I requested permission from the copyright owner but have not heard back. Can I use the material anyway?
No. If you asked for the copyright owner’s authority to use his copyrighted material but have not heard back you cannot assume that the copyright owner would not object. The copyright owner has no affirmative duty to respond to requests. However, you may want to make sure you have the correct contact information for the copyright owner or wait a bit longer for a response because most copyright owner are more than happy to license their works to others and, in fact, some may be overloaded with requests.