Impact of dietary acids on the surface roughness and morphology of composite resins.

This in vitro study was performed to evaluate the surface roughness (Ra) and morphology by scanning electron microscopy (SEM) of composite resins that had been stored in acidic solutions typical of those present in the diet. Three composite resins (4 Seasons, Z250, and P90) were selected and divided into three groups (n = 7) according to the solutions tested: G1: distilled water; G2, Coca-cola, and G3: orange juice. The Ra test was repeated after immersion periods of 15, 90, and 180 days. The mean Ra values were subjected to LS means analysis and the Tukey-Kramer (P < 0.05). One test specimen of each composite resin was selected for SEM analysis after each period. The Ra data indicated that P90 had the lowest Ra values. 4 Seasons and Z250 had statistically similar roughness values for all the solutions and evaluation periods. With the exception of 180-day immersion in Coca-cola, 4 Seasons showed significantly higher values than Z250. SEM analysis showed that P90 was the composite resin most resistant to the actions of all acid solutions for the periods analyzed. Interaction between components of the solutions and the active components of other dietary items, as well as oral hygiene, may affect the chemical degradation of composite resins.

Correlation between degree of conversion, resin-dentin bond strength and nanoleakage of simplified etch-and-rinse adhesives.

OBJECTIVES: The aim of this study was to correlate the degree of conversion measured inside the hybrid layer (DC) with the microtensile resin-dentin bond strength (µTBS) and silver nitrate uptake or nanoleakage (SNU) for five simplified etch-and-rinse adhesive systems. METHODS: Fifty-five caries free extracted molars were used in this study. Thirty teeth were used for µTBS/SNU [n=6] and 25 teeth for DC [n=5]. The dentin surfaces were bonded with the following adhesives: Adper Single Bond 2 (SB), Ambar (AB), XP Bond (XP), Tetric N-Bond (TE) and Stae (ST) followed by composite resin build-ups. For µTBS and SNU test, bonded teeth were sectioned in order to obtain stick-shaped specimens (0.8mm(2)), which were tested under tensile stress (0.5mm/min). Three bonded sticks, from each tooth, were not tested in tensile stress and they were immersed in 50% silver nitrate, photo-developed and analyzed by scanning electron microscopy. Longitudinal 1-mm thick sections were prepared for the teeth assigned for DC measurement and evaluated by micro-Raman spectroscopy. RESULTS: ST showed lowest DC, µTBS, and higher SNU (p<0.05). All other adhesives showed similar DC, µTBS, and SNU (p>0.05), except for TE which showed an intermediate SNU level. The DC was positively correlated with µTBS and negatively correlated with SNU (p<0.05). SNU was also negatively correlated with µTBS (p<0.05). SIGNIFICANCE: The measurement of DC inside the hybrid layer can provide some information about bonding performance of adhesive systems since this property showed a good correlation with resin-dentin bond strength and SNU values.