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Author: Subject: "Chelating" HEDTA with Calcium ions | Growing bio-mimetic enamel on your teeth?
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biggrin.gif posted on 12-2-2018 at 03:03
"Chelating" HEDTA with Calcium ions | Growing bio-mimetic enamel on your teeth?

It's been years since I took chemistry in college, and I've been studying this research over the years as a hobby. This forum looks very friendly, so Hi! I hope you find this interesting. Everyone has teeth and gets cavities.

I'm interested in trying to grow bio-mimetic hydroxylapatite/fluorapatite crystals. Approximating enamel of teeth.

HEDTA-Ca doesn't appear to be available OTC, or is stocked/listed anywhere. So, I presume I must buy HEDTA and chelate it with Ca. Any suggestions on the best way? Without contaminating it with CaO [1], and there may be other things that would make the resultant apetite structure weaker (I think carbon isn't good off the top of my head, so calcium carbonate may be bad). I think CaCl2 is most appropriate? Here is a Technical Data Sheet on an aqueous solution of HEDTA.

Some example research [2][3]. There is a wealth of research on simulated body fluid as well, where as with human blood, hydroxylapetite will precipitate out of onto any suitable substrate [6]

This paper [4] differs a bit from [2] by using HEDTA & CaCl2 instead of HEDTA-Ca, and uses NaF instead of KF. [4] explains more on HEDTA, such as:
By contrast, the addition of HEDTA can either chelate Ca2+ or bind to the surface of pre-nucleating clusters (PNCs) and amorphous calcium phosphate (ACP). The binding of HEDTA will make those particles negatively charged, thus maintaining the stability of particles through electrostatic repulsion.

See equations 5 & 6 from [8]:
EDTA4- + Ca2+ = EDTA-Ca2- (5)
EDTA-H3- + Ca2+ = EDTA-HCa- (6)

Neither [2] or [4] used Mg, or other trace elements which appear in enamel. You can see that Mg has significant effect on the nanometer scale looking at figure 1 of [5]. I suspect the macro sized rods would be stronger with finer micro crystals? But the setups are different. [4] does talk a lot about nucleation.

EDIT: The enamel prisms form on the micrometer scale:

Enamel prisms are approximately 5 μm in cross section, are grown along the c-axis, and are approximately 1–2 mm in length. The micro- to nanoscale multi-hierarchical structures of dental enamel provide the remarkable mechanical strength for chewing food and protecting pulp nerves from external stimuli.[4]

I wonder how Mg addition would affect the system (note HEDTA chelates Mg as well[7][8]).

It appears possible to use EDTA, but the authors of [2] prefered HEDTA:

By experiments with different chelating reagents, in the presence or the absence of F and at different temperatures and pressures (Fig. S2 and S3, ESIw), we finally choose to use HEDTA. Although HEDTA is not safe for consumption, we’re trying to design a device to separate the solution from the oral cavity for the clinical application.

Ca-EDTA is OTC and cheap though. Also HEDTA didn't look that bad. My suggestion for a device would be a wad of beeswax the "patient" wears & reapplies for a week, but it wouldn't work long on a chewing surface though.

I've looked at many SEM images of synthetic hydroxylapetite, and Figure 4 of [2] is beautiful! My end goal is replicating [2] by the way. It looks very simple, wouldn't you agree?

Some more background literature on the topic, but not directly related to my question:
In remineralizing solution, Ca/P ratio is important, as is the ionic strength
Fanstastic detailed write-up (read about hydroxylapatite and fluroapatite’s “critical pH”)
Fantastic visual reference on enamel, and what enamel rods are!

If anyone else reading this is interested, here are the cheapest OTC reagents I could find (U.S. sources):
Potassium Fluoride 1oz $4.49
Sodium Fluoride 8oz $9.99 As with [4] I think it can be used instead of KF.
Potassium Phosphate Monobasic 8oz $10.99
Ca-EDTA 100g $14 But Ca-HEDTA probably better given [2]'s experience.

EDIT: NaOH and HCl were used to balance the pH to 6.0. [4] shows their may be an issue with longevity of the solution, so they had to replace it every so often. May be mitigated as "supersaturated simulated body fluid" has done with "simulated body fluid" in regards to this problem.

EDIT2: Maybe the rate can be adjusted a bit by adjusting pH [9]. Increased pH by adding a little NaOH, converting some acetic acid group to a salt, and making the bond of EDTA to Ca weaker.

[Edited on 13-2-2018 by andy1988]
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