Physicochemical basis of the biologic properties of mineral trioxide aggregate.

This study characterized the interactions of mineral trioxide aggregate with a synthetic tissue fluid composed of a neutral phosphate buffer saline solution and root canal dentin in extracted human teeth using inductively coupled plasma-atomic emission spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis, and X-ray diffraction. Mineral trioxide aggregate exposed to synthetic tissue fluid at 37 degrees C released its metallic constituents and produced precipitates with a composition and structure similar to that of hydroxyapatite [Ca10(PO4)6(OH)2-HA]. Endodontically prepared teeth filled with mineral trioxide aggregate and stored in synthetic tissue fluid at 37 degrees C for 2 months produced at the dentin wall an adherent interfacial layer that resembled hydroxyapatite in composition. The authors conclude that Ca, the dominant ion released from mineral trioxide aggregate, reacts with phosphates in synthetic tissue fluid, yielding hydroxyapatite. The dentin-mineral trioxide aggregate interfacial layer results from a similar reaction. The sealing ability, biocompatibility, and dentinogenic activity of mineral trioxide aggregate is attributed to these physicochemical reactions.

Long-term corrosion of a Ga-containing restorative material.

OBJECTIVE: The aim was to simulate and characterize the long-term corrosion of a Ga-containing alloy (Galloy, SDI). METHODS: To induce corrosion, cylindrical specimens, 8 x 4 mm, of the material were subject to potentiostatic polarization at -0.1 V (SCE) in a phosphated buffered saline (PBS) solution at 20 degrees C for d. The current-time transients during polarization were recorded and the corresponding anodic charge, Q, was calculated. Parallel potentiostatic corrosion tests in a Cl-free PBS solution were also conducted to demonstrate the significance of the Cl- ion in corrosion. In addition, potentiodynamic anodic polarization tests were performed to characterize the overall corrosion behavior of the alloy in both electrolytes. The external and internal corroded layers, formed during potentiostatic corrosion in PBS, were measured by optical microscopy. SEM and EDXA were used to characterize the morphology and composition of the potentiostatically polarized surfaces. RESULTS: Galloy was passive in Cl-free PBS. The Cl- ion in PBS destroyed passivity and initiated a "dissolution-precipitation" type reaction during potentiostatic corrosion. The latter led to circumferential internal corrosion and growth of a layer of external corrosion products. The thickness of the internal and external corrosion layers was 0.77 +/- 0.07 and 0.86 +/- 0.37 mm, respectively. The Q value (89.3 +/- 13.7 C/cm2) in PBS was about two orders of magnitude higher than that (0.66 +/- 0.24 C/cm2) in Cl-free PBS. The corrosion products contained Sn, Ga, In, Cu, O and Cl. SIGNIFICANCE: Massive internal and external corrosion in a Cl-containing medium as in saliva, accumulation of corrosion products at the cavity wall, and the consequent stress build-up contribute to post-operative pain, tooth straining, marginal breakdown and fractured teeth reported with the clinical use of Galloy.