In vitro evaluation of marginal and internal adaptation of three-unit fixed dental prostheses produced by stereolithography

Micro-CT analysis of 3D printed provisional crowns fitting

BACKGROUND

The provisional crowns (PR) play an important role during the course of fixed prosthesis treatment. The fitting of PR varies and depends on various factors.

OBJECTIVE

The aim of the study was to evaluate the marginal and internal fit of PR produced by three-dimensional (3D) printing technique and to compare those with PR made by the milling technique by using micro computed tomography (μCT) on three commonly used finish line designs.

METHOD

Ninety study models were made using metal die of #14 tooth (i.e. maxillary 1st premolar molar) prepared for full veneer crown with three different finish line chamfer (C), rounded shoulder (RS) and rounded shoulder with bevel (RSB). PR was fabricated on each study model, using milling (MiL group, n= 45), and 3D printing technique (3D-P group, n= 45). Marginal and internal fit of each study model was measured by micro computed tomography, at 7 Zones Pr-1- Pr-7 on each finish line. Recorded data were statistically analysed by one-way analysis of variance (ANOVA) and using Dunnett t-Test (p> 0.05).

RESULTS

The mean gap at margins was minimum for provisional crowns in 3D-P group in any finish line with minimum in rounded shoulder with bevel at zone Pr-1 30.9 ± 5.3 and at zone Pr-7 32.7 ± 5.3. In the axial region, i.e. zone Pr-2, the smallest gap was recorded in the 3D-P group and in the occlusal region, for zone Pr-3, 4 and 5, the maximum gap was recorded in the MiL group.

CONCLUSION

The provisional crowns fabricated by 3D printed technique have better marginal and internal fit than the provisional crowns made by milling technique.

Marginal and internal fit of provisional crowns fabricated using 3D printing technology

BACKGROUND

Clinicians routinely provide provisional crowns following teeth preparation. Three-dimensional (3D) printing technology could be used over conventional methods for better fit as lack of adequate fit would result in plaque accumulation, micro-leakage, teeth sensitivity, caries and periodontal diseases.

OBJECTIVE

The aim of the study was to evaluate the marginal and internal fit of provisional crowns fabricated using 3D printing technology and to compare it with that of compression molding and milling methods.

METHODS

Ninety study models were fabricated by duplicating metal master models of the maxillary first premolar molar with three different finish line chamfer, rounded shoulder and rounded shoulder with bevel. On each study model, provisional crowns were fabricated using compression molding (Mo. group, n= 30 - by over impression technique), milling (Mi. group, n= 30 - by 5-axis dental milling machine), and 3D printing method (3D-P. group, n= 30 - by 3D printer). Marginal and internal fit of the samples were evaluated by measuring gap using a scanning electron microscope with a magnification of 27 ×, at 7 zones A-G on different finish line models. The data were statistically analysed using one-way analysis of variance (ANOVA) at the 0.05 significance level. The p-values were calculated using Dunnett's test.

RESULTS

The marginal gap was minimal for the 3D-P. group for each finish line with lowest for rounded shoulder with bevel at zone A 30.6 ± 5.3 and at zone G 32.8 ± 5.4. In axial area, i.e. zones B and F, the minimum gap was noticed for the Mo. group and in Occlusal area (cusp and fossa), for zones C-E maximum gap was determined in Mi. group followed by Mo. and 3D-P. groups.

CONCLUSIONS

3D printed provisional crowns have better marginal and internal fit compared to milled and molded provisional crowns.

Accuracy of provisional crowns made using stereolithography apparatus and subtractive technique

PURPOSE

To compare and analyze trueness and precision of provisional crowns made using stereolithography apparatus and subtractive technology.

MATERIALS AND METHODS

Digital impressions were made using a master model and an intraoral scanner and the crowns were designed with CAD software; in total, 22 crowns were produced. After superimposing CAD design data and scan data using a 3D program, quantitative and qualitative data were obtained for analysis of trueness and precision. Statistical analysis was performed using normality test combined with Levene test for equal variance analysis and independent sample t-test. Type 1 error was set at 0.05.

