The accuracy comparison of 3D-printed post and core using castable resin and castable wax resin

Evaluation of custom posts and cores fabricated by two digital technologies in core and post space dimensions

PURPOSE

To evaluate the adaptability between posts and post spaces and the rationality of cores fabricated by two digital custom post-and-core processes.

MATERIALS AND METHODS

Titanium post-and-cores were fabricated by digital scanning impression technology or digital scanning wax-pattern technology on tooth defect molds of incisors, premolars, and molars, with traditional lost-wax casts of these teeth as the controls. Micro-CT and a laboratory scanner were used to determine intervals between post wall and root canal wall of the root apex, middle, and cervix of each sample in cross-, sagittal, and coronal sections; intervals between the end of post and tooth; diameters of cervical, middle, and incisal part at cross-, sagittal, and coronal sections of each sample, as well as shoulder widths.

RESULTS

The three fabrication processes showed significant differences in intervals between post-and-core prostheses and root canal walls, diameters of all parts of cores, and shoulder widths. Scanning impressions showed significant advantages in the main part of post-and-cores in incisors and premolars, while the scanning wax-pattern process showed obvious inferiorities in premolars and molars. As to core spatial size, values of measured sites in the scanning impression process were closer to the standard than those of the traditional process, while differences between the measured value of the scanning wax-pattern process were much more obvious than in the traditional process.

CONCLUSIONS

The use of digital custom post-and-core scanning impressions improved the rationality and precision of post-and-core dimensions compared with two other processes.

Evaluation of two printing techniques for maxillary removable partial denture frameworks

STATEMENT OF PROBLEM

Three-dimensional (3D) printing technology has gained popularity in producing removable partial denture (RPD) frameworks, including direct 3D printing of the metal framework and framework printing using castable resin, subsequently cast and processed. However, whether the technology is sufficiently accurate and precise to supersede traditional methods is unclear.

PURPOSE

The purpose of this in vitro study was to determine the accuracy and precision of 2 different methods in the fabrication of RPD frameworks, including 3D printing by selective laser melting (SLM) and digital light processing (DLP).

MATERIAL AND METHODS

Maxillary casts were digitized to design RPD frameworks. Thereby, 8 frameworks were produced for each group. The SLM group underwent a thermal finishing process after printing. In the DLP group, castable resin was printed but not cast. All frameworks were scanned to generate digital files, which were then compared with the original design using a metrology software program and manual measurements. Statistical analysis was executed using the t-test for independent specimens (α=.05) and by comparing heatmaps of the overlaid meshes.

RESULTS

The analysis of the frameworks indicated minor deviations across all specimens. Regarding accuracy, there were no significant differences between the groups (P=.986). The SLM frameworks demonstrated greater precision, with absolute deviation values of 0.13 mm compared with 0.17 mm in the DLP group (P<.001).

CONCLUSIONS

The findings underscored a high consistency between the 2 printing techniques, demonstrating a sufficiently advanced production process to yield predictable results. While the accuracy of both techniques was at a comparably high level and did not differ significantly, the SLM technique delivered RPDs with higher precision.

The impact of print orientation on the fracture resistance and failure patterns of additively manufactured cobalt-chromium post and cores

PURPOSE

The aim of this study was to evaluate the impact of the print orientation of direct metal laser sintering (DMLS) posts and cores on the fracture resistance and failure patterns of endodontically treated mandibular premolar teeth.

MATERIALS AND METHODS

Sixty intact human mandibular premolars were endodontically treated. The teeth were then randomly divided into four groups (n = 15). Cobalt-chromium (Co-Cr) metal posts were fabricated by traditional casting (Group C), and DMLS method in 0-, 45-, and 90-degree print orientations (Group DMLS 0, Group DMLS 45, and Group DMLS 90). The posts and cores were cemented with composite resin cement and subjected to compression test at a crosshead speed of 1 mm/min. Data was analyzed by using one-way analysis of variance ANOVA and multiple comparison post hoc Tukey tests (α = 0.05). Specimens were viewed under a stereo microscope with x20 magnification to evaluate the fracture types.

RESULTS

No significant differences were found among the groups tested in terms of fracture resistance (p > 0.05). Group C and Group DMLS 0 group exhibited similar fracture patterns.

CONCLUSIONS

It is possible to produce post and core restorations with the DMLS technique and use them clinically.  Print orientation did not influence the fracture resistance. However, fracture patterns were different. Group C outperformed all DMLS groups in terms of fracture patterns.