Abstract: An antimicrobial light treatment is provided as preventative maintenance for or treatment of periodontal diseases. The light treatment may be administered to a patient with an applicator (41) that is similar in shape to a periodontal probe. The antimicrobial light energy may be applied at the time a dentist or clinician takes periodontal probe measurements. An applicator is provided for delivery of the antimicrobial light treatment. The applicator may include, for example, an ergonomic handpiece (42) and a probe (47). A light source (34), such as a laser source, may be attached to the handpiece (42). The probe (47) includes a tip (52) that is designed to deliver light energy from the light source (34) to the periodontium of a patient, for example to the gingival sulcus of a patient. The tip (52) is designed to disperse light energy in a broad pattern so that a large portion of the gingival sulcus may be treated.