Abutment preparation intra-oral vs on model: What are the pros and cons?

The biggest con is the loss in production time. Why have a patient in the chair for something you can do in the lab, freeing the chair up for other production? You may want to refine the prep in the chair, but most of the prep should be done on a model. I usually just take a good full arch impression with a good material, pour up the model myself so I am confident the analog is correct (do a small pour placing the stone with a brush w/o a vibrator to lock the analog in place, let that harden and then pour up the rest of the model), and send the whole thing off to the lab and let them refine the abutment and make the crown and get the finished case back.

If adjusting intraorally, use COPIOUS water spray to avoid killing the bone around your implant. In the lab, I don't know how much heat destroys the temper of the metal, but use caution.

Adjusting in the mouth also makes it difficult to know exactly the material dimensions. This can lead to small or thin areas of Zr which can been prone to fracture. If ti- the risk is leaving bits in the tissue and discoloring it. H.eat and sparks and very difficult to get as smooth as a machined or milled abutment Best abutment design is with Cad-Cam systems now. Procera and Atlantis are best examples, same price as off the shelf abutments. If adjustments required I would do this on the replica out of the mouth

Without a doubt, have the abutment prepped and/or modified on the model in the lab. 1. Instruments and access to abutment are easier in the lab. 2. If experianced, your lab technician can more easily modify the abutment relative to the surrounding teeth and all space available in order to give a good aesthetic result. The Technician should design from the final morphology, back to the desired dimensions for the abutment. Even more important in the anterior aesthetic zone. I would recommend using a titanium link to be screwed from abutment to fixture, and then with the use of CAD/CAM, design a Zirconia abutment, colour co-ordinated to final shading, followed by CAD/CAM designed Zr coping to be veneered with ceramic. Best of all worlds! I like FJ DuCoin's method of locking the lab analogue into impression before forwarding to lab, thus avoiding discrepancy!

Addition to previous comment

It is best to save chair time and enhanced production by prepping at the bench. The patients do appreciate this consideration! One can fine tune in the mouth if necessary.

if its a single crown implant(either anterior or posterior)i would prefer to finish the abutment preparation intra-oraly.if its a full mouth or more than three abutment better to do preparation in lab.