Assessment of the Adaptation of Interim Crowns using Different Measurement Techniques

To compare the internal fit and marginal discrepancy of acrylic resin interim crowns fabricated by different manufacturing methods, and to test the consistency of measuring marginal discrepancy and internal fit between different measuring techniques.

A dentoform mandibular left first molar was prepared for an all-ceramic crown. Thirty-six interim crowns were fabricated and divided into three groups (n = 12): group BAC (Bis-acrylic composite, fabricated manually), group CAM (CAD/CAM polymethylmethacrylate resin, milled), and group 3DP (3D printed methacrylic oligomers, printed). The internal fit of the interim crowns was evaluated by the silicone replica technique and by X-ray microcomputed tomography (µCT) technique. The marginal discrepancy of the interim crowns was evaluated by the vinyl polysiloxane (VPS) (Aquasil Ultra XLV) impression technique and by optical coherence tomography (OCT) technique. Data were statistically analyzed using ANOVA and Turkey tests at α = 0.05. Pearson correlation test was used to evaluate the correlation between the different measurement techniques and marginal discrepancy/internal fit.

The manually fabricated interim crowns (group BAC) had significantly greater discrepancy of internal fit than did the digitally fabricated crowns (group CAM and group 3DP) measured by both silicone replica technique and µCT 2-dimensional (2D) image measurement. There were no statistically significant differences in the cement space volume values obtained by the µCT image technique between group BAC and group 3DP (p = 0.285). The coefficient of determination between the two volumetric measurement techniques was low (R² = 0.30). For marginal discrepancy, the manually fabricated interim crowns had a wider absolute marginal discrepancy than both digitally fabricated groups (p < 0.05). In both the VPS impression and OCT assessment, there was no statistically significant difference between group CAM and group 3DP (p = 0.798 and 0.994, respectively). The coefficient of determination between the VPS impression and OCT techniques for marginal discrepancy measurement was low (R² = 0.23).

Digitally fabricated interim crowns (group CAM and group 3DP) had better internal fit and smaller marginal discrepancy than manually fabricated interim crowns (group BAC). For comparison of the different evaluation techniques, the silicone replica technique and µCT measurements had low correlation for internal fit assessment, as did the PVS impression and OCT techniques for marginal discrepancy test.