Can wife work under husband's sponsorship in ksa?

No, it's still not legal as of today !!

There was a big discussion regarding this issue here in Saudi Last year and the year before, this discussion was sparked by the fact that most teachers working in international schools were dependent wives.

When the Ministry of Labor started their campaign to crack down illegal workers, international schools were het badly, some even had to close down leaving student and parents with little options to solve the situation. After few weeks, schools owners manage to reach to an agreement with Ministry of Labor and Ministry of Education to issue a one year permeate for dependent wives allowing them to work and this license needs to be renewed yearly. This license is issued by Ministry of Education after reviewing the teacher qualifications, the problem with that is sometimes Ministry of Labor will say that they got nothing to do with This license therefor they don’t recognized their validity.

After this history brief  Now let’s go to answering  your question about your wife working as a dentist, to do so her degree should be testified by The Saudi Commission for Health Specialties, also she needs to be a member with this commission  and only if she is working under a healthcare provider sponsorship she can gain this membership.
So to make it simple , NO she can’t work if she continue being under your sponsorship as a dependent specially as a healthcare professional and she will be facing jail time for donning so in case of any medical malpractice. She will be looked at as someone how is  threatening the public health.

Can't have said more elaborately !!