Substituted Nano-Hydroxyapatite Toothpastes Reduce Biofilm Formation on Enamel and Resin-Based Composite Surfaces

Published In: Journal of Functional Biomaterials
Publication Year: 2020

Study Design

This was an in vitro experimental study examining how two different substituted nano-hydroxyapatite (n-HAp) toothpastes influence bacterial colonization and biofilm formation on enamel and resin-based composite (RBC) surfaces under simulated day and night oral conditions.

Funding Sources

The study received no external funding and the authors reported no conflicts of interest.

PICO Framework – what was studied and how?

Population:
Extracted human enamel and resin-based composite (RBC) specimens.

Intervention:
Brushing with substituted nano-hydroxyapatite toothpastes:

• α toothpaste (Zn-carbonate substituted n-HAp)

• β toothpaste (F, Mg, Sr-carbonate substituted n-HAp)

Comparison:
Brushing with distilled water (control group).

Outcomes:

• Early colonization (EC) measured after 12 hours.

• Biofilm formation (BF) measured after 24 hours.

• Viable biomass assessed using MTT assay and microscopy.

• Fluoride release measured in treated specimens.

In Paragraph Form:
This study assessed the ability of two nano-hydroxyapatite-based toothpastes—one containing zinc and the other a combination of fluoride, magnesium, and strontium—to reduce bacterial colonization and biofilm formation on both enamel and resin-based composite surfaces. The outcomes included the amount of viable bacteria after 12 and 24 hours, fluoride release from the toothpastes, and visualization of microbial growth using advanced imaging techniques.

Inclusion and Exclusion Criteria

Inclusion Criteria:

• Extracted human teeth used to create enamel disks.

• Fabricated RBC disks with polished surfaces (Ra < 0.2 µm).

Exclusion Criteria:

• Teeth with cracks or defects.

• RBC disks that did not meet finishing or curing specifications.

Demographics and Study Design

• 213 enamel disks and 213 RBC disks were prepared.

• Samples were randomly divided into three groups:

  • α toothpaste (Zn-nHAp) group: n = 71

  • β toothpaste (F, Mg, Sr-nHAp) group: n = 71

  • Control (distilled water) group: n = 71

• Each group was exposed to either Streptococcus mutans or a mixed oral microcosm.

• Test environments included a shaking multiwell plate (to simulate night) and a modified drip-flow reactor (to simulate day).

Primary Outcome Variables and Results

Outcome: Viable Bacterial Biomass (Optical Density - OD)

Key Findings:

• β toothpaste significantly reduced early colonization and biofilm formation compared to both α toothpaste and control.

• These effects were consistent across both enamel and RBC surfaces.

• No significant effect was observed in the Streptococcus mutans-only model; the mixed-species model showed clearer differences.

• The greatest antimicrobial effect was seen after 12 hours, suggesting better outcomes with twice-daily brushing.

Simple Chart: Viable Biomass (Artificial Oral Microcosm, 12 h – MDFR Setup)

Conclusions

The study concluded that:

• β toothpaste (containing fluoride, magnesium, and strontium-substituted n-HAp) significantly reduced early bacterial colonization and biofilm formation on both enamel and RBC surfaces.

• α toothpaste (zinc-substituted n-HAp) showed moderate antimicrobial effects, better than control but less than β toothpaste.

• Twice-daily brushing provided better inhibition than single exposure, reinforcing the importance of consistent oral hygiene.

Discussion: Strengths and Limitations

Strengths:

• Simulated real-world oral conditions (daytime and nighttime).

• Used both single-species and complex oral microbiome models.

• Employed multiple analysis methods (MTT assay, CLSM imaging, EDS surface analysis).

Limitations:

• In vitro results may not fully translate to real-life clinical settings.

• RBC autofluorescence slightly impacted imaging clarity.

• Short experimental time frames (12–24 hours).

• Fluoride release was minimal and likely not the primary antimicrobial mechanism.

Citation

Ionescu AC, Cazzaniga G, Ottobelli M, Garcia-Godoy F, Brambilla E. Substituted nano-hydroxyapatite toothpastes reduce biofilm formation on enamel and resin-based composite surfaces. J Funct Biomater. 2020;11(2):36.
PubMed: https://pubmed.ncbi.nlm.nih.gov/