Micro-CT Scanning Confirms Acceptable Marginal Fit of Chairside Composite Crown

Objectives: An experimental composite crown (CC) that can be fabricated and delivered chairside has been developed by 3M™. The objective of this in-vitro study was to test the marginal fit of CCs and compare it to to an established crown production method (IPS-e.max-Press; IvoclarVivadent (EMAX).
Methods: 21 CC and EMAX crowns were produced on 42 individual plastic lower right premolar teeth prepared for a crown with a 1mm shoulder (model:A3-ZPK-45;Frasaco). Each crown was fabricated then cemented onto the prepared tooth using an ultra light bodied VPS impression material (Imprint™4, 3M™). Each crown was then scanned on an X-ray microscope (XRadia 410 Versa X-ray microscope, Zeiss) at 5.2μm voxel size resolution. Scans were reconstructed (XMReconstructor software, Zeiss) then analysed using Aviso-Fire 8.0(FEI software).

The central coordinate of each crown was manually configured then 25 equally spaced vertical sections were generated around its circumference. A single operator manually analysed each section and measured, at 2 points per section, the marginal gap (MG) and absolute marginal discrepancy (MD).

The resulting data were non-normally distributed, so group medians and interquartile ranges were calculated. Significant differences were tested using the Mann-Whitney-U-test.
Results: The MG of CC (median: 44μm (IQR: 27-68)) were significantly smaller (P=<0.001) than the EMAX (46μm (31-88). Similarly, the MD of CC (median: 109μm (IQR: 76-150)) were significantly smaller (P=<0.001) than the MD of EMAX (186μm IQR=120-249)

After excluding from the analysis crowns that we deemed clinically unsatisfactory (median MG=≥120μm, CC (n=1), EMAX (n=3)) then no significant difference (P=0.318) was found between the MG for CC (43μm (IQR:27-61)) or EMAX (42μm (IQR 29-62)).
Conclusions: This in-vitro study indicated that CCs produce a clinically acceptable marginal fit. In this study CCs are at least comparable to an existing technology (EMAX) in terms of marginal gap and have a statistically superior absolute marginal discrepancy.