Thermophysical properties and bonding with composite resin of premixed mineral trioxide aggregate for use as base material

Dental bases require low thermal conductivity and good mechanical properties, such as bonding with composite resins. This study aims to elucidate the physicochemical properties of premixed mineral trioxide aggregate (MTA) for its suitability as a dental base and to explore the optimal adhesive strategy with composite resin. The thermal conductivity and compressive strength of this premixed MTA are 0.12 W/(m•K) and 93.76 MPa, respectively, Which are deemed adequate for its application as dental base. When bonded to composite resin, the use of 37% phosphoric acid etching before applying the Clearfil SE bond significantly reduced the bonding strength between composite resin and premixed MTA. This was because the compressive strength and Vickers hardness of premixed MTA decreased, and tricalcium silicate was dissolved from the surface during acid etching. Therefore, it is recommended to avoid using 37% phosphoric acid etching when bonding premixed MTA and composite resin as a dental base.

High-Temperature Gaseous Reaction of Cesium with Siliceous Thermal Insulation: The Potential Implication to the Provenance of Enigmatic Fukushima Cesium-Bearing Material

Here, we report an investigation of the gas-solid reaction between cesium hydroxide (CsOH) and siliceous (calcium silicate) thermal insulation at high temperature, which is postulated as the origin for the formation mechanism of cesium-bearing material emitted from the Fukushima Daiichi nuclear power plant. A developed reaction furnace consisting of two heating compartments was used to study the reaction at temperatures of 873, 973, and 1073 K. Under the influence of hydrogen-steam atmospheric conditions (H₂/H₂O = 0.2), the reaction between cesium hydroxide vapor and solid thermal insulation was confirmed to occur at temperatures of 973 and 1073 K with the formation of dicalcium silicate (Ca₂SiO₄) and cesium aluminum silicate (CsAlSiO₄). Water-dissolution analyses of the reaction products have demonstrated their stability, in particular, CsAlSiO₄. Constituent similarity of the field-observed cesium-bearing materials near the Fukushima Daiichi nuclear power plants with CsAlSiO₄ suggests for the first time that gaseous reaction between CsOH with calcium silicate thermal insulation could be one of the original formation mechanisms of the cesium-bearing materials.

Ab initio mechanism revealing for tricalcium silicate dissolution

Dissolution of minerals in water is ubiquitous in nature and industry, especially for the calcium silicate species. However, the behavior of such a complex chemical reaction is still unclear at atomic level. Here, we show that the ab initio molecular dynamics and metadynamics simulations enable quantitative analyses of reaction pathways, thermodynamics and kinetics of the calcium ion dissolution from the tricalcium silicate (Ca₃SiO₅) surface. The calcium sites with different coordination environments lead to different reaction pathways and free energy barriers. The low free energy barriers result in that the detachment of the calcium ion is a ligand exchange and auto-catalytic process. Moreover, the water adsorption, proton exchange and diffusion of water into the surface layer accelerate the leaching of the calcium ion from the surface step by step. The discovery in this work thus would be a landmark for revealing the mechanism of tricalcium silicate hydration.

Porosity of Calcium Silicate Hydrates Synthesized from Natural Rocks

In this work, the suitability of natural raw materials with various modifications of SiO₂—granite sawing waste (quartz) and opoka (a mixture of cristobalite, tridymite, quartz, and an amorphous part)—for the 1.13 nm tobermorite and xonotlite synthesis is examined, and their specific surface area, pore diameter and volume, and the predominant pores are determined. Hydrothermal syntheses were carried out at 200 °C for 12 and 72 h from mixtures with a molar ratio of CaO/SiO₂ = 1.0. X-ray diffraction analysis, simultaneous thermal analysis, and scanning electronic microscopy were used, which showed that in the lime–calcined opoka mixture the formation of crystalline calcium silicate hydrates takes place much faster than in the lime–granite sawing waste mixture. The high reactivity of amorphous SiO₂ results in the rapid formation of 1.13 nm tobermorite and xonotlite (12 h). According to Brunauer, Emmet and Taller (BET) analysis data, this product features a specific surface area of ~68 m²/g, a total pore volume of 245 × 10⁻³ cm³/g, and has dominating 1–2.5 nm and 5–20 nm diameter pores. This porosity of the material should provide good thermal insulation properties of the products made from it as no air convection occurs in the fine pores.

Pulpal Temperature Rise: Evaluation after Light Activation of Newer Pulp-Capping Materials and Resin Composite

Background:

To evaluate temperature changes in pulp chamber during light activation of newer pulp- capping materials and composite resin using light-emitting diode.

Materials and Methods:

A standardized Class I cavity was prepared in 80 extracted, intact, noncarious mandibular first molars, keeping remaining dentin thickness of 0.5 mm. The teeth were divided into four groups of 20 teeth each. Following this, apical third of the mesial root of each tooth was cut and a K type thermocouple attached to digital thermometer was inserted into pulp chamber from the sectioned mesial root. Whole assembly with teeth was suspended in water bath with constant temperature at 37°C. The previously divided teeth in four groups, were lined with Calcimol LC (Group A), Activa (Group B), TheraCal LC (Group C), and Ionoseal (Group D), followed by 3 increments of Filtek Z350 × T universal restorative. The temperature rise following light activation of pulp-capping material, bonding agent, and composite was noted.

Results:

The temperature rise in the pulp chamber after light activation of Activa was highest among all pulp-capping materials, followed by teeth lined with Calcimol LC, Ionoseal, and least in teeth with TheraCal LC.

Conclusions:

Temperature rise in the pulp chamber after light activation of newer pulp-capping materials and composite was below critical threshold for irreversible pulpal damage. Among all the pulp-capping materials, TheraCal LC showed lowest temperature rise in pulp chamber.