You can probably hang on as long as you want. However, unless you get further specialized education, you'll be hanging on to the bottom rung of the ladder. Of course, you can increase your income by working at multiple dental practices. You can also obtain your dental hygienist certificate, which provides good cross-training and increases your value to any employer.
Perhaps you'd like to channel your dental assistant skills in another direction. Consider dental office management, dental product sales, or dental insurance claims processing work. If you have the proper teaching credentials, you may also earn a job as a dental assisting instructor.