Evaluation of marginal and internal adaptation of veneers generated by the guided prosthetic tooth preparation system

OBJECTIVE

This in vitro study aimed to assess and contrast the marginal and internal adaptation of all-ceramic prefabricated veneers manufactured via the FirstFit guided tooth preparation system against all-ceramic veneers produced using the chairside Computer-Aided Design/Computer Aided Manufacture (CAD/CAM) system following identical guided preparation protocols.

MATERIALS AND METHODS

Two main groups were included, with 16 lithium disilicate veneers per group. Four typodonts were used for the test (FirstFit) and control CAD/CAM groups. Intraoral scans created master casts and preparation guides. Guides performed preparations on typodont teeth (two central incisors and two lateral incisors). Prepared teeth were scanned (CEREC Omnicam) to design and mill CAD/CAM veneers. Marginal gap thickness and cement space thickness were measured using light microscopy at four locations: marginal, cervical internal, middle internal, and incisal internal.

RESULTS

No significant difference existed between groups for marginal adaptation (p = 0.058) or incisal internal adaptation (p = 0.076). The control group had significantly lower values for middle internal adaptation (p = 0.023) and cervical internal adaptation (p = 0.019).

CONCLUSIONS

Guided preparation evaluation showed no significant differences in marginal or incisal internal adaptation. The CAD/CAM group had significantly lower middle and cervical internal adaptation values.

Biaxial flexural strength of various CAD-CAM glass-ceramic materials

PURPOSE

To evaluate and compare the flexural strength of three CAD-CAM glass-ceramic materials and to investigate the effect of various surface treatments on their flexural strength.

METHODS

120 rectangular specimens were fabricated from three different types of CAD-CAM ceramic blocks and were divided into three groups: zirconia-reinforced lithium silicate (Celtra Duo, Group 1), leucite-reinforced glass-ceramic (IPS Empress CAD, Group 2), and lithium disilicate ceramic (IPS e.max CAD, Group 3). Dimensions of the specimens were standardized to 14.5x12.5 mm and 1.5 mm thickness. Specimens in each group were randomized into four subgroups. The first subgroup (NS) did not undergo any surface treatment; the second subgroup (P) underwent polishing only; the third subgroup (G) underwent glazing only; and the fourth subgroup (PG) underwent both polishing and glazing surface treatments. Biaxial flexural strength (FS) testing was performed until fracture occurred; FS was calculated in MPa. All analyses were performed using SPSS version 24.

RESULTS

Group NS2 showed the lowest FS (89.34 ± 25.30 MPa). Group PG3 showed a significantly higher FS (365.38 ± 52.52 MPa) than Group P3 (268.15 ± 48.34). There was a statistically significant difference among the material groups for each surface treatment: IPS e.max CAD showed the highest FS, which was significantly greater than that of both Celtra Duo and IPS Empress CAD. The combination of polishing and glazing surface treatment resulted in significantly higher flexural strength than polishing alone for all three materials tested. For each material, no significant difference was found between the following surface treatments: control and polishing-only surface treatments; glazing-alone and the combination of polishing and glazing surface treatments. For each surface treatment, Celtra Duo showed significantly lower flexural strength than IPS e.max CAD. However, it displayed higher flexural strength than IPS Empress CAD, although the difference was only significant for glazing and the combination of polishing and glazing.

CLINICAL SIGNIFICANCE

This study provides the clinician with an estimate of the flexural strength of glass-ceramic materials and shows how various surface treatments affect their strength.

Accuracy of 3D Printed Implant Casts Versus Stone Casts: A Comparative Study in the Anterior Maxilla

PURPOSE

To conduct an in vitro comparison of the amount of three-dimensional (3D) deviation of 3D printed casts generated from digital implant impressions with an intraoral scanner (IOS) to stone casts made of conventional impressions.

MATERIAL AND METHODS

A maxillary master cast with partially edentulous anterior area was fabricated with two internal connection implants (Regular CrossFit, Straumann). Stone casts (n = 10) that served as a control were fabricated with the splinted open-tray impression technique. Twenty digital impressions were made using a white light IOS (TRIOS, 3shape) and the Standard Tesselation Language (STL) files obtained were saved. Based on the STL files, a digital light processing (DLP) and a stereolithographic (SLA) 3D printer (Varseo S and Form 2) were used to print casts (n = 10 from each 3D printer). The master cast and all casts generated from each group were digitized using the same IOS. The STL files obtained were superimposed on the master cast STL file (reference) to evaluate the amount of 3D deviation with inspection software using the root mean square value (RMS). The independent-samples Kruskal-Wallis test and Dunn's test with Bonferroni correction (for post hoc comparisons) were used for statistical analyses.

RESULTS

The Varseo S group had the lowest median RMS value [77.5 µm (IQR = 91.4-135.4)], followed closely by the Conventional group [77.7 µm (IQR = 61.5-93.4)]. The Form 2 had the highest mean value [98.8 µm (IQR = 57.6-87.9)]. The independent-samples Kruskal-Wallis test revealed a significant difference between the groups (p = 0.018). Post hoc testing revealed a significant difference between Varseo S and Form 2 (p = 0.009).

CONCLUSION

The casts generated from the Varseo S 3D printer had better 3D accuracy than did those from the Form 2 3D printer. Both the Varseo S group and the conventional stone casts groups had similar 3D accuracy.