Calcium Phosphate Cement: High Early-Strength with DCPD and Absorbable Fibers

Calcium phosphate cement (CPC) sets to form resorbable hydroxyapatite and is promising for dental, periodontal and craniofacial use.  OBJECTIVES:  To develop a CPC with fast-setting and high strength in the early stage of implantation.  METHODS:  Two methods were combined to impart high early-strength to the cement: the use of dicalcium phosphate dihydrate (DCPD) with a high solubility (which formed the cement CPC_D) instead of dicalcium phosphate anhydrous (which formed conventional CPC_A), and the incorporation of absorbable fibers.  A 2x8 design was used to test two materials (CPC_A and CPC_D) and 8 reaction times: 15 min, 30 min, 1 h, 1.5 h, 2 h, 4 h, 8 h, and 24 h.  An absorbable fiber was incorporated at 25% volume fraction.  RESULTS:  The Gilmore needle method measured a hardening-time (mean ± sd; n = 4) of (15.8±0.5) min for CPC_D, significantly faster than (81.5±5.3) min for CPC_A (Tukey's multiple comparison at 0.95), at a powder:water ratio of 3:1.  SEM revealed the formation of nano-sized rod-like hydroxyapatite crystals and platelet crystals.  At 30 min, the flexural strength (mean ± sd; n = 5) was 0 MPa for CPC_A, (4.2±0.3) MPa for CPC_D, and (10.7±2.4) MPa for CPC_D-fiber specimens, significantly different from each other (Tukey's at 0.95).  The high early-strength of CPC_D-fiber cement matched the reported strength for cancellous bone and sintered porous hydroxyapatite implants.  The composite strength S_c was correlated to the matrix strength S_m: S_c = 2.16 S_m, with correlation coefficient R = 0.93.  CONCLUSION:  Substantial early-strength was imparted to a moldable, self-hardening and resorbable hydroxyapatite via two synergistic approaches: dicalcium phosphate dihydrate with a high solubility, and absorbable fibers.  The new fast-setting and strong cement may help prevent catastrophic fracture or disintegration in moderate stress-bearing dental and bone repairs.  Support: NIDCR DE14190 and DE11789, NIST, and ADAF.