Thinning hair and very bad tooth cavity. Could they be related? (Photo)

I suggest a formal consultation to see what is best.  Typically PRP, progesterone, viviscal, finesteride (male) / spironolactone (female) can help.  Biopsy would be needed and blood tests if you have widespread loss. Best, Dr. Emer.

It
is doubtful that your cavity would be related to hair loss given the history
you supplied regarding balding on your mothers side of the family.   You most likely inherited the gene.  Having said that, it is possible that the
stress from severe pain may be a contributing factor to hair loss ie telogen
effluvium.  Furthermore, it is best you
see a hair restoration specialist for a consultation.  While you are deciding to schedule an appointment see
another dentist to treat your oral condition.

I would recommend the revolutionary treatment known as PRP, or “Platelet Rich Plasma” It has been shown to be very safe and effective for hair loss for both men and women.

Thinning hair and tooth cavity are not related with each other. you may have a androgenetic type hair
loss. You may start to use minoxidil %5 to thicken the crown area and stop hair
loss.You would better planning to have an exam at
hair loss expert  when you fell uncomfortable about hair styling or
total loss of hair..

About 50% of men and 25% of women will inherit a gene from their parents (which their parents may not display - it can be recessive) that makes the hair on their scalp (and their prostate) sensitive to DHT.  On the scalp this reflects as early onset male pattern baldness.  In the prostate this can lead to BPH and eventually prostate cancer. 
I recommend that you see a specialist who can provide you with a fully comprehensive consultation that reviews your genetics and your scalp to determine if you are one of those 50% of men.  If you are you should take action now to prevent problems later on.

There are rare conditions and situations where a few cavities in the mouth actually can be tied into new onset hair loss (conditions known as ectodermal dysplasias for example or various autoimmune conditions like Sjogren's syndrome). For the typical male however, cavities of the mouth and hair loss are completely separate with no connection or relation whatsoever.

Having stress, even as simple as a painful tooth cavity can accelerate genetic hair loss. Your biggest enemy is the progressive thinning leading to a balding pattern that is not evident at this point in time. The degree of thinning that you are experiencing would suggest that you should see a doctor who most likely will get Bulk Measurements of your hair to determine the degree of the thinning that you are presently having. If the diagnosis is early genetic hair loss (the most common cause of hair loss in young men), then the best treatment would be the drug finasteride which is highly effective in men of your age and may not only stop the hair loss but possibly reverse it. If you are developing a more advanced balding pattern the best test to get will determine the Bulk Measurements of your hair and this will show, over a one-year time frame, how effective the treatment will be. Once you know this information, then you and your doctor need to develop a MASTER PLAN which will define what you need to do over the years to come.