Which option is least likely to restore a 1.5 mm diastema?

The least likely option to effectively restore a 1.5 mm diastema is likely to be composite materials. Although composite can be used to close gaps between teeth, especially smaller ones, the technique often requires a certain level of skill for aesthetic results and may not provide the same level of durability or structural integrity as other restorative options. In the case of a 1.5 mm diastema, composite can be a less predictable choice, particularly if the gap is larger or if the patient desires a more permanent solution.

On the other hand, dental bonding is specifically designed for these types of minor restorative issues and can provide a seamless finish, while porcelain veneers allow for a more comprehensive aesthetic improvement by covering the front surface of the teeth completely. Dental bridges are used to replace missing teeth and while they wouldn't directly close a diastema, they provide a fixed solution for larger gaps resulting from tooth loss. Given this context, composite material may not provide the same effectiveness in aesthetics and durability compared to these other methods.