The pooled estimates of lesion response, changes of size, VAS, and TH, revealed that PDT could not only reduce the lesions size, but also reduce pain of the patients. PDT is a new noninvasive treatment that is assumed to be effective for OLP.
We found that topical use of 5-ALA had a higher efficacy compared to gargling MB in terms of PR. The relatively poor outcome from MB can be possibly due to the short gargle time of only five minutes. The time of topical use 5-ALA can continue 30–120 minutes. The longer the PS stays on the lesions, the better efficacy of PDT. Constant saliva secretion and frequent tissue movement may impair drug absorption. Thus, high local concentration of PS may achieve better potency. In 4 studies of using 5-ALA as PS, the range of 5-ALA was from 4–5%. Therefore, the topical use of 5% ALA may be recommended as the optimal modality.
When 5% ALA is used, wavelength of 630 nm is recommended. Because 635 nm corresponds to the absorption peak of 5-ALA. In studies involving gargling MB, the chosen wavelength of 632–660 nm did not reach the maximum absorption wavelength of MB (around 665 nm), which also explain partially why the effect of MB was less than 5-ALA. Therefore, it is important to choose suitable wavelength to adapt PS.
In terms of VAS, the diode laser showed better clinic partial response in treatment of OLP, perhaps because of its one wave length of light, which made it more effective. We recommended the diode laser as the first option when the patients want to relieve pain. But on changes of lesion size, the efficacy of semiconductor laser is higher than diode laser.
Some scholars [26] supported a hypothesis that PDT stimulates healing processes which become even more evident over long-term observation, particularly within masticatory mucosa. This tentative hypothesis needs to be confirmed by a greater number of cured cases. In the study of [23], the mean size reduction was 62.91%, which was significant, showing a slightly higher value for the lesions on the buccal mucosa and lips (63.54%) than the gingiva and tongue (61.43%). While in our study, the lesions on BM/L and T/F/G achieved similar effect from PDT.
Previous study had compared the cellular apoptosis level in reticular and erosive OLP, and the results showed a significantly increased apoptosis in the erosive type and a marked reduction in the thickness of oral epithelium in erosive oral lichen planus compared to the reticular type, which indicated that a higher inflammation and cell destruction in erosive OLP [31]. PS tends to accumulate in abnormal hyperplasia and tumor tissue, some researchers believe that it may be related to the defect of the cell membrane structure. We speculated that PDT of erosive OLP is more effective than reticular OLP. However, the subgroup analysis of disease type in our study, has no statistical significance based on u test. The reason may be that two studies were included for erosive OLP, and only one for reticular OLP.
PDT of OLP has fewer adverse reactions, Majority of patients experienced no discomfort or only minor adverse effects (pain, mild burning sensation) during treatments and disappeared immediately.
At present the definite recurrence rate of OLP after PDT is unknown, but the onset features of OLP include easy recurrence. In all studies, 6 patients in 2 studies were found recurrence after PDT, but 3 studies reported no recurrence in 1–12 months follow-up. OLP is a chronic disease, thus the follow-up periods need to be longer. PDT can reduce the risk of malignant transformation. A study revealed that the malignant transformation rate of OLP is about 1.4%, but all above studies did not record the malignant rate [3]. So, the long-term effects remain unclear, there is an urgently need to carry out large sample, multi-center clinical research to explore and verify the influencing factors of the efficacy of PDT.
Currently the most common treatment for OLP is topical corticosteroids [4]. We compared the efficacy of PDT to the methods of topical corticosteroid. The similar efficacy of PDT and corticosteroid therapy was confirmed. In spite of several side effects of steroid, PDT has rare side effects. Therefore, PDT can be used as one of the optional treatment methods for resistant or recurrent OLP.
A few weaknesses of this study need to be addressed. Insufficient trials met the included criteria, which reduced the significance of the results, especially for the subgroup analysis and the comparison with topical corticosteroids. Outcome measures were varied in the different trails, that hindered data combination. In addition, the heterogeneities of wavelength, energy density, etc. may lead to low statistical power. Although above disadvantages exist in this study, it provides clinicians a comprehensive view of the efficacy of PDT in OLP. More high-quality clinical studies are required to improve the reliability of the results.