Effects of Temperature and Aging on Working/Setting Time of Dual-cured Resin Cements.

OBJECTIVES: To evaluate the effects of aging and temperature on working time (WT) and setting time (ST) of several dual-cured resin cements. METHODS: WT and ST were determined with a thermo-controlled stage oscillating rheometer. New cement kits were used for the study. Cements were mixed according to instructions and dispensed on the oscillating stage that was preset at 22°C or 37°C. Rheologic charts were generated from the beginning of mixing until no further oscillation was detected. After initial measurements, cement kits were aged at 37°C for 12 weeks, and WT/ST was determined again at both temperatures. Five samples were read for each material and condition. Data were analyzed with repeated measures analysis of variance and a Tukey test at α=5% for each individual material. RESULTS: The WT and ST of all cements were significantly affected by temperature and aging (p<0.05). In general, higher temperature accelerated WT/ST, but aging effects were material dependent. Some materials presented reduced WT/ST, whereas others showed increased WT/ST, regardless of the temperature. CONCLUSIONS: The WT and ST were significantly affected by temperature variation and aging condition. Although temperature changes appeared to affect all materials similarly, aging effects were material dependent.

Micropush-out dentine bond strength of a new gutta-percha and niobium phosphate glass composite.

AIM: To characterize an experimental gutta-percha and niobium phosphate glass composite (GNB) applied with a thermoplastic technique to the root canals without sealer in a moist environment and to evaluate its micropush-out bond strength to root canal wall dentine. METHODOLOGY: The root canals of sixty human mandibular pre-molars were prepared using rotary NiTi instruments and irrigation with sodium hypochlorite and EDTA. The teeth were then randomly divided into three groups according to the root filling material used: AH plus sealer and gutta-percha (AH), EndoSequence BC gutta-percha without sealer (GBC), and GNB without sealer. The root canals were filled with a single cone using warm vertical condensation. Push-out bond strengths associated with the filling materials in slices from middle root thirds was determined 30 days after root filling. The failure mode was analyzed with SEM. Analysis using EDX and SEM-EDS was carried out to verify the composition and distribution of the particles of the tested materials. Data were statistically analyzed by one-way anova and Tukey's test (P < 0.05). RESULTS: AH and GNB groups had bond strengths of 2.83 ± 0.64 MPa and 2.68 ± 0.84 MPa, respectively, with no significant difference between them (P > 0.05). The GBC group had the lowest mean bond strength (1.34 ± 0.42 MPa), which was significantly different compared with the other groups (P < 0.05). Cohesive failures prevailed in the AH group, whereas failures were mixed in the GBC and GNB groups. The SEM-EDS analysis on the surface and in the bulk of GBC revealed only a superficial coating of bioceramic particles. Glass particles were detected both on the surface and in the bulk of GNB. CONCLUSIONS: The experimental root filling composite (GNB) had an ability to adhere to root canal wall dentine equal to the current gold standard root filling with gutta-percha and sealer (AH Plus).