Enhanced Delivery of F-, Ca2+, K+, and Na+ Ions into Enamel by Electrokinetic Flows

Enamel Remineralization and Crystallization after Fluoride Iontophoresis

Early caries lesions consist of noncavitated subsurface demineralization caused by the dissolution of hydroxyapatite from the surface to the subsurface area of the enamel. Such lesions cannot be remineralized effectively by the conventional treatment. Thus, there is a need for a noninvasive technique capable of delivering the remineralizing agent to subsurface sites. For this purpose, fluoride iontophoresis (IP) using weak currents has been investigated with some conflicting results and no information on the crystal structure and composition. Because enamel remineralization involves the role of fluid from dentin, the presence of enamel fluid is necessary to determine the repair associated with the physiological condition. This study aimed to investigate structural and compositional characteristics, including the remineralizing effect of 5% sodium fluoride (NaF) IP with different polarities, cathodal iontophoresis (CIP), and anodal iontophoresis (AIP) for the treatment of natural enamel caries under simulated pulpal pressure. A bulk measurement of the crystal structure inside the lesion was first determined using calcium (Ca) K-edge X-ray absorption spectroscopy. IP with both polarities significantly promoted subsurface remineralization. The CIP generated a significant increase in the Ca/phosphorus ratio, and fluoride at the surface lesion significantly correlated with higher mineral density (MD) and more strengthening crystal structure of the lesion volume, while the lesion's MD and other impurities at the lesion surface, mostly the carbonate ions, affected the significant increase in MD with the unchanged structure of the lesion volume after AIP. The CIP of NaF is an ideal method for rapid enamel remineralization and recrystallization of fluoroapatite/fluorohydroxyapatite.

Improved mineralization of dental enamel by electrokinetic delivery of F- and Ca2+ ions

This in vitro study evaluated the effects of the infiltration of F^- and Ca²⁺ ions into human enamel by electrokinetic flow (EKF) on the enamel microhardness and F^- content. Sound human enamel ground sections of unerupted third molars were infiltrated with de-ionized water by EKF and with F^- ion by EKF respectively. All samples were submitted to two successive transverse acid-etch biopsies (etching times of 30 s and 20 min) to quantify F^- ion infiltrated deep into enamel. Remarkably, sound enamel showed a large increase in microhardness (MH) after infiltration of NaF (p < 0.00001) and CaCl₂ (p = 0.013) by EKF. Additionally, NaF-EKF increased the remineralization in the lesion body of artificial enamel caries lesions compared to controls (p < 0.01). With the enamel biopsy technique, at both etching times, more F^- ions were found in the EKF-treated group than the control group (p << 0.05), and more fluoride was extracted from deeper biopsies in the NaF-EKF group. In conclusion, our results show that EKF treatment is superior in transporting Ca²⁺ and F^- ions into sound enamel when compared to molecular diffusion, enhancing both the mineralization of sound enamel and the remineralization of artificial enamel caries.

Effects of an orthodontic primer containing amorphous fluorinated calcium phosphate nanoparticles on enamel white spot lesions

OBJECTIVES

The study investigated the effects of an orthodontic primer containing amorphous fluorinated calcium phosphate (AFCP) nanoparticles on enamel white spot lesions (WSLs).

MATERIALS AND METHODS

The AFCP nanoparticles were prepared and incorporated into Transbond XT Primer. Thirty-two human enamel slices were highly polished and randomly divided into four groups: no part covered (control), half covered with a primer containing 0 wt%, 25 wt%, and 35 wt% AFCP. Subsequently, samples were challenged by a modified pH-cycling and characterized by color measurement, micro-computed tomography, and scanning electron microscope (SEM). The bonding properties of the primers containing AFCP were assessed using shear bond strength test, and the mouse fibroblasts (L929) were employed to evaluate the cytotoxicity.

RESULTS

When the enamel was challenged by pH cycling, 25 wt% and 35 wt% AFCP groups exhibited less color change (ΔE) and less mineral loss than the control and 0 wt% AFCP groups. The SEM images showed that the original microstructural integrity and mineral deposition rate of the enamel surface were better in the 25 wt% and 35 wt% AFCP groups. In particular, the 35 wt% AFCP group exhibited the best performance after 3 weeks of pH cycling. The shear bond strength and cell viability revealed no significant difference among the tested groups (P > 0.05).

CONCLUSION

Using the primer containing 35 wt% AFCP might be a promising strategy for preventing the occurrence and development of WSLs during orthodontic treatment.

Iontophoresis application for drug delivery in high resistivity membranes: nails and teeth

Iontophoresis has been vastly explored to improve drug permeation, mainly for transdermal delivery. Despite the skin's electrical resistance and barrier properties, it has a relatively high aqueous content and is permeable to many drugs. In contrast, nails and teeth are accessible structures for target drug delivery but possess low water content compared to the skin and impose significant barriers to drug permeation. Common diseases of these sites, such as nail onychomycosis and endodontic microbial infections that reach inaccessible regions for mechanical removal, often depend on time-consuming and ineffective treatments relying on drug's passive permeation. Iontophoresis application in nail and teeth structures may be a safe and effective way to improve drug transport across the nail and drug distribution through dental structures, making treatments more effective and comfortable for patients. Here, we provide an overview of iontophoresis applications in these "hard tissues," considering specificities such as their high electrical resistivity. Iontophoresis presents a promising option to enhance drug permeation through the nail and dental tissues, and further developments in these areas could lead to widespread clinical use.

