Tooth discoloration is a common dental concern with clinical and aesthetic implications. It is classified as extrinsic, intrinsic, or internalized. Extrinsic discoloration occurs on the tooth surface or pellicle due to deposition of colored compounds or chemical reactions. Intrinsic stains arise when pigmented substances incorporate into the tooth structure during development. Internalized discoloration refers to extrinsic stains penetrating into the tooth substance after development.

Black stain (BS), also termed chromogenic stain, is an extrinsic discoloration characterized by pigmented dark lines or dots along the gingival margin, usually limited to the cervical third of the crown. Its prevalence ranges from 1% to 20%, peaking in childhood. Despite professional care, recurrence remains a challenge. The exact etiology is unclear, but evidence suggests involvement of chromogenic microorganisms, diet, and oral hygiene. Black-pigmented anaerobes such as Porphyromonas gingivalis, Prevotella intermedia, P. melaninogenica, and P. nigrescens contribute to pigment formation. Actinomyces species have also been implicated. These organisms produce ferric sulfides through a reaction of hydrogen sulfide (from bacterial metabolism) with salivary iron. The resulting black pigment is mainly iron protoporphyrin derivatives.

Laser therapy offers a promising alternative to conventional treatments like polishing, microabrasion, bleaching, and whitening pastes. Lasers generate coherent, collimated light with tissue interactions depending on wavelength. In periodontology, lasers are used for calculus removal, soft tissue incision, decontamination, biostimulation, bacterial reduction, and osseous surgery. For example, Er:YAG and Er,Cr:YSGG are effective for hard tissues, while diode and Nd:YAG lasers target pigmented tissues and hemoglobin, making them suitable for coagulation and pigmentation removal.

Low-Level Laser Therapy (LLLT), or photobiomodulation, utilizes low-power red (600–700 nm) or infrared (770–1200 nm) light for non-thermal, photochemical effects. It enhances healing, reduces inflammation and pain, and stimulates cellular metabolism by activating mitochondrial cytochrome c oxidase. LLLT avoids tissue overheating and works through mechanisms similar to lethal laser photosensitization.

For BS management, LLLT targets bacterial chromophores such as protohaem and protoporphyrin, which absorb red light and generate a lethal effect on pigmented bacteria without additional dyes. This approach may improve stain removal and reduce recurrence compared to conventional therapies, offering a minimally invasive, biologically based treatment modality.