Biological properties of experimental dental alginate modified for self-disinfection using green nanotechnology

Abstract

Objectives: Disinfection of alginate impression materials is a mandatory step to prevent cross-infection in dental clinics. However, alginate disinfection methods are time-consuming and exert a negative impact on accuracy and mechanical properties. Thus, this study aimed to prepare disinfecting agents (CHX and AgNO₃) and silver nanoparticles reduced by a natural plant extract to produce a self-disinfecting dental alginate.

Methods: Conventional alginate impression material was used in this study. Silver nitrate (0.2% AgNO₃ group) and chlorohexidine (0.2% CHX group) solutions were prepared using distilled water, and these solutions were later employed for alginate preparation. Moreover, a 90% aqueous plant extract was prepared from Boswellia sacra (BS) oleoresin and used to reduce silver nitrate to form silver nanoparticles that were incorporated in the dental alginate preparation (BS+AgNPs group). The plant extract was characterized by gas chromatography/mass spectrometry (GC/MS) analysis while green-synthesized silver nanoparticles (AgNPs) were characterized by UV-visible (UV-vis) spectroscopy and scanning electron microscopy (SEM). An agar disc diffusion assay was used to test the antimicrobial activity against Candida albicans, Streptococcus mutans, Escherichia coli, methicillin-resistant and susceptible Staphylococcus aureus strains, and Micrococcus luteus. Agar plates were incubated at 37 ± 1 °C for 24 h to allow microbial growth. Diameters of the circular inhibition zones formed around each specimen were measured digitally by using ImageJ software.

Results: Chemical analysis of the plant extract revealed the presence of 41 volatile and semi-volatile active compounds. UV-Vis spectrophotometry, SEM, and EDX confirmed the formation of spherical silver nanoparticles using the BS extract. CHX, AgNO₃, and the BS+AgNPs modified groups showed significantly larger inhibition zones than the control group against all tested strains. BS+AgNPs and CHX groups showed comparable efficacy against all tested strains except for Staphylococcus aureus, where the CHX-modified alginate had a significantly higher effect.

Conclusions and clinical relevance: CHX, silver nitrate, and biosynthesized silver nanoparticles could be promising inexpensive potential candidates for the preparation of a self-disinfecting alginate impression material without affecting its performance. Green synthesis of metal nanoparticles using Boswellia sacra extract could be a very safe, efficient, and nontoxic way with the additional advantage of a synergistic action between metal ions and the phytotherapeutic agents of the plant extract.

Keywords: Antimicrobial activity; Boswellia sacra; Green synthesis; Irreversible hydrocolloids; Nanotechnology.

Fig. 1

Schematic diagram showing steps of preparation of B. sacra extract and green nanoparticles

Fig. 2

UV–Vis absorption spectra of Ag NPs green synthesized by Boswellia sacra extract at different time intervals

Fig 3

SEM magnified images: a AgNO₃ and (b) Boswellia sacra extract

Fig. 4

a SEM magnified image (500x) confirming the formation of spherical nanoparticles and nanoclusters in-between micro particles. b SEM magnified image (1500x) showing clusters and different sizes of silver nanoparticles sizes, microparticles, and B. sacra constituents

Fig. 5

Inhibition zones for all four tested groups against a C. albicans, b M. luteus, and (c) the MRSA S. aureus USA300

Fig 6

Bar chart representing the mean inhibition zone values and standard of error of the four tested alginate groups