People had naturally better teeth before eating modern diets high in sugar and carbs. Modern diets hurt more than people's teeth. Modern diets cause inflammation, which leads to obesity. Paleo type diets are much better for people's health overall. There were studies on peoples in the past who were not yet introduced to modern diets. They were studied before and after. Before they were very healthy, had good teeth (straighter and whiter), and were getting enough nutrients. After they had generally worse health, had bad teeth, and were more malnourished. Many obese people are also malnourished. It's a myth that people in the past were worse off in every way. Traditional societies built up long term cultural adaptations which helped them to be healthy and to survive. As traditional cultural memes were displaced by modern technology much of the wisdom collected that was passed down through the constraints of natural selection that helped people survive was lost. When traditional societies of long legacy were dismantled, their cultural adaptations lost, they became more reliant on technology or aid to solve their problems. When they were helped to survive the constraints which helped the original societies to build up cultural memes that helped them to survive were perverted, and so they became dependent without actually regaining the behaviors that made them more fit. This is partially why we think older peoples were less well off in every way. Yes, they had poor understand of how diseases worked, but traditional societies also developed rituals which for them was effective at dealing with the spread of diseases - they had rituals they did which had the benefit of giving them better hygiene.

Went on a few tangents there but my point is that people in the past didn't necessarily have bad skin / bad health / bad teeth and so on. Not getting enough food to eat was the real major problem for people in the past. When the food problem was solved it also created other problems. When technology progressed it became a crutch that swept away traditional cultural adaptations which gave peoples general advantages for survival, which once displaced and the crutch enabled were never able to be recovered as the constraints necessary to create them were no longer there.