RESULTS

Trueness for the outer and inner surfaces of the SLA crown (SLAC) were 49.6±9.3 µm and 22.5±5.1 µm, respectively, and those of the subtractive crown (SUBC) were 31.8±7.5 µm and 14.6±1.2 µm, respectively. Precision values for the outer and inner surfaces of the SLAC were 18.7±6.2 µm and 26.9±8.5 µm, and those of the SUBC were 25.4±3.1 µm and 13.8±0.6 µm, respectively. Trueness values for the outer and inner surfaces of the SLAC and SUBC showed statistically significant differences (P<.001). Precision for the inner surface showed significance (P<.03), whereas that for the outer surface showed no significance (P<.58).

CONCLUSION

The study demonstrates that provisional crowns produced by subtractive technology are superior to crowns fabricated by stereolithography in terms of accuracy.

Three-dimensional evaluation of marginal and internal fit of 3D-printed interim restorations fabricated on different finish line designs

PurposeTo evaluate the influence of fabrication method and finish line design on marginal and internal fit of full-coverage interim restorations. MethodsFour typodont models of maxillary central-incisor were prepared for full-coverage restorations. Four groups were defined; knife-edge (KE), chamfer (C), rounded-shoulder (RS), rounded-shoulder with bevel (RSB). All preparations were digitally scanned. A total of 80 restorations were fabricated; 20 per group (SLA/3D-printed n=10, milled n=10). All restorations were positioned on the master die and scanned using micro-computed tomography. The mean gaps were measured digitally (ImageJ). The results were compared using MANOVA (α=.05). ResultsInternal and marginal gaps were significantly influenced by fabrication method (P=.000) and finish-line design (P=.000). 3D-Printed restorations showed statistically significant lower mean gap compared to milled restorations at all points (P=.000). The mean internal gap for 3D-printed restorations were 66, 149, 130, 95μm and for milled restorations were 89, 177, 185, 154μm for KE, C, RS, RSB respectively. The mean absolute marginal discrepancy in 3D-printed restorations were (30, 41, 30, 28μm) and in milled restorations were (56, 54, 52, 38μm) for KE, C, RS, RSB respectively. ConclusionsThe fabrication methods showed more of an influence on the fit compared to the effect of the finish-line design in both milled and printed restorations. SLA-printed interim restorations exhibit lower marginal and internal gap than milled restorations. Nonetheless, for both techniques, all values were within the reported values for CAD/CAM restorations. Significance3D-printing can offer an alternative fabrication method comparable to those of milled restorations.

Comparison of prosthetic models produced by traditional and additive manufacturing methods

PURPOSE

The purpose of this study was to verify the clinical-feasibility of additive manufacturing by comparing the accuracy of four different manufacturing methods for metal coping: the conventional lost wax technique (CLWT); subtractive methods with wax blank milling (WBM); and two additive methods, multi jet modeling (MJM), and micro-stereolithography (Micro-SLA).

MATERIALS AND METHODS

Thirty study models were created using an acrylic model with the maxillary upper right canine, first premolar, and first molar teeth. Based on the scan files from a non-contact blue light scanner (Identica; Medit Co. Ltd., Seoul, Korea), thirty cores were produced using the WBM, MJM, and Micro-SLA methods, respectively, and another thirty frameworks were produced using the CLWT method. To measure the marginal and internal gap, the silicone replica method was adopted, and the silicone images obtained were evaluated using a digital microscope (KH-7700; Hirox, Tokyo, Japan) at 140X magnification. Analyses were performed using two-way analysis of variance (ANOVA) and Tukey post hoc test (α=.05).

RESULTS

The mean marginal gaps and internal gaps showed significant differences according to tooth type (P<.001 and P<.001, respectively) and manufacturing method (P<.037 and P<.001, respectively). Micro-SLA did not show any significant difference from CLWT regarding mean marginal gap compared to the WBM and MJM methods.

CONCLUSION

The mean values of gaps resulting from the four different manufacturing methods were within a clinically allowable range, and, thus, the clinical use of additive manufacturing methods is acceptable as an alternative to the traditional lost wax-technique and subtractive manufacturing.