RESUMO
This research assessed the effects of pre-heating on the physical-mechanical-chemical properties of different resin composites. For this, resin composites were evaluated in 6 levels: Admira/ADM, Vitra/VIT, Filtek Supreme/FS, Filtek Supreme Flowable/FSF, Filtek One/FO, and Filtek Bulk Fill Flowable/FBF; temperature was evaluated in 4 levels using a composite heater: room temperature/22 ºC, 37 ºC, 54 ºC, and 68 ºC. Response variables were: degree of conversion/DC, flexural strength/FS and color stability/ΔE (immediately after light curing/LC, after 7 days of dark-dry-storage, and after 24 h and 3 days of artificial aging in water at 60 ºC). Data were subjected to 2-way ANOVA (DC and FR) and 3-way repeated measurements ANOVA (ΔE), all followed by Tukey's test (α = 5%). DC were similar (FBF, FS, and FSF) or increased (ADM, FO, and VIT) as the temperature increased. Results of FR were unchanged or increased for all composites except VIT and ADM. High-viscosity composites (VIT and FS) showed higher FR values than low-viscosity composite (FSF). For bulk-fill composites, FBF and FO showed similar results, but lower than high-viscosity composites. Results of color stability showed acceptable values up to 3 days aging except for ADM and FSF. ΔE was not influenced by pre-heating and, overall, ΔE: FS < VIT < FO < FSF < ADM < FBF. Only VIT and FS showed ΔE ≤ 3.3 (clinical threshold). Therefore, the effects of pre-heating depend on the material. The tested materials generally showed similar or enhanced properties after pre-heating (except ADM and VIT).
RESUMO
BACKGROUND: Previous studies have shown that radiotherapy of the head and neck region can cause direct changes in dental structure. This study evaluated the effect of different solutions on the dentin chemical composition and collagen structure of irradiated dentin. MATERIAL AND METHODS: Sixty maxillary canines were distributed in 2 groups (n = 30): non-irradiated and irradiated (radiotherapy: X-rays of 6 MV in 30 cycles of 2 Gy to 60 Gy). The teeth were sectioned, sanded, and polished to obtain 3x3x2 mm fragments, which were redistributed in 3 subgroups (n = 10) according to the treatment employed: chlorhexidine 2% (CL), chitosan 0.2% (QT), and 0.5 M carbodiimide (EDC). The samples were analyzed in FTIR at time zero (T0-control) and after 1 (T1), 3 (T3), and 5 (T5) minutes of immersion in the tested solutions. The data for the areas of the carbonate (C), amide I (AI) bands, and the ratio between the areas of the amide III/proline and hydroxyproline (AIII/PH) bands were analyzed using ANOVA and Tukey test (alpha = 5%).RESULTS: QT showed lower C values at T1, T3, and T5 (P < 0.0001), presenting lower values when compared to CL and EDC subgroups (P < 0.05). AI values at T3 and T5 were higher than T0-control and T1, independently of the radiotherapy and dentin treatment factors (P < 0.05). At T0-control, the AIII/PH ratio was lower in the irradiated group (P < 0.05), whereas the EDC treatment at T1, T3, and T5 and QT at T3 and T5 increased these values (P < 0.05), making them similar to non-irradiated subgroups (P>0.05). CONCLUSIONS: Radiotherapy changes the secondary structure of collagen, and EDC was able to restore collagen integrity after 1 minute of immersion, without changing dentin inorganic composition
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