Evaluating 3D fit of lithium disilicate restorations with a novel virtual measuring technique
Chien, Edward Chaoho
MetadataShow full item record
OBJECTIVE: To explore a novel virtual inspection approach with a 3D metrology software to provide a non-destructive in situ analysis in digital workflow. Also, to evaluate the fit discrepancies of lithium disilicate crowns by using such a novel virtual measuring technique. MATERIALS AND METHODS: Maxillary arch typodont was used to design abutment for tooth #8 and #14 (hand prepared) and #4 and #10 (titanium custom abutment). All four abutments were placed into a duplicated maxillary arch solid stone model for scanning with laboratory scanner. Four crown patterns were designed and exported as STL files. The internal control group consists of the four original digital STL files and the external control group which was the 32-milled lithium disilicate crowns (IPS e.max® CAD, Ivoclar Vivadent, Inc.), eight patterns for each tooth. Thirty-two pressable wax patterns (8 of each) was fabricated for each of the three different technique systems. Two printed wax systems, Varseo Wax CAD/Cast (BEGO) and Press-E-Cast (EnvisionTec). Two milled wax systems Harvest Wax (Ivoclar Vivadent, Inc.) and Polycon Cast (Straumann), and a set of conventional cutbacks of 1.5mm with applied marginal wax. All patterns were pressed into lithium disilicate crowns, then fine polished and scanned. Each file was imported into a quality control metrology software (Geomagic Control X, 3D Systems) for marginal fit and internal fit evaluation with respective digital abutment. RESULTS: Mean of marginal gap for all groups were all lower than the preset gap space of 40 microns. Statistically significant differences in the fit accuracy were found among tooth number, technique system and measurement locations, but the differences are in clinically acceptable range. New scope of analyzing a restoration in a 3D fashion can help solve clinical complications. The study has shown that lower marginal gap does not necessary indicates a better fit restoration, as every level of the crown should be evaluated for. CONCLUSION: This novel inspection method can be used as a replacement of fit checker and help clinician to work in a full digital workflow. Lithium disilicate restorations fabricated through printed wax pattern, milled wax pattern and conventional hand wax are all clinically acceptable techniques.