Dentist Insurance can be confusing. Insurance normally covers a percentage of each procedure, and the patient is responsible for the rest, as a copay, as well as tax.
Code on Dental Procedures and Nomeclature (CDT):
This is essentially the guide book for dental insurance in order to help accurately document dental procedures that were performed. It is not a flawless system, but it is what is currently used.
There are codes for each dental procedure, so the amount of time it takes or the difficulty is irrelevant to the cost. Also, whether you need anesthetic or not, is irrelevant. Fillings are billed based on the number of surfaces, so in general larger fillings cost more, but a filling on a front tooth may take 10 min, and one in the far back may take 30-40 min but cost the same.
Or root canals can have varying degrees of difficulty, but cost just depends on which tooth it is.
All plans are different, but dental insurance often covers almost all of the cost of exams, xrays, cleanings, and other preventative procedures or services. Often ~80%. For other procedures, such as root canals, it is often covered at around 60-80%, but crowns and dentures are often covered at around 50%. Implants range from no coverage, to 50% or higher. Some plans help cover orthodontics, but this is often a fixed dollar amount.
DENTIST INSURANCE MAXIMUMS:
Some insurance plans have a maximum amount they will cover per year, whether it is a calendar year or year from when it started. For example, if the maximum is $1000, after the insurance pays $1000 towards any combination of procedures, it will not pay anything else until the year renews, so the patient will be responsible to pay 100% of all procedures after that point. Some maximums are as low as $500, some do not have any maximums.
Like car insurance, some dentist insurance plans have deductibles which need to be paid prior to the insurance covering procedures.
Some plans have wait periods, meaning they won't cover certain procedures until after the plan has been active for a year (for example). If a procedure is needed in the first year, the patient can either pay full fee, or try to wait until the wait period is up to have the insurance help with the costs.
Some procedures are only covered every certain number of years. For example, crowns are usually covered every 5-7 years, so if you have a crown on a tooth that for whatever reason needs to be redone, it won't be covered until the crown is 5-7 years old.
Dentures and partial dentures usually have a similar time frame until insurance will pay again. If it needs to be redone in less than the elapsed time frame, the patient is normally responsible for 100% of the cost.
Implants are normally covered only once in a lifetime, meaning that they have a very high success rate, and should not need to be redone very often.
MISSING TOOTH CLAUSE:
This is not the norm, but some insurance companies have a missing tooth clause, stating that they won't pay to replace a missing tooth (usually with a bridge or implant) if it was a pre-existing condition. For example, if the tooth was removed when you had a different insurance, your new insurance company may not pay to have the tooth replaced.
Sometimes insurance companies pay less than (or more than) the amount estimated, so on occasion after the procedure your dental office may ask you to cover the difference, or you may have a small credit if the insurance estimate wasn't exactly as noted. This is a normal occurrence and does not mean that your dental office is cheating you.
Below is another sample page from the CDT guidebook on types of fillings.