Final answer:
Polysulfide impression materials are known for their strong odor and potential to permanently stain clothing, and they should be used carefully in dental practices to avoid such issues.
Step-by-step explanation:
The impression materials that have a very strong odor and will permanently stain clothing are polysulfide materials. Polysulfide impression materials, also known as mercaptan-based impression materials, are notable for their distinct and unpleasant smell. They have a potent sulfur odor due to the presence of sulfur compounds within the material. In addition, because of their chemical composition, polysulfides have a tendency to cause permanent stains on fabrics and are therefore handled with caution in dental practice settings to avoid damage to clothing.