Because BDS degree holders typically start out earning money sooner than medical doctors, initially yes, they earn more money. At some point, MBBS degree holders will earn more money after completing their post-graduate work and training. However, BDS holders typically can work in a number of fields after graduation, and then within dentistry, there are a number of different types of dentistry that one can practice.
While being an orthodontist is one way to use the degree, professionals can also benefit from dental tourism, they can also teach (which does not pay a lot), and they can also be dental surgeons (which might require extra education and training) depending on the country. Typically, while BDS holders do make a lot initially, the education and the training a medical doctor must undergo is one of the reasons why salaries of these professionals is slightly higher per year than for professionals with a BDS.