperature rise is still controversial, it is widely accepted that the temperature rise in the pulp should be kept as low as possible during dental procedures involving the polymerization of light cured materials [18,19,20,21]
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