Characterization of 3D Printed Yttria-Stabilized Zirconia Parts for Use in Prostheses.

The main aim of the present paper is to study and analyze surface roughness, shrinkage, porosity, and mechanical strength of dense yttria-stabilized zirconia (YSZ) samples obtained by means of the extrusion printing technique. In the experiments, both print speed and layer height were varied, according to a 22 factorial design. Cuboid samples were defined, and three replicates were obtained for each experiment. After sintering, the shrinkage percentage was calculated in width and in height. Areal surface roughness, Sa, was measured on the lateral walls of the cuboids, and total porosity was determined by means of weight measurement. The compressive strength of the samples was determined. The lowest Sa value of 9.4 µm was obtained with low layer height and high print speed. Shrinkage percentage values ranged between 19% and 28%, and porosity values between 12% and 24%, depending on the printing conditions. Lowest porosity values correspond to low layer height and low print speed. The same conditions allow obtaining the highest average compressive strength value of 176 MPa, although high variability was observed. For this reason, further research will be carried out about mechanical strength of ceramic 3D printed samples. The results of this work will help choose appropriate printing conditions extrusion processes for ceramics.

Analysis of the Compression Behaviour of Reinforced Photocurable Materials Used in Additive Manufacturing Processes Based on a Mask Image Projection System.

Mask image projection based on stereolithography is an additive manufactured technology based on a Frontal Photopolymerization Process. Therefore, photocurable resins are used to build-up parts layer by layer. In this paper, alumina particles have been used as a reinforcement filler in order to improve the material stress-strain behaviour. In addition, the increment of the photoconversion ratio is a key factor to enhance the mechanical properties. Consequently, a numerical model has been used to determine the optimal printing parameters to enhance the elastic mechanical properties of printed parts according to the characteristics of photocurable materials. Stable and homogeneous reinforced materials have been obtained with an alumina content ranging from 5 to 15 wt%. Furthermore, the compression behaviour of reinforced materials has been analysed by means of experimental tests. The results show an enhancement of mechanical properties after the addition of reinforcement fillers, obtaining a maximum improvement in 10 wt% of solid load content. Finally, the influence of the sample's orientation on the construction platform has been discussed.

Anomalías dentales de desarrollo asociadas a la colección prehispánica Tzompantli / Developmental tooth anomalies associated with the prehispanic Tzompantli collection

Se revisa la colección prehispánica Tzompantli de Tlatelolco, perteneciente al Instituto Nacional de Antropología e Historia de la ciudad de México, consistente en 185 cráneos para investigar la presencia de anomalías dentales del desarrollo, hallando en cuatro cráneos un diente supernumerario; una retención prolongada de un molar deciduo; un mesiodens y ausencia congénita de laterales inferiores. En tres fragmentos de maxilares superiores: dos dientes caninos con vía de brote anormal y retención de un canino deciduo; una ausencia congénita de un lateral superior y un mesiondens. Estos hallazgos demuestran su presencia desde la época prehispánica y el interés de su etiología

Retención de dientes caninos en cráneos de la colección Tzompantli de Tlatelolco / Impaction of canine teeth in skulls from the collection Tzompantli of Tlatelolco

Se revisa la colección prehispánica Tzompantli de Tlatelolco perteneciente al Instituto Nacional de Antropología e Historia de la ciudad de México, que consiste en 185 cráneos. Se investiga la presencia de dientes caninos retenidos, hallando tres caninos retenidos encontrados en dos cráneos de dicha colección correspondiente a la época prehispánica. Se realizó un diagnóstico dental y clasificación radiográfica, encontrando que la retención de caninos no es exclusiva de la época actual, sino que ya existía antes del descubrimiento de América. Estos hallazgos brindan la oportunidad para discutir los aspectos etiológicos de esta condición