The intraoral accessories of fixed appliances increase the retention areas for dental biofilm, thus hindering oral hygiene [1,2]. During orthodontic treatment, professionals may observe generalized gingivitis [3]. Increases in anaerobic pathogenic bacteria levels may occur in both supra- and subgingival biofilms during treatment [2].

At the end of the orthodontic treatment and accessory removal, areas of demineralization may be observed adjacent to the position of the brackets, which appear as white spots resulting from biofilm accumulation in the accessories [4]. These white spots can be detected after four weeks and become clinically visible in the first six months of treatment [5]. Thus, early diagnosis is crucial to prevent these lesions from appearing and developing into carious lesions [6].

Several methods are commonly described in the literature to evaluate and detect orthodontic biofilm indices [7], most of which are easy to use and manage. These methods can assay several areas and elements or specific regions and characteristics [8]. The diagnosis of dental biofilm can use dyes applied to the surface of the teeth; however, dyes may be contraindicated because they can interfere with esthetic procedures, cause allergic reactions, and overestimate the biofilm by non-selectively staining organic substances such as food residues [9].

An alternative diagnostic method for these patients is fluorescence spectroscopy. Fluorescence is an optical phenomenon in which various materials and biological tissues absorb radiation and emit a different wavelength of light than that was absorbed. Each tissue and material has characteristic fluorescence [10].

The detection of dental biofilm using spectroscopy identifies bacteria that produce porphyrins during metabolism. When presenting externally, porphyrins easily penetrate the bacterial cell membrane, especially gram (+) organisms, due to membrane permeability [11]. Porphyrin is also a fluorophore that emits reddish-orange fluorescence when excited by violet light [12]. Thus, the present study applied fluorescence spectroscopy associated with porphyrin (Photogen®) to assess the presence of dental biofilm in users of fixed orthodontic appliances and verify the null hypothesis that the maximum values and mode of the red pixels do not differ between the methods of biofilm evaluation when using porphyrin.