The marginal gaps of sequentially milled lithium disilicate crowns using two different milling units

BACKGROUND: The purpose of this study was to compare the marginal gaps of sequentially milled lithium disilicate (LDS) crowns using two different milling units. METHODS: One lower left first molar typodont tooth prepared for an LDS crown by an undergraduate student in a simulation clinic was selected. The crown preparation was scanned by a TRIOS 3 scanner and twelve LDS crowns milled by an E4D (E4DM) and a Sirona inLab MC X5 (MCX5) milling unit using identical settings. The crowns were seated onto the original crown preparation and three vertical marginal gap measurements were taken at four locations (mid‐buccal, mid‐lingual, mid‐mesial and mid‐distal) using a stereomicroscope. The mean marginal gap (MMG) was calculated for each individual tooth surface and each crown. RESULTS: The MMG for the E4DM (100.40 μm) was not significantly different to the MCX5 (101.08 μm) milling unit (P = 0.8809). In both units, there was a statistically significant trend of increasing MMG with sequentially milled crowns using the same burs (E4DM P = 0.0133; MCX5 P = 0.0240). CONCLUSIONS: The E4DM and MCX5 milling units produced LDS crowns with similar MMG’s and within a clinically acceptable range but with a trend of increasing MMG when analysed sequentially. © 2022 Australian Dental Association