From an assessment of multiple chelators, clodronate has potential for use in continuous chelation

To identify chelators which when mixed with sodium hypochlorite (NaOCl) are stable, exhibiting minimal loss of free available chlorine (FAC) over 80 min and to further investigate potential mixtures by assessing FAC over 18 h and the capacity to remove smear layer.

0.25 mol L^-1 EDTA (10%), 0.25 mol L^-1 EGTA (egtazic acid), 0.25 mol L^-1 CDTA (cyclohexanediaminetetraacetic acid), 0.25 mol L^-1 DTPA (pentetic acid), 0.5 mol L^-1 ATMP (aminotri(methylene phosphonic acid)) and 1 mol L^-1 HPAA, (hydroxyphosphonoacetic acid), all at alkaline pH, were mixed equally with 5% NaOCl. 0.5 mol L^-1 alkaline clodronate and 0.5 mol L^-1 Na₄ etidronate (15%) were mixed equally with 10% NaOCl. For all mixtures, the pH and temperature were measured over 80 min and additionally for the clodronate mixture over 18 h. Iodometric titration was used to measure the FAC of all mixtures except for HPAA. The following were compared with respect to their ability to remove smear layer: 1 mol L^-1 clodronate + 10% NaOCl, 0.5 mol L^-1 clodronate + 10% NaOCl, 1 mol L^-1 etidronate + 10% NaOCl, 0.5 mol L^-1 clodronate + 10% NaOCl and the sequences 5% NaOCl/17% EDTA/5% NaOCl and 5% NaOCl/17% EDTA. The area fraction occupied by open dentinal tubules as a percentage of the total area (% AF) from scanning electron microscopy micrographs was calculated using Image J. The results were statistically analysed with alpha set at 0.05.

Compared to its control, the mixture 0.5 mol L^-1 clodronate + 10% NaOCl lost no FAC over 18 h (P > 0.05). The FAC of 0.25 mol L^-1 CDTA mixed with 5% NaOCl fell to 96%, 92%, 75% and 4.9% at 20, 40, 60 and 80 min, respectively. Temperature rises were observed in all cases except in the etidronate and clodronate mixtures. Only in the clodronate mixture did the pH remain above pH 12 for the whole experiment. Although smear layer was removed, the % AF in 1 mol L^-1 clodronate + 10% NaOCl, 0.5 mol L^-1 clodronate + 10% NaOCl, 1 mol L^-1 etidronate + 10% NaOCl was less than for 0.5 mol L^-1 etidronate + 10% NaOCl and 5% NaOCl/17% EDTA/5% NaOCl and 5% NaOCl/17% EDTA.

Alkaline 0.5 mol L^-1 clodronate mixed equally with 10% NaOCl has potential for use in continuous chelation, based on this assessment of stability and smear layer removal. Further research is needed to establish its efficacy and safety.