Influence of different post-polymerization methods on the dimensional accuracy of additively manufactured dental crowns

TL;DR

This study examines how different post-polymerization methods affect the accuracy of 3D-printed dental crowns, finding that using glycerine improves dimensional precision.

Contribution

The study identifies glycerine-based post-polymerization as a novel method to enhance dimensional accuracy of additively manufactured dental crowns.

Findings

Crowns post-polymerized in glycerine showed lower RMS values, indicating better dimensional accuracy.

Glass filler-reinforced resin (Crowntec) consistently had higher RMS values across all regions.

Post-polymerization temperature had no significant effect on dimensional accuracy.

Abstract

To evaluate the influence of different post-polymerization methods and types of polymerization units on the dimensional accuracy of additive manufactured (AM) permanent crown resins.

Three crown materials were evaluated: two permanent restoration-indicated resins (Saremco print Crowntec and Varseosmile Crownplus) and one long-term temporary resin (NextDent C&B MFH). These were additively manufactured and post-polymerized using four different polymerization units with varying protocols. Post-polymerization was performed either at room temperature or at 60°C, as well as without an inert medium, with glycerine, or with nitrogen as the inert medium. A typical mandibular molar full crown design was used and subtractively manufactured (SM) crowns served as the control group. Post-processed AM crowns were digitally scanned, and three specific regions (margin, intaglio surface and interproximal contacts) of the STL of the crowns were analyzed using Geomagic Control X software. Root Mean Square (RMS) and average deviation values were collected and statistically analyzed in PRISM version 9. Additionally, scanning electron microscopy analysis was conducted.

The SM crowns exhibited the highest accuracy (the lowest RMS) for both the intaglio (18.6 ± 0.9 µm) and marginal surfaces (32.5 ± 3 µm). AM crowns showed variable accuracy depending on the post-polymerization method. Crowns post-polymerized in glycerine generally demonstrated lower RMS values. The glass filler-reinforced resin composite (Crowntec) material consistently exhibited higher RMS values (89 ± 5.4 µm to 120 ± 8.1 µm) across all regions studied. Post-polymerization temperatures did not significantly impact the dimensional accuracy of any of the materials studied (p > 0.05).

Using glycerine during post-polymerization, alongside the manufacturer’s recommended polymerization unit, generally enhanced the dimensional accuracy of AM dental crowns. SM crowns demonstrated superior accuracy in the intaglio and marginal surfaces; however, no significant differences were observed in the interproximal compared to AM crowns.

Given the variety of available post-polymerization units and protocols, dental practitioners should consider their impact on the dimensional accuracy of AM dental crowns. Awareness of these effects can help to prevent issues with crown accuracy, including adaptation to preparations and the contact points. Furthermore, this study provides alternative post-polymerization methods for practitioners lacking access to the manufacturer’s recommended equipment.

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