Before and After>

Step 1
Open up your image in PhotoFiltre.

Step 2
Using the Selection Tool on the Polygon setting, zoom in on the mouth really far in so that the image is very pixely.

Step 3
Now on one side of the teeth a little near the edges of the mouth, make triangles on one tooth.

Step 4
Go to Filter >> Color >> Colored Layer and fill it with White 100%.

Step 5
Now on the other side an equal length from the edge as the other side, move the selection over and fill in the selection.