Permanent Printed Crowns: How Much Can We Trust Them?

Resins intended for definitive restorations have taken 3D printing beyond provisional restorations. Lower material consumption and potentially lower production costs are appealing, but how well does the term “permanent” align with the evidence?

The review by Flottes and colleagues examined 42 studies of these materials. All were laboratory studies, so their findings do not establish the long-term intraoral durability of crowns.

Are these materials really ceramics?

The materials reviewed are mainly resin composites containing fillers: reinforcing mineral or ceramic particles. Ceramic fillers do not turn them into zirconia or lithium disilicate. The resin component still affects strength, water absorption, and discoloration.

Most information concerned Crowntec, Permanent Crown, and VarseoSmile Crown; their findings cannot be generalized to all printable resins.

How strong are they?

These resins showed promising strength in many tests, but overall their mechanical properties were weaker than those of composites supplied as ready-made blocks, from which a milling machine cuts the restoration. Direct composites also performed better for some properties.

In some studies, specimens were exposed to water, temperature changes, or repeated loading to simulate aspects of the oral environment; this process is called aging. After aging, the performance of some materials declined, but the extent of this decline was not the same for every product.

Withstanding a large load in a fracture test therefore does not, by itself, show that a crown will endure years of chewing forces.

How important is fabrication?

Final quality depends on more than the resin name. Print orientation, layer thickness, washing, and post-curing, meaning additional polymerization after printing, can change material properties.

In some studies, post-curing significantly increased strength. Conversely, prolonged ethanol washing weakened bonding to cement in one study.

Longer processing is therefore not necessarily better; the material-specific instructions matter.

What about the surface and color?

The surface hardness of these resins was lower in many comparisons. Surface roughness also depended on the material and finishing method, which matters for restoration appearance and plaque accumulation.

Polishing and some light-cured protective coatings—coatings hardened with light—improved surface quality or resistance to staining, but results were not the same for every product.

Color stability in water or artificial saliva was sometimes acceptable, whereas tea and coffee caused substantial discoloration in several tests. An appropriate shade at delivery does not mean that shade will remain unchanged over time.

How should they be bonded?

Sandblasting, meaning roughening the surface with abrasive particles, improved bonding in several studies. However, the effects of silane, primer, and acid etching varied between materials.

This review does not provide one bonding protocol for all printable resins. Ceramic particles alone do not justify repeating a glass-ceramic bonding protocol.

(Surface preparation should follow the instructions for the particular resin and cement system.)

Are they biologically reliable?

Most cell studies found acceptable results, but some unfavorable findings were also reported. Information about monomer release—unreacted resin molecules—and long-term effects remains limited. These laboratory findings alone establish neither clinical harm nor long-term safety.

What does this mean clinically?

These materials are promising for single-unit definitive restorations, but there is not yet enough evidence to say they are as reliable as the materials commonly used for definitive restorations. In evaluating them, we should consider not only strength but also fabrication quality, bonding, surface finishing, and color retention over time.

(This review alone is insufficient to endorse their use for multi-unit bridges, extensive rehabilitations, or patients with high loading forces.)

“Permanent” describes the product's proposed use; long-term durability must be demonstrated in clinical studies.