Which advantage of porcelain veneers is not true compared to direct composite veneers?

The correct choice highlights that the claim regarding porcelain veneers requiring multiple appointments is not true when compared to direct composite veneers. In fact, porcelain veneers often require at least two visits: one for diagnostics, impressions, and the preparation of the teeth, and a second visit for placement. Conversely, direct composite veneers can usually be completed in a single appointment, as the dentist can shape and mold the composite material directly on the patient's teeth without the need for laboratory processing.

The other advantages attributed to porcelain veneers, such as being less sensitive to operator technique, having greater longevity, and providing a more rapid approach in terms of handling by the dentist, are indeed true. Porcelain veneers generally require a more controlled and precise application technique, making them less forgiving of operator error. They also tend to last longer than composite veneers, offering better durability and resistance to staining. While the placement of porcelain veneers might initially seem more time-consuming due to the laboratory fabrication, the final result can often justify the wait due to the aesthetic and functional longevity they provide when compared to the quicker, but less durable, composite alternatives.