Effect of Manipulation Methods and Storage Environments on the Microstructural, Chemical, and Mechanical Properties of Calcium-Enriched Mixture Cement

Abstract

This study aimed to evaluate the impact of different manipulation methods and storage environments on the microstructural, chemical, and mechanical properties of calcium-enriched mixture (CEM) cement. Four sample groups were examined, including nondried (ND-I) and dried (D-I) groups placed directly in an incubator, dried samples stored in phosphate-buffered saline (PBS) (D-P), and dried samples stored in distilled water (D-W). Various analyses, including Vickers microhardness, compressive strength, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) were conducted after incubating the samples for 7 days. The data were analyzed by Shapiro-Wilk, Levene, independent t, one-way ANOVA, and Tukey HSD tests. Key findings include the ND-I group exhibited a significantly longer setting time but the lowest microhardness and compressive strength. D-P showed the highest microhardness, while D-W displayed the highest compressive strength. FTIR analysis revealed vibration modes related to (PO4)^3- ions and Si compounds in all groups, with dried groups showing more vibrations of (PO4)^3- ions and OH groups, and D-P and D-W groups displayed vibration modes of (CO3)^2- ions. XRD analysis indicated increased tri/dicalcium silicate reflections in CEM groups exposed to PBS or distilled water. D-I and D-W groups presented hexagonal or rectangular cubic and needle-like crystals, while D-P showed a homogeneous globular structure covered with fine crystals. The order of the weight percentage of major elemental constituents of D-P group was oxygen, calcium, phosphorus, zirconium, barium, carbon, silicon, and sulfur. Incremental placement, drying each increment, and exposing CEM to PBS/tissue fluids result in a faster set and more tolerant cement with a more uniform microstructure. The formation of hydroxyapatite can occur on the surface of the set cement.

Keywords: Fourier transform infrared spectroscopy; X-ray diffraction; biomaterials; calcium-enriched mixture cement; energy-dispersive X-ray spectroscopy; mechanical properties.

Figure 1

Fourier transform infrared (FTIR) spectra used to analyze chemical structural properties of four groups of calcium-enriched mixture cement samples with different placement methods and storage environments including Group 1, not dried and stored in the incubator; Group 2, dried/directly into the incubator; Group 3, dried—stored in PBS; Group 4, dried—stored in distilled water. For a better comparison, the graphs of all four groups were placed and superimposed in one figure. The vertical axis shows how much (percentage of) infrared light the substance absorbs. The horizontal axis represents the wavelength of the light. The spectra show various vibration modes at different wavelengths characteristic of various chemical/functional groups. In our study, all specimens showed absorption peaks characteristic of the (PO₄)³⁻ group at 560–600 cm⁻¹ and 1198 − 1090 cm⁻¹. Additionally, vibrations attributed to Si compounds at 1050–1100 cm⁻¹ were observed in the samples of all tested groups. Groups 2, 3, and 4 (dried groups) also exhibited peaks at 3780 and 3682 cm⁻¹, related to the OH groups and Si(OH)₂, respectively. Moreover, Group 3 (dried—stored in PBS) and Group 4 (dried—stored in distilled water) displayed vibration modes of (CO₃)²⁻ ions at 1488 cm⁻¹ and bands characteristic of OH groups from 3650 to 3290 cm⁻¹.

Figure 2

Field emission scanning electron microscopic photomicrographs of samples of CEM cement: (a) Group 1, not dried and stored in the incubator; (b) Group 2, dried/directly into the incubator; (c) Group 3, dried—stored in PBS; (d) Group 4, dried—stored in distilled water.

Figure 3

X-ray dot mapping analysis of elemental distributions of calcium (Ca) and phosphorous (P) in the four groups of CEM cement samples: Group 1, not dried and stored in the incubator; Group 2, dried/directly into the incubator; Group 3, dried—stored in PBS; Group 4, dried—stored in distilled water.

Figure 4

X-ray diffraction analysis of samples of CEM cement showing peaks of different crystalline phases and their relevant counts: Group 1, not dried and stored in the incubator; Group 2, dried/directly into the incubator; Group 3, dried—stored in PBS; Group 4, dried—stored in distilled water.