Yes, your Diabetes can be a factor, because sometimes healing is difficult. Many diabetics have gum infection. About the scaling, it depends on the effectiveness as to how often, but if you have metals in your mouth such as mercury, and nickel under the crown, they can cause gum disease and hamper healing efforts. There may be certain nutrients you are lacking or not absorbing. Minerals are especially important. Fluoride in it's natural form is good for teeth. Neydent is the toothpaste I use and it is excellent for sensitivity. You will notice a difference right away. The links below should give you all the information you are looking for, including minerals that are essential for good teeth.
Conventional dental cleaning removes a thin layer of enamel from the teeth with each trip to the dental office.
Hydrogen peroxide, commonly used as a hair dye, can aggravate gum disease and cause sensitive teeth - or even chemical burns to the mouth.