# Photodynamic Therapy Effects on Oral Dysplastic Keratinocyte Cell Cultures: A Systematic Review
## 4 Discussion  
OED grading is one of the most valuable prognostic indicators for predicting the transformation of potentially malignant oral cavity disorders to squamous cell carcinoma. It is also used as a rationale for determining management options. Molecular and genetic markers have been identified with encouraging results in determining which potentially malignant disorders are at risk of malignant transformation [3]. Nevertheless, oral cancer is a long-term process; thus, it is possible to design preventive steps to avoid cancerization long before the beginning of malignancy [32]. Conventional therapies for OPDM extend from careful observation to complete resection. Surgery is currently advised for the excision of high-risk lesions; nonetheless, proof of its success is lacking. In some cases, there is an increase in the recurrence of malignancy after surgical excision has been registered; the surgical procedure does not prevent all pre-malignant lesions from evolving into malignancy [33]. Non-surgical therapies should be the approach for lesions affecting an extensive area of the oral mucosa or occurring in patients with high surgical risks or when patients refuse surgical treatment [32]. The treatment of these lesions has always been a matter of debate as early diagnosis and subsequent early application of therapy are still critical in the prognosis and survival of patients with neoplastic oral cavity lesions. Intervening in pre-malignant lesions with a method that is non-invasive, well-tolerated by the patient, and free of side effects on neighboring healthy cells would be an important goal to achieve in improving the therapeutic approach to these lesions. In this context, analyzing the recent literature is a necessary step toward achieving this goal. The study of PDT in vitro is essential in order to fully understand and obtain information on the most effective therapeutic protocols for using this method in treating the pre-malignant lesions of the oral cavity. The seven selected studies analyzed the effects of PDT on dysplastic human cell cultures: six studies on human dysplastic oral keratinocytes (DOK) [24; 25; 26; 27; 28; 29; 30] and only one study on dysplastic leukoplastic tongue cells (MSK-leuk1) [34]. Homogeneity was also evident concerning the light source used as a photo-activating source. All the devices explored were set to similar wavelengths (Table 1). In contrast, considerable heterogeneity was found in photosensitizers. Three of the seven papers used ALA. [25; 29; 30]. One study applied erythrosine B sodium salt [24], one paper Methylene blue [26], one work hydroxy aluminum [27], and one study methyl aminolevulinate [29]. Although this heterogeneity makes direct comparison of results difficult, it is nevertheless possible to point out that all authors report favorable results. One of the fundamental objectives that in vitro studies can help achieve is establishing the optimal dosage based on the photosensitizer used. Indeed, several authors [24; 27] have pointed out that the effects on DOK cells are dose-related. [PERSON] et al. [29] suggested that the optimum inhibition efficiencies for DOK cell lines are 1 mM ALA. This dosage is influenced by the type of photosensitizer and the cell line. Interestingly, while the authors of the study mentioned above showed a better apoptosis-inducing effect in oral cancer CAL-27 cells than in DOK cells, other authors showed a resistance of other oral cancer cell lines (SCC9) to ALA-PDT [35]. Furthermore, the role of matrix metalloproteinases (MMPs) has been indicated in relation to the efficacy of photodynamic therapy in OSCC [36]. MMPs are enzymes that potentiate tumor invasion and metastasis by degrading the extracellular matrix. MMP-2 and MMP-9 are overexpressed in oral dysplasias and oral cancers [37; 38; 39]. [PERSON] et al. [36] registered that after exposure to PDT, the total activity of MMP-2 and MMP-9 in malignant human keratinocytes culture was down-regulated.