A Hydroxypropyl Methylcellulose Film Loaded with AFCP Nanoparticles for Inhibiting Formation of Enamel White Spot Lesions

Objective

This study investigated the effects of mineralizing film consisting of hydroxypropyl methylcellulose (HPMC) and amorphous fluorinated calcium phosphate (AFCP) nanoparticles on enamel white spot lesions (WSLs).

Material and Methods

The AFCP nanoparticles and mineralizing film were prepared via nanoprecipitation and solvent evaporation, respectively. They were characterized with Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), inductively coupled plasma atomic emission spectrometry (ICP-AES), and fluoride ion selective electrode. Thirty-two human enamel slices (4 mm × 4 mm × 1.5 mm) were highly polished and randomly assigned to four groups: negative control (no treatment); pure HPMC film; mineralizing film; GC Tooth Mousse Plus^® (contains 10% CPP-ACP and 0.2% NaF). Subsequently, samples were challenged by a modified pH-cycling and characterized by color measurement, Micro-CT, SEM/EDX, and nanoindentation.

Results

The mineralizing film could sustain release of Ca, P and F ions over 24 h and maintain AFCP nanoparticles in metastable state over 8~12 h. During 4 weeks of pH cycling, the mineralizing film group exhibited least color change (∆E), mineral loss and lesion depth (120 ± 10 µm) among four groups (p < 0.05). SEM findings revealed that the porosities among enamel crystals increased in negative control and pure HPMC film groups after pH cycling, whereas in mineralizing film group, the original microstructure of enamel was well conserved and mineral deposits were detected between enamel prisms. Mineralizing film group demonstrated a least reduction of nanomechanical properties such as elastic modulus of 77.02 ± 6.84 GPa and hardness of 3.62 ± 0.57 GPa (p < 0.05).

Conclusion

The mineralizing film might be a promising strategy for prevention and management of WSLs via inhibiting enamel demineralization and promoting enamel remineralization.

Biomimetic mineralisation systems for in situ enamel restoration inspired by amelogenesis

Caries and dental erosion are common oral diseases. Traditional treatments involve the mechanical removal of decay and filling but these methods are not suitable for cases involving large-scale enamel erosion, such as hypoplasia. To develop a noninvasive treatment, promoting remineralisation in the early stage of caries is of considerable clinical significance. Therefore, biomimetic mineralisation is an ideal approach for restoring enamel. Biomimetic mineralisation forms a new mineral layer that is tightly attached to the surface of the enamel. This review details the state-of-art achievements on the application of amelogenin and non-amelogenin, amorphous calcium phosphate, ions flow and other techniques in the biomimetic mineralisation of enamel. The ultimate goal of this review was to shed light on the requirements for enamel biomineralisation. Hence, herein, we summarise two strategies of biological minimisation systems for in situ enamel restoration inspired by amelogenesis that have been developed in recent years and compare their advantages and disadvantages.

Drug Delivery (Nano)Platforms for Oral and Dental Applications: Tissue Regeneration, Infection Control, and Cancer Management

The oral cavity and oropharynx are complex environments that are susceptible to physical, chemical, and microbiological insults. They are also common sites for pathological and cancerous changes. The effectiveness of conventional locally-administered medications against diseases affecting these oral milieus may be compromised by constant salivary flow. For systemically-administered medications, drug resistance and adverse side-effects are issues that need to be resolved. New strategies for drug delivery have been investigated over the last decade to overcome these obstacles. Synthesis of nanoparticle-containing agents that promote healing represents a quantum leap in ensuring safe, efficient drug delivery to the affected tissues. Micro/nanoencapsulants with unique structures and properties function as more favorable drug-release platforms than conventional treatment approaches. The present review provides an overview of newly-developed nanocarriers and discusses their potential applications and limitations in various fields of dentistry and oral medicine.

Enhanced teeth whitening by nanofluidic transport of hydrogen peroxide into enamel with electrokinetic flows

Tooth whitening, a routine procedure in dentistry, is one of the examples of medical procedures that are limited by the challenge of delivering molecules into various types of nanoporous tissues. Current bleaching methods rely on simple diffusion of peroxides into enamel nano channels, therefore requires sufficient contact time with peroxides. In-office treatments often involve enamel etching or light activation which often results in patient sensitivity and potential soft tissue damage.

OBJECTIVE

To demonstrate a robust method to transport hydrogen peroxide to greater depths into enamel nanopores through nanofluidic flows driven by electrokinetics, with the intention to increase efficacy while reducing treatment time.

METHODS

Freshly extracted human teeth were subjected to electrokinetic flow treatment with hydrogen peroxide under different electric fields with varying operation times. Pre- and post-operative shade matching was done using a photospectrometer.

RESULTS

It is demonstrated that the operation time for the same concentration of hydrogen peroxide can be shortened by 10 times. The proposed method showed significant improvements in whitening effects over control groups and thus offers promising clinically-viable chairside applications with efficacy.

SIGNIFICANCE

The demonstrated nanofluidic transport of hydrogen peroxide into enamel has a potential to be applied for enhancing tooth whitening, compared to simple diffusion, without heating the hard dental tissues.