Comparison of 3-dimensional printing technologies on the precision, trueness, and accuracy of printed retainers.

INTRODUCTION: This study aimed to evaluate the differences in the precision, trueness, and accuracy of 3-dimensional (3D) printed clear orthodontic retainers fabricated using printer systems with different printing technologies. METHODS: Retainers (n = 15) were 3D printed using 4 different printers: stereolithography (SLA), digital light processing (DLP), continuous DLP, and polyjet photopolymer (PPP) printers. Printed retainers were transformed into a digital image through a cone-beam computed tomography scan and compared with the original image using 3D superimposition analysis software. At previously chosen landmarks (R6, L6, R3, L3, R1, and L1), intaglio surfaces of the retainers were compared to that of the reference model. The intercanine and the intermolar width measurements were also assessed. A discrepancy of up to 0.25 mm between the printed retainer and the reference retainer intaglio surfaces indicated accuracy and clinical acceptability. Precision and trueness were also determined. Root mean square and percent of points within the tolerance level were calculated for precision and trueness for each retainer. Statistical significance was set at P <0.05. RESULTS: Interrater correlation coefficient indicated good agreement. Statistically significant differences were found between printer types among the 6 landmarks and the arch width measurements. When evaluating tolerance level and root mean square, statistically significant differences in median precision and trueness among each printer type were found. CONCLUSION: Retainers fabricated by SLA, DLP, continuous DLP, and PPP technologies were shown to be clinically acceptable and accurate compared to the standard reference file. Based on both high precision and trueness, SLA and PPP printers yielded the most accurate retainers.

Microshear bond strength of resin luting agents to monolithic zirconia.

The objective of this study was to evaluate the effects of different surface treatments on the microshear bond strength (µSBS) of resin cements to zirconia. Twenty-four zirconia wafers measuring 2.0 × 9.0 × 15.0 mm were sintered and randomly distributed into 3 groups based on the resin cement (n = 8): Panavia F 2.0, NX3, and RelyX Ultimate. The resin cement groups were divided into 4 subgroups based on the surface treatment: a control subgroup (air abrasion with 50-µm alumina particles) and 3 experimental surface treatments (Alloy Primer, Ea-Z-y Primer, and tribochemical silicoating using CoJet Sand). Each surface treatment was applied to the zirconia wafers according to its manufacturer's instructions. The resin cements were mixed and placed in thermoplastic tubes, producing cylinders measuring 0.8 mm in diameter × 2.0 mm in height. Five tubes containing the resin cements were placed on each of the pretreated zirconia wafers, resulting in a sample size of 10 specimens per treatment per resin cement. The luting agents were allowed to cure chemically for 4 minutes and then light cured for 30 seconds. The thermoplastic tubes were removed after 24 hours, and specimens were stored in deionized water (37°C) for 24 hours. A shear force was applied using a wire loop attached to a universal testing machine with a crosshead speed of 0.5 mm/min, and the microshear forces required for failure were recorded. The parametric data were analyzed with a 2-way analysis of variance with post hoc Tukey and Dunnett tests (P < 0.05). The mean (SD) µSBS values ranged from 3.6 (0.9) to 9.3 (2.4) MPa. Surface treatment with Alloy Primer and Ea-Z-y Primer increased the µSBS of the 3 cements compared to their controls, but the difference was not always statistically significant. CoJet Sand only increased the µSBS of Panavia F 2.0. The results suggest that the effects of different surface treatments may be specific for each cement.