Evaluation of two different self-disinfection alginate impression material

Initial impressions are routine procedures in dental practice to obtain accurate gypsum models. Accuracy and dimensional stability are critical and can be affected by environmental factors, setting time, water content, and material composition. Alginate is a widely used, affordable primary impression material capable of duplicating fine oral details. After removal from the mouth, impressions are typically washed and disinfected, but because alginate is hydrophilic, spray or immersion disinfection can cause water uptake, distortion, and dimensional changes, potentially compromising cast accuracy. Cross-infection control protocols require disinfection of impressions to prevent transmission of pathogens. Various chemical disinfectants have been used, yet dimensional instability remains a problem. To address this, disinfectants have been incorporated into irreversible hydrocolloids to create self-disinfecting materials. This study compares silver nanoparticles (AgNPs) and povidone-iodine (PV-I) incorporated into alginate for self-disinfection efficacy against Staphylococcus aureus (Gram-positive), Escherichia coli (Gram-negative), and Candida albicans (yeast). The null hypothesis is that adding PV-I and AgNPs could adversely affect mechanical properties and the accuracy of alginate impressions.

Ethics: Approved by the Research Ethics Committee, Faculty of Pharmacy, Delta University for Science and Technology (FPDU-REC; approval no. FPDU7/2024). Materials: Commercial alginate (IQ green, Lascod, Italy, Batch 0159311) and povidone-iodine (Merck, Germany). AgNPs synthesis reagents: PVP (MW~40,000), AgNO3, NaOH, Na2CO3, acetone (HPLC grade), glucose. Media: Mueller-Hinton agar and Sabouraud dextrose agar (Oxoid, UK). Microorganisms: Clinical isolates of S. aureus (G+), E. coli (G−), and C. albicans sourced from the Faculty of Pharmacy, Delta University. Preparation and characterization of AgNPs: AgNPs synthesized by chemical reduction of 0.01 M AgNO3 with glucose in presence of 1% PVP at 55 °C for 1 h with vigorous stirring; pH maintained at 8.5–9.0 using NaOH and Na2CO3. Particles were precipitated by repeated acetone washing, centrifuged at 6000 rpm for 10 min, air-dried, then re-dispersed in deionized water by ultrasonication. Characterization by UV–Vis spectrophotometry (Shimadzu UV-9001) and TEM (JEOL JEM 2100); particle size distribution recorded. Preparation of self-disinfecting alginate: 0.45 g alginate powder mixed for 45 s with 1 mL of either water (control), 10% PV-I (PV-I-alginate), or 0.05% AgNPs suspension (AgNPs-alginate). Pastes were spread to 0.5 mm thickness; 5 mm diameter discs cut and stored sterile for use within 1 h. Antimicrobial testing (disc diffusion): Log-phase cultures adjusted to ~10^4 CFU/mL (0.5 McFarland). 100 µL inoculated onto Mueller-Hinton agar (bacteria) or Sabouraud dextrose agar (C. albicans). After 10 min, alginate discs were applied; plates incubated 18 h at 37 °C (bacteria) or 4 days at 28 °C (C. albicans). Inhibition zone diameters measured; experiments repeated three times and means calculated. Surface details reproduction test: Following ISO 1563, six samples per group were tested using a copper mold engraved with three parallel lines (50, 20, 75 µm width; 25 mm length) spaced 2.5 mm apart; auxiliary lines X and X′ aided assessment. Material was placed in a ring-matrix assembly, covered with a rigid plate, weighted by 2 kg during setting to simulate clinical pressure and allow excess escape. The assembly was immersed in 35 °C water until set, then specimens examined and scored 0–1 based on full-length reproduction of the 50 µm line. Elastic recovery test: Per ISO 1563:1990 using a split cylindrical mold (20 mm length; 12.5 mm internal diameter) within a securing ring. Each sample (n=6/group) was set in the mold and tested on a universal testing machine (Zwick Zmart Pro). Specimens were deformed to 20% of original length (L) over 5 s, unloaded, and allowed 40 s for recovery. Elastic recovery (%) was calculated as (ΔL/L − 1) × 100, where L is original length and ΔL length after deformation. Statistical analysis: SPSS v20; significance p ≤ 0.05. Data normality by Shapiro–Wilk. When ANOVA significant, group comparisons by Duncan’s multiple range and Tukey post-hoc tests.

AgNPs characterization: UV–Vis showed a single surface plasmon resonance band at 420 nm with peak broadening indicating wide size distribution. TEM revealed well-dispersed spherical nanoparticles with size range 20–55 nm and mean 38.6 ± 0.3 nm. Antimicrobial activity: Both AgNPs-alginate and PV-I-alginate showed broad-spectrum activity against S. aureus, E. coli, and C. albicans and were significantly more active against S. aureus (G+) than E. coli (G−) (p ≤ 0.05). PV-I-alginate was significantly more active against C. albicans than AgNPs-alginate. Reported inhibition zones (mm; mean ± SD): AgNPs-alginate—S. aureus 22.5 ± 3.0, E. coli 20.0 ± 2.0, C. albicans 13.0 ± 1.0; PV-I-alginate—S. aureus 15.0 ± 2.0, E. coli 11.0 ± 1.5, C. albicans 21.0 ± 2.5. Surface detail reproduction: All samples in all groups fully reproduced the 50 µm line and complied with ISO 1563, scoring 1. Elastic recovery: No statistically significant differences among control, PV-I-alginate, and AgNPs-alginate (p > 0.05). Mean ± SD recovery values: control 94.36 ± 0.26%, PV-I-alginate 91.53 ± 0.47%, AgNPs-alginate 95.55 ± 0.34%. Control and AgNPs-alginate were close to the ANSI/ADA Specification No. 18 minimum of 95% recovery; PV-I showed a lower mean but not significantly different from other groups.

Incorporating disinfectants directly into alginate aimed to overcome distortions associated with post-impression spray or immersion disinfection while ensuring cross-infection control. The study demonstrated that both AgNPs and PV-I imparted self-disinfecting properties to alginate against representative Gram-positive, Gram-negative, and yeast organisms without compromising surface detail reproduction or significantly altering elastic recovery. The AgNPs’ antimicrobial effect is attributed to Ag+ ion release and interaction with negatively charged microbial membranes; particle size (mean ~38.6 nm) supports effective activity. PV-I showed strong, broad-spectrum microbicidal activity, notably superior against C. albicans, consistent with iodine’s rapid oxidative mechanisms on cellular components and enzymes. Despite PV-I’s lower elastic recovery mean, overall mechanical performance met ISO detail reproduction criteria and did not differ significantly among groups, suggesting the additives did not disrupt alginate gel network integrity. The findings address the research hypothesis by showing that self-disinfecting formulations can maintain critical mechanical and accuracy parameters while providing effective antimicrobial action, satisfying ADA and ISO standards relevant to alginate use.

Incorporation of povidone-iodine and silver nanoparticles into alginate imparted broad-spectrum antimicrobial activity without adverse effects on surface detail reproduction or significant changes in elastic recovery. Both agents can be used as efficient disinfectants for alginate impressions; PV-I is recommended due to lower cost and accessibility.