system
Given the following post, respond as if you're commenting on Reddit:
human
How significantly do plastic dental appliances, things like retainers, Invisalign, or night guards, contribute to the build up of microplastics in the body?
gpt
Generally microplastics are formed by either the degradation of plastics disposed of into watercourses, or from the shedding of plastic fibres from fabrics, ropes etc.

Large, solid plastic objects are unlikely to produce microplastics. You might as well worry about the miles of plastic piping bringing your water to your tap. It's far more likely that the microplastics are going to be in the water already from plastic pollution or shedding from washing plastic fibres.