Every time after eating dry foods like dry bread, chips and etc 1 scar appeared in my mouth, specially behind my upper teeth, is it normal?

Need saliva: Saliva in normal amounts usually protects your mouth tissues and helps digest carbohydrates in your mouth. If you have little saliva then these sharp foods can irritate your gums, cheek or palate. We see this in people taking medications which causes dry mouth. Try using Biotene before eating to see if this helps it comes in mouthwash and toothpaste You don't want to keep causing tissue to be hurt

No.: No, you may have dry mouth. See your dentist for exam and advice.

Can Be: You are describing rough crusty sharp-edged foods which can easily scratch the tissue behind the upper front teeth as you bite into them. Try being more careful and slow down when eating these and see how you do. If it continues, see your Dentist. You may simply have a shallow palate in that area or flared upper front teeth which makes this easier to occur. Good Luck.

Xerostomia: also termed dry mouth. There are many causes of dry mouth, as well as many treatments for the problem. Salivary flow is reduced in patients treated with omeprazole. See your PCP or dentist for evaluation.