I don’t know if any schools let you sit in on classes- it’s certainly something you could ask the dental school admissions office. Trying it out for a semester- no. I think though what you need to keep in mind is that anything you see is such a small snippet of the dental school experience- sitting in on a histology class isn’t representative of the experience of being in a clinical class for example. You’re really not going to get a great sense of the overall experience- you would be better off having the admissions office put you in touch with other students so that you could talk to them about their overall experience. Often the experience is vastly different each year of school. You should also ask if there are any oral surgery residents you could talk to, as that is a significantly different experience from dental school.
Also, you may get more value out of contacting local oral surgeons and seeing if you can shadow them. Oral surgery is a long challenging (but worthwhile) path. I think there would be more value in seeing if you enjoy the career and the day to day job experience than if you enjoy the schooling that leads up to it.