The sealing units around the piston in the combustion chamber are the Pontiac Piston Ring. They are present to help prevent any blow by from moving around the edges of the piston and escaping into the crank case instead of pushing down on the piston after the explosion occurs.
In total there are three piston rings for each piston in your Pontiac engine. They are lined up from the top down with two compression rings and a set of oil rings. The oil rings are considered to be one piston ring but actuality there are three of them that make up this one working in unison to help prevent the oil from entering the combustion chamber and fouling the spark plug.
The leading reason for replacing the Pontiac piston rings in your engine are due to the level of compression it produces is below the specifications for a properly working engine. When this is noticed the piston has to be pulled from the engine so the rings can be removed.
Once the piston has been removed, the cylinder walls will have to be honed. This process will smooth the cylinder walls and permit the new piston rings to form a new seal creating an area where the expected level of compression can be made for the Pontiac owner to enjoy at their disposal.
The most common reason for a set of piston rings to go bad on your Pontiac engine is because the owner did not change their oil on a regular bases. This left particulates in the oil which damaged the cylinder walls creating the low compression condition in their engine. If your oil is changed as scheduled then you should never have to worry about this engine component.