how to reslove ttf's sawtooth

[BruceLin]

software ver: FontCreator12
font : simsun.ttf
modify: I modified 0 in the font. Just add a horizontal line in the middle space, export as ttf.
export to ttf's setting:
a. OpenType Layout : No
b. Lagacy 'kern' Table : No
c. Glyph Names : No
d. Hiting : Keep Original

Follow the above settings, 0 The top will appear a sawtooth.
If I choose "Hiting: Autohinting", the sawtooth disappear, But there will be problems with other letters.
Can someone tell me why? How can we solve this problem?
Thank you first here.

[Bhikkhu Pesala]

In font export settings, try, hinting, keep original.

[BruceLin]

Thank you for your reply.
Set "keep original" , it doesn't work.
I have tested all the export font setting, and these can't achieve the effect.
I also try set font->properties->smoothing, also the same.
It's frustrating.