I came across this article on Dental Insurance, it gives a good overview of Dental Insurance.

Let us first understand the idea of dental insurance.  Dental insurance is a type of insurance in which a person buys a dental insurance plan by paying a monthly or annual premium to a dental insurance company...

In turn the dental insurance company provides dental insurance coverage against dental costs.  That is if there are any dental costs borne by the insured during the insurance period, the dental insurance company will reimburse the costs incurred by the insured.

Most of the health insurance provided today has dental insurance provided in it. So usually there is no need to buy a separate dental insurance. If your medical or health insurance does not provide dental insurance , you can obtain dental insurance in your health insurance by increasing your premium by a small amount. There are tax benefits also for going for this type of dental insurance plan . In the united states, the premium you pay for health insurance is straightaway deducted from the taxable income, thereby you end up paying lesser taxes . 

Family dental insurance provides dental insurance to the entire family.  It is better to go for this type of dental insurance compared to individual dental insurance .  Since family dental insurance is much cheaper than individual dental insurance. In insurance as the number of people increase in the plan the premium per head reduces.  This is because the risk gets distributed.

If your employer is providing dental insurance, then it is the best bet. You should go for this type of insurance if your employer is providing it as the major part of the premium is paid by the employer and the remaining part is paid by you.

Studies have also indicated that people with dental plans , have the tendency to have better dental health as they go for preventive dental checkups. This is good as bad dental health may ruin your looks as well as increase your costs.