Your observations are 100% on target. Just because odontoma are seen on the X-ray does not unequivocally mean that they should be removed at that time. The vet in FL that probably does more odontoma surgery than any other vet has a statement that she repeats over and over. "I don't treat X-rays. I treat the patient." She will only remove odontoma when they are causing problems such as breathing problems. I attended a conference that she gave and she said she will not remove small odontoma that are not causing issues. She said if they are removed too soon they can and will grow back. She said that every cell of germinal tissue has to be removed or it will grow back. Typically it's the top odontoma that cause problems. That's why I always suspect odontoma when older squirrels have vague respiratory issues. I don't know that many that have had the bottoms removed.
Rodents teeth always grow. If the incisors appear to stop growing it's because they are growing backwards and forming the large bony mass at the tooth base a.k.a. odontoma.
I want to be honest with you. The surgery is brutal and I'm being 100% serious. Most survive the surgery but some don't survive the recovery period. About a month ago I became discouraged by this surgery. A person showed up on TSB just like yourself. Her squirrel clearly had the symptoms of advanced odontoma. She got X-rays from her local vet which confirmed the diagnosis. I need to confirm but I believe her squirrel is 7 yo. I shared with her the options regarding surgery privately. I also mentioned that without surgery there is no cure other than treating symptoms with antibiotics, anti-inflammatories and pain meds. The next message I received from her was that she had an appointment in FL and would be traveling in a matter of days. The surgery was done and squirrel had an extremely difficult night. She said she held her for 14 hrs. She wouldn't eat. Apparently that first week was a nightmare and keep in mind that she had returned home and was a 1000 miles away from the vet that performed the surgery. She said her squirrel was afraid of her now as she shoved meds in her face. I felt terrible. I started questioning whether this surgery was 'worth it'. Put them through THIS or love them to the end and allow them to pass peacefully in a controlled setting. I agonized over it. A few days ago, I received another email from this person. After a week of not eating, she turned the corner and started recuperating. Her mom is ecstatic that she is now eating enthusiastically and beginning to act normal. I asked her if in light of all the major issues... 'WAS IT WORTH IT?' She assured me that it was. I needed to hear that as I was beginning to think that maybe it shouldn't be done.
It is a decision that only you can make. The surgery can be either a curse or a blessing. A double edged sword so to speak. Successful surgery can buy many more years with your friend OR a bad outcome can, well ....
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It is a tough decision. I personally haven't faced it so I can only share others experience.
Definitely treat the infection first and go from there.
There are no scopes that will give helpful information as far as size. It's all about the symptoms. If they are having respiratory issues it's time to start thinking about surgery if you are considering it. If I was going to have surgery done I would have it done before the symptoms are extreme. The odontoma can block the sinuses. Squirrels are not effective mouth breathers so 'other' humane options would need to be considered if surgery isn't an option.