I am not qualified to answer these questions because I am an orthodontist and have had much easier time than the general dentists. So I represent my sister, who has practiced general dentistry since the early 2000s, to answer the OP's questions.
1. My sister owed approximately $80-100k in student loan. Her husband, who is a physician, made around $100-120k at that time. After graduation, they both lived with my parents for 3 years to save money…and free babysitting. I don’t know how soon she paid off her student loan but I know that she currently owns 4 properties (including her $800k house and $1.2 million office building), which she already paid them off.
2. She started an office from scratch in 2003 or 2004…about 2-3 years after graduation. 7-8 years later, she sold it (a leasehold sale) and moved all her patients to the new office building, which she owns. It’s a small practice with 3 chairs, 1 front desk, 1 assistant.
3. Yes, she thinks it is worth it but she wants all her kids to become doctors like her husband. After 2 years of college, she applied for pharmacy schools but didn’t get accepted. So she went on to complete her BS degree, applied for dental schools, and got accepted to a cheap state school. She’s glad that she is not a pharmacist….no autonomy, non-flexible work hours etc.
4. She practices in Orange County, CA.