Which statement is considered a contraindication for provisional coverage?

The correct choice highlights a situation where provisional coverage is not appropriate. Covering the facial aspect of a veneer preparation with provisional material detracts from the esthetic outcome and functional considerations of the veneer itself. In veneer procedures, the provisional should ideally maintain the original tooth structure's form and aesthetics until the final veneer restoration can be placed, ensuring that it does not interfere with the intended treatment's goals.

In this context, the other choices do not represent contraindications in the same way. For example, using a lighter shade than the natural tooth can sometimes be acceptable, depending on the aesthetic goals of the treatment. Placing a provisional on a non-prepared tooth might not be ideal for protecting unprepared surfaces but isn't a direct contraindication regarding the use of provisionals. Sealing with a thick layer of resin may affect the ease of removal or contribute to excess material that needs to be managed, but it does not contradict the use of provisional coverage.