Say you have a figure wielding Sawtooth and you attack using Thunder Blow. How is the difference in the roll taken? Is the damage dealt based on the initial attack roll and still add one for each successful roll after that from thunder blow? Just curious.

I think that its on the last Thunderblow attack u make and u check the difference and with that final result u add the damage of TB...

Yes, i too have heard that it is the last attack

yeah. It's the last attack. Also, if your last attack roll on thunderblow is a miss, sawtooth's ability does not trigger.