Dr. Hanif warmly welcomes you with thanks for a consult!
   I have carefully worked through your case, and can well realize your health worries. Being your physician, I want to assure, I will take care all of your medical concerns according to the latest medical guidelines.
Onychorrhexis ( Brittle nails) causes breakage of finger or toenails that may result from:
*A strong soap
*Excessive water exposure
*nail polish remover
*hypothyroidism-a disease of the thyroid gland.
*anemia-low Red blood cells and low 
hemoglobin than normal.
*
anorexia nervosa or 
bulimia nervosa-disorders of the food intake.
*after oral 
retinoid treatment.
Yes it  may also be associated with teeth as this is due to the 
nutritional deficiency and/or some underlying disease. So you need to consult your treating physician to rule out the causes. Treatment goes according to the cause.
   Hope I answered all of your questions. Please click on 'I Find This Answer Helpful' and don't forget to add your precious positive feedback to help me able to assist you better in future too.
For any disease you have, a timely follow-up regarding the treatment efficacy and to see if there is any need to change the treatment options is very necessary. So keep a follow up to see how you doing. Remember to write down my name in the start of your question next time, & I will be with you right away. I am available 24/7 for providing you expert 
medical opinion on any health issue. Have a blessed time ahead.
Regards!
DR. MUHAMMAD HANIF
USA
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