Assessment of the trueness of additively manufactured mol3% zirconia crowns at different printing orientations with an industrial and desktop 3D printer compared to subtractive manufacturing

OBJECTIVES

This study endeavours to investigate the effect of printing orientation on the trueness of additively manufactured molar zirconia crowns. The areal surface roughness and the characteristics of the marginal regions of the crowns were also considered.

METHODS

Twelve molar crowns were manufactured at 0°, 45°, and, 90° printing orientations in a Lithoz and AON zirconia printer, respectively. Twelve milled crowns were used as a comparison. Samples were scanned and analysed in metrology software to determine the trueness of the groups. Regions of interest were defined as the margins, intaglio surface and contact points. Areal surface roughness and print layer thickness were further analysed using a confocal laser scanning microscope.

RESULTS

The results indicate that there are clear differences between the investigated desktop (AON) and industrial (Lithoz) 3D printer. The 45° Lithoz group is the only sample group showing no significantly different results in trueness for all regions analysed compared to the milled group. Areal surface roughness analysis indicates that the print layers in the marginal regions are within clinically tolerable limits and surface characteristics.

CONCLUSIONS

The printing orientation for zirconia crowns is critical to trueness, and differences are evident between different AM apparatuses. Considerations for design and orientation between different apparatuses should therefore be considered when utilising direct additive manufacturing processes. The areal surface roughness of the marginal regions is within acceptable clinical limits for all manufacturing processes and print orientations considered.

CLINICAL SIGNIFICANCE

The materials and apparatuses for additive manufacturing of zirconia crowns are now clinically acceptable from the perspective of the trueness of a final crown for critical functional surfaces and areal surface roughness of the marginal regions.

Trueness assessment of additively manufactured maxillary complete denture bases produced at different orientations

STATEMENT OF PROBLEM

The trueness of the intaglio surface of an additively manufactured maxillary denture base may be influenced by the build orientation and the inclusion of support struts.

PURPOSE

The purpose of this in vitro study was to compare the trueness of a photopolymer additively manufactured maxillary complete denture base created at different orientations with different support strut designs. Optimizing the build is critical for adopting best practice when fabricating maxillary complete dentures through additive manufacturing techniques.

MATERIAL AND METHODS

Denture bases (N=70) were additively manufactured at 5 different build orientations (0-, 15-, 45-, 60-, and 90-degrees) with 10 specimens per orientation. Another 2 groups of 10 were manufactured by using the optimal printing orientation with and without support struts. The denture bases were scanned after storage in artificial saliva at 37 °C, and the scan data were analyzed with a 3D metrology software program. Statistical differences were determined with 1-way analysis of variance (ANOVA) and the Kruskal-Wallis test (α=.05). Color deviation heat maps were used to determine areas of clinically significant dimensional errors.

RESULTS

Significant differences were found among groups for positive mean deviation (F=44.09, P<.001), negative mean deviation (F=11.69, P<.001), and root mean square deviation (F=17.11, P<.001) for the different orientations. One-way ANOVA revealed significant differences with the use of support struts in relation to negative mean deviation (F=3.857, P<.001) and RMSE (F=11.215, P<.001) and positive mean deviation (Kruskal-Wallis H=0.070, P=.007). The color deviation maps showed that a 45- to 90-degree print orientation was truest overall and that the addition of support struts to the cameo and intaglio surfaces improved the trueness of the maxillary denture bases.

CONCLUSIONS

The build orientation and inclusion of support struts influenced the accuracy of the intaglio surface of additively manufactured maxillary denture bases. A 45- to 90-degree build orientation with support struts on the cameo and intaglio surfaces resulted in the truest denture base.

Effect of build orientation on the trueness of occlusal splints fabricated by three-dimensional printing

PURPOSE

Scientific evidence pertaining to the evaluation of trueness of occlusal splints fabricated using different three-dimensional (3D) printers and build orientations compared to subtractive technologies is lacking.

METHODS

Overall, one hundred and ten occlusal splints were manufactured using two different 3D printers and a dental mill. Five groups of ten were fabricated using the 3D printers at different build orientations (0, 30, 45, 60, and 90 degrees). In addition, a comparison group of ten occlusal splints was subtractively manufactured using a five-axis dental mill. All occlusal splints were scanned and exported as a standard tessellation language file. Analysis was conducted with metrology software with root mean square estimate average positive deviation and average negative deviation used as the measured outcome.

RESULTS

The 0 degree printing orientation was the most accurate for printer one with the root mean square value of 0.05 ± 0.01 mm, and 60 degree printing orientation was most accurate for printer two with the RMS value of 0.11 ± 0.01 mm. Subtractively manufactured occlusal splint had significantly higher trueness with the lowest RMS value of 0.03 ± 0.05 mm.

CONCLUSION

Build orientations influence the trueness of additively manufactured occlusal splints while occlusal splints produced by subtractive manufacturing were statistically significantly more accurate.

CBCT Segmentation and Additive Manufacturing for the Management of Root Canals with Ledges: A Case Report and Technique

Cone-beam computed tomography (CBCT) assessment of a ledge could be useful to a clinician; however, using this information effectively during a treatment procedure can be challenging. Advanced additive manufacturing technologies combined with semi-automated segmentation of root canals can help simulate the ledge and help in management of these iatrogenic complications. A patient presented after unsuccessful root canal treatment with a ledge on the left mandibular first molar. A CBCT was taken, and the images imported into a segmentation software (Mimics, Materialise). The canal was isolated, and segmentation performed along with the other structures of the tooth. A 3-dimensional digital model of the internal structures of the canal were used to design a mock-up which was additively manufactured. This was used as a preclinical guide to simulate the procedure, precurve the file, and manage the canal. This novel technique using virtual modeling from CBCT data post ledge formation allowed for successful and quick management of a tooth with ledges.

A technical and clinical digital approach to the altered cast technique with an intraoral scanner and polyvinyl siloxane impression material

This technique digitalizes the clinical and laboratory steps of fabricating removable partial dentures (RPDs) with the altered cast technique. An intraoral scanner was used to capture the mandibular Kennedy class II partially edentulous arch. An RPD framework was fabricated digitally and then combined with a custom tray with a wax occlusal rim. A conventional polyvinyl siloxane altered cast impression was made and then digitalized both intraorally and extraorally, followed by a digital interocclusal record. The resulting scan was modified to produce an additively manufactured cast. The teeth and gingival components were then designed and fabricated with a combination of additive and subtractive manufacturing, followed by the conventional acrylic resin pour technique. The definitive prosthesis was completed with minimal conventional techniques and without the use of gypsum, prefabricated teeth, or a physical articulator. The technique reduces the number of appointments and achieves the functional extension of the prosthesis through border molding, which is not possible with intraoral scanning.

Exploring the consistency, transparency and portability of dental technology education: benchmarking across Norway, Ireland and Australia

Dental technology programmes of study must prepare students to practice in a broad range of contemporary workplaces. Currently, there is limited evidence to benchmark dental technology education - locally, nationally or internationally. This research aims to improve consistency, transparency and portability of dental technology qualifications across three countries. Data were accessed from open-source curriculum documents and five calibrated assessment items. Three institutions collaborated with Oslo and Akershus University College, Norway; Trinity College Dublin, Ireland; and Griffith University, Australia. From these, 29-44 students completed 174 assessments. The curricula reflect the community needs of each country and display common themes that underpin professional dental technology practice. Assessment results differed between institutions but no more than a normal distribution. Face-to-face assessment moderation was critical to achieve consistency. This collaborative research has led to the development of a set of guidelines for other dental technology education providers interested in developing or aligning courses internationally to enhance the portability of qualifications.