There are six tooth options available for the 900 series: The original Greenteeth Red & Green, as well as four options of our new Wearsharp teeth. The unique design of our Wearsharp allows the tooth to retain a sharp cutting surface, unlike traditional teeth that tend to round over. This provides a consistent cut throughout the life of the tooth, allowing you to maintain a faster sweep speed. Because we believe that performance is never a one size fits all scenario, we have done extensive testing & found that we can fine tune performance with slight variations in the design of the teeth. Depending on the size of your wheel and how it cuts, we offer four different versions of the Wearsharp tooth. While we recommend our Wearsharp teeth for this series, we do continue to offer the original Greenteeth series Red (deep dish) & Green (standard dish)