Can wearing my plastic retainers cause dental caries?

Not directly: Caries is a result of bacterial activity and the resultant acid that activity produces. Poor oral hygiene and poor diet are directly contributory so if the retainer is, say, not removed for thorough home care it can certainly contribute to poor oral hygiene which may then lead to caries. It is not directly the cause but may contribute to the problem. OK to wear in conjunction with good hygiene tho

Indirectly, yes: Clear retainers have many advantages, but the down side is that they do not allow saliva to easily get under them and if you miss brushing a spot they hold the food and bacteria right up against your teeth. The ways to solve this problem is to brush your teeth well and use a fluoride mouthwash each time before you put the retainers in.