Dental impression making is a critical step in restorative treatment, providing a precise three-dimensional replica of the oral structures.^[1] This replica allows for the fabrication of restorations that reconstruct tooth form and function and enables laboratory work to proceed in the patient’s absence.^[2,3] Dental impressions are a potential source of infection in prosthetic workflow and can lead to the transmission of infection, especially in individuals with weakened immune systems.^[4,5] For this reason, the American Dental Association (ADA) and the Centers for Disease Control and Prevention have published guidelines for the disinfection of dental impressions.^[6] All patients should be considered potential carriers, and their impressions should be handled similarly to those of a high-risk patient.^[7] Rinsing under water cannot completely remove saliva and blood from the impression surface because salivary mucins and adhesive salivary proteins interfere with simple washing.^[8] Therefore, a suitable method for disinfecting dental impressions is essential. Since impressions cannot be sterilized by heat, chemical disinfection is the most common disinfection method. Chemical disinfection is divided into two methods: immersion and spraying.^[7] The hydrophilic nature of the materials, the presence or absence of surfactants, and their tolerance to immersion in water or other fluids are key elements in selecting the appropriate chemical protocol for impression materials.^[9,10] To date, a global standard method for disinfecting impression materials has not been achieved.^[11,12] An alternative disinfection strategy employs ultraviolet (UV) radiation. The efficacy of UV light is contingent upon several factors, including exposure duration, intensity, ambient humidity, and the requirement for direct line-of-sight to the microbial organisms. Furthermore, its application is constrained by significant limitations: the need for multiangular exposure to ensure comprehensive surface coverage and the imperative to remove organic debris from the impression before treatment to achieve optimal efficacy. However, the nonchemical nature of this method, the lack of dimensional changes in the impression, and its broad spectrum of effectiveness are advantages of this method.^[13] Therefore, given the critical role of impression disinfection in preventing cross-contamination and the potential advantages of UV radiation such as avoiding dimensional change and chemical residue over conventional chemical disinfectants, this in vitro study aimed to comparatively evaluate the antibacterial efficacy of a specific UV radiation device (“Fast Steril”) against the standard chemical agent, 0.525% sodium hypochlorite, on two widely used impression materials: Condensation silicone and alginate.

The validation of experimental conditions was confirmed by the control groups. All positive control samples demonstrated 100% microbial growth, while all negative control samples maintained 100% sterility throughout the study. The quantitative assessment of disinfection efficacy is presented in Figure 2, which illustrates the mean CFU counts and corresponding standard deviations for three microbial species on both alginate and condensation silicone impression materials following application of two disinfection protocols: UV irradiation and sodium hypochlorite treatment. The bar chart provides a comparative visualization of the bacterial reduction achieved by each disinfection method across both material types.

Dental impressions frequently come into contact with blood and saliva, which can harbor pathogenic microorganisms capable of transmitting infectious diseases. This risk of cross-contamination underscores the need for stringent infection control measures throughout impression-making and subsequent laboratory processing.^[15] The present study evaluated the antibacterial efficacy of UV irradiation on condensation silicone and alginate impression materials in comparison with 0.525% sodium hypochlorite. The selection of test microorganisms was guided by their clinical relevance, high pathogenicity, and documented resistance to disinfectants. Pseudomonas aeruginosa presents a significant cross-infection risk in dental environments due to its intrinsic antibiotic resistance and potential to cause nosocomial infections. Staphylococcus aureus was included as a benchmark organism for disinfectant efficacy testing owing to its widespread antibiotic resistance. S. pyogenes (Group A beta-hemolytic) was selected for its established pathogenic role in oral and systemic infections.^[12] Although this study focused on highly resistant pathogenic strains, future research should incorporate representative members of the normal oral microbiota to enhance clinical generalizability.

Two disinfection methods were evaluated for impression materials: UV irradiation using a fast-sterilizer device and spray application of 0.525% sodium hypochlorite with a 10-min contact time. Although the ADA recommends immersion in 0.5% sodium hypochlorite (5000 ppm free chlorine) for 10 min,^[6] and manufacturers report 99.8% tuberculocidal efficacy with this protocol,^[16] the spray method was selected for this investigation due to concerns regarding dimensional instability associated with immersion techniques.^[17] While immersion remains the gold standard for disinfectant reliability,^[12,18,19] spraying represents a clinically acceptable alternative that minimizes potential material distortion.

