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.

Impact of Removable Partial Dentures on Masticatory Performance in Partial Edentulism: A Systematic Review

PURPOSE

Removable partial dentures (RPDs) are widely used in clinical dental practice as a cost-effective treatment to restore the oral function. Clear understanding of the effect of partial dentures on masticatory performance is important for clinical decision making in prosthodontics. The purpose of this systematic review is to evaluate the impact of RPDs on masticatory performance (MP) of partially edentulous subjects.

MATERIAL AND METHODS

Electronic database and hand searches were conducted to explore clinical trials reporting the evidence of the effect of metal and acrylic based removable partial dentures on mastication. The validated objective and subjective measures of assessment of mastication were included. The article selection, data extraction and assessment of risk of bias were conducted by two reviewers independently.

RESULTS

Out of 11200 studies, one randomised control trial and 23 clinical trials met the inclusion criteria. Positive impact on different parameters of masticatory function after RPD treatment, was reported in 14 studies. Subjective evaluation of chewing ability (CA) displayed an improvement in 83.3% of studies, while improvement was evidenced only in 69.5% of studies upon objective evaluation. Majority of the studies were reporting data on free end saddles. Out of the 13 studies associated with bilateral free end saddle dentures, 9 studies showed a positive effect on masticatory efficiency. Various factors were found to have an impact on the masticatory performance (MP) of RPDs. Conclusion Subjective evaluation displays higher positive impact of RPDs in MP than objective evaluation. Assessment of patients' perspectives is important in clinical decision making. Multiple factors affect the MP with RPD treatment.