The leaf of the tea tree (melaleuca alternifolia) contains oil that is a strong antimicrobial agent against the strains of oral bacteria, as shown by the 1987 study "The Antimicrobial Effects of an Essential Oil on Selected Oral Pathogens." A separate study in 2004 also showed that it inhibits the adhesion-ability of the common oral bacterium, bacteria P. ginigvalis. It's this adhesion-ability that the bacteria use to anchor themselves while forming a biofilm. Besides affecting microbes on the surface, tea tree can penetrate below the surface where it can be anti-inflammatory, analgesic (pain relieving), and antimicrobial.
Tea tree has such great antimicrobial characteristics (as well as some antiviral and antifungal properties) that only non-natural disinfectants have more. The natural properties of tea tree were discovered centuries ago by the aboriginal Bundjalung people of Eastern Australia, who applied the crushed leaves to wounds, inhaled the released vapors, and drank teas from the leaves of the melaleuca alternifolia (tea tree).
Since the 1920's the natural oil from tea tree leaves has been extracted and concentrated by steam distillation into a very powerful liquid. Powdered leaves can still be found and is the form of tree tea incorporated into the Good Gums® formula. This is closer to the form originally used by the Bundjalung, where its beneficial properties are available without the irritation possible from the super concentration of distilled oil.