Application of blue light for phototherapy of dental tissues

S A Mohamad

Research output: ThesisMaster's Thesis (not awarded by UHI)


The direct application of blue light provides a non-invasive modality for both disinfecting dentine (photodisinfection) as well as enhancing the mineralisation processes of dental pulp cells (photobiomodulation) using a single wavelength. Dentine acquires the highest absorption for blue wavelengths of light. This permits the delivery of relatively higher doses of light limiting the cariogenic bacterial infections (Streptococcus mutans) within dentine, while allowing lower doses to reach the pulp cells stimulating odontoblastic differentiation. However, previous studies in the literature have not reported the orientation of dentine discs used as bacterial substrate surfaces. Notably, there has been variations among the experimental set-ups and irradiation parameters for both bacteria and mesenchymal stem cells, the stem cell type existing within the dental pulp. This study aimed to i) characterize the pattern of transmission of 405 nm light through coronal molar dentine at different tooth locations, and ii) determine the irradiation parameters that are antibacterial for Streptococcus mutans and iii) stimulatory for dental pulp cells.

To determine the effect of dentinal tubule orientation on light transmission, the amount of light (470 - 4054 mW/cm
) transmitted through occlusal, oblique and buccal dentine (1, 2, 3 mm) was investigated by recording the irradiance of the traversed light. Scanning electron micrographs of 2 mm outer (dentine-enamel junction) and inner (pulp) dentine sections were analysed to detect the influence of tubular density on light transmission. Regarding photodisinfection studies, cariogenic bacteria were irradiated at a range of doses (110 – 1254 J/cm
) in agar lawns, planktonic cultures and mature biofilms. For photobiomodulation investigations, human dental pulp cells were irradiated using doses of 2, 4, 5 and 6 J/cm
. Data indicated that dentine thickness as well as dentinal tubule orientation and density significantly affected 405 nm light transmission. Occlusal and oblique dentine allowed higher transmission compared with buccal dentine. Blue light irradiation inhibited initial biofilm formation as demonstrated by zones of inhibition. The 405 nm wavelength also killed bacteria in planktonic cultures and mature biofilms. At lower doses, blue light enhanced the mineralisation processes of human dental pulp cells. These data suggest that phototherapy approaches utilising a 405 nm wavelength have therapeutic potential to both limit cariogenic bacterial infections within dentine and stimulate the mineralisation potential of pulp cells. However, limiting bacterial infections can be restricted by the bacterial species irradiated, its oxidative state and anti-oxidative
potential. The protocols established in the current investigation can be further explored in ex-vivo models, clinical trials, along with the development of a therapeutic light source.
Original languageEnglish
Publication statusPublished - 2022


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