The aim of this study was to carry out a literature review on the accuracy of conventional and digital dental impression methods, as well as present the various three-dimensional intraoral scanning systems. A bibliographic search was carried out in PUBMED's main health database, in which works published between 2008 and 2018 were collected. Laboratory studies, case reports and systematic reviews were included, addressing topics that deal with conventional digital materials, impression and precision. Articles that did not evaluate impression materials, their behavior and techniques to obtain a good impression of oral structures were excluded. Through a review in the literature, obtained the following findings: the most critical stage in macking a dental prothesis is to take the dental impression. The conventional technique of impression consists of obtaining a negative copy of the intra-oral situation that will be poured into gypsum, obtaining a positive copy, on which the work will be carried out. Digital scanning systems were not superior to conventional moldings when comparing fidelity, accuracy and detail reproduction; in contrast, they were superior to conventional impression when considering clinical chair time, patient and operator preference, and patient comfort.

PEIXOTO, N. M.; DE MATOS, J. D. M.; ANDRADE, V. C.; BOTTINO, M. A. & ZOGHEIB, L. V. Evaluación de la resistencia de unión de brackets ortodónticos fijados a cerámica de disilicato de litio. Int. J. Odontostomat., 13(2):207-218, 2019. RESUMEN: El objetivo de este trabajo consistió en evaluar la resistencia al cizallamiento de brackets ortodónticos cementados a una cerámica odontológica a base de disilicato de litio. Fueron confeccionadas 80 muestras rectangulares de cerámica vítrea a base de disilicato de litio. Las muestras fueron divididas inicialmente en 4 grupos de 20 discos según el tratamiento de superficie: ácido fosfórico 37 % por 30 segundos (HP); ácido hidrofluorhidro 10 % por 60 segundos (HF); óxido de aluminio durante 4 segundos (SB); y aspersión con punta diamantada durante 10 segundos (DW). Cada grupo fue dividido en dos subgrupos para la cementación de brackets Edgwise: metálico y cerámico. Los dos nuevos grupos fueron subdivididos en termociclados o no termociclados. Las muestras termocicladas pasaron por 500 ciclos con variaciones de temperatura entre 5 °C a 55 °C. Los valores numéricos obtenidos en la prueba de cizallamiento se sometieron al análisis estadístico descriptivo (media y desviación estándar), habiéndose realizado la prueba de normalidad Shapiro-Wilk y las pruebas no paramétricas de Kruskal-Wallis y Mann-Whitney. Se verificó que no hubo diferencia estadísticamente significativa en relación al tipo de tratamiento de superficie y la realización o no de termociclado, observándose diferencia estadísticamente significativa sólo en el tipo de bracket, siendo la resistencia de unión en el bracket metálico mayor que en el de cerámica. Así, el tipo de tratamiento de superficie y el envejecimiento por termociclaje no fueron decisivos en la resistencia de unión de brackets ortodónticos a la cerámica de disilicato de litio.

The most common failure in implantology are due to mechanical instability. Torque loosening or fracture of the screws are the most frequent complications. Furthermore, the fractured screw retrieval is complicated and time-consuming. So, modifications in the design of implant systems are justifiable to offer a greater degree of biomechanical stability. Thus, the present study proposes to evaluate an experimental geometry for abutment screw regarding failure probability and torque loss. Twenty implant/abutments sets (e-fix, A.S. Technology -Titanium Fix) were divided into the following groups (n=10 in each group): (1) Conventional screw (Screw neck ø 1.5 mm) and (2) Experimental screw (screw neck constricted ø 1.2 mm). The abutments were tightened with a controlled torque meter device following the manufacturer's recommendations. Mechanical cycling was carried out with a load of 50 N.cm during 5 x 10 6 cycles with a frequency of 2 Hz at a temperature of 37 °C (ISO 14801). A digital torque meter was used to measure the reverse torque values of the prosthetic screw and the micro abutment screw, before and after loading. Data were statistically analyzed by One-way Anova and Tukey test (95 %). The results of the mean values of torque loss of the micro abutment screw were 58.44 % for the control group and 55.31 % for the experimental group and the mean torque loss for the prosthetic screw was 53.3 % and 61.3 % of the conventional and experimental groups, respectively. The survival probability was 100 % for both screw groups. It was concluded that experimental screw showed a similar behavior to conventional screws, showing similar reliability after fatigue life testing.

To evaluate the stresses generated in upper premolars rehabilitated with ceramic fragments (table-top) of lithium disilicate on the occlusal surface. An upper premolar was modeled following its anatomical references using computer aided design software (Rhinoceros version 5.0 SR8, USA). The dental tissues were individually designed containing enamel, dentin and periodontal ligament. The main anatomical points were used as parameters for model creation. Ceramic fragments were modeled varying their maximum thicknesses as: 0.5 mm, 1.0 mm and 1.5 mm. Solid geometries were exported to the analysis software (ANSYS 17.2, USA) in STEP format. The materials were considered isotropic, homogeneous and linear, and the values of the elastic modulus of the materials and structures were used to perform a static structural mechanical analysis. The set was submitted to 200 N load. The system fixation was defined on the basis of the threedimensional model, and the results were obtained in MPa according to the failure criteria of the analyzed materials (tensile stress). Occlusal restoration was not detrimental to mechanical behavior. Stress distribution in the internal region of the restoration was similar between the groups. Thicker fragments presented a lower concentration of tensile stress, therefore suggesting better prognosis in attenuating tensile stresses in the tooth region. More conservative occlusal ceramic fragments presented worse prognosis. However, all evaluated thickness for table-tops support the occlusal rehabilitation of upper premolars when submitted to 200 N loading.