3D printing in dentistry: the resin is chosen for the load, not for its stated application

3D printing entered dental laboratories faster than the literature managed to document it, and that has left a space in which manufacturers' claims carry more weight than evidence.

Three technologies are used in dentistry, differing in how they cure the resin. SLA uses a laser tracing the outline point by point; DLP projects the entire layer with a digital projector; LCD uses a liquid-crystal screen as a mask.

The practical difference lies in the trade-off between speed and resolution. SLA offers high resolution and long times; DLP prints a whole layer in the same time regardless of how many objects it contains; LCD costs less but its screens degrade and must be replaced.

For a laboratory printing many models, DLP holds the decisive advantage: filling the platform does not lengthen print time.

Resins differ in mechanical properties and in certified use, and the two do not coincide. A model resin is rigid and dimensionally stable but is not certified for prolonged mucosal contact.

Surgical guide resins must be transparent, sterilisable and certified for temporary contact. Transparency is not cosmetic: it allows the guide's seating on the teeth to be seen during surgery.

Resins for provisional restorations have higher flexural strength and are certified for prolonged contact. Using a model resin in the mouth is an error that occurs more often than supposed, and produces no immediately visible consequence.

Post-curing determines the final properties, and it is the step most often shortened. A freshly printed object has incomplete conversion: it is the UV chamber treatment that brings the resin to its stated characteristics.

Residual monomer from insufficient post-curing is cytotoxic. An under-cured provisional is not merely mechanically weaker: it releases substances into the oral cavity.

Washing before post-curing also matters. Isopropyl alcohol removes uncured resin from the surface, but washing for too long allows it to penetrate the object and degrade its properties.

Orientation on the platform influences accuracy more than intuition suggests. Surfaces in contact with supports carry defects after removal, which is why models are printed with the occlusal surface facing upward.

On printed definitive prostheses the documentation remains limited compared with conventional techniques. Long-term dimensional stability and ageing resistance are the open questions, and it is reasonable to regard them as an evolving solution rather than an established substitute.

In summary: choose resin by certified use and mechanical properties, do not shorten post-curing, and decide platform orientation according to where support defects can be accepted.