My temporary crown (vital tooth #30) becomes cold-sensitive after I eat something hot?

Having cold or hot sensation or sensitivity while you have a temp crown is not abnormal.  The tooth was prepared down to the dentin which has nerve innervation and can sense thermal and pressure changes.  The tooth feeling cold and/or hot does mean that the nerve is still alive and if the temp crown is high then it might be tender to pressure as well. I would contact your dentist and ask for their opinion on the matter.  Most of the time when the permanent crown is cemented on the problem is resolved immediately or within a few days.

The symptoms which you described can be a result of the nerve of your tooth. Since you are not complaining about throbbing, aching pain, chances are that these symptoms may be accommodated readily by placing a special medicine in the temporary crown to help settle down the tooth. Please call you provider and ask him/her to remove the temporary and place IRM inside the temporary. Leave that for one to two weeks and you should be able to tell if your tooth is settling down. Also while there make sure your temporary crown is not high. If the tooth settles down in this time then chances are you should be fine without a root canal. However final decision is up to your provider.All the best

Normally with temporary crowns the tooth can be cold, hot or pressure sensitive.  Temporary crowns can never be as completely sealed as the final permenant crowns.  However, if the tooth hurts by itself without any cold, hot or pressure that could possibly mean there is nerve problem.  Be sure to let your dentist know of your Sensetivity prior to cementation of your final crwon.