Enamel and Dentine Remineralization by Nano-Hydroxyapatite Toothpastes

Published In: Journal of Dentistry
Publication Year: 2011

Study Design

This is a controlled in vitro laboratory study that compares the remineralizing effects of nano-hydroxyapatite (n-HAp) toothpastes with an amine fluoride toothpaste and a remineralizing solution alone.

Funding Sources

The study was partially supported by Dr. Kurt Wolff GmbH & Co KG (Bielefeld, Germany). The authors declared no conflicts of interest.

PICO Framework – What Was Studied and How?

Population:
Bovine enamel and dentine specimens with artificially induced subsurface lesions.

Intervention:
Brushing with nano-hydroxyapatite toothpastes (7 wt% n-HAp and two formulations of ZnCO₃/n-HAp: 20 wt% and 24 wt%).

Comparison:
Brushing with amine fluoride toothpaste (0.14 wt%) and storage in remineralizing solution without any brushing.

Outcomes:
Change in mineral content (ΔDZ) and lesion depth (ΔLD) of enamel and dentine over 2 and 5 weeks, measured using transverse microradiography.

In Paragraph Form:

This study evaluated how different formulations of nano-hydroxyapatite toothpastes affect the remineralization of artificially demineralized bovine enamel and dentine. It compared these effects with those from a fluoride toothpaste and a remineralizing solution without brushing, measuring mineral gain and lesion depth as outcomes.

Inclusion and Exclusion Criteria

Inclusion Criteria:

• Extracted healthy bovine incisors.

• Enamel and dentine surfaces prepared to standard dimensions.

• Artificial demineralization to create subsurface lesions.

Exclusion Criteria:

• Specimens lost or damaged during preparation (e.g., due to brittleness or surface loss during sawing/polishing).

Demographics and Sample Size

Total Initial Samples:

• Enamel: 70 specimens

• Dentine: 85 specimens

Final Sample After Preparation Losses:

• Enamel: 57 specimens (13 lost)

• Dentine: 83 specimens (2 lost)

Groups (Each with ~14 enamel and ~17 dentine specimens):

• Group 0: Storage only (no brushing)

• Group B: ZnCO₃/n-HAp 20 wt%

• Group BS: ZnCO₃/n-HAp 24 wt%

• Group E: Amine fluoride 0.14 wt%

• Group A: Pure n-HAp 7 wt%

Primary Outcome Variables and Results

Dentine Remineralization (After 5 Weeks)

🟢 All nano-hydroxyapatite groups showed significantly better dentine remineralization than fluoride toothpaste (p < 0.05).

Enamel Remineralization (After 5 Weeks)

• Group A (n-HAp 7%) showed significantly more mineral gain than Group E (Fluoride) with p = 0.017.

• However, differences between other n-HAp groups and fluoride or control were not statistically significant (p > 0.221).

Conclusions

• Nano-hydroxyapatite toothpastes promoted dentine remineralization significantly better than the amine fluoride toothpaste under the in vitro conditions used.

• For enamel, n-HAp performed comparably to fluoride, with some formulations (e.g., 7% n-HAp) showing slightly higher mineral gain.

• Fluoride toothpaste caused surface hypermineralization that may have blocked further ion diffusion, limiting remineralization depth, especially in dentine.

Discussion: Strengths and Limitations

Strengths:

• Detailed quantitative analysis using transverse microradiography.

• Inclusion of both enamel and dentine substrates.

• Evaluation across two time points (2 and 5 weeks).

Limitations:

• In vitro design cannot fully simulate the complex oral environment (saliva, pellicle, biofilm).

• Manual brushing introduced variability (no standardized brushing machine used).

• High remineralizing potential of the control solution may have masked additional benefits of n-HAp.

• No pH cycling to simulate demin/remin cycles in real life.

Citation

Tschoppe P, Zandim DL, Martus P, Kielbassa AM. Enamel and dentine remineralization by nano-hydroxyapatite toothpastes. J Dent. 2011 May;39(6):430-7.
https://pubmed.ncbi.nlm.nih.gov/

Simple Chart: Dentine Remineralization (ΔDZ after 5 weeks)

Higher ΔDZ = More remineralization
All n-HAp groups outperformed fluoride for dentine remineralization.