Provided herein is a pharmaceutical or oral care product for treating or preventing oral diseases that is prepared with proteoglycan 4 (PRG4) as an active ingredient, the preparing method thereof and the use thereof in manufacturing medicaments or oral care products for treating or preventing oral diseases and maintenance of oral health. PRG4 may have efficacy in maintaining oral health and treating or preventing oral disease. This secreted glycoprotein, which is also called lubricin and superficial zone protein, is known to protect against frictional forces, cell adhesion and protein deposition.