Effect of staining layer on roughness after progressive wear of monolithic ceramics.

PURPOSE: The aim of this study was to evaluate staining layer behavior applied to high-translucency zirconia (YZHT), feldspathic ceramics (FD), and zirconia-reinforced lithium silicate (ZLS) surfaces against different antagonists. METHODS AND MATERIALS: Monolithic ceramic discs (n = 120) (ø 12 mm; thickness, 1.2 mm; ISO 6872) were obtained, 30 from YZHT and FD, and 60 from ZLS CAD/CAM blocks (staining layer applied before or after the crystallization procedure). The specimens were divided into 12 subgroups (n = 10) according to the antagonists: steatite, polymer-infiltrated ceramic, or zirconia. Mechanical cycling (1.5 × 104 cycles; 15 N; horizontal displacement, 6 mm; 1.7 Hz) and flexural strength tests (1 mm/min-1000 kg cell) were performed. The differences between final and initial roughnesses (Ra, Rz, and Rsm), the mass loss, and the flexural strength data were individually analyzed by two-way ANOVA and Tukey's test (α = 0.05). RESULTS: The roughnesses of all ceramics did not present a statistically significant difference before wear simulation: Ra (p = 0.3348), Rz (p = 0.5590), and Rsm (p = 0.5330). After the wear simulation, the Ra parameter was not affected by an interaction between ceramic and antagonist (p = 0.595). The Rz and Rsm parameters were affected only by the antagonist pistons (both, p = 0.000). The ceramics used in this study showed statistically significant differences in mass loss after the wear test (p < 0.0001). The additional firing (2 steps) of the ZLS2 led to a higher lost mass quantity. CONCLUSION: All ceramics presented similar initial roughnesses and similar roughnesses after the wear simulation. The zirconia antagonist showed better performance against ceramics with high crystalline content. CLINICAL SIGNIFICANCE: It is clear that restorative materials must be carefully selected by dental practitioners according to indications, properties, and antagonists. The steatite antagonist, that is, an enamel analog, showed better performance against vitreous ceramics, while the zirconia antagonist showed better performance against ceramics with high crystalline content. Wear affects the surface roughnesses of the ceramics. Additional firing for the staining of the zirconia-reinforced lithium silicate ceramic led to a greater loss of mass.

Implant-Abutment Misfit after Cyclic Loading: An In Vitro Experimental Study.

This study aimed to evaluate the influence of thermomechanical cycling (TMC) and type of abutment on the misfit and compressive strength of the implant−abutment interface. Forty 3.75-mm external hexagon implants with 25° angled abutments were divided into four groups (N = 10). Group A: overcast plus TMC; Group B: overcast without TMC; Group C: completely cast plus TMC; Group D: completely cast without TMC. Abutments were fixed to the implants with 32-Ncm torque, and groups A and C specimens were cyclically loaded at 80 N with 2 Hz for 1 million cycles. The misfit on the implant−abutment interface was evaluated by optical microscope (100×) and the compressive strength test was performed in a universal test machine. For statistical analysis, a two-way ANOVA and post hoc Tukey test were used. There was no difference in misfit presented by all the abutments in the absence of TMC (p > 0.05). When TMC was performed, the completely cast abutments showed greater misfit than overcast ones (p = 0.001). Regarding compressive strength, irrespective of TMC performed, the overcast abutments showed higher compressive strength values than completely cast abutments (p = 0.003). Moreover, disregarding the type of abutment used, the absence of TMC provided higher compressive strength values (p < 0.001). It was concluded that thermomechanical cyclic loading aggravated the misfit, especially in completely cast abutments, regardless of material or fabrication technique, and reduced the compressive strength of the two types of abutments tested.

Biomechanical evaluation of 3-unit fixed partial dentures on monotype and two-piece zirconia dental implants.

This study aimed to evaluate the biomechanical behavior, stress distributions and bone microstrain of fixed partial dentures (FPD) with ceramic abutments supported on monotype zirconia implants, titanium implants and two-piece zirconia implants, using finite element analysis. A three-dimensional model of the jaw was simulated containing 1.0 mm thick cortical bone and cancellous bone tissue. A FPD and implant models (4.1 x 10 mm) were modeled containing a cement-retained implant abutment. These models were replicated in three groups with similar geometries: Titanium Implant and Zirconia Abutment (Ti-Zr); Zirconia Implant and Zirconia Abutment (Zr-Zr) and Monotype Zirconia Implant (Zr-S). An axial load of 300 N was applied to the center of the first premolar. The microstrain (µÎµ) and the Von-Mises stress (MPa) were assumed as failures criteria. For the three groups, a higher stress concentration was observed in the region of FPD connectors. The Ti-Zr group showed a higher stress concentration in the prosthesis and implant when compared to the other groups. However, the smaller elastic modulus of the titanium implant, in relation to the zirconia, provided a lower stress in the abutment and in the prosthetic screw. The monotype implant system allowed a more homogeneous stress distribution and its strain were predominantly located in the cervical region of the peri-implant bone tissue. Monotype or two-piece zirconia implants can be used for rehabilitation with FPD. However, the absence of separation between implant and abutment in the monotype system avoids the stress concentration in the prosthetic screw and reduced the peri-implant bone strain.

