Purpose / Aim: To evaluate the influence of different post-curing methods, type of light curing machines and temperatures on the dimensional accuracy of additively manufactured (3D-printed) permanent crown resins.

Materials & Methods: Two different permanent crowns (Varseosmile Plus, Bego and Crowntec, Saremco) and one long-term temporary (NextDent C&B, NextDent B/V) were additively manufactured (Asiga Max UV) and post-cured in four different post-curing units (Otoflash, NextDent LC, Kulzer Cura Print, InnoDental LED with varying protocols (temperature; 20/60ºC and medium; glycerin/nitrogen). A typical mandibular molar full crown design was used and compared to subtractively manufactured (milled) crowns (Teliocad, Ivoclar milled in PM7, Ivoclar). Post-processed additively manufactured crowns were digitally scanned, and three regions (margin, internal surface and interproximal contacts) of the STL of the crowns were analysed using Geomagic control X software. Root Mean Square (RMS) and average deviation values were collected and statistically analysed in PRISM version 9. Scanning electron microscopy (SEM) was used to examine crown surfaces.

Results: The milled crowns exhibited the highest accuracy (the lowest RMS) for both internal (18.6±0.9µm) and marginal surfaces (32.5±3µm) while additively manufactured crowns had varying results depending on how they were post-cured. 3D-printed crowns post-cured in glycerin generally showed lower RMS values. The Crowntec material had higher RMS values (89±5.4µm-120±8.1µm) than other material groups in all regions studied, having the lowest dimensional accuracy and above clinically acceptable threshold. Post-curing at different temperatures showed no statistical significant differences for all materials studied in regard to dimensional accuracy (P>.05). The average deviation values of milled crowns were similar to additively manufactured crowns for both the marginal and interproximal surfaces. Crowntec crowns showed RMS values that were significantly higher than the clinically acceptable range of 100µm.

Conclusions: The use of glycerine alongside the post-curing unit recommended by the manufacturers generally improved the dimensional accuracy of the dental crowns. Post-curing at 20°C did not significantly differ when compared to 60°C. The milled crowns had the highest dimensional accuracy for the internal and marginal surfaces, however, interproximal contacts did not differ significantly compared to additively manufactured crowns. With the wide variety of post-curing units as well as different types of oxygen inhibition methods and curing temperature range available, dental practitioners should be aware of the effects those will have on the dimensional accuracy of their additively manufactured dental crowns, especially when they do not have the manufacturers recommended post-curing units.