Comparison of fit and trueness of zirconia crowns fabricated by different combinations of open CAD-CAM systems

Abstract

Purpose: This study aims to clinically compare the fitness and trueness of zirconia crowns fabricated by different combinations of open CAD-CAM systems.

Materials and methods: Total of 40 patients were enrolled in this study, and 9 different zirconia crowns were prepared per patient. Each crown was made through the cross-application of 3 different design software (EZIS VR, 3Shape Dental System, Exocad) with 3 different processing devices (Aegis HM, Trione Z, Motion 2). The marginal gap, absolute marginal discrepancy, internal gap(axial, line angle, occlusal) by a silicone replica technique were measured to compare the fit of the crown. The scanned inner and outer surfaces of the crowns were compared to CAD data using 3D metrology software to evaluate trueness.

Results: There were significant differences in the marginal gap, absolute marginal discrepancy, axial and line angle internal gap among the groups (P < .05) in the comparison of fit. There was no statistically significant difference among the groups in terms of occlusal internal gap. The trueness ranged from 36.19 to 43.78 µm but there was no statistically significant difference within the groups (P > .05).

Conclusion: All 9 groups showed clinically acceptable level of marginal gaps ranging from 74.26 to 112.20 µm in terms of fit comparison. In the comparison of trueness, no significant difference within each group was spotted. Within the limitation of this study, open CAD-CAM systems used in this study can be assembled properly to fabricate zirconia crown.

Keywords: CAD-CAM; Fitness; Trueness; Zirconia crown.

Fig. 1. Flow chart of zirconia crown fabrication in this study.

Fig. 2. Fabricated zirconia crowns of each group (mandibular second premolar).

EZIS/Ae: EZIS VR/Aegis HM, EZIS/Tri: EZIS VR/Trione Z, EZIS/Mo: EZIS VR/Ceramil motion 2, 3Shape/Ae: 3Shape Dental System/Aegis HM, 3Shape/Tri: 3Shape Dental System/Trione Z, 3Shape/Mo: 3Shape Dental System/Ceramil motion 2, Exocad/Ae: Exocad/Aegis HM, Exocad/Tri: Exocad/Trione Z, Exocad/Mo: Exocad/Ceramil motion 2.

Fig. 3. Flow chart of the zirconia crown evaluation.

Fig. 4. (A, B) Right and occlusal views of final zirconia crown (mandibular right first molar), (C) Periapical radiograph.

Fig. 5. (A) Prepared mandibular right first molar, (B) The zirconia crown was filled by Fit Checker Advanced (GC, Tokyo, Japan) and placed on the abutment, (C, D) The zirconia crown and Fit Checker film was carefully removed from the abutment, (E) A vinyl polysiloxane impression material (Imprint II; 3M, St. Paul, MN, USA) was injected into the Fit Checker applied inner surface of the crown.

Fig. 6. (A, B) 3D printed jig for silicone replica technique, (C) Blue-colored Fit Checker and yellow-colored vinyl polysiloxane impression material separated from zirconia crown are buried in the jig, (D) Filling remaining space with green-colored vinyl polysiloxane impression material, (E) Bucco-lingual and mesio-distal cutting of replica.

Fig. 7. Reference points to measure the thickness of the Fit Checker.

[A, a, I, i: Absolute marginal discrepancy (AMD); B, b, H, h: Marginal gap (MG); C, c, G, g: Axial internal gap (AG); D, d, F, f: Line angle internal gap (LG); E: Occlusal internal gap (OG)].

Fig. 8. Bucco-lingual cross-section view of replica specimen at measuring points. [Magnification: × 100; (A) Absolute marginal discrepancy (AMD) and Marginal gap (MG), (B) Axial internal gap (AG), (C) Line angle internal gap (LG), (D) Occlusal internal gap (OG)].

Fig. 9. Comparison of the 3D color difference map of trueness. The deviation range is color coded from -100 µm (blue) to +100 µm (red). A negative deviation (blue) indicates more removal of block during the milling process, while a positive deviation (red) indicates less removal of block compared to the digital-calculated crown dimensions. (A) outer surfaces of the crowns. (B) inner surfaces of the crowns.