Sealants came on strong in the late 1980’s. There were touted as the best decay prevention since fluoride. Some even believed that they were a cure for cavities. Time has proven that they can be good restorations, but they have limitations just like everything else we put in a person’s mouth.
The positives: In decay prone individuals with deep grooves in their teeth, they can provide 10 to 15 years of service when they are placed properly. The materials that they are made of have improved over the years. In children who do not receive routine dental care for whatever reason, sealants may be able to stave off cavities until their diet improves or they begin to have better dental care in general.
The negatives: The primary reason for problems with sealants is that when they start to break down, it is difficult, if not impossible, for the dentist to tell they are failing. If you imagine the grove of the tooth being like a mountain valley with a river channel at the bottom, a sealant fills the valley and runs up the slope of the mountain. As it runs up the slope, it tapers to nothing. That thin edge is the first to fail.
One reason it fails is that sealants are runny. They need to be runny to get into all of the cracks and crevices. Cavities usually start in the deepest part of the valley, but the failure is up the slope. The failing area on the slope is usually very hard enamel, but bacteria is leaking underneath and running down the valley causing a cavity in the river channel below. The only way to know that there is a cavity is by symptoms or seeing it on an x-ray. Both of those instances indicate a very large cavity and on occasion those teeth need root canals. I’ve had to do a root canal on a 12 year old because of a failed sealant and have conversations with other parents on multiple occasions.
Another reason they fail is the bond of the sealant to the tooth may not be as good as it should be. Imagine the edges of the slope are glued very well, but that edge breaks because of the weak material and the bacteria have a straight shot to the river channel if the whole thing is not glued very well. It only takes a small area of no glue for the whole thing to fail. If the bond runs from the channel all the way up the slope all the way around, there is still resistance to bacterial invasion if the edge breaks. Most often this lack of bond is due to operator error and case selection. I believe that all sealants should be placed only when a rubber dam can be used. This device isolates teeth (keeps them dry) unlike anything else. Some other devices can be effective, like the Isolite, but almost anything else is inferior to the rubber dam. The bond to the tooth requires it be exceedingly dry. Any contamination will compromise the bond. Unfortunately, many of the teeth in question on children are just coming into the mouth. Not much of those teeth are exposed, and isolation is sometimes impossible. This is a reason to NOT place a sealant. Unfortunately, virtually all sealants are place without adequate isolation by non-dentists. They will have the problems discussed above.
Where isolation cannot be achieved, or in a population that receives routine dental care, it is my belief that sealants are contraindicated. Some of the teeth with deep grooves will never develop cavities. The use of a Diagnodent can detect very tiny cavities that cannot be seen or felt by the dentist. If a cavity is found, then a small conservative filling can be placed in the tooth. Even though this does cut away some tooth structure, the life cycle of restoration is much more predictable and conservative over the life of the tooth. The material used is much more stiff (not as likely to fracture) than sealant material. The filling is placed in a space created that is like a bigger river channel, but none of it runs up the slope. When that edge of the river bank fails, it can be seen by the naked eye; so the failure is caught much earlier, and a new restoration can be placed that is not as large as it might be when a sealant fails.
As you can see, in my opinion, there are far greater negatives with sealants than positives, so we don’t place many in my practice. Sealants can be a very good restoration that can serve many years, but the conditions have to be just right.