• Could this paste be made into a toothpaste that people could brush with daily?

No, this paste cannot be made into a toothpaste because of its strong acidity. When this paste is applied, the gum must be protected under a dentist's supervision, otherwise the gum will be chemical-burned.

• Does it help natural enamel grow back, or plug holes?

This synthetic enamel not only repairs teeth but also protects teeth from cavity at the same time.

• When might this be available for use by dentists?

I don't think it will take long, maybe within two to three years, because presently there is no method for tooth cavity prevention which everyone needs.
However, we need to do more clinical testing to confirm the safety of this therapy for the approval.
The small number of the clinical application at my clinic may not be enough clinical data.

• How far along in development is this paste? Is it in clinical trials?

Yes, it is now in clinical trials. I'm running clinical trials for the approval in Japan, but there is no plans to run clinical trials in EU or USA, yet.

• How is synthetic enamel applied?

Procedures of the treatment:
(1) Brush the tooth to clean the surface of early dental caries using toothbrush with toothpaste on it.
(2) Apply the synthetic enamel paste to the decayed part of the tooth, and allow it to act for 15 minutes.
(3) Wipe off the paste from the tooth surface of the dental enamel, and wash in water, then dry.
(4) Brush up the crystallized synthetic enamel to make it shiny.

• Once applied, is the bond so integrated that the repair cannot be detected later?

The bond is integrated in the composition level, but the color of the apatite is whiter than that of the normal tooth.

• how does this paste repair cavities?

This dissolution and regrowth process occurs due to the low pH(< 2) of the mother solution and the paste, which forms a continuous structure from the enamel to the re-grown layer on a nanometer scale.

• Your paper mentions that the synthetic material works best on "tiny, early lesions." Could you please give an approximate size range?

Dental caries causes the crystal forming the teeth to melt under the teeth surface before it actually creates holes on the teeth surface. The teeth in such a condition look white (white spotted).
The synthetic enamel can be applied to the lesions that have no holes but melted under teeth surface to the lesions that have holes of tens of micrometer depth. Since the grown layer is estimated to be 30-50 μm thick, whether this paste works or not depends on the depth of the hole, not the width.

• Do you have to color the paste to match the patient's tooth color?

No, coloring of the paste is not necessary since the tooth becomes whiter after the treatment.
Also, if you put some pigment to color the paste, it causes the crystal to change its structure, and the reaction of the synthetic enamel will change, so I don't recommend it.

• Was the premolar tooth you tested it on a human tooth?

Yes, it was an extracted human premolar tooth.

• Was that tooth treated while it was in a person's mouth, or was it isolated in a laboratory?

The tooth was extracted for the reason of orthodontic treatment. It was kept in distilled water for less than 1 year before used in a laboratory.

• What is the treatment using acidic phosphate flouride solution as you mentioned in your paper? Is this how dentists normally repair early caries lesions?

The acidic phosphate fluoride solution is applied to the early caries lesion for the purpose of remineralization.
This remineralization therapy is recommended by FDI and accepted by most of the dentists. However, this method requires the multiple appointments with the dentist and long period for the remineralization of the caries lesions.

• How do dentists normally treat such tiny early caries? Do they treat them at all?

Instead of the remineralization therapy, filling of dental materials such as composite resin and amalgam, are applied to the drilled cavity. This restoration technique was dramatically improved by the development of adhesive filling materials.
This method is the so-called minimally invasive restoration technique. In this treatment, the amount of the intact tooth substance is limited since the filling can be bonded to the tooth. However, the bonding is still not perfect, and the recurrent caries around the filling often occurs.
Another option is the observation of the early lesion. During this period, the tooth brushing instruction and topical phosphate fluoride application are done.

• Why is it important to treat such tiny caries?

Such tiny caries is the critical situation between the healthy condition and cavity formation.
Once the cavity is formed, the drill-and-fill treatment has to be applied. Most of the early caries lesions are confirmed to be reversible stage of dental caries. If the cavity and the lesions become larger, the life of the tooth will be shortened.

• What happens to the decayed parts of the tooth when this paste is put over them? Do they continue to decay? Or does the application of the paste stop the decay?

It stops the decay. Because, the decay occurs and continues by bacteria. Synthetic enamel covers the tooth surface. Therefore bacteria cannot survive because of lack of nutrition.

• How long will the material last on a tooth? Can it decay in the same way as normal tooth enamel?

I cannot tell you the accurate period, but it stands after 10,000 times of brushing. It will decay in the same way, but its acid tolerance becomes higher because of its highly crystalline F-HAP crystals.