Here is my take. A DDS will always be able to find work. Now, you may not be able to work in Newton, MA or San Fransisco, CA, but you will be able to find work. Setting up shop in an area where there's a dentist on every corner MIGHT not be the best business model. You have to understand, that dentistry is entrepreneurship. It's business. Everyone wants to live in the most exclusive suburbs with the best school system and the best weather and lowest crime etc. you may have to move.
Because of the economy many DGs are delaying retirement. When I was in D-school, the model was run your practice grow it as much as possible and then sell it off to a partner/associate. Nowadays GDs run their practice into the ground.
California is a saturated market for dentistry - and for pretty much everything else. As far as the "aging population" frenzy that's being thrown around in healthcare. Yes, I suppose to some extent the elderly will need more dental care. Is this dental care going to fall to the GDs? Or more the endos and perios? That's a different story.
Dentistry is safer than other professions - but no profession is 100% safe. We're in tough times. You will have to tough it out.