Analysis of bond strength between a nylon reinforcement structure and dental resins.

BACKGROUND: Nylon is a polymer that its use to reinforce dental resins has shown positive results such as increased flexural strength. The aim of this study was to evaluate the bond strength between dental resins and a nylon reinforcement. MATERIAL AND METHODS: Forty cylindrical nylon blocks with 13 x 23 mm with 0.5% by volume of silica and 40 without were made. Half of the samples of each nylon composition were sandblasted with aluminum oxide (50µm) for 3 s (2.8 bar pressure, distance: 20 mm, incidence angle: 90o). On the nylon blocks, cylinders of chemically activated acrylic resin and indirect composite resin were made, with a bonding area of 6,28 mm2. Eight different groups were obtained according to the material used and the surface treatment (n = 10): Acrylic Resin + Nylon; GAS: Acrylic Resin + Nylon with Silica; GAT: Acrylic Resin + Nylon (Al2O3); GAST: Acrylic Resin + Nylon with Silica (Al2O3); GC: Composite Resin + Nylon; GCS: Composite Resin + Nylon with Silica; GCT: Composite Resin + Nylon (Al2O3); GCST: Composite Resin + Nylon with Silica (Al2O3). The shear test was carried out. The Student's and the Kruskal-Wallis test was adopted. RESULTS: There was no statistically difference in the bond strength for nylon with silica for the acrylic resin group. For the composite groups, nylon with silica did not present a statistically difference without surface treatment (p = 0.10) and with surface treatment the bond strength decreased (p = 0.000). The GCT showed a higher bond strength (0.89 MPa). The surface treatment improved the bond strength for the both groups. CONCLUSIONS: The presence of silica in the nylon composition did not influence the bond strength between materials evaluated. However, the surface treatment with aluminum oxide proved to be favorable for this adhesion. Key words:Nylons - Resins, Synthetic - Structures Strengthening - Dental Research.

Evaluación de la Resistencia de Unión de Brackets Ortodónticos Fijados a Cerámica de Disilicato de Litio / Evaluation of Union Resistance of Orthodontic Bracelets Fixed to Lithium Dissylate Ceramic

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.

ABSTRACT: To evaluate the shear strength of cemented orthodontic brackets to a dental ceramic based on lithium disilicate. Rectangular samples 80 based glassceramic lithium disilicate were prepared. The samples were initially divided into 4 groups of 20 discs according to surface treatment: 37 % phosphoric acid for 30 seconds (HP); 10 % hydrofluoric acid for 60 seconds (HF); blasting with aluminum oxide for 4 seconds (SB); and diamond-tipped for 10 seconds (DW). Each group was divided into two subgroups for the Edgwise bracket cementation: metallic and ceramic. The two new groups were subdivided into thermocyclers or nonthermocyclics. The thermocycled samples passed 500 cycles with temperature variations between 5 ° C to 55 ° C. The numerical values obtained in the shear test were submitted to descriptive statistical analysis (mean and standard deviation), and the Shapiro-Wilk normality test and nonparametric Kruskal-Wallis and Mann-Whitney tests were performed. It was found that there was no statistically significant difference in the type of surface treatment and conducting or not thermocycling, observing statistically significant difference only on the bracket type, and the bond strength at higher metal bracket than in ceramics. Thus, the type of surface treatment and thermocycling aging were not decisive in the bond strength of orthodontic brackets to the lithium disilicate ceramic.

Evaluation of the Accuracy of Conventional and Digital Methods of Obtaining Dental Impressions / Evaluación de la Exactitud de los Métodos Convencionales y Digitales de la Obtención de Impresiones Dentales

ABSTRACT: 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.

RESUMEN: El objetivo de este estudio consistió en realizar una revisión bibliográfica sobre la precisión de los métodos de moldeo dental convencionales y digitales, así como presentar los diversos sistemas de escaneo intraoral tridimensionales. Se realizó una búsqueda bibliográfica en la base de datos de salud principal de PUBMED en la cual se recopilaron trabajos publicados entre 2008 y 2018. Se incluyeron estudios de laboratorio, informes de casos y revisiones sistemáticas, abordando temas que tratan con materiales digitales convencionales, moldeo y precisión. Se excluyeron los artículos que no evaluaron los materiales de moldeo, su comportamiento y técnicas para obtener una buena impresión de las estructuras orales. A través de una revisión exhaustiva en la literatura, obtuvimos los siguientes hallazgos: el paso más crítico en la preparación de una pieza protésica es la impresión de la preparación. La técnica convencional de moldeo consiste en obtener una copia negativa de la situación intraoral que se verterá en el yeso, obteniendo una copia positiva, sobre la cual se realizará el trabajo. Resulta que los sistemas de escaneo digital no fueron superiores a las molduras convencionales al comparar la fidelidad, precisión y reproducción de detalles; en cambio, fueron superiores a las molduras convencionales al considerar el tiempo de trabajo clínico, la preferencia del paciente y del operador y la comodidad del paciente.