Efficacy of a Copper-Calcium-Hydroxide Solution in Reducing Microbial Plaque on Orthodontic Clear Aligners: A Case Report

Abstract

The aim of this study was to investigate the ability of a copper-calcium-hydroxide-based compound to remove microbial plaque naturally produced onto orthodontic clear aligners. A commercially available dental paste, named Cupral, based on copper-calcium-hydroxide, was used. A healthy volunteer (female, 32 years old), undergoing orthodontic treatment with thermoplastic clear aligners was enrolled. By conventional/confocal microscopy and colony-forming unit (CFU) assay, 2-week used aligners were examined for microbial plaque, prior and following exposure to Cupral. Confocal microscopy revealed abundant plaque irregularly distributed onto the aligner surface. Following Cupral treatment, a drastic decrease occurred in plaque thickness and matrix presence. As assessed by the CFU assay, total microbial load approached 10⁹ CFUs/aligner, with slight differences in aerobiosis and anaerobiosis culture conditions; six macroscopically different types of colonies were detected and identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry. Following Cupral treatment, microbial load dropped to undetectable levels, irrespectively of the conditions considered. Exposure of clear aligners to Cupral results in the elimination of contaminating microorganisms; the antimicrobial activity is retained up to 1.25% concentration. Overall, our data describe a novel use of Cupral, a copper-calcium-hydroxide-based compound, in daily hygiene practices with promising results.

Fig. 1

Flowchart of the microbiological analysis performed on clear aligners. Two-weeks-used clear aligners (upper and lower) were split in two equal parts. A part was maintained in saline buffer ( A ), while the other was exposed to Cupral 1.25% ( B ); both groups were incubated for 1 hour and sonicated for 15 minutes. The supernatants were harvested, diluted, and plated on TSA and SAB plates; each set of plates was incubated, under aerobiosis or anaerobiosis conditions, for 24 hours. Total and residual microbial loads were evaluated by colony-forming unit analysis; each group was tested in triplicate plates.

Fig. 2

Confocal microscopy of microbial plaque on orthodontic clear aligner. The upper panel shows a representative image of the untreated clear aligner; an abundant microbial biofilm is observed ( A ), as confirmed by the three-dimensional (3D) reconstruction of the same capture ( B ), according to the thickness scale ( C ). The lower panel shows a representative image of the Cupral-treated aligner; the device surface with minimal residual cells is observed ( A ), as confirmed by the 3D reconstruction of the same capture ( B ), according to the thickness scale ( C ).

Fig. 3

TSA Total and residual microbial load detected on winter months. The clear aligners were exposed or not to Cupral 1.25%. The colonies isolated after incubation in TSA or SAB medium were counted and clustered. The upper table shows the total and residual microbial load expressed as colony-forming units/aligners. The values represent the mean of three independent analyses, where each sample had been assessed in triplicate. The standard errors, less than 10%, are omitted. The lower pie graphs represent the percent of species detected in aerobiosis and anaerobiosis conditions. n.d.: not detected.

Fig. 4

Total and residual microbial load detected on summer months. The clear aligners were exposed or not to Cupral 1.25%. The colonies isolated after incubation in SAB medium were counted and clustered. The upper table shows the total and residual microbial load expressed as colony-forming units/aligners. The values represent the mean of three independent analyses, where each sample had been assessed in triplicate. The standard errors, less than 10%, are omitted. The lower pie graphs represent the percent of species detected in aerobiosis and anaerobiosis conditions. n.d.: not detected.

Fig. 5

Morphological peculiarities of the isolated colonies observed by inverted light microscope. Images (10x magnification) of the most representative colonies in TSA or SAB medium: ( A ) translucent white, coccobacilli Gram- ( Haemophilus parainfluenzae ); ( B ) wrinkled large yellow, diplococci Gram- ( Neisseria mucosa/sicca ); ( C ) large white, cocci Gram+ ( Staphylococcus aureus ); ( D ) small white, streptococci Gram+ ( Streptococcus mitis/oralis ); ( E ) irregular margins, streptococci Gram+ ( Streptococcus sanguinis ); ( F ) large beige, cocci Gram+ ( Rothia aeria ).