The present study also evaluated UV-C (UVC) irradiation as a disinfection alternative using a fast-sterilization device. The biocidal mechanism of UVC radiation primarily involves induction of genomic damage through thymine dimer formation in microbial DNA, leading to irreversible inactivation of pathogens.^[20] Notable advantages of UVC over chemical disinfectants include exceptional preservation of impression dimensional accuracy and complete avoidance of chemical residue on material surfaces.^[21] While this technology demonstrates well-documented efficacy in surface disinfection, it also shows promising applications in endodontic therapy, including root canal disinfection and management of periapical inflammatory conditions. These findings are consistent with previous research by Ishida et al.,^[13] who reported complete eradication of Candida species on silicone impression materials following 5 min of UVC exposure, with no statistically significant alterations in dimensional stability or surface characteristics. In a 2019 investigation, Nimunkar et al.^[22] evaluated the dimensional stability of polyvinyl siloxane impressions following disinfection using 2% glutaraldehyde, 1% sodium hypochlorite, and UV irradiation. Their findings indicated that UV irradiation, in contrast to chemical disinfectants, produced no measurable dimensional alterations. This is consistent with a body of research documenting dimensional changes resulting from chemical disinfection of dental impressions,^[23,24] although some studies have reported no significant effects on dimensional stability from disinfection procedures.^[25,26]

Alginate, a representative irreversible hydrocolloid, remains one of the most frequently utilized dental impression materials owing to its user-friendly application, procedural simplicity, and cost-effectiveness.^[27] Nevertheless, its inherent hydrophilicity increases its susceptibility to microbial retention, while its dimensional accuracy and stability are notably compromised upon exposure to liquid disinfectants.^[28] Condensation silicones, similarly employed in routine prosthetic impression procedures, represent another mainstream material in clinical dentistry.^[27] Based on their prevalence and distinct material characteristics, these two impression materials were selected for the current investigation. Results demonstrated that UV irradiation yielded superior disinfection efficacy compared to sodium hypochlorite solution when applied to condensation silicone impressions. Furthermore, a statistically significant difference was observed between the two materials, with alginate exhibiting reduced susceptibility to disinfection, a phenomenon likely attributable to its heightened porosity and consequent increased potential for microbial entrapment.

In a 2010 comparative study, Samra et al. evaluated the disinfection efficacy of UV irradiation versus sodium hypochlorite on alginate and silicone impression materials. Their findings indicated that UV chamber disinfection yielded superior results compared to hypochlorite a conclusion consistent with the present study regarding silicone materials, though not observed with alginate. Further supporting the utility of UV irradiation, Aran et al. demonstrated its potential for significantly reducing colony counts of oral pathogens on various patient-derived impression materials, including alginate, addition silicone, and polyether. However, as their study utilized clinical impressions, the precise microbial composition remained uncharacterized. Notably, Aran et al. also reported that impression material type did not influence the efficacy of UV disinfection.^[29] The observed differential efficacy of disinfection between alginate and silicone impression materials in the present study may be attributed to alginate’s characteristically porous microstructure and its reported capacity for two to three times greater microbial absorption compared to silicone. This inherent property may necessitate extended disinfection durations beyond the 10-s UV exposure protocol employed herein. Furthermore, the use of a multidirectional UV chamber as opposed to the single-angle portable device utilized in this study may provide more uniform irradiation and enhance disinfection outcomes. It is also noteworthy that discrepancies between our results and those of earlier studies may stem from differences in microbial strains; prior investigations predominantly used normal oral flora, whereas the present study employed standardized ATCC strains with well-defined profiles. These findings are nevertheless consistent with recent work by Wezgowiec et al.,^[30] who demonstrated the effectiveness of UV irradiation in disinfecting both condensation and addition silicones of varying consistencies against P. aeruginosa, S. aureus, and Candida albicans, further supporting the utility of UV-based disinfection in dental practice.

One notable finding of this study was the significantly higher colony counts observed for S. aureus and P. aeruginosa compared to Group A beta-hemolytic Streptococcus (GAS). This differential efficacy may be attributed to the higher intrinsic resistance of S. aureus and P. aeruginosa both recognized as resilient nosocomial pathogens to various disinfection methods and antibiotics when compared to GAS.^[31,32] The effective elimination of resistant nosocomial pathogens such as S. aureus and P. aeruginosa suggests potential applications of the UV disinfection device beyond dental settings, including hospital environments where such pathogens pose significant challenges to infection control. However, this extrapolation requires further validation through targeted clinical studies. In conjunction with the established advantage of superior dimensional stability reported in literature when using UV irradiation compared to chemical alternatives, the findings of this study support the conclusion that UV irradiation presents a superior alternative to chemical disinfectants for both condensation silicone and alginate impression materials.

Based on the results of this study, UVC irradiation demonstrated superior disinfection efficacy compared to sodium hypochlorite for condensation silicone impressions, while both methods showed comparable results for alginate. The differential efficacy between materials highlights the influence of material composition and porosity on disinfection outcomes. Given its minimal impact on dimensional stability and clinical practicality, UV irradiation is recommended as a preferable disinfection method for dental impression materials.