Yes his swollen gum is painful. It's an infection. His body, like our bodies, use swelling and pus formation to push up on a foreign object to get it out of the body. But sometimes a vet must intervene. In the wild, there are very few or none of ways to get that particular injury. Also he will need anesthesia, because no ig will hold still for probes in such sensitive tissue. If it gets bigger or moves, you have an emergency.
Who told you he needs supplemental calcium?? I'd like you to give me the source of that information so I can try to correct it. That's just not true. He needs a high nutrition, calcium rich diet+enough UVB. Kale and collard greens are examples. Plus other nutritious food, such as grated hard squash, and many more. Do not feed him spinach, because it causes his body to lock dietary calcium in a molecule that his digestive system can't break.
AFIK the dent is not over anything vital, unless the blow penetrated to his spine, and shaking means two things:
1.) nerve damage, which in your case once the swelling declines, the vertebrae are OK again.
2) Lack of high enough blood calcium levels. I assume you are providing UVB, or he wouldn't have been able to grow to the general maximum size for Captive Green Iguanas.
Plus 3)Which you never want to see in any ig that you come across. An iguana who has been severely abused by years of neglect. Caused by a bad diet, it's body robbing it's nerves of calcium, and dehydration. When these guys shake, they are on the very brink of death.
But I assure you, feeding supplemental calcium does not help his level of serum calcium. The only way that iguanas can produce the necessary serum levels is to bask in UVB light along with a good, correct diet of greens and some fruit. There is a lot about iguana diet on the I-net. REad up on it to make sure the diet you feed him doesn't need to be tweaked. There is more than enough calcium in the meals for a large iguana on a well constructed diet if there is enough UVB on his back for three or more hours per day. I used to never supplement my rescued and pet iguanas, unless they were in bad shape. The vets gave me calcium glubionate and I provided UVB to bring them back to health.
Yours should not be eating calcium or mineral supplements They go in the mouth, and travel out the vent unchanged, and can cause crystalline formations inside his body, such as kidney stones, bladder stones and probably bile gland stones.
Some people disagree with me about some things, and that's alright. My facts here are valid. A fact is, you can supplement calcium and minerals, but only in very very tiny amounts, once per week. Take a small pinch of the powder, reduce it's size by 1/2. This should leave a very small amount, and may make you think that so little can't help. But, more can hurt.
Check out the I-net for " big bladder stone in an iguana". Calcium citrate just crystallizes and it passed out of his body. The same with calcium powder made from bones and oyster shells. Unless the vet orders a prescription of calcium glubionate (sp). That is a form of calcium that he can absorb and use, if there is enough UVB.
Well cared for iguanas almost never need calcium supplements, except for females during the process of shelling their eggs.
In the tropics, humidity, UVB, and good food are available, and wild igs never need a vet to help them to shell eggs or keep their nervous systems healthy.
BTW, in six months if the dent remains, you could try to find a professional who will inject enough collegen to bring the ear back to it's proper shape. You just never know. LOL Ha ha ha ha!