For example, take a look at this dental insurance plan. The premium for this plan is $120 per month. In a year, you would have paid $1,440.
During the first year, you will lose $440, as the maximum you can claim is $1000. You will also lose $440 on the second year. Thereafter you will lose $190 each year.
Basic services such as hygiene are paid only at 80%. You need to pay the balance despite paying $1,440 annual premium. Which means for the first year, you will lose $440 plus the 20% that you are paying out of pocket.
Major service can only be claimed on the third year and only payable at 50%. If you are planning to do, say a crown, you can only do it on the third year, no earlier than that and on top of that, it is payable at 50% only. So if the crown is $800, you will pay $400 on your own. Your loss, if I may recap, is you will lose $440 plus 20% for basic services (such as your hygiene) and $400 for the crown.
Now, lets say, your major services costs $1600, payable at 50% means insurance company pays $800 and you pay $800. During that same year, you have your teeth cleaned and some basic work done, you have claimed so far $600 for the basic services. In this case, you will not be able to claim the full $800 for the major services because your basic and major is $800 + $600 = $1400. The combined maximum you can claim in your third year is $1250 so you can only claim $1250 out of that $1400. Your losses during this year is heavy: you pay $440 for the premium, plus 20% for the basic services, plus 50% for the major services and $150 ($1400-$1250) for the combined maximum.
So you see, if you are thinking of saving money by buying dental insurance, you are wrong. You are better off, having some disciplined, put the $120 every month into a savings account that will be used solely for dental expenses, rather than using the $120 to pay for monthly dental insurance premiums.
No company would operate at a loss and insurance companies is no different, they will not offer dental insurance at a loss.