Dean actually is the proper salutation. One could say: Dean Redmond, would you please sign this form? Alternatively you could just use the Dr. salutation or the Professor salutation if those are appropriate, which they generally are.
You would normally capitalize nouns in the salutation, Dear Residents: (but this is not a significant aspect of the letter and is often ignored). If you use a longer salutation, such as "My dear Neighbors," the word dear would not be capitalized.