What are the disadvantages of ceramic coated teeth?

It can break off: Cosmetically ceramic layered crowns can fracture off and break through wear and tear, but they look the best and appear most natural. This usually happens much more on crowns in the back teeth versus the front teeth. The bite balance is very important to decreases the chances of the ceramic/porcelain to fracture off in pieces.

Sensitivity: All ceramic crowns generally require more tooth to be removed and hence more chance for a sensitive tooth than an all metal crown. There are different kinds of "ceramic crowns. Lava crowns are strong but color match not as good as an empress ceramic crown. Empress are not as strong as lava crowns. Bruxer crowns are simllar to lava , but are the next generation. Ask questions of your dentist.

A few but not major: Biggest concern is fracture of material. It is usually from operator error for not creating enough clearance on the tooth. Thus, crown is too thin & can break. Fortunately, the material nowadays is really strong. Since crown needs to be a certain thickness, one has to remove a bit more tooth compared to metal crown which can lead to tooth sensitivity. Overall, benefits are greater with ceramic.

Ceramics vary: There are many different types of ceramics used in dentistry. As a general rule the disadvantage to ceramics is that they can break and require removal to predictably repair in a kiln. If made properly and used in the right way, today's ceramic are very long lasting restorations.

Many: I infer from your question that you are considering porcelain veneers to change your smile. Consider that there is nothing that is healthier for your mouth than a healthy stable tooth. Veneers will need to be replaced every 15-20 years. Veneers are more susceptible to decay. They are a good alternative if you want to change the color or shape of your teeth, but there are significant caveats.