Degree of conversion of nano-hybrid resin-based composites with novel and conventional matrix formulation.

OBJECTIVES: This study aimed to determine the degree of conversion (DC) of two nano-hybrid resin-based composites (RBCs) with novel monomer composition based on dimer acid derivates (hydrogenated dimer acid) and tricyclodecane-urethane structure compared to three nano-hybrid materials containing conventional matrices. DC was evaluated at 0.1, 2, and 6 mm depth at varying irradiation times (10, 20, and 40 s) and layering techniques (bulk and incremental). MATERIALS AND METHODS: DC was measured in real time by a Fourier transform infrared spectroscopy (FTIR) spectrometer with attenuated total reflectance accessory. The FTIR spectra were recorded on the bottom of the samples in real time for 5 min from photoinitiation. Results were compared using one- and multiple-way ANOVA, Tukey's HSD post hoc test (α = 0.05), and partial eta-squared statistic. RESULTS: After 5 min of measurement, DC showed no significant difference by varying cure time for specimens of 0.1 mm thickness. At 2 mm depth, the DC significantly increased after a cure time of 20 s compared to 10 s, remaining equal after 40 s of irradiation. At 6 mm depth, bulk curing showed significantly lower DC compared to incremental curing for all polymerization times. Specimen geometry revealed a strong effect on DC (η (2) = 0.90) followed by curing time (η (2) = 0.39). CONCLUSIONS: The RBCs containing the dimer acid and tricyclodecane-urethane structure showed a relatively low decrease of DC with increasing incremental thickness compared to the conventionally formulated materials. The former reached the highest DC among the tested materials. CLINICAL RELEVANCE: For the tested RBCs, increments of 2 mm and irradiation time of at least 20 s may be recommended for clinical practice. The two materials containing novel monomer composition might be applied for enlarged increments because of the low decrease of DC they demonstrated for 6-mm increments.

Depth of cure and mechanical properties of nano-hybrid resin-based composites with novel and conventional matrix formulation.

OBJECTIVES: This study's purpose was to evaluate the depth of cure (DOC) and the variation of mechanical properties with depth of two nano-hybrid resin-based composites (RBCs) containing a novel monomer composition based on dimer-acid derivatives (h-Da) or rather tricyclodecane-urethane structure (TCD-urethane) compared to three conventionally formulated nano-hybrid RBCs based on hardness-profile measurements. MATERIALS AND METHODS: Specimens were produced through different layering techniques (bulk, incremental) and curing times (10, 20, and 40 s). Mechanical properties (Vickers hardness (HV), modulus of elasticity (E)) were evaluated every 100 µm longitudinally throughout the bisected samples using an automatic micro-hardness indenter. DOC was determined as the depth at which the 80% hardness cutoff value in relation to the surface hardness was reached. Results were compared using one- and multiple-way ANOVA, Tukey HSD post-hoc test (α = 0.05) and partial eta-squared statistic. RESULTS: Increasing curing time resulted in a significant increase in DOC. Generally, the novel-formulated materials showed higher DOC values. "Curing time" and "material" showed the strongest effect on DOC. Starting in 4 mm depth, significantly higher HV and E was reached for incremental compared to bulk-curing technique. Values in 0.1 and 2 mm depth (bulk, incremental) as well as in 4 mm depth (incremental) were independent from curing time, while in greater depths, values generally increased with curing time. "Filling technique" and "material" performed the strongest influence on mechanical properties. CONCLUSIONS: Within the limits of this study, the novel-formulated RBCs showed better performance concerning DOC compared to conventional materials. CLINICAL RELEVANCE: For cavities deeper than 3 mm, all tested materials should be placed incrementally to ensure adequate polymerization. In large cavities (≥6 mm), the lowest increment should be cured at least 40 s. The novel-formulated RBCs might be cured in comparatively bigger increments.