The cutting edge of the bucket slips into V-shaped slots in the back of each of the teeth (that's hard to see in the attached photo). When you seat the toothbar completely into these V-slots, it ends up looking like you see it in the attachment. That way the tooth bar is completely supported by the bucket cutting edge.
That's why Markham advises you that the cutting edge of your bucket has to be in good shape before you try to install their toothbar. My bucket was slightly bent from all the wear and tear I put on it, so I had to straighten the cutting edge a bit before the toothbar would slip into position without a lot of hammering.