9 or 10 teeth startermotors

:confused::confused:I am confused. I needed to replace the starter motor on my Kangoo 1.4i but every dealer told me that the original starter motor (with 9 teeth) has been replaced with one with 10 teeth. My logic tells me this cant work. More teeth will increase the diameter of the gear and therefor will not fit. If the diameter stays the same then the teeth wont match the flywheel's teeth. I even googled this subject and found that ie Landrover's had changed from 8 to 11 teeth. Can some one please set me straight?

I played it safe and replaced it with second hand original part