What are potential complications associated with having temporary crowns for too long?

LeavingTemporary crowns for a prolonged period of time is a bad idea.  There are mainly three problems that could arise.1. Recurrent decay2. Gum inflammation3. Cold sensitivityIf left too long this could lead to the need for tooth extraction.  Best of luck.  

Temporary restorations are just that and thank you for an excellent question!
We generally don't like to have patients in temporaries for more than a few weeks. As you mentioned, the temporary cement tends to wash out over time and gaps open up around the margins creating micro-leakage. After an extended amount of time, bacteria builds up which can lead to gum inflammation and decay. 
Unless your wearing the temporary while healing from an extraction, I would advise to minimize the amount of time in temps. 

Having temporary crowns for an extended amount of time can be ok if the crowns are well made. Sometimes for larger cases, we will have temporary crowns made in a lab if we know the patient will have them for awhile. You should be monitored closely while the temporary crowns are in place. If you get decay under the gum line, you may need crown lengthening where the gums and bone of that tooth are moved further up the root to expose more tooth structure. This can affect the adjacent teeth as well as affect the esthetics of your teeth. It would also be possible that the decay would be too extensive and you may need an extraction. If you know you will be in temporary crowns for an extended amount of time, it's very important to maintain impeccable oral hygiene and keep all of your appointments with your doctor.

Temporary crowns are not meant to be worn for long periods of time. They can fracture and not hold the space of the original tooth accurately creating a loss of arch space. Food may get lodged near temp crown over time creating cavities. Tooth structure under the crown may be questionable if received too much pressure. If the tooth is not root canal treated, tooth can become very sensitive or damage to the nerve can result. Not moving forward with crowns can lead to many unforeseen problems.

Hi:In terms of bacteria and decay if it is below gum line, then you might need the gums to be pulled away to ge to the decayed area.  The second possible danger is gum inflammation due to the temporary material.Best,Dr. Maddahi