Amorphous calcium carbonate (ACC) plays a crucial role in the formation of biogenic carbonates. It is widely accepted that ACC and organic macromolecules alter the fracture properties of Echinoderm calcite from the well-defined cleavage planes of the raw material to conchoidal. However, the influence of ACC on the outstanding macromechanical properties of Echinoderm calcite is unknown. To address this question, full-grown spines of the slate pencil urchin are shortly heated to 250 C. Differential scanning calorimetry indicates that all ACC is crystallized at this temperature. Heated spines are compared with an untreated control group and no significant differences in compressive strength, bending strength, damage tolerance, and Young's modulus are detected. This highlights the weak influence of %6 wt% ACC on the macromechanical properties of Echinoderm calcite, which are likely established by its intricate and damage tolerant microstructure. When heating Echinoderm calcite, organics decompose, Mg calcite transforms, water is lost, and cracks and micropores form. All these processes are analyzed to exclude their influence on the mechanical properties, and it is imperative to consider them all. Only this way meaningful results can be achieved as these processes are temperature and dwelling time dependent and may even occur below 250 C.

Biodegradable materials investigation has become a necessity and a direction for many researchers worldwide. The main goal is to find sustainable alternatives which gradually replace plastics based on fossil resources from the market, because they are very harmful to the environment and to overall quality of life. In order to get to the stage of obtaining different functional parts from biodegradable materials, it is necessary to study their properties. Taking into account these shortcomings, this paper aims at the mechanical characterization (DMA—Dynamic Mechanical Analysis) and thermal degradation (thermogravimetric analysis (TGA)) of lignin-based biopolymers: Arboform LV3 Nature®, Arboblend® V2 Nature, and Arbofill® Fichte Arboform® LV3 Nature reinforced with aramid fibers. The tested samples were obtained by using the most common fabrication technique for polymers—injection molding. The obtained results for the DMA analysis showed separate polymeric-specific regions for each material and, based on the tanδ values between (0.37–0.54), a series of plastics could be proposed for replacement. The mechano-dynamic behavior could be correlated with the thermal expansion of biopolymers for temperatures higher than 50/55 °C, which are thermally stable up to temperatures of at least 250 °C.

The two-step production process of glass-ceramic dental restorations involves a computer-aided design/computer-aided machining step followed by a crystallization firing for the final material properties to be achieved. Certain firing parameters are believed to trigger spontaneous fracture of crowns during the cooling process. In this study, cooling fractures have been reproducibly observed and investigated using fractography combined with material (glass transition temperature) and process (cooling rate) characterization. Stress distribution was visualized using birefringence measurements. Fractographic observations revealed fracture starting at the intaglio side of the crowns specifically at contact points with the support firing pins. Further analysis showed that a fast cooling rate was applied during the glass transition region. Thermal stresses were concentrated around the firing pin supports and released the fracture. To prevent such fractures, a slow cooling protocol below the glass transition temperature is our recommendation to dental technicians. Furthermore, the use of planar firing pad or paste supports is advised over the use of point contact supports.

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