The formation of hydroxyapatite-calcium polyacrylate composites

Area of Science:

• Biomaterials Science
• Dental Materials Science
• Materials Chemistry

Background:

• Tetracalcium phosphate (TetCP) reacts rapidly with polyacrylic acid (PAA), forming hydroxyapatite (HAp) and calcium polyacrylate, suitable for dental cement.
• The rapid reaction rate of TetCP and PAA limits homogeneous mixture formation for dental restorations.
• Prehydration of TetCP to form surface HAp layers is explored to extend working time.

Purpose of the Study:

• To investigate the effects of prehydrating TetCP on extending the working time of TetCP-PAA dental cements.
• To examine the influence of TetCP and PAA proportions, with and without HAp filler, on cement properties.
• To analyze reaction extent, neutralization, pore structure, microstructure, and compressive strength.

Main Methods:

• X-ray diffraction (XRD) analysis to determine reaction extents.
• Fourier transform infrared spectroscopy (FTIR) to study PAA neutralization.
• Mercury intrusion porosimetry (MIP) for pore structure analysis.
• Scanning electron microscopy (SEM) for microstructure observation.
• Compressive strength testing and load-deflection curve analysis.

Main Results:

• Prehydration effectively extended working time, allowing for workable mixtures.
• Almost complete PAA neutralization occurred after 17 days, but residual TetCP and PAA were detected.
• Compressive strength decreased with increasing liquid-to-solid ratio and HAp filler content.
• HAp filler increased porosity, attributed to porosity within the filler itself, reducing compressive strength.
• Load-deflection curves showed distinct characteristics: two slopes without filler, and a linear, ceramic-like curve with HAp filler.

Conclusions:

• Prehydration of TetCP is an effective strategy to control the reaction rate and improve workability of TetCP-PAA dental cements.
• The presence and proportion of HAp filler significantly impact cement properties, notably reducing compressive strength and increasing porosity.
• The study provides insights into optimizing TetCP-PAA cement formulations for dental applications by understanding filler effects on microstructure and mechanical performance.