Dimensional stability and fit of additively manufactured removable dies in dental cast resins with different chemical compositions.

Statement of problem: Additive manufacturing has enabled the fabrication of removable dies in various resins with different compositions. However, the knowledge on the dimensional stability and fit of removable dies fabricated with different dental cast resins is lacking.

Purpose: The purpose of this in vitro study was to evaluate the effect of dental cast resin type and storage time on the dimensional stability and fit of AM removable dies throughout a 4-week period.

Material and methods: A typodont model with a prepared right first mandibular molar was digitized with an intraoral scanner (IOS) (CEREC Primescan) to generate a standard tessellation language (STL) file. The STL file was imported into a dental design software program to design a removable die with 10-degree shaft taper angle and a hollow partial arch cast with and without the die. The removable die and hollow partial arch cast without the die STLs were used to additively manufacture 48 removable dies (n=16) and 3 hollow casts (n=1) by using a dental cast resin (DentaMODEL) (AM-DM), a bio-based dental cast resin (FotoDent biobased model) (AM-FD), and a nanographene-reinforced dental cast resin (G-Print) (AM-GP). The same IOS was used to digitize each die and when the die was seated into its respective hollow cast 1 day (T0), 1 week (T1), 2 weeks (T2), 3 weeks (T3), and 4 weeks (T4) after fabrication. All STL files were imported into a metrology-grade 3-dimensional analysis software program (Geomagic Control X). The root mean square (RMS) was used to assess deviations in different die regions (crown, root, base of the root, and overall) over 4 weeks, along with fit evaluation by calculating RMS for the crown portion within the cast and measuring mean distance deviations at 5 points on the die. The generalized linear model analysis and Bonferroni-corrected post hoc tests were used to evaluate the data (α=.05).

Results: The dimensional stability of the removable dies was affected by the interaction between resin type and die region and by the interaction between the resin type and time point, while the fit of the dies was impacted by the interaction between resin type and time point (P<.001). AM-GP dies mostly had higher crown RMS than AM-FD dies (P<.001), while AM-DM dies had the highest root and base of the root RMS (P≤.027). AM-FD dies had the lowest overall RMS (P≤.038). The base of the root led to the highest RMS for each resin (P<.001). AM-FD dies had lower RMS than AM-GP at T0 and AM-DM at T2, while AM-GP dies had lower RMS than AM-DM at T1 (P≤.010). The RMS values of AM-GP dies were lower at T1 than at T0 and T3 (P<.001). When the fit of the dies was considered, AM-FD dies had the lowest and AM-DM dies had the highest crown portion RMS and point-based deviations at each time point (P<.001). In addition, AM-DM dies' RMS values and deviations were the lowest at T0, while AM-FD dies had the highest point-based deviations at T4 (P≤.034).

Conclusions: Within tested regions and time points, AM-FD dies mostly had higher dimensional stability and better fit. Therefore, the crowns to be adjusted on AM-FD dies may require fewer interproximal and occlusal adjustments.