A few notes on temporary crowns

 Temporary crowns can be tight when seating for a few reasons:

-One is that the crown is too well fitting due to the accuracy of the material. Hydraulic pressure from a very parallel crown preparation may stop the crown from seating especially once there is temporary cement in it. Therefore the occlusion may be spot on when trying the crown on but may be too high once it is cemented. 

-Deformation on removing the temporary crown can cause it not to seat completely. If the crown comes off in the putty matrix, don't touch it for at least a few minutes to let it fully set before it is manipulated

-Shrinkage of the material can cause it not to seat well even if it had fit well initially. This is especially noticeable if there are fine preparation features on the tooth e.g thin slots, grooves or pin preps.

-If you have added composite resin to the temporary crown to fix an open contact, it can stop the crown from seating if you have added too much. Therefore it is safer to do one side at a time if both contacts are open and ensure the crown seats full before doing the second contact. The same is true for final crowns; if the crown isn't seating fully but is seating on the die stone it may be the contacts holding it up. Usually the contact on the same side as the open margin is the one that is too tight. You can check the tightness with floss and/or shimstock but to mark the contact point it is easier to use whiteboard marker than trying to fit articulating paper in between the teeth.

-If you want to stop temporary crowns from locking onto the tooth, you'll want your putty key to go a fair way into the embrasures to ensure that the material doesn't get locked in under the contour of the adjacent tooth. If there is no space for the putty to go into these embrasures because your impression didn't flow in there or that was the preexisting condition you can use a tapered bur or a carver to open up the embrasures on the model especially under the contact point and take a putty key of this. 

-When removing a temporary crown after setting, use minimal lifting force at various points around the crown but tend to put more force where the crown margin is thickest and for the final removal pull up under the margin on the shorter side of the crown preparation. Lifting at the crown margin produces a rotational force on the temporary crown and this is the same force that will dislodge the final crown. You can use the geometry of the prep to assist you in this regard.

-If there is no space for the patient to fit in an interdental brush, then use soflex discs or a bur to reduce the amount of material under the contact point to open this embrasure up. The patient should be using the brushes daily and avoiding floss in this area.

A thin temporary crown will show where you've underreduced the prep. This is especially important to note on the occlusal surface. Underreduction relative to the preoperative state is fine if you plan to make additives changes with the final crown e.g raise the vertical dimension or make the tooth more bulky on the smooth surfaces. To ensure your temporary crown is thick enough at fabrication you can add wax to the primary model and take a putty of that or add composite to the tooth before preparation and take an alginate of this. This will be handy as well to guide the depth of preparation.