Infection caused by fungi is considered as one of the foremost issues in public health, being diagnosed in millions of people annually [1]. The oral cavity represents a common site for fungal infection establishment and development. In majority of cases, fungal infection may be detected in immunocompromised patients or newborns with severe systemic diseases, patients who had undergone radiotherapy, patients who had received long-term antibiotic therapy as well as partially or totally edentulous patients with removable dentures [2,3].

Chronic atrophic candidiasis or denture stomatitis (DS) has been known as very common oral cavity disease that affects around 70% of patients with removable complete or partial acrylic dentures [4,5]. Denture material characteristics such as porosity and roughness have the ability to provide an anaerobic and acidic ecological niche in which microorganisms, including Candida species [6] and bacteria (Streptococci, Fusobacteria, and Bacteroides) could colonize, grow, and multiply, respectively [7,8]. DS can be caused by Candida albicans, which is an opportunistic microbe of the oral cavity. However, in acidic conditions, C. albicans can transform into a pathogen, changing the morphological forms from blastophore to hyphae and penetrating deeper tissue layers. Furthermore, other species of the Candida genus such as C. glabrata, C. tropicalis, C. parapsilosis, C. pseudotropicalis, C. krusei, and C. guilliermondii [9] were isolated from acrylic removable restorations and the palate, [10] and might contribute to disease development. In addition to microbes, numerous etiological and risk factors, including poor oral hygiene associated with poor-fitting dentures, nocturnal denture wearing, smoking, reduced saliva flow, and xerostomia, facilitate denture stomatitis onset [5,11,12]. These factors can altogether lead to various grades of oral mucosa inflammation from petechiae to generalized inflammation and hyperplasia [13]. Although DS is an asymptomatic disease, it has been noted that some cases with sensations and symptoms such as burning, dysgeusia, dysphagia, and halitosis [11] can significantly impair the patients’ quality of life [14].

Denture stomatitis requires a multidisciplinary approach which includes not only antifungal therapy in gels, creams, or oral suspensions but also identification and correction of etiological and risk factors and proper oral hygiene maintenance [15]. It has been shown that several species, including C. glabrata and C. krusei, can decrease treatment efficacy, and thus are substantial for detection. Antifungal therapy administered topically often involves repeated treatment on a long-term basis, which could contribute to resistant strain development and the systemic antifungal drug prescription, respectively [16]. Unfortunately, systemic antifungal drugs, such as amphotericin B and fluconazole, have shown to be ineffective in Candida colonies eradication from the palate [16], hence resulting in treatment failure, disease recurrence, and impaired quality of life. Furthermore, it is essential to find alternatives to conventional antifungal therapy so as to eradicate resistant strains and persistent infections while simultaneously decreasing treatment time.

As a non-invasive approach, photodynamic therapy (PDT) appears to be highly effective in the treatment of various oral infections, particularly fungal and bacterial ones [17]. The PDT working mechanism is based on the photochemical reaction in which highly reactive oxygen species (ROS), including single oxygen, are produced in the presense of tissue oxygen, causing pathogen death. Thus, this treatment modality has been proposed as a beneficial approach for numerous oral diseases, including periodontitis [18], [19], [20], peri-implant disease [20], [21], [22], chronic periapical periodontitis [23], [24], [25], [26], and oral candidiasis [27], [28], [29], [30], [31], [32]. Furthermore, in oral candidiasis treatment, ROS generated by the PDT [33] turned out to be effective at removing fungus-resistant stains [34]. As a result, PDT has shown efficient elimination of the Candida spp. completely or partially in several experiments and animal studies [28,30,[34], [35], [36]]. Despite the fact that clinical studies have demonstrated substantial Candida spp. eradication from the palate and dentures [29,34], more clinical studies found no difference between PDT and antifungal therapy [31]. Additionally, reappearance and recurrence of fungal infection was detected after 30 to 45 days following PDT [27,37]. Subsequently, a lack of treatment protocol standardization [34], the number of PDT applications, different pre-irradiation and irradiation time, and ongoing full-time denture wear during and after the treatment could be considered as reasons for inconsistent results. Considering the structure of removable acrylic dentures, which are said to be difficult to completely eradicate microbes from, the question arises whether these dentures have to be worn during the therapy and the follow-ups and whether new dentures are required to be made following the treatment.

The aim of this study was to to assess the clinical and microbiological outcomes after a one-session single application PDT compared to conventional antifungal therapy in patients without denture wearing during the treatment and follow-ups. A hypothesis was that a single one-session PDT application could produce significant improvements in clinical and microbiological outcomes compared to conventional antifungal therapy.