1.) How many practicing dentists are there in the United States?
2.) What is the average salary range for dentists?
3.) How many licensed Physician Assistants (PA) are there in the United States?
4.) What is the salary range for PA's

The US Department of Labor Bureau of Labor Statistics has a web site
which lists employment information for many occupations.  The
information is at a national level and unfortunately does not break
down into state-by-state data.  The site lists total employment in
2000 (last year data is available) as well as projected employment in
2010.  They also lists median annual earnings and a few other things.

For dentists, the information is available here:

http://data.bls.gov/servlet/oep.noeted.servlet.ActionServlet?Action=emprprt&Occ=2910710449&Number=10&Sort=emp_base&Base=2000&Proj=2010&EdLevel=&Search=List&Type=Occupation&Phrase=&StartItem=0

For Physicians Assistants the information can be found here:

http://data.bls.gov/servlet/oep.noeted.servlet.ActionServlet?Action=emprprt&Occ=2910710449&Number=10&Sort=emp_base&Base=2000&Proj=2010&EdLevel=&Search=List&Type=Occupation&Phrase=&StartItem=0

The Bureau does not include salary range, only median salary.  Salary
range varies quite a bit from state to state.  Nationally, dentists'
salaries range from about $105,000 to $175,000 according to Dr.
Roderick King in this article:

http://www.black-collegian.com/career/career-reports/biomedicine2000-2nd.shtml

In South Carolina it ranges from $89,500 to $141,000 according to this
publication by the South Carolina Department of Labor:

http://www.llr.state.sc.us/pidocs/Nav2002.pdf

But, to demonstrate the inter-state variation, dentists in Montana
state government earn $68,000 to $112,500 according to this document
by the Montana Department of Labor and Industry:

http://mcis.dli.state.mt.us/pdf/licocbk.pdf

Of course, it is also difficult to give a reasonable range of salaries
because some dentists are in private practice, while others work for
the government.  A recent job posting on USAJobs.com, the US
Government official job search site, shows salary range for a military
dentist as $54,000 to $70,000.  This positing is here:

http://jsearch.usajobs.opm.gov/summary.asp?OPMControl=IE1639

And as a final example, dentists in Minnesota make an average of
$124,500 but specialists average $196,000, according to this document
from the Minnesota Department of Health:

http://www.health.state.mn.us/divs/chs/rhpc/PDFdocs/ddsprofile.pdf

So clearly there is a fair bit of variation.  Overall it seems that
you're looking at a low end of around $55,000 to a high end of around
$175,000.  If you still need more information you may be able to find
it in the American Dental Association statistics publications, but
these must be ordered from the ADA.  The order area can be found here:

http://www.ada.org/prof/prac/issues/survey/workforce.html

As for PAs, again, concensus is that the occupation varies so much
that the range is somewhat meaningless.  Still, that information is
available in a PA Salary Profile which is available for order from the
American Academy of Physicians Assistants at:

http://www.aapa.org/research/salary.html

To give you some idea though, while median earning is $61,910
(according to the BLS which is linked above), Western Michigan
University lists the salary range for PAs as $50,000 to $70,000 here:

http://www.wmich.edu/paprog/job3_99.htm

In this posting for a Physican Assistant in Orthopedics, salary range
is $23.80 to $31.73/hr:

http://www.medhunters.com/job/346519.html

Other PA jobs are listed on the site here: 

http://www.medhunters.com/jobs/Physician_Assistant.html

but these do not include salary ranges.  You might consider contacting
some of the employers for more detail.

According to this publication from the Oregon Department of Human
Resources (be aware that it's from 1995), average starting salary
range in that state is $31,000 to $50,000:

http://www.ohd.hr.state.or.us/ocs/capacity/capacity.pdf

But then recruiting firm Allied Physicians lists average 1st year
salary as $56,000 and salary range as $50,000 to $105,000 here:

http://www.allied-physicians.com/salary_surveys/physician_assistant_salaries.htm

Should you decide you want to be a PA and also sideline as a spy, you
could consider working for the CIA who pays from $54,000 to $62,000. 
Info is here:

http://www.cia.gov/cia/employment/jobpostings/physician_assistant.htm

So once again, salary range is quite wide for PAs, but all evidence
points to an average range starting around $50,000 and going as high
as $100,000 in some cases, though usually somewhat lower.

I hope this proved useful to you, please let me know if you need
clarification.

---

Clarification of Answer by hibiscus-ga on 13 Nov 2002 18:41 PST

Here's a little bit of extra info I found.  The BLS National
Compensation Survey can be queried here:
http://data.bls.gov/labjava/outside.jsp?survey=nc and for Physician
Assistants the compensation ranged (in 1998, last year for which this
data was available at all levels) from $11.29/hr to $35.67/hr
depending on various factors like experience, qualifications, etc.

There is unfortunately no similar per-level data for dentists.

